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Hey all, looking for budget inexpensive recommendations for a 1-piece rear main seal 383 stroker crankshaft.
Block is an 880 Vortec roller block, bored over and 383 clearanced.
Pistons are Icon 9914-030
Not sure on rods. I guess I am open to getting new rods of that is recommended.
Application is a 1991 ZF6 car. I was going to just reuse my stock dual mass flywheel and the damper from the current L98 motor.
That means any external balance crankshaft should work as I can just bolt my already balanced dual mass flywheel and damper up to the crank and spin away right?
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Except you need to find a balancer capable of adding heavy weight. Unless it's changed, Scat 9000's requires a bit of "heavy metal" to balance. Back when I didn't mine, "THE GUY" to do that was booked up for 1.5-2yrs on engine balancing. I found another guy who drilled the crank to balance it (vs adding heavy weight). It worked but I don't call it ideal. Put another way, I would not choose that option again***. I don't know how many people are capable in your area...so there's that. Eagle used to make the best budget line SBC 3.75" crank 10-15yrs ago. I'm not current about now, so I can't confirm.
That said, Scat 9000's are theoretically stronger if you're willing to weight it correctly (for 1pc RMS applications). So, it's complicated enough I'm thinking this MIGHT be a better question for who you have lined up for the engine work.
***Note: Balancer needs to understand how that heavy weight requirement relates to harmonic balancer and how drilling a crank alters reciprocal and rotational forces. Meaning you NEED to do the weight per manufacturer recommendation. Also, the piston weight factors in this equation. An Eagle is simpler when it comes to piece-mealing an RA.
Is there no bolt together affair where I can just bolt my current ZF6 dual mass flywheel to the back of the crank and bolt the front damper to the front?
I was hoping to avoid the machine shop, but is it going to be unavoidable in order to get everything balanced up?
Crank needs to be balanced to rotating assembly. There wouldn't be buy and go solution unless you buy a new assembly.
When I had mine balanced, they told me a standard neutral balance sbc balancer is fine and to use the weighted standard 1 piece flywheel. Depends who does the work. I've always been told internal balance is preferred. Less stress on the crank snout at high rpms. Being it isn't an exotic parts list, you're probably not going to have an odd balance job and it'll probably balance to some off the shelf parts.
Okay does rotating assembly for a 1-piece RMS setup then just mean the rods, pistons, and crank? Or does it also include the front damper and the rear flywheel or flex plate?
If it includes the rear flywheel, then it seems like there isn't a buy and go solution at all then, because I doubt anyone is balancing and packaging ZF6 flywheels with 383 kits?
Am I understanding correctly? Should I start calling local machine shops asking about balancing rotating assemblies?
Okay does rotating assembly for a 1-piece RMS setup then just mean the rods, pistons, and crank? Or does it also include the front damper and the rear flywheel or flex plate?
If it includes the rear flywheel, then it seems like there isn't a buy and go solution at all then, because I doubt anyone is balancing and packaging ZF6 flywheels with 383 kits?
Am I understanding correctly? Should I start calling local machine shops asking about balancing rotating assemblies?
Rotating assembly is the crank pistons and rods. All of this needs to be balanced some shops will want the flywheel unless you are expecting a zero balance without the flywheel. Then you need a neutral balance on the flywheel.
Have you disassembled and determined that your block is actually a 1 piece with a conversion to a 2 piece?
The stock ZF6 dual mass flywheel only came on GM one piece rear main seal motors. I think that means that the oem ZF6 dual mass flywheel is balanced and set up for an "external" balance crankshaft? So does that mean I want a crankshaft that is specified for "external" balance?
It would be nice to get a crank I can just bolt my factory 1991 harmonic damper to as well as my stock ZF6 dual mass flywheel. Is this not possible?
I am confident that the crank currently in the assembled 383 shortblock is a two-piece RMS crankshaft making use of a one to two piece RMS adapter so as to work in the 880 casting vortec block that is a one piece RMS block.
