Sorta OT, Any F/I experts here?

[flmcoupe]

Anyone here have experience with Superchargers? Neal? How do aftermarket cams (Schrick) affect S/C? Do they provide too much overlap? Does bottom end suffer like in a N/A engine or is it not an issue with the S/C? I've heard claims of 20-30 rwhp. Are they worth the money or am I better off saving money for a fresh set of Hoosiers? Schrick cams cost $1100!!! Car is in the shop getting a new head gasket, I'm trying to see what I can do while they got her opened up.

How about intake manifold? 95 M3 came with wider intake manifold, which is great for top end but bottom end does suffer a little. What do you think the results would be with a S/C?

Thanks for any advice!

[PseudoRealityX]

Being that you're using a Centrifugal supercharger (not my favorite), it's not going to really add any bottom end. They build boost by the cube(or square, I can't remember off the top of my head) of the rpm of the blades, and that's directly related to engine rpm on a supercharger. Therefore, you get little boost through the first half of your RPM band, with it then exponetially going up as you get close to redline. Basically, you're ONLY at full boost at redline. Of course there's ways to "gear it down", and stuff like that, but it's goign to take away efficiency at the top then...

Superchargers have a tendency of lessing the "peakyness" of a set of cams. Sure wild cams with huge overlap are going to gut the bottom end, but depending on how aggressive the stock cams are, a set of more aggressive ones should only help.

http://www.grapeaperacing.com/GrapeApeRacing/tech/superposcams.cfm
http://www.grapeaperacing.com/GrapeApeRacing/tech/supercencams.cfm

As in wider intake manifold, do you mean larger plenum? What do the runners look like?

Also, not sure if you have a header on that bad boy or not, but it'll REALLY help out with the supercharger. Look for something that's designed to work with the SC, or otherwise, look for something with nice big primaries and big collectors....I'd guess at least over 3" for the final one. (or does yours stay true twins all the way back?)

[flmcoupe]

Thanks for the info Jesse! Very helpful! Here's a dyno from the same setup on another M Coupe:
http://www.twofools.com/images/scvsstk.bmp

As you can see there's more torque available with the kit compare to stock, but not big numbers I guess.

Here's some info on the AA S/C kit (http://www.aatuning.com/Supercharged/Rotrex%20Supercharger.asp) to give you an idea.

95 M3 have larger/wider runners, you can notice it when you compare my car to Keith's, he's got an 95 M3.

No header yet, not a big help without removing the catalytic converters on my car, not gonna worry about it now, it's still a street car. This was tested by other S/C M3.

Thanks!

[Muddy]

That is an awful lot of money for such a small gain. You should have started with a FI car. :lol:

[OversteerS2K]

Boost that baby!! You've got the suspension/traction and the driving skill to catch Bob. Now all you need is a similar Hp. to Lb. ratio.

[PseudoRealityX]

Cams....definately.:)

[0HP930]

Damn, and I thought $450 for a set of performance cams for my car was pricey.

Then again if you are only looking for 20-30 HP from a supercharger I see no reason to change the cams.

If you want to get real power out of such a set up it would be better to start with changing the pistons and cams since the stock high compression is going to seriously limit your boost.

Any by the way Jesse, as an engineer in training I would think you would know better about the relationship of compressor wheel speed and pressure. Since its a centerfugal device the correct answer is squared. Looks like it might be time to brush up on your first year physics notes. ;) :P

[flmcoupe]

Muddy, I'm not paying full price for the kit, it's used with 1100 miles on it. Even brand new, it's one the lowest priced kits out there for my car, over 100 hp for $5700 is not bad actually (for BMW), that includes everything.

20-30 additional rwhp just by changing cams, and about 90 rwhp from the S/C. $1100 for parts only, no labor charge, car is already apart. Is the additional 20-30 rwhp worth it or am I better off saving money for a fresh set of Hoosiers for my car??? Personally I think tires are more important.

[Chin]

Er, im not sure how you are tring to relate this to autoX, but there is a forced induction Forum, just you let you know they would be much mroe helpful I think.

[PseudoRealityX]

Originally posted by 400HP930

Any by the way Jesse, as an engineer in training I would think you would know better about the relationship of compressor wheel speed and pressure. Since its a centerfugal device the correct answer is squared. Looks like it might be time to brush up on your first year physics notes. ;) :P


We don't study that in freshman physics, or even through sophomore year...as im now fully completed with the new ciriculum through the first 2 years. I'm so behind:)

[PseudoRealityX]

Originally posted by 400HP930

If you want to get real power out of such a set up it would be better to start with changing the pistons and cams since the stock high compression is going to seriously limit your boost.


awww...

man, I still don't like this philosophy. With proper tuning, and some decent headwork and worked pistons, you can run large (relatively) amounts of boost with decent static CR.

my comment about the cams was because the powerband, even WITH a supercharger is dropping after ~4500 rpm. I think the torque curve needs to continue....and some cams will definately help.

[oilleak]

I don't know, that torque curve looks pretty flat to me. What do the dyno results from the cams look like? Sometimes you wind up getting real peaky with cams. As far as blower or tires, you need tires but they only last a short time. If you amortize the blower (or cams) over their life, they're probabley less expensive than tires. I think the dirt cheap hoosier's I scored over the summer have cost about $5/run amortized. I try not to think about that.

[flmcoupe]

As far as blower or tires, you need tires but they only last a short time. If you amortize the blower (or cams) over their life, they're probabley less expensive than tires.

Well, when you put it that way it makes more sense to get the cams now! :) Specially since I don't have to pay for labor. Thanks Brian!

Couldn't find any dynos with the same setup but I found one with a different S/C kit. You can see the gains throughout the RPM band and bottom end doesn't suffer either!

Here's a link (http://www.bimmerforums.com/forum/showthread.php?threadid=89652&perpage=25&pagenumber=2) to the dyno with cams.

Additional tuning has to be done by AA down in Miami. So, now what do you think about cams???