Hi all. This is my first post here so thanks in advance for your replies. I have a '99 4x4 with light mods - Van Aaken V5, new good brand lift pump, and an AFE Stage II intake... all with the OE exaust (I don't have a CAT). I'm looking to eek every inch of performance I can from this truck but not go wild as I need it reliable and to get reasonable milage. The next mod will probably be a built valve body and then injectors and I'll call it good for a while. My quesiton is how much performance gain will I get if I go with a good 4" exhaust? Is it worth it for economy, low end, top end, etc?

Thanks much, Mike.

 

youll never be able to tell it over just going to straight thru muffler on stock exhaust.save your money and just ditch the factory muffler.....if you plan on doing alot more mods down the road,then it would be benificial......bama

 

Thanks.. what about turbo spool up time?

 

I'd stick with the stock exhaust until you upgrade the turbo. If you never upgrade the turbo, you don't need bigger exhaust, imo.

How restrictive can a 3.5" exhaust be after a turbo that's the equivalent of 1.75"?

 

You should see a slight reduction in EGT and spool up times.

 

Yeah thats about it...

and a much better sound...

Rick

 

same questions but im goin from all stock to a bullydog 4" full system.. thanks

 

Spool up time is the same, if anything it'll be a little slower. EGT's will drop though.

 

ok some say spool will increase?? some say decease??
what is the reasoning behind your claims.. since they are opposite??? (stock for stock)

 

I dont think you will notice any spool up change if you ask me with stock turbo its still going to spool really fast so i think its just up to you on the exhaust.

Also i didnt see you say anything about guages that would be my next mod if i were you when wanting to stay reliable

 

The way I see it, the exhaust gas is traveling faster in a smaller diameter pipe so the exhaust turbine will spin faster with the stock downpipe. Also, with a bigger diameter pipe the gas expands and cools off, then it has to be pushed out; hence, lag in spool up. Now a 4" downpipe isn't much bigger than stock so you won't notice a difference. But move up to a bigger turbo exhaust housing or go to a 5" downpipe (if you can fit it) and you will notice a lag in spool up.

 

let me see if i can find the site agean, one of the big exhaust componies put some of there reasearch out on the web, 4" is the optimal size for performance anything bigger does more to hurt then help, as for this siduation, i think it said the stock exhaust with no muff will be better for the setup you have now, but depending on the injectors you go with 4" might endup being what u want

 

save your money, you will not notice anything other than a different sound, and the drone that is annoying.
to get rid of the drone on mine, a second muffler was added

 

yep if i was running mild performance like a #10 plate and 215's i would just stick to a stock straight pipe. the 5in does seem to slow spool only if you have a full 5in. if you want to go with anything bigger than a 4 i would just get a system that is from the downpipe and back and keep the 4in downpipe.

 

my 5" made a decrease in egts by about 150-200 degrees...and with just all straight it sounds awesome also.