Just doing some calculations, how many CFM does the Fiero's 2.8L suck in?

2.8L at 6000rpm draws in 300cfm.

O.K., but check my math on this. The 2.8 litres figure is the displacement, right? I don't know the bore and stroke, so I'm guessing that's the total displacement of all six cyliders. So, easy enough, it has to suck up 2.8 litres of air per revolution. So 6,000 x 2.8 = 16,800 litres per minute. Seems wrong. I looked it up : a litre is 0.035314662471284765 cubic feet. That seems wrong, too. It takes 14 two-litres (like the cola bottles) to make one cubic foot? No way. So a 2.8 litre engine at 6,000 rmp uses 593.2863295175841 cfm?

Presuming that Oreif knows what he's doing (and I know he does), I came out with a number twice as large. Where did I go wrong?

I'll bet it's my assumption that an engine with a displacement of 2.8 litres will actually take in 2.8 litres of air (at ambient) on each stroke. (Remember, when you make an assumption, you make an "ass" out of "u" and "umption".) Is it because the air is drawn in at vacuum, and therefore isn't the same volume of ambient air? Is it because the cylinder isn't competely emptied each time?

If I account for the 4-strokes (air is only drawn in on every other revolution) that gets me close, but then the partial pressure theory takes me farther away again. Does anyone know the answer to this pointless exercise? Does anyone care? I stopped caring two paragraphs ago, but I jast can't seem to stop typing...

http://www.csgnetwork.com/cfmcalc.html

the easy way....

------------------
1985 Fiero SE - Plain Red V6 Coupe
3.1 Crane272 MSD 4.10-4spd DarthChip Borla
D.A.M.M. - Drunks Against Mad Mothers

quote Originally posted by Pyrthian:http://www.csgnetwork.com/cfmcalc.html the easy way....

The easy way? First, it did cubic inches or cc's, but not litres. Second, who the heck knows the "Volumetric Efficiency Of [their] Engine"? Sorry, Pyrthian, gotta disagree.

quote Originally posted by badger: The easy way? First, it did cubic inches or cc's, but not litres.

I promised myself I wouldn't poke fun... :-)

A liter is a thousand CCs. 2.8L = 2800 CC. Also, for future edification, 2.8L - 173 CI.

Volumetric efficiency is pretty close to 80% on naturally aspirated 2.8s if I'm not mistaken, use the 83% they have as a default. As a general rule of thumb, volumetric efficiency will typically be around 80% on all but race-tuned engines.

-Shawn

**EDIT**

I didn't mean to sound rude, I apologize if I did. I just thought it was a classic line: "It does CC's but not liters."

[This message has been edited by 85-GT (edited 08-25-2005).]

No, no. You deserve to poke fun. Pesky metric system. I honestly didn't remember that a centilitre equaled a cubic centimeter. (I blame France.)

Alas, knowing the volumetric efficiency only takes my equation further from the right answer of 300cfm. I came very close with the simple equation, once I realized that we're talking about a 4-stroke engine and cut my answer in half. But multiply it by .8, and I'm back with the wrong answer again. Where's the error?

quote Originally posted by badger: O.K., but check my math on this. The 2.8 litres figure is the displacement, right? I don't know the bore and stroke, so I'm guessing that's the total displacement of all six cyliders. So, easy enough, it has to suck up 2.8 litres of air per revolution. So 6,000 x 2.8 = 16,800 litres per minute. Seems wrong. I looked it up : a litre is 0.035314662471284765 cubic feet. That seems wrong, too. It takes 14 two-litres (like the cola bottles) to make one cubic foot? No way. So a 2.8 litre engine at 6,000 rmp uses 593.2863295175841 cfm? Presuming that Oreif knows what he's doing (and I know he does), I came out with a number twice as large. Where did I go wrong?

You forgot to take into account that CFM is 1 cubic foot of air moving 1 cubic foot in 1 minute. So you would need to divide your cfm by 2. Which would give you 296.6 cfm. The reason I get 300 is the Fiero 2.8L is really 2.85L (see below.) Then you would times it by the V/E of the engine.

