Bart K

I have the 427 with the M21 trans and 3:73 rear end gears. The speed limit in AZ is 75 and you can get away with 80 all day long. Just wondering what kind of RPM I will be turning with that set up at that speed. I hope to find out for myself in a week or so, but until them, can you all help me out????

Tiger Joe

http://www.csgnetwork.com/multirpmcalc.html


use the bottom calculator, just need to know tire height


heres some basic info for your setup:


27" tall tire (stock) - 3700 rpm
28" tire- 3580
29" tire- 3450


FWIW- stock 27" tire with OD added ~ 2,800 rpm

Bart K

Thanks Tiger Joe! Either way, it sounds like I will be looking for a 5th gear, but hey, what the hell!

Bart K

Looks like 3856 with a 26.1" tire (P235x60xR15) at 80 mph. That big block will be screaming!!!

20mercury

FWIW, I have a 68 with a 454, 80mph does 3500 rpm +/- with a 3.36 rear. No problem all day long.

IMHO, these engines will run 3000 4000rpm with no problems all day long. I think we see the modern Corvettes with 1500rpm on the tach at 85mph and therefore think a steady 3000 4000 is unacceptable.

Now no doubt, 1500 is better and less wear, and certainly running 3500 you will need to stop for gas a lot more often

doorgunner

Rookie here......how about settling for 2500 rpm for a highway car....it gives the engine and the fuel gauge a "break"

Bart K

Yeah, I am not sure what the rear end gearing in the newer Vettes is, but I am sure they have either automatic or 6+ speed transmissions that make that 1500 RPM possible. Fortunately, I do not plan on cross country road trips at that speed. My trips on the freeway are 50 to maybe an occasional 150 mile trip. It should be a blast around town!

joewill

the new corvettes run a 50% overdrive in 6th gear..

Bart K

I could have had a new one or the 69. I am happy with the bed I made for myself!

20mercury

Great choice, 69 with a 427 and 4sp!!!

(And in the meantime, the 69 should increase in value and the new one, well, would have depreciated a bit when you drove it around the block)

Wrecked82

About 2450 for my 82 with 3.55 rear end and AOD. Right on calculation from website. Only get 15 mpg if I am good about driving. 13 if I get on it all the time. Yes, the 3.55 rear end does improve performance, even on a lowly 82.

derekderek

The 365 hp mrrcruiser is basically a clone of iron head 71 LS-6. Touch milder cam with 114 lobe sep to avoid exhaust water reversion. Those engines run 4to 5k all day at 3/4 throttle. A throttle setting you can only use in a car for 5 seconds...maybe 12.5 seconds at the track. You ain't gonna hurt a 427 or 454 at3500 light throttle.

Eljay

70 LS5 M21 3:70 rear 3400@75

Bart K

Good point 20mercury!

Bart K

Nothing lowly about an 82 Larry! I love the look of those cars. As for gas mileage.............not worried about it! This car will not be driven all the time, so I can afford a tank of gas now and then!!!

Bart K

Good to know, thanks for the info derekderek! Did I mention that this is my first big block? I am used to high winding 283, 327, 350's. I know I have to keep a good watch on the rpm on the big block. I did have this engine balanced and it has a roller top end, so maybe that will a bit more forgiving at or near the redline!

Bart K

Thanks for the live action pic! I should expect nothing less from the C3 forum!!!

scrappy76

I get in my 1976 vette with a transplanted big block 454 and a 3:73 rear, and I am screaming down the highway pleasantly doing 70 at about 3100 rpm's. Then I go to work the next day in my 1994 vette lt1, I am rumbling down the highway doing 70 at 1900 rpm's.

I prefer the big block.

joewill

As stated earlier, this is what a 3.43 and a 50% overdrive does on a 6-speed 2001.. comes out to a 1.71 final drive ratio

AboveTheLogic

FWIW...

4th:


6th:


Specs below.