ITS Tranny

W

wlfpkrcn

New member
I'm wondering how many RPM's do you drop on shifts. I figured out the gear ratios and came up with some numbers can you guys let me know if they are close.
1-2 3440 rpm
2-3 2560
3-4 2160

Thanks,
Eric
 
This is what I got:

1st - 3.475
2nd - 2.002 = -3392 rpm drop
3rd - 1.366 = -2216 rpm drop
4th - 1.000 = -2144 rpm drop
5th - .756 (GTUs) = 1952 drop

From that you can see that the spacing is closer using 3-4-5 instead of 2-3-4. Choose whichever suits your driving style and engine characteristics, depending on your rear end ratio and the track configuration.

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Chris Wire
Team Wire Racing
ITS Mazda RX7 #35
 
Thanks for verifing my numbers. I thought in the Racing Beat catalog they had different 1-4 ratios for the 86-87 trannys, but my brother-in-law stole it from me so I can't verify it. The numbers I used were out of the Mazda Comp catalog and the only difference they list is 5th gear for non turbo cars 86-91. As for 5th gear i don't use it. I personally perfer just using the standard H, plus I never get into first on track so that drop in rpm doesn't bother me.

Eric
 
Well, it sounds like what Chris is saying, if you move up to a shorter rear gear, and use 5th, RPM differentials are smaller in the 3-4-5 band than they are in the 2-3-4 area, keeping you in your power band longer. OTOH, running out of 5th gear at the end of a very long straight sucks too
smile.gif


The 5th gear Chris mentioned is the GTUs gearing, which is ITS legal to run. 99.9% of the NA 2nd gen RX-7s have the .71 5th gear.

Now if they'd just let us run the 16" wheels that the GTUs has, we'd be set!
smile.gif


PaulC
88 PS1/ITS RX-7
 
I just find the 4-5/5-4 shift awkward. I have tried a couple different times, and have never gotten comfortable with it. Currently I run a Pro-7 car so I really don't need fifth. This question is related to another project I'm working on. If I need fifth I will probably use a fifth out of a 84 SE (.807) and install in a second gen tranny. Just trying to avoid the close ratio Miata gear set($2k) or a PBS (approx. $8k with all the optional gears). Thanks for all the info.

Eric
 
If you're looking for the Miata set check out Pineapple Racing. They list a conversion at a little over $900 + core. I had the ratios here somewhere but misplaced them.

Chris
 
The Miata set is similar to the old Mazda close ratio 5 speed.
1-2.35
2-1.608
3-1.24
4-1.0
5-.881
This would also require sending out at least the input shaft to be machined and a few other alterations to an RX7 gear box to make it work.I guess thats why they are called projects. I also realized that 79-83 use .825 for 5th. I will definetly check out Pinapple Racing.

Eric
 
If the 2nd Gen trans is anything like the 1st Gen trans, then 3rd gear is the weakest link. The idea is to be able to use as many gears as possible along with just about hitting the redline at the end of the straight. This allows for drafting, a very high exit speed from that last turn, and very agressive passing. I would want to be able to use 3,4,5 if available, regardles of the inconvienience of the shift pattern. It really depends on the tracks that you race on. What may be good for one may not be so good for another. The option of change will be better your advantage. I don't know how many of you that carry 2-3 transmissions to the track each weekend, but I bet some of you carry at least 1 diff gear pumpkins to change or replace, short of taking the whole shop/garage with you. The ability to tune will make you the faster driver. Set your car up one way for one track, and different for another.

I figured tire sizes that are used, and from a 225/50 series to a 225/45 series, with the same gear ratios, and there is almost 1 inch different in diameter. That equates to about a 300 RPM drop at the same speed. Does it make a difference? You bet it does . . . depending on the track. Maximize your options, and even ask the racers you race with. I bet that they might even share some secrets with you. If everyone has the same options in use, then it becomes the driver that makes a difference. THAT is what builds comradery in a club, and the class will grow. Remember, we all have the same set of rules, and it is the interpetation of the rules that gives you an advantage, not the manipulation of those rules. We all want to win...eventually, and are not doing this for money (maybe some of us are). It is a hobby, and a desire for all of us to do this, or we would be doing something else that doesn't cost so much.

This site can be used to your advantage. There are many people that have "been there, done that" (Paul), and you can learn form their mistakes. If that means one more person to race with, then do what it takes...almost. You guys provide excellent reading material for new-comers with all of your views and opinions. I have a lot to learn, but I will always look to this site before modifying a thing on my car.

WE CAN BEAT THOSE 240's!!! ITS belongs to the Mazda's.



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Corey L. Clough
Ex-1st Gen, Pre-2nd Gen
[email protected]
 
I have rebuilt many first and second gen trannys. Usually it is 2nd and 3rd gear synchros that are worn. This excessive wear is not the trannys fault it is the person driving it. The sychros are either broken from speed shifting, or worn from forcing the car into gear and using the tranny to stop the car and not the brakes. In one tranny I did the slider was discolored from the heat generated when the guy downshifted from 4th to 2nd.He definetly believed trannys were for stopping the car. On the othe hand the tranny in my car came out of a donor car with 135k on it. It has been in my car since 97 for open track days,and competion use since 98. The last race it ran was the 12 hour at Thunderhill and it never missed a shift. I double clutch all my down shifts so that helps synchro wear. If anybody has tranny problems give it a shot and see if it extends the time between rebuilds.

Eric
 
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