Adding headers/exhaust to SC = less HP?
03-22-2007, 04:02 AM
#31
Pro
There has been no talk about cooling here. I once killed a Yamaha YZ Motocross engine by trying to silence it to much (to be able to drive in the neighbourhood). The restrictive exhaust simply caused overheating because an important part of keeping the chamber temperaures down is blowthrough.
My point is: If you want power, and a less restrictive exhaust system combined with overlap is giving you lower pressure in the cylinder when the exhaust valve closes, then turn the the boost back up till you reach the same number (or even a little higher - the cooling effect will help you avoid detonation)
My point is: If you want power, and a less restrictive exhaust system combined with overlap is giving you lower pressure in the cylinder when the exhaust valve closes, then turn the the boost back up till you reach the same number (or even a little higher - the cooling effect will help you avoid detonation)
03-22-2007, 04:15 AM
#32
Three Wheelin'
Originally Posted by all4woody
Heres what I found. 89S4, Twin screwed, intercooled
Stock manifold, X-pipe, RMB, 8.5psi boost = 460rwhp
DEVEK Level 2, dual 3" exhaust and X-pipe, dual Borlas = 435-440rwhp
At high RPM I had major blowby with fuel and gas milage was worse.
I purchased some 3" baffles that slide in the end of my exhaust, it is a 1 1/2" pipe with 3 3" plates attached. All have holes that allow airflow. They are adjustable by means of a cap that can be placed inside at the end of the pipe, one solid and one with an inch hole in it. By changing the cap, or removing it alltogether, you can adjust the backpressure. I currently have the cap with the hole tig welded on. Car feels much faster with less blowby. My dyno shop is working on two cars for Barrett Jackson next week, so I can't get in to see where I'm at. When they get back, I will dyno with the current setup, pull out the insert and install the solid cap and dyno again. This should give a clear indication on the backpressure needed.
Hope that helps.
Later, Woody
Stock manifold, X-pipe, RMB, 8.5psi boost = 460rwhp
DEVEK Level 2, dual 3" exhaust and X-pipe, dual Borlas = 435-440rwhp
At high RPM I had major blowby with fuel and gas milage was worse.
I purchased some 3" baffles that slide in the end of my exhaust, it is a 1 1/2" pipe with 3 3" plates attached. All have holes that allow airflow. They are adjustable by means of a cap that can be placed inside at the end of the pipe, one solid and one with an inch hole in it. By changing the cap, or removing it alltogether, you can adjust the backpressure. I currently have the cap with the hole tig welded on. Car feels much faster with less blowby. My dyno shop is working on two cars for Barrett Jackson next week, so I can't get in to see where I'm at. When they get back, I will dyno with the current setup, pull out the insert and install the solid cap and dyno again. This should give a clear indication on the backpressure needed.
Hope that helps.
Later, Woody
https://rennlist.com/forums/attachme...d=179573&stc=1
GT cam tming.jpg
Last edited by Louie928; 03-18-2008 at 01:11 PM.
03-22-2007, 12:09 PM
#33
Rennlist Member
Originally Posted by Louie928
I must admit that I also figured what was good for a NA engine exhaust should be even more good for a SC engine. I accidently ran across a post on the Innovate forum where one of the tuner experts made a comment on a thread about why a certain turbo engine was showing lean. While turbo engines and SC engines react differently to cam overlap, here is his comments regarding blow through during the cam overlap period, and its effect on measured AFR. Here is the whole thread. http://www.innovatemotorsports.com/f...?t=5526&page=2
That got me thinking. About the same time I was talking with Tim Murphy about what exhaust to use on SC 928 engines. He mentioned that modelling using Engine Analyzer Pro didn't show any advantage with headers over the stock exhaust manifolds. I was about to start on some work to fit a better exhaust on a SC 928 and I figured headers and a 3" dual exhaust would be the ticket. I spent some time with Engine Analyzer Pro and found that there was no particular gain with headers and 3" exhaust over the stock manifolds and 2.5" exhaust. It did show about 3% improvement at 5000 rpm, but about the same below 4000 and above 5500. This was with 10 psi boost at the intake. Was that small gain worth the effort? The stock manifold/2.5" exhaust showed about 5 psi back pressure while the headers and 3" duals only showed 0.7 psi back pressure. The engine needed that 5 psi backpressure to keep more mixture in the cylinders. Without it, a lot simply blew out. Since it would have been unburned oxygen going out, the mixture would have shown leaner than it actually would have been too so more fuel would be added. I think I'd have created a fuel hungry car with not much more power than it had originally. In the end, I decided to stay with the stock manifolds, but go to 2.5" duals all the way back since that modeled pretty good in EAP and was a bit better than the stock rear exhaust.