The formula is: RPM x CID x VE / 3456 = CFM (or RPM X CID / 3456 X V/E =CFM)
So 6000 (rpm) times 173 ci is 1038000 with a VE of 1 divided by 3456 is 300.34 cfm. This would be the max a normally aspirated 2.8L could ever draw.

Now V/E of an engine is dependent on the intake. A street carb is usually .80 to .85, stock EFI throttle bodies are more like .85, Finally a full race carb or a large open EFI multi-barrel TB is 1.0

The formula breakdown is:
RPM: Revolutions per minute
CID: Displacement of engine
V/E: Volumetric Efficiency of the intake.
3456: A Cubic Foot of air moving 1 foot in 1 minute measured in inches.

To convert between Liters and cubic inches the factor is 60.7 (a liter is 60.7 cubic inches.)
So 173 divided by 60.7 = 2.850 liters
A 5.7L engine would be 5.7 X 60.7= 345.99ci and a 350ci engine would be 5.766L

Most U.S. manufacturer's have the bore and stroke in inches so the CID is the accurate number where most imports use MM's for bore and stroke so Liter's is more accurate.

So the stock 2.8L is 255.29cfm actual CFM's consumed. Most performance engine designers/builders set the intake size using a V/E of 1 as this helps the engine breathe thru the entire RPM range by offering basically no restriction.

[This message has been edited by Oreif (edited 08-25-2005).]

quote Originally posted by badger: O.K., but check my math on this. The 2.8 litres figure is the displacement, right? I don't know the bore and stroke, so I'm guessing that's the total displacement of all six cyliders. So, easy enough, it has to suck up 2.8 litres of air per revolution. So 6,000 x 2.8 = 16,800 litres per minute. Seems wrong. I looked it up : a litre is 0.035314662471284765 cubic feet. That seems wrong, too. It takes 14 two-litres (like the cola bottles) to make one cubic foot? No way. So a 2.8 litre engine at 6,000 rmp uses 593.2863295175841 cfm? Presuming that Oreif knows what he's doing (and I know he does), I came out with a number twice as large. Where did I go wrong? I'll bet it's my assumption that an engine with a displacement of 2.8 litres will actually take in 2.8 litres of air (at ambient) on each stroke. (Remember, when you make an assumption, you make an "ass" out of "u" and "umption".) Is it because the air is drawn in at vacuum, and therefore isn't the same volume of ambient air? Is it because the cylinder isn't competely emptied each time? If I account for the 4-strokes (air is only drawn in on every other revolution) that gets me close, but then the partial pressure theory takes me farther away again. Does anyone know the answer to this pointless exercise? Does anyone care? I stopped caring two paragraphs ago, but I jast can't seem to stop typing...

You have to account for the strokes. It takes TWO complete revolutions for all cylinders to have achieved an intake stroke. In this sense, you would divide that number by half.

Trying to determine CFM by engine volume and maybe RPMs is ambiguous at best, whereas, head design, intake design, cam profile etc. etc, will figure heavily into what the actuality is opposed to what the formula says you’ll get. This is especially true with certain engines. But there’s nothing wrong with having fun with formulas.
BTW: doesn’t CFM at times, also stand for ‘Confusing For Many?’

quote Originally posted by Oreif: The formula breakdown is: 3456: A Cubic Foot of air moving 1 foot in 1 minute measured in inches.

Actually, a cubic foot of air is equal to 1728 cubic inches. As others have indicated, a 4-stroke engine only draws air in during every other crankshaft revolution. The formula takes this into consideration. This is why the denominator of the equation is 2 * 1728 = 3456.

actually, it's just a unit conversion problem. start with your 6k rpm figure and keep multiplying by ratios that equal 1 (conversion factors)....

