This discussion has come up in another thread and evidently I have confused a lot of people by the way I explained the differences. That is my fault and I think the best way to get the right information out is to start over from the beginning and explain the basics.

When you turbocharge or supercharge an engine you are forcing more air into the engine/cylinder than it would normally hold if it were naturally asperated. Well obviously more pressure means increased load and dynamic compression. Dynamic compression ratio is the maximum pressure that develops inside the cylinder during the compression stroke. Dynamic compression ratio is influenced by the overall engine breathing efficiency. So, with boost you can conclude that your dynamic compression ratio or cylinder pressure is going to be much higher than what it would have naturally asperated.

So how does this relate to the 300hp N/A vs. 300hp under boost and how this relates to which is harder on the engine?

Well first off, HP is a calculated number based on RPM and Torque. HP = Torque x RPM / 5252. This means that the higher the RPM, the higher the HP will be IF you can maintain the torque output. Lets use the 1992 3.4 DOHC engine as an example:

210hp @ 5200 rpm
215tq @ 4000 rpm

From these numbers we can determine that this engine produces 208 ft/lbs of torque at 5200 rpm and 164 HP at 4000 rpm. Now if we could do some kind of mod to this engine that would allow it to hold the torque curve out a little longer than stock, say by the use of bigger cams, we could actually produce 300hp off of just 208 ft/lbs of torque if we could make the engine develop that much torque at 7500 rpm. 208tq x 7500rpm / 5252 = 297hp. (~300hp @ 7500 rpm)

With the cam upgrade we do increase the engine's effecientcy at higher RPMs but we probably aren't increasing the dynamic compression ratio because the torque output is the same as stock, but the difference is now it is just making the power LATER in the RPM range. Obviously larger cams will probably result in increased torque production as well but remember our goal here is 300hp and peak torque and when it occurs will vary depending on the cam specs. This is why a honda Vtec 4 cyl can make 200hp at 8500 or so RPM but peak torque is only about 95 ft/lbs. In other words HP is just a function of math.

Now hopefully I have not lost anyone up to this point because it is important you understand how HP is calculated and how we arrive at those numbers. If you are still with me lets move on to turbocharging (boost).

Whenever you put boost on an engine, in this case turbocharge, you are increasing the amount of air entering the engine, as I described earlier. Increased air means increased cylinder fill, which translates into increased dynamic compression ratio, which translates into increased power output. The nice thing about boost is we can have a little more say in when the engine is going to make most of its power. For sake of arguement lets say we use a relatively small turbo, in this case on a 3.4 DOHC engine, because we only want to make 300hp but we want the engine to have good street manners and we don't want a lot of turbo lag (bigger turbos have more lag). The amount of power we can produce is going to be determined by the amount of boost we put on the engine and what octane fuel we are using along with a host of other variables, but those are just the basics.

As I just described, with turbocharging under boost we are forcing more air into the engine, and most of the time earlier as well, than it would normally "breathe". With the increased cylinder fill we increase torque output, in this case lets say we are now able to make 320 ft/lbs of torque at 4000rpm and that torque output only falls to 300 ft/lbs by the time we hit 5200rpm. Turbocharger size and design plays a huge role in how your torque curve is going to look, along with other things like cam profile. So if we can make 300 ft/lbs of torque at 5200 rpm by the equation we are now making 297hp at 5200rpm. Obviously if we could hold the torque curve up longer then peak HP we be further up the RPM band. But for sake of arguement lets just assume we are using a small turbo and the torque curve drops off rapidly after 5200 rpm.

So what is the difference between 300hp n/a and 300hp turbocharged and how it relates to load on the engine? Well quite simply put the higher cylinder pressures present due to forced induction (boost) are going to put more stress on engine internals and the block. Head gaskets, pistons, piston rings, connecting rods, crankshaft, bearings, main caps, and the block are all going to have to "tolerate" these higher pressures.

