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Rpm??

S

SteveH

Guest
I own a stock 81, recently switched to a 355 rear end. I hit approx 3,000 RPM at 70 MPH. The mechanic who installed it told me he had an 81 that he put a 373 rear end in and drove it on the express way for hours on end without a problem I am interested in comments on running the car at that RPM for anything more than an hour. Will the stock 350 handle that RPM for an extended period of time?
 

Yoda

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Oct 12, 2000
Messages
4,884
Location
Amarillo, TX
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1981 UL5
Steve,
I by no means am an expert on this, but I do know a friend that runs his 80 somewhere between 2800 and 3100 on the highway. Last year he ran from California to Bowling Green with me and I was turning around 2200 to 2400 we ran above 65mph and usually more like around 75mph most the way across the USA.

BudD
:w
 

Tom Bryant

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Edgerton, Ohio, United States
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1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
Steve,

I have had Corvettes and other Chevys with both 3.70 and 3.36 rears. The 3.36 turns about 3000 at 70 mph also and is easy to live with. My '65 327/300 hp would get close to 18 1/2 mpg running 70 with the 3.36s. I never could get comfortable running 70+ with the 3.70s for long distances. I just felt like I was twisting the small block too hard on long trips of 2 to 3 hours between stops. Tends to get noisy with a solid lifter small block. If I was going to run 3.73 or 4.11 gears on a long distance cruiser I would have a trans with an overdrive top gear. I'm not saying that a well built engine can't take it, just that I can't shake the feeling that I'm overly abusing and wearing my engine. I would usually find myself cruising at 60-65 mph with the 3.70s.

Tom
 
S

SteveH

Guest
Thanks for the info. I will feel a lot more comfortable driving my car. Next year I am considering having some engine work done to improve performance. I am thinking about spending 2,500 - 3,000. Any suggestions would be appreaciated. If possible list the mods according to what you consider must haves and nice to haves.

One other question, will the vette 5 and 6 speed trans bolt up to my car without major mods, any idea what those trans cost?
 

JHL

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Oct 24, 2000
Messages
403
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Everywhere
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81 4 speed
Hi,

I have never really checked my rear gears but on the flat at 3000 rpm it is going just over 60 or so. Like Tom I find my self settling into cruising around 60 - 65 to keep the rpm around 3000 but occasionally I have ran with a steady 4000+ rpm for good distances and so far no problems even before I added the Edelbrock kit.

I would think that the standard motor should be able to cope with constant higher rpm`s around 3000 - 4000 without any problem so long as you don`t have it stuck in the red bit of the rev counter all the time you should be ok.
 

Tom Bryant

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1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
Steve,
I didn't see where you said what trans you have now. If you have an automatic you can convert to a 700R4 4 speed auto wth a .7 overdrive fairly easily. There are several companies that will custom build one for your specific application including converter for well under 2 Gs. Its an easy swap too. As for a 6 speed, the ZF is very hard to swap to the older cars and would end up costing as much as a new Richmond 6 speed, which is a far better choice. You won't get the Richmond in your car for what you want to spend though.

A matched components pachage such as JHL used in his car would be you best bet for most bang for the buck. The Edelbrock system with Performer RPM heads, RPM cam and RPM Air Gap intake/carb would give you great performance in a system that has been designed to work together. Saves you the hassle of trying to match components and maybe not getting the combo right. Add headers and a free flowing real dual exhaust system to this and you will be running strong. I might consider a Demon carb in place of the Edelbrock though.

Tom
 
S

SteveH

Guest
I have a 4 speed in my 81 and am considering a 5 or 6 to lower my RPM at crusing speeds. But from what I am hearing here it sounds like that may not be necessary?? I have no idea the cost of doing that type of mod.

Again, thanks for all the info. I will begin looking into the cost for the Eldebrock setup. I am assuming I can find that on their web site
 

Stingray6974

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494
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Garland,Texas
Steve,
You can run your motor for days at 3000 rpm without doing any harm. Although you have increased the rpm you have decreased the load on the engine.
Mike
 
S

SteveH

Guest
Mike:
I am confused by your comment that I have decreased the load on my engine. Being a novice at this stuff I was under the impression that increasing RPM increased the load on the engine . Could you please explain?
Thanks
 

Stingray6974

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Messages
494
Location
Garland,Texas
Hmmm. OK imagine this. You're driving along and you head up a long hill. You start to lose speed so you give it more gas. But you're still losing speed so you downshift to third. Although you're turning more rpm you're no longer losing speed without giving it any more gas. Do to the gear reduction you have now reduced the load on the engine.

Mike
 

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