What Size for twin turbos on a 3800?

[bs009]

So I'm sort of in a planning stage for my next build and I'd like to run twin turbos. It'll make things easier to package in a RWD car and will give me the neat option of going with a true dual exhaust system. Plus it looks cool too.
I know there are very few who have done twins because most of these cars are FWD so I haven't had a lot of luck doing research here aside from throwing guess data into compressor maps.
The only twin turbo build I'm aware of was Matt M's twin turbo build from ZZP but I don't know what size turbos they ran on that thing at all.

The goal is to be able to hit 600+ rwhp with the build while still being relatively streetable. It'll get an ST5 cam down the road, just not sure if that'll happen right away. I'd like to show off what these motors can do with stock blocks everywhere I go with it and maybe break some power records since it'll be a RWD platform that can actually handle the abuse. Ideally this will have a T56 and an 8.8 rear behind the motor.
There's also a good possibility that this ends up just being a pipe dream too

Right now I'm debating between going with some ebay gt30's or gt35's. I figure if one is good for ~600chp, two together should be able to easily hit 800hp.
GT30 is a 55mm compressor
GT35 is a 61mm compressor

Also not sure on what A/R to run on the exhaust side as well. I know spool times aren't going to be amazing with these sizes so I was leaning towards something like a .64 A/R, but honestly I have no idea if that's going to be restrictive or not on the top end when the cam comes in.
Anyone here a turbo guru?

Click to read more...

 

[Yaj Yak]

The smaller one

But like even smaller.

But one would work better...

 

[Mook]

May need to update the thread title to better drag in the 3800 crew.

 

[bs009]

Updated the title!

My heart is pretty set on running two here honestly even if one large turbo does perform a bit better. The look of one on each side of a v-motor is so satisfying to me
I've been reading a lot of people say that a large single is better than twins and I'm really having a hard time seeing why. Most other places where people talk about it I will generally read that twins can spool up faster and make the same level of power as a large single.

So for sizing the turbos:
Looks like the next step down from the gt30 would be the gt2871. Supposedly good for 280-475 chp each:

GT2871R – Garrett Motion

GT2871R ORIGINAL GT SERIES AERODYNAMICS INTERNALLY WASTEGATED TURBINE HOUSING OPTIONS NON WASTEGATED TURBINE HOUSINGS AVAILABLE SOLD AS A COMPLETE TURBO (INCLUDES TURBINE KIT & ACTUATOR)...

www.garrettmotion.com

and below that would be a gt2860. Supposedly good for 250-360 chp each

GT2860R – Garrett Motion

GT2860R ORIGINAL GT SERIES AERODYNAMICS INTERNALLY WASTEGATED TURBINE HOUSING SOLD AS A COMPLETE TURBO (INCLUDES TURBINE KIT & ACTUATOR) BALL BEARING CONFIGURATION WITH WATER COOLED...

www.garrettmotion.com

Both of those are t25's which honestly is probably better since that's closer to the size of the secondaries on the manifolds I built. Of those two, the 2871 looks good on paper.

 

[GTPpower]

I'm thinking Matt used a pair of 60-1's, but that's going to be really hard for you to spool. My vote goes for the 2871r with as small of A/R available. Those I think will work decent.

 

[Mattstrike]

How about you help me max the boost out on my truck so you can see how a set of tiny t25's does? Isn't that the whole point of twins, using turbos half the size that spool faster for the same power? Auto vs. manual makes a difference too, you're going to feel all of the lag with the stick.

 

[bs009]

How about you help me max the boost out on my truck so you can see how a set of tiny t25's does? Isn't that the whole point of twins, using turbos half the size that spool faster for the same power? Auto vs. manual makes a difference too, you're going to feel all of the lag with the stick.

Yeah going with two with half the potential is what the internet says but the more I look into it the more it seems like the main benefit is that it's easier to package a parallel twin setup on a v-motor. Seems like the real spool time benefits happen when you're using twins sequentially. At least that's what I've been finding last night.

I'm not too worried about the lag right now, it's not necessarily going to be built for drag racing.
Also I'm down to help you tune your truck, but you need to get some sort of oxygen sensor on that thing so we can see what it's doing.