What gear for a TH350

[cmegga]

Yes its the origoanl block, but it was boared to around a 362 or so , also did new crankshaft , rod's, pistons etc. I beleive he out a crank from a 400 block in, if thats possible it was suposed to be a bit more durable. MSD 6a ignotion, dynomax coated headers the works. I have decent power form the engine bery happy with its outcome. However the car is still a complete dog until above 50 MPH or so. Above that it feels like a rocket. That miserable 2:81 gear I hate so much !!

Thanks for all the input you have helped me allot, just a few other little tid bits. Are these all the avalible gear options , 3:23, 3:36 or 3:55 in the mid range I am looking in ??

Also anyone know where RPM can be calculated by , tranie , gear speed, etc ?? So I can get and idea of what Ill be turning at 65-70 MPH with in the gear options??

 

[Alwyn678]

Thanx for clearing that up for me. I wasn't sure about those gear ratios. Just about the 3.90 gear that I helped put in my buddies 79 'vette. Glad to hear your Richmonds are quiet. Maybe they improved. They are good ring & pinion sets. I was getting mine from National Drive Line. I've got a set of 3.36 gears in my '72 right now. Want to upgrage to 3.55 (maybe 3.73). My motor's the original one that came with the car, but I since rebuilt it to the 350/300HP specs of, I believe, the '70 vette. Yeah......That's the way I do my rears, nothing to it putting it in. Just have to have the right equiptment & the knowledge to use the equiptment when setting up the ring & pinion. So I send it out, but that costs. If you don't mind my asking you, how much did you pay the shop to set up your gears? I asked about the clutch pack only because I didn't change mine either as they looked good to me also. But, with my luck, I started having problems with the "pack" about 6 mos. later & had to go back in & change 'em. Oh well, that's the way it goes. Lotta fun, these autos are............... Dave

Dave.....I paid the guy 10 bucks...........Yes 10 dollars to set the clearanaces..........He is the same guy that did my head work on my 041 heads. He also checked the clutch pack and said it looked Great.no problems so far knock on wood. BTW.........Some folks classify the gears on the 3:70 line as 3:70 or 3:73 depending on manufacturer however the 3:55 is always 3:55...Go figure. Also if you do not have a transgo shift improver kit I would recommend that highly. I have mine set to extremely aggressive and it rips 2nd and chirps 3rd....It is a real neck snapper. The trick is to set the rear gear the cam and the tourque convertor to all operate as a unit. Once they do it is a real joy to drive and you maximize your performance....

 

[cruisin-davey-g]

Yes its the origoanl block, but it was boared to around a 362 or so , also did new crankshaft , rod's, pistons etc. I beleive he out a crank from a 400 block in, if thats possible it was suposed to be a bit more durable. MSD 6a ignotion, dynomax coated headers the works. I have decent power form the engine bery happy with its outcome. However the car is still a complete dog until above 50 MPH or so. Above that it feels like a rocket. That miserable 2:81 gear I hate so much !!

Thanks for all the input you have helped me allot, just a few other little tid bits. Are these all the avalible gear options , 3:23, 3:36 or 3:55 in the mid range I am looking in ??

Also anyone know where RPM can be calculated by , tranie , gear speed, etc ?? So I can get and idea of what Ill be turning at 65-70 MPH with in the gear options??

The motor sounds like a beast. Never really heard of getting 362 cubes out of a 350. But I guess anything's possible. Maybe the crank/rod combo? Did you do 30, 40 or 60 over? Yeah........your problem's definately in your rear gearing. Betcha can go from 50 to 130 MPH in a real hurry. Even changing to the 3.50 ratio in the rear will astound you. Most guys are worried about the higher R's a tall gear will produce. it could be a fuel issue the way gas prices are. Still some don't want to tire their motor out. But, the way I look at it, if you have a hi-performance motor that can take it, use it as it was intended. I like the OD trannies, but I'm not too sure that if you put a high horsepowered/high torqued motor in front of it & then "hammer" it alot, something's gotta give & the OD trans would be the likely suspect. Just some thoughts on the subject. Dave................BTW: about your tach readings: the right way to do it would be to put it on a dyno. But, if that's not available.........the way I do it is get along side of another vehicle on the freeway that you know has an accurate speedo, & get your tach readings like that. Also, tire size has a bearing on the outcome of final gear ratio. Speedo shops can accurately adjust your speedometer by using an adjustable transducer to the speedo gear. Chao!

