83 / 84 trannys

[bcarter]

I've race an early '84, with the disc rear brakes, and unknown year transmission. This weekend, I missed a lot of shifts, I think the syncro is shot, hard to find third sometimes, like stirring soup. I have an old parts car, an '83, with a decent tranny. I read that there is some slight difference in some of the ratios in the '81/'83's and the '83/'84's. Example is 1st gear, either 3.674 or 3.622, 2nd either 2.217 or 2.186, 3rd 1.432 or 1.419. Is there much difference? Will I notice it? Will the differences affect my lap times?

[This message has been edited by bcarter (edited July 22, 2002).]

[Allen Brown]

I don't think you'll see a noticable difference. The way I see it, at 7000 rpm the 1.432 ratio will be approx. 64 rpm more than the 1.419, which is less than 1%.

However, the difference in the tires I switched to, reduced my gearing by only 3.3%. I noticed I wasn't able to pull you or Marlow on the front straight....with the smaller OD tires I could....

Bye for now.

[Quickshoe]

Re: Lap Times

If you have corners where you have this wonderful choice: 3rd gear at 7800rpm or 4th at about 5300...you will probably be faster with the taller 3rd gear...unless there are alot of 2nd gear corners requiring a 3rd gear upshift up an uphill straight.

[bcarter]

Allen, interesting about the tires, because I do remember you as a bit faster, are they the same size, or just different manufacturer? You still get me in the cornering though. As well, that 64 rpm, altho not much, is relevant when we are at the top end and trying not to go much over 7500.... Kind of a moot point, I'm putting in the tranny anyway. http://Forums.ImprovedTouring.com/it/smile.gif

As to Quickshoe, we have a pretty good sweeper corner, but I don't think I'm up around 7800 in third in it.

Thanks guys

[lateapex911]

Originally posted by bcarter:
As well, that 64 rpm, altho not much, is relevant when we are at the top end and trying not to go much over 7500
Thanks guys

Hmmmm....7500? I know lots of guys who routinely shift around 8k+....I wonder what the consensus is.

I dynoed my motor....of unknown origin, but not a race motor, with a jetted carb, and the ususl header twin long primary setup, and the power peak was just over 7K, which matched what I felt down the front straight!

What have others found?

------------------
Jake Gulick
ITA 57 RX-7
[email protected]

[bcarter]

I dynoed mine as well, we are in a class that allows street ports, and I found that power dropped off at almost exactly 7500...

[Boswoj]

OK - a bit off topic but bcarter - did you port your own motor or have someone do it, and what did it dyno out at?

Rick

[bcarter]

I can drive it, I can put the engine in, and take it out, but I leave the skillful part to the pros. There is a very good engine builder here in Calgary who does great street port motors.

I got about 135 hp at the wheels, and about 170 hp at the flywheel on a chassis dyno. Power maxed out at about 7500. Could be that's also when we backed off...relatively new motor..

Four runs, with amazy drop off by moving timing even a little bit. I have a stock carb built by Paul Yaw, like really stock, because we can't jet, but it is clean, and the air/fuel is a straight line throughout the whole rpm range. Tidy engine, and legal for our class, probably more than can be said for one or two others.

We run street port, headers, off the shelf carb specs, no emission stuff, coil-overs etc. Stock (yeech) fuel pump, K/N air filters with maybe some ducting, stock rad, double pulleys...you get the idea.

[Allen Brown]

The tires I have on now are 225/50-15, before I was running a 205/50-15 (Silver rims) or 205/55-14 (yellow rims). The 225 tire is taller, I lost some of my gearing/ability to accelerate out of corners or down the straights.

Next set will be 225/45-15 or 225/50-14...just to get my gearing back.

Before I get flamed....I run under WCMA (Western Canada Motorsports Association). We use SCCA IT rules as a base, but allow only a few slight differences. One is tire dia. As long as you can fit it under the stock fender (w/ optional rolled lip) then you can run them...Another difference is we can made weight adjustments to a vehicle if it is dominant...yes, fully prepped, good driver, etc, etc.

See you in August Brook

[Allen Brown]

Just as a slight side note, My SE 13b see's 7800 to 8000 rpm all the time. My engine is now into it's 4th year since a (cheap)rebuild, many reused components. First year and a half, I shifted at 7200, but then I dynoed it. I changed my shift point to 7800 rpm from then on. I was giving up a lot of HP by shifting at 7200, and wasn't high enough up on the HP scale when shifting up into the next gear.

Stock bearings and seals are good for all day use at 8000 and can take blasts to 8500 once in a while....as I've been told.

If my engine blows, I really can't complain about a $2400 (approx. $1575 US) engine rebuilt 4 years ago with used pieces...