What gear for a TH350

[cmegga]

Guys I know this topic has been discussed quite a bit, but I havent been having much luck finding a old thread for my application. The cars in the shop for a new rear spring and some other goodies, so Im thinking its probably a good time to address the 2:81 gear in the rear end. Im extimating about 350 or so HP and absolutly hating the lack of low end power from this gear.

Im not quite ready to toss that TH350 just yet, it only has about 25k on it, it was almost new when I bought the car. Im looking for something quite a bit more then the 2:81 , in the low to mid range. But that will also not wind too high at high speeds, as I do alot of highway miles as well. Im thinking a 3:30 or 3:50 gear, but not sure what will give me the desired ride and not be too hard on the motor at high speeds.

Also Im trying to keep on mind that when the trany does give up on me I ll be going to a th400 or 7004r.

Any sugestions as Im not well educated in this areina.

 

[Alwyn678]

I have a 3:73 and I would have it no other way

 

[cmegga]

alwyn,

you had a th350 ? How high are the RPMS on the highway ?

 

[page62]

Fuhgeddabboudit! I had a TH350 with a 3.70 rear end. Highway driving was absolutely miserable! 3200-3500 rpm was the norm just to keep up with traffic around here. The first mod I did to my car was an OD tranny.

Wait until you do a tranny swap before swapping out the rear gears. BTW: The 200-4R is highly recommended as an OD tranny in C3 Vettes.

 

[Alwyn678]

I have a 3:73 and I would have it no other way

I have a Th-400 But I do not do a lot of interstate driving. When I do it is really not that bad at all. My car is mainly for cruising around town and not cross country touring. I wanted it to launch and do well light to light not state to state.

 

[cmegga]

I can understand on a th400, but with the th350 is a 3 speed,

I think that gear would be way too much for highway in my application.

 

[Alwyn678]

I can understand on a th400, but with the th350 is a 3 speed,

I think that gear would be way too much for highway in my application.

Th-400 is a 3 speed it is the tranny that came before the 350:L

 

[cruisin-davey-g]

3.50 or 3.55 is the best all around gear for your turbo 350. If you do go to an overdrive tranny, you can always shoot up to a 4.11. So, if your're gonna do a tranny swap in the near future (to an OD), don't do the gear swap until then, otherwise you'll be swapping gears twice. If you can do this yourself, no "biggie", but......... if 'ya gotta pay somebody else to do it "Mucho Big Bucks"

Dave ("IT depends on just how big is your pocket book?)

 

[AmosF16]

I'm with Cruisin-Davey-G on the 3.55 with the TH350 if all you do is drive your Vette around town. 3.55 is not good on the highway--had that very installation in my 68 Camaro and was always looking for that 4th gear that wasn't there. If you're gonna drive on the highway, I'd go with like a 3.06 or so. Andy

 

[cruisin-davey-g]

Also, remember too that the lower gear (taller) you go the more effect you'll have on the trans & how much power you'll actually get to the rear wheels. The things to remember when doing gears in Automatics 1) Cam Combinations 2) torque convertor size & stall 3) rear gear. The trick is getting the right combinations & make 'em work. I've seen guys put big lift & duration cams in their cars (made the motor sound mean), shove a low gear in the rear. But, didn't do anything about torque convertor stall & then can't figure out why they don't go anywhere when they put their foot into it. Also, remember too ...........that when you put a "tall gear ratio" in the rear of an automatic, without the proper torque convertor stall speed & you're criuisin' 'round town, you're trans will tend to run hotter, 'cause it's working harder to keep up with the taller gear (sort of like dragging the trans around). So, that's why I would recommend nothing bigger than a 3.50 (or 3.55) unless you're gonna do the cam, convertor, rear gear combination deal. It's a good all around gear. One thing though, the TH350 seems to run cooler than the TH400, so that's a good point.

 

[Don&Kelly]

We put a 700R4 Transmission in our '81 just exactly because of high RPM's when we were driving on the highway.

We just took a long highway cruise last weekend with our Corvette Club & the other C-3's were really gripping about how high their motors were reving (believe me I used to gripe also) - but the whole group were cruising around 70 mph & I was running 1200 to 1400 RPM's lower than the other C-3's ...

I believe that we have the stock 2:87 rear end in our '81 & I may change to something in the 3:07 range - I do not want high RPM's again ..

I changed my C5's rearend from a 3:15 to a 3:42 & the increased accelleration was great w/o any RPM problems ...

