We've currently got 3.73s out back, and I figure while doing a refresh on the posi I could step up to a set of 4.33s. If I decide to take the plunge and add a Gear Vendors unit, that'll put the final drive at 3.42 or thereabouts.

I'd like the extra gear for the strip, though the ideal gear of around 4.77 is way too high even for an overdrive unit to use on the highway.

What might be some things I should consider when swapping to such a steep gear? Is this going to be acceleration nirvana or am I going to be replacing clutches, axles, tires, etc on such a regular basis that it'll end up being no fun?

We do drive this thing to the strip. I like to drive it on the street when the opportunity arises as well. I'd love to have the dual ability to put down a sweet ET, pack it all up, and then cruise cross country if I feel like it. :cool:

Your thoughts?

Tom,what does the car run now at the track? What is the combo?
EDIT-I just looked at that very cool website you have..IMHO,I'd stick with 3.73's..no more than 4.10's if you really wanted to change them
Another option instead of the GV's unit would be to go to 3.42's or 3.55's and use a Richmond 5 speed (5th is 1:1) with a 3.27 to 1st gear..reverse engineering!

You'll be shifting at 6700+ with those 4.33s incase you hadn't done the math.

Tom,

I'm no expert but I think it depends on your combo and what kind of rpm you use. What is your engine combination? What rpms do you turn? Trap speed?

I have a U.S. Gear 4.30 rear gear and 29" tall tires on my '71. With the tall tires and the manual tranny (no torque converter slippage) the rpms driving around town are not bad at all. On the interstate at 60mph, it turns just under 3000 rpm's. At 40, it is around 2000 rpm's.
I run a 454 with a fairly healthy Isky mechanical roller cam (248/252 @.050, .602"/.646") and shift at about 6500 rpm. A lot of people would say I'm over-geared (and I may be a little bit), but it sure don't seem like it! graemlins/thumbsup.gif With that said, when I freshen up my rear end (new posi, bearings and welded tubes) I might (not sure though) drop down to a 4.10 gear. I think it might run a smidge better with the 4.30, but I don't race much and the extra 150-200rpm less on the interstate would be nice. smile.gif

It is my understanding that you have to gear a stick car a little more than an automatic. I think you get a little more torque multiplication with an auto because of the torque converter. (to be equivalent). If you had an auto car with 3.73's, to be comparable a stick car might need 3.90's or 4.10's.

Where abouts in Indy are you located? Do you visit any of the cruising spots during the summer months? (Suds or Walmart)

I have 4.66's and a 4 speed. If you don't have the overdrive, the only advice I have is make sure you have a good driveshaft, and make really darned sure it's straight and balanced WELL. I cruise at 3800-4000 rpm at about 65mph, and any little imbalance in the driveshaft will show up at those speeds. And when severe enough, will break other stuff.....(ask my tailhousing how it liked that "little" vibration... :D )

Well, I had thought that I did the math properly for this exercise.

Currently my brother shifts at 5800, and crosses the lights just as he is shifting into fourth, so the car only uses three gears the length of the quarter.

The math I did gave me 4.77 or thereabouts as an optimum gear to cross the line at 5800 in 4th gear. It sounds like my information was incorrect.

I'd appreciate any help with the math on this. Sounds like something's not correct.

I figured that, if 4.77 was optimum, that a fair compromise would be to shoot for the middle and go for 4.33s.

The trans is an M21, tires are 28". Trap speed currently is right around 108mph.

mr 4 speed,
I had thought of the Richmond option, but I believe one problem with that might have been the placement of the shifter (our car has a bench seat), and then the other that we would have had to go with a new clutch, and the one in there now doesn't have much use on it. Thank you for the positive comment on the web site. My brother built it. My dad and I took the pics.


71454,
I try to hit the cruise spots. I play in a band, which knocks me out of a lot of weekend evening activities. I live on the north side of town, which isn't so hot with its gearhead population (not as far as I can tell, and I've lived there a good long while). I was out last night just burnin' fossil fuel. I drove all the way through town on 31, and then took 465W up around to 56th street exit. Email me & see if I can't make it out to a cruise some time this summer. It does happen, just not as often as I'd like.

bulb122,
Thanks for the driveshaft advice. We're running the stock shaft at the moment. It seems to work okay. However, I will be sure to take a look at things and keep that in mind. Of course, if the tranny broke in any way the ONLY recourse would be to go with an M22...naturally ;) .

If any of you need some info I have not provided, much of it is on the web site in the link below.

