GT4294R 1.15 vs. 1.28 Turbine A/R
 

I'm currently running a GT4294R with a T4 1.15 A/R turbine housing on a half-bridge 13b cosmo. I see 20 psi by 4500 rpm in 3rd gear with 26" tires and a 4.30:1 rear end. The last time the car was on the dyno, it made 530 rwhp at 19-20 psi. My EGTs get a tad over 1800 degrees F @ 8000 RPM. The car runs at 11.5 AFR on C16 with 630cc of water/meth and 15 degrees of timing. The exhaust manifold is ceramic coated inside and out and the turbine is ceramic coated on the outside. I'm on a constant quest to lower the EGTs without just richening up the mixture.

If I were to switch from a 1.15 A/R turbine housing to a 1.28, would it reduce the EGTs due to lower exhaust manifold pressure? What would the difference in spool be? What would the difference in power be by letting the engine breathe better at high RPM?

Check manifold pressure and that will tell you if you will pick up any power going to the bigger rear housing.
1800f is not that bad.

The 1.28 turbine housing went on tonight. Going to get some data logs tomorrow to find the answers to the questions.

[quote]I see 20 psi by 4500 rpm in 3rd gear with 26" tires and a 4.30:1 rear[quote]

I know this is off topic, but do you have a log of this you could post? Thats rather impressive.

Disregard the graph in the post above. I looked back at my logs and that one was with 4.30 gears and 28" slicks.....not the 26" tires I originally thought. Sorry! :blush:

BOOST RESPONSE

I was able to get a data log before taking the car in to have the 4.30 gears swapped for 4.56s so the data wouldn't be skewed. The results were somewhat surprising. I expected the 1.28 housing to spool significantly later than the 1.15 housing, but the data logs show no appreciable difference at first glance. Using a point-to-point comparison, the 1.15 housing hit 20 psi by 4800 rpm and the 1.28 housing hit 20 psi by 4700 rpm......a difference too minor to consider given an imperfect testing environment. Shortly, I'll overlay the boost curves on a single graph to be able to compare the entire curves better, but for now............

1.15 A/R Log.........

http://i1236.photobucket.com/albums/...stResponse.jpg


1.28 A/R Log........

http://i1236.photobucket.com/albums/...stResponse.jpg

EGT

With the 1.15 turbine housing, EGTs were 1842F/1818F (Rotor 1/Rotor 2) @ 7750 RPM, 11.8 AFR, and 21.5 psi, with 15 degrees of timing.

With the 1.28 turbine housing, EGTs were 1760F/1740F (Rotor 1/Rotor 2) @ 7750 RPM, 11.8 AFR, and 21.2 psi, with 15 degrees of timing.

This averages to an 80 degree reduction in EGT.



1.15 A/R Log......

http://i1236.photobucket.com/albums/...HousingEGT.jpg


1.28 A/R Log......

http://i1236.photobucket.com/albums/...HousingEGT.jpg

Sweet man thanks... I have been seriouly considering ditching my 35r and going 4294r, this answers a few questions I had.

Love the Nova!!

good info here. nice car btw you dont see a nova with a rotary in it every day. any pics of it?

Here is the graph for the spool comparison. I stopped the plot before maximum boost was reached to keep the closed loop boost controller out of the equation. When you look at it this way, the 1.28 housing shows to spool about 70-80 RPM slower than the 1.15. Negligable in my opinion.

http://i1236.photobucket.com/albums/...risonChart.jpg

Here is the EGT comparison. Interpreting this one isn't as easy as the boost curves, since you have to take into account the differences in AFR, which I have also shown on the graph for reference. I have definitely seen the EGTs lower when richening up the AFRs, but don't have a really good feel for the exact relationship between the two. Boost between the two logs was so close it can be considered a constant. Sufficive to say, there was a significant reduction in EGT going to the larger turbine housing.

http://i1236.photobucket.com/albums/...risonChart.jpg

Some more details about this setup........

13b-re Cosmo Half Bridge
3mm Apex Seals
Dowel Pinned
GT4294R T4 Turbo
3" Intercooler Piping
Stock Bored Out Throttle Body
LIM EGR passages welded shut
4x1680 cc injectors
600cc water/meth @ 50/50 mix
C16 Leaded Gas
Haltech Platinum Sport PS1000 ECU
Closed Loop Boost control via haltech
Custom exhaust manifold with 14" equal length runners, dual 38mm wastegates (Jet-Hot coated as well as the turbine housing)
4" Downpipe with thermal wrap
S4 TII transmission
4.30 gears
315/30/18 Tires

Link to the build if you are interested........https://www.rx7club.com/old-school-o...e-nova-727207/