Questions on gear ratios selection.

[George]

Roo, I am wanting to start a discussion on gear selection. I suppose this question could fit in other threads as well ? I have changed my 223" FED from an injected SBC to a blown SBC and a lot of questions have come to mind. How does one optimize a starting line ratio? I know trans gearing, convertor/clutch, R & P and tire selection as well as the wheelie bar are the main considerations. Engine location and weight location, I'm sure  have to be considered.


I have only considered a "finish line" rpm in determining gear selection and would like to learn more about a start to finish package.

Thanks. George

[dreracecar]

You fail to mention (like others) what type of racing you are planning to run, Index,Bracket, heads-up, no-brakeout, 1/4 0r 1/8?
Each senario has it own particular needs and requirments.

[wideopen231]

Not sure this helps. I just got new gear for my FED,225",526 injected Hemi.PG 1.69 low. I picked 4.11 with 1.69 low because I will mainly be doing bracket and 90% will be 1/8 mile. 4.11 is low enough to give good performance w/o being on edge traction wise on sometimes questionable tracks. Being consistent is my main goal. If had not gotten deal on 1.69 and had gotten 1.80 I would have went with 3.90. I want to keep it mangable on starting line but I want to make sure car can get up on tire and not shake.

 Now with 526 hemi I ave 4.5" crank and good amount of lowend torque.Im looking to keep rpm  around8500 in 1/4 max. With my combo I should be right about 8400 to 8600 in 1/4 and its rare to run barcket race around here on 1/4.I do have little different combo than most.RED's are different  my nature of design and most FED's are sbc  or blown and not alot in brackets.Well not around here anyway. I did hit up on good set of gears for 100 bucks and I figure its cheap to see if I am where I want to be or if I need something else.

If ran more headsup I would have went with 4.30,but rpm at line would be 9100 to 9300 range.

[George]

You fail to mention (like others) what type of racing you are planning to run, Index,Bracket, heads-up, no-brakeout, 1/4 0r 1/8?
Each senario has it own particular needs and requirments.

No Bruce, with your help my package was decided in another thread. Our car and yours are very similar. That is a done deal for now.

 I was looking to open up a discussion on  the process of gear selection. I guess its just a matter of what has worked and what hasn't?

Thanks as always. George

[masracingtd1167]

I think that before you start you need to have an idea of what your motor is capable of and be realistic . I would like to think that my motor makes 900 hp but I know it's more like 800 . There are some calculators on the internet that will give you an idea of what your car will run based on weight and hp . Now if you look at a gear ratio calculator [ Mark William's has a good one on line ] you can play with some different gear and tire sizes . You also need to know the rpm your motor is capable of . Don't plan on crossing at 9000rpm if your motor can only make power to 7000! If want to go as fast as your motor will allow gear it so it crosses right around it's peak power range . I have tried a bunch of different gear ratios in mine but I always end up back at a 4.56 It just seems to work the best for me ! Ok that's my opinion what dose every one else think ? Bill   

[wideopen231]

If unsure of ratio ebay has good deals on gears at times. Buy used set and try it,if works great if not you will have good idea which way you want to go.I just picked up two use 4.11'a for 190 bucks.Lil brother took one for backup and Im going to test with other.

  As for honest idea of what engine will do I have desktop dyno program and give it correct head flow ,cam,compression and few other things and it will get you very close. Have run dozen or more comparison to real world dyno numbers and gotten with then 2 to 4 %.