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Discussion Starter #1
Its been a while since I've been here, so I have a lot of catching up to do. I've had some time to spend on the vette lately and like always I'm trying to make it better.

I made a mistake when I replaced my rear. I went with 410's. I have a richmond 6 speed with a 327 first gear and a .86 od. My rear tires are 28 inches tall. I have to row through the gears fast. In the quarter mile I am at the top of fifth at around 7000 rpms. My best time is a 11.68 at 125mph. Not bad but I am wondering if it might pick up some if I change my rear. What do you guys think? If it was your car and it was only driven for fun what would you put in the rear? I should have around 500 horses without the juice. And I have a 100 shot if needed. Its a full solid roller motor and has no problem with 7000rpms or a few more. Help!
 

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You may want to be down in the 3.08 3.36 3.55 range....

First let me say that I dont drag race... So this is thinking for a street driven car that will see some autoX an occasional trip to the test and tune night at the local 1/8 mile strip and the rare track day...

I've changed from a 3.55 4 speed small block set up to a Ramjet 502 ROD 6 speed with 3.27 1st and the 0.80 od and 28" tall tires w/3.36 rear and after some modeling with Microsoft excel looking the torque curve of the engine and the RPM drop between gears I decided that 3.36's give me a good choice between RPM in 6th at 55-75 Mph and acceleration. A ramjet has a pretty flat torque curve so a 6 speed is not really required but for a winding small block figure on .78 reduction between each gear as you'll want to keep in the meat of the curve at each shift.

In general the flatter (and bigger) the torque curve the wider the gear spacing you can use.

Assuming you dont change tire diameter you can just multiply the trans ratio by the diff ratio and get effective gearing to compare...

Also with the Richmond transmission there are a variety of ratio choices for each gear so you could set up a dual box with closer ratios down low for drag racing and 5th at 1:1 and put a taller OD but be careful as they dont recommend the trans for full torque in OD with anything other than the 0.80 6th gear set.

Other that are more into this may want to respond...

Hope this helps!

:cheers:
 

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The general rule I have followed is to multiply your 1st gear ratio x diff ratio, the magic number is 10 (in your case 3.27 x 4.10 = 13.4).

This is for a street car. However, if your car is race only, you might want a higher number.
 

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Will you notice...

I dont know... Thats kind of subjective :D

I had the 3.55 M21 setup with my BBC and it was a pain around town even with all that torque from the injected 502.... I wanted a gear below the old 1st so that stop and go driving will be easier and i wanted to lowner the RPM's in teh 55-75MPH range... Admittedly it will be a short gear in performance applications but with the 6 speed and the 3.36 rear gear change I get nearly the same 4 gears as I had with 4 speed and 1 under and 1 over. Pun inteneded :laughing:

Plus it's :cool: :cool:
 

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Len, The logic here is to make first gear more "usable" for a street car. Remember, you are in 1st gear a lot more than 4th. Modern transmissions use a higher ratio first gear than Muncies because there is less stress on the gear teeth (with the higher ratio).

The difference between a multiplied ratio of 10:1 or 9:1 is probably not going to be noticeable with your BB.:D

Whats the progress on your user name?
 

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Discussion Starter #7
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Have you had any problems with your richmond? I've blown up 2nd, 6th and the 5th and 6th mainshaft. All fixed under warranty. Since then I have installed a hydraulic throw out bearing and a softer 12 clutch which seems to be helping. Well at least I haven't broke the tranny in a while.

I still cannot figure out what I need. Will I lose performance with a lower gear ratio?? Or will I pick it up?? My power band is between 3000 and 7000 rpms. I feel like I am always in it now but not for long enough.
 

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Discussion Starter #9
Its a 385 stroker. It should be around 500 hp and 500tq without the nitrous.
 

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"11.68 at 125mph" :WTF ?????
I have NO idea what you are complaining about. There about a ZILLION guys who would cut off their right nad to have that kind of performance. Sounds to me like you have the right combination right now. Doesn't matter that you are at the top of 5th at 7000 RPM as long as the car is still accelerating through the 1/4. Now if you have valve float BEFORE the end of the 1/4 and you are in 5th gear, then I would say go to a lower gear (3.91, 3.83).
You say the car is "Only driven for fun". Well for me, that describes strip-only. Why drive something that wild on the street? :D

Dep
 

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If you're running a stock 79 diff you may want to look into beefing it up a bit more then stock before it's too late.
 

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Discussion Starter #12
Those et's were with a 1.8 60 ft time, the car pulls real hard at the top. I am horrible off the line. I think I need to drop the clutch around 5000 rpms. I've always been to scared to drop it that high. I worried that I will blow the tranny again.

The rear is a rebuilt unit with a new ring and pinion and carrier from fast corvette. If you look at my pics you will see what happened to the old one.

I still wondering if I only had to go through three or four gear, if I have enough power, would it cut down on my ets??
 

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robconner
OK IVE JUST GOTTA ASK?
why not shift into 6th gear?
rather than pull 5th to 7000rpm?
since you have the option to do so?

http://users.erols.com/srweiss/calcrpm.htm

youll be running closer to 5700rpm at 130mph

http://users.erols.com/srweiss/calcmph.htm

btw, Im going to use a 4L80E with a 3500 stall and at least in theory pull about 6000 rpm in the lights with a 4.11:1 rear gear, but ILL be hopefully exceeding 130mph with a bbc
 

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Discussion Starter #14
I've done that before and shreaded 6th. That was when I had the .68 od. Richmond put in the road race .80 after that. They said it was stronger, but still only a od and not for beating on.
 

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Hmmmm...strange that you are blowing gears in a trans. Are you running gigantic wrinkle wall slicks when you race?? If not, then perhaps there is a different problem...like alignment of the engine/trans/rear end.
 

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I would probably run a 4.88 or 5.13 rear gear and use 1st through 5th gear.
Is 5th direct drive and 6th an overdrive?. You may be looking for trans trouble if you use 6th. What is the redline for your engine (as best you know)?

There are lots of things that come to play in picking gears but that's where I would start. Keep 6th gear in your pocket to help keep the Rs down on the street.
 

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Discussion Starter #18
I run nitto drag radials all the time. I don't drive the car much so the short life span dosen't bother me. I should put a smaller less sticky tire on the front when I drag, but I haven't done that yet either. I've considered swithching trannys but money is a problem. I cannot seem to find anybody that wants to buy mine. I have considered an auto venders/gear (cannot remember exact name) muncie. I haven't had any problems since I switched to a full faced organic 12 mcloed clutch, from the button style kevlar 12 one that I had on there previously. It was pretty harsh and did not slip. I also got rid of all the 79 linkage and put on a hydroulic throw out berring which I think helps out also.
 

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I have the TKO 600 and 4.11 Even with a 2.87 first gear it is very worthless. I would yank the 6 speed out and sell it while it is still working and buy a quality 5 speed.

You might want to refigure everything and come up with a good tranny and rear ratio mix. You are not doing 7000 at that low of mph if your tires are 28 inchers. I don't even have to shift into 5th untill over 140 mph.

http://www.angelfire.com/fl/procrastination/rear.html
 
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