Turbo down pipe

[sLoWnStEaDy]

At what point is bigger NOT better? running a 70mm turbo on a 302, 10-12 PSI, what size down pipe would be best, I was thinking 3.5" would be good? the turbine outlet is 3.25", I am just going to get a "tail pipe kit" that costs about $100~ they have 3", 3.5" or 4". They are mandrel bends and slip fits.

http://cgi.ebay.com/ebaymotors/3-5-UNIV ... ccessories (http://cgi.ebay.com/ebaymotors/3-5-UNIVERSAL-4-PC-EXHAUST-TAILPIPE-KIT-TRUCK-VAN-SUV-_W0QQcmdZViewItemQQhashZitem5889fe16b5QQitemZ38027 2252597QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccesso ries)

I have the MindTrain dual 2.5" "catback" in the car still from when it was a rotary. basically it s just 4 glass packs (on each side) and straight pipe. The plan is to just run the down pipe back to that.

[TbTalon94]

3.5"-4" would be good.

[Drifte]

3.5" dp, and 3.5" exhaust. keeping it all the same size is your best performance option. Even a tip of some sort (any change in size) has negative effects.

[sLoWnStEaDy]

Well, I am, once again on a tight budget so I just have to use as much of what I have as I can. I am trying to keep it a "$2500 car" so I am recycling. Using money from stuff I am selling off the car to buy the stuff I need for the turbo setup.

[AutoMods]

the best exhaust is no exhaust for turbo cars. the bigger the better. 3" should be fine for 500whp. I've heard of 800whp on a 3" downpipe but there is power to be released by going bigger.

Colton, I would guess that as long as your exhaust gets bigger the furthur away from the motor and never smaller then it will not hurt power. I've heard you say a tip hurts power before but i really can't see how it would unless it is smaller than the exhaust or restricts. i'd like to see the article. a big 5" tip would flow so good probabaly the same as no tip at all

[sLoWnStEaDy]

a 2.5" pipe has a cross sectional area of 4.9", where as a 3.5" pipe is 9.2". So, a pair of 2.5" pipes would be 9.8". So, that would mean the exhaust would be getting bigger as it goes back.

I.E. I think I bought the mindtrain catback from you didn't I? If so then you know what it is, I would just be connecting a 3.5" downpipe to that right where it splits. I replaced the single 2.5" inlet with a 3.5" already so...

[s13kid]

So, that would mean the exhaust would be getting bigger as it goes back.

What?

*edit Oh I think I got it. 3.5" downpipe splits into two 2.5" pipes?

[TbTalon94]

Just like Ryan said a 3" exhaust would be good for 500whp. Many people tend to think that because it's a big motor and all it needs bigger exhaust. When it comes down to it your still going through a small turbine wheel.

It seams that 3" exhausts are good for right up to around 750whp. From then on you benefit from going bigger, and you also DON'T benefit from going bigger below that hp level.

Even though I don't like Buschur, he did some great testing back in the day with exhaust sizes...and so did AMS. There's a reason why one of their R35's made 700+whp on a single 3" exhaust.

[sLoWnStEaDy]

I ended up getting the 3.5", it actually found it cheaper than the 3" so I figured, what the hell. Also, the v-band flange I got has a 3.5" inner diameter to so I won't have to mess with shrinking or enlarging the pipe to fit in the v-band flange.

[Drifte]

just fyi, we stock v-band flanges and clamps at work, Precision, vibrant, turbonetics etc.

[sLoWnStEaDy]

just fyi, we stock v-band flanges and clamps at work, Precision, vibrant, turbonetics etc.

You guys don't have any used stuff at all do you? I am coming up on my budget but all I really need now is a wastegate and wideband setup.