rustnever sleeps

Hi all, Mid Life crisis decided I should purchase myself a new car after 16 years. I have purchased a super tidy 327 350 hp 1967 that originally had a 4.11 diff. Included in the sale is the old rear end which has been replaced with a 3.55 for more highway use. I am curious to know of anyone who has the same rear end what top end highway speed they get out of it?
Thanks in advance.

wmf62

any of the speed calculators should give you and idea of tire/rearend = speed at any rpm.

http://www.wallaceracing.com/calc-gear-tire-rpm-mph.php

for instance: if you have a 27.5" diameter tire (which is about the right # for a 205x75x15)

so if you can run 5500 in top gear, then about 110mph
Bill

ps: for grins and giggles; with OD giving me an effective rearend ratio of 2.4, theoretically i could do 170mph at 5000...

rustnever sleeps

Call me a bit thick, just did a calculation on http://wahiduddin.net/calc/calc_speed_rpm.htm
and came out at 253 mph!
The car I have not driven yet, I pick it up in about 6 weeks, has redline tyres on it standard size, the car is super original as it was ex factory in 1967, engine is a standard 327 350 hp, diff has been changed from 4.11 to 3.55. Gearbox is a M21. I assumed it had a ratio in 4th gear of 1:1? Guess not.

MikeM

Yes, it did.

With the 4.11, your engine will be turning about 3000 rpm@60 mph. 6000@120 mph. I doubt you will see 120 with that gear as your engine will be out of breath.

I'd predict 110-115 if your engine is in good shape/tune.

1965corvettecop

I have 350hp 65 with 3.70 gears. Not enjoyable on the highway at all, so not much difference then a 3.55, to give you an example. I had 3.55 in my 69 camaro, and it stunk on highway too. All transmissions of that era are 1:1 final drive. I am really considering a five speed to pick up drive ability. Otherwise you need to get a 3.08 or lower to have any top end, in which bottom end is lost. Five speed tremek has lower first gear, then overdrive for top end. you pick up bottom end and top end. Of course no more number matching transmission in car. I plan on keeping mine in attic, if I decide to go that route. I have a 3.08 chunk to do swap, but don't want to lose bottom end. I rarely drive my car because gears are just too low to enjoy.

MasterDave

Wow bro, that's harsh. Mine also has a 3.70 and while it spins the engine up in the 3,000 range at 70 mph, that engine will be pretty happy there. We are all used to the modern cars that go down the freeway doing 70 mph at 1600 rpm. Old vettes aren't like that. I recently drove mine 100 miles at 75+ mph on I-10 and loved it. Just drive it and enjoy it!

dahogan

and I have a L 79 '66 with 3.70 gears. However, I am older and just like to keep it at 65 mph on the freeway. Otherwise I am using those gears and having a blast.

Powershift

I remember moving from Texas to West Virginia in the 1970's. Drove at 3000-3500 RPM all the way. A few "short bursts" past 4000-4500 RPM when passing. Didn't hurt the car one bit. No A/C either (removed to save weight).

I think some of us are getting soft in our old age.

Larry

MikeM

I don't enjoy driving a midyear (or anything for that matter) on an interstate or other four lane road. So I don't do it and for that reason low gears doesn't offend me in the least. I like the lower speed performance of those gears. Same reason the 5 speed transmissions would be a big waste of money for me.

No need for the power brakes or power steering either. If you drove for years without it, it's no problem not having it on an old car.

1965corvettecop

I have gotten used to my 6 speed Z06 with A/C and supercharger. So, maybe I am spoiled. I do own a Sunbeam Tiger as well as the 65 Vette. Tiger has 3.31 rear end, and I don't mind it on hwy at all. Most car shows around here require you to get on hwy at some point, so that is why I get frustrated with low gears. I also don't like the tall 1st gear in close ratio Muncie. I would rather have wide ratio with lower 1st.

