.
of us have run 4.56 & lower full time on the street. If you don't run 100+ on the hwy. cross country you might like the gears.
too many RPMs?
Thread Starter
Racer
Joined: Oct 2010
Posts: 395
Likes: 0
From: winterville NC
too many RPMs?
hey guys really in a bind here...looking at another 1 with these specs but what some of my frinds has told me is to be leary of the gear in rear end...they are saying it might could cause the motor to run more RPMs that i would want and could cause cooling isssues?...here are the specs form car I am considering
Less than 15K miles since extensive restoration (over $ 20K) including:
GM ZZ-3 Crate Engine 345HP
Totally rebuilt 350 transmission with shift kit
All new suspension with upgrades
New brakes(stainless steel) including calipers and pads
New headers and stainless exhaust from engine back(sounds awesome)
New wheels and tires
New headlight actuators
New interior, even replaced seat foam, killer sound system
Vette drives and handles better than new and has more than ample power with the new GM ZZ-3
crate engine.Everything works including the clock,Has ice cold AC,PS,PB,PW,PDL and3:73 positrac rear.
Less than 15K miles since extensive restoration (over $ 20K) including:
GM ZZ-3 Crate Engine 345HP
Totally rebuilt 350 transmission with shift kit
All new suspension with upgrades
New brakes(stainless steel) including calipers and pads
New headers and stainless exhaust from engine back(sounds awesome)
New wheels and tires
New headlight actuators
New interior, even replaced seat foam, killer sound system
Vette drives and handles better than new and has more than ample power with the new GM ZZ-3
crate engine.Everything works including the clock,Has ice cold AC,PS,PB,PW,PDL and3:73 positrac rear.
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
Hmmm, that's kind of a low gear for a non-overdrive car, but it's not ridiculous. I'm sure you will be hearing very soon from some folks who have 4.11s, and just don't drive it much on the highway. The car in question sounds like a good candidate for a 2004r overdrive tranny upgrade.
Scott
Scott
Pro
Joined: Jul 2011
Posts: 511
Likes: 0
Two things about that rear end.. First - those are pretty close to racing gears, which means you'll be revving high on the freeway and burning lots of gas.. Take it for a spin and see what speed it'll do before it hits 3000 RPM. 3000 RPM is kind of the magic number where fuel efficiency starts to really fall off. If you can stay below 3000 RPM on the highway you'll burn much less gas. Your gears might be OK but it's close so drive it and see..
Next.. True Posi is a one-piece rear axle. The wheels always turn together - including when you are turning and the wheels need to travel different distances (the wheel on the inside of the circle travels less distance). This will make the wheels chirp, and each chirp is a little less tire.. It can also impact performance around turns since a chirping tire has less grip. But again - drive it and see what you think..
Next.. True Posi is a one-piece rear axle. The wheels always turn together - including when you are turning and the wheels need to travel different distances (the wheel on the inside of the circle travels less distance). This will make the wheels chirp, and each chirp is a little less tire.. It can also impact performance around turns since a chirping tire has less grip. But again - drive it and see what you think..
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
Two things about that rear end.. First - those are pretty close to racing gears, which means you'll be revving high on the freeway and burning lots of gas.. Take it for a spin and see what speed it'll do before it hits 3000 RPM. 3000 RPM is kind of the magic number where fuel efficiency starts to really fall off. If you can stay below 3000 RPM on the highway you'll burn much less gas. Your gears might be OK but it's close so drive it and see..
Next.. True Posi is a one-piece rear axle. The wheels always turn together - including when you are turning and the wheels need to travel different distances (the wheel on the inside of the circle travels less distance). This will make the wheels chirp, and each chirp is a little less tire.. It can also impact performance around turns since a chirping tire has less grip. But again - drive it and see what you think..
Next.. True Posi is a one-piece rear axle. The wheels always turn together - including when you are turning and the wheels need to travel different distances (the wheel on the inside of the circle travels less distance). This will make the wheels chirp, and each chirp is a little less tire.. It can also impact performance around turns since a chirping tire has less grip. But again - drive it and see what you think..
Scott
Le Mans Master
Joined: Oct 2005
Posts: 6,247
Likes: 471
From: Glen Allen, VA
if it's a factory gear set in that car, it's a 3.70, not a 3.73, and that's what is in mine. I drive 2 long road trips in mine each year, both times keeping right up with cars in our caravan with overdrive. Sometimes I'm running over 4000 rpm pushing 80 and above. I don't worry about it, and have no plans to install an overdrive. Granted, if I could afford a 5 spd in place of my 4 spd, I'd do it in a minute, but it's hard to justify 1000's of dollars for a conversion vs. burning some more gas. I'd have to burn a lot of extra gas to justify that cost.
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Racer
Joined: Mar 2005
Posts: 287
Likes: 0
Yeah, I would just drive it and pay attention to your numbers at highway speeds and decide how it feels to you.
I bought mine with a very low gear (maybe 4:11?) in it.
I was in 4th before I got to the mailbox, and my driveway was only about 75 feet long!
Of course a competent mechanic can change out the gears if you love everything else about the car.
I bought mine with a very low gear (maybe 4:11?) in it.
I was in 4th before I got to the mailbox, and my driveway was only about 75 feet long!
