i'm running a mp t70 ptrim .68 ar on a stock 3.8 v6 mustang .the turbo has a bad wheel so need to replace or upgrade .thinking about getting a mp t76 ptrim .96 ar being i can switch between the housing if needed .i'm very happy with the t70 but plan on going to a built 4.3 down the road and alot more boost only running 10 pounds plan to be around 15-20 on pump and 25-30 on race gas and need help making up my mind on what to do

 

I say stick with the T70. The 76 will be very slow spooling on the 3.8. Take a look at the turbo's the Buick GN 3.8 guys are running. They typically stay in the 61 - 66 range on even the fast cars (10's).

 

I like to look at HP goals to help determine turbo size.

If you think you'll eventually be making over 500HP, then yes I'd step up to the T76. If under 500HP, I'd stay with the T70.

 

i'm in the 11's now hoping for high 9's bottom 10's

i'm looking to around 550-600 when everything is done

 

That's about the max that the T70 can support. So this makes it a tricky decision. The 70 will spool sooner, but will be getting pretty inefficient on the top end. The 76 would be more efficient at 550-600Hp, but will take longer to spool. Everyone always seems to want to go bigger than originally planned..you might want the 76.

 

The 76 is an 1100 hp turbo. Putting it on a 3.8 and asking for 550 hp is overkill. The PT61 is a very popular Buick turbo and it will support 680 hp. I think the MPT70 only supports 550-600 hp on 5.0 liters, which means it will support much more on a smaller motor at higher pressures. Precision and Garrett turbos with similar specs to the MPT70 support over 800 hp.

 

Your numbers seem high to me.

General consensus is that the MPT70 gets very inefficient past 600hp. I really doubt the MPT76 can support nearly double the HP. Especially considering is still uses the P-trim housing. Yes, there are other T76 turbos out there that may support 1100HP, but they all use a Q-Trim housing.

MP T70 maxed out a 650ish HP. MP T76 maxed out at a little over 700HP

 

This is correct. On a smaller displacment engine a turbo is worth a lot more power. If a turbo can squeek out 650rwhp on an LS1 it is likely pretty efficient at 650rwhp on a 3.8L.

 

Gotta keep in mind it's a smaller engine, so it'll have less backpressure to contend with.

 

Depends on PR it operates at.
A T70 will only push about 75lbs at 2.0 and 85 at 3.0 and still be on the same part of the eff. curve. -the last line whatever that is.
A T76 is only good for 90lbs at 22psi+ and 75lbs at 15psi. And that is completely ignoring the turbines ability to power that much air and not choke the motor.

Keep the T70 until it starts running high air temps. It will do what you listed.
http://www.squirrelpf.com/turbocalc/index.php?version=4&target_peak_power=600&pr_ref=14.696&engine_disp=3.8&engine_disp_factor=0&target_af=12&bfsc=0.5&max_ic_loss=0.2&rpm_redline=6000&rpm_peak_power=5500&rpm_max_boost=4500&rpm_min_boost=3800&vol_1=89&vol_2=93&vol_3=90&vol_4=87&vol_1=89&vol_2=93&vol_3=90&vol_4=87&intake_temp_1=90&intake_temp_2=120&intake_temp_3=135&intake_temp_4=140&turbo_n=1&map_sel0=72

 

OK, I stand corrected. The T70 will work efficiently at 600HP on a smaller displacement engine.
Although I really don't think 4.3L (he's planning to stroke to 4.3 when stepping up to 600HP) is all that much less displacement. Anything more than 600HP and I would seriously consider stepping up to something larger.

I modified that calculator for 4.3L engine size and 25PSI and the graph doesn't look nearly as good. But only looks a little better with the T76

 

+1. The T76GTS makes way more power on 3.0 liters than it does on 5.7 liters. Likewise, an MPT70 will make more power on a 3.8 than it will on 5.0 - 5.7 liters.

 

wow thanks everyone for the input and info looks like i'm keping the t70

 

now the next question do i stick with the .68ar or go bigger on the new one just in case i need it down the road ?