Let me start with my setup
Mustang Notchback
306 dss pro bullet
tfs street heat heads/intake/ and stage on cam
3.73 gears if that matters
And i will be using a B&G turbo kit
i make most of my power i would say between 3000 and 5000 so by 5800 i shift because it seems to flatline at that point and not make anymore power

I assume i will spool up a bit faster with a .68 and have a bit of lag with a .98
which would be a better Street A/R that will once a summer probly see track time the .68 or .96
thanks in advance

 

I would use the .68 if you are talking about a MP T70 on that combo.

 

It would be a t67 garrett

 

get the .96

 

.68 would bring it on quicker and harder. A .96 will take longer to spool and would be a smoother power build and would not choke out the engine as much at the top end (but you said you shift at 5800 so that is negligible). The 3.73's will add a little boost lag factor because the engine is not as stressed as running something like 3.27's. A 67mm will also take some time to build up boost on just 5 liters, so just break down what you really want, housings can always be interchanged down the road also........
If you like the way a roots S/C feels on the street with the tire-ripping at lower RPM's, then the .68 would be more fun factor.

 

thanks guys for the input i think i will try the .68 for now and like you said they can always be changed later on.
thanks again guys

 

The 0.68A/R will spool roughly 600 rpms sooner than the 0.96.

This will make the 0.68 much more fun on the street; however, if you are looking for the best timeslip, the 0.96 will likely be better due to lower backpressure at high massflow.

 

I got tired of the .68 on my precision 61mm turbo...I would have much rather had the .96 the way the .68 choked off up top.

thaaaaaaaaaaaank you...

 

I was only getting a little over 2:1 max pre-turbine to intake pressure ratio on my last setup with the 0.68 A/R p-trim. This was from a 13-14 PSI run. Didn't seem to be too high; however, my exhaust "system" consisted of a Dynomax bullet off the downpipe.

Here is a comparison plot of my 0.68 vs 0.81 A/R on the same exact setup (except boost setpoint was a little different).

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I had experience with a 60mm with a .81 housing in the past and it was the best of both worlds. Still had some punch to it and the boost wasn't like hitting the nitrous button and the engine still revved well.

 

What does this mean?

 

As a general rule, your turbine is too restrictive if it is causing you to produce in the ballpark of 3 PSI of back pressure per PSI of manifold pressure. I was just barely over 2, which isn't too bad. This ratio would be lower if I used a larger A/R housing.

Lower back pressure is better for making power (naturally); however, the proper selection of a turbine and housing is based upon a compromise between quick spool and lower back pressure. TINSTAAFL

Where the optimal compromise point for you is depends on your goals. For me (at this time), I like quicker spool and can accept the loss of some top end power.

 

after what i have seen here i am goin g to go with the .96 ..besides i can always changer it later on.

 

I still think that's too much backpressure personally. I like to see around 1:1. As far as 600rpm between .68 and .96 I don't think it would be quite that extravagant. From your logs it looks like the difference in your .68 to .81 was only about 200rpm, no?

Tested the difference between a .85 A/R GT4088R (63.5mm comp. inducer with a 77 mm turbine - larger than a P trim) and moved up to a 1.06, it only gave up about 3-400 rpms of spool (boost @ xxxx RPM) on a 183ci engine. Also saw similar results moving from a .96 a/r on a GT4718 to a 1.23 with a 185ci engine.

 

It was 283 RPMs later with the 0.81 vs the 0.68. So maybe it is really 500 not 600 RPMs different going from 0.68 to 0.96. Call it 550 +/- 100 diff with a pretty high confidence.

Either way, the 0.68 gives a large area under the curve increase on the street (nice "fun factor"); but it is obviously not going to be optimal at the track.

What combo do you see a 1:1 ratio with?

 

GT5533 @ 3.5 bar give or take. Also had a PT98 @ 4bar making about a .6:1 ratio - that one was way too big for the app.

 

Supra I take it? What RWHP?

 

Supra engine. About 215-220mph in the 1/4 at 2350 weight break class. (1800hp-ish I'd guess give or take 100)

 

Nice ride. I cannot imagine that kind of power.

So this is a 100% drag car I would guess. In that case I would agree, that 2:1 Turbine/Intake PR is too high to yield optimal results.

My car is 95% street and 5% drag. Thus, the balance tilts in favor or quicker spool response over max HP.

 

For a stock block car, will the lag of the .96 be worth anything at the track over the .68? Considering max rwhp at 550 or less?

Cld12pk2go, do you have any dyno #'s or track #'s with the different exhaut housings?

Fathouse