While a higher revving, naturally asperated engine also puts more stress on engine internals, the forces are different. For example, 90% of all connecting rod failures due to excessive RPM were a result of connecting rod stretch. This happens between the exhaust and intake strokes when the piston is traveling upwards in a cylinder and inertia trys to keep the piston moving upwards while the crank starts to yank the piston back down for the intake stroke. (you don't have this issue during the compression stroke because pressure is present in the cylinder trying to push the piston back down into the bore) The connecting rod litteraly gets pulled apart. At some point ALL connecting rods will fail in this manner, its just a matter of how much pulling force they can endure before failure, in other words, how much RPM they can withstand and for how long. With higher RPMs you don't have the loading that results from the increased cylinder pressures you have with boost, so long as you can keep your bearings lubricated and keep your connecting rods from stretching.

As I said before, under boost you are putting more physical pressure on all of the engine internals, and you are doing it at lower RPMs which usually stresses the bearings more than any other component. Another thing that has to be paid close attention to when using boost is detonation or knock. Most stock pistons can't survive well when detonation occurs at high cylinder pressures. Boost + detonation = very high cylinder temps which actually melt the piston. Higher cylinder pressures by themselves also result in higher cylinder temps which cause piston ring gaps to close. Natually asperated engines are set up with tight piston ring gaps from the factory to increase effecientcy and reduce emissions. Tight piston ring gaps are not boost friendly. This is another reason why you can only build so much boost on a stock naturally asperated engine, they are just not designed nor built to handle the increased cylinder temps and pressures. Piston material also plays a big role in how much boost you can build. Stock cast pistons are the weakest while stock cast hypereutectic pistons are slightly better. Neither one of these materials are "great" for boost that is why forged is the piston of choice for serious boosted applications. Forged pistons can better tolerate the higher pressures and temperatures and even some detonation, but they do have their limits.

Static compression ratio also plays a big role in how much boost you can ultimately put on an engine. In stock form the 3.4 DOHC engine has about 9.5:1 compression which is a little too high for a lot of boost. The recommended compression ratio for street-turbocharged applications is 8.0-8.5:1. The difference here is obvious, 6psi of boost on a 9.5:1 compression engine is going to have higher cylinder pressures/temperatures than 6psi on an 8.5:1 compression engine.

The amount of boost you can build on an engine is going to depend on how strong your engine internals are, as well as how strong the block is. There are several publications available that also explain other variables like cylinder wall thickness that also play a big part in just how much boost you can produce. But I think it is safe to say that 300hp naturally asperated does not have as much stress on it's engine internals as an engine that is making 300hp turbocharged.

Hope this helps better explain the differences.

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power corrupts. absolute power corrupts absolutely.

Custom Chip Burning | Fiero Engine Conversions | Turbocharging | www.gmtuners.com

[This message has been edited by Darth Fiero (edited 10-28-2004).]

Well that was educational. some of that i knew, (like HP and stuff) some i did not...

so which to you prefer, Turbo or N/A?

right now i like turbos (see sig)

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[This message has been edited by cooguyfish (edited 10-28-2004).]

So how does this apply to Supercharged motors???? hehehe Nice write up. + fer ya.!

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4.9 Caddy in Garage! Car in Driveway! ACK!

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quote Originally posted by cooguyfish: so which to you prefer, Turbo or N/A?

Very good question, and for most people it is going to depend on personal preference. In my case, I prefer turbos because I don't have to spin the engine as high to make the power (which usually requires valvetrain upgrades) and with boost I have a much broader power band and make power earlier, at least with my application. A broad power band low in the RPM range is going to win a drag race every time (assuming you can hook up) compared to an engine that makes more peak HP. A good example of this is the difference between my Fiero and my GTA. While I know there is a 500 lb difference, the 350 MPFI engine in my GTA makes over 400hp and 450tq which was only good enough to sport a 13.1et @ 109mph in the 1/4. (simply put: et translates into torque and torque curve and MPH translates into HP)

On the other hand my Fiero ran a 12.38et @ 110mph which tells me the engine in the Fiero is making a better torque to weight ratio to the car compared to the GTA. I can also tell you that the power band in my Fiero is MUCH BROADER than what my 350SBC engine produces in the GTA.

[This message has been edited by Darth Fiero (edited 10-28-2004).]

yeah what he said

quote Originally posted by Kento: So how does this apply to Supercharged motors????

