how much difference would it make if i put an aftermarket system on instead of the stock lg4 exhaust, im runnin a brand new 350 bored .060 over built basically stock but should run better than a 17.8, just wondering how much this is affecting my crappy times.

 

I'd say it's hurting you at least half a second. Maybe more. Go with an aftermarket system asap.

What kind of 350 is it?

 

I have an 86 with a 350 bored .030 over and the LG4 exhaust all so. I ran the stock exhaust set up on a desk top dyno and came out with 215hp and then swapped it to a dual 2.5 setup and the horses jumped to 330!! The reason behind this drastic increase (i was told) is because GM heads on a latter model 350 favored the exhaust, so basiclly it is well worth it. After pay day my exhaust is getting redon!

 

hahaha, sorry i had to laugh. LG4 exhaust sucks! it has no purpose on any engine. after my exhaust, my car was much quicker not to mention it sounded a lot better. car craft did a build up of a '84 LG4. they dynoed it after they put a full exhaust on it and the hp jumped by about 50 hp.


http://www.goingfaster.com/spo/carcraft325hp305.html

 

I'm gonna assume that the LG4 exhaust is the same as what I used to have when it was stock. Get rid of it! Now! Or actually it'll be 10 times easier to put the headers in when you swap motors I'd just do it then.

BTW - about desktop dyno. Don't entirely go by what it says, only used it as a guestimate. Its very optimistic and always says more than you'll ever see in the real world. But its useful for figuring out maybe where you should open things up next. But don't go trying to say "Desktop dyno said my new motor should have such n such HP" because it'll proabbly be way off. Not that Im trying to say thats what you're doing, I'm just saying its something you might not want to.

 

Yeah i know that desktop dyno isn't very accurate, but it gives a good idea on wheather or not it will hurt your car or make it better and that was my point. Besides my friend that uses it all the time is a mustang owner so go figure!

 

I'm ditching LG4 manifolds and Y pipe this weekend for Hedman 1 3/4" and Hedman Y into a Flowtech raceready cutout immediately after the Y pipe.

I will post track times.

 

I believe that the headmans are 1 5/8 but I would be interested to see your results.

Ben

 

I knew that the stock exhaust was very restrictive but i didnt know that it could be holding back up to 50hp, if i replaced my whole exhaust headers, y pipe, cat back etc...that should be enough to get my at least 16s

 

You are right... I meant to type 1 5/8. I will post results ASAP.

 

I got an LG4 hence my name.
These are the 68470's which go for $105 from jeg's.
Let me know what you think.

 

 

 

On a bone stock LG4, I believe that replacing the entire exhaust system (including very restrictive exhaust manifolds) would be an immediate torque increase and roughly 25 HP to be sure...

The stock system on my 84 Firebird with LG4 sucked so that even when i replaced the catback with no cat and a free-flowing exhaust...I noticed a performance increase...if I would have replaced the manifolds with headers, it would have been more dramatic.

If I had a stock LG4, the exhaust system would be the 1st thing I replace. More free power and a gas mileage increase due to increased efficiency...

Just my $.02.

 

Note the difference between the LG4 and an L69 Y-pipe.

JamesC

 

Oops. Restrictive? You bet.

JamesC

 

Going from a stock LG4 exhaust to a headers/3" cat/3" cat back is worth about 50hp on a dead stock motor (150 to 200 hp). On a moded motor or 350, it maybe worth 75 hp (or more). The stock y-pipe and cat are 2-1/4", which can only support 200hp in a small displacement/high rpm motor (like a 3L V6), has no place behind any V8 (unless it is a dual 2-1/4" exhaust).

When I swapped my stock LG4 exhaust for the Banks y/3" cat/3" cat back it was like night and day, maybe a 17.0 car became a 15.5 car with no other changes. I blew the stock tranny after a month or so because the motor picked up so much power from the exhuast, dual snorkel, and timing computer (about 220-225hp total).