Tom,

I live on the southside (around Southport Rd & SR 135) and only about 10 minutes from the Suds in Greenwood. May try to make it down there tomorrow night if I get the chance. You ought to try and stop by. graemlins/waving.gif

I think you'll find that your gears are in fact in the neighbourhood of 3.08's, not 3.73's. What rpm do you turn at 60mph in fourth??

71454,
Shoot, man, I KNEW you were going to say Saturday night! I have to play Saturday night, then have to go check out my buddies' band after my own gig. Saturday is booked.
Naturally, Friday night is open for a change.
Don't they have a cruise-in out on the west side of town at the Sam's Club?

TJC,
I'm obviously gettin' ganked on the math equations here, as I'm way off from what others seem to be saying.
Unfortunately, I believe that the speedo is incorrect on the Chevelle. When I'm out on the highway with speedometer reading 65mph and tach at 2400 I'm being passed by everyone, including semi trailers. I really wish I could say for sure.

Not to be argumentative with you, but when I bought the rear end I gave the axle one full turn, and the pinion spun almost 3 and 3/4 of a turn, leading me to believe that it is a 3.73 gear. However, I've been wrong in the past, and maybe there are some facts I've got wrong here.

Is there a web site that has the math I can use to compute 1/4 times, RPM shift points, rear gearing, etc, etc, etc? I'd love to be able to sit down and do some figuring on the combo.

If this helps, our current quickest ET is 12.5 at about 109 or so. I have a timeslip on my bulletin board here that shows a different run of:

R/T .568
60' 1.873
330 5.373
1/8 8.123
MPH 86.67
1000 10.661
1/4 12.740
MPH 107.46

We broke out - dial was a 12.80 time. It's not consistent, but it IS consistently fast! graemlins/hurray.gif

Try here

http://www.woodyg.com/fairlane/finfo/rpm.html

It's a ford site, but the math works the same for them, only much slower ET's :D

To make it work for 3rd gear, just plug in the 3rd gear ratio where it says high gear ratio.

Originally posted by TH:
Currently my brother shifts at 5800, and crosses the lights just as he is shifting into fourth, so the car only uses three gears the length of the quarter. With a 28" tire, 1.46 third gear ratio, 108mph trap speed, 5800 rpm

= roughly a 3.08 rear end ratio.

However, you must be super tuner dude if you are running these excellent numbers with a 3.08 rear.
I suspect your brother is shifting into 4th earlier than he recolects.

A link to a calc site.

http://users.erols.com/srweiss/index.html#jcalc

TJC,

Yes, something is not right here. At the very least, I need to solidify my data accuracy.

However, I would appreciate it, in the meantime, if you would all think of me as a super tuner who has figured out how to do a 1/4 in 12.5 with a 3.08 gear ;) .

I'll have to talk with him. Funny thing is, I could have sworn when I drove the car, that it did hit 4th just as it was going through the lights.

You know, though, I could be off on tire height as well or something like that. It would be pointless at this time to go further without getting my facts down for sure.

Okay, I have verified several things, one of those being that I have a bad memory. graemlins/clonk.gif

I re-measured the strip tires and they are 26" tall, not frickin' 28" as I had mistakenly told you all. Apologies.

My dad has a GPS doodad, so we went out last night and I was able to verify MPH/RPMs (which was absolutely fantastic). These numbers were done with the street tires on, which are 25" tall.
At 3000rpm the car is doing 64.6mph.
At 2500rpm it's at 54mph.
At 2000rpm it's at 43.7 mph.

I know you don't need all of those figures, but I wanted to put them out here, mostly because it was just pretty cool to verify the speeds. The speedo is off by about 7mph or thereabouts.

I appreciate all the help you've given me so far. Any more that you can give me would be great.

I calculate that you currently have a gear ratio of 3.55

Yeah, that's what it looks like, doesn't it?
I wonder what's up with that. :confused:
Coulda sworn that it was a 3.73 when I checked it with the diff cover off.
Lovely.
Either my measurements for tires are off, or the rear gears are actually lower than I thought them to be.

*sigh*

What I really need is some more confusion! tongue.gif

It still could be 3.73's. If you have an error of only 100rpm in your tach ( commmon ), it makes the 3.73's a possibility. But it's defintely not less than 3.55's as I originally calculated. Your tuning aura is diminishing, :D but they're still great numbers.

pull the rearend cover and count the ring and pinion teeth, divide the pinion count into the ring count and you'll have your ratio. Might as well know for sure what is in there before you start picking a new ratio. Those original gears are an easy sell on ebay-I've sold many sets, good way to recoop some of your investment on the new gears. JMO

Thank you both.