Another good question. A supercharger builds boost in much the same way as a turbo but the only difference now is you are using power made by the engine to turn the supercharger. Depending on design you could be losing as much as 20% of the power you make just to turn the supercharger! So in effect the engine making 300hp SC is actually making more power than an engine making 300hp turbocharged, but that extra power is being sapped by driving the blower. In other words the SC engine has to work HARDER than the turbocharged engine to produce the same results. BUT a benefit of a supercharger is you have no lag time, or don't have to wait for the boost to come up. Inversely turbocharged engines do have a small benefit in that the backpressure built in the exhaust system (to turn the turbo) actually helps in some small way the connecting rod from the stretching effect you would normally see between the exhaust and intake strokes. Probably only matters in extreme cases though.

quote Originally posted by Darth Fiero: Very good question, and for most people it is going to depend on personal preference. In my case, I prefer turbos because I don't have to spin the engine as high to make the power (which usually requires valvetrain upgrades) and with boost I have a much broader power band and make power earlier, at least with my application. A broad power band low in the RPM range is going to win a drag race every time (assuming you can hook up) compared to an engine that makes more peak HP. A good example of this is the difference between my Fiero and my GTA. While I know there is a 500 lb difference, the 350 MPFI engine in my GTA makes over 400hp and 450tq which was only good enough to sport a 13.1et @ 109mph in the 1/4. (simply put: et translates into torque and torque curve and MPH translates into HP) On the other hand my Fiero ran a 12.38et @ 110mph which tells me the engine in the Fiero is making a better torque to weight ratio to the car compared to the GTA. I can also tell you that the power band in my Fiero is MUCH BROADER than what my 350SBC engine produces in the GTA.

yes, but what you forgot is that gearing can make a difference too. if you have a high revving (9K+ RPM's) N/A engine, and say, a 4.76 FD trans, it's going to be fast, even somewhat fast off the line. but you are right in that the torque curve won't be as good. But, on the other hand, less torque, better gears, and high RPM's are easier on the drivetrain itself.

i'd say this, for a daily driver/race car, go with boost. for a race only weekend car, it'd still be personal preference, but i'd go N/A myself.

quote Originally posted by cooguyfish: yes, but what you forgot is that gearing can make a difference too. if you have a high revving (9K+ RPM's) N/A engine, and say, a 4.76 FD trans, it's going to be fast, even somewhat fast off the line. but you are right in that the torque curve won't be as good. But, on the other hand, less torque, better gears, and high RPM's are easier on the drivetrain itself. i'd say this, for a daily driver/race car, go with boost. for a race only weekend car, it'd still be personal preference, but i'd go N/A myself.

Very true because in drag racing the number we are trying to get is the power produced at the wheels. Unfortuneately with gas prices as high as they are we can't all drive around on the street with 4.76:1 gears. Another drawback is higher rpms on the highway due to the higher gears means your engine's rpms are going to be higher all the time which means the engine is going to wear out faster. I understand what you are saying, and to add to your comment a higher revving engine would also have the benefit of a transmission with more gears, like a 6-speeed with close ratios because you can keep the revs in your powerband, whereas an engine with a broad torque curve works best with less gears (you lose time every time you shift).

[This message has been edited by Darth Fiero (edited 10-28-2004).]

quote Originally posted by Darth Fiero: BUT a benefit of a supercharger is you have no lag time,.

Another Benefit, Lifting Deck Lids and Having the BLOWER THERE!

Another thing I want to add to the gear ratio discussion is that you can actually over-gear your car and get slower. This is something that is going to be dependant on how fast your engine can rev.

Well said Darth.

Roy

quote Originally posted by Darth Fiero: Another thing I want to add to the gear ratio discussion is that you can actually over-gear your car and get slower. This is something that is going to be dependant on how fast your engine can rev.

like say, a 4.9 with a 4:10 four speed?

i know what you are saying, and i think i'm going to go with the best possible engine (for me anyways), i want the new 60 degree V6, the 2.8 VVT peaks torque at 3300 RPM, HP peaks at 6700 RPM and it redlines at 7200 RPM, matched with the short first gear of a getrag, it should be great. and i will be happy

IMO, I like superchargers better. But they do stress the bottom end alot more then turbos do. The torque is there from IDLE up. The newer Eaton blowers are close in efficiency to a turbo. I also love how the flow rate VS RPM for the blower is the same at almost any reasonable boost level. It also flows Linear (Predictable) amounts of air. That basically means, you have an almost fixed amount of torque and have it throughout the powerband. Fun! But that also means that the faster you spin the engine, the more horsepower you will make. Thats why I'm Supercharging the 3.4 DOHC. But I will have to make a bullet proof bottom end for it. Thats my logic and I'm sticking to it. I don't think there is an engine out there that will be as much fun to drive (and even just to look at) as this one.