 

[cruisin-davey-g]

Dave.....I paid the guy 10 bucks...........Yes 10 dollars to set the clearanaces..........He is the same guy that did my head work on my 041 heads. He also checked the clutch pack and said it looked Great.no problems so far knock on wood. BTW.........Some folks classify the gears on the 3:70 line as 3:70 or 3:73 depending on manufacturer however the 3:55 is always 3:55...Go figure. Also if you do not have a transgo shift improver kit I would recommend that highly. I have mine set to extremely aggressive and it rips 2nd and chirps 3rd....It is a real neck snapper. The trick is to set the rear gear the cam and the tourque convertor to all operate as a unit. Once they do it is a real joy to drive and you maximize your performance....

Yes: The Cam, trans converter, & rear gear ratios combos are the trick to getting the power produced to the rear wheels. Getting the right combo can prove to be "trial & error", But when you get it "Look out". You'll have a "screamer" on your hands (& maybe the cops on your tail all the time? (L*O*L)) I've got a shift kit in mine. Had it for years. Just added a Cheetah Valve body (Manual/Automatic). The harder you stomp on it, the firmer the shifts. Really a trip. Like you said; "will snap your neck"

 

[cruisin-davey-g]

Dave.....I paid the guy 10 bucks...........Yes 10 dollars to set the clearanaces..........He is the same guy that did my head work on my 041 heads. He also checked the clutch pack and said it looked Great.no problems so far knock on wood. BTW.........Some folks classify the gears on the 3:70 line as 3:70 or 3:73 depending on manufacturer however the 3:55 is always 3:55...Go figure. Also if you do not have a transgo shift improver kit I would recommend that highly. I have mine set to extremely aggressive and it rips 2nd and chirps 3rd....It is a real neck snapper. The trick is to set the rear gear the cam and the tourque convertor to all operate as a unit. Once they do it is a real joy to drive and you maximize your performance....

10 BUCKS! Man, where's this guy at? With the clutch pack. Just change the rear dope every once in a while & put in the gear climbing addative (used to be whale oil, but now I think it's synthetic) & you should be allright. I didn't do that. That's why I think my clutch pack may have given out. When I go to the newer gear ratio; I'm tapping in a drain plug to the casing (really don't know why GM didn't do that in the first place)

 

[cmegga]

Now Im off to the shopping part. I have decided to go with a 3:36 or 3:42 which ever i can find. Close to the 3:55 but a bit more conservitave just for the highway.

The Interesting thing is I cant find my car listed anywhere. I have the Covette America , Covette Central and Jegs books here and all three are listing the gear options for 63 to 79. Well I have an 1981 is it any diffrent in the rear end ?? I guess it has to be if they arent listing it.

Any idea where I can try ?? I did also check the Richmond site they show the same 63-79 .... so now Im really frustrated !!

 

[cruisin-davey-g]

Now Im off to the shopping part. I have decided to go with a 3:36 or 3:42 which ever i can find. Close to the 3:55 but a bit more conservitave just for the highway.

The Interesting thing is I cant find my car listed anywhere. I have the Covette America , Covette Central and Jegs books here and all three are listing the gear options for 63 to 79. Well I have an 1981 is it any diffrent in the rear end ?? I guess it has to be if they arent listing it.

Any idea where I can try ?? I did also check the Richmond site they show the same 63-79 .... so now Im really frustrated !!

Just a thought: I really can't help you out with your issue of not being able to find the correct gear for your '81. I'd call one of those places & ask 'em what the deal is. If your willing to go 3.42 ratio, 3.55 isn't much "Taller" & I really think the 3.55 will work best for you. Just my thought though. Also, I think you won't be happy with the 3.36 ratio either. I know I'm not. So, go back & check the charts at the places your tried already & see what it says about the 3.55 ratio. Good luck & whatever you decide, let me know how the car performs after you work out all of the bugs.