Possibly on low boost SC engines freeing up the exhaust flow would help similar to the way it does on NA engines. And I'm sure that on higher boost engines having a too restricted exhaust isn't good either. There is probably an optimum point between exhaust back pressure and boost, and cam overlap. Right now, I don't know what it is. Bigger may not always better, for exhaust at least.
That got me thinking. About the same time I was talking with Tim Murphy about what exhaust to use on SC 928 engines. He mentioned that modelling using Engine Analyzer Pro didn't show any advantage with headers over the stock exhaust manifolds. I was about to start on some work to fit a better exhaust on a SC 928 and I figured headers and a 3" dual exhaust would be the ticket. I spent some time with Engine Analyzer Pro and found that there was no particular gain with headers and 3" exhaust over the stock manifolds and 2.5" exhaust. It did show about 3% improvement at 5000 rpm, but about the same below 4000 and above 5500. This was with 10 psi boost at the intake. Was that small gain worth the effort? The stock manifold/2.5" exhaust showed about 5 psi back pressure while the headers and 3" duals only showed 0.7 psi back pressure. The engine needed that 5 psi backpressure to keep more mixture in the cylinders. Without it, a lot simply blew out. Since it would have been unburned oxygen going out, the mixture would have shown leaner than it actually would have been too so more fuel would be added. I think I'd have created a fuel hungry car with not much more power than it had originally. In the end, I decided to stay with the stock manifolds, but go to 2.5" duals all the way back since that modeled pretty good in EAP and was a bit better than the stock rear exhaust.
Possibly on low boost SC engines freeing up the exhaust flow would help similar to the way it does on NA engines. And I'm sure that on higher boost engines having a too restricted exhaust isn't good either. There is probably an optimum point between exhaust back pressure and boost, and cam overlap. Right now, I don't know what it is. Bigger may not always better, for exhaust at least.
This from Rob:
That is interesting, we've found similar on 03 cobra's. We have a
customer who made 600rwhp with a KB 2.3L supercharger, it picked up a
whopping 5hp going from stock manifolds and a aftermarket H-pipe to
longtube headers. Now, with the correct camshafts that goes out the
window because the overlap is eliminated, or significantly reduced.
The catch is that they are using the exhaust to make up for the lack of
the correct camshafts. Higher exhaust backpressure leads to higher EGT's
and on really high hp cars this can become an issue.
customer who made 600rwhp with a KB 2.3L supercharger, it picked up a
whopping 5hp going from stock manifolds and a aftermarket H-pipe to
longtube headers. Now, with the correct camshafts that goes out the
window because the overlap is eliminated, or significantly reduced.
The catch is that they are using the exhaust to make up for the lack of
the correct camshafts. Higher exhaust backpressure leads to higher EGT's
and on really high hp cars this can become an issue.
03-22-2007, 01:24 PM
#34
I am going tomorrow to dyno with the baffle in and partially closed. It will be nice to know if there is a difference from the dyno with open 3".
I guess I did mean blow through. When driving, and at the dyno, since I went with big exhaust, at high RPM you get a vapor cloud from the back. No open flames, please. You can smell the fuel. The fuel reading on the dyno starts rich but ends up around 13.5 from 5k on up.
Marc, call when you get a chance.
Thanks, Woody
I guess I did mean blow through. When driving, and at the dyno, since I went with big exhaust, at high RPM you get a vapor cloud from the back. No open flames, please. You can smell the fuel. The fuel reading on the dyno starts rich but ends up around 13.5 from 5k on up.
Marc, call when you get a chance.
Thanks, Woody
03-22-2007, 01:34 PM
#35
Three Wheelin'
Originally Posted by all4woody
I am going tomorrow to dyno with the baffle in and partially closed. It will be nice to know if there is a difference from the dyno with open 3".