Hello. Darth ok that was interesting, but since we have three dohc fieros here what do we need to start a turbo project here as building cams for these engines is not feasible as no one wants to do it unless of course you have a loooot of money.. We have ported a set of heads by Ben from the V6 60 degree site with shims for the springs (Ben knows more about it than me). Love your work and text, thanks Norm.

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Norm Vandermee

ALL HAIL DARTH, THE FREAKIN EVERYTHING GOD

Bows

quote Originally posted by Darth Fiero: Another good question. A supercharger builds boost in much the same way as a turbo but the only difference now is you are using power made by the engine to turn the supercharger. Depending on design you could be losing as much as 20% of the power you make just to turn the supercharger! So in effect the engine making 300hp SC is actually making more power than an engine making 300hp turbocharged, but that extra power is being sapped by driving the blower. In other words the SC engine has to work HARDER than the turbocharged engine to produce the same results. BUT a benefit of a supercharger is you have no lag time, or don't have to wait for the boost to come up. Inversely turbocharged engines do have a small benefit in that the backpressure built in the exhaust system (to turn the turbo) actually helps in some small way the connecting rod from the stretching effect you would normally see between the exhaust and intake strokes. Probably only matters in extreme cases though.

I have to disagree...

The turbo charged engine would also be making "more" than 300HP, but some of the power is lost by throwing a huge obstruction in the exhaust. Like you said, turbos create backpressure which causes a parasitic loss, only this time its an internal loss rather than an external one. Pumping friction vs the force of turning the blades of the SC is the trade off you make in turbo vs supercharger.

Although Im not sure of the logic of the "more" than 300HP. If you took off the supercharger, it would be making much less than 300HP. I guess you could say theoretical HP [(1+boost/14.7)*NA_HP] vs actual HP seen, but you can do the same with a turbo and the actual power you see at the crank will always be less than the theoretical.

[This message has been edited by PontiacMan (edited 10-29-2004).]

quote Originally posted by Darth Fiero: Another good question. A supercharger builds boost in much the same way as a turbo but the only difference now is you are using power made by the engine to turn the supercharger. Depending on design you could be losing as much as 20% of the power you make just to turn the supercharger! So in effect the engine making 300hp SC is actually making more power than an engine making 300hp turbocharged, but that extra power is being sapped by driving the blower. In other words the SC engine has to work HARDER than the turbocharged engine to produce the same results. BUT a benefit of a supercharger is you have no lag time, or don't have to wait for the boost to come up. Inversely turbocharged engines do have a small benefit in that the backpressure built in the exhaust system (to turn the turbo) actually helps in some small way the connecting rod from the stretching effect you would normally see between the exhaust and intake strokes. Probably only matters in extreme cases though.

yeah.. I'm gonna have to disagree with you on that.. how much HP can it possibly take to drive ONE pulley? it's not a very good argument and something i never understood from the turbo fanatics who claim that an SC robs there engine of power.. it takes a few HP from the engine to drive the SC's pulley, sure, but it doesn't rob 20% of the power, that's complete BS, unless of course your engine only produces like 20 or 30 HP to begin with. so, yeah maybe if i was supercharging a lawnmower, I would agree with you.

Oh SCs definitly take a good amount of power to turn, but I agree 20% is a bit much. It would be a constant number if anything. I think I remember reading somewhere it takes 20 HP to make like 5 PSI of boost? Compressing air takes a good amount of force, but its a function based on PSI and volume, not engine HP.

Power loss turning a supercharger depends on the supercharger design. Some designs sap more power than others but rest assured your engine has to work harder to put the same amount of power to the ground.

