Well, I finally got my new 3.73 gears in. I thought I had 2.73 gears, but after pulling the cover, they turned out to be 2.56 (pinion = 16). So, I am pretty excited that my car could run 14.6 with 2.56 gears and no posi. I can't wait to see the new ET with the new gears and Eaton posi. Driving home from the shop it felt like the tranny was in 2nd gear, haha. These 3.73s were more than I expected, but I love 'em. Plus, I will be upgrading from these 14" wheels soon, so bigger tires/wheels should bring my highway rpm down a bit. Anyway, considering I am already in the mid 14s, should I be able to hit the 13s with this change?

I would definately think you're gonna see a 13 sec run. You may want to consider a Performer RPM/RPM Air Gap intake change down the road. Might run quicker/more MPH with a 750 as well. But run it like is with carb/timing curve tweaks until you get everything out of your current combo. Might surprise you ! What does timing curve/total timing look like ? The 14" tires will make it act like it's possibly got a 3.90/4.10 gear as well. What have you got in the converter department ? Good luck. Dave H

I have a stock converter, and as far as timing, the engine has not really been fine tuned yet, so I am not even sure. A friend of mine helped get it all set up, and I think he did a ballpark on the timing just to get the engine going after it was rebuilt.

It should be right around 3/4 of a second drop.

I sure hope so. Once I get into timing/tuning, I hope to maybe see some low 13s.

What ignition/distributor do you have ? Regardless of what you have, vortecs like 32* total. Start off with 12* initial. You'll also probably want a adjustable vacuum advance canister to squeeze max mileage/drivability out of this combo as well. But first off, you want to determine what your initial timing is (check at idle with vacuum cannister on distributor unhooked & vacuum port on carb temporarily plugged). After you have hooked everything back up, rev the engine to 3000 rpm and hold it there while using a dial-back timing light to determine what your timing is at this point. I'm using a Summit HEI with (1) light spring & (1) medium spring from the kit that came with the HEI. This was the only way for me to get a decent repeatable idle everytime I come to a stop during street driving. I tried using two light springs at first, but when coming to a stop, sometimes it idled fine & sometimes it would stall. Hope this helps. Dave H

The springs don't determine what total timing is, they determine how soon it comes in. In other words the lighter the springs, the sooner (in terms of rpm) total timing is reached.

ya i can remember the days when my car was running 14.40's with 2.19 60 ft times with a 2.56 open rear end and stock tranny and convertor.......i had the tranny rebuilt with a 2500 stall and bought a posi rearend with 4.56 gears and bought me a set of slicks too...............to my surprise i was still in the 14 sec range......i only dropped two tenths of my time with no other changes......i was so mad.........i hope you have better luck......lol........i thought too i was going to run 13's.....this was back in 1990....

Originally posted by ddeennis:
ya i can remember the days when my car was running 14.40's with 2.19 60 ft times with a 2.56 open rear end and stock tranny and convertor.......i had the tranny rebuilt with a 2500 stall and bought a posi rearend with 4.56 gears and bought me a set of slicks too...............to my surprise i was still in the 14 sec range......i only dropped two tenths of my time with no other changes......i was so mad.........i hope you have better luck......lol........i thought too i was going to run 13's.....this was back in 1990.... What car, motor, tranny, and weight was it? I'd imagine a small/slightly modded car/motor with 4.56s would be too much, and would be the reason there wasn't a drastic drop in et. When I went from my 2.73s to my 4.11s, I noticed a BIG change. I never ran my car before my gears, so I have no idea what to compare to, but I think for what I got, it's pretty damn decent graemlins/thumbsup.gif

My son's 72 went from a 2.78 (or is it 2.73?) to a 3.73 with Eaton posi and we saw about 1/2 second using a fairly crude timing method. The best thing is the smiles last for minutes after the burnouts and the 2 second tire squeals from 1st to 2nd gear with the TH350.

Gas mileage sucks, so we are planning an overdrive in the near future. I already have one in my 69 but the gears haven't been changed yet.

Yeah, the gas mileage totally sux!! I have driven the car the past two days, going on short 20 mile trips as directed by the guy at the shop to break in the Richmond gears. From just these little trips alone, I can see I am gonna have to get an OD tranny. I must admit, it is way more gear than I expected. I can't get much past 55 mph and the engine is revving very high! I don't have a tach yet, but I am sure the rpms are over 4500!! Hopefully I can make it to the track this weekend, and see how much my ET improves. I just have to drive 40 mph to get there, haha.

