90RS305

Ok, I've been told mixed things about the power-to-backpressure on the stock L03's (305 TBI) engines in the late 3rdgens. Of course you know, that on the stock setup, where the headers connect to the beggining of the exhaust tubes on the drivers side the pipe kinks imediatley right to meet up with the tube on the passenger side then goes down into the cat. Some people tell me that this is necessary for the proper amount of backpressure becuase the stock numbers on the car arent powerful enough to fully benefit from a true-dual setup. On the other hand, some people tell me that that extreme kink to the right is very restricting and is why car isn't performing at the potential that a 5.0L should. They are about 50/50 on either side of the argument. As raving car lunatic as I am, I can't figure out who is correct. If anyone is 100% on what the case is (or anyone, for that matter) please enlighten me on what is better for my car. Thanks in advance!

bigals87z28

well its really early, and reading that i can tell you neither of them is right, but the 2nd guy sounds like hes on to something. Ok, you need SOME back pressure or you wont make a little bit more torque. There are members on this site that have dual set ups, and im sure there not losing hp or torque. They also have built motors. They kink off to the right because if it didnt, that cat would be torn off after the first 10 miles of the car. Hence the wounderful cat bump on the passenger side. Free flowing is what you want. Get some headers, hi flow cat, and cat back and im sure you will be happy.

Mark A Shields

YOU DON'T WANT ANY BACKPRESSURE. BACKPRESSURE CAUSES THE ENGINE TO STRUGGLE AND A LOSS OF POWER HAPPENS. PEOPLE CONFUSE BACKPRESSURE WITH VELOCITY.

People that say the stock Y pipe is good, are retarded. That thing is so restrictive it's not funny. I guess we should shove potatos up are pipes as well, hey more backpressure, we'll make more power

Granted dual 3'' pipes on a stock L03 there would be some power loss due to loss of scavenging. But any 3rd Gen would benefit from a set of headers with a better flowing y pipe and a mandrel bent 3" cat-back.

AJ_92RS

Not to throw another wrench in the gears..... but on our cars, the EGR valve does need some backpressure to work properly.

If it doesn't have the backpressure it needs to work, you'll get a code 32. It really only happens while you're cruising at steady highway speeds, but if you don't expect it, it's a little surprising.

Mark A Shields

What's an EGR valve

90RS305

Ok yeah, I know what your talking about on the EGR valve. Do you think though, if I go to a true-dual setup on my car but left the cats on it, that would create a well balanced nutritional car? How much backpressure does it need to function properly and how much hp/trq. do I need to be pushing to where it really doesn't matter? Hmm......

AJ_92RS

I guess I should have added....... the SES light will come on while cruising like that, but you can often ignore it.

I didn't want to say that because I was afraid you'd never take the SES light serious after that. Don't assume that everytime the light comes on that it's the EGR. The one time you don't check it, it won't be the EGR causing it to come on.

Once you come to a stop and start again, the SES light will go off, and you won't see it again until you start cruising again. At least that's what mine did.

ctandc

I hate to tell you, but if you have ANY KIND of exhaust hooked to the manifolds / headers, you HAVE backpressure.

Any loss in torque is only really felt on small displacement engines that NEED every ounce of torque they can muster to push them to a higher RPM range where they can rev...


Now there is OVERKILL on exhaust, where it comes down to HP gains vs. time / $$$ spent, but most every internal combustion engine bigger than a go kart will GAIN power by taking restriction out of the exhaust.

As for the code 32 on the highway.... or intermittent...

MAKE ABSOLUTELY sure that the intake where the EGR mounts is clean of carbon...this is a COMMON, EVERYDAY problem with alot of GM's cars. The 4.3 Vortec engines are notorious for this....


It's normally not a bad EGR valve on most cars, it's the carbon building up and closing off the intake....


Cleaning the valve and the intake has fixed every code 32 problem I've ever seen except the RARE bad EGR valve.




HTH

MikeS

Yeah, let's beat the backpressure topic into the ground! If you search for backpressure, scavenging, etc, you'll find that there have been some in depth discussions on it.

I don't think anybody can make an argument for stock exhaust pieces over aftermarket. The only valid points about too big of an exhaust are with ridiculously oversized aftermarket exhausts on stock engines. On that topic, I'm running 1-3/4" SLP headers with 3" SLP cat back on a stock LB9 right now. That's neither here nor there though I guess. Anyways, backpressure is bad. You'd be well advised to replace the stock system with any one of the aftermarket 3" single exhaust systems.

90RS305

Great thats exactly what I wanted to know. Now the next question is (Well, more of how about your opinion) should I upgrade my headers first or go with the exhaust first? I definetely want to go with a true-dual setup...

AJ_92RS

Who said ANYTHING about the EGR valve being bad?

I thought the same thing after I put on a new cat and got a code 32. I changed the EGR assuming it was bad also. Guess what?????? I still got code 32 when driving on the highway for extented periods of time. I still do get it occasionally.

Perhaps you know of another reason mine (as well as MANY other's) is doing this after they install a free flowing exhaust? A brand new EGR can't have that much carbon built up.

ctandc

Read my post again......I said that most EGR valves WERE NOT bad. And the carbon isn't in the EGR valve, it's in the EGR passage inside the intake where the EGR mounts to.

Pull your EGR and stick a pick or small screwdriver down in there and see if you don't find out what I'm referring to.


HTH

AJ_92RS

Read my post again......

The code 32 has nothing to do with the EGR being bad after you put a low pressure exhaust (free flowing) on. The EGR just doesn't have enough positive backpressure at low RPMs (cruising at 65 MPH for long periods of time) because of the new exhaust. That's what causes the code 32.

The EGR works fine, but the ECM gets a multitude of signals from the O2 sensor, the MAP, etc. confuses the ECM into thinking the EGR is bad.

Formula305FI

Will puttin in an aftermarket chip solve the code 32 problem???? I go for inspection, and the emissions next week, i cant afford to fail it.... so im willing to do whatever to pass it for the last time :-) after this the egr comes off

bigals87z28

You could make your own gas mixture. get some 94 octane, 2-3 bottles of drygass, bottle of octane booster, and one of thoes "never fail" mixes... you should be good to go.