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Highway friendly?

4K views 18 replies 11 participants last post by  Just 1 More 
#1 ·
Looking for input to make the Camaro more comfortable at speed on the highway by dropping cruising RPM to around 2000 at 70 mph. Current setup is a 406 cu in SBC with AFR 195 street eliminator heads, dual plane intake, forged internals and Isky roller cam RR282. About 10:1 compression. Turbo 350 GV overdrive (.78) 2800 stall converter and 3:73 rear end. Rear tire size 275/40/17. Thinking I have enough torque to change rear end gear ratio although I’m guessing I would probably need to change the carrier if I move much. I have thought also about a 5 or 6 speed manual to gain more of an overdrive reduction. Your thoughts appreciated.
 
#4 ·
Gear vender is a good option if you want to keep an automatic in the car. I'm running a 235-60-15 tire, 3.73 rear with my 5 speed tko. Rpm's are around 2300 @ 80 mph if that helps you. Gear maybe cheaper and easier, but you are sacrificing one way or the other. Most people never use 6th gear in the 6 speed.
 
#8 ·
I’m concerned about the impact of the 2800 stall converter and the cam on reducing rear end gearing. The cam is 282 degrees both intake and exhaust or 234 degrees both intake and exhaust at .050 lifter rise. Any thoughts how that would impact drivability throughout the RPM range by going to a 3:23 or even 3:08 ratio. I thought the 3:73 used the same carrier as the 4:11 etc sets.
 
#9 ·
You are likely seeing a lot of converter slippage, which will only get worse as you reduce the gearing & increase the load on the engine. You're at the point of diminishing returns when reducing gearing.

You really need a trans with a lock up converter, or a manual, to take full advantage of the overdrive reduction.

Keep your 3.73's & get a 6 speed manual. A T-56, for example has a .5 OD in 6th which will do what you want without sacrificing your acceleration. Keep in mind, you built a high HP engine so it runs well, now you want to take the gear out to make it less responsive & have less overall performance.
 
#10 ·
Tough spot.

You need the RPM for the cam but running along a 2800 rpm on the highway gets old fast.

If you do a gear change the TC will generate a lot of heat at the lower rpm and eventually fry the tranny.

IMHO to make it work you will need a cam change, and lower stall TC and gears. Either 3.08 or 3.23.
 
#11 ·
Thanks for input, I thought there wasn’t an easy solution here. I’m not sure if a manual trans would be the answer with the current cam when in overdrive gear. I thought perhaps advancing the cam might help but probably not. Good thing winter is coming here to work on it. Currently the car is very fun to drive around town and very responsive but longer trips are in my future.
 
#12 ·
You could always swap in a 700R4 or 4L60E. It has a .7 OD ratio & will also give you a lockup converter.

If you get the same 2800 stall converter, you should see even better performance with the deeper first gear these transmissions have (3.06:1 first)
 
#17 ·
I have a 3.50 rear gear with my TH400. I've planned for 3 years to do a 4L80E but then at the last minute, I decided to do a T56 Magnum conversion. I'm buying mine from SST.
 
#18 ·
I have a very similar set up to yours.. 400 sb. Hydraulic cam, etc on 69 z28.. Got tired of running on interstate at such high rpm as I travel to Freedom Road Rally etc.. Just put in Tremec 5 speed manual and I cant express how much of a positive impact that has had on everything!! Now running about 1775 tpm at 60 mph on speedo which is actually 66mph.. Its truly crazy how much it has improved the car.
 
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