How fast is too fast?
Thread Starter
Burning Brakes
Joined: Mar 2011
Posts: 969
Likes: 1
From: NJ
How fast is too fast?
My 70 4-speed has a 3.7 rear which spins at 3000RPMs at around 62-63 mph. I'm not used to driving in the right lane on the highway but I also don't want to push it too hard and drive too long at 3k.
Question is .... how far do you guys push your RPMs and feel safe driving at those speeds over longer distances? Am I just paranoid thinking I'll destroy the motor going any faster than 65mph and over 3k rpm?
Question is .... how far do you guys push your RPMs and feel safe driving at those speeds over longer distances? Am I just paranoid thinking I'll destroy the motor going any faster than 65mph and over 3k rpm?
Le Mans Master
Joined: Sep 2004
Posts: 5,116
Likes: 5
From: Livonia MI
I know what you're talking about, as have a car with a 3.73 axle, and didn't like like high rpm highway driving. Changed the tranny out to an od unit, and much more confortable now. This has been talked about before, with many saying don't worry about engine damage. However friend of mine took his 396 Chevelle 4.11 accross country at highway speeds, and never ran the same after that.
Racer
Joined: Oct 2003
Posts: 424
Likes: 9
From: Killeen Texas
If the hi-way driving
Yes, feels uncomfortable f/ the driver, but not terrible f/ a SBC that's in proper operating condition. If you drive the car on the hi-way everyday and very often, then install smaller gears, ie; 2:80s or 3:20s. If it's just a once in awhile thing, then leave the existing gears in there. I personally wouldn't have 3:70s in a car that I drove on the hi-way very often. I don't like the feel of a SBC spinning at 3 grand on a regular constant basis. I'd install something that let me run at about 2300 rpms when at 70 or 75 mph. If you only run the car on the hi-way now and then, just leave it the way it is. Good Luck.
Instructor
Joined: Apr 2012
Posts: 224
Likes: 2
From: St. Charles Missouri
Drifting
Joined: Nov 2007
Posts: 1,716
Likes: 279
From: New York
Depends, my old stock 350/350 motor had forged pistons, heat treated connecting rods and forged cranks. They could live all day at more than 3K.
A new strong motor, should take more. On track, you take it to redline all the time.
A new strong motor, should take more. On track, you take it to redline all the time.
Thread Starter
Burning Brakes
Joined: Mar 2011
Posts: 969
Likes: 1
From: NJ
Im concerned about an occasional drive to work and back....30miles each way on the highway going over 3k the entire way. Just wanted to see how others feel about it with more mechanical/motor experience than me.
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Instructor
Joined: Jul 2012
Posts: 198
Likes: 2
From: St. Catharines Ontario
Mine runs 3500 rpm at 120 km/hr (75 mph) and I drive twice a year to Mosport about 2 hours away with no problems. Is it annoying running high rpm the whole way?? Yes...will it hurt a good running motor?? No. If this was my daily driver and I drove highway everyday I would change gears or tranny but for occasional highway driving just have fun and enjoy the ride.
Instructor
Joined: Oct 2009
Posts: 230
Likes: 4
From: Woodbridge VA
I feel the same, driving around 3K RPM at 65 MPH makes me a bit uncomfortable (1970 454 4-speed). I'm looking into changing to a 5-speed manual for the long cruises to the beach and back home to show off in Pittsburgh.
The rebuilt engine is strong, but gas mileage suffers a great degree. I already have the factory trans in storage so replacing the current installed Richmond is no big deal. I may never see the cost benefit, but I'm a cruiser these days and the highway will serve as an important part of my destination.
The rebuilt engine is strong, but gas mileage suffers a great degree. I already have the factory trans in storage so replacing the current installed Richmond is no big deal. I may never see the cost benefit, but I'm a cruiser these days and the highway will serve as an important part of my destination.
Race Director
Joined: Nov 2002
Posts: 12,142
Likes: 54
From: Taylor Michigan
My ratios in the toys are from 4.1 and 4.56.....they use to travel 500+ miles a week end from Dearborn to Boyne and back at 3500 RPM`s and above on U.S.75....with the 4.1, 3500 is 70MPH and the 4.56, 70MPR is 4000RPM`s....Built right, you wont have any worries as I know I dont and they are all the highest advertised HP available either BB or SB......
Drive it, thats what there for.....they are tougher than you think.....
PS, 3K is nothing...run all day long
Drive it, thats what there for.....they are tougher than you think.....
PS, 3K is nothing...run all day long
Drifting
Joined: Jan 2011
Posts: 1,853
Likes: 81
From: Hamilton Virginia
If ya think about it, back then when most these cars were built, the speed limit was mainly 70-75 on the highway and all the most were only offered in the higher gear range with the autos or manuals. They are built for it. I think for most its the annoyance of the high rpm sound. I drove my 350 with 3:73 gears for almost two years daily to work and kept it about 3k. Now I am running the bigblock the same just not as often because of gas milage.
Instructor
Joined: Feb 2013
Posts: 197
Likes: 0
I share the OP's concerns.
I like the idea that OD can reduce:
1. Wear and tear on the mill.
2. Noise. (I like headers & pipes--I don't like D-R-O-N-E, for 6 hours, one way).
3. Gas consumption.
I've seen mention of both Tremac and Richmond trannies, in both 5 and 6 speeds. I like to shift, so I'd like a 6 speed.
My Questions:
1. Cost of Tremac 5spd conversion? 6spd? (Parts only--my labor).
2. Cost of Richmond 5spd conversion? 6spd? (Parts only--my labor).
3. What 5spd is in early '80's Z28's? I read (here) it was a Tremac, and that buying a rusted out Z28 for hundreds of dollars would be, by far, the cheapest conversion. Discuss?
4. When doing these conversions, are new cross members available? And I'm guessing I get to drill new holes? Or are the cross members engineered to use the existing holes in the frame.
Thank you.
Safety Car
Joined: Sep 2005
Posts: 4,062
Likes: 103
From: Southeast, Tennessee
St. Jude Donor '09 thru '26
my 78 runs at approx 3200 rpm at 70 and i cruise there or a bit higher for hours without any concerns. i would just make certain that if you are running an original engine or a rebuild to original specs that you use a good, zinc rich oil for the flat tappets in the block. personally i have been using joe gibbs HR2 10-40 ever since the rebuild of my engine 2000 or so miles ago and other than a distributor module failure at about 600 miles it runs like a top and will cruise all day at high speeds. i'm sure you rev it loads higher taking off or going through the gears, so why be afraid of a constant 3-4000 rpm ride? if on the other hand you are running a tired engine, you could experience a problem at 2k just as easy as you could at 3 or 4k rpm. corvettes were designed to be driven (even those that were made strangled in the 70's) so drive it and enjoy it.