Highway friendly? - Team Camaro Tech
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post #1 of 19 (permalink) Old Sep 21st, 19, 12:24 AM Thread Starter
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Lorne
 
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Highway friendly?

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 Iím 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.
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post #2 of 19 (permalink) Old Sep 21st, 19, 02:51 AM
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Re: Highway friendly?

What is your RPM at 70 mph now?

Easiest and least expensive would be a rear end gear change to 3.23 or 3.31. Can keep your 3 series carrier.

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post #3 of 19 (permalink) Old Sep 21st, 19, 04:06 AM
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Re: Highway friendly?

with my SB, 26" tire, Muncie with gear vendor and 3:55 gear. I can run 80 mph at 2600 rpm
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post #4 of 19 (permalink) Old Sep 21st, 19, 04:37 AM
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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.

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post #5 of 19 (permalink) Old Sep 21st, 19, 07:51 AM
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Re: Highway friendly?

Quote:
Originally Posted by X-77 keith View Post
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.
OPs post reads he has a TH350 with GV already. With 3.73s his 70 mph rpm is about 2750. Going 3.08 will run at 2175 rpm

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post #6 of 19 (permalink) Old Sep 21st, 19, 09:32 AM
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Yep I skipped right over the gv part.

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post #7 of 19 (permalink) Old Sep 21st, 19, 11:20 AM
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Re: Highway friendly?

Here's an online calculator.
https://crawlpedia.com/rpm_gear_calculator.htm

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post #8 of 19 (permalink) Old Sep 21st, 19, 10:57 PM Thread Starter
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Re: Highway friendly?

Iím 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.
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post #9 of 19 (permalink) Old Sep 22nd, 19, 09:17 AM
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Re: Highway friendly?

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.
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post #10 of 19 (permalink) Old Sep 22nd, 19, 10:42 AM
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Re: Highway friendly?

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.

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post #11 of 19 (permalink) Old Sep 22nd, 19, 08:22 PM Thread Starter
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Re: Highway friendly?

Thanks for input, I thought there wasnít an easy solution here. Iím 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.
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post #12 of 19 (permalink) Old Sep 22nd, 19, 08:32 PM
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Re: Highway friendly?

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)
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post #13 of 19 (permalink) Old Sep 22nd, 19, 08:37 PM Thread Starter
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Re: Highway friendly?

Thanks for the thought, the GV is .78 so I think I need an overdrive gear ratio that is a bigger change.
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post #14 of 19 (permalink) Old Sep 23rd, 19, 09:07 AM
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Re: Highway friendly?

I'm running 4.10 with 275/40/18, a t-56 close ratio with .63 6th gear. It runs 2500 rpm at 75.

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post #15 of 19 (permalink) Old Sep 25th, 19, 12:21 AM Thread Starter
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Re: Highway friendly?

Sounds like a nice setup
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