I am new to the RX7 game, just picked up an 89 RX7 Turbo imported from Japan. I noticed that a lot of you say the GT28R is too small from the 13B motor. What I have not found out about is how does the GT28R compare to the stock turbo. Will I be able to make 280WHP on this car with a GT28R? Please excuse my n00bness

Thanks!

 

That's a pretty small turbo for a rotary.

 

Too small...

This ain't no stinkin' SR20...

"GT28R" could mean a lot of things...
What size compressor?
They make em up to GT2876's I think now.


-Ted

 

you'd need to give the specs of the 28R in question for a comparison to be made to the Hitachi.

 

GT28 comes in at least 2 iterations as to the critical hotside.

standard is hot wheel 1.64 X 2.09 or 2.77 sq inches.

76 trim is 1.85 X 2.12 or 3.1 sq inches.

a GT35 for comparison is 2.45 X 2.68 or 5.17 sq inches.

the GT28 cold side is 1.83 X 2.37 or 3.52 sq inches.

so the stock GT28 hot to cold ratio is only .78
the optional GT28 is getting to 1 to 1 at .88

the rotary needs significantly more hot to cold than a piston engine and the GT28 falls short on the ratio and the actual hot side sizing.

another important area is the hot side A/R. too small and it will cause temperatures and pressures to rise and will make poor hp and eventually split the housing.

i believe there are two GT28 options... a .64 and .86. you would definitely need the .86.

finally as to hp.

the gt28 makes tops 37 pounds per minute.

37 X 10/1.3 = 284 rear wheel ROTARY hp.

or:

37 X 14.471 = 535 CFM/1.92 = 278 rwRhp.

so it will make at max your objective but it may be too much on the restrictive side and cause you warped apex seals and split turbine housings.

i suggest a TO4 46 trim. 44 pounds V 37 pounds. not as large as a GT35 at 55 pounds. 4.99 sq inches compressor w a stage 3 hotside at 4.52 sq inches. use a .82 A/R hot side housing. lots of options these days w it. water cooled center section and ball bearing if you wish though i recommend regular journal bearing.

340 max rwRhp. max flow at lowish boost.

howard coleman

 

It may be small but it looks like a good single to go with if you want quick spool and hp at stock levels.

 

does anyone know if the GT28r or a like sized turbo comes with an on center housing, or a right and left opposed tang

I want to setup a parallel twin with a similar design to the stock twins, that is cold sides facing away from each other

sorry to thread jack.

 

Those numbers are maximum power potential of the compressor side.
It's the tiny turbine side that'll choke on a 13B.
I'd be surprised if the GT28R even makes half of that power potential...


-Ted

 

Nope, not that I am aware of...

That turbine housing only comes in only one design according to the Garrett catalog.


-Ted

 

It'd be a great turbo, just make sure and get two.

 

So what's the gt28 turbo size compared to an S5 Rx7 stock turbo? Is it not bigger?

 

How about twin gt30's ?

 

It depends...

http://www.turbobygarrett.com/turbob...ison_sheet.htm

According to the Garrett catalog, there are...
GT2854R
GT2860R (2 different compressor wheels)
GT2860RS (same compressor wheel as one of the GT2860R)
GT2871R (3 different compressor wheels)
GT2876R

Which makes 7 different "GT28R" compressor wheels...

They have them listed for applications from 170hp to 480hp.


-Ted

 

i'm tryin to find out how far i should push this turbo it came on my engine...but i have 2 550cc injectors in my IC piping and 2 in my UIM

the coldside is garrett a/r 60 3" inlet....the center is oil cooled only no coolant lines and there is no markings on the hotside to see what a/r it is
i was thinkin its a gt28 or similiar

 

Thats sounds like the old HKS turbo kit that they made for the RX7

 

GT28 doubtful. From the info you gave, NO ONE can guess what it is untill you took it aprt and measure the wheels diammeters both major and minor. ALL GARRETT ball bearing center sections are water cooled unless its a one off built unit (race team only). Sounds like a T04B or T04b turbo.


~Mike.................

 

the engine was built and tuned by Tom's racing in japan
i wanted to put a picture up of it but i couldn't gget them small enough
does anyone have a picture of the gt28 hotside or an S5

 

on an s5 turbo there is no reason to put in a GT28R. remember that with a stage 1 or 2 BNR hybrid he could have 280-300rwhp and not need a new manifold etc, and considering the stock manifold is fully divided you will have decent spool at those power levels

 

for the fd guys i guess a t04 (e?)

my buddy's looking into going turbo on his na fc. i'll mention the BNR hybrid. sounds like a good cost effective option.