Last edited by yakmastermax; 08-06-2023 at 08:53 PM.
If it is a 1 piece block and the rear cap has been swapped. You will need to get a replacement cap and have the block line bored the next size up and get the appropriate bearings. This is all stuff you can and need to discuss with a machine shop.
Get the engine on the stand and take the pan off and verify what you are dealing with.
Just buy a SCAT, Eagle, Ohio crank, RPM or similar, they will all work fine. Your ZF6 speed flywheel is externally balanced and will work fine with the 1 pc crank.
The 1986 and latter cranks from the factory all used the same external weight on the flywheel so as long as the machine shop has the correct weight it can be balanced and you can swap flywheels or flex plates for the one piece cranks. The front balancer is neutral balanced.
Your block looks OK to me, it just has a 2pc crank adapter, remove the 2 pc adapter and bolt on the one piece seal.
Just buy a SCAT, Eagle, Ohio crank, RPM or similar, they will all work fine. Your ZF6 speed flywheel is externally balanced and will work fine with the 1 pc crank.
The 1986 and latter cranks from the factory all used the same external weight on the flywheel so as long as the machine shop has the correct weight it can be balanced and you can swap flywheels or flex plates for the one piece cranks. The front balancer is neutral balanced.
Your block looks OK to me, it just has a 2pc crank adapter, remove the 2 pc adapter and bolt on the one piece seal.
Okay so I just need an "external balance" one piece rear main seal stroker crankshaft?
But then I need to bring that crank, the pistons, rods, rings, harmonic damper, and the ZF6 dual mass flywheel to a machine shop to have it balanced?
Okay so I just need an one piece rear main seal stroker crankshaft?
Yes
Originally Posted by yakmastermax
But then I need to bring that crank, the pistons, rods, rings, harmonic damper, and the ZF6 dual mass flywheel to a machine shop to have it balanced?
No. You CAN...and "should", but don't need to. Buying what bjankusi is telling you to get, will be as well balanced as the OEM parts were...or better.
One time, I bored one cylinder of an engine .010" over and put in one, .010" over aftermarket piston. Was that engine "balanced"? No, it wasn't.
You couldn't discern any difference at all in running, smoothness, anything up to 7000 RPM.....and it ran for years until I sold it. Need/want.
No. You CAN...and "should", but don't need to. Buying what bjankusi is telling you to get, will be as well balanced as the OEM parts were...or better.
Tom, thanks that makes good sense!
I have read from a few different sources now at least that for a factory application to a 1-piece RMS post 86 "externally" balanced motor that all flywheels and flexplates are interchangeable, because the amount of additional weight added to the flywheel or flex plate in such an application is the same. This seems to mean to me that if I found some factory GM "externally" balanced one piece RMS shortblock, I could bolt on my OE GM ZF6 dual mass flywheel and the front OE harmonic damper, and be balanced decently enough for a factory GM redline? And so similarly if an aftermarket one piece RMS 383 crankshaft, piston, and rod assembly were properly "externally" balanced by Eagle or Scat or whoever put the kit together, then such a kit could be bolted into a one piece RMS bare block, and then a factory one piece compatible flywheel and damper combo could be bolted to that and could be spun up to GM factory redlines without any additional shop balancing or work?
Am I understanding correctly? Obviously this is worth a phone call to whichever vendor or manufacturer I go with for a 383 stroker kit? This being the case, it seems advisable to just get a whole new 383 stroker kit so long as it is externally balanced to GM spec? I don't mind this especially if it allows me to skip the machine shop, and also allows me to select dish pistons so I can reuse my 58cc chamber 113 heads to offset the build cost.
As we have established the harmonic damper on the front is more or less interchangeable for all years? Because the balancing of the rotating assembly isn't generally done by adjusting the mass of the harmonic balancer?
