How much will it change my gear ratio to drop 3" in tire diameter?

[hodgesdodges]

Ok,don't laugh!!This is for my 93 Caravan 3.0...I have a grudge race coming up against my nephews "2000 Honda SI 5 speed"...I have driven it,and I think I can take it!!!Now my van is not dead stock.I took all the seats out but the drivers.I took out the old air box,put in a straight pipe with cone K&N filter,and ran fresh air to it.Also adjusted the timing,put on bigger throttle body,took off old stock muffler system,and now run no cat with a 40 series Flowmaster(now sounds like a big rice killer).And I installed bigger badder plugs and wires...Now this thing is pretty surprising above 3000RPM,but comes off the line like a dog.So I'm wanting to change my gear ratio for the "big race"!I am running a 14" rim with about 3 1/2" of rubber,I'm wanting to swap on a pair off 13" rims with a low profile(about 1 1/2)tire,so that would drop about 3" in diameter...How much do you think this will help??? PS...I run the 8th...

[cuda66]

I'm not sure but it would seem to me that if you have anti lock brakes on this van you may want to be carefull when stopping...iit may think that the rear wheels are sliding and pulse all the pressure to the front...should be OK but just be prepared for it....