As much as I hate it, I have come to a very bitter end as far as fighting CARB about my headers. Now the decision is whether to make the car a race car or suck it up and pull the headers off to keep it street legal.

So, I was looking around on the forum for exhaust ideas that would help compensate for the power I am going to lose. I was wondering if some folks who have performed any of these can give me some feedback on it. As of right now, I have Hooker long tube headers, high flow catalytic converter, Borla Y-pipe and Borla mufflers.

Ideas:
1)Porting the stock exhaust manifold. Brzezinski ports their ram horns and they say it makes a bit of a difference. From the pictures they show, they ported the hell out of the exhaust ports which should make them flow better. (BTW, the factory L98 manifolds are 2 1/2" right?)
2)Extrude honing the stock exhaust manifolds (I am almost certain no one here has done this...). Damn expensive for questionable results.
3)Switching over from the L98 exhaust to the LTx exhaust. I saw pictures that TJWong has done it and heard from others that this is definately doable for a garage mechanic. My question here is do you think there will be gain from switching from my current aftermarket Y-pipe (I am not sure about the size but I was told it is 3") to the factory (or even aftermarket if I can find one) 2.5" LTx exhaust with my Borla mufflers? If the 2.5" LTx exhaust tucks up better, my cross frame will fit much better which is a plus (3" will definately hang low).

I have read that the headers are probably giving me ~15HP. My goal is to get half of that back just from "stealth" exhaust modifications (8HP+). If I can do that, I think I will be satisfied.

 

ttt for all the daywalkers.

 

Sorry, I'm not sure about this first statement-"fighting CARB about my headers", what exactly does this mean? and it almost sounds like your intentions are to lose HP, is that correct?

 

I asked the same question a while back and didn't get much of a response (actually there were a few more replies but I think this thread was corrupted when CF made the switch to different forum software back then):

http://forums.corvetteforum.com/show...hlight=extrude

I also contacted the outfit below. I was told that they had heard extrude honing the LT1 exhaust manifolds was good for 10-15HP. I don't know about L98, though:

http://www.gesslerheadporting.com/me...enu/Services03

 

California Smog Police http://www.arb.ca.gov/homepage.htm Another good reason not to live there.

 

The problem is that C.A.R.B (California Air Resourse Board) won't allow any non-OEM parts on a regulated car that don't have an E.O. (Exemption Order) number. Therefore, since there are no headers for the C4 with an E.O. number, the headers have to go. It isn't his "intention" to lose power but he is being realistic in realizing that the change is going to cost him power. This post is about keeping that loss to a minimum.

RACE ON!!!

 

You only need to run it carb legal for one day every two years.

It's the game we play.

 

If I want long tubes, I'm running long tubes.

 

Why not use the SLP or Hooker Shorty headers. While they will not perform as well as a set of Long Tubes, they certainly will flow considerably better than the stock cast iron manifolds that some on a LTx engine. Given you have a L98 system which comes with similar tubular style manifolds, but there is still some gains to be had with the shorty headers. As for installing a LTx style exhaust, that should definitely give you some gains. A factory LTx exhaust system carries 2.75" tubes all the way back. They neck down a little at the resonator, and the rear section as far as I know are 2.75" tubes as well. You could even install a complete Borla system, which carries a CARB stamp, however for a 92 and up car. I don't know how the smog ***** there would take to installing a later model year system on an earlier car.

 

Thanks TJ. The smog jockeys out here dont know much about C4's. If it wasnt for the damn Hooker logo on the headers, the smog tech would of believed that they were stock headers (he asked me are they stock, oh wait a second).

The LTx install it something I am considering because I highly doubt, to the untrained eye, you could tell whether or not that is stock or not. All he looked for was the presence of a catalytic converter(s) and that was it. Then when they ask if the exhaust is stock, I can honestly say that it is truely a stock Corvette exhaust <cough> for a late model C4.

Centralcoaster, I dont know about you but the CHP are pulling that vehicle inspection crap up here. And CHP love to hang out on the highways around my area. Not worth the fraking fines and impound fees involved.

 

All you need to install the LTx exhaust is the center hanger that is bolted to your tranmission tail shaft housing and a left and right rear hangers. All of which are still available via GM. Here are the part numbers:

Transmission tail shaft exhaust hanger: 10157948
Left rear hanger: 10258672
Right Rear hanger: 10258673

You also need to 8mm x 1.25 x 25 0r 30mm long bolts to secure the transmission hanger

Then order the exhaust system of your choice or find a nice used LT4 take out system from a forum member. You can add two bullet CATs like what I have in my car or add them to the collectors of your EM or TPIS Long tube headers. I install them just after the transmission hanger and in front of the X pipe or resonator. They work fine in that location.

 

Hey cool, part numbers and everything! Thanks.

Hopefully with an LTx exhaust and bullet cats, I can get back some of the power I am going to lose by reinstalling the stock exhaust manifolds. Thanks for the help.

 

What about another brand of header that doesn't have the logo? Exotic Muscle headers are completely plain. Does CARB say you can't run anything non OEM? I hought it was something about moving cats from the stock location. Could be another state though. If you run shorty headers and use late model C4 exhaust, the cats stay in the stock location. If you must use exhaust manifolds there are some gains to be had by extrude/honing and port matching them, but they will not compete with headers. It's ironic that CARB prevents the use of a part (headers) that would actually allow the car to run more efficiently thus reducing pollution.

 

See CFI-EFI post. As for extrude honing, I havent seen any non-biased results that show if spending $750+shipping is worth it.

 

Ah I see. $750 plus shipping for maybe what 10 HP? That doesn't sound worth it. Save the cash.

 

I dont know if would be 10HP. If long tubes are 15HP and the best shorties are 8-10HP (maybe), I am not putting much stock in what extrude honing will do.

Then again, I am no expert. I put more value on fact and not speculation. Extrude honing may very well do 10-15HP like I have read... might shoot them an email to discuss this with them.

 

I was just throwing out a number, I have no idea really. As I understand it all the process does is smooth the rough surface caused by the metal casting process. Maybe enlarges passages slightly? I had an old roommate with an SVT contour that did this to his intake manifold. Can't say he had any appreciable gains but he never dynoed it. Then he got a turbo and said nuts to the little stuff.

 

I have been talking with Extrude Hone about using their process on my stock manifolds. Their response was "We have conducted horse power tests using the LT-1 cast exhaust manifolds. The power gains were 12-15 horse power using a stock engine. We also offer group buy discounts."

Hmm...

 

As soon as I buy a house, I'm getting a welder and making my own damn stock lookalike long tubes. fek the police

 

Putting them on the 90 this summer. Worst comes to worst, change em out and back again, no big deal