Just got back tuning a car with a GT40 (8082) using our manifold. Looks like the turbo is too small and doesn't want to hold boost more than 16-17psi at higher rpm like expected. I'll post the dyno charts later once I scan it.

341rwhp@12psi
380rwhp@15psi
390rwhp@17psi

 

Ports?

 

stage 2 port w/ 3mm apex seals

 

So, what turbo would hold up top and spool 15psi around 3k with a half bridge? Or am I just dreaming about this one. I thought the gt40 could hold up top on that amount of porting...

 

Remember, it is a GT40 not a 40R. The GT40 has similar specs to the GT35R. I don't know what the specs are on the GT40R compressor, but I have been told by a few people that is is larger than the GT40. This would be consistent with the relationship between the GT35 and GT35R.

GT40:
wheel Dia: 82mm
Trim: 50
AR: .56

GT35R:
Wheel Dia: 82mm
Trim: 56
AR: .70

 

No, I just got off the phone with Steve and talked numbers. CCarlisi hit it on the head. The GT40 is like a weak GT35R, spools the same(with the poperly designed manifold) as the GT35R, but drops out up top. A GT35 would be more like a RX6 turbo. So the GT40R is bigger and spools like it and holds like it. I'm not knocking A-spec, cause I've seen their work(great stuff), the manifold runners are just to short for proper thermal dynamics on the GT40. Steve was just seeing what the deal was with the power output on the GT40, not the GT40R. If you want 16-17 psi max, its great, but no more(with Steve's porting).

 

any numbers on your set-up yet?

 

I used photoshop to scale and overlay the GT35R, GT40 (88), and the GT40R compressor maps.

GT35R - Green
GT40 88 mm wheel - Red
GT40R - Blue

Black lines are roughly 10, 15, and 20 PSI.

You can see that the GT35R and the GT40 (88) should put down almost the same numbers at 15 and 20 PSI... around 10 PSI (who runs that on a single anyhow?), the GT40 (88) does outflow the 35R by a decent bit.

The GT40R is clearly different from those two.

 

Brian,

Can you overlay an 82mm GT40 chart? I believe 8082 refers to the 82mm compressor size rather than the 88mm.

Modrx7,

I think you're taking this way too personally...on A-spec's behalf.

Assuming the dyno is setup correctly I think Steve's numbers are a good indication of what this specific type of GT40 is capable of. I spoke to Steve briefly about timing earlier today and the leading values he used for this car were hardly conservative.

 

I'm going to wait until I see the sheets before I say anything.
However those number don't seem to be all that far off. Besides there are a number of variables that come into play in regards to horsepower.

 

Just to concur w/ steves results, i've seen the same thing with my motor and stock ports with a gt-40 50 trim. the turbo chokes.

I'll be buying a t66 =[

for the naysayers, heres a little graph (a bit conservative)

 

for some reason, it wouldn't allow me to attach it so here's the link.

http://www.gothamracing.com/pics/Ste...yno%20pull.jpg

 

on the 17psi run, I tried to boost as much as I can and it made 22psi at 5000rpm and drops off to 17psi no matter how much i adjust the duty cycle on the AVC-R, so the big mid-range spike is actually at 22psi of boost.

 

It will not hold 22psi all the way. It falls down to 17psi by 7500 every time. Maybe with a little less port on the intake side it would hold better, but you would see little power difference. It just isn't a big enough turbo to hold higher psi with that port job.

Edit: He^^ had asked about a 22psi run, before he edited that post.

 

So how is a GT35/40R able to hold 20psi to redline and the similar sized GT40 can only hold 17psi?

I would think the regular GT40 would flow better. I understand it is not the GT40R but it should flow the same or a little better then a GT35/40R just spool up later.


Anyone else confused?

Maybe there is a problem with the setup?

 

the gt40 is NOT the gt40r.

you guys gotta realize its not just a bearing difference, there is a different wheel being used. a gt40r can EASILY flow 500 hp.

in fact a gt35r can outflow a gt40



Anyway, I'm looking to pickup a T61 now =[

 

Just thinking out loud here...

1 - On the GT40 82 mm map, at 17 PSI you should be able to get roughly 450 rwhp I think before you hit the choke area on the map. In the case of this car, we topped out around 390 rwhp.

2 - Steve said that on the 17 PSI run, the boost went up to as high as 22, then fell to 17.

Could it be that the exhaust side is just too restrictive? If you think about it, to compress all that air to make all that power, you need to HARNESS power from the exhaust. If the exhaust is too small and the wastegate is bypassing a lot of air, or the air just can't get through... wouldn't that mean that less power is available to compress air (leading to observation #1), and less power is available to make high boost pressures (observation #2 - low wheel speed)....

Could I be right? Am I wrong?

Thanks for listening!

B

 

Well there are a lot of variables that can happen from one car to the next.

I guess the main point I was wanting to make on the first page was just that the GT40 has nothing to do with the GT40R. The 40R has a different compressor wheel with a much better map. The compressor maps for the GT40 SUCK and the numbers Steve got are spot on with what I thought a GT40 would make. The 40R is a different case. I think people were making assumptions against Steve thinking that he was refering to the 40R kit that Aspec sells when in fact this is a very different turbo.

 

I don't think a 4" dp step down to a 3.5" is hardly restrictive in my opinion.

I think that the turbo ran out of steam at that boost level.

 

I know this post is about the GT40 not the "R" but I think I can see 500rwhp in my future on the GT40R!! Does not seem that hard. Someone on here already made 457 with a very light ported motor at 22psi. Bigger port job and a tad more boost. I made 427 at 20 psi on a stock motor. Boost was holding great in fact I let off by 6800rpm due to my boost control set to high.

I will not argue with you Steve as I know you have forgot more than I know! I Just know you are not a fan of the gt series turbo's. I guess it really does not matter until some one actually makes 500! right!

 

Jus a little fyi that turbo is a killa,it loves high boost.never had any luck w/ low boost.the GT turbos are cool,but i perfer the gts turbos.last week i was tunning
a 3 rotor w/ a microtech and we laid down 475whp @ 10 psi on pump gas w/
"easy on your *** timing"this is the same turbo i use on my 13B. it made 540rwhp
@ 25psi and it too "easy on your *** timing" though it a really "laggy"but I will
make it work w/ more RND

 

....
what in the hell are you talking about

 

 

If you want to laugh at him at least make a coherent(sp) post.

 

yeah seriously we were having a decent discussion and sharing/providing lots of information on the GT series of turbos, and how a GT40 (NOT A GT40R) cannot even fllow what a gt35r can. If you want to contribute at least try using sentences and writing out what you're referring to.

It amazes me that the GT-40 just falls on its face (choke line) so hard/fast. Pisses me off that I need to change it out.

Anyone want a GT-40 cheap? t4 .96 back w/ v-band =]