You will need slicks now.

I went from 9.59 with 2.56s to 9.12 with the 3.73s at Irwindale. Mid 13s sounds like a reasonable time.

Thanks for the tips Dave H. If it does not rain the next few days, I will try and see what my timing looks like. (I might have to post back with questions.)

Originally posted by eduardo69chevelle:
My son's 72 went from a 2.78 (or is it 2.73?) to a 3.73 with Eaton posi and we saw about 1/2 second using a fairly crude timing method. The best thing is the smiles last for minutes after the burnouts and the 2 second tire squeals from 1st to 2nd gear with the TH350.
Gas mileage sucks, so we are planning an overdrive in the near future. </font><blockquote>quote:</font><hr />
Yeah, the gas mileage totally sux!! I have driven the car the past two days, going on short 20 mile trips as directed by the guy at the shop to break in the Richmond gears. From just these little trips alone, I can see I am gonna have to get an OD tranny. I must admit, it is way more gear than I expected. I can't get much past 55 mph and the engine is revving very high! I don't have a tach yet, but I am sure the rpms are over 4500!! Hopefully I can make it to the track this weekend, and see how much my ET improves. I just have to drive 40 mph to get there, haha. </font>[/QUOTE]how much worse? :(

I can't say what the 72 did before the change, but after the 3.73 it probably struggles to get 14 on the highway with a 350. My 69 also is a 350 with overdrive but I can't say because it has only been on the road about 200 miles so far.

All I can say is that if you have 3.73s or higher (numerically), you might as well forget about gas mileage/fuel economy. I mean, gears in the 3-4 series are for performance anyway, right? They are not meant for cruising I don't think.

Originally posted by 71boo:
I can't get much past 55 mph and the engine is revving very high! I don't have a tach yet, but I am sure the rpms are over 4500!!Boo, what size tire are you running? A 20" tire diameter would put you at 3440 (approx) RPM at 55 MPH (I am assuming a trans ratio of 1:1). Determine your tire height and find any of the dozens of RPM calculators that are available on the web.

graemlins/clonk.gif Ooops, I meant around 3500 rpms, thanx. I have 245/60/14 BFG out back, and those are about 25.5 inches. Here is the site I use most often:

http://www.speedworldmotorplex.com/calc.htm

Had a glide and stock converter with/3.08 gears behind a basicly stock small block in a 68 chevelle. It went 15.70's with 2.4 60's. Then put a turbo 350 and a approx 2200 11 inch and it went 14.90s at the same mph but 2.0 60's. The car went from being a dog off the line (not even close to spinning the tires) to pretty decent. If you can decrease the 60' by a tenth it is around a 1.5 tenth better ET.

I went from a 3.08 open 10 bolt to a 3.73 posi 12 bolt and WOW! what a difference. didn't care much about gas mileage as this is not my daily driver.

Well, I made it to the track today and got in 2 passes. They were:

1 - 14.146@89.16
2 - 14.149@98.26 (60ft was 2.061)

On the first run, I pulled up before I tripped the beams!! graemlins/clonk.gif Then on the 2nd run, I ran it all the way out, but the ET did not change. :confused:
Still though, my best ET before the gears was 14.61@95.9, so I am pleased with the results. Now, on to timing/tuning......... still seeking 13s!!!! :cool:

what was your 60 ft time on the first pass? was the 2.06 your best 60 ft time?

i know the feeling i thought i would have gain more as well when i was running 2.56 gears with a bbc 396 going from 14.40's to 14.20's with 4.56 gears and slicks and rebuilt tranny with shift kit and 2500 stall.....but i guess not my mph didnt change much either if memory serves right i think i lost maybe 1 mph.....the 396 was less then stock form.....lol ...7.7 to 1 compression ,open chambered heads, 44 degrees total timming,stock low rise intake , little 650 vacuum secondary carb , 272 crane cam, and open headers.........

Also what was the difference in weather conditions between your old best and your current best?

To answer the questions, the 2.06 was my best 60ft. The weather today was very mild, high 80s I think, as compared to my previous best it was in the 90s that day.