6000 revs....1 intake stroke.....173 cubic in.........cubic foot
----------X---------------X-------------X--------------------
minute.........2 revolutions........intake stroke.....(12 cubed) cubic in

cancel out all the units that are in both the top and bottom, since anything over itself is 1 anyway,

6000 X 173 cubic feet
-------------------- = 300 cubic ft / minute
2 X (12x12x12) minutes

edit, to make the spacing work

[This message has been edited by D B Cooper (edited 08-25-2005).]

Mark and D B Cooper are right.

And now, for some real fun. Let's find the intake air velocity (in the throttle body) at 6000RPM, wide open throttle. Let's assume an intake airflow of 260CFM, i.e. an almost-stock 2.8.

According to my calculations, the cross-sectional area of the throttle body, at wide open throttle, is approximately 3 square inches, i.e. 0.0208 square feet (counting the obstruction from the throttle plate).

To find the air velocity, we'll use the equation S = (R x 60) / (A x 5280)

S = Speed (miles per hour)
R = Rate of Flow (cubic feet per minute)
A = Area (square feet)
5280 = conversion factor (feet to miles)
60 = conversion factor (minutes to hours)

So our equation (rounded off) would look like 142MPH = (260CFM x 60min) / (0.0208ft² x 5280ft)

Yes, that's 142 miles per hour. If you upgrade the cam, port the intake and/or heads, or increase displacement, the airspeed through the throttle body will be even higher.

When I started typing this post, I was trying to make a point. But I forgot what it was.

[This message has been edited by Blacktree (edited 08-25-2005).]

quote Originally posted by Blacktree: So our equation (rounded off) would look like 142MPH = (260CFM x 60min) / (0.0208ft2 x 5280ft) Yes, that's 142 miles per hour. If you upgrade the cam, port the intake and/or heads, or increase displacement, the airspeed through the throttle body will be even higher.

No the airspeed does not change with cam, heads or displacement. Your formula only uses the CFM flow of the intake and the RPM of the engine as it's data. Even if you put a 350ci V-8 at 6000 rpm behind the intake, you will still have the same cubic feet per minute because the intake is the same area. So even though you increased displacement of the engine, The airspeed thru the intake is the same. Since the engine requires more intake flow area to feed the higher displacement, you now have a restriction.
The airspeed will change with porting the intake because as you increase the size of the ports you also increase the CFM's of the intake which would change one part of the formula.
Increasing displacement will not make the intake flow more than it's area. Hence the problem with using a stock Fiero intake on a 3.4L engine.

[This message has been edited by Oreif (edited 08-25-2005).]

Sweet. That helps a lot! I had NO IDEA exactly how the mathematics for it went... I'm good at inventing things, just not very good at figuring out the math behind them to know whether or not my idea will work.

Thanks guys!!

-Mulholland GT

http://www.virtualengine2000.com/VirtualEngineCalculatorTour.htm

FREE SOFTWARE

quote Oreif said: No the airspeed does not change with cam, heads or displacement.

This implies that the stock 2.8 throttle body can't flow more than 260CFM.

quote Originally posted by Oreif: No the airspeed does not change with cam, heads or displacement. Your formula only uses the CFM flow of the intake and the RPM of the engine as it's data. Even if you put a 350ci V-8 at 6000 rpm behind the intake, you will still have the same cubic feet per minute because the intake is the same area. So even though you increased displacement of the engine, ...

That's not correct. The airspeed will change if the engine size is changed --- provided that the Mach Index for the intake flow is not greater than 0.5. Mach Index = flowSpeed/340 (meters/sec). The Mach Index can exceed 0.5, but the coefficient of discharge for the runner/valve/area will decrease so the mass flow doesn't proportionally increase with the increase in engine size, or engine rpm, or cam change etc. C.F. Taylor showed this a long time ago and you can find discussion of it in a number of places on the web.

My math on intake flow:

Using the 3.4 liter v6, you start with 207 cid, or 34.5 cid per cylinder, or 0.020 cubic feet per cylinder.

At 6000 rpm you have an intake stroke once for every two revolutions of the crank. So one cylinder pulls 0.020*6000/2 = 59.9 cfm.

