I've been looking at a few GT40 and a few T78 dynos (4 of each - on different cars).... and here's what I think (flame suit on!)

From what I've seen by looking at the dynos, the T78 cars and the GT40 cars perform about the same on spool up, with the edge going to the T78 cars.

The T78 cars also have the edge on top end power.

Overall, they are very similar performers with the info available from the dynos.

4 of each turbo isn't a huge sample, but it is better than nothing at all.

The T78 kit was a bit cheaper when I did a fast search (3,400 for T78 at rx7store vs 3,800 for the GT40 at a-spec).

I've also heard on the other forum that getting replacement parts for the GT40 is a pain in the butt.... I dunno how hard or expensive Greddy parts are to get. Probably hard too

Just throwing some observations out there... not really saying which is "better", since in the end, TUNING probably makes the biggest difference.

Anyone driven both turbos care to comment on the "real life" factor?

Brian

 

Just curious were any of the T-78's sampled running the upgraded GT40R wheels on them? I remember when it was hard to get parts for 35R's now I can get them whenever needed. Replacement parts that were hard to get ahold of are due to the fact the wheels needed aren't made at that time, I got ahold of the wheel that person needs, you just need to know where to look. He also got ahold of a preproduction turbo so parts were a little different than now as well. I'm not flaming you either, or even being biased, I'm thinking in the end once all the initial issues are resolved (tuning, parts availability etc.)the only benefit the T78 will have will be the cheaper price, and most of the kits out went out at a sale price of $3499. They are very similar in size.

 

There are T78s with upgraded GT40R wheels installed on them? Hmm, I didn't know this was possible. Is a GT40 compressor different from a GT40R compressor? I thought that the "R" was Garrett-speak for a BB center section and had nothing to do with the compressor. UGH, now that I look in my Garrett literature, I see that a GT35 and GT35R do in fact list DIFFERENT compressors, which shoots down my theory of R=BB. Why can't these guys just come up with some standard naming schemes!? I do know that there are two wheel sizes available for the GT40 (88 and 82 mm)... I assume that all the RX-7 kits have the 88 mm wheel on them.

All the T78 dynos I have are at least 1-2 years old; was the GT40R wheel available then? Nobody explicitly told me that their "T78" was anything other than a pure T78... but then again, a lot of people do get confused about what they have, especially if they didn't do the install themselves.

Here's the exact 8 cars I was talking about. To do the comparison, I actually imported the data points into Excel so I could color-code them better and make the graph bigger...

http://www.catenet.net/graph.php?car...1&SUBMIT=GRAPH

As you can see, overall the differences are quite small.

 

Oh yeah... you know if/where you can get this compressor here? On paper, it LOOKS like it would kick *** on an RX-7.....

https://www.rx7club.com/showthread.p...ghlight=GTP38R

Dunno if you could make that into something that would work on an RX... or if it's ONLY available in the internal wastegate setup....

 

I think Jason's car had a T78 with 40R wheel. If I had to pick, I think I would get the 40R. The T78 is very nice but its played out and the new stuff seems very promising.

 

I will check on that unit for you and see what I can find out. There are a few different wheels for the GT40R 52trim and 56trim/88mm wheels, then there are 54trim/82mm wheels on the straight GT40, I'm not sure if the 50trim is still available or not.

 

Someone just posted a GT40R (not regular GT40) comp map in another thread, and I compared it in photoshop to my mystery GTP38R. They are VERY close to each other.

 

the only thing i didn't like about my T78 was the fact my greddy manifold cracked three times in very little use

 

jason had a 79mm gt series turbine with the stock mitsubishi 67mm compressor

t78 parts are readily available from any dealer that sells mitsubishi turbo parts, which is pretty common. also, stock t78 exhaust wheels are 73mm.

if it helps any, i have a streetported motor with a stock t78. i hit full boost around 4000-4200 in 4th, but the power really can't be felt until around 5k. i'm sure that's partially due to tuning and efficiency. by full boost, i also mean 16psi, which is what i run every day

 

hey b, do you think you can help a brother out? i want to put in a roll bar after my clutch is done. like in a week. same one you have the kirk 4pt. if you can't physically help just some pointers. thanks kvn

 

pm'ed you fd3virgin...

I ended up writing you such a long pm, I will put my kirk racing bar tips in another thread in the 3rd gen forum...

https://www.rx7club.com/showthread.p...28#post3583428

 

My dyno graph is a greddy t78, no upgraded wheel.

 

Bringing it back from the dead...the upgraded compressors are not GT40's, they're GT55's. If my caliper measurements are correct (crappy pair of calipers) the inducer is 70mm and the exducer is 90 or 91mm.
Michel

 

What I am thinking-

GT series compressor and exhaust wheels are newer design.

Compressor performance-
It is going to be better since the flow models will work for RX-7 or piston engine once it is properly matched by mapping/luck.

Exhaust wheel performance-
Is NOT necessarily going to be better since it was modeled with piston engines over 4 cylinders in mind.

Look at how in the 80's when Mazda and Hitachi modeled and exhaust wheel for the rotary they invented the "Impact" design that works well with the rotary exhaust dynamics. They gained response and performance over the traditional exhaust wheel.

Look at the shape of the new GTQ exhaust wheels, it is an extension of the traditional shape that to me looks like it has come about since designers now know how to properly set up the manifolds to take advantage of smooth flow.

Nothing like the "Impact" wheels shape.

Then throw in the fact that the sizing of the whole GT line is still set-up for the primary piston engine market with "undersized" exhaust sides.

This isn't to say I think the GTQ wheels can't work GREAT on a rotary, but my feeling is they may require a very long smaller diameter matched manifold to smooth the pulses.

And size the exhaust wheel/housing properly to the rotary! A non piston oriented GT series hybrid is needed.

 

With your above theory in mind, all of the T-series turbines are made for piston applications as well.

 

Turbos work great on a rotary engine since we have constant smooth exhaust flow. Anything that works well on a piston engine should work even better on a rotary. The issue with turbine sizings though is very valid. Typically rotaries because of the constant exhaust flow need larger turbines to handle the flow without building massive back pressure.

 

Kevin,
You up in Bel Air yet?