I have no previous experience with rotaries or the GT42R turbo, so I need a little guidance. Take a look at the following trend and tell me if you think the spool is about what it should be, or if it looks a little laggy. I was shifting slow, so I know a quicker shift and the Haltech's no-lift shift will help considerably. I'm also running a tilton clutch reverse flow restrictor. You can see the RPM's climb a little before the clutch grabs fully after every shift. Since, I have moved from the 0.028 oriface to the 0.040 to let the clutch engage a little quicker.

T4 Flanged GT42R with 1.15 hotside
Divided, equal length manifold with 2" ID / 16" long runners
2 Tial 38mm wastegates
Half Bridgeport 13b-re
TII Transmission
4.88:1 Gears
4" downpipe & exhaust
no cat

 

Is it roller bearing?
How much boost are you running?

Who ported the engine? ALl these factors make a huge difference


I have 35psi by just about 5000rpm

 

Currently 18 psi. Yes, the turbo is dual ball bearing. Not sure who ported the motor.

 

What are you using to control boost? have you pressure tested for boost leaks?

 

Wastegate spring pressure for now. I have an EBC controlled by the Haltech for future use.

 

I thought you had a T6 housing? hmmm... 18psi for one, will effect spool versus RX72c's higher boost, running the 1.15 will definitely set you in the 5krpm range nine times out of ten. I see very few people getting good solid boost numbers in the mid 4krpm range unless they are running higher boost settings.

~S~

 

So the spool looks normal too you? Good to hear that higher boost will shift sull spool to a lower RPM. Plans are to crank it up here in the very near future. How do you think moving to a 1.01 hotside will affect the spool and peak power potential?

 

A boost controller will improve spool because the wastegate (in your case there are 2) valve will open later. Right now it is cracking open more progressively and that is slowing your spool.

Take your 3 port Haltech solenoid and hook it to the top port of the gate (use the two ports on the side of the solenoid). Set your duty cycles very high (about 95%) up until at least 3500-4000rpm and that will basically force the gate completely shut. The higher the solenoid duty, the more pressure being applied to the gate to resist the opening of the valve.

 

Boost controller will make alittle bit of difference. i have a t6 .91 rear housing. you need that or at least a 1.01 rear. 1.15 is huge.

 

I agree. I set up the EBC last night. I'm definitely thinking about going with the 1.01. I could handle a 5000 rpm spool, but 5700 is a little high for my taste.

Found that the v-band for the turbine housing to the center section was fairly loose. You could see that there was an exhaust leak between the two, so I snugged it up. Might gain a 100 rpm or so, but I doubt it'll bring it to the level I want.

 

Your gearing seems really low, I'm not familiar with the T2 transmission gearing but if it's anywhere close to the 3rd gen tranny then 4.88 seems very low.

If it is similar to a 3rd gen in terms of gearing then this will also effect your spool. Lower gearing puts less load on the engine.

 

T2 gearing is the same as FD except for 5th gear. 4.10 is stock rear end for the T2, just like most FD's. The 4.10 is too short for a big turbo IMO. I would like to try a 3.9 .

 

I agree, 4.10 in a high horspower rotary is almost too short. The first 3 gears go by so fast, and it's worse on street tires since there's no traction. I can't imagine 4.88's. I think with higher gearing, a boost controller, and maybe a smaller housing you could get that lag down to mid 4k. I would do one at a time and report back. How quick do you build boost in 4th gear?

 

Don't know. Haven't had it in 4th gear yet. Traction hasn't been too much of a problem yet with 315/30/18 drag radials. As I start cranking up the boost, I imagine it will be. I'll just swap out the street meat for the slicks. Tried it with the EBC and boost response was about the same. Thinking about swapping the housing out with the 1.01. We'll see what the dyno shows tomorrow and how things feel with the no-lift-shift.

 

Agreed! Your A/R needs to be smaller and you'll be fine.

 

i have a 42r with a .96 i can sell you

2300 shipped!

 

4.10 is way too tall for a 42r.

4.4-4.56 is good. considering your engine will make power to 9500-10000rpm if ported correctly it will trap 155mph in 4th gear easily.

 

i have a street port and the same turbo, i get 16 psi by 4500rpm!

( T4 1.15ar on a GT4294r)

 

a/f and timing make a big differences too.

 

In 4th gear, on a dynojet, it builds full boost by 4500 rpm. I think the steep gears are delaying the spool.

 

That sounds right to me!