 

[cruisin-davey-g]

Now Im off to the shopping part. I have decided to go with a 3:36 or 3:42 which ever i can find. Close to the 3:55 but a bit more conservitave just for the highway.

The Interesting thing is I cant find my car listed anywhere. I have the Covette America , Covette Central and Jegs books here and all three are listing the gear options for 63 to 79. Well I have an 1981 is it any diffrent in the rear end ?? I guess it has to be if they arent listing it.

Any idea where I can try ?? I did also check the Richmond site they show the same 63-79 .... so now Im really frustrated !!

Ok..........I did a little investigating on my own & your '81 differental (pumpkin) is different than my '72. I did find a couple of gear ratios which will fit. one's a 3.54 & the other's a 3.73. Don't think you'll be able to get a 3.36 or 3.42 (think that one's a non-corvette GM gear). But, like I said: not too much difference between 3.42 & 3.54 ratios. Found these ratios at ZIP PRODUCTS (believe they're out of PA.) Should call 'em to see what else they may have. Let me know how you make out & what you decide. Good luck.

 

[Alwyn678]

10 BUCKS! Man, where's this guy at? With the clutch pack. Just change the rear dope every once in a while & put in the gear climbing addative (used to be whale oil, but now I think it's synthetic) & you should be allright. I didn't do that. That's why I think my clutch pack may have given out. When I go to the newer gear ratio; I'm tapping in a drain plug to the casing (really don't know why GM didn't do that in the first place)

Yep if you forget the Pose-additive you can Kiss your clutch pack good bye...............I also heard tht it used to be whale oil as well...... that is pretty wild huh?? I agree there should have been a drain plug in the casing cause that stuff really is a pain to drain and sTinks to High Heaven

 

[cruisin-davey-g]

Yep if you forget the Pose-additive you can Kiss your clutch pack good bye...............I also heard tht it used to be whale oil as well...... that is pretty wild huh?? I agree there should have been a drain plug in the casing cause that stuff really is a pain to drain and sTinks to High Heaven

Yeah.........you're right there. I was just too lazy to do it, I guess.

So, here's a new(?) saying: "Laziness can prove to be costly!"

Have a good one!...................Dave

 

[cruisin-davey-g]

Gear Ratios for 80-82

To "cmegga": I found this on a 'vette web site.

Gear ratios for 80-82 'Vettes: 2.72; 2.88; 3.07; 3.55; 3.70;

These were the available gear ratios for 1980 to 1982 Vettes according to this particular web site. Maybe the vette web sites you mentioned & richmond gear don't list 'em on their web sites 'cause there might not be a real big demand for changing ratios in those years, but I'm sure that they'll have 'em. Hope this helps you out.

Take care.................. Dave

 

[cmegga]

Exactly what Im finding . So It look like it going to be the 3:55 after all, I think 3:08 is too low for what I want.


Also came across a decet site to look at as well.


http://www.ikerds.com

 

[cruisin-davey-g]

Exactly what Im finding . So It look like it going to be the 3:55 after all, I think 3:08 is too low for what I want.


Also came across a decet site to look at as well.


http://www.ikerds.com

cmegga: Yeah.............I think you'll be happy with the 3.55 ratio.

The 3.08 ratio may of been a good upgrade for the 82 motor & trannie, but you changed all of that by rebuilding the motor to different specs & changing converter & such, thereby changing the characteristics of the drivetrain & the whole car. That's why I think that the 3.07 available for the '81 won't do the trick in your case & the next one up is the 3.55 ratio. The 3.70 would even be a better choice if you were just doing street cruisin', but wouldn't do well on a lot of high speed highway driving. So, the choice is your's. Good luck with you 'vette..................Dave

"I'VE GOT THE NEED FOR SPEED!"

 

[cruisin-davey-g]

Exactly what Im finding . So It look like it going to be the 3:55 after all, I think 3:08 is too low for what I want.


Also came across a decet site to look at as well.


http://www.ikerds.com

CMEGGA: one more thing I forgot to mention. If your going into the rear, make sure you drill & tap a drain hole into the differential casing, so it'll be easier to drain out & rechange the rear fluid & additive every so often. I found this to be necessary in Corvette rears, as the clutch packs tend to dry out & chatter if the fluid & additive gets real old & tends to break down. Guess it's just a preventive maintenence thing.