Yes turbochargers are a restriction in the exhaust, however the power loss is not as easily measured. You have to remember that a turbocharger gets its energy from the heat of the exhaust, more accurately the expansion of exhaust gases. So basically you are using wasted energy produced by the engine in the form of heat to turn the turbocharger. Whatever "restriction" that exists in the exhaust because of the turbo is offset by the boost pressure it pushes into the engine. Remember the key here is a turbocharger runs off heat energy.

A supercharger has to be physically driven by the engine. The typical supercharger probably draws about 13% of the engine's power just to turn it, poorer designs can sap up to 20% or even more. I know it sounds like a lot but go talk to the people trying to build up SC engines and you will quickly find out they do go through a lot of belts. Its going to take a lot more than 5 or 10hp to burn up a 6-rib serpentine belt.

The point is this: Look at some of the fastest 3800 powered cars out there today, the very fastest ones run a turbo not a supercharger. There is a reason for that. I am sure someone is going to bring up the arguement of why do top fuel dragsters only run blowers and not turbos, well thats easy turbos are NOT ALLOWED. There was a special on the history channel about drag racing which featured a guy that built up a drag car powered by a twin turbo 4 cyl engine. It ran deep in the 6's with a 4 cyl! I have personally witnessed a Buick V6 twin turbo in a Grand National run a 7.90 in the 1/4 mile! I talked with Kenny Dutweiler on the phone last season right after he dynoned his big block V8 powered by twin turbos that made over 3000 horsepower. According to him, turbos are far more effecient than ANY supercharger. If you don't believe me take it up with him, he has been working with turbos for years.

Funny, I read that a 426 hemi doesn't have enough power to turn a top fuel dragsters supercharger. They do require alot of hp to turn, especially on a 6000hp engine.

Excellent piece!! I'm thinking of turboing a 3800S1 and hadn't thought about the ring gap. Nobody says much about that in "You can bolt on a turbo/supercharger" articles.

I agree that blowers do take a lot of power to drive and it stresses the bottom end. Oddy designed a support to bolt to the block and support the front of the crank in front of the blower drive pulley (at 3 HP/CI levels). He said he got better crank and bearing life. Screw type blowers heat the air less and use less power than roots types.

Here's another one: http://www.rcdengineering.com/crank1.html

Turbos are more efficient but they put a lot of heat stress on the exhaust and cylinder. Things do need to be set up for the high temps.

GL

quote Originally posted by Darth Fiero: Whatever "restriction" that exists in the exhaust because of the turbo is offset by the boost pressure it pushes into the engine. Remember the key here is a turbocharger runs off heat energy.

But the same thing can be said for a supercharger. Whatever drag it puts on the crank if offset by its boost.

Im not disagreeing with the fact that turbos run off heat, Im just saying that you cant say that turbos dont cause a power loss.

For craps sake... this is a pointless arguement! I like Game Cube! I like XBOX! I like PS2!

Hondas are better... no Mopars are better... heck no Ford Racing rocks!

Its the ends that justify the means in this case. You get more power... period. Each has its ups and downs.

Either way... you end up with a heck of a lot more power than you started with. They both cause parasitic loss, but you end up with more in the end so, what difference does it make!?

Well written darth...
Ok let us keep it simple...I will use a 3800S2, I know more about it than the Q-motors...anywayz 231ci can ultimately make 300HP under its own power...we now know that and we also know it will cost an arm and leg but more importantly more REVOLUTION per minute. Unaturally about 10psi of efficient turbo boost will make 300HP...more importantly here too @ a lower RPM. My thesis? simple...the 231 ci N/A motor will create more forces...destructive forces at that than the 231 boosted motor!!

Let me ask you this...we are removing heat from this equation, it is a variable that is potentially detrimental to both engines and its cumulative effects cannot really be calculated...on our level at least...lol!!
Do you agree that the inertia loads created by our theoretical N/A motor is more than our 10 psi boosted engine?
The compressive load created by our hairdrier is less forgiving than tensile load in this situation...stock parts or forged, the physics say tensile loads increases geometrically!! it has been suggested that one is at the MAX compressive load at BDC at redline...meaing more or less forces pusing down, are easier on engine parts (the rotating assembly)...to a point!! This point has NOT been reached by our boosted engine!!
On the exhaust stroke, it is a whole different issue, because now you have more combine loads eg tensile loads, end gas etc, etc acting against the connecting parts of our bottom end...it is quick to see that TDC is really what stresses and engine more at this point of our 300HP engines
You have to proof or rather show that all the combined load exceeds our boosted load @ BDC!!
Do you know the loads created by burning gasses before expansion on a stock engine? adding more atms to create another ~60% power is nothing...REALLY!!

