Swapping in my 3800SC and I'm thinking about putting a cam in it before I install the motor. I'm probably going to go turbo at some point, but I don't know how soon that will be.

Trying to decide if I should just get the turbo cam now so I don't have to do it later, will it work well with the SC for now? That or just get an SC cam in case I never go turbo... If I do that would a Supercharger cam work well if I go turbo?

It wont be too big a cam, VS or XP at most, not sure what turbo cam it would be.

I will guess it will be a bad idea. Cams are made specifically for what you used them for. Yes, you could use a turbo cam with a supercharger but since they both have different characteristics they won't be optimal for the opposite. It's like using a high performance N/A cam for a turbo, yeah it would work but it's not ideal.

Since you aren't sure about your plans, I would NOT install a turbo cam on the S/C.

my vote

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The List;
1) 98 Jetta TDI (55+ MPG) 2) 95 BMW 325i 5 spd (Wife's car) 3) 82 Chevy Scottsdale 6.2 (tow duty)
4) 87 Fiero 3800 S1 S/C 5spd (almost road ready) 5) 85 S10 diesel 5spd (engine donor) 6) 84 S10 (receiver) 7) 84 S10 2.5 5spd (parts)
8) 87 GMC S15 2.8 5spd parts truck 9) 91 Mercedes 190E (diesel 5spd swap) 10) 84 Mercedes 190D (donor) 11) 85 Fiero (parts)
12) 85 Fiero SE (7730 ecm, 3500) 13) 87 GT (7730 ecm, hybrid 2800, izusu 5spd swap soon)

There are several out there running the XP cam with a Turbo. They did the same thing as you did--started out SCed and then went turbo down the road. The XP responds well to a turbo just look at JNs dyno thread where he put down 500 HP.

The stock production cam is usually a good start regardless until you start to get high into boost when swapping in a turbo. This is one area I agree with the old rule of thumb on. If you're not looking for all out performance and will be using the car predominantly as a daily driver the stock SC cam should work fine in both scenarios. The area that makes the turbo cam different from the SC cam is the exhaust back pressure involved with the turbo. If your exhaust system breaths better than stock after the turbo you should get very good results. If your manifolds to the turbo breath well that will be even better (headers as opposed to log style manifolds). With a properly sized turbo your exhaust to boost pressure ratio will be in a good range which should be close to 2:1 again depending on how much boost you're running which will determine in part at what boost pressure you reach that point. I've been reading up on camshaft dynamics as of resent because I'm trying to make a decision about regrinding or keeping the stock cam.

Your driving habits need to be considered, I believe we all immediately get caught up in the high horsepower craze but when you're spending most of your driving in street light to street light traffic with an occasional stretch you will appreciate high torque more than high hp which you will probably be on the brakes for by the time it really starts to kick in. Currently my turbo grind has great top end but I would prefer more bottom end power because taking off from a light and getting up to the speed limit as quick as I can is where I get the most enjoyment out of driving the car.


Here is a link to an article in Pontiac HP where a company installs a turbo in place of the SC on the 3800 and on the naturally aspirated 3800 without a cam change and produce results that could cause you not to bother with the cam at all.

http://www.highperformancep...rand_prix/index.html

quote Originally posted by jaybeezi: It wont be too big a cam, VS or XP at most, not sure what turbo cam it would be.

Why?

An xpz would be a good choice on either count, turbo or SC. The SC setup would need to have an IC most likely to get worth while gains.

[This message has been edited by darkhorizon (edited 12-19-2009).]

quote Originally posted by Joseph Upson: Your driving habits need to be considered, I believe we all immediately get caught up in the high horsepower craze but when you're spending most of your driving in street light to street light traffic with an occasional stretch you will appreciate high torque more than high hp which you will probably be on the brakes for by the time it really starts to kick in.

Joseph touched on something that I would like to elaborate on...

is this going to be a DD and/or are you going for all out power?

this is a can of worms that I'm going to open, I shouldn't, but I am.

why I ask is this; the HP vs torque argument is really simple. If you look at the HP curve of an engine it is EXACTLY how it will perform and or feel as you drive. So, as you move the power band up it will be less daily driver friendly.

so, if you do a lot of DD'ing and stop and go, you really don't want to push the power band up, it will be slower as a DD.

as an example, I have two cars that are good for this point. I drive a jetta TDI, it makes 90 HP and 150 ft lbs. torque peaks at 1600 RPM. I also have a 95 BMW 325i, 190 HP 180 ft lbs, torque is up at 4000 RPM. The jetta is a few hundred lbs lighter, has longer gears (like 2100 RPM @ 60 where the BMW has to run 2600 RPM at 60). but is faster below 3K RPM because it has more HP below 3K RPM. From there up though, the BMW can walk it like nothing. The point is this, the HP curve is literally exactly what it will feel like when you drive, you can completely ingore peak numbers, and the torque curve altogether and see what it will be like.

