TwinCharged RX7

iTrader: (14)

I've got a Greddy T78-33d, but its pretty old and I'm looking at upgrades.

Here are the specs on the T78:

Compressor wheel
In dia : 65.8 mm
Out dia : 90.0 mm

Turbine wheel
Out dia : 65.0 mm
Ex dia : 74.0mm

So if I were looking for a Garrett GT dual ball bearing turbo, would this be similar in size?


A Guide To Garrett’s "GT" Model Numbers

GTxxyyzz:
"xx" refers to the frame size of the turbine wheel inducer
"yy" designate the compressor wheel exducer (major) diameter in millimeters
"zz" may be used to designate special features of a particular turbocharger where applicable

So... the Greddy T78 would be close to the following Garrett model:
GT3788

GT37 looks like it means 72.5mm for the exhaust turbine, which is a tad smaller than the T78 (74mm). Then next size up is a GT40, which is 78mm. So the closest on the exhaust side of things is the GT37

The GT37's closest compressor wheel is 88mm (just a tad smaller than the T78)

The GT3788 also comes in an A/R of 1.11 (I'm not sure what the T78 is, but I think it is a 1.1)

Everyone usually refers to the Greddy T78 being a 66-67mm turbo, which must be due to the compressor inducer size at 65.8mm. The GT3788 is only 63.5mm. So the GT3788 looks to be a bit smaller in general, but if I get the dual ball bearing, and if they come out with the GTX version eventually, will the GT3788 perform better in responsiveness (spool time) as well as top end power (despite is size disadvantage)?

My next question is the exhaust inlet, how can i tell if the flange is the same?

Thanks.

TwinCharged RX7

iTrader: (14)

Or since I can get the GT4088R in dual ball bearing, which has a 4mm larger exhaust turbine, does the ball bearing and newer design make up for the potentially less responsive larger exhaust turbine?

Zero R

iTrader: (1)

PM sent.

Howard Coleman

iTrader: (6)

compressor average area in sq inches

Garretts nearby:

TO4z/A-Spec GT500r/PT67.......7.002
GT3788r.................................. 7.155
GT4088r.................................. 7.167
GT4088.....................................7.26
T66...........................................7.56 7
T78...........................................7.58 4
GT4094r....................................8.175

Howard Coleman

iTrader: (6)

turbine aver sq area and % of compressor:

GT3788r........5.694 79%
TO4z etc.......5.894 84%
GT4088r........6.423 89%
GT4088..........6.633 91%
T78................5.903 78%
T66................5.894 77%
GT4094r.........6.423 79%

arghx

iTrader: (3)

which turbine housing do you have?

TwinCharged RX7

iTrader: (14)

I have the 33d model, but unsure if that indicates which housing i have.

Howard Coleman

iTrader: (6)

33d:

turbine area:

7.577 av sq in

Zero R

iTrader: (1)

If you have the 33D you're going to want to look more at the 4294R if you want to keep near the same turbine flow.

~S~

donrotor

4294R or 4094R

AaronJ

iTrader: (12)

im thinking more along the lines of a t04z but i could be wrong

davidleonardi

Hi Howard,

Is yr email address still; howracing@gmail.com ? I sent an email yesterday to you. Did you receive it ? I need to ask you about my engine conversion project. Awaiting for yr reply. Thanks.

Liborek

If I understand, this is going to be used on your twincharged project?

If so, then you shouldn't just pick similar sized turbocharger as your old unit, but something what will work with high efficiency at your desired power levels.

Supercharger will make engine appear "bigger" and turbo will work at lower pressure ratio for given manifold absolute pressure and desired mass flow. Bottom line is, that compressor should support high airflow at low PR with high eff. and turbine can be sized on the large side for even lower backpressure without compromising responsiveness of whole setup.