This is all a bit of a bummer as I spent a fair bit on the 383 shortblock with the one to two piece RMS adapter shenanigans hoping it would be a typical one piece RMS "externally" balanced short block meaning I could just bolt my GM OE ZF6 DMF up and the front OE harmonic damper and be good to go...
Alas
Guy did say it was a one piece RMS...
Last edited by yakmastermax; 08-07-2023 at 01:11 PM.
I have read from a few different sources now at least that for a factory application to a 1-piece RMS post 86 "externally" balanced motor that all flywheels and flexplates are interchangeable, because the amount of additional weight added to the flywheel or flex plate in such an application is the same.
That is correct. ALL 1 pc RMS SBC have the same balance weight on the flywheel or flexplate.
Originally Posted by yakmastermax
This seems to mean to me that if I found some factory GM "externally" balanced one piece RMS shortblock, I could bolt on my OE GM ZF6 dual mass flywheel and the front OE harmonic damper, and be balanced decently enough for a factory GM redline?
Iagree, again. That is a reasonable deduction based on correct information.
Originally Posted by yakmastermax
And so similarly if an aftermarket one piece RMS 383 crankshaft, piston, and rod assembly were properly "externally" balanced by Eagle or Scat or whoever put the kit together, then such a kit could be bolted into a one piece RMS bare block, and then a factory one piece compatible flywheel and damper combo could be bolted to that and could be spun up to GM factory redlines without any additional shop balancing or work?
Originally Posted by yakmastermax
Am I understanding correctly? Obviously this is worth a phone call to whichever vendor or manufacturer I go with for a 383 stroker kit? This being the case, it seems advisable to just get a whole new 383 stroker kit so long as it is externally balanced to GM spec? I don't mind this especially if it allows me to skip the machine shop, and also allows me to select dish pistons so I can reuse my 58cc chamber 113 heads to offset the build cost.
Seems like a reasonable plan, to me. I would do it....and likely will do that one day for my own car.
Originally Posted by yakmastermax
As we have established the harmonic damper on the front is more or less interchangeable for all years? Because the balancing of the rotating assembly isn't generally done by adjusting the mass of the harmonic balancer?
On SBC's, other than the 400, the harmonic damper is neutral balanced. It has or should have, no influence on the balance of the rotating assy, and thus, need no attention as it relates to balance.
I called some Albuquerque local machine shops and got some rough estimates.
One shop said balancing a rotating assembly is 1-2 weeks turn around and $350-$500 depending.
Another shop had the same turn around, but said $200-$225 for a rotating assembly balance, assuming no Mallory slugs were required. If slugs were required, each slugs is $100.
I wonder what additional RPM redline (assuming I have the valvetrain, cam, and intake to support it) I could achieve by spending the $250-$500 for a local machine shop to balance my setup?
This is assuming I order a whole new 1-piece RMS "externally" balanced crank, rod, and piston kit, then drop said kit off at the machine shop with my OE GM ZF6 dual mass flywheel and potentially the front harmonic damper...
One of my 383 machined vortec blocks is a 4 bolt main... perhaps this block plus a good balance job and I could have an honest 6750 rpm track and time attack redline?
Or am I better off saving the money and time and just getting such an externally balanced kit, slapping it together, maybe using the saved money for new cylinder heads, and just keeping the RPMs under 5750 or so?
Overall though thanks all again as now I do see a reasonable path forward.
An externally balanced 383 crank, rod, and piston kit should be bolt on (assuming tolerances are good) and maybe by going with dish pistons i can stick with my 113 cylinder heads, reuse the LT4 hot cam even, and keep this as a much milder 383... more like 325rwhp or something... In that case I would probably build on the two bolt mains 383 vortec block I have and save the 4 bolt one for something else!
Such a milder 383 would only cost the stroker kit plus odds and ends, so maybe $1000 or so...
A middle option would be to skip the balancing but upgrade the heads, so maybe $1700-$2200 depending, but that would result in more power, maybe another 25rwhp? 350rwhp total?