There are actually calculations out there that can proof or refute both our points...I am not an engineer...but I have been working with one who cannot accept he should quit his day job ...yes the condition of the engine is a giving, removing heat from the system is a giving, avoiding detonation is a given...231ci will make 300HP either natually or Unaturally...but 10 psi is definately easier than spinning to 8k...key word here easier!!
It is a subjective topic without data to back up...ppl have been doing this for years and with the advent of key sensors and mutiple tables to fall back on..."your theory doesn't not hold water"...

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3800 II v6 intercooled turbo...CWP!

quote Originally posted by Darth Fiero: You have to remember that a turbocharger gets its energy from the heat of the exhaust, more accurately the expansion of exhaust gases. So basically you are using wasted energy produced by the engine in the form of heat to turn the turbocharger. Whatever "restriction" that exists in the exhaust because of the turbo is offset by the boost pressure it pushes into the engine. Remember the key here is a turbocharger runs off heat energy.

Excellent topic and write up.

I thought that I’d point out a common misconception. A turbo is essentially a twin turbine, it uses a pressure differential to transfer its power from one turbine to the other, the temperature differential is a consequence of the pressure change and the surrounding material (the temperature differential is largely a waste of heat into surrounding metal).

Darth Fiero is right here but emphasized on the wrong aspect, what he said is “a turbocharger gets its energy from the heat of the exhaust, more accurately the expansion of exhaust gases”, what this means is the expansion of gas causes a pressure differential across the turbine which turns the turbine wich in turn (parden the pun) turns the other turbine. The lager the pressure differential the more the potential energy.

A turbo does not operate on heat! I suppose that’s the only point I’m trying to make here.

Please don’t hate me for saying the above but I think it’s important to understand how things work, and being a good thread I wanted to try to add to it without getting my head pounded on.

Aaron

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Darth,

Well written. I would love to drop by your shop sometime and chat. You are a credit to Iowans everywhere. +

quote Originally posted by cooguyfish: like say, a 4.9 with a 4:10 four speed? i know what you are saying, and i think i'm going to go with the best possible engine (for me anyways), i want the new 60 degree V6, the 2.8 VVT peaks torque at 3300 RPM, HP peaks at 6700 RPM and it redlines at 7200 RPM, matched with the short first gear of a getrag, it should be great. and i will be happy

I'm not aware of any 2.8 in GM's lineup?!?! There is the new 3.5 and the up-coming 3.9, but neither one has a 7200rpm redline? The only current 2.8 I'm aware of is the 4cyl used in the Colorado/Canyon.

quote Originally posted by PontiacMan: But the same thing can be said for a supercharger. Whatever drag it puts on the crank if offset by its boost. Im not disagreeing with the fact that turbos run off heat, Im just saying that you cant say that turbos dont cause a power loss.

The power loss is not the same. I am not going to argue this any further because it is off topic of what this thread is about. No offense, but no matter what I say you still will not believe me that turbos are more effecient and sap less power than superchargers. If you feel that your point of view is correct then call Kenny Dutweiler and discuss it with him.

As far as the turbocharger heat arguement: A turbocharger has a turbine which powers the compressor using waste energy from the exhaust gases. When you ignite the air/fuel mixture in the cylinder, heat is produced (a/f mixture burns) which causes the gases to expand. These expanding gases exit the cylinder on the exhaust stroke and turn the turbine wheel in the turbocharger. Therefore turbos work off HEAT, which is the expanding of the combustion gases. Without ignition there is no HEAT therefore there is not expansion of the gases therefore there is no energy to turn the turbine in the turbocharger, nor power the engine.