ChattanoogaJSB

Top speed isn't much of a concern for me, over 100 feels lightning fast in one of these cars. I have a 3.73, and the aerodynamics of the car just don't lend themselves to comfortable high speed runs, but I will down the road need an overdrive for "comfortable" long trips. I drove almost 600 miles home last year as I recall, and 3K rpm feels too high for someone who grew up exclusively in an overdrive era. I'm much more comfortable in the low 2K rpm, and I do like to be on the highway/interstate

63Corvette

The L79 is a very stout engine (Ask Donny Brass). He is currently running over 110mph in a standing quarter mile with 4.56 gears
Although "your results may differ"......any reasonably maintained L79 will easily run to (or above ) 6000rpm. The speed calculator below gives these results with a tire size of 27" (about a 6.70X15): http://www.apexgarage.com/tech/gear_ratios.shtml
4.11 = 20mph per 1000 rpm = 120mph@6000rpm
3.70 = 22 = 132
3.55 = 23 = 138
3.36 = 24 = 144

These speeds are attainable on a racetrack or closed course, such as the Texas Mile etc. I run my 63 Z06 at much higher speeds than these, BUT it is a RACE car, and I find that (for my car) significant lift does not affect handling until above 150mph. (Kids....don't try this at home)

MikeM

The tall first gear in the M 21 and the 3.70 gear was the perfect compromise for your engine. Put a 3.08 in your car with that transmission and you'll kill it.

You can change the transmission to wide ratio and go to a 3.08 rear gear for good results but why bother? You say you don't drive it much anyway.

rustnever sleeps

Thanks for the varied opinions everyone. Dont know what its like in the US but here our highway(joke) in New Zealand at best is 2 lanes in one direction. I purchased my vette to go to the beach house 2 hours away and its a pretty drive anyway you do it. Our main roads are nothing better than one lane wide the odd passing lane but generally one lane in each direction with a painted strip in the middle called a white line(we joke as we call it a safety strip) To drive 100 miles takes 2 hours in just about any sort of car due to the windy roads and its rare to have a straight road. When we do we normally have a POlice camera or the real thing sitting on the side of the road to keep us under control. A squirt to 70 mph is only going to be a minute or so before you expose yourself to one one of these cameras or the Police. I am hoping the undriven vette as yet with 3.55 ratio will be enjoyable on our highway at 50mph in 4th? Guess I will find out as the virgin test drive is 600 miles through our roads which are super scenic and I have a set of side pipes to keep me awake!

steampunk c1

Sounds like a nice ride but with a m21 you will have a high first gear. I have 61 impala with 3.7 diff and m21 and I have swoped it out for w55 toyota box now it will jump in the low gears and cruise at 100k at 2400 rpm just right. In my ci I have strong 327 and th350 auto with 2.7 gears its a super cruiser. PS whot part of nz are you.

rustnever sleeps

Im located iin Auckland heading North from South Island to pick up.
By high first gear, high ratio(hard to get going?) or a long set of legs in first? I havent driven it yet and to be honest its the first C2 I have ever had a ride in. Cant be any worse than my current driver a Toyota Landcruiser short wheel base with 50"s design spring leave suspension!

MikeM

I think a 3.55 or 3.70 gear will be all you want on those kind of roads you describe. Matter of fact, they're more like 4.11 roads.

MikeM

I think a 3.55 or 3.70 gear will be all you want on those kind of roads you describe. Matter of fact, they're more like 4.11 roads. You may be able to break the speed limit in first gear.

1965corvettecop

True.. i wont ever change rear end. I MIGHT do five speed though. Someone gave me the 3.08 chunk so i took it. I went through my engine in 2008. Had it all balanced and went back all stock 350hp stuff except cam. I put in solid lift. It will pull to 6500 or so now. So keeping 3.70 fot sure. Still hate it on hwy though. I think 5 or 6 speed would be awesome!

leif.anderson93

You're going to LOVE your L79!! I have a '67 L79 with the M21 and side pipes and cruising down the highway at 70MPH is music to my ears...gears, exhaust note, the whole thing. Granted these cars aren't like modern day cars but isn't that one of the biggest reasons we love them so much. If your top speed is going to 50MPH on winding, scenic roads in New Zealand you're going to think you've died and gone to heaven driving that sweet small block...one of the best the General ever made. I can only dream of roads like that here in Texas.