Scat 9000 crankshaft vs forged
 

Hello all,
Quick question for all you engine builders.
My present 406/409 build project in another thread, I showed where the crank in the block I bought is a Eagle internal balance crank with a 3.75 stroke.
In very good condition but it is according to Eagle a cast crank.
Now I know that Eagle doesn't always have the best reputation and I am looking for longevity in this build.

So...the question is...
For a 500hp target build, 10.7-11.0 CR would you recommend the Scat 9000 crank over their forged crank?
Pistons and rods to be used are forged. Dart 200cc aluminum heads.
Block going to shop tomorrow.
ARP studs used through out.
It is a 2 bolt main block.

Thanks for any and all comments.

Dennis (Bman) :thumbs:

I honestly think the factory 400 block would give up before a Scat 9000 crank would..... Those cranks are pretty decent at the power level you are shooting for. I've used many at the 450-500HP level in street cars and never had a problem.

These days I look at building factory 400 SBC based engines much like I do 331 and 347 302 based Fords with stock blocks....... the block is the weakest part of the whole thing. No reason to spend big $$$$ on the rotating assembly when the block is just going to let go once you start making some real power. Do whats good enough and keep the power within reason.

Will

I agree with Will. Even the Eagle crank should hold up to 500 horse on the street. Now if you are going to be road racing it or drag racing it all the time, then I would worry about it, but not on the street. I do like the Scat cranks better than the Eagle, but again if the Eagle is in good shape, why spend money on another crank.

Mike

I don't trust Eagle. The Scat 9000 should handle 500 hp all day long.

I would normally agree with Will and Mike but your target compression ratio is pretty high. Assuming your rods and pistons are new, I’d be tempted to go with the Scat.

Also, with a stock 400 block, 2 bolt is said to be stronger than 4 bolt. You’ll be fine there, especially with the ARP studs.

While putting together the parts for my 496 build everyone told me that that a cast SCAT crank would stand up to much more HP than my motor would put out.
I'm the type who overbuilds everything so it lasts and never gives me trouble.
I spent the extra $600.00 for the SCAT forged crank for additional insurance.
Same thing with the Mark IV 4 bolt block I picked up.
Everyone told my the OEM 2 bolt block would work, but my OCD kicked in and I searched until I found a good 4 bolt block for the extra insurance.

I did the same thing with my LQ9 build back in 2009. All forged (scat crank even), balanced, etc. Built RIGHT by one of the best builders in the country (slow but very detailed oriented). Fast forward 10 years, motor is still plugging away. I'd say at LEAST 100 quarter mile passes at 7,000 rpm. STILL GOING STRONG. No power adders, no nitrous or boost.

On the other hand I had basically the same motor BEFORE that build, lasted about 1 1/2 year, then grenaded. It had forged internals also, BUT it had an Eagle forged crank. Not to say that was the reason why it grenaded, but I've never touched an Eagle crank since then.

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Thanks for all replies.

I agree with using the existing crank if keeping it mild.

Additional info...

Pistons are Probe forged but no markings/id #s so hard to identify.
They have a mild dish across the entire top....see pics
No way to figure CR unless I can do further measurements like piping the top with a burette for the CC displacement and measuring the compression height. Rings are 1/16-1/16-3/16
May or may not be reusable if this block needs to be bored out .040 over but could use them in 2nd build of 421 and the new Dart SHP block I have.

Now the rods are Eagle SIR rods with ARP cap screws but no identifying marks other than ES and Eagle on the cap screws.
My main concern is that there was a lot of grinding on the bottom of a couple of these.
Have not taken one off a piston to get accurate length measurement.
No easy way to tell if they are 5.7 or 6.0 length or even some other length.

Gut tells me go all forged Scat crank and rods.
My wallet says put the Eagle crank back in.

I may end up buying new 4.165 pistons anyway if block will not clean up and allow me to use the existing pistons.

Too many factors without knowing shop's verdict on the block.

