Don Terrill’s Speed-Talk

Another pedestrian 383 in the works and I've a quick question regarding SCAT's 9000 series crankshafts. Plenty of hits here searching but nothing specific.
The collection of parts is looking to keep peak RPMs to 6000. Maybe a couple of hundred more for some overspeed headroom. HP and TQ are not going to exceed 500. In street trim, I'd expect 450-475.
The proposed build direction will include drag racing and may include an open road event or two. It'll certainly be going across the country once or twice. The open road event gives me the greatest concern. That could be steady state 5000 RPM+ for minutes at a time.
So the question is: Is this power and RPM approaching the limits of the 9000 series crank? SCAT's Pro Comp rods w/ 7/16ths hardware are part of the pile.

Barring part to part variability and potential quality issues due to loose process controls when they are made, you really have zero to worry about. Keep in mind, a stock iron crank SBC would have been subjected to a LOT of wide open throttle hours at redline as part of the validation & release criteria for production.

You have nothing to worry about if the parts are free of defects and made to print, even if print info isn't NASA-quality. Lots of these types of parts are out there in rigorous applications that exceed what you have in mind. Stock parts would probably also work just fine too, for that matter, if they were in new condition to begin with.

Just as a frame of reference....I come from an era when all that existed were either stock parts or uber-expensive parts, no in-betweens.

I personally drag raced a Boss 351-style Ford on a weekly basis, turning the engine 7500-8000 RPM. Stock rods & iron cranks, never blew any of that up. Bore walls, another story.

Another friend raced a 355 SBC with stock rods that had stock bolts in them & stock steel crank, turning it 8000 RPM. It lasted "forever".

A lot of local-based pavement late model and sportsman guys had stock parts in their engines too. A typical combination back then would be a 351W Ford with 318 Mopar rods (longer) and a 302 Ford piston.....Turning 6500-6800 on the fast 1/2-mile oval. We also had garden varieties of SBC combinations like that too, Stock rocker arms on .550" lift flat tappets, GM pink rods turning more RPM in a late model than I will say because nobody will believe it anyway, and soforth.

If you want a 383 and you are concerned with durability and what you spend (equals value) you should consider a Chevrolet Performance 383 crate variant. Cottage industry will cry a river about that recommendation, but the GM piece comes with a 2 yr/24K mile warranty or thereabouts.

I'm from an old school "racing" background too. This is a return (or a 2nd return I should say) to being a regular again.
That said, I've experienced racing modestly with the OEM cast crank and rods (20 years ago with 1979 vintage stuff) with no more than ARP rod bolts and an improved valve train. I would drag race without any concern (limits were 6k or so) but I wouldn't subject that package to flat out for half an hour. The circle track engines that you've referred to are (I would hope) being disassembled and inspected regularly. The regular parts can take it obviously but it's a question of how long. I'm more in the one and done camp.
As for SCAT and their QC, yeah, I guess that's always part of the gamble. This is why I've thrown this out there. I've heard contrary stories of success and failure and I would expect that you'd have to pay particular attention to those details. Not that you wouldn't anyway.
As for the GM 383 (Short Block 19355719), I've looked into that and there are concerns there too. Nice crank. Rod durability unknown. And the external balance is a little unsettling. I'll take feedback on that too if there's anyone racing one.

skinny z wrote: ↑Sun Mar 22, 2020 3:29 pm As for the GM 383 (Short Block 19355719), I've looked into that and there are concerns there too. Nice crank. Rod durability unknown. And the external balance is a little unsettling. I'll take feedback on that too if there's anyone racing one.

Most crate engines are subjected to a 50-hr GED test, with the throttle pegged the entire time and RPM stepped up & down from a starting point (like 2K RPM) up to redline, then back down to baseline & up again, in increments that may be 100 or 200 RPM steps. The PM rods aren't really unproven. Same as CT400 and lots of those out there.

What I see is that the HT383 has Max HP of 323 at 4200 and peak TQ of 440 at 3000 RPM. Does testing at those values translate to 500 HP/500 TQ at 6000 and 4500 RPM (respectively)? Or is GM saying that this particular engine, though rigourosly tested, is RPM limited (cam spec and compression notwithstanding).

Still looking for information and experiences with the 9000 series cranks.

You shouldn't have any problems. I've ran several over the years. One was in a 12.5:1 383, with roller cam and AFR heads. Ran 6.40s in a 3100# camaro shifting at 7000. Sprayed a bunch of street engines, one with a 300 shot on a Big Shot plate. Sometimes ignorance is bliss. lol

Certainly encouraging.
Any idea of the lifespan on any of those engines?
The 9000 cranks come reasonably well recommended but it seems it's always drag racing or on the street performance. Which is essentially drag racing...High RPM for however long it takes to get down the highway in Nevada is what I'm talking about.
And as was posted earlier, weaker crankshafts than the SCAT version are doing yeoman service on the ovals. But again, these aren't long living engines.
But as an example, the LS3 (and I know this isn't apples to apples) have cast iron cranks (wet sump) and PM rods. And I'd suspect that you could race that thing all day. That said, the dry sump version ends up with a forged steel crank. I think GM is saying something there.

