408 Scat Stroker Kits

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mopowers said:
How do you guys like the Scat 408 cast crank rotating assemblies? I'm thinking of throwing together a "semi-budget" 408 shortblock and have begun pricing out kits.

Are the Scat cast crank kits with Icon 745 pistons worth a crap? $1,500 for a balanced rotating assembly seems pretty inexpensive. Are there any corners cut with these?
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I run that in my 416 340 based stroker. Cast crank and balanced kit.

I’m running a sub 500 HP combo.

I’ve got 20K or so hard miles on it.

Scat machines and balences in house at their Redondo Beach California plant.
 
mopowers said:
How do you guys like the Scat 408 cast crank rotating assemblies? I'm thinking of throwing together a "semi-budget" 408 shortblock and have begun pricing out kits.

Are the Scat cast crank kits with Icon 745 pistons worth a crap? $1,500 for a balanced rotating assembly seems pretty inexpensive. Are there any corners cut with these?
Click to expand...

I'm going with a stock stroke 3.580 for lower piston speed, and because I have 4.10 gearing. Otherwise, I'm pretty much doing the Scat cast crank thing.
 
Ottmundr said:
I'm going with a stock stroke 3.580 for lower piston speed, and because I have 4.10 gearing. Otherwise, I'm pretty much doing the Scat cast crank thing.
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Put a 4” stroker and 3.91 gears.

Your piston speed will lower because you make the same HP and TQ at lower RPM.

So what’s the percentage increase in piston speed from 3.58 to 4.00 stroke? How does that compare to a Chevy 350?

3.58 to 4.00 stroke difference is .42”; about 7/16”. But that is the total diameter is the circle the crank journal travels. The throw or radius of the rod journer only increases .21”; less than 1/4”.
 
autoxcuda said:
Put a 4” stroker and 3.91 gears.

Your piston speed will lower because you make the same HP and TQ at lower RPM.

So what’s the percentage increase in piston speed from 3.58 to 4.00 stroke? How does that compare to a Chevy 350?

3.58 to 4.00 stroke difference is .42”; about 7/16”. But that is the total diameter is the circle the crank journal travels. The throw or radius of the rod journer only increases .21”; less than 1/4”.
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I am still a neophyte here.

This is from Performance Automotive Engine Math by John Baechtel
The chevy 350 is shown on the final picture.
It's $25 on Amazon, don't waste your time or money on the kindle one.

gearing and speed tools http://www.grimmjeeper.com/gears.html

Average piston speed calculations

Piston Speed in feet per minute = stroke * rpm / 6

3.58 * 6000 / 6 = 3,580
4.00 * 6000 / 6 = 4,000

Maximum Piston Speed in feet per minute = (stroke x pi / 12) x rpm

(3.58 * 3.14159 / 12) * 6000 = 5,623
(4.00 * 3.14159 / 12) * 6000 = 6,283

Now, the RPM is going to be different at the same speed with the 3.58" vs 4.00" rolling down the road I just picked 6000.

Now, from what I gather from the third page posted, and just thinking about it, I suspect that you want to keep a close eye on piston acceleration (the third page), the longer the stroke, the more severe the acceleration will be, and the more acceleration, the more stress on components like crank, bearings, rods, pins, and pistons. I suspect that whatever you can do to reduce those stresses on your engine components, the better off you will be for longer engine life. Especially for a street driven car.

It's midnight, and I have to get to sleep now. I don't have the energy at this moment to figure piston speeds for the same car speed with different length strokes and optimal gearing for cam, stroke, TC.

The more I read over this stuff, the more I want to stick to shorter stroke engines and higher rear end gearing. I know that there is a LOT more that needs to be accounted for, like torque converters, and bsfc, cam, timing, air pressure, density, temperature, humidity, et cetera.

-Aaron

p42.jpg


p43.jpg


p44.jpg


p45.jpg
 
I wouldn’t hesitate to run a 4” crank up to 6500 in a street car forever!!!!!!!
 
zsn0w said:
Is this referring to a cast crank as well as the forged? Wouldn't 6500 RPM with a 4 inch stroke be a pretty high piston speed for cast?
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Q1; Crank material doesn’t matter at this 6500 rpm level.
A; No, not really. 7500+, yea.
 
rumblefish360 said:
Q1; Crank material doesn’t matter at this 6500 rpm level.
A; No, not really. 7500+, yea.
Click to expand...
What would you say the redline is in a 4 inch stroke smallblock like this?

edit: sorry, asked that before you edited your answer to include the 7500 part
 
Last edited:
zsn0w said:
Is this referring to a cast crank as well as the forged? Wouldn't 6500 RPM with a 4 inch stroke be a pretty high piston speed for cast?
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55,000 plus street miles 700 plus runs at 6400 rpm. Used to drive it to the track race it and drive it home. CT to Cecil county. Cast crank. Still running it, but with 12.2 to 1 compression now.
 