As a matter of fact the internal combustion engine is classified as a type of a heat engine.

quote Originally posted by Darth Fiero: so much for trying to keep it simple! But lets use your test mule of a 231cu 3.8L for the new comparo. I too don't doubt that the 3800 is capable of making 300hp naturally asperated, however, like you said you are going to spend a lot of money on aftermarket parts to get it to do so. One of these is undoubtedly going to be a bigger cam. The problem enharent with larger cams is they usually make more peak hp and tq at the expense of low RPM power and idle quality. Unfortuneatly by moving the power band and power peaks higher in the RPM range also means now we have to make sure the moving parts of the engine can withstand the higher revs without failing. All 3.8L Buick engines with the exception of the 3800 Series III use CAST iron connecting rods. One thing we know about cast material is that it tends to be more brittle than forged steel. While cast material can absorb a large amount of compression loads it cannot withstand great stretching forces -- the same type of forces that increase exponentially as the RPMs go higher and higher. There are also other factors we need to examine when considering the maximum reliable RPM an engine is capable of, like piston speed. The longer the stroke of an engine the higher the piston speed will be. Besides these limitations of course we have to consider the limitations of the valvetrain.

Cannot disagree there, tensile loads + power loads = more headaches...forged or not...a matter of time!!

quote Now with boost (either by turbo or SC), you are going to be increasing the cylinder pressure which puts more stress on the engine and its internal components. Also it is far more likely that with boost the engine will be making more power at lower RPMs than what it would normally see. This is particularly more harsh on the main and rod bearings.

After a said limit!! That limit is subjective and not written on stone...of course increased cyl. psi puts stress on an engine...one does not expect to put over 50% power into an otherwise stock engine and expect added longevity, my issue is more of "the way it is been portrayed". Like I said, there are a multiple of methods now that weren't available to common folks...keep heat management down, avoid detonation, fuel and ignition tables must be managed properly etc...I particularly removed about 4 degrees of spark at the top end in my ignition map...just because of the 91 piss-owl octane...and I am only running 4.5psi of PK boost on the street. The setup WAS ok since '98!!

I think we are on opposite sides of the SAME coin...it is good to think different and out of the box...I respect your view just don't agree with your particular thesis for this thread

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3800 II v6 intercooled turbo...CWP!

Not a problem, and I agree we are both probably making the same arguement just in different ways.

The main reason I'd like to go turbo is laziness.............

Turbochargers will accomodate for atmospheric pressure changes. Superchargers will not.

Driving into the mountains where the air pressure is a little less? No prob...the turbo accounts for it.
Driving to the coast where the air is a little heavier? No prob..the turbo makes up for it.

quote Originally posted by aaronrus: yeah.. I'm gonna have to disagree with you on that.. how much HP can it possibly take to drive ONE pulley? it's not a very good argument and something i never understood from the turbo fanatics who claim that an SC robs there engine of power.. it takes a few HP from the engine to drive the SC's pulley, sure, but it doesn't rob 20% of the power, that's complete BS, unless of course your engine only produces like 20 or 30 HP to begin with. so, yeah maybe if i was supercharging a lawnmower, I would agree with you.

weve calculated on a series II 3800, with a 2.8" pulley, the supercharger sucks about 55 hp off the crank. At these levels of boost, you will be making about 350 hp though. Without the supercharger but with the boost (turbo), you will be making over 400.

Also, someone mentioned something about Eatons superchargers being as effecient as turbos. I say no way. The Eaton M90 on the L67 is about 55% effecient, when spun at levels talked about above. It is more effecient at lower boost levels, but obviously the power output will be less. With a properly chosen turbo, the effeciency can exceed 75%. My T66 is 76% effecient at 19 psi of boost.

My engine dyno'd 301 whp and 351 wheel tq with an M90 making 14 psi of boost, (no n2o, no IC). My engine with the turbo pumping 19 psi of boost (only 5 more lbs) made 431 wheel hp and 454 wheel tq (no n2o, no IC). Thats 130 more hp on only 5 more psi of boost. Thats the difference between turbo and supercharger. Although, the supercharger will break your neck on the launch, and the turbo will blow the tires off at 40 mph.