Ignorance may be bliss until you drive over your crankshaft at 100 miles an hour!

The lack of failure info on the Scat 9000 crank should tell you that few or failing. 7000 RPM and 500 hp could be a problem?, 600+ boosted could be a problem?... but not many seem to be reporting a known limit with these cranks.

I suppose one could take the absence of information as a positive sign.
There isn't a whole lot of recent information regarding failures doing a quick Google search for "SCAT 9000 crankshaft failures". I did come across a question and answer with Tom Lieb from SCAT.

Can you tell me the RPM limit on the Scat 9000 windage-cut crankshaft for a Chevy 4.030-inch bore x 3.750-inch stoke with 6.000-inch rods? Which of those specs is the major determining factor in how high I can spin the engine? Thank you!

– Willie J. Price

Tom Lieb: Willie, a 9000-series crank is a casting and has one-third less strength and stiffness than a forging. Type, size and weight of damper and flywheel, clutch, torque converter, etc. all play into how high you can spin the engine. Typically, we’d say 5,500 to 6,500 rpm is the limit based on the specifics of the engine build.

https://www.enginelabs.com/engine-tech/ ... xperience/

That's as close as an endorsement to my using one that I've come across yet.

I have heard they are good but why not pony up more for the scat forged and know its fine

skinny z wrote: ↑Mon Mar 23, 2020 9:01 pm I suppose one could take the absence of information as a positive sign.
There isn't a whole lot of recent information regarding failures doing a quick Google search for "SCAT 9000 crankshaft failures". I did come across a question and answer with Tom Lieb from SCAT.

Can you tell me the RPM limit on the Scat 9000 windage-cut crankshaft for a Chevy 4.030-inch bore x 3.750-inch stoke with 6.000-inch rods? Which of those specs is the major determining factor in how high I can spin the engine? Thank you!

– Willie J. Price

Tom Lieb: Willie, a 9000-series crank is a casting and has one-third less strength and stiffness than a forging. Type, size and weight of damper and flywheel, clutch, torque converter, etc. all play into how high you can spin the engine. Typically, we’d say 5,500 to 6,500 rpm is the limit based on the specifics of the engine build.

https://www.enginelabs.com/engine-tech/ ... xperience/

That's as close as an endorsement to my using one that I've come across yet.

If you know any credible long standing dirt track engine builders then you will here plenty of broken crank stories that were virtually eliminated when they started using the 9000 crank, these would be 7000 ish 500 hp ish engines. At that point the main webs are probably weaker than the 9000 crank. RPM seems to be harder on cranks and rods then power and load.

Orr89rocz wrote: ↑Mon Mar 23, 2020 9:07 pm I have heard they are good but why not pony up more for the scat forged and know its fine

That was the original plan. All forged and make it a bullet. What came up was a pretty good deal on a package through one of the local vendors (which includes a machined block). That package included the 9000 crank. I've been in touch with SCAT and have talked with the guy who handles that vendor. I'm hoping to tailor the reciprocating assembly to better suit my needs. I'll see where it goes.
Interestingly, what I could save on the assembled shortblock would leave enough in the budget (real or imagined) for a nice set of cylinder heads.
Here we go...

viewtopic.php?f=1&t=23938&hilit=2814


This is an old engine of mine that had one of those cast cranks in it, may have been an eagle...but cast.

GARY C wrote: ↑Mon Mar 23, 2020 9:10 pm If you know any credible long standing dirt track engine builders then you will here plenty of broken crank stories that were virtually eliminated when they started using the 9000 crank, these would be 7000 ish 500 hp ish engines. At that point the main webs are probably weaker than the 9000 crank. RPM seems to be harder on cranks and rods then power and load.

At one time I was well connected with builders and racers. That all changed when I moved across the country. I'm kind of my own out here and am trying to find the right people to help me along.
I've paid attention the circle track guys and what works for them. But as was posted earlier the longevity is the concern for what I'm putting together. I've no interest in having to do a season ending tear down because I'm running components to the edge.
I will say I'm not building a rocket ship (my first post mentioned "another pedestrian 383 build" ) but at the same time I don't want to have to rebuild anything. Or worse.

CGT wrote: ↑Mon Mar 23, 2020 9:24 pm viewtopic.php?f=1&t=23938&hilit=2814

This is an old engine of mine that had one of those cast cranks in it, may have been an eagle...but cast.

Would you keep that engine at 90% WOT for 5 minutes or more? I'm not taking anything away from the results or the build but that's kind of where this thread is heading.