Im currently running in a street class for autocross and am fighting a battle of spoolup. Im usually hitting full boost at 4k rpm. Im trying to stay in 2nd gear. When coming out of corners i have no power under 4k rpm, because of this im only able to get 3rd in IMS class. Call me crazy but ive been experimenting by using a ebay 60-1 with a .68 exhaust side, been using this setup for 2 years. Also using straight meth injection to keep things cool also. Using an hks cast log mani all undivided. I know going divided would help things but what are you t2 guys using to get power on the bottom end.

 

What ecu, exhaust, rotors, port do you have?

 

ball bearing turbo

 

better manifold would help. smaller compressor might help too (not sure if you've got a 60-1 or a t67).

what kind of exhaust are you running behind the turbo?

 

If money's no object, check out borg warner's new EFR line

 

get a better manifold. the downpipe will also help.

 

Manifold is biggest problem. Not so much that its undivided but because its log style.
Also target boost is big factor.

 

I noticed a huge difference in spool when I went from a 2.25 inch exhaust to a 3 inch exhaust.

 

manifold is killing you. a divided setup will make a big difference. There is a reason Mazda went from this kind of turbo manifold in ~1984 (12A turbo)



to this kind of manifold in ~1989 (s5 T2):



Here is data from actual Mazda testing on single scroll vs twin scroll w/ fully divided manifold:

 

The biggest reason why a divided turbing housing and manifold make a significant difference is the high pressure exhaust pulses from a peripheral exhaust port (pre-Renesis) engine.





Separating the exhaust pulses takes advantage of this special rotary engine characteristic.

 

Nos.

 

4.3 ratio rear from japan and or the smaller wheels from markets ( aus ) with 6 port gxl's
( which are 5 stud , 15 inch rims that clear the turbo brakes )

this should keep the engine up 500 or more revs at the same corner speeds and so still into the turbo delivery

 

Thats the main reason why i went with such a small turbine housing, to increase velocity but i think im hurting flow at .68 ar which may be countering spoolup. I think im going to get a divided setup and bump it up to .84 a/r and see how much it helps. When i do i will post differences in spoolup and anything else i notice.

 

Cant use nos at autocross lol


I thought about this but i use the top of 2nd gear to the max (7k-8k rpm) so shortening the gearing would top me out sooner. I just need to improve my spoolup in the 2-3k rpm range and it would be perfect.

 

then use the 3.9 from the auto???

 

stay in first gear?

 

Increase the compression ratio (S5NA rotors)
Increase the port area (substitute in a late 12A centre iron)
Port wide not tall (as wide as you can and still use rubber plug corner seals)
Put a FD upper intake onto a S5 lower intake.
Freer intercooler (bar and plate)
Intercooler design with more parallel flow paths.
Bigger intercooler pipework (3" and gentle bend radius)
4" dump pipe (or whole exhaust)
Change fuel to E85 and tune to 7:1 air fuel

Downsize turbo to ~55mm turbine exducer and ~55mm compressor inducer
aka V-trim S5 turbo highflow or GTX3071R (custom ATP split pulse T3 or T4 1.06 housing)

Change to ball bearing turbo
Change to stainless steel or inconel manifold
Ceramic coat exhaust manifold and turbine housing

 

actually ball bearing dont spool faster. the added rotating mass of center race cancels out any gains in spool from less friction

 

I'm not sure you are right about this.

In fact, I am pretty sure that you are wrong about this.























Yup.












Pretty sure....

 

haha well i could be wrong, but i did a back to back comparison and there was no difference in spool.

i started a thread on it on RCC about it, but basically i built a pair of hybrid turbos with a 60-1 compressor and p-trim exhaust using garrett journal and bb centers. initially i had an exhaust leak problem, but after i fixed that the BB would hit 15psi at 3500 and the journal around 3300. i am inclined to believe the journal bearing is faster due to less rotating mass. have you ever taken a bb turbo apart? there is a race pressed on the center of the shaft, adding weight

 

Ball bearing unit should be better in transient response and in lower gears - lower load.
Otherwise turbo spool up is solely based on exhaust gas flow and turbine since these means are propeling compressor.

 

Hands down, an open down pipe will give you the spool you want.