Then I could do that plus a cam so $2000-$2500 for maybe an additional 25rwhp on top of that so 375rwhp or so total?
Finally I could get the rotating bits balanced by the shop for another $250-$500 so $2250-$3000 total but at that point I would be damn disappointed if it wasn't making 400rwhp... for the money
All in all I am leaning towards the first cheapest option. 325rwhp would be a solid gain over the car's last dyno numbers of 240rwhp. That plus saving some money...
Last edited by yakmastermax; 08-07-2023 at 07:06 PM.
I wonder what additional RPM redline (assuming I have the valvetrain, cam, and intake to support it) I could achieve by spending the $250-$500 for a local machine shop to balance my setup? One of my 383 machined vortec blocks is a 4 bolt main... perhaps this block plus a good balance job and I could have an honest 6750 rpm track and time attack redline?
Basically, none? I think the redline is pretty unaffected by a pro balance job, vs. the manufacturers balance job. Like the difference between 5.7" and 6" rods. If you got the cam/heads/intake/exhaust, it'll go "6750" ...or whatever....whether you spend on more balance or not.
Originally Posted by yakmastermax
Or am I better off saving the money and time and just getting such an externally balanced kit, slapping it together, maybe using the saved money for new cylinder heads, and just keeping the RPMs under 5750 or so?
What "external balance kit" are you talking about? For the most part, balancing those parts vs. not balancing them is not going to change the RPM limit or the stress most of those parts.
Originally Posted by yakmastermax
In that case I would probably build on the two bolt mains 383 vortec block I have and save the 4 bolt one for something else!
4 bolt roller (vortec) blocks are a dime a dozen. I'd use whatever and not worry about it too much. [/QUOTE]
I used the Scat 9000 crank when I built my 383.
Simply used a Chev 400 balancer - which is just a 350 balancer with a weight inside it. Summit sell the SFI rated version.
Check out the Scat website, you can get the cranks in different configurations, internally balanced / externally balanced, different rod lengths etc.
Anyone heard anything about the Speedway Kits?
They have one-piece RMS 383 crank, rods, and piston kits for around $750-$1000
They have one flat top kit that says it should be 11.2:1 compression ratio with 58cc heads like the 113 castings. Perhaps I could make that work with a slightly oversized head gasket? Get it down to 10.9:1 or so?
@Tom400CFI
I while back I made a thread asking about what it takes to get a high revving (consistent 6750-7000 RPM track and road race redline) small block chevy. I had assumed forged lightweight crank, rods, and pistons were the way to go. I forget who but several people posted something along the lines of it all being in the balance job, and the valvetrain.
That being said I really don't mind a 5750 RPM redline if it means I can avoid the extra cost of machine shop balancing, the extra turn around time, and keep things simple.
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Originally Posted by bjankuski
Just buy a SCAT, Eagle, Ohio crank, RPM or similar, they will all work fine. Your ZF6 speed flywheel is externally balanced and will work fine with the 1 pc crank.
The 1986 and latter cranks from the factory all used the same external weight on the flywheel so as long as the machine shop has the correct weight it can be balanced and you can swap flywheels or flex plates for the one piece cranks. The front balancer is neutral balanced.
Originally Posted by blackozvet
I used the Scat 9000 crank when I built my 383. Simply used a Chev 400 balancer - which is just a 350 balancer with a weight inside it. Summit sell the SFI rated version. Check out the Scat website, you can get the cranks in different configurations, internally balanced / externally balanced, different rod lengths etc.
This is what I was talking about. The nose on a Scat9000 requires 1 slug of Mallory to achieve "neutral" balance. My shop said "Hell no! We can just drill the counter-weights (cause the wackjobs couldn't install Mallory without it flying off on their dirt track cars. They decided drilling was a better choice. (I decided they were amateurs)
08-06-2023, 12:12 PM
Budget 383 Stroker Crankshaft recommendations
