I have always heard that the S4C Si transmission is better for quarter mile racing then a GSR transmission. In my case, this has not proven to be true. Looking for some explanation or reasoning behind what happened.

When the car had a GSR trans, it went 14.3@101 and ran consistent 14.40@99-100 mph.

Swapped out for an S4C Si transmission. Car ran best of 14.59 and at a later date only managed 14.7 but this does not worry me. Trap speed dropped between 4-5 mph, this worries me.

When I ran the GSR transmission, I shifted into 4th gear. Same with Si, shifted into 4th but sooner.

Researched some with a transmission ratio calculator.

The GSR transmission with my tire size and shifting at 8500 puts me at 99 mph at the end of third (remember I still use part of 4th which explains my 100-101 trap speeds.

S4C Si transmission with my tire size and shifting at 8500 puts me at 92 mph. I shift into 4th and trap around 95mph through 1/4 mile.

With this last statements does it prove that the GSR gearing is better for MY car, or am I missing something here that would cause this problem? It seems that it is better to stay in 3rd gear with a GSR trans and shift at 99mph then to shift to 4th at 92 with the S4C. Someone with knowledge please enlighten me on what I should do. Car is basic build B18C with combo of ITR/CTR parts and bolt ons.

From what I researched on my own, the GSR is hands down better then the S4C on MY car, unless Im an idiot and am missing something here.

 

Basically I feel like shifting to 4th at around 90-92 mph with the S4C is hurting my quarter mile and I should stay with the GSR since I can ride it out to 98-99 mph and shift to 4th.

 

redline..?

 

According to OEM tach, 8500 rpm.

 

With your trap speed (power-to-weight) the B16 trans will work better. I'm going to guess that something else is up with the car.

Provided that this is the same track and done in similar weather with the same engine setup (nothing changed like header / cams / etc. without tuning...

How is compression / leakdown on the engine between transmissions / track days?
How do the spark plugs look? What is the gap at?
Are IDENTICAL tires and air pressures being used? Not just tire size?
Did you add a front lip or anything that increases the frontal size of the car?

Like I said, I bet something else is up with the car that' you're missing.

 

Compression test = 240/235/240/235

Same header/exhaust

I had a PWJDM Carbon intake on the fast runs and an Injen SRI on the slow runs. That was weird to me, thought the Injen would do a lil better or equal the PWJDM one.

Different tires, should have been better but they are the same size 195/55/15

Track was the same, not sure on humidity at the track but warm on both days.

Spark plugs look good.

Since the last track run I have made some changes that will need a tune. I added a RMF Narrow replica, 3" Thermal Research exhaust but I have not tracked. Just called Phearable to get a chip to last until I can actually get it tuned properly.

 

First set of runs were on the some cheap toe worn/camber worn almost bald Falken's, the second set of runs were on Dunlop Direzza DZ101, pretty much fresh. I only made a couple of passes on slicks before an axle broke, but the first set of runs we did manage a 14.01 with slicks. I had never raced with them before and bogged off the line pretty bad, axle broke on next pass so we never got to finish.

Right now the car still feels like it pulls hard, just not sure if it's on par with the first set of runs.

Could a bad valve adjustment cause any issues?

 

60' times, 330 times, etc. Look at your logs and see what your wheel speed was doing. Were you spinning? Match it to RPM. The car should be quicker with the Si box in it.

 

honestly im not too sure as to what is going on but i know for a fact that you shouldnt be at the same speed when shifting gears because the B16 tranny has pretty short gears compared to the GSR tranny which is good for acceleration but bad for top end, i think the gsr tranny supposedly tops out at around 145-155 mph from what ive read (i personally had my GSR tranny up to about 150 with not much more to go) where as also from what ive read the B16 tranny tops out at somewhere between 130-140 MPH, ive only had my B16 tranny up to about 110 MPH

 

Post up your time slips for both GSR and Si tranny. I'm sure it has to do something with your 60' times.