HP Junkies - Question about A/R's?

[WydRyd]

Just curious, can anyone explain or compare the spooling characteristics between a 0.82 A/R & 1.06 A/R turbine housing on a ball bearing Garrett GT series turbo?

[Charlie V]

one is faster than the other...........

[strokher racing]

Merv your motor is too small for the 1.06

[Lukesportsman]

Your not thinking dual .82's? I've got a .63 in the garage for trade

[WydRyd]

Yes, I know that much, but how much faster is the question

[WydRyd]

Eric, I think you're right. Perhaps the 0.82 A/R is best. Just thinking out aloud for future upgradability.

[beepbeep]

Hello!


A/R is a unitless measure of steepnes of "snail". It doesn't tell you if turbo is "too big" or "too small".

It's just "gearing" of turbo. If you "roll up the snail" it will look like a cone. A/R is a measure of cone "steepnes".

Higher A/R means "higher gearing" -> more air but harder to spool. You can have very small turbo with high A/R. There are more factors to take into equation.

[WydRyd]

Thanks beepbeep for that explanation.

Later on, when I'm ready to upgrade the K27hf I have, I'm thinking a Garrett GT35/40R would be a nice unit for a 3.3L EFI GT2-EVO CAM'd motor.

Then again, I think @ 1.2-1.3bar, the GT40 compressor is out of its efficiency range.

Be nice if there was such a thing as a GT35/42R

Anyone know whether such hybrids exist?

I'm thinking a GT35 0.82A/R Turbine housing with a GT42R compressor would be a very nice and efficient unit at those boost pressures. Dual ball bearings would make the unit spool-up nicely with that A/R

[beepbeep]

Originally posted by WydRyd
Then again, I think @ 1.2-1.3bar, the GT40 compressor is out of its efficiency range.

Naah. I doubt it. It all boils down to how much boost and at what speed. I'm at work now (don't have my Excel spreadsheets available) but I'll try to do some calculations on GT40R compressor when I come home. GT40R is good for 500+ HP and is a good turbo indeed.

Do you want to win a dyno competition or do you want a quick car? You can easily gain extra 100hp but loose it all on the street due to lag and peaky torque curve.

There are shops that can mate all kind of hybrids for you but they often lack equipment to measure what they did. Most of the time it's just expensive black-magic mumbo-jumbo with TD04E compressores and different turbines w/o posibility to verify improvements over "stock" turbo. I recomend you to stick to tried and true designs with available maps.

GT40R would be a great snail for hot 3.3L motor.

[WydRyd]

Thanks beepbeep.

Nah, I'm not looking for BIG HP #'s on the dyno. All I'm after is a responsive street car with great compressor efficiencies at the boost levels I'll be running (~1.25bar).

If the GT35/40R compressor does the trick, then I'm happy to go down that path when I'm ready to.

A GT40R turbo has either a 0.95 or 1.06 A/R Turbine Housing. Too big for a 3.3L Porsche engine I think. Perhaps more suited to a stroked 3.4L, 3.5L big bore, or 3.6.

A GT35/40R, comes with 0.63, 0.82 & 1.06 A/R turbine housing. The 0.63 would literally choke the engine and the 1.06 would make the setup a pig under 4K RPM's.

IMO, I think the 0.82 would be ideal for a *hot* 3.3L with racing headers. ~620HP capability and excellent quick spooling response

One of these fitted with a T4 Turbine Housing would be ultra cool

No harm in dreaming I guess

[juan ruiz]

Just as an example............................

If you put a Turbo that is cabable of supporting 900hp with a .84 hot housing, all do the turbo will support the power and will do wonders on other platforms, on our cars you will beed over 2 miles of wide open road to get the full use of it.

In other words what a lot of people are using outthere will not work as well on the 911s.

[beepbeep]

I'm at home now.

3.3 930 motor spinning @ 6000 RPM and boosted 1.2 bar will inhale around 50 lbs of air per minute. With typical efficiency numbers, you can expect something like 500hp.

A quick look at GT35R map reveals it's perfect turbocharger for the job. GT40 is arguably better in case you want to compete in dragracing but I advise against it.

There is no point in attaching a gigantic turbo whose "sweet spot" is nailed at peak power. You want a turbo where you traverse trough sweet spot somewhere between peak torque and peak power revs (prefferably around peak torque revs).

[WydRyd]

Thanks for the input.

The difference in end result HP between 911's and other Jap cars is that the 911 2-valve motor will make about 8.5HP/lb/hr VS a Jap motor with watercooled 4 valve heads making 10HP/lb/hr. Jap cars breathe really well up top due to their more modern head design.

What that means is that a 70# compressor on a Honda can make ~700HP, whereas on a 911 engine, it'll only make ~595HP and that's running the compressor to its limits where the efficiencies suck!

SO, if one were aiming for ~600HP @ 1.3bar on a boosted Porsche engine, they'd need to consider a 85# compressor (HUGE MUTHA) if they wanted to stay in the max efficiency island.

A typical example of such a huge compressor would be a GT42R or T70 Compressor The bigger the compressor, the laggier it gets. You could counter the lag effect with a smaller turbine A/R, but that introduces back pressure, chokes the engine and hurts top end.

[WydRyd]

BTW, I heard that David of ProtoTech put a GT35/40R on a modified, but CIS 930, and ran out of Turbo in the top end

That's a bit of a worry!

[YermanCars]

Merv, i will be installing the gt37/40 this weekend and will be heading to the strip. so I will tell you how it goes.

Right Now I still have the To4 on it, torque but no top end, still made 380rwhp on 1bar, running way rich because the injectors are over sized.

[Mike Bonkalski]

Tony,

Are you still going to the dyno on the 18th? I am curious to see the changes with the new turbo.

[YermanCars]

Yes Mike, we will dyno it with the new turbo and see what she can really put out.

[WydRyd]

Keep us posted.