I guess I did mean blow through. When driving, and at the dyno, since I went with big exhaust, at high RPM you get a vapor cloud from the back. No open flames, please. You can smell the fuel. The fuel reading on the dyno starts rich but ends up around 13.5 from 5k on up.
Marc, call when you get a chance.
Thanks, Woody
I guess I did mean blow through. When driving, and at the dyno, since I went with big exhaust, at high RPM you get a vapor cloud from the back. No open flames, please. You can smell the fuel. The fuel reading on the dyno starts rich but ends up around 13.5 from 5k on up.
Marc, call when you get a chance.
Thanks, Woody
Spark plugs in the tailpipe!
03-22-2007, 02:21 PM
#36
Originally Posted by all4woody
I am going tomorrow to dyno with the baffle in and partially closed. It will be nice to know if there is a difference from the dyno with open 3".
I guess I did mean blow through. When driving, and at the dyno, since I went with big exhaust, at high RPM you get a vapor cloud from the back. No open flames, please. You can smell the fuel. The fuel reading on the dyno starts rich but ends up around 13.5 from 5k on up.
Marc, call when you get a chance.
Thanks, Woody
I guess I did mean blow through. When driving, and at the dyno, since I went with big exhaust, at high RPM you get a vapor cloud from the back. No open flames, please. You can smell the fuel. The fuel reading on the dyno starts rich but ends up around 13.5 from 5k on up.
Marc, call when you get a chance.
Thanks, Woody
The Higher (or I guess, some) overlap of the 85-86 cams, as well as the GT cams allow more boost in the first place because of their influence over the engine on "Effective compression"
If there is too much fuel, there is not enough air to burn it. There is a distinct possibility that some people may not be accepting this info as it should be, and I may be one of them.
Headers and a more free-breathing exhasut WILL help the engine become more efficient at what it does - which is an air pump. If there is an opportunity to raise the boost safely to a new, higher level because of the freer-flowing exhaust, then that may be the key to getting what can be had.
The fact that there is a 13.5 Air fuel ratio above 5k seems like there may be some room for more fine tuning of the maps on Woody's car, correct?
And as it was stated above, it is better to have a lower EGT, because that gives you more safety room. Higher EGT's mean higher Combustion temps, and higher combustion temps means higher metal temps, and higher metal temps means more detonation.
The variable valve idea is a great one. Up to about 3500rpm on a Vortech equipped car, it seems like it would be a good idea to get *some* backpressure, as long as its not too much.
03-22-2007, 02:28 PM
#37
Rennlist Member
This is an easy fix.
First, take off those silly hairdryers that blow the mixture through the combustion chamber.
Second, get really teenie tiny exhaust valves, I'm talking like off a briggs and stratton.
Next, surround the cylinders with magnets to further "hold" the mixture in there to make sure it burns completely.
No way that mixture is going anywhere until its good and burned up.
Actually, a very interesting thread.
A definite juggling of variables.
First, take off those silly hairdryers that blow the mixture through the combustion chamber.
Second, get really teenie tiny exhaust valves, I'm talking like off a briggs and stratton.
Next, surround the cylinders with magnets to further "hold" the mixture in there to make sure it burns completely.
No way that mixture is going anywhere until its good and burned up.
Actually, a very interesting thread.
A definite juggling of variables.
03-22-2007, 03:59 PM
#38
The size of my air filter may restrict the amount of air getting to the combustion chamber. This may be why the fuel is not burning. I will run at the dyno with no filter and see if that helps.
