ranedoss27

iTrader: (4)

Currently have a built 408 iron block, 9:1 with truck heads and twin tc70 journal bearing turbos. I want to make the car more efficient so thinking about swapping to PTE 6766 ball bearing turbos with a set of AFR 230cc heads. Anyone think the 67's would be two small? I don't want to choke the motor out. I'm make a little over 800 right now and want to push it to about 950-1000

LS1NOVA

iTrader: (12)

Your current turbos or the 6766's can make your power goals. If it were mine I'd put PT7675's or Turbonetics 7575's on it.

DavidBoren

The 6766's would make your power goals, but if you want efficiency, then the 7675's or 7575's Nova mentioned would be better.

Get the larger turbos, or at least larger exhaust housings, to reduce backpressure.

Either way, you will probably notice the biggest difference, in both power and efficiency, by installing the afr heads, regardless of which turbos you choose.

stevieturbo

6766's will easily do 1000, and then some.

For only 1000hp, they are not too small.

ranedoss27

iTrader: (4)

Ya I want the smallest most efficient turbos to reach that goal so the car isn't so laggy on the street. I understand it's a turbo car so lag is part of the game

DavidBoren

I would invest in those afr heads and see what that gets you before changing turbos, but bigger exhaust housings would help with efficiency by reducing back pressure. And you did say you wanted efficiency out of the combo.

The heads will make a huge difference, and I think they would be a smarter choice, over new turbos.

coltboostin

Have you tried to make it on your current set up? I dont see why twin 70's would not make it with more boost.

If you want an exucst to throw money at the car, have at it. But, I would try with what you got first.

Jefro6996

iTrader: (21)

6766's are more than enough for 1000hp on a 408. These are the turbos I went with for a 408 street car.

slowride

iTrader: (3)

6766 are sold in both t4 and t3 format so not sure which ones you are looking at comparing. The tc70 would be a s cover compressor cast wheel 7068 with some sort of t4 exhaust housing. I would think those tc70's are good for quite a bit more jam depending on fuel.

Are you wanting less lag than the tc70 currently has?

ranedoss27

iTrader: (4)

I could probably make 1k with the turbos I have and the afr heads. As I stated though, I want the car to have less lag and be more efficient. Throwing the biggest turbos at a car is a dumb way to build unless you just want the wow factor. You want the smallest turbo possible to reach your goal. My question was if anyone knew If they would be too small. Finding compressor maps for that specific turbo has been a challenge for me. That's why I posted this. Looks like I'm going to just buy the heads and see how that works first

DavidBoren

I agree with you that you want to use the smallest possible turbos/heads/cam that will achieve your goals. It's called efficiency, and just throwing bigger and bigger parts at it is an effort in stupidity.

However, small turbos create more back pressure than larger turbos, and back pressure is in no way conducive to efficiency.

So, in theory, you want the smallest turbo(s) that will achieve your goals AND give you the least amount of back pressure. Sometimes you have to step up a size on the exhaust housing to get back pressure down closer to 1:1.

But I think you are on the right track with retaining the turbos you already have, and installing the afr heads.

stevieturbo

On the same note, many run in the 2:1, 3:1 with no untoward issues.

I've BW 6468's on mine on a 382. Some might say the turbine is on the small side. But certainly as far as around 25psi and to about 5500rpm I'm right around 1:1

Only over those two things does EGBP rise slightly higher than manifold pressure. But it still wouldnt even be as high as 1.25:1

At 28psi from 6-7000rpm EGBP was just a little higher. But at all times below 25psi it's around 1:1

IMO if he wants new turbos and very responsive, I'd be inclined to go smaller than the 6766's. Maybe more like a 6266 if Precision

Or for the BW either the 6268SXE or maybe 6373SXE

http://www.agpturbo.com/s300sx-e-series/