Best exhaust to intake match?

MikeKanterakis

SCCoA Member
Hey guys, I was thinking of saving up my money and getting the best "bang" for my buck when it comes to the cheapest upgrade to my Most Prized 35'th SC. I'm only willing to get a bigger intake (whatever's easily purchasable) and exhaust system for my "Entirely and Completely Stock Set-up". Also, I may consider adjusting the SC Pulley to a 5% or 10% overdrive if it would get better timing. I looked for posts on intake, sc pulley, exhaust, and camshafts, but the reading is daunting, and if I really want an "indepth" opinion of what's going on, i need to read all the "ancient" posts to make sure I'm not missing any good information.

Any help would be greatly appreciated, and if there's a better category for this post, please feel free to move it there., Just make sure I get a note letting me know where it is moved :)

1. 5% Overdrive Pulley.


2. 10% Overdrive Pulley.


P.S. I also want to pass California Smog. :(

P.S.S. There's a great post in the member's only section about the new COMPcams camshaft.
 
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Whatever else you do get a better exhaust first. Bill Evanoff at supercoupe proformance sells a great system for the early style gas tank. I went with a late model tank. They are easy and cheap to find in boneyards. If you have the money its also a good time to up grade your fuel pump. From there your choice of exhaust is a lot bigger and better. Do the exhaust before a pulley. Intake choices are plentiful. Use a system that pulls cold air, not under the hood like I did. Tim
 
Thanks for the advice Tim, but I'm more interested in trying to match the intake "ability" to the exhaust "ability". I have been under the impression that you need an exhaust with "some" back-pressure in order to suppress the explosion from leaving the head. The reason this is important is b/c if the explosion leaves the cylinder, the exhaust valves started to get cooked.

So I was wondering if there is any way of knowing, given that the 5% and 10% pulleys would be the focus of the upgrade, what the best match is regarding the intake and exhaust?
 
Do the exhaust first, you can't get in if you can't get it out. Get a good exhaust and you can do whatever you want with the intake commensurate with the horsepower level of your particular engine. Keep in mind you won't get huge improvements with an overkill intake (larger maf and tb) on a basically stock engine. It is fallacy that you need back pressure, especially on a supercharged engine. However, you can go too big which results in lost exhaust velocity and scavenge. Don't worry about the exhaust valves, that's the environment they live in. The exhaust valve is closed at the moment of combustion. As the piston travels back up on the exhaust stroke some of the new intake charge is drawn out past the open exhaust valve which actually cools it. If you think about it there would be no way you could get enough back pressure to overcome the huge pressure created by the burning of the compressed intake charge. With a basically stock engine I wouldn't go bigger than a 5% overdrive pulley. Anything bigger and I believe you heat the compressed air to where detonation is a factor which would need a better intercooler setup to cool it down. John
 
Thanks for the input, I am qurious as to what exactly you mean when you say that you don't need back-pressure "especially on a supercharged engine". How would the supercharger lessen the need for backpressure?

Also, I fully agree with your other statements, however, the real crux of my question is, "what's the best match" between an exhaust setup and the available intake mods? Maybe this hasn't been really looked into before, b/c generally bigger is better, so we've all just headed in that general direction, but I'm really wondering where the "perfect" match is when setting up an intake and exhaust together.

Or am I looking at it all wrong. Maybe once I've opened up the intake as much as possible, and the exhaust as much as possible (or more than enough), then those aren't the limiting factors anymore, and THAT is the perfect match.

However, I'm still of the belief that you can over do a modification such that the negatives of said modification start working against any benefits your creating. Kinda like spinning the supercharger too fast, after a point, the super charger starts creating too much heat and robbing the crank of too much horsepower to be of benefit anymore.

Any light that can be shed on the benefits and negatives of exhaust and intake design would probably help me understand this.
 
MikeKanterakis said:
Hey guys, I was thinking of saving up my money and getting the best "bang" for my buck when it comes to the cheapest upgrade to my Most Prized 35'th SC. I'm only willing to get a bigger intake (whatever's easily purchasable) and exhaust system for my "Entirely and Completely Stock Set-up".

I would suggest the exhaust first. The best bang for the buck would be to go with a set of manifolds ported out either by Tbird88 or have them ported out locally. The collectors are really really small on the stock manifolds. It will look "stock" for the inspectors at your local smog shop.

Also, get a cat back system. You can go with the SuperCoupe Performance cat back system but if money is tight a competant shop should be able to fab up something similar for less money. The SuperCoupe Performance exhaust consists of 2 1/2 inch downtubes into a magnaflow resonator with a single 3 inch outlet that follows the stock route around the gas tank. then back into 2 1/2 inch dual outlets. Just like stock just bigger pipe.

My exhaust is Supercoupe Performance from heads to tail pipe, Kook headers, highflow cats, cat back exhaust. I like the sound so far. I haven't been able to see about any performance increase since the motor has only been runing for a few days. In hind sight I think I should have had the system after the headers fabbed localy, but I didn't want to bang heads with the "if it ain't a 350 chevy it ain't worth the time" locals.

