Same turbo t3 or divided t4

[race_me89]

I have been looking into turbos to run in the true street class at MIR and the class limits you to a 67.5mm inducer. Now that falls to a few different turbos but I kind of fell in love with the HTA 3794 the question I have is what will make more sense, if I ran a .82a/r t3 or a 1.10 a/r or in a bigger t4.

I'm going to add that to be "compteative" in the class I need to be in the mid to low 9's with a 2900lbs car with driver

I understand a bigger a/r should give me more top end power but how to do I make the decision on how big is big enough? And if bigger is better then I guess a divided manifold is in order?

 

[LandSpeed-DSM]

Here's something to consider - On a couple of setups I've had and others I've been involved with.. the switch to a bigger housing has always resulted in more power/psi.

Some have had seemingly counter-intuitive results. As an example of a setup I had no part in (so no bias on my behalf) the owner of a certain 42R powered White EVO relayed the results of some housing swaps on turbo in the neighborhood of what you are looking at:

On the larger turbos (Re: 3794R) I wouldnt run less than a 1.15 based on what I have seen on the dyno.

...

For reference, the 42R that was initially on the White Evo had a 1.15 TS. When swapped to a 1.28 it picked up 70whp and 200rpm spool, the 1.44 was never dyno'd before that kit went away and it was on a 1.01 Tial. It doesnt look impressive on ****'s car on the dyno but the 1.44 with his 105HTA can make basically any amount of boost we want from 4500rpm+ against the converter at the track.

This is why I opted for the 16cm2 (1.2x A/R) Housing on my 71mm turbo. I had similar results even on a 59mm turbo, just scaled down of course. The spool results are surprising at first but make sense when you consider that it makes the whole system more efficient at inducting and evacuating the charge.

 

[Michael@FP]

There are numerous people running >800WHP and trapping 150MPH+ using the .82 Garrett T3 Housing. Boostin performance ran low 8's at 170+MPH in that housing. We have a .85 housing that's better matched that's the go to housing on our GT35/37 turbos now.

I would run a 3794HTA in our .85 housing and it'll do what you want it to do. If you want to run a T4 housing run it in a .82 Open Garrett housing the divided housing that we used to use were discontinued and hard to find and in our testing didn't yield spectacular results. The larger frame stuff like 42R can see some benefit but from what we've seen the T4 divided and a 37R just doesn't add a lot of value.

-Michael