Dave

 

[cmegga]

Well I just order the gear , 3:54 it is !!! I called richmond an they did not have any other options except 3:70 up. So the sent me to Dana Transmisson, that made the gear for the Dana 44 rear end. They actually had many options I did find else where. Such as 3:18, 3:31 etc, but we did some calculations an with the 3:54 I should turn just under 3400 RPM at 75 MPH. That works for me.

If anyone wants to look in to the dana gear you can reach them at

DTS 800-521-0628, they were very helpful with calculations !
And the gear was on $195 too boot !!!

cruisin-davey-g ,

Thank for all your help with this , you have been ver insiteful and right on with the gear choice.

Not a bad idea on the drain hole

 

[cruisin-davey-g]

Well I just order the gear , 3:54 it is !!! I called richmond an they did not have any other options except 3:70 up. So the sent me to Dana Transmisson, that made the gear for the Dana 44 rear end. They actually had many options I did find else where. Such as 3:18, 3:31 etc, but we did some calculations an with the 3:54 I should turn just under 3400 RPM at 75 MPH. That works for me.

If anyone wants to look in to the dana gear you can reach them at

DTS 800-521-0628, they were very helpful with calculations !
And the gear was on $195 too boot !!!

cruisin-davey-g ,

Thank for all your help with this , you have been ver insiteful and right on with the gear choice.


cmegga: Thanx, glad I could of been some help. Now, go get that "gear in the rear" & HOOK-UP!!!!!!!

Dave

Not a bad idea on the drain hole

 

[69autoXr]

In case this hasn't been posted yet, here is a useful formula:

mph = (rpm x tire dia")/(trans x gear x 336)

 

[cmegga]

Sorry to re open this can off worms, but after driving around this weekend I have some concerns again.

I got the 3:54 gear here and is schedualed to be installed tommarow, but Im not so sure its the right move. The technician as Dana Trans. Estimated with the gear I have now (2:81) I should be turning 2200 Rpm at 70 MPH . Well it was nice here this weekend and I got to do some dirving. I acutally run 2600 RPM at at 70 MPH.

So Im asuming that will throw our origonal calculation for the 3:54 off as well. We estimated 3400 RPM , so if it is off by 400 that would really put me at 3800 RPM !!

Is that going to be too high for highway driving ?? It is going to be a big expence to this in so I want to be sure its not going to driveable or not cuase more problems.

 

[Don&Kelly]

I now have a 3:07 rear end in my 1981 and I put in a 700R4 transmission - I happen to check the RPM's this weekend & they were 2100 RPM's @ 70 MPH - I went to the 3:07 from my stock 2:87 .. more pickup, but still good gas mileage & lower RPM's - Much highway driving @ 3800 RPM's will kill you motor over time - IMHO - hope this helps

 

[cruisin-davey-g]

cmegga: OK............ I'll go over this one more time. If what you are looking for is great "launches" off of the line at stop lights, with "g-force" like acceleration, then you'll have to go with a taller gear. I doubt that a 3.07 gear with a 700-R4 will give you the feel that you are looking for. On the other hand, having a smaller gear (such as the 3.07) & an overdrive "trannie" will give you less R's on the highway & great gas milage, but it won't give you that awsome "launch" feeling. So, you'll have to decide & kinda trade one off for the other. In this case, you probably are not gonna "have your cake, & eat it too". I really do not think that a 3.54 gear with your TH350 is gonna jeporadize your engine that much, unless your're doing constant high speeds (a few hundred miles at a time on the freeway; two or three times a week). A 3.73 or taller would be a problem. I once drove from Michigan to Flordia with a 4.11 gear & 4-speed manual trans. Although it sounded like the car was straining, not to mention all of that gas!, the motor still ran strong long after that trip & was sold. Your engine sounds like it will be producing alot of power & if it doesn't get to the rear wheels like you want, you'll be dissapointed. These are just my thoughts on this subject. Boy, isn't living in America great............. Decisions, decisions, decisions!

Take Care & what ever you decide...........good luck!