TJC,
Good to know, and very reassuring. We were doing it at night, and pop was turning the light on the GPS on and off for me while I drove, so I had to eyeball the tach and the GPS as needed. I can see one instance where it'd be nice to have a Monster tach, and to have a mechanical tach instead of electrical. Really, if you just go up and down a small hill it could throw you way off on your RPM calcs.

I am almost dead positive that the gears are 3.73s, because I wasn't going to pay for what I wasn't getting. The rear had the cover loose when we picked it up, so I looked at everything. In addition, it is a coded C1 rear axle for a '69 ElCamino, which works out to a 3.73 with posi. The tag was even still on it for the fluid.

It didn't seem to have been rebuilt, so my guess would be that it has the original gears in it.

When I get to the point of disassembly I will do a count on the ring gear teeth.

I am wondering, though, what size gears I should be looking for in order to maximize the engine's potential.
Am I correct in assuming that you want to cross the finish line just as you reach your shift point in fourth gear?

Our optimum shift point is 5800rpm.

With 4.11's you should be through the traps at about 6K. I do not understand how you can currently be in 3rd at the finish. Doesn't add up.... what does your car weigh?

I would tell you my personal preference for a 4 speed 'street' car, but it would only start a 10 page pissing contest.

Tom,
I've got a driveshaft you can have. Take it to Pattersons in Avon and have them balance it. Joints should be OK.

I took it out of my 65 when I went to the 9"

TJC,
Car weighs 3500lbs with driver.

marooned,
Well, I don't think I need a driveshaft just yet. I'll have to keep that in mind. I appreciate the offer.

Pattersons do real nice work when it comes to driveshafts.

I had them build a custom 3.5" (I think) diameter shaft with the the 1350 u-joints on both ends. A nice piece. graemlins/thumbsup.gif

This is not the original shaft it's bigger than that, but not as big as the one I run now. ;)

Originally posted by TH:
TJC,
Car weighs 3500lbs with driver.

That's what I figured. 4.11's would be the ideal for the 1/4.

For the street.... well graemlins/angry.gif

Exactly, which is precisely why I'm asking the question.

I figure if 4.11s or thereabouts are an ideal track gear, then it would be my excuse to put in overdrive. I love the dual-purpose ability that it gives to the car.

I really like to drive it on the street and the track. As it is now, even with the 3.73s, it's not the optimum cruiser on the highway. It'd be nice to knock down the RPMs a little and be able to hit the road for longer trips. It's just all about max fun potential.

Hmmm overdrive. Gear Vendors is $2K. That's alot of gas. And your still taxing that muncie.

This would be better.. same price. 2 overdrive ratios!

http://www.sallee-chevrolet.com/BorgWarner/bwt56.html

Interesting. Two OD ratios.

I do see that I would need to purchase a new shifter as well as a new clutch. Our trans is a coarse spline. That affects the budget.

One critical measurement that I couldn't find was the measurement for how far back the shifter is placed, especially when compared to a Muncie. I was under the impression that it would interfere with the bench seat on our car.

The shifter has two locations on the housing, you can see the access plate forward of the installed unit.
The other issue is the weight and size of the unit. It is large by large. I was just throwing it out as another scenario. Tremec is ( or has ) brought out 2 new HD 5 speeds, that would be worth looking at. I have not read any reviews on them yet though. Physically they are the same dimensions as the T5.
Another scenario, and one that I used personally, was to install a 9" ford. I had 3 pigs that I could swap in and out with different gearsets. Worked really well. I was able to pick up assembled pigs for $300 from a local ford restorer. 3.23(fav), 4.11, 4.56.

TJC,

Yes, I looked into the Tremec initially. At the time (and it was a little while back) they did not have the multiple shifter positioning, so it was pretty much out of the question. I think, though the one in your link was not equipped as such, that they have some options for that now.

The Tremec does have a lower buy-in price, but I'd have to weigh the additional costs of the shifter and the new clutch plate. There are not the same issues with installation either.

I thought about the gear swapping you describe, but I quickly dismissed that one due to increased trackside downtime. When the car goes to the track it goes under its own power, so there would be one more thing to swap once we got there. We already have our hands full with the exhaust and the slicks.

Actually, I've considered the idea of electric header cuouts also as a way to minimize pre-race maintenance. It has often happened that we've missed a round of practice while we were under the car getting things all race-ready. In addition, there have been an equal number of times where we were the last ones in the pits at the end of a long night, working to get the exhuast hooked back up and the tires bolted up - even had the lights turned out on us a few times.

I have looked at old videos from when I raced back in the early 90s, and there were not nearly the number of trailers present as there are now. It used to be far more common practice to drive your car to the track. I guess things just change.