59.9 cfm is the average flow for one cylinder at 100% VE. At the rpm for peak torque, the VE is usually around 80 to 85%. At the rpm for peak power, the VE is less and typically around 60 to 70%. I'll use VE = 0.65. (There may be more accurate values for VE here on PFF but these will do for now).

59.9*0.65 = 38.9 cfm

Remember that's the average flow in cfm for one cylinder of a 3.4 v6, at 65% VE, at 6000 rpm. It's the average flow because the induction occurs in pulses for one cylinder --- it's not continuous. So if 38.9 cfm is the average, then what is the peak flow during the valve open state? The valve opens for approx 190 degrees (camshaft dependent) out of 720 total crankshaft degrees, so the duty cycle for the valve being open is 26%. I used the 0.050" lift duration but effectively the valve isn't open much so I could have used a smaller duty cycle to reflect the reduction of airflow when the valve is nearly closed. So if you invert the duty cycle, that gives you the scaling factor you need to figure out what the average flow would be during and only during the valve open condition.

So the aiflow now looks like:

38.9 * (720/190) = 38.9*(3.79) = 147.5 cfm, for one cylinder, 65% VE, pulsed max volume flow rate.

The engine will need 1.5 times this amount because it's a 6 cylinder engine (multiply by 6) but it's a 4 stroke, so you only get intake in one of the four strokes (so divide by 4). 147.5*6/4 = 221 cfm. A 2.8 will breath 82% of this value, in a first order engineering sense, because it has 82% of the displacement of the 3.4. So 221 cfm * 0.82 = 182 cfm. A typical 5.7 liter v8 (like an LT1) had dual 48 mm throttle blades and can flow over 600 cfm, even though the engine only needed to pull 380 cfm to reach 260 fwhp. And engine half that size (a 2.8) similarly needs a TB that flows a maximum of 300 cfm, even though it doesn't ever use all the flow. The reason why no one ever uses all the flow is because the air flow power losses become excessive when you get close to the flow limits of the TB. So they are always oversized, slightly, to avoid that from happening.

One last point. The number 147.5 cfm assumed the flow in the smallest section area of the intake tract (usually past the valve) is uniform. But that's not true because the flow speed at the walls of the intake has to go to zero. So there is a flow distribution across the intake tract that has a peak at the center and zero along the walls. The average across the flow area will be 147.5, so the peak value will be higher than 147.5 cfm. For the sake of writing economy I'll assume that the peak flow is some 20% higher at the center, so the peak is roughly 177 cfm.

177 cfm is substantially higher than the stock intake flow data on Trueleo's web site, and it's also higher than the stock flow of the head. That means the stock 3.4 engine, with the stock heads and stock intake (and stock erxhaust) can't breath to 65% VE at 6000 rpm. At 5000 rpm, the VE will be roughly 75% and the flow will be 153 cfm.... which is still too much for the stock heads/intake. If I take the head flow limit (at 0.300") of approx 124 cfm, then 124/177 = 0.70, so I would expect the stock engine to start running out of breathing at 70% of 6000 rpm, or by 4200 rpm. I could munge the calcs and get "better" numbers, but the point has already been made.

You can also work the math (as above) for the 2.8 v6 by making the right substitutions above. The math shown above isn't perfect, it wasn't meant to be. But it is representative and that's good enough for now. Better methods would require better math (than the simple calcs above) and you would need to include the acoustic wave effects and inertia --- and that means a code having the same core elements of Dynomation. I'll stop now.

[This message has been edited by kdrolt (edited 09-28-2005).]

quote Originally posted by kdrolt: That's not correct. The airspeed will change is the engine size is changed --- provided that the Mach Index for the intake flow is not greater than 0.5. Mach Index = flowSpeed/340 (meters/sec). The Mach Index can exceed 0.5, but the coefficient of discharge for the runner/valve/area will decrease so the mass flow doesn't proportionally increase with the increase in engine size, or engine rpm, or cam change etc. C.F. Taylor showed this a long time ago and you can find discussion of it in a number of places on the web.

