Anyone running a .64 OD TKO600 with 4.10 rear gears?

[76z28]

Exactly, does not help with the timing curve being setup correctly and then cruising 500-800 rpm below that, your mileage suffers, and your headers and exhaust valves are not happy.
There's a reason why GM set the lower limit on rear gears on the Z28 to 3.73's back then, 1972 had the option, 4.10 was it I think.

My buddy hit's 46 mph in first gear on the shift, and I hit 54+ mph, so 1st gear is not that useless.

Yeah I was amazed at the difference in heat too.
I would run 190 driving at 70 at 2000rpm(that was with roughly 24 degrees of timing.)
I did the same drive, with an even warmer temperature and it ran at 175 with about 32 degrees of timing plus 8* for the vacuum advance.

 

[G72Zed]

Bingo, And I bet you got better mileage because the engine was more efficient.

My record is 20.4 MPG (11.53 Litres per 100 kms) at a steady speed of 78-80 mph. Not to shabby for a 333 cubic inch making 535 HP.

Out to beat my "mileage" goal this year with a 362 cubic inch, we'll see.

 

[DesmoEd]

Yes, running a .64 fifth TKO 600 with 4.10 gears in my 71Z28. 28" diameter rear tire. At 70mph it turns at tad over 2200rpm. Yes, First gear is shorter than I'd like. I've posted my combo several times on the forum. After doing the 2019 HRPT for 1983 miles and a total of 9K miles with this engine, trans and rear I feel, unless you have a very mild cam the rpm's are too low on the highway. Going to a 27 or 26 diameter rear tire would help sum. A mildly built (400hp) gen1 SBC isn't very efficient below 2500rpm in that state of tune. With the first to fourth gear ratios of the TKO 600 I think the ,82 fifth gear version with a 3.55 or 3.42 might be better overall. My engine is a flat top 355, 180 aluminum Dart heads, Lunati Voodoo FT hydraulic cam, 103LK are last digits of I remember correctly. 10.6 static CR, Holley Street Dominator dual plane intake, Holley 3310-2 780 vacuum secondaries carb, MSD pro billet distributor, and Hooker long tubes. The .64 fifth is about a 900 rpm drop from the 1 to 1 fourth gear.

My engine setup is very similar to yours and I agree in that there is really no reason to run it much below 2500rpm in steady cruise.

I have the .82 OD TKO in my '69 vette with 3.73 out back and its a nice combo for a sbc that likes to spin. I didn't even consider it for the Camaro but now that you have brought it up the .82 OD looks like a good match with 3.42 out back.

 

[DesmoEd]

Been through this very similar scenario with a friends/customer's car. TKO 600 w/.64 and uses a 28" rear tire (275/60/15), 12 bolt with 3.73, mild 396 BBC O/P with a dual plane and custom built carb and tune by yours truly. The 3.73 with the .64 was lugging on fifth most times, and although he was happy with the first overall gear ratio, he did not like the 5th gear.

After discussing this based on my input, he changed out to 4.10, everything stayed the same. He could not be happier. The engine gets the best mileage at 2,500 rpm (+/-), and before with the 3.73's, that was 87 mph /140 kph and up here that's an instant ticket on the highway.

The 4.10's got him down to 79 mph or 127 KPH, right in the sweet spot for him. He has 40K + miles on it now, and gets 18+ MPG, (better than the 3.73) not bad for a carb'd 470HP BBC with a flat tappet Hyd. cam (that's still not flat LOL). He also went with a lighter flywheel later on.

As a 2nd comparative, I use 27.3" rear tire, and a .77 5th with 3.73 rear gears, my carb'd SBC engine combo get's the best MPG at 2,800 RPM, and that's 79 MPH for me. We drive to many events together, and we are not only in the "engine's" sweet spot, but better yet in our happy place, driving our muscle cars LOL.

That's exactly the type of feedback I was looking for. Much appreciated

With the 4 speed I was usually shifting around 3000rpm for everyday driving and with 4.10 out back that makes the 1-2 shift @ 20 mph which should be just fine. I'm really looking forward to being able to stay in 2nd for any type of rolling stop without having to slip the clutch to get her moving.

I'll post back when I get her on the road.

Thanks, Ed

 

[G72Zed]

Your welcome Ed. And please post back with the results and your opinion on the new setup.