I have a pretty much stock 5.7 TBi with a high lift/duration cam. Edelbrock Headers with a y-pipe that narrows to 2 1/2 inches. 2-1/2 inch exhaust is what everyone recommends for the HP that i have. People are recommending that i stay with 2.5 " all the way out because they say if i go to 3 " the reduced backpressure will cause the computer to do screwy things with the idle mixture or something like that.

BUt everyone on here is saying anything less than 3" sux.

Anyway, Ive got this complete spintech 3" catback, I want to hurry up an get on the car, but i have this 2.5 " y pipe and stock cat.

Should i just cut the y -pipe at the reducer and get a cat with 3"in and out? and what about this backpressure deal?

 

I'd say put it on. For now you can leave the cat the way it is. After you have more funds then I would recommend getting a 3 inch cat and getting rid of the reducer. At that point your system should flow pretty good. Remember that the less back pressure that you have, the better the car is going to run. Some poeple will tell you differently though. For more info, do a search for back pressure. This is definatly a subject that has been beat to death and then beat again. Also, since you have a bigger cam your getting more fuel and getting more air out so the more flow you have the better it will run.

Hope that helps.

 

You would benifit from a 3" exhaust. Backpressure is bad and you never want it. People get this confused with scavaging. Chip work will make the most of every mod on a TBI set-up.

 

Thanks guys, Then thats it The 3 inch spintech will be on by the weekend, if the cat gets here by then.....I can hardly wait. :lala:

 

if your bored take a look some time

https://www.thirdgen.org/techbb2/sho...t=backpressure

has lots of interesting info, link, and other ppl chiming in
but good read none the less

993

 

Wow...lol....Okay ive come to the conclusion that backpressure is bad anyway you look at it.

the fact of the matter is that going to a too large exhaust pipe actually can create more backpressure because of the eddies and swirling gas effect thing happening. Its so ez.

I think 3" is fine for my car. Oh and i went with a magnaflow cat.

 

No Muffler, no cat, and hardley any pipe. Exits right at the Y pipe. Noticed increased throttle response, and power all the way around. Did I do good? hehe

 

...

 

I hope you keep your windows open a crack all the time.

 

usualy all the way down. stupid poison gasses.

 

not much back pressure though!