-Brandon

You can throw all of this cam theory crap out the window... we are talking about boosted setups.

The ONLY reason to discuss cams in 3800 boosted setups is taking as much advantage of the head as possible. Cam installation is what determines powerband.

[This message has been edited by darkhorizon (edited 12-19-2009).]

That's why the production turbo cars tend to have turbos on the small side, it makes the car feel faster by reaching the effective power range faster. I expected traction problems with my setup but failed to account for the increased duration of the cam as well as an install position that was way off from the recommended install angle. The stock cam would certainly have been more aggressive off the line and although that's the kind of driving I do, that is not what I had my cam ground for so I'm about to do it over.

quote Originally posted by Joseph Upson: That's why the production turbo cars tend to have turbos on the small side, it makes the car feel faster by reaching the effective power range faster. I expected traction problems with my setup but failed to account for the increased duration of the cam as well as an install position that was way off from the recommended install angle. The stock cam would certainly have been more aggressive off the line and although that's the kind of driving I do, that is not what I had my cam ground for so I'm about to do it over.

The .2-.4 seconds you are out of boost, I am POSITIVE you do not care that you are making 10hp less than you would be normally.

quote Originally posted by darkhorizon: You can throw all of this cam theory crap out the window... we are talking about boosted setups. The ONLY reason to discuss cams in 3800 boosted setups is taking as much advantage of the head as possible. Cam installation is what determines powerband.

You'll have to expand on that a bit more, because in my experience particularly now, not considering the effects of the cam specs is exactly why I'm not happy with my offline performance vs. previous turbo builds using the stock cam. If install was all that mattered changing the position of my cam from an initial negative degree angle to positive relative to TDC should have cleared things up but aside from improving idle vacuum the increased duration compared to stock still took away quite a bit of my bottom end. To some degree you can ignore cam theory, but I would not suggest it to anyone trying to make an informed decision on what to do in this area.

Torque is more easily, as you said, added via cam degree'ing, and gear ratio. The cam itself decides total horsepower available. You typically want to install the cam in as advanced a position as possible and still retain the torque you want.

I dont see how if you are at full boost, with a aggressive "low torque " cam, you would be making "low" torque. I have a feeling that your issues are lying in turbo selection more so than anything else if you are not getting the powercurve you want, and have a cam setup to produce alot of power, as the torque just comes in from the fact you are turbo.

In a few of the DOHC cars I have played with, the cams in those cars will increase lag a bit and or delay turbo spooling, in turn for high end power, but they will not effect torque. In pushrod motors, this does not seem to be as apparent, due to a few of the benefits of pushrod motors.

quote Originally posted by darkhorizon: Torque is more easily, as you said, added via cam degree'ing, and gear ratio. The cam itself decides total horsepower available. You typically want to install the cam in as advanced a position as possible and still retain the torque you want. I dont see how if you are at full boost, with a aggressive "low torque " cam, you would be making "low" torque. I have a feeling that your issues are lying in turbo selection more so than anything else if you are not getting the powercurve you want, and have a cam setup to produce alot of power, as the torque just comes in from the fact you are turbo. In a few of the DOHC cars I have played with, the cams in those cars will increase lag a bit and or delay turbo spooling, in turn for high end power, but they will not effect torque. In pushrod motors, this does not seem to be as apparent, due to a few of the benefits of pushrod motors.

The torque peak shifts to the right along with the peak HP when duration is increased as well as the bulk of the area under both curves, hence the recommendation for higher stall converters and compression ratio with increasing duration or you'll have a dog off the line with or without a turbo. If the duration of my reground cam is as much as I think it is above stock, I'm missing at least 25 lb/ft off the line. Understand offline performance is where my focus is so taking off from a stop in the same car with 25 lb/ft shifted from 2000 rpm to say 5000 rpm due to a duration increase is not going to have the same feel on acceleration from a stand still even if in the end I have more peak torque, it boils down to abrupt vs gradual and that's the difference being felt. If I'm running 0-60 and reaching 60 mph in the final gear for the run before 5000 rpm then clearly having that 25 lb/ft back down around 2000 rpm will be more beneficial than in an area of the curve that I will not reach to utilize it before reaching the goal.