Your math is based on engine displacement and using the proper throttle body/intake size. But if you have a smaller throttle body/intake then the engine requires, The max CFM of the throttle will not change. It will restrict the flow to the engine and the max airspeed at the throttle body will never go higher than what the throttle body can flow. You can only flow a given amount of air thru a given size throttle body.

Got to give Oreif a + on this. The engine, as a pump for air, is a SUCTION pump. Which does have a majior difficulty when restricted. Anyone care to recall how high a vacume pump can lift a collum of water? Not nearly what a pushin pump can do...

Sorry if I over simplified that without the math guys!

[This message has been edited by KA (edited 09-26-2005).]

quote Originally posted by Blacktree: According to my calculations, the cross-sectional area of the throttle body, at wide open throttle, is approximately 3 square inches, i.e. 0.0208 square feet (counting the obstruction from the throttle plate).

Assuming that Blacktree's calculation is correct, the inlet section area is 3 sq inches from a TB of approx 50 mm inside diam. That's the same basic area of one-half of a dual opening 48mm TB used on L98, LT1, LT4 engines. My old LT1 flowed 220 grams/sec (Diamcom data via MAF sensor) at 5000 rpm when the engine was putting out approx 270 fwhp. 220 grams/sec mass flow rate is around 388 cfm. FWIW that's a 600 cfm TB that's capable of more than 400 fwhp if I had changed the cam and ported the heads, so that 48mm dual TB is not taxed when flowing only 388 cfm. All of this info (TB airflow, engine dyno numbers) is easily verified by looking at the many websites on L98/LT1/LT4 engines that use the stock factory 48mm dual TB because it's not a restriction until you are well over 400 fwhp.

Using the same logic for the v6, if that same dual 48mm TB had half the area, by using only one 48mm bore, then the TB would have flowed 194 cfm to make 135 fwhp from an engine half the size of the 5.7 (2.85 liters). Since the 48mm dual TB can flow in excess of 600 cfm, then the single 48mm bore TB (like the one used on the v6) can support a max flow of 300+ cfm. 300 cfm is greater than either of the engine flow estimates in my last post for either the 3.4 or 2.8 application. So the single 48mm TB is not undersized, and by extension neither is the single 50mm TB mentioned by Blacktree.

Many v8 owners mistakenly think that adding a dual 50mm TB will help engine power... but it results in no extra power and an idle (pneumatic) circuit that needs revision. IMO that same comment applies here, because you have a 50mm monoblade TB that's almost the same size as the one used on the v8s, and you have nearly half the engine size of the v8.

The reason why an engine's output power won't increase, or the airflow moving through the engine won't increase, with a change to the engine size or cam, is IF and only IF there is already a flow restriction somewhere in the intake tract such that the local Mach Index for airflow is 0.5 or greater. If the Mach Index is less than 0.5, then you can alter the cam or engine size and get a proportional increase in airflow so long as ther Mach Index stays less than 0.5.

For the 3.4 engine, using 65% VE and 6000 rpm, needing 215 cfm total flow (remember the 50mm monoblade TB supports 300+ cfm per the above), and using an area of 3 square inches, then the spatial-avg max speed past the TB is 215*12*12*12/60 or 6192 in/sec. That's 516 ft/sec. The sound speed at an air intake temp of 105 deg F is going to be around 1200 ft/sec, so the Mach Index past the TB is 516/1200 = 0.43. For the 2.8, the Mach Index will be even less. FWIW 215 cfm is approx 150 fwhp. So a modified engine in excess of 150 fwhp probably needs a larger TB. I'm showing the reason why.

Mach Index:

C.F. Taylor (book), "The Internal Combustion Engine" Vol I and II, MIT Press.

J. B. Heywood (book), "Internal Combustion Engine Fundamentals (1988).

web sites:

http://www.wallaceracing.com/machcalc.php

http://speedtalk.com/forum/viewtopic.php?p=4835&sid=e2e54578a93d8639a9abe0f48927c4c1

or just search here on Mach Index:

http://speedtalk.com/forum/viewforum.php?f=1

And thanks for reminding me that the engine is a suction pump.

