Twin Precision 6766's

[CMac455]

Wanted to revive this thread, too.

I have a 4.5L V6, which is a different story than a 4xx CI motor or even a V8. I can make more since I have a smaller engine with less pulses per 2 crank revolutions (excluding the increase in RPM I'll have.)

I think i'll start with .81 AR T4s, but I'm not sure on H or S-cover? I'm thinking that if an S-cover can't keep up, then it's time for a new turbo. It's possible I'll run into turbine sizing issues before the compressor regardless of used cover.

I'll be going about 8500RPM and will be maxing these puppies out. Has anyone ever back-to-backed an H and S-cover?

[stevieturbo]

I think the bigger covers are just more efficient, so if you have the room, go big.

[Crusty Nova]

I ran Forced Performance Super 94's to 1382whp on 400" LS7 head engine. They are very simalar compressor and turbine dimensions to the Precisions. They were out of compressor at 29# and back pressure was around 1.3 with TiAl 1.03 v band housings.

[CMac455]

Originally Posted by TurboBu

I ran Forced Performance Super 94's to 1382whp on 400" LS7 head engine. They are very simalar compressor and turbine dimensions to the Precisions. They were out of compressor at 29# and back pressure was around 1.3 with TiAl 1.03 v band housings.

I'd love to run some Tials, but I feel those would be too large for my setup. Was this through an auto?

[Legacy]

I have a 427 TT C6Z06 with 6766 we have made over 1200 on T'3 but we have back pressure issues. We are looking into the T4 but there isnt a lot of room in a vette. Also going to change the cam to help with back pressure.

[saintnik]

Originally Posted by Legacy

I have a 427 TT C6Z06 with 6766 we have made over 1200 on T'3 but we have back pressure issues. We are looking into the T4 but there isnt a lot of room in a vette. Also going to change the cam to help with back pressure.

What characteristics in a cam are beneficial when encountering high exhaust back pressure?

More lobe separation?

[PrecisionTurbo]

With most of the applications that have been discussed in this thread we would suggest a T4 turbine housing and the A/R would depend on what the application is doing, fuel and goals. The T3 turbine housings are just slightly too small when you start dealing with applications that are over 331ci in twin configuration.

[stevieturbo]

Originally Posted by saintnik

What characteristics in a cam are beneficial when encountering high exhaust back pressure?

More lobe separation?

less overlap ( or none...or negative ), shorter duration, perhaps earlier or later EVO depending how bad it is.

Anything to stop that pressure affecting incoming charge or cooking anything

[saintnik]

Originally Posted by stevieturbo

less overlap ( or none...or negative ), shorter duration, perhaps earlier or later EVO depending how bad it is.

Anything to stop that pressure affecting incoming charge or cooking anything

Thanks.

[CMac455]

Here's an interesting one; what single turbo would be equivalent to twin Precision 6766s?

[Crusty Nova]

Originally Posted by CMac455

I'd love to run some Tials, but I feel those would be too large for my setup. Was this through an auto?

Check out http://www.xonarotor.com/products/xrturbochargers
Their models are by exducer measurements largest are 94 67 which is 67x94 compressor 67x73 (I think) exhaust wheel.

[PrecisionTurbo]

Originally Posted by CMac455

Here's an interesting one; what single turbo would be equivalent to twin Precision 6766s?

This is rather difficult to answer as every engine combination is different. However if all things were equal you would want to look at either a Pro-mod 91 or Pro-mod 94 as a single equivalent to twin 6766's.