well on my single project im expecting 430 to 450 hp, but i dont know if 3.5" will be enough or better go with the 4" dowpipe and cat back combination, we dont have emission controls of anytipe here in my country so there will be no cat or after cats , just the dowpipe follow of the cat back pipe let me know what yiu think and if the 4" make the effor.
i think ill have to make the 4"dowpipe custom made since i dont find any aftermarket or store that sell it.

thanks

 

I back off the turbo with 3.5" - then i have it coupled to 4" just shortly after (about 6-8 inches).

The HP is going to depend on your turbo setup, fuel, etc etc.

 

i know it will depend on my set up i have verething to achieve the goal fmic,fuel sistem upgrade fpr,power fc,fuel pump 3 mm pettit engine etc just to know the gains of the 4"in hp, exhaust noise, less lag. etc
atp turbo sell a great vband flange 3" to 4" and custom made the downpipe.

 

then stick with the 4"

 

I have been having trouble finding a 3.5 " v-band to go with my 3.5" v-band turbine outlet on my new turbo. Any have any suggestions of where I can find one? The rest of my exhuast system is still 3" (midpipe and catback). What woud you guys recomend doing, perhaps making the custom 3.5" DP and just attaching that to my current midpipe. Where can I find a 3.5 -to- 3" piece? Any help or suggestions would be appreciated. Thanks

 

If you can't get it from Burns Stainless, I doubt you will ever get it. brunsstainless.com

 

It is proven that many have reached your goals with a 3" DP. Wasa mata wid u?

You're not talking enough of a goal for the effort of doing 3.5" let alone 4"

 

Bigger is better when it comes to after turbine tubing diameter. For those goals though 3" won't hinder much, but 3.5" is better (thers a big differance in spool between a 3" and 3.5" when talking about a car making over 300 hp). 4" is even better from a paper standpoint, but will there be a noticable gain in spool over the 3.5"? Most likely not and the noise level WIll be noticabley louder. Personally I'd go 3.5" (infact, thats what I'll be running).

~Mike.........

 

i made 463 on a 3" downpipe, STOCK CAT, and hks 3" cat back ! ive since swithed to full 3"no cat and could definatley tell the spool up difference and power gain.

for the power you want i would say do the 3" but i would imagine the 3.5 would spool even faster! what turbo are you going to use?

 

I use 3" for 488hp. De que parte de vene eres? yo soy de valencia.

 

I could be wrong, but isnt a smaller diameter in exhaust better for spool up since theres more pressure being built?

 

Wrong. Turbines work on a pressure differentual. More ahead of the turbine and less behind it. Only way to make less behind it is less restrictive exhaust. NO a smaller exhaust after the turbo will not increase bottom end, NO a smaller exhaust after the turbo will not increase torque, and NO a smaller exhaust after the turbo will not spool faster. Quite theopposite actually. The bigger the better for both quicker spooling AND more power / torque EVERY WERE in the power band.

YES, you can make great power using 3". But 3.5" will yield quicker spool yet, so why limit yourself if your going through the trouble of making an entire exhaust?

Hes asking about 3.5" to 4". I say 3.5" will be pleanty, 4" even better. But will the 4" yield better results ? Probly minimal at a cost of a LOT more noise. So best bet for 400~450 is the 3.5".

~Mike.............

 

3.5" is much louder. Why, I don't realy know. I can't say anthing about spool, as I just finished my 3.5" exhaust and need to actually drive the car. Hopefully, I can check it out this weekend.

How much of a change in the A/F ratio when going from 3 to 3.5", did you guys notice?

I'm hoping it won't be to much, but if it is, I'll give Ralph Friend@GZ motorsports a call for a retune.

Also, I wonder how much this effects guys like me who run way to big of a turbo for the amount of boost they run. I'm using a engine with around 50k miles on it, so I'm trying to keep the boost below 14lbs at most. Hoping this will keep the engine together for a little while longer. It would be nice to pickup anouther 15+rwhp at the same amount of boost. Anyone have an idea of power gains for the 10-14psi crowd? CJ

 

I didn't have to change fuel when going from 3" to 3.5". Don't think I picked up HP in the process, but I know I lowered pressure post turbo.

 

My friend made 450rwhp@15psi w/ full 3" through the RB Turboback (FC) w/ a t70 and a streetport, thats 450rwhp on pump gas.

 

I had a chance to drive my car. I can't realy tell a difference in power, but boost control is much more difficult. Instead of 11psi with my profec off, now I see 12-12.5, according to the commander. Boost does come on a bit earlier as I'm seeing 11-12psi by 3,200rpms in 3rd gear.

I'll know what the bottom line is once the local drag strip opens. CJ

 

At what rpm did you get your boost befor?

 

the goal is 450 hp daily 500hp race use.we are going to custom made the the downpipe with a v band clamp (atpturbo.com)and planning to add the hks racing titanium exhaust .
probably will have spikes on the boost reads,but i thing we will have less lag, the noise is not a complain yo can see the video on the hks web site is not tha loud.
i thing will gain also a few hp in the entire rpm band.

 

I saw the same amount of boost around 3,400 or so. Not a major difference, but a little is better than none. This decrease could also from me changing my IC piping. CJ