[This message has been edited by kdrolt (edited 09-27-2005).]

quote kdrolt said: Assuming that Blacktree's calculation is correct, the inlet section area is 3 sq inches from a TB of approx 50 mm inside diam.

That's close enough. I measured 52mm diameter, but the throttle plate blocks some of it.

quote Originally posted by Oreif: No the airspeed does not change with cam, heads or displacement. Your formula only uses the CFM flow of the intake and the RPM of the engine as it's data.

and later you also said

quote Originally posted by Oreif: Your math is based on engine displacement and using the proper throttle body/intake size. But if you have a smaller throttle body/intake then the engine requires, The max CFM of the throttle will not change. It will restrict the flow to the engine and the max airspeed at the throttle body will never go higher than what the throttle body can flow. You can only flow a given amount of air thru a given size throttle body.

In the first statement you said nothing about restrictions, that's why I said you were incorrect.

In the 2nd statement you revised the comment and included the restriction. I agree, which should have been obvious by what I already wrote. The Mach Index is the reason, and engineering explaination for why, the flow won't increase if the intake restriction is too large. The VE will continue to decrease with rpm once the Mach Index (or what Taylor called Z, his symbol for the Mach Index) exceeds the region of 0.5 to 0.6.

Mach Index doesn't appear on PFF (prior to this thread) so I'm not surprised that no one (here) has heard of it before.

All this is very interesting reading, but what about us guys with non-standard internals?

My 2.8 or 173ci is .050 overbored. It has fully ported heads, with the Torker II intake.

I understand the Torker flows at 360 cfm max, but other than that, I have no clue how to measure the overbore and porting in terms of how the engine flows.

Arn

quote Originally posted by kdrolt: In the first statement you said nothing about restrictions, that's why I said you were incorrect. In the 2nd statement you revised the comment and included the restriction. I agree, which should have been obvious by what I already wrote. The Mach Index is the reason, and engineering explaination for why, the flow won't increase if the intake restriction is too large. The VE will continue to decrease with rpm once the Mach Index (or what Taylor called Z, his symbol for the Mach Index) exceeds the region of 0.5 to 0.6. Mach Index doesn't appear on PFF (prior to this thread) so I'm not surprised that no one (here) has heard of it before.

The first statement does state the use of a restriction by using a 3.4L with a Fiero intake. Look at the last sentence of the first post:
"Increasing displacement will not make the intake flow more than it's area. Hence the problem with using a stock Fiero intake on a 3.4L engine."
ALthough I did not specifically use the word "restriction", It is common knowledge that the stock 2.8L intake is a restrictive intake when used on a 3.4L.

Arn ~ The Edelbrock intake flows 410cfm max, not 360cfm.

Thanks for the correct info Oreif.

I looked at the website posted above (gunnie's) and it looks pretty good, but I am at work and unable to download.

So with 300 cfm vs 410 cfm, my engine is somewhere in between. This is not bad, but I am still curious.

My ported 2.9 may be flowing closer to a 3.4 stock, than a 2.8 stock, but I don't know for sure.

Arn

[This message has been edited by Arns85GT (edited 09-27-2005).]

Everyone talks about TB size but, that really has nothing to do with what the stock manifold can flow. I've cut open an upper plenum and the neck behind the TB only measures about 2.5 square inches or 18 sq cm's. Anything over about a 48 cm TB is a waste.

I ran the Virtual Engine Calculator for CFM for my 2.9 and it came up as 309 cfm @ 6000 rpm at 100%VE.

So now I am puzzled. If the stock engine draws 300 cfm stock and the stock intake is rated at 318 cfm, and the stock intake is seen to be a restriction for the engine, how do you calculate the amount of intake required to satisfy the engine's maximum requirement for fuel mixture?

For instance, my engine with a 309 cfm requirement is increasing its HP quite a bit by running a 390 cfm intake/carb.

What is the formula that tells us how much additional available cfm is required for the maximum performance for the engine?

