Does this sound right?

[sneakyfast]

Guys....let me apologize in advance for the dumb question as I am relatively new to the old and performance truck game.

I have a 1973 with a 383 stroker engine at the mechanics getting some carburetor work done. The mechanic sounds pretty knowledgeable about them but he made a comment to me that didn't sound right.

I told him that I recently was on the interstate and at those speeds was running around 3900 - 4000 rpm. He mentioned that I would damage the motor if I had any sustained running of the engine above 3200 rpm. He said no problem blasting up to 6000 rpm but that the problem was that sustained rpm.

Does that sound right? I have never heard of any engine that was below red line having damage due to sustained rpm.

[Blessed66]

Can't say it makes much sense to me. Doesn't mean he's incapable of building a solid engine, just that he might be wrong on a rather minor detail.

[sneakyfast]

For clarity, he didn't build the engine but was commenting on it. I always thought that the very definition of redline was that an engine could run safely at anything below it. I just can't imagine what would fail or be stressed.

[slotard]

The faster you spin it the more wear you get. I wouldn't expect anything catastrophic, but spinning 4k is going to wear everything out significantly faster than 3k and will also guzzle gas. The extra stroke your 383 has means it enjoys high RPM less than a 350, which doesn't rev as high as a 327, which doesn't rev as high as a 302.

When it comes to a non-stock engine, it's hard to define redline. There is a difference between what RPM is ok to hit on a drag strip and what RPM is ok to sit at towing a trailer up a long hill.

[Blessed66]

Mean Piston Speed

Post #16 here.

There is a method of determining redline, besides the above, that references head, intake and/or cam limitations on a dyno. A whole bunch of little details all add up to put a near-exact number for near-any engine.

[Blessed66]

However, there are dozens of factors that can determine wear. Desnity of molecules (i.e. Why German blocks show less wear than american blocks), tolerances of the assembly, type of engine oil (low-ZDDP oil in older engines tends to be a hot debate), how you (the owner) drive and maintain your vehicle, etc.

In a perfect world, I'd love to tear down my engines at 50k to check how much wear has actually occured. However, until there's a "problem," I highly doubt many people would bother doing that.

[Jake Wade]

You could really use an overdrive.

[nvrenuf]

Gear ratio??

[slotard]

TH350 or TH400 with 4.56 could certainly lead to those rpms at reasonable speeds with fairly small tires.

[cadillac_al]

It might take it but it will wear out faster.

[Blessed66]

OP is concerned with damage, I believe. Wear and damage are not the same thing.

[sneakyfast]

Originally Posted by Blessed66

OP is concerned with damage, I believe. Wear and damage are not the same thing.

Yes correct about the damage concern. Wear I don't think can be avoided but I don't want to damage the engine if I take a 20 minute drive on the interstate. That's why it sounded so strange as I can't imagine what damage it would do.

Anyway, yes I am running a TH350 and 4.11 gears and could really use an overdrive.

[slotard]

I'd be very surprised at catastrophic failure, but it might mean the engine lasts 50k rather than double that.

Another option that would help is looking for a 3.73 rear end to replace the 4.11, I've had my eyes open for one for a while for the same reason (although I have a 350 rather than a 383, so the rings are happy at higher rpm).

[sneakyfast]

Originally Posted by slotard

I'd be very surprised at catastrophic failure, but it might mean the engine lasts 50k rather than double that.

Another option that would help is looking for a 3.73 rear end to replace the 4.11, I've had my eyes open for one for a while for the same reason (although I have a 350 rather than a 383, so the rings are happy at higher rpm).

Yes I've thought about the same...but man that pop off the line is addictive.

[Blessed66]

Originally Posted by sneakyfast

Yes I've thought about the same...but man that pop off the line is addictive.

It is.

But there are some considerations to think about. I'd be more of an advocate for a higher stall converter over steep gears, honestly.

[slotard]

My '73 also has 4.10s and I'd love to have taller gearing, my engine is just a truck motor and doesn't seem to enjoy sustained high RPM. Sure, it'll do it, but it sure does scream. It's kinda fun to be able to burn rubber all day even with a utility bed full of tools though.

Another option would be to swap to an overdrive trans - if you have a 700R4 now you wouldn't lose much going to a TH350.