The duration is going to have more effect than the degree angle, in some cases the cam grind itself will limit how much benefit can be had with retarding or advancing a cam beyond the recommended install angle. There was about a 6 point difference in vacuum with my camshaft installed fully retarded vs fully advanced and although it wound up with far more advance than what was necessary, the better vacuum suggesting better low end efficiency didn''t result in remarkably better acceleration. In addition to that, a simulation of my cam specs showed that any retarding of the cam beyond 0 deg resulted in a loss of power where advancing it as much as 10 deg showed a gain of about 9 lb/ft but that's less than half of what was lost when the duration was increased above stock. So a balance of half or more of the area under the horsepower and torque curve needs to favor the left side of the performance grid for sprint type driving as opposed to hwy and quarter mile running which I would still have very good results with. I would prefer 400hp and 400 lb/ft by 5000 rpm than 500/500 by 7500 rpm because that's the way I drive. I just didn't use that reasoning before sending the cam off for the regrind.

I have an XP cam with a larger sized turbo. I do NOT have any lack of torque on the low end. Once the car hits 3600 rpms, it ****ing flies. Below that, the engine has PLENTY of torque to get you around very happily.

300 ft.lbs at 3000 RPMs is plenty in a fiero.



I know the graph looks funny, I was having clutch issues.

[This message has been edited by Jncomutt (edited 12-20-2009).]

quote Originally posted by Jncomutt: I have an XP cam with a larger sized turbo. I do NOT have any lack of torque on the low end. Once the car hits 3600 rpms, it ****ing flies. Below that, the engine has PLENTY of torque to get you around very happily. 300 ft.lbs at 3000 RPMs is plenty in a fiero.

What's a larger size turbo in terms of numerical equivalents that can be understood and is it the Holset with VGT which would void the comparison to anything else not using it since it can easily compensate for a good bit of bottom end efficiency lost to a more top end oriented camshaft. Also the boost level you're running is important to know as well as your engine specs compared to stock. The graph is impressive but not very helpful without all of the important specs. I don't know what an XP cam is to have an idea of its effects relative to stock.

So far I've run a max of 8 psi and the bulk of my torque loss is off the line through 2000 rpm, it may be pretty descent by 3000 rpm but I want it back down low. If I had given it more thought I could have reasoned that turning the boost up on the stock cam would have produced a quicker car with the stock camshaft in the range that I drive it in than a considerably long duration cam swap optimized for an area of the power band that I don't spend much time in. The stock cam already has a 6000 rpm hp peak, I can't imagine where its at now reground for more duration and top end. My twin turbo TPI 305 did the same thing with a performance roller cam meant for a 350 installed and an automatic trans.

In stock trim with a 3.23 rear end I could spin the wheels on take off from a stop naturally aspirated, with the crane compu cam intended for a 350 and rear end change to 3.73 gears with twin T3s and .48 turbine housings it would not spin the tires from a stand still because it had too much cam, but by the time it shifted to second gear where the cam came on the efficiency curve it was like night and day requiring left right steering to keep the car pointed straight ahead, it literally went from mild to wild in one gear change however an identical car lined up next to it with the stock cam would have been much quicker in the quarter due to the time lost waiting for it to blossom and then trying to keep the rear wheels behind it at 7 psi.

If you're an off the line and 0-60 driver I wouldn't bother the stock cam unless it's felt to be inadequate, or unresponsive to more boost. I can honestly say that my cam change was driven purely by a quest for a level of horsepower that I could have achieved with the stock cam and the appropriate boost level and not only kept the typical bottom end performance but added to it. This is one area I ignored reason in and am having to address it again as a result. Except in extreme performance use I see no reason to take the stock cam which also offers good fuel economy and swap it out to achieve what turning the boost up will accomplish. For an SC with limitations maybe, but not for a turbo which offers much more effective flexibility. I won't do it again except to add more bottom end torque and economy. I want fuel efficiency and performance and the neat thing about a turbo is that turning up the boost will not affect your fuel economy during off boost driving.

You may be able to increase fuel economy on a turbo car with an external wastegate by using a second boost control solenoid connected to the top of the wastegate that allows vacuum from the manifold to act on it and open it off boost to reduce exhaust restriction and allows it to close at WOT just before boost pressure onset. Just an interesting off topic piece of knowledge I thought I'd share.

Justinbart has the $50 VGT turbo on his manual setup, John has a regular "crappy" $700 turbo.

My crappy 70mm turbo was actually less than $600...

Joseph may be right with an automatic, although its a matter of preference. With a fiero manual transaxle, I will GLADLY give up that low end torque. The auto on the otherhand, I may miss it, but I doubt it. A decent converter will get the car to spool at the line, and then once at WOT the auto should not shift below the cam's 'efficient' area.

Jncomutt

Please check PM

quote Originally posted by Jncomutt: My crappy 70mm turbo was actually less than $600... Joseph may be right with an automatic, although its a matter of preference. With a fiero manual transaxle, I will GLADLY give up that low end torque. The auto on the otherhand, I may miss it, but I doubt it. A decent converter will get the car to spool at the line, and then once at WOT the auto should not shift below the cam's 'efficient' area.

Yea, the point of most of my posts was that it is really hard to push the "no torque" point into the areas you use.