That is exactly what I would like to use on my HBP.

B

 

What ports are you running? I'm interested to know if the GT40 would do better with larger ports, or if the PT61 would still give similar performance when compared to the GT40.

- Steiner

 

the t61 is a larger turbo than the gt40 i posted about. my ports are stock. the gt40 runs out of breath where the t61 is still efficient. They both spool about the same. Actually the t61 built max boost (20 psi at 4500rpm) 500rpm faster than the gt40. However, they both built low boost the same, maybe the slight edge went to the gt40.. the gt40 compressor map is shaped strange.. and its overhyped by garrett so keep that in mind



same lines as other graphs.

 

Interesting. When all the hype started about the GT40 everyone was saying that it didn't lose it's breath at the top end like the GT35-40 did. But it's interesting to see that in comparison with the PT61, which seems to be more efficient all around, the Gt40 really does lose out top end wise. Very interesting. Thanks for you comparison as I think it sheds a lot of light on the differences between these turbos, and gets rid of some of the hype that was going on for the GT40.

- Steiner

 

just fyi, the t61 is a gt35r compressor wheel =] the gt4088 will not lose its breath, neither will the gt40r =]

 

Interesting, so, when you say it is a little big for 20psi, what are you looking at, I see on the right that we are crossing the surge line, what RPM does that represent? Does that mean that at that RPM at part throttle the turbo may surge? What airlow(what is the correct term? ) do you use for a street ported motor, when doing these calculations? So using my road race car as an example, I am boosting hard about 1/2 the time, and part throttle at ~4500-5000 rpm the rest of the time(generalization). My goal is to have ~450-500rwhp available at 20-25psi. My thought was that the T66 was a little big, but that by going to the .81Q trim AR I would get the flow I needed, just earlier in the RPMs. Thoughts?

BTW sorry for all the questions, but it's always refreshing to find someone willing to spend the time to answer this sort of question. I also have a PT67 .68 P trim, I may bolt up, just to see what smaller ARs on larger turbos do. Anyone have experience trying that route? If I am experimenting with small Ars, what do I need to watch for, ie could I create a situation where there was a harmful amount of back pressure?

 

Hmm. So theoretically, the GT40 should be capable of flowing more through the compressor because it is larger correct? If this is true, than would it be the size of the exducer which is causing the PT61 to perform better at higher rpms? I'm a little confused now ha, so any explanation would be appreciated, thank you.

- Steiner

 

Turbo design is pretty darn complicated, but here are some general thoughts and observations I've made:

1 - Larger exducers on the compressor favor more horsepower potential at a given boost level. (This does not mean you will GET that hp, just that the turbo will do it)

2 - Larger inducers on the compressor tend to hurt spool up, but they seem to work better for higher boosts and horsepowers than a smaller inducer would.

The points above seem to have the most validity when comparing two compressors with at least one parameter in common or close. For instance, a T72 and a T76. They both have the same sized exducer, but the inducer size is different.

So if this is true, why not just build a turbo with a big *** exducer for top end and a little tiny inducer to help spool? Well, like I implied in point 2, a little inducer will make it so you can't take advantage of that fat exducer. So it is a balancing act.

If you calculate the trim value for a bunch of different compressors, they usually come in around 0.5 or so. It must be that there is a nice balance of characteristics around that value.

Compressor wheel size isn't the only factor.... there are many other factors that contribute to your turbo's response and potential... to name a few: A/R of the housings, flow map of the turbine wheel, design of the blades, your engine/manifolds flow... etc, etc, etc. The list is long!

Brian

 

There are 3-4 different gt40 compressors, 50,52,54,56 trim.. all vary in size from smaller than a 60-1 (the one that i had) to about the size of a t66

 

The one I tried to get PT to spec was a T66 sized piece two years ago. At that time it was not available. Carl

 

sometimes they run out of parts for a couple of weeks... they seem to be stocked up now though =]

 

bringing this thread back up.......... so would u say the 84mm 54 trim (.72 a/r) compressor with a 73 trim .94 turbine side would be better suited for up top so that it wouldn't lose those 4 lbs of boost? or should i step up to the 84 trim 1.19? reason i ask is that since i can't find the gt40r that i want i'm thinking of getting a gt40 for the time being and eventually swapping them out when they do become more available

 

https://www.rx7club.com/showthread.php?t=375596

easy solution

 

Which is the GT40R that you want?

 

the 1.06 a/r, and i want just the turbo not the kit because i have someone making me everything already, not having any luck finding one tho

 

the bigger gt-40 wheels are great.. i have a 56 trim wheel in my fd's turbo.

 

I'm pretty sure you can get that size turbine housing in any GT40(R). I meant what trim compressor wheel... 52-trim or 56-trim?

 

i wanted the 56....... ok so now i'm confused, u CAN get the bigger wheel in the regular gt40 now? basically what i want is 450whp without going over 20psi on pump gas, that will hold boost to redline, and i'm partial to garrett and the gt series

 

Here is a thread regarding all the GT40/GT40R's commonly available:
https://www.rx7club.com/showthread.p...ighlight=gt40r

There are a number of different turbo's that should get you 450rwhp at under 20psi. A T04R (67mm turbo) is one of those choices. A T66 might be able to do it as well... T78 should be able to... Turbonetics T70 (not the Master Power pieces of *****) should be able to... R85 should be able to (although there hasn't been any proof in the form of dyno sheets yet.

 

reason i'd like to stick with garrett is cause i have a friend who works there, and could get the turbo for a pretty good price i'll definitly check that thread u gave the link to, i'll let u know if i have any more questions :P thanks!

 

nyt, when you say the GT-40 would not build full boost in first or second gear, but how much boost where you seeing? I'm actually switching over to a GT-40 turbo with an 88mm exducer running on my stock port motor. Just wondering what to expect. I'm also going to be running a 4inch dp with the rest being 3 inches. Don't know how big of a difference that would make. Thanks.

 

saw 15-17 in first and 17-18 in second with the gt-40

 

This gives me high hopes for my setup

although ive got a divided 1.0 housing on my exhaust side. (t61 with same hks manifold) and street porting on the engine.

 

My experiences have been slightly different than NYT's. I run a GT4082, divided with the .96 rear housing. Definitely don't get full boost in 1st and I don't need it as the tires go up in smoke anyway. Definitely DO get full boost in second. Top end wise, now that I have a new clutch, it doesn't seem to be trailing off like it did before. I'm going to do some logs just to make sure. But the midrange with this turbo is amazing as is the response going from no boost to full boost in gear. It's almost instantaneous. I tend to run 1.1kg daily but it's tuned up to 1.25kg. I'll try and log at that boost level and see if she tapers off up top. I have a ported Cosmo motor. But looking at the compressor maps, the 82 doesn't seem to fit. It's working very well for me however, and the car is just stupid fast. If I had a wish list, it would be a bit more bottom end spool and a bit more top end. I might actually be happy then! I think if I "optimized" my turbo setup however, that this turbo would be great. I currently have an undivided manifold and a 3" downpipe that isn't perfect either. The V-band discharge on the compressor cover has given me fits too because I cannot find a v-band flange or connector for my IC piping. I essentially have pulled a piece of sillicone around the discharge and clamped it down below the v-band flange on the housing. I'm sure it leaks boost. I should take a pic...it'll make you laugh! I just don't have the resources down here to fix it unfortunately. I may take the compressor cover off and grind the v-band flange off. Dunno yet.

The reason why the GT turbines are more curved than the "standard" P/Q whatever is because they're "supposedly" more agressive. Check the blade count between the two as well (weight and backpressure).

 

with my pt61 i was seeing about 20psi in first gear