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Differential gearing possibilities ...

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swift6

swift6

Yoda
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So I have been kicking around some ideas to improve the overall driveability of my TR6. Mainly in the area of RPM's for a given gear etc...

Basically, the problem is that for the much improved torque curve of my engine, the gearing of the rear differential is not quite right. My thinking is that if I went with the 3:45 gear set over the stock 3:70 I could get a bit more speed out of each gear. In "quarter mile speak" I believe my E.T. would drop but my trap speed would go up. It certainly seems that it is geared too "short" now. On many of the roads that I get to play on in my area, I tend to either have to hold a gear to long or shift part way through some of the larger corners if I want to keep the power on. Neither of which are ideal. BTW this is also during normal, slightly spirited driving, which is sometimes required so as not be an impediment on the road in this area, not just in all out canyon storming mode. /ubbthreads/images/graemlins/grin.gif

I have toyed with the idea of a five speed conversion which would help with dropping RPM's while cruising but that is not the overall solution I was hoping for. The toyota box is also a bit vague and rubbery compared to a TR box in good shape and I really enjoy the way the TR box feels when shifting. It's also part of the charm of the car.

If I remember correctly, the 3:45 was used on some/all of the PI TR6's (maybe just the early 150hp cars?). I have alo thought of the possibility of using the Nissan R200 diff kit from Richard Good but have not found out about taller gear sets available for that diff, although there are shorter sets. /ubbthreads/images/graemlins/computer.gif

Thoughts anyone... Am I mis-thinking the gearing concept?

/ubbthreads/images/graemlins/cheers.gif
 
He does a 3.45:1. I've seen them going up to 4.9:1, but not the other way.

Are you really going to see that much benefit? I mean it's going to drop you from 3700 to 3450... If you are "just" at the top end of your revs in the corners then you'll see a benefit, but if not you'll probably still need to shift.

The 5-speed is very similar to the stock in ratios for the first 4 gears. In your case I'd consider an o/d (I'm assuming you don't have one). It gives you that extra half gear for overtaking and going round corners...
 
Shawn, dropping to the 3.45 is only a 7% ratio change. You will be able to run each gear longer, but acceleration will be somewhat slower. With the new torque curve, I doubt if it will make all that much difference in the overall driveability, other than to allow you to stay in any given gear for a longer period of time.
Which, if I'm not mistaken, is exactly what you are looking to accomplish. /ubbthreads/images/graemlins/grin.gif
Jeff
 
Essentially I'm looking for something to back me off of the rev limiter in spririted driving. On track days (before the local tracks started getting shut down due to growth and the resulting noise complaints... but that's another topic) I could often adjust my line enough to compensate (and what a difference it could make!) but I can't adjust my line on public roads without garnering some unwanted attention. /ubbthreads/images/graemlins/nonono.gif

When the canyons get crowded I am content to just pop into top gear and motor along. But when there is no crowd, getting rarer these days, /ubbthreads/images/graemlins/mad.gif It's nice to have everything feel right. It also keeps the whole process smoother and doesn't upset the balance of the car.

I realized that the toyota box is nearly identical for 1-4 which is why I knew it would only help with cruising. I did not realize that you could get the R200 with a 3:45, that may be the way to go and get posi at the same time. /ubbthreads/images/graemlins/driving.gif

I do not currently have an overdrive. Maybe I'm just stubborn for some reason and I have been accused of being strange and peculiar in my tastes, but I just don't like overdrives. I've driven them before, not in my car but other TR6's, through the types of roads and what not that I get to play on and I have to say that I don't like them. I can't put my finger on why, I just don't. Maybe I've driven some poor examples, again I don't know why, I just don't.

I was just sort of wondering if my thinking was going in the right direction. After all, if my TR8 can get away with a 3:08 rear end and still be pretty quick because of the copious amount of V8 torque. I could see no reason why my TR6 would not benefit from a taller rear end due to its much broader and flatter torque curve over stock. I have no allusions about a 3:45 solving high RPMs while cruising. But I don't really drive long distances on Interstates with my TR6 so that is really not an issue for me.

Thanks for the input.

/ubbthreads/images/graemlins/cheers.gif
 
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