Of course a competent mechanic can change out the gears if you love everything else about the car.
Melting Slicks
Joined: Aug 2008
Posts: 2,200
Likes: 3
From: Lehigh county Pennsylvania
Cooling issues at speed? I can't see how, with all that air rushing through the radiator. I have had 3.70's for decades with both 350 and lately 302 cubic inch motors. I even removed my engine driven fan and replaced with an electric which only cycles on in traffic during the dog days of summer.
With 27.5" rear tires, I'm turning 32-3500 rpm's at interstate speeds and get 15 mpg. Not terrific, but I can live with it. I'd get way better mileage if I poked along at 55-60 mph. But that's no fun!
With 27.5" rear tires, I'm turning 32-3500 rpm's at interstate speeds and get 15 mpg. Not terrific, but I can live with it. I'd get way better mileage if I poked along at 55-60 mph. But that's no fun!
Le Mans Master
Joined: Nov 1999
Posts: 5,768
Likes: 3
From: San Diego CA
hey guys really in a bind here...looking at another 1 with these specs but what some of my frinds has told me is to be leary of the gear in rear end...they are saying it might could cause the motor to run more RPMs that i would want and could cause cooling isssues?...here are the specs form car I am considering
Less than 15K miles since extensive restoration (over $ 20K) including:
GM ZZ-3 Crate Engine 345HP
Totally rebuilt 350 transmission with shift kit
All new suspension with upgrades
New brakes(stainless steel) including calipers and pads
New headers and stainless exhaust from engine back(sounds awesome)
New wheels and tires
New headlight actuators
New interior, even replaced seat foam, killer sound system
Vette drives and handles better than new and has more than ample power with the new GM ZZ-3
crate engine.Everything works including the clock,Has ice cold AC,PS,PB,PW,PDL and3:73 positrac rear.
Less than 15K miles since extensive restoration (over $ 20K) including:
GM ZZ-3 Crate Engine 345HP
Totally rebuilt 350 transmission with shift kit
All new suspension with upgrades
New brakes(stainless steel) including calipers and pads
New headers and stainless exhaust from engine back(sounds awesome)
New wheels and tires
New headlight actuators
New interior, even replaced seat foam, killer sound system
Vette drives and handles better than new and has more than ample power with the new GM ZZ-3
crate engine.Everything works including the clock,Has ice cold AC,PS,PB,PW,PDL and3:73 positrac rear.
Of course I cant comment on how many rpm's you "Want" to run but there is nothing damaging about the rpms you will see with that gear, this is not to say that it wouldnt be more comfortable with an overdrive, or that lower rpm's wouldnt be of benefit when it comes to cooling.
I can tell you my 78 with all its emissions gear never had problems cooling the L-82 with the 3.70:1 rear gears before I put in the overdrive. Corvettes often have cooling issues and its rarely because of gearing.
Hop in and enjoy what sounds like a great ride.
Last edited by fauxrs; Aug 2, 2011 at 01:14 PM.
Pro
Joined: Jul 2011
Posts: 511
Likes: 0
My 78 L48 will also do about 67 MPH at about 2900 RPM, where I get about the rated 20 MPG. That's not too bad..
They geared the emissions cars down lower to get as much acceleration as possible out of the lower yield engines, but the speed limit back then was only 55.. You won't want to drive 80 on a road trip unless you don't care how much gas you burn.
Just remember that at 3000 or more RPM you start paying a major MPG penalty when you test drive. Get her up to 2900 RPM on the highway and see if that's fast enough for 'efficient' highway use. If it is, you are ok. Or if you can tow it whenever you drive past the end of your driveway... At $4.00 a gallon - these things matter more and more!
They geared the emissions cars down lower to get as much acceleration as possible out of the lower yield engines, but the speed limit back then was only 55.. You won't want to drive 80 on a road trip unless you don't care how much gas you burn.
Just remember that at 3000 or more RPM you start paying a major MPG penalty when you test drive. Get her up to 2900 RPM on the highway and see if that's fast enough for 'efficient' highway use. If it is, you are ok. Or if you can tow it whenever you drive past the end of your driveway... At $4.00 a gallon - these things matter more and more!
Team Owner
Joined: Jul 2008
Posts: 23,419
Likes: 22
From: In limbo
St. Jude Donor '13-'15, '17 thru '22
It's cheaper and easier to change rear gear ratios than to replace a transmission. If you are concerned about it, you could put a 3.08 in it (that's what I have in my car) if you want. But before you did it, I would encourage you to ask yourself "why?". 3.70 or 3.73 are fine gears for what I do with my car, mostly cruising around my house, rarely sustaining more than 55-60 mph on back roads just having a blast. The 3.08 works fine for that, but so would a 3.73. Last year I went to Carlisle in my car, 350 highway miles, 3000 rpm at 75 mph with the 3.08 would be 3633 rpm with the 3.73. From a "can the engine handle it" standpoint, that isn't bad at all. Any decent engine will handle that all day long. But look at the other side, if I wanted to take my car to the drags, the first thing I would do is swap out that 3.08 for something lower. I think the 3.73 is the better ratio all around, pair it or a 4.11 with a 5 or 6 speed, and you get the best of all worlds.