8 lbs?
we ran 50 lbs cast crank
it's not the compression or the boost
it's detonation that breaks cranks
cast cranks are more "brittle" and forged more "ductile" but you can break anything
worry more about your rod bolts and little nicks on your rods
 
zsn0w said:
What would you say the redline is in a 4 inch stroke smallblock like this?

edit: sorry, asked that before you edited your answer to include the 7500 part
Click to expand...
No, I did not answer that question.
No, I do not think 7500 is the red line.
I do not think I can accurately answer that question. Reason being is I have not yet met anyone going to the ultimate max using a 4.00 arm
 
Yeah, most of the guys I race with that have 4" crank small blocks are at max HP by 6200-6800. No reason to spin it higher...that is the main benefit to the 4" crank, big power at a lower RPM. My current motor pulls hard to my self imposed red line of 7000 (I have a rev limiter at 7), but there is probably no reason to go over 6500...my old 410 stroker ran the same ET shifting between 6000 and 6500.
 
flyfish said:
Yeah, most of the guys I race with that have 4" crank small blocks are at max HP by 6200-6800. No reason to spin it higher...that is the main benefit to the 4" crank, big power at a lower RPM. My current motor pulls hard to my self imposed red line of 7000 (I have a rev limiter at 7), but there is probably no reason to go over 6500...my old 410 stroker ran the same ET shifting between 6000 and 6500.
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Not to hijack, but this thread has pretty much changed my mind on using the forged crank. If the cast crank from scat is a little lighter and is close to $500 cheaper, and I don't plan on ever going over 6500 rpm or 500 HP, I guess I should go with the cast? I'm probably gonna be around 425-450 HP on a 408 from the components I'm looking at I think..
 
you would need really big heads like ported W2 to need more than the rpm mentioned above (well not if you are YR)
We ran 4.25 stroke with 6" rods and could not even run the over 6000 rpm speeds mentioned above- well not much over 6000 chevy with ported 283 "fulie" heads
did have a big wide torque curve and won "Top fuel" (alky) at the 62 AHRA nationals at Cado Mills Texas- really greasy track
the 4" stroke motors (400 inches also 6" rods) would rev 500 rpm higher with the same heads- it won "top gas" at the same meet
flyfish said "Yeah, most of the guys I race with that have 4" crank small blocks are at max HP by 6200-6800"
physics has not changed in 50 years even if the mopar does have 1/8 longer rod
hint- run the longest rod you can- there are tradeoffs but bottom line -longer rod is better- but you have to change the cam timing

OZN you will be fine power is in the heads you want the most flow at the lowest lift not just highest flow at max lift, get flow numbers and then cam to utilize
 
zsn0w said:
Is this referring to a cast crank as well as the forged? Wouldn't 6500 RPM with a 4 inch stroke be a pretty high piston speed for cast?
Click to expand...

zsn0w said:
Not to hijack, but this thread has pretty much changed my mind on using the forged crank. If the cast crank from scat is a little lighter and is close to $500 cheaper, and I don't plan on ever going over 6500 rpm or 500 HP, I guess I should go with the cast? I'm probably gonna be around 425-450 HP on a 408 from the components I'm looking at I think..
Click to expand...

And to grow that combo significantly to need a forged crank (100-150 more HP), you’ll have new cam, new valve springs, new heads or lots of $$$ to race port what you have, possibly improved rockers, and most likely new pistons.

At that point do you just build another motor and save/sell/transfer the old stroker motor?
 
zsn0w said:
Not to hijack, but this thread has pretty much changed my mind on using the forged crank. If the cast crank from scat is a little lighter and is close to $500 cheaper, and I don't plan on ever going over 6500 rpm or 500 HP, I guess I should go with the cast? I'm probably gonna be around 425-450 HP on a 408 from the components I'm looking at I think..
Click to expand...
At that power level you would be fine with either crank (425-450). I went forged because I race a lot, and I'm close to 600hp, give or take. From what I have read, Scat cast cranks are pretty stout...unlike Eagle cast cranks.
 
autoxcuda said:
And to grow that combo significantly to need a forged crank (100-150 more HP), you’ll have new cam, new valve springs, new heads or lots of $$$ to race port what you have, possibly improved rockers, and most likely new pistons.

At that point do you just build another motor and save/sell/transfer the old stroker motor?
Click to expand...
That is the point I’m at, when I pursue more power I will just build another short block. Forged crank and bush the lifter bores for roller. I have to run the same top end.
 
flyfish said:
At that power level you would be fine with either crank (425-450). I went forged because I race a lot, and I'm close to 600hp, give or take. From what I have read, Scat cast cranks are pretty stout...unlike Eagle cast cranks.
Click to expand...
Hey Flyfish curious of your set up as I’m heading in that direction as well with a build .
 
Larry Lampkins said:
My 360 broke a crank just cruising at 45 mph!! Haven't pulled it apart yet but the starter spins the back of the engine and the front pulley don't move!?
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Post the picture...
Welcome to the club...
Nice.. first post to dispute the unknown...
 
I had a Mickey Thompson cast crank break in a stroked 392 hemi blown boat motor
motor would start but if you gae it any gas it would slip
idled back to the trailer
Mickey gave me a new one and helped pull the motor
 
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