03-22-2007, 04:08 PM
#39
Three Wheelin'
I experimented some more with Engine Analyser Pro to see if I could figure out what might be happening with the seemingly not much gain when fitting a better exhaust to SC engines. I plotted Boost, % of residual exhaust left in the cylinders, and % of short circuit (blow through). As expected, the residual exhaust in the cylinders is quite a bit higher with the stock manifolds than with headers. It peaks out at about 3.8% at about 5500 RPM vs. about 2% for the better flowing exhaust. The short circuit amount is more with the header exhaust too, but still doesn't seem like much. Less than 1% max tapering down to about 0.5% at above 5500. I can't see that hurting much. The bigger difference is in the boost. There's between 1/2 to over 1 lb less with the better flowing exhaust between 4700 and 6000. It could be that the stock manifold's backpressure, while a detriment on one hand, allows the higher boost (denser charge) which about equals out the lower pumping loss of the lower back pressure high flow exhaust. The resultant lower boost with the better exhaust gives about the same resultant power. As someone else said, change pully size to get the boost back and the power would come up. I think Dave Lomas reported about 22 - 23 hp per lb of boost. Therefore, I think that with equivalent levels of boost, the better exhaust should give 20+ hp gain over the stock manifold. Naturally, that begs the question of why not simply go to higher boost with the stock manifolds and get about the same power increase? Probably a limit to the backpressure, residual exhaust %, and heat build up. One thing I did notice when analyzing ignition timing advance was that the stock manifold could tolerate more advance than the better flowing exhaust. I think because the residual exhaust (EGR) slowed the burn yet maybe wasn't so much as to cause too much heat. Engine Analyzer isn't the greatest software engine modeling app and exhaust is one of the weak areas. Could be my viewpoint that it's mostly a boost loss issue is wrong especially in light of Woody's fuel vapor trail.
https://rennlist.com/forums/attachme...d=179664&stc=1
Boost exhaust data.jpg
https://rennlist.com/forums/attachme...d=179664&stc=1
Boost exhaust data.jpg
Last edited by Louie928; 03-18-2008 at 01:11 PM.
03-22-2007, 06:18 PM
#40
Inventor
Rennlist Member
Rennlist Member
As I was putting around in traffic today I was thinking about EGR. As I understand it, EGR cools combustion temps. (That's why it's used for NOx reduction.) The loss of natural EGR because of the freer flowing exhaust raises the combustion temps, and may make for some predetonation, which would cause the EZK to back out the ignition timing?
With the large exhaust, maybe some valve timing advance would close the exhaust 'window' a little?
Originally Posted by Louie928
One thing I did notice when analyzing ignition timing advance was that the stock manifold could tolerate more advance than the better flowing exhaust. I think because the residual exhaust (EGR) slowed the burn yet maybe wasn't so much as to cause too much heat.
03-22-2007, 06:35 PM
#41
Three Wheelin'
Originally Posted by PorKen
As I was putting around in traffic today I was thinking about EGR. As I understand it, EGR cools combustion temps. (That's why it's used for NOx reduction.) The loss of natural EGR because of the freer flowing exhaust raises the combustion temps, and may make for some predetonation, which would cause the EZK to back out the ignition timing?
With the large exhaust, maybe some valve timing advance would close the exhaust 'window' a little?
With the large exhaust, maybe some valve timing advance would close the exhaust 'window' a little?
I think you are right there. Plotting the EGT with stock manifold and better flowing exhaust shows higher EGT for the free flowing exhaust. I don't really think there is enough valve overlap to cause the small power increase with better exhaust. I think it is the boost (mixture density) loss with the reduction of back pressure that does it. I went back to EAP and changed SC pulley ratio to get the same boost from 5000 to 6000 with bigger exhaust as it was with the stock manifolds. There was 39hp more at 5000, 21 hp more at 5500, and 21 hp more at 6000. This was at 8.5 - 9 psi boost. Now leaving the same pulley ratio for the big exhaust and going back to the stock manifold didn't lose a lot on the top end, but made a neg diffence from about 3500 to 4500 rpm. Exhaust back presure was getting up there.
Last edited by Louie928; 03-22-2007 at 07:00 PM.
03-22-2007, 07:53 PM
#43
If you can safely go to 10psi with the rest of the system, that means you have more power at 3000rpm because the ramp up is sooner. 5psi at 3500rpm would be nice.
03-22-2007, 09:17 PM
#44
Three Wheelin'
Originally Posted by all4woody
Wow, too much info to digest.
So, if I go to a 10psi pulley, with the open 3" exhaust, I should be fine?
So, if I go to a 10psi pulley, with the open 3" exhaust, I should be fine?
03-22-2007, 10:48 PM
#45
My boost gauge shows 8.5 to 9 psi. I will try to get as much info as possible. Gio will be there for a second set of eyes. I plan to make three pulls with the baffle and three without. we'll see.
Woody
Woody