I will be rebuilding my tranny with new synchors/lsd/ and possibly FD.
I have never driven any car with aftermarket FD's and my question is
which FD would be optimal for road racing. Is the 4.9 FD way to crazy,
or should i stick with the 4.73 FD? SRR makes both of them, and ATS
makes a 4.7 for my car also.
Thanks is advance,
Regards,
Marek

 

4.9 gets my vote.....

i will be running a 4.9 with a d15 here shortly,.....

 

we're seeing a shift light in 5th gear coming off the banking (before the kink) at LMS with the 4.73 FD. Would think the 4.9 would run out of revs but I am not sure. Might be one of the only places where this would happen too.

 

it'd be nice to know what tranny you have to start with

 

4.73 without a doubt is the best for most tracks.... If it is a ITA car....crx/civic...it is a must have if you want to be fast. Get the ATS.....got some in stock if you need one.

 

it's so simple guys, just plug in the #'s. i'm going with 4.9 for remix (94 civic si, d16z6)

Here's a look at the effect of final drive change assuming 205/50/15 tire size (23.0" diameter used for the calculation):



1st 3.250 37 33 32
2nd 1.900 63 57 54
3rd 1.250 95 86 83
4th 0.909 131 119 114
5th 0.750 159 144 138
reverse 3.153 38 34 33
rpm @ 65 3000 3300 3500
rpm @ 75 3500 3900 4000
final drive 4.25 4.7 4

 

Depends on your tire size and car. On the ITA CRXs that run 205-/55 14s, then most everyone runs the 4.71-4.73. If you are running the taller 205/50 15s on a non-ITA car then the 4.9 might be more appropriate. I have a Houseman 4.71 in mu Prod car with 23/8.5 15 slicks.

I know one person who had a 4.9 in his ITA CRX on 14s once at Road Atlanta and said he was twisting the poo out of his engine on the straights and wished for something not so steep.

 

if anyone wants a spreadsheet i made up dealing with d series hydro trannies, just PM me on this board with your EMail.

It has maximum speed in each gear (7200rpm) for SI trannys with stock 4.25 FD,4.7 FD, 4.9 FD
It also includes 71-72mph cruising RPM
It also has CX trannies with stock 3.250, 4.25,4.7, 4.9 each gear maximum RPM, etc etc
And i didnt get around to DX, but i have a SI tranny with each of the above FD's (-3.250) and then the CX 3rd to replace SI 4th.


i calculated it all with 205/50/15s

 

guys, just download this. http://www.ghettoracer.com/goodies/speedcalc.exe

 

thank you for your comments/opinions,
i apologize for not specifying before,
its going into the d16y8 tranny.

regards,
marek