ok i have an 89 360 with roller performance RV cam 28" tires 904 trans
this motor is about 8.5 to 1
stock stall converter so it doggie iam not going back into the motor to make changes( cant do that work anymore) so a new rear n ratio change is were iam going car will be around town. i just don't want to kill the motor with rpms but would like to get a little more out the hole math was not a good subject 4 me tks
Let's
call that RV cam a 262/110 and,
the MAGNUMS were 9.4Scr engines IIRC,
and you have the 2.74-1.54-1.00 gearset,
with a 2200 TC.
then the Wallace spits out
Static compression ratio of 9.4:1.
Ica of 57*, at 500ft elevation.
Effective stroke is 2.95 inches.
Your dynamic compression ratio is 7.92:1 .
Your dynamic cranking pressure is .............................158.75 PSI.
V/P (Volume to Pressure Index) is ............................ 143
That 159psi pressure is borderline for 87/89 gas
That 143 VP says you have the potential to have an awesome street engine. She would be happier with more stall cuz you could run less rear gear............. but you have that 2.74 low in the trans so;
IMO, a starter gear of 10:1 will be just right; and you get that by;
10/2.74=3.65s.. Ok so this is halfway between 3.55s and 3.73s so you can go either way.
Ok but, I bet you want some nice pull at 30mph on the kickdown into first; right?. Ok that will take something like 3500 rpm so; doing the math I get 29mph with 3.55s and 27.5 with 3.73s; no big thing there. However, 3.73s will multiply your torque an extra 5% over 3.55s. So if your combo is capable of say 380ftlbs at 3500. then the 3.73s will give you a 19 ftlb kick in the azz over 3.55s. And that 5% will be there at every rpm; only the number of ftlbs changes. Now; 19 ftlbs doesn't sound like much , but that 5% applys to the power too. So if your engine makes 300hp then the 3.73s will make it feel 5% bigger than if it had 3.55s; therefore the 3.73s will make it feel like the engine is 15hp more powerful........... which is about the same as one camsize.
So, getting back to the kickdown at 30 mph; I vote 3.73s. For two reasons;
1) it's a city car, and
2) the extra gear will help compensate for the lack of stall. So you don't have to pay someone to install one.
Finally;
going from a 2.25 to a 3.73 will multiply your engine torque an additional ; 3.73/2.25=64.8% ......... which is a huge increase , that you can only match with supercharging.
Say your current engine is sitting at .83 hp per cube, which is 300 hp. This is an easy build. Adding 64.8% to that will get you the performance of guessing 425hp into those earlier 2.25s. That's a real nice improvement.
It sure won't be doggie any more.
Remember I guessed at the camsize, to come up with thischit.lol.But even If I am, you can see the Science from the math
Whichever you chose it will vastly outperform those 2.24-2.26s