It has to be a percentage of the capacity of the engine, but what is it?

Arn

quote Originally posted by Arns85GT: I ran the Virtual Engine Calculator for CFM for my 2.9 and it came up as 309 cfm @ 6000 rpm at 100%VE. So now I am puzzled. If the stock engine draws 300 cfm stock and the stock intake is rated at 318 cfm, and the stock intake is seen to be a restriction for the engine, how do you calculate the amount of intake required to satisfy the engine's maximum requirement for fuel mixture? For instance, my engine with a 309 cfm requirement is increasing its HP quite a bit by running a 390 cfm intake/carb. What is the formula that tells us how much additional available cfm is required for the maximum performance for the engine? It has to be a percentage of the capacity of the engine, but what is it? Arn

the stock intake is almost pefect for a stock engine. its the modded 2.8's/3.1/3.4's that have the troubles with the stock intake. they need a little more flow in the upped end. the 20% more displacement needs 20% more intake. then if you got a cam with longer duration & more lift, the intake needs even more. and if you get stronger valve springs, and get the engines redline up some, you need even more. a 3.4 with a good cam & valvetrain will redline at 7000. but, the stock intake only lets in enough air to 4500-5000 rpm

So, the engine breathes at 300 cfm, in theory. If you do almost any mod, such as porting the exhaust manifolds, you will add at least 5 hp (actually 6-8) which is about 3+% increase.

3% of 300 cfm brings you to ~309 cfm, (what my 2.9 uses in theory without further mods). Add another mod to accumulate improvement to a total 14 hp or 10% and you need 330 cfm which the stock intake cannot deliver. Hence wasted money if you don't do something with the intake.

It stands to reason that if you add a power pulley (4+), port the exhaust manifolds (6 min+), add 1.6 rockers (5+?) to a stock engine you have reached a theoretical 15 extra horses, (or more) and a theoretical 10% improvement, therefore the maximum breathing of the stock intake is theoretically unable to keep up.

Either way, doing mods without doing something with your intake is "p*ssing in the wind". Do I have this right?

Arn

quote Originally posted by Arns85GT: Either way, doing mods without doing something with your intake is "p*ssing in the wind". Do I have this right? Arn

Basically yes. In order to get the most gains from performance mods, You should always make mods thru the entire path (intake thru exhaust). Just changing one section but not the others may give you a little gain, But changing/matching the entire path gives better performance and a better responding engine.

Which is why I keep telling people that there's no point in getting a Truleo and then running a stock exhaust.

Hence my stock ported intake with freer exhaust made 150rwhp and 3.4's with Trueleo's typically max out at 142rwhp.

Hence Oreif's ported crossover motor(s) (carb +F.I.) made lots more power by letting the engine inhale AND exhale properly.

But what do I know...

[This message has been edited by lou_dias (edited 09-28-2005).]

[QUOTE]Originally posted by lou_dias:

Which is why I keep telling people that there's no point in getting a Truleo and then running a stock exhaust.

Hence my stock ported intake with freer exhaust made 150rwhp and 3.4's with Trueleo's typically max out at 142rwhp.

Hence Oreif's ported crossover motor(s) (carb +F.I.) made lots more power by letting the engine inhale AND exhale properly.

I agree, like the intake the exhaust headers are a very poor designe. Whereas the intake is the bigest flow restriction, our intake will still provide some major gains in HP/TQ and RPM with a stock exhaust (just look at Matt's dyno chart), however, with a good set of headers it will do even better.

quote Originally posted by Francis T: I agree, like the intake the exhaust headers are a very poor designe. Whereas the intake is the bigest flow restriction, our intake will still provide some major gains in HP/TQ and RPM with a stock exhaust (just look at Matt's dyno chart), however, with a good set of headers it will do even better.

But, If you use the Trueleo and a decent exhaust you now need a decent cam and a good port job on the heads. With just the intake and exhaust changes, The head is what will now be limiting flow. The main reason the two 3.4L engines I built were able to get over 200hp was because the entire flow path was opened up and compression was increased.