:cool

 

[cmegga]

I had the cam & stall converter new last year, with a whole engine rebuld. Its around a 3300 Rpm cam , and the converter was custome made to kick in 2300, al though it actually closer to 2200 from what I see on the tach. The problem is the engine is making power, but nothing behind it.

Why couldnt I go with like a 3:23 or so ? Would that be a good match for both tranies ?

My logic is almost the whole rear end is going to be a part , so I can save some $$ doing it now as this is definatly something I would not atempt on my own.

 

[cruisin-davey-g]

I had the cam & stall converter new last year, with a whole engine rebuld. Its around a 3300 Rpm cam , and the converter was custome made to kick in 2300, al though it actually closer to 2200 from what I see on the tach. The problem is the engine is making power, but nothing behind it.

Why couldnt I go with like a 3:23 or so ? Would that be a good match for both tranies ?

My logic is almost the whole rear end is going to be a part , so I can save some $$ doing it now as this is definatly something I would not atempt on my own.

You state that you have a 3300RPM Cam? Look at the specs of your cam & see what the operating range is. If your cam doesn't start to power up until 3300RPM, then the 2300 stall convertor is useless for that cam. T0 effectively operate that cam in accordance with the converter, you would need at least a 4000 or better stall converter (like a 8 or 9 inch conveter). Most street cams have an operating range of either "off-idle to 5500" or for performance "1500 to around 6000 or 6500 RPM" range. The latter cam would at least need a 2800 stall convertor for power to be effective through the trans to the rear wheels. I have an "off-idle to 5500 RPM" operating cam & it works effectivily with pretty much the same converter you have (which is a step up from stock (stock is about 1600 to 1700 RPM). Now I'm running a 3.36 gear which is one up from my stock gear of 3.08. It really doesn't seem to be enough to get it to launch off the line like I want it to. So, if you've got sort of the same set-up as me, that's why I would suggest to going to the 3.50 gear (I believe that's the ratio for a Corvette similiar to a 3.55). Also, I might add, I have the TH400 in mine as opposed to your TH300. I have a buddy that has the performance cam set-up "1500 to 6000RPM" range, he's got the TH300 with a 3000 stall converter & 3.90 gears in the rear. It's a real screamer for the street, but on the highway, it "sucks". He's taching out at about the 5500 RPM range & at 70 or 80 MPH cruisin speeds (freeway), his motor is straining after long hauls. So, take all of this into consideration, & depending on how you plan to use the vechile "street" or highway (maybe a combo of both), I would still suggest the 3.50 gear.

 

[cruisin-davey-g]

You state that you have a 3300RPM Cam? Look at the specs of your cam & see what the operating range is. If your cam doesn't start to power up until 3300RPM, then the 2300 stall convertor is useless for that cam. T0 effectively operate that cam in accordance with the converter, you would need at least a 4000 or better stall converter (like a 8 or 9 inch conveter). Most street cams have an operating range of either "off-idle to 5500" or for performance "1500 to around 6000 or 6500 RPM" range. The latter cam would at least need a 2800 stall convertor for power to be effective through the trans to the rear wheels. I have an "off-idle to 5500 RPM" operating cam & it works effectivily with pretty much the same converter you have (which is a step up from stock (stock is about 1600 to 1700 RPM). Now I'm running a 3.36 gear which is one up from my stock gear of 3.08. It really doesn't seem to be enough to get it to launch off the line like I want it to. So, if you've got sort of the same set-up as me, that's why I would suggest to going to the 3.50 gear (I believe that's the ratio for a Corvette similiar to a 3.55). Also, I might add, I have the TH400 in mine as opposed to your TH300. I have a buddy that has the performance cam set-up "1500 to 6000RPM" range, he's got the TH300 with a 3000 stall converter & 3.90 gears in the rear. It's a real screamer for the street, but on the highway, it "sucks". He's taching out at about the 5500 RPM range & at 70 or 80 MPH cruisin speeds (freeway), his motor is straining after long hauls. So, take all of this into consideration, & depending on how you plan to use the vechile "street" or highway (maybe a combo of both), I would still suggest the 3.50 gear.

Where's my head at???????? I meant TH350. Don't wanna confuse everybody & get jumped on at the same time. WOW!

 

[cmegga]

Ill try and find the cam spec, it probably is not a 3300 cam like I said, but the powerband on the diagram show between that an 5500.

Below are the basics on the engine build.