MikeKanterakis said:
Also, I may consider adjusting the SC Pulley to a 5% or 10% overdrive if it would get better timing. I looked for posts on intake, sc pulley, exhaust, and camshafts, but the reading is daunting, and if I really want an "indepth" opinion of what's going on, i need to read all the "ancient" posts to make sure I'm not missing any good information.

10 % drives the supercharger a bit above Eaton's maximum rated RPM for the supercharger. People have also seen slipping problems with the 10% if you are only changing out the pulley on the superchager. High overdrive ratios can be obtained by swapping out the jackshaft/idler pulley without the slipping problem.

5% is a good spot to start since I don't believe you would be exceding Eaton's RPM limit or at least not that much. It is a place I plan on starting. But I can't give a hands on opinion of the pulley swaps since my blower is a 1994 model on a 1991 car. And I'm not sure what the stock diameter is, I know it's posted here someplace.

MikeKanterakis said:
Any help would be greatly appreciated, and if there's a better category for this post, please feel free to move it there., Just make sure I get a note letting me know where it is moved :)

1. 5% Overdrive Pulley.


2. 10% Overdrive Pulley.


P.S. I also want to pass California Smog. :(

I feel for you. But I live where there is no emisions check.... for now.

MikeKanterakis said:
P.S.S. There's a great post in the member's only section about the new COMPcams camshaft.

Yep, that is going to be sweet when I get around to putting a new cam in... hopefully for not some time, my credit cards are hurting as it is.
 
You raise a good question but the answer to that is not going to be practical to give. I can only hope to give you some food for thought.

First of all, backpressure is never a good thing. However, since backpressure exists, systems are designed to account for some backpressure and therefore removing backpressure can have a detrimental effect in certain cases.

People often confuse backpressure with exhaust velocity and efficiency. Since it is very difficult to measure exhaust gas velocity at all points in the exhaust system it is easier just to refer to back pressure and not address the real concerns.

The key with exhaust is to maintain good velocity so that the gases get out of the pipes as quickly as possible without losing too much energy. If the exhaust gases have the opportunity to cool off and subsequently slow down too much while still inside the pipes, then energy will be required to push them out. There is also the issue with maintaining airflow in the cylinder that works in cooperation with the camshaft profile. If a motor is simply operated only in the rpm ranges that the camshaft was designed for, this is not such a problem, however, when the motor is operated away from the ideal operating range of the cam design (that includes most of us) then it becomes relevant that we match the exhaust system to the driving style.

One small example of this is if you have a cam profile that is timed for high rpm running and lets say you install a set of long tube headers on it that are tuned for low rpm use, you will find that the increased scavenging effect of the longtubes at low rpm will draw unburnt fuel past the chamber due to the large overlap period of the high rpm cam design. Then at higher rpms where the cam profile is working ideally, those same long tube headers that were designed for low rpm torque will create a restriction and the motor will end up being inneffient at low rpm and weak at high rpm. Hence matching components is a science that we cannot begin to get into here with these cars and our limited resources.

In the case of our stock motors, they do not have much overlap in the first place, so there is no danger of drawing raw fuel into the exhaust. The only danger we have is making the exhaust too big so that exhaust velocity drops and backpressure actually increases.

For any and all stock or mostly stock SC's, 2.25" headpipes are quite adequate and it would be of benefit to move the converters as far downstream as you possibly can. 18" to 24" would be best. Then maintain cross-sectional area of your pipes out the back. Straight through mufflers are preffered on any boosted application. A 2-1-2 design will be more efficient compared to a true dual design. Maintaining velocity throughout the system is very important.

As for the intake in front of the supercharger, bigger is better and that is about all there is to that. The supercharger actually regulates flow through the motor, so big or small on the intake side will only have a marginal effect on boost levels and will have no effect on driveability or mileage.

Regarding the blower, I feel that a stock blower should not be overdriven more than 5% or perhaps I should say no more than about 14psi. Once the blower has been ported it will have lower outlet temps that allow you to run up to about 16-17psi but then a bigger intercooler should still be used.

One of the problems that we have in this community in really quantifying some of these theories is that we have had such a hard time getting these cars to run consistently regardless of mods or upgrades. What has worked wonderfully for me and supports my theories has not worked for other people for whatever reason and so establishing a firm guideline is very difficult. People simply won't agree on what works or doesn't.

For what it is worth, some of the best computer modelling suggests that our motors should make good power up to 5500 with the stock camshaft. For some reason our motors peak at 4600. Obviously there are some other factors other than intake and exhaust parts that are standing in the way. ;) :cool:
 
Mike - What I meant by my statement that exhaust back pressure is more detrimental on a supercharged engine than a normally aspirated engine is this. Back pressure will cause higher boost pressures without attendant power increases because of higher heat and less efficiency. Thats why when you open up the exhaust you will usually see lower boost pressure but you can feel a power gain. Any engine benefits from less back pressure, but I believe a supercharged engine benefits more. I concur with everything XR7Dave said, as I don't think this is a "one size fits all" issue. John
 
Wow guys, that's some really great info. I see what you're saying about trying to have consistent results. But that's the burden of our kind, we're re-inventing the wheel.

