Hi everyone, Im in the process of a 3.8 engine build and need some turbo advice. Does anyone know the power band differences between .63 and .82 hotside on our engines? I am aware that the smaller a/r will give me better spool but by how much? Will the increase back pressure affect top end power that much with a .63ar? I am leaning towards hta gt35.63ar turbo. I will be looking to make 900whp max and shifting at 7.2k rpm, the car will be more for highway pulls as opposed to a track. Any advice would be great Thanks again.

Stick with the .82's. Lag will not be an issue.

Agreed

Great! Anyone running .63 ar for comparison.

I had 3 sets of gt35r variants.... all with .82s... but going to a .63 is not a bad idea...
spool up is about 300 rpms better.....
Rob MD bought from me gt35rs with .63s and he has a 3.8L motor and he put down 1100 rwhp with 953rwTQ... but that was also with other components like our headers, exhaust, ICs, intake etc....
good luck.
markski

I hear someone is getting an insane build Start the thread now so we can all enjoy the pics. Nothing is like a turbo that pulls on top end though, just my 2 cents. GL with the build bro.

I would use the .82 on a 3.8L motor.. Spend some time researching the new Billet wheel designs like from Precision Turbo.. I would not use old cast wheel technology on a build like this.. You can lb for lb make more power with the Billet Wheels and more Power on TOP.. Consider the 6262 and the 6057.. Good luck!!!

Mike

I agree but I did have a standard gt35r with .82s and then I switched to HTA gt35rs... same result... maybe 100 rpms spool up difference.... HTA is the Tial Alpha wheel for those who do not know....
Problem with all this new technology is that the wheels are not tested at 1 bar... where most of us run the gt35rs on pump gas.... Thus we need C16 to run 1.5+bar... and yet these garrets are still not efficient... most are optimal at 28 to 35 psi... boost levels few of us actually dare to run....
My point was and is that I actually did back to back comparison in real life
on the dyno.... Many new custom garret wheels are tested on Evos and supras where 30+ psi is like 1.2 bar for us....
The trick is to find a wheel that is efficient at the boost levels between 1 bar and 2 bar and not between 2 to 3 bar... otherwise you get a gt35r with lots of pull at 5.5K but nothing at 4 to 5K...
Many turbo companies swear that their product is better, quicker spool, more HP etc etc.. I have been disappointed before because such was not the case... when they show me a dyno on a P car is when I will be convinced.
I am now on HTA Gt35rs with .82s V banded... I will soon show some new Dyno figures...
best markski

My set up....

You are correct the Billet turbos dont spool quicker in Equal comparisons to cast.. The rear wheel dictates the spool and the lighter front wheel will change nothing more than 100rpm if you even notice that..

You are also correct about low boost efficiency.. 1 of the issues of the billet wheel turbos on a Porsche would be that they make more power higher pressure ratios where the cast aero falls off.. I havent been playing with Porsches long enough to know what it takes for a 3.8L to make 900whp.. For sure its not as much boost as an evo..

Here is something that i have tested and found to help.. For lower boost efficiency we use 7 blade designs such as 6057 billet Pte.. Fore higher boost applications a smaller 6 blade 58mm turbo will make more power which most wont beleive.. A smaller turbo make more power?? certainly in 6 blade it will if the aeros are equal and the turbo is run at HIGH BOOST..

I hope ill be able to provide more testing with the billet turbos as i get some Porsche Turbo customers in here.. for now though our shop car is a Gt3 so no boost for me.. LOL

Mike

My HTA is a 7 blade.. the previous 35r was 6....
I have not taken my car to 2 bar so I do not know.. all my testing was from .8 bar to 1.6 bar....
mark

Great information guys, I think ill be doing the .63 ar, the nice thing is we can always change the housing if im not happy. I'll keep you guys posted, look forward to the dyno #'s Mark.

I definetly will, once we near completion I will begin a new post of the build. It wont be as insane as yours but it still should be fun. Thanks Art.

You and Mark are talking about two different things; the Billets and HTAs are totally different compressors. The HTA's are a specific product built by Forced Performance and are worthless for P-cars.

Im aware of who FP is as we have been using them for years.. While The HTA aero is different its still billet and still makes more than cast size turbos of the same size.. Unfortunately we dont have a TT test subject but i wouldn't say an HTA 35 would be worthless on a Pcar.. It may not work on certain setups such as low pressure setups, but an engine is an engine and there must be combinations that will see gains on a billet compressor like an HTA.. If not Porsche would be the only car to date to not be able to take advantage of the Billet Technology and i find it hard to believe..

I agree that Billet technology has tremendous advantages, just not the HTA designs. When most people talk about Billet compressors on this forum, I believe most of them are talking about compressors that are different than HTA. I also think that some people believe that HTA is the only Billet design available, which as you already know, is not the case.