Heads Edelbrock Perfomer RPM 60899
Cam Comp Cams Extreme Enegry CL12-242-2
Carborator Edelbrock Performer 750 CFM 350-1411
Intake Manofold Edlebrock Performer 350-2101

 

[cruisin-davey-g]

Ill try and find the cam spec, it probably is not a 3300 cam like I said, but the powerband on the diagram show between that an 5500.

Below are the basics on the engine build.

Heads Edelbrock Perfomer RPM 60899
Cam Comp Cams Extreme Enegry CL12-242-2
Carborator Edelbrock Performer 750 CFM 350-1411
Intake Manofold Edlebrock Performer 350-2101

Is your motor a "crate"? Or is it the original? You've got a nice set-up for the street.

OK.............I believe that cam; Comp Cams 242 is an off idle to 5500 cam & will work with your set-up. Go with the 3.50 rear. I believe that if you go with this gear, you'll be able to break the tires at a 10 to 15 MPH roll. Not to mention from a "Dead Dig".

Does the cam have a nice lope to it? What is your curb idle speed?

That gear will also work OK if you decide to goto an OD trans later with the set-up you mentioned. OD trans will lower you RPM range slightly & maybe save you some gas money to boot. If you're gonna drive it mostly on the street, you probably won't be using the OD gear in the trans anyway. But it's nice to have OD when you hit the Highway. Hey, the best of both worlds!

 

[Alwyn678]

With your set-up the 3:55 or 3:73 will be vey close in performance and driveability. I would also recommend adding a Trans-go shift improver kit(with a cooler) and also a Stall convertor with your set-up. I would think somewhere around a 2500 stall speed would be ideal to launch the car in it's power band and take full advantage of the car's potential. Btw am running richmond gears and I have been very happy with them. I installed everything myself and It was not that difficult to do


Good Luck!!

 

[cruisin-davey-g]

With your set-up the 3:55 or 3:73 will be vey close in performance and driveability. I would also recommend adding a Trans-go shift improver kit(with a cooler) and also a Stall convertor with your set-up. I would think somewhere around a 2500 stall speed would be ideal to launch the car in it's power band and take full advantage of the car's potential. Btw am running richmond gears and I have been very happy with them. I installed everything myself and It was not that difficult to do


Good Luck!!

Hi: What size do you have in your car? I believe that the size for the 'vette is 3.50 (I may be wrong). Also, I don't know if you can put a 3.73 in a C-3 'vette rear(?). I do know that they make a 3.90 ratio for the C-3. I may be wrong, so please correct me if I'm wrong. What did you use to set the clearances between the ring & pinion. Also, did you change the clutch pack in the rear? Also, I was always told & had friends that ran richmond gears in their rears & they were "noisy". My buddies that ran them loved Richmond gears & used 'em in drag applaciations & didn't care about 'em being noisy. But, on the street, they might be a problem.

Dave

 

[Alwyn678]

Hi: What size do you have in your car? I believe that the size for the 'vette is 3.50 (I may be wrong). Also, I don't know if you can put a 3.73 in a C-3 'vette rear(?). I do know that they make a 3.90 ratio for the C-3. I may be wrong, so please correct me if I'm wrong. What did you use to set the clearances between the ring & pinion. Also, did you change the clutch pack in the rear? Also, I was always told & had friends that ran richmond gears in their rears & they were "noisy". My buddies that ran them loved Richmond gears & used 'em in drag applaciations & didn't care about 'em being noisy. But, on the street, they might be a problem.

Dave

Yes you are wrong in that case they do make a 3:55 but not a 3:50.....I am pretty sure that you can put a 3:73 gear in the rear as I bought and installed one myself. The clearances are the only thing I would not attempt to set. They have to be perfect and should be set by a pro. I used a machine shop locally. No I did not change the clutch pack in the rear no need it looked new. Richmond gears are not noisy at all....at least not in my case. I also wanted a strong set in the car as I will eventually install a BB and a richmond 6 speed.Good luck

 

[cruisin-davey-g]

Yes you are wrong in that case they do make a 3:55 but not a 3:50.....I am pretty sure that you can put a 3:73 gear in the rear as I bought and installed one myself. The clearances are the only thing I would not attempt to set. They have to be perfect and should be set by a pro. I used a machine shop locally. No I did not change the clutch pack in the rear no need it looked new. Richmond gears are not noisy at all....at least not in my case. I also wanted a strong set in the car as I will eventually install a BB and a richmond 6 speed.Good luck

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