I really appreciate all the information, but I have another question that I'm not seeing the answer to from what has been discussed here and what I've read elsewhere. If we open up the intake, and raise the rpm of the supercharger, then we're increasing boost. However, if we open up the exhaust, we lower boost. So, if we spin the supercharger fast enough, but keep the exhaust proportionally open, won't that keep boost levels at say approximately normal range, but increase the power production of the vehicle? (I'm also purposefully leaving out any mention of the increased heat produced by the supercharger. I'm trying to get a grasp of where the true gains are with regard to power production and leaving the associated drawbacks for a later time.)

Or, are the internals of the engine, cylinder size, and camshaft the true limiting factor on any engine, and therefore, the only way to produce more power is to spin that engine as fast as possible, thereby burning more fuel in a shorter period of time and porpelling the car that much faster?

Also, XR7 Dave, what are the backpressure considerations that are built into the system that, removing the backpressure, would be detrimental to?
 
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the way the sc works the more exhaust you get out the more new fresh air will come in i ported my exhaust and exhaust side of heads with no intake work and wow i wanna take the heads back off and do some more , my other car with stock exhaust is under boost a lot more because it has to push the exhaust out too and it is not accelerating as much
 
rlong, could you describe a little more what you noticed to be the differences after you ported out the exhaust? Was the rest of the system stock?
 
if you search for the pics of the cutaway heads you will see the big restriction in the exhast side of the heads . i got a bigger resonator in the middle and used the stock mufflers in the rear they are pretty good . i tried the stock resonator without the rear mufflers and it was kinda loud for me not too bad i ran it about a year that way but the head porting made my car rip abd i just did the exhaust ports on the head with a dremel i didnt even do a lot just smoothed that big ridege behind the valve mainly and matched the exhaust manifold to the gasket
 
So, if we spin the supercharger fast enough, but keep the exhaust proportionally open, won't that keep boost levels at say approximately normal range, but increase the power production of the vehicle? (I'm also purposefully leaving out any mention of the increased heat produced by the supercharger.
It's not that simple. There are many other restrictions in the system besides the exhaust. You will find that even with a more or less open exhaust boost will still climb when overdriving the supercharger. You are on the right track though. My wife's XR7 makes 340rwhp at "only" 13.5psi boost.
 
Summary

That's so simple, it's perfect. I can't believe I didn't think of it myself. I always just assumed that there would be no way for me to know just how well the exhaust manifold would line up with the head, but once i put the exhaust gasket over the manifold, it was clear as day. And I know that the exhaust gasket is a good pattern, because it lines up perfectly with the head. :) Now, i'm gonna take my bastard file and grind away.

So, to sum up this thread, my initial "bang for the buck" upgrade to the bird will be to leave the intake as is for now, get the 5% pully for the supercharger, clean up the exhaust manifolds so they at least line up better with the heads, and put my money down on a decent exhaust system with 2.25'' pipe, in a 2-1-2 fashion, following the stock exhaust path already layed out, using magnaflow "straight-through" mufflers.


Thanks everyone for your help, your comments were highly informative and I appreciate them. That's what makes SCCOA great!
 
Less pipe surface area = less heat loss and less friction/resistance to airflow. It is also a narrower package meaning larger bend radii for smoother flow around/past the tank and dif.

It also weighs less and is easier to make. ;)
 
And I know that the exhaust gasket is a good pattern, because it lines up perfectly with the head. Now, i'm gonna take my bastard file and grind away.

Mike,

I hope your talking about grinding on the exhaust manifold and not the head. Making the exhaust ports larger won't necessarly make them flow better. My exhaust ports are actually smaller than stock.

David
 
Yes, to clarify, I am only grinding away on the exhaust manifold. Too bad I finished all but one before placing the gasket on the head to check the match up. The exhaust ports on the head are much smaller than the exhaust manifold ports. And here I thought I was making up for the fact that the exhaust manifolds "warped" a little during the course of this Head Job.

In the end, the exhaust manifold now matches the gasket which is a "much" bigger opening than the hole on the head. Maybe I have a hold in my head. I swear, my hands have about had it with this head-gasket job. btwn sanding the block, heads, and grinding out the bolt holes on the exhaust manifolds (and the ports on the exhaust manifold, and those two bolts I had to easy out of the other exhaust manifold...) I put the SC in SuCker!!! :p
 
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I hope that before you spent all that time grinding on the ports that you opened up the collectors to a full 2" first. :cool:
 
Interesting idea. I looked at the collector end, and it's at 2.75'' inner diameter. So, that's about an 1/8th of an inch on either end. sounds like a good idea. What did you use? An engine hone kit?

My only consideration is that the sealing seat on the collector end will end up about 1/2 the current size. What did you find after honeing yours out? Any problems matching it back up to the stock exhaust pipes?
 
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