So my car is 1989 crx si. Almost all factory trimmings except for back panels (hoping to.get it weighted soon)
Current engine on the car:
B20 84.5 12.1c/r
B16 head
Pro 3 cams
Dyno was 240whp.

Tranny consists of:
1st --- 3.07
2nd --- 2.10
3rd --- 1.69
4th --- 1.38
4.05 fd
This is a gear x close ratio kit.
Shifting around 9,400rpm
I'm currently using some MT street drag 225-50-15r which by using the mfactory gear calculator are.around 23.8".
Went to the track and got a 12.7@112mph with 2.1 on the 60ft. So using the mfactory gear calculator again it.says that on 4th gear I should be around 119mph.

I was considering changing.my final drive for ITR 4.40 which would bring down my 4th gear top speed down to 111mph at 9,400rpm. If I up the.rev.limiter to 9,800rpm I get a top speed of 115mph.

Have somebody. sed this ratios before with a 4.40 fd??? Any recomendations on fd?

 

Why not a 4.266 FD

 

Well the gear calculator said I would get 115 with the 4.26 at 9,400rpms. So I hope to up the rev limiter to 9,800rpms (which would put me around 115mph also) if by any chance I needed the additional rpms for the 1/4 mile using the 4.40.


I was just looking for feedback of people who has done this before.

 

Just be careful with the oil pump up at that RPM if you are concerned about engine longevity at all. What does the dyno plot look like? I'm assuming with Pro3s it carries torque pretty well through there, but just thought I'd ask.

I'd probably look into the 4.266 final drive and just bump RPM up a hair if needed. You don't want to risk going too short bc sometimes the B-series trans is awkward going to the 5th gear gate at speed. If you ever plan on running 22" or 23" slicks, I'd keep the 4.05 FD.

 

The gear calculators are great tools but, they are not exact. They don't account for traction loss. That changes things

Do you ever plan to run slicks or keeping it on those tires? I ran 12.8 with the following on a stock block B20 Vtec w/ ITR cams on 22" slicks in a 91 hatch street car:

3.307
2.105
1.458
1.107
0.880
4.78 Final Drive

Shifted at 8500(or atleast tried to..LOL) finishing at the top of 4th pushing it...almost having to shift into 5th

Final drive increases acceleration speed. Meaning your 1-4 gear spacing is the same but, getting there will be quicker. As Bull said...I would go atleast to a 4.26 and give it a shot.

 

ET Street Radial II's are 24" OD.

I'd keep the tranny as is and try some 22" or 23" slicks like Bull posted. They will hook better and end up trapping at a lower speed, but faster ET as well.

Gearing by tire size is the easist to test.

Now if only MT/Avon would start making 20" slicks again, ARGH!