Now, on the subject of NA vs turbo, lets take my engine for example and put it against a small block chevy (sorry for being such an SBC bully). Ok, youve got a NA sbc making 431 hp at the wheels (no n2o allowed, i didnt use my nitrous number), thats about 525 hp at the crank. First off how streetable is that? Id say fairly streetable, but your going to need some pretty high compression, a pretty lopey cam, and possibly stuff like intakes and such, that just wont fit under the decklid of a fiero. No problem for some, they just dont have a decklid, but how streetable is that? What happens when it rains? How much gas is that thing gonna use driving around town? What will the gas mileage be like on the highway? What about keeping it cool in rush hour traffic on a 100 degree day? Now you have my engine. It lopes a little, runs on pump gas, everything fits under the decklid, and it is very streetable. Doesnt have cooling issues even with the stock V6 radiator. Car gets 17 mpg in the city, and 28-30 on the highway. Not too shabby.

Thats the main difference I see between NA and boosted. With a boosted car, you can build it much more subtle, and during normal driving, its a normal machine. You dont have to worry about the reliability issues of having a 525 horse beast all the time. You cant "turn down" the power on a NA car. I could turn mine down and make 250 hp if i wanted to, and never have to worry about a thing. Of course what fun would that be

Okay now i getcha as far as what i was asking regarding NA vs Boost. Good point.

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1984 Indy Fiero 3.4L 4spd
www.cardomain.com/id/donk_316

Sorry Ryan...you have gone on a tangent...
While you have a point about drivability, you are still comparing apples to oranges!! I agree 100% with your efficiency argument regarding Sc vs Turbo, but 500hp on a 23ci is nothing compared to 500 hp on 350ci (base)...you can argue that point from morning to night a 231ci 500 motor whether built to the hilt CANNOT compare to 500hp 350ci. We don't care about mpg...POWER and how it is MANAGED & MAINTAINED is the crux...don't get me wrong, I love my lowly 3.8 but common...let's be real CUBIC INCHES...that is the difference between a 2.8 and 3.8 lol!!

[This message has been edited by nocutt (edited 10-31-2004).]

quote Originally posted by nocutt: 500hp on a 23ci is nothing compared to 500 hp on 350ci (base)...you can argue that point from morning to night a 231ci 500 motor whether built to the hilt CANNOT compare to 500hp 350ci.

How do you figure? 500 hp is 500 hp. Whether its a BBC or an Iron duke. Im just saying its more feasable and economical with a turbo'd engine.

Someone should make a general list of things youll need and optional bits for a turbo install. So it can be referred to when someone asks "what do i need to turbo my <insert motor here>"

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1984 Indy Fiero 3.4L 4spd
www.cardomain.com/id/donk_316

[This message has been edited by donk316 (edited 10-31-2004).]

quote Originally posted by fieroX: How do you figure? 500 hp is 500 hp. Whether its a BBC or an Iron duke. Im just saying its more feasable and economical with a turbo'd engine.

LOL!! like I said the argument can start in the morning and end at night...of course 500hp is 500hp removing the factors of gearing and where the power it is made. However let us use a candidate we can all agree on. In the import scene, for example we are always bombarded with the fact that 1.9L or 2.2L engines will make 500hp and generally that facts hold true because those things are overly built...nothwithstanding, I HAVE SEEN a fair enough damage to this engines, in the marketing world this numbers can be bent as a neglible variable, in the engineering world where things are based on stats...it sucks!
So putting this into our 3.8L engine...you can put 500hp into it but assuming you are using boost you need a lot of lb/min of air to ascertain this goal. A 350 ci (base: meaning we could be starting with 350 ci but can end up with whatever configuration to net 500hp still keeping the SBC).
I digress...

Well, the reason I'm going SBC as opposed to 3.8 sc or northstar or 3.4 is pretty simple.

It's what I'm comfortable with.

I've worked on and around SBC since I can remember. The first car I owned was a 74 nova. My Dad helped me rip a 283 out of a rust bucket truck and we installed it in the 74. Parts availability for a SBC is probably second to none. There's probably more SBC out there than anything else. I could probably be in the middle of buttcrack Saskatchewan and still find parts for one, not to mention the redneck behind the parts counter would know what a 350 was. IF I mentioned a 3.4 DOHC he'd chew twice on his tabacker and say "huh?".

Turbos? DOHC? Superchargers? Haven't worked with many except the HUGE ( A few of them are probably bigger than the SBC itself) turbos on some of the natural gas engines I've worked on. SO I'm just not that comfortable with them. I'm sure in the next ten years I'll be toying with them. At that time I'll probably let ya know what I think of those compared to SBC.