loss of torque after intake and exhaust

I am contemplating putting in a 3" cat back thermal exhaust onto my SC GSR and is expecting to lose torque on the low end.

It is well known that if you put in a free flowing intake and exhaust your car will gain hp on the top end and suffer the loss of torque on the low end. The normal explanation is your engine needs back pressure to operate properly, but why is that ? I was wondering if anyone has the answer to this.

Thanks,
Carson19

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94 GSR JRSC 8 psi

heah carson19 check the archives man
See here for alittle info:
http://www.hostboard.com/ubb/Forum40/HTML/001298.html


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'95 Civic Ex Coupe
JRSC 6psi w/Nos 25 shot
1/4 et: 14.4@98mph w/o NOS
13.98 w/NOS

Hey you finally posted Carson! Hehehe...
Here's what somebody (i.e. TOO) posted on exhausts for SC appllications:

_____________________________________________
Headers: Blown engines have nothing in common with their N/A
counterparts. The headers based on TriY configurations and long 4 tube
designs simply do not perform as well under pressure as the short primary
4-1 designs. The Kamikaze is very similar in size and length to our best R&E
headers and its performance is also the best of any "available" header on
the market. Don't let the price fool you either, for a blower engine, this
is the ticket and money doesn't equal better performance here.

Exh. Systems: All of our testing over the years has clearly shown that
blown engines like to have exhaust systems that present very little
backpressure. Since a restrictive exhaust system can make boost gauge
readings higher, this is another instance, where making the trip out easier,
will actually drop the boost on the gauge and make the car accelerate
harder. Scavenging isn't a necessity, as with N/A engines, as the exhaust
gets quite a push during overlap by the blower pressure.
3" diameter systems seem to work the best with blowers.
Remember that additional exhaust area must be created to make
more power. Measure the dual exhaust pipes on a high performance
V-6 or V-8 car with similar power to yours. Calculate the respective
areas then add them together. I think you'll see that they typically
more area than the single 3" tube.
Also recommended is a 3" CAT to spread the area for the exhaust
travel without restriction.
The components that we've identified as being the most efficient
and easiest to install are from Thermal Research and Development.

_____________________________________________

http://greddy.com/media/products/PEexhaust156.jpg

Yes Zip, I am out of the closet. Following the previous post from Dec 29, TOO is recommending a short but large diameter intake, 3" cat, piping and exhaust. This better be worth it as it will be ear splitting loud regardless of how you drive.

I still have my reservations to the short intake as it will be sucking in nothing but hot air which the supercharger is very sensitive to.

The Feb 2000 issue of SCC have an article on a JR supercharged SI and gotten favourable results when using the AEM CAI versus a short air intake. On a hot day, the short air intake cause the engine to bog off idle adding a second or two before picking up speed. The bog was completely gone when they installed the AEM CAI. They tested this on a dyno and on the streets. I also spoke to the folks at Motorsport Techniques over at Hayward and was told the same thing. Henry Chan of Revolutions motorsports (The JR distributor where I got my SC) also advise me to to go with the AEM CAI. It makes a big difference during stop and go traffic on a hot day.

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94 GSR JRSC 8 psi

It's not that the engine needs back pressure, rather the engine needs velocity.

You see if the pipe is too big, the exhaust will flow well, but it won't flow fast. No engine want's back pressure, it just wants volocity.

Now with the SC, you'll have enough exhaust gas, that it won't be a problem keeping the velocity up, if was a turbo, you *might* feel a little more lag, but on the SC, a 3 inch exaust simply makes more power. It also makes a lot more noise.

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Lundgren
Lundgren's Integra Site
My AllAdvantage Page

The Groupbuy Center

The SCC article failed to realize that at elevated Fuel Pressures, and retarded timing, the engine is going to bog more on a hot day. It has very little to do with the intake.

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The engine only takes in heated air when your at idle. Once your moving, the deviance in the ambient air temp and your engine compartment temp should no more than be 15-20 degrees. I believe SSBP, "the orginal smack talker of the JRSC", conducted a test a few months ago, in which he tested an AEM versus your common "filter on a stick". He concluded that the filter on a stick filter performed much better on the dyno. The SC isn't "sensitive" to heated air because it's the component that increases your intake temp. Compressing air always produces heat, its the law of thermodynamics. The only solution to effectively reduce compressed air temp is to use a H2O kit, or 25shot NOS. But I doubt you'll need it because many members on the board are running the 8lbs pulley w/out any problems.

Carson your 94 teg is OBDI, so compared to the temp. sensitive OBDII civic Si, your car won't retard timing as aggressively as the SCC car did.

Thanks for your insight guys. Lungdren, what you're saying is exhaust back pressure is not really an issue with a blower, I am wondering whether if it is worthwhile to go with a 3" piping and exhaust as TOO suggested. The original SCC review on the supercharged GSR claimed it achieved 235 to 230hp at the wheel on a GSR with headers, intake and exhaust running 6 psi versus 208 running stock. Does anyone know what kind of intake and exhaust would produce that kind of power without going 8 psi ? Could it be a 3" exhaust ? From the picture in the article, a short intake was used.

Thanks
Carson19

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94 GSR JRSC 8 psi