xbgs351

I have spoken to two Melbourne based machine shops that have stated a Scat 9000 crank, Scat I beam Windsor rod and Probe pistons will most likely require heavy metal to balance. The balcancing is almost as expensive as the kit.

Can anybody confirm or deny this? I was also left with the impression that the same problem would occur with 6' chev H beam rods and SRP Pistons.

Here is somebody else who has found this problem, although the manufacturer is not named:
http://www.network54.com/Forum/threa...eid=1086229684

The Eagle kits from High Performance world are meant to balance up well, but cost an additional $1300 for a 3.75" stroke cf 3.85 for the SCAT. 4" stroke is $810 dearer, but crank is ground 10/10. The Eagle kits require some clearancing.
www.highperformanceworld.com.au

STROKEXD

Interesting find and confirms my suspicions about using a Scat crank.

Personally I went with a custom ground 351 crank myself for my stroker and guess I'm glad I did it that way.

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davis

I've never had any problems balancing my SCAT cranks. Ring up SCAT and talk to them first and foremost. You may also save money buying direct from them. They charge a minimalist fee for balancing it when you buy directly from them. Of course, it is much easier here in the USA, because of shipping costs/delays. I'd give Brian a call and ask him what can SCAT do for me.

You may also want to consider moving away from a Windsor rod and just use a Chevy 6" rod. The difference may just be in the larger big-end of the Windsor rod. A 5.956 length isn't going to be different in any critical way over a 6" rod, and the smaller 2.100" (vs 2.311" C and W sized) journal is likely to require less offset weight in the counterweights, while giving slightly more clearance, too.

I'm starting to think that you're getting a too outrageous balancing price from the people you talked to in Melbourne. Here, mallory is $55/slug. If you figure $400 for labor, which is a lot, you've got about 8-10 slugs of mallory left over in the cost...or thereabouts...maybe more! That is a lot of heavy metal. Either something isn't right, or someone is dressing you up for dinner and taking you out on the town on your charge card.

I'd ask SCAT what the intended bob weight is for the 9000 series crank you're looking at buying and try to get a handle on what it will take to balance it without simply throwing it over the fence to some balancer to price.

A set of I beams and flat tops aren't exactly a "new idea" for rotating assemblies in this stroke range. Usually you have to add weight when you:

Internally (neutral) balance
Have very high bob weight and want to bring to neutral or externally balanced.

Nobody builds (or at least nobody should build!) a stroker crank and expect you to not to run rods long enough to use the stroke with "conventional" piston designs, that are not likely to fluctuate more than maybe 100g between various designs per slug.

I don't think that the thead in the link you posted really applies here. I thought that you were doing a 393, are you doing a 408? I thought that you were talking about using the: 9-351-3850-5955-2311C part from SCAT. I would personally call SCAT and talk to them about it. Maybe they designed it to be used with a 50oz setup, which would represent the "late model" stuff.

I don't "believe" that internal balancing is that much better, if any better. The history behind internal balancing is much more like having no way to run a cast iron dampener on the end of a 9000 RPM crank without having a ballistic weapon ready to go off. Then, with "ultra" blown nitro combinations, "harmonic dampeners" just don't due to the severity of the environment.

One has to have something connected to the crank to use the power, who cares if it is a 28oz or 50oz balancing weight? Maybe guys who want to reduce the external weight as much as possible? You gotta have whatever weight is necessary to balance it somewhere, the question is really does it matter very much where? I generally like the idea of having weight on both sides of all of the main journals. Some like the idea of keeping all of the weight inside the main journals. The discussion tends to focus on flexing the crank. For really high speed applications, I just tend to go with the "proven" internally balanced choice, but I'm not so sure that an externally balanced engine wouldn't work just as well and live just as long if not perhaps in some way even better. With today's excellent, low cost SFI-rated dampeners, I don't think that external balancing is a bad choice for even a very "serious" race engine. I don't think that any of us here are in the "throw it away after 5 passes" crowd, so what "works" for Pro Stockers really doesn't matter very much for us, IMO.

:davis:

marcuss

Speak to the guys at RC Automotive in Bacchus Marsh. Good advice, no BS.
(03)53674521

XDman

i'd be very interested xbgs to see exactly what it costs for a 9000 series scat stroker rebuild, im thinking of doin the same thing in the latta part of the year, going for alloy heads etc. If you could please tell me any info whether it be PM or right here as to how much it will cost (just for crank - balanced etc)

Thanks

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xbgs351

$1900 for the Scat 393 kit.

davis

I agree with this list except for one minor point. Using "NOS" in typing is OK to indicate nitrous use whilst saving keystrokes, but actually *saying* Nahhsss is definitely a WANKER deal. Anyone who calls nitrous nitro should be put out of our misery immediately. Nitro has been the abbrieviated form of one of nitroglycerine or nitromethane practically since the steam engine. Comparing it to an inert gas is criminal! The "utes with rear spoilers" is a good one! ...like a ute needs the additional "down force" or drag!

:davis:

xbgs351

I will see if they answer there emails. Otherwise will have to call them. Are they on the west or east coast?

So questions to ask?
Intended Bobweight
50 oz setep?

The 2.1" journal is my prefered option, however I am unaware of any off the shelf dishtop pistons to suit this setup. Is there enough material in your SRP pistons to machine a dish?

Prices here are generally twice that of the US. The first machine shop I spoke to actually makes there own cranks, hence I thought they may be pulling my leg. The second doesn't even sell stroker kits. The second machine shop recomended the Eagle kits.

I agree. It wouldn't be good for return business if you were selling such kits.

I would prefer to a 393C, however the cheapest Eagle Stroker kit just happened to be a 408C.

The 351C is externally balanced, and that is what I want for the 393C. I do however want to use a factory flywheel.

I am just a bit nervous to proceed until I get some firm information.

:davis:[/QUOTE]

davis

"Left Coast" (California)


How about I follow up the rest of these questions in a PM and then you provide your "lessons learned" from your process and parts selection back to the forum to avoid monopolizing the thread? Alternatively, you can email me directly at "davisNOSPAMatNOSPAMazpowerNOSPAMdotNOSPAMcom" if that's OK?

:davis:

Racer

I personally have seen several broken 28oz 351 cranks, with the snout snapped clean off. With 50 ounce, it can only be a hundred times worse.
This is one of, if not the main reason, serious 351C's are usually internal balanced.