Need some insight, recommendations, advice etc.
Thread Starter
Burning Brakes
Joined: Mar 2019
Posts: 1,057
Likes: 41
From: Chehalis, WA
Okay guys, are any of you familiar with Gear Vendors? They make an overdrive unit for transmissions, including the TH350 3 speed auto. That way I keep my original 350 (with mild cam, FiTech EFI, and dual exhaust) with a 3.55 rear end. More acceleration and cruising at 70 mph without stressing the engine. Doable, stupid idea, won't work, too expensive for trade off etc.? What say you?
Thread Starter
Burning Brakes
Joined: Mar 2019
Posts: 1,057
Likes: 41
From: Chehalis, WA
Forget the Gear Vendor overdrive piece. After installation it would be as costly as a 700r4 or close to it. I may just go forward with the 3.55 rear end, and if I want to spend more time at hiway speeds, install the 700r4. Thanks again for learnin me up all your Corvette know how.
Burning Brakes
Joined: Jun 2020
Posts: 881
Likes: 113
700r4; not only does it have a 0.696:1 overdrive, but (when compared to THM350's 2.52:1 first)
700r4 also has a rather deep 1st gear (3.059:1); pretty good match w/ 3.08:1 rear
JMO, small chamber heads & 700r4 will transform L48
700r4 also has a rather deep 1st gear (3.059:1); pretty good match w/ 3.08:1 rear
JMO, small chamber heads & 700r4 will transform L48
Old Pro Solo Guy
Joined: Dec 2017
Posts: 8,097
Likes: 4,451
From: Marlton NJ
700r4 $1500
Diff re-gear & rebuild $1100
https://www.vansteel.com/index.cfm?f...&SubGroup=1819
Cylinder heads $1000ish
https://www.summitracing.com/search/...r%20heads&ar=1
Plus labor
Could be a step wise approach, each building on the other. For biggest bang/buck the order could be:
1st - 3:55
2nd - heads
3rd - 700r4
Diff re-gear & rebuild $1100
https://www.vansteel.com/index.cfm?f...&SubGroup=1819
Cylinder heads $1000ish
https://www.summitracing.com/search/...r%20heads&ar=1
Plus labor
Could be a step wise approach, each building on the other. For biggest bang/buck the order could be:
1st - 3:55
2nd - heads
3rd - 700r4
Last edited by leigh1322; Aug 16, 2020 at 02:04 PM.
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,063
From: altered state
St. Jude Donor '05
GV and 700r both have positives and negatives, neither is bad
For a mild say 350-400hp sbc your gear, increased stall speed and a nice 700 should do the job. Make sure and run a separate trans cooler so it lives, I always bypass the radiator.
For a mild say 350-400hp sbc your gear, increased stall speed and a nice 700 should do the job. Make sure and run a separate trans cooler so it lives, I always bypass the radiator.
Last edited by cv67; Aug 18, 2020 at 01:49 AM.
Thread Starter
Burning Brakes
Joined: Mar 2019
Posts: 1,057
Likes: 41
From: Chehalis, WA
Thanks, all great suggestions.I don't want to get too radical here. I'm an old fart; don't want a race car, just a little more get up and go. Also, I don't have an endless supply of dough to sink into upgrades. So I'm seriously thinking the 3:55 ring and pinion to start and later if I want hiway RPM, switch to a 700r4 w/OD. Retired, but sold a Harley a couple of months ago, so have a little with which to play. Damn you guys, now you have me thinking about a composite spring for the rear end too. I already have the Bilstein shocks.
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
Thanks for the insights-all good ones. I would save a hell of a lot of dough just by leaving well enough alone. The car runs very well as is, and with what the PO had done, it is not nearly the dog that it was in 76. Unfortunately, there's a lingering itch for the giddy up experienced in my 68 Goat many moons ago. Damn it, I just need to grow up. If I do anything at all, it will probably be the crate route. Even though the engine seems to be in fine shape for 40+ years, there is an old saying about throwing good money after bad. Thanks again; I'm in awe at the depth of knowledge in this forum.
Last edited by Little Mouse; Aug 16, 2020 at 09:04 PM.
Thread Starter
Burning Brakes
Joined: Mar 2019
Posts: 1,057
Likes: 41
From: Chehalis, WA
Mouse, that's a capital idea, just a bit out of my price range though right now. But you know, knock off one or two liquor stores, and I'd be good to go. Hmmm, the thought of Bubba standing behind me in the shower , waiting for me to pick up the soap, kind of puts a damper on that plan.
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Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
Nothing is cheap to do anymore. You try to do a trans and rear gearing will be far more to do it right then buying chevy crate engine. But then its a never ending spending deal. More power will the trans and rear hold up and how long. Try to add more power to existing engine maybe it lasts maybe not.
Last edited by Little Mouse; Aug 17, 2020 at 11:50 PM.
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
Im not an auto man but from everything i have read, if you beef up in strength an 700 R4 and the 200R4 you can make the 200 stronger. Its kind of like the new version of the old power glide weak in stock form but strong as all get out in modded form. The 3.05 low of the 700R4 to low if you combine it with a 3.55 rear the 200R4 first gear 2.74 good match for a 3.55 rear and both trans have really the same overdrive 200R4 .067, 700R4 .069. A couple of grand should put you into a good 200R4. Its 2.74 a bit lower then your current trans around 2.54. Combine it with a well matched TQ converter and you wood most likely be happy. Then down the road a 3.55 when money comes along for it. 2.74 x 3.55 = 9.72. 3.05 x 3.55 = 10.82. 10.0 pretty ideal for a street car low gear. Right now your current trans i think is a 2.54. 2.54 x 3.08 = 7.82. Need less to say a 7.82 is crap for accel. The overdrive' in both trans are extreme 31 and 33 percent.
Last edited by Little Mouse; Aug 18, 2020 at 10:03 PM.
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
So you overdrive a 3.08 rear 33 percent its now the same as a 2.07 rear direct drive. 3.55 rear 33 percent 2.38. Go to a 3.70 rear at 33 percent your at a good 2.50 hwy gear.
Last edited by Little Mouse; Aug 18, 2020 at 11:17 PM.
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
So a 200R4. Trans with 3.70 rear gives you a perfect 10.13 first gear and with 33 percent overdrive same as a 2.50 perfect hwy gearing. Then you do the right TQ converter to match your current engine.
Last edited by Little Mouse; Aug 18, 2020 at 11:37 PM.
Instructor
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From: San Carlos Ca.