Thanks to all.....
https://cimg0.ibsrv.net/gimg/www.cor...3754efe5dc.jpg
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Those pistons were orginally flat tops... someone machined that dish in them on a lathe removing the PN which is stamped in that area of the top. You will have to cc one with a burrett or since its round, its easy measure the OD and depth of the cut... then do a little math to figure the volume..... add 7cc for the valve reliefs.

The rods are 5.7" which means 1.425 compression height pistons.... its easy to tell the differece because a 3.75 stroke and 6" rods use a 1.125 compression height and the wrist pin is in the oil ring groove, which yours is not.

As for the grinding on the rods.... done to equalize the rod big end weights during balancing. Very common and nothing to worry over.
Will

Thanks Will.
Great info.
I had planned on using 6" rods with an internal balanced 3.75 stroke crank...so this rules out using these pistons also.
Or go with Scat 5.7" rods.
I don't want to use the Eagle rods either way.

So basically I have an internal balanced 406 sbc setup for use in a 400 block. Complete with cast crank, Eagle forged rods and Probe forged pistons.
Fully balanced (I saved and marked each piston by position when removed).

So options are...
Reuse as-is (if cylinders clean up well) with new bearings and rings.
or go completely new set up using all forged pieces.
Sell the current setup on ebay to recoup some costs....or sell it off in pieces...or maybe keeping the pistons with the understanding that I will need to buy 5.7 rods.
????

Tough call.

Thanks

The Eagle and Scat cranks are pretty much made of the same material. One calls it cast steel, the other "9000" material. There's not a nickel's worth of difference in the two. Either should hold up fine to your power goals.

your conrod length quick check
 

OP
pin OD ~ 0.927" ---------------------------------------- 1/2 that ~ 0.464"
rod journal OD ~ 2.100" ------------------------------ 1/2 that ~ 1.050"

0.464 + 1.050 = 1.514"

6.0" - 1.514" = 4.486" between bottom of pin and top of rod shell = 6" rod
5.7" - 1.514" = 4.186" between bottom of pin and top of rod shell = 5.7" rod

saw a pic with pistons on rods with shells in bore.
reach in there with a steel rule or caliper & measure from top of shell to bottom of pin. My bet's on 6.

it'd also pay to get a cheap, small graduated cylinder and cc piston top; also measure compression height.

Seems Eagle did make a cast 3.75 internal balance crank for 5.7 rod; I recall it was for 350 mains & it cost more than their typical external.

Thanks.....:thumbs:

Saves tearing out one set of spirolocks which would be unusable.

Thanks...:thumbs:

I went with Scat9000 in my 383 w 5.7 scat 4340 rods and diamond billett CNC cut pistons and gapless rings. (Way overkill)...but my leakdown avg per cylinder =3%. The bottom end is a beast. I believe these cranks are good to 550hp+. I did use the ARP bolts for everything.

This could be a dumb question but,
If you have a 400 block, need to buy new pistons, rods, and crank,
Why not buy a SCAT 427 stroker kit and build a mild 427 cu in sbc?
Seems like a no brainier to me and you don't need to make it a fire breathing monster.

since that can of worms is opened why mess with the stock block then when he said in another post ha has plans for a 421 Dart SBC. Save the money and do the 421 now instead of the 400 then the 421.

Yeah except the first project car is to be sold when complete. The SBC 421 car is mine to keep after the first one is gone.
Cash flow.....:yesnod:

Thanks for the suggestion but a 4" stroke in a stock sbc 400 would require clearancing....would it not?
More machine work at the shop = more money.
Plus the sbc 400 is a stock block with 2 bolt mains.
Want to stay on the mild (500hp tops) side.
:thumbs:

Update on my strategy....

I am using paypal 0% financing (my balance is zero right now) to buy any part over $600...it gives me 24 months to complete the project and sell it while making small payments
So....the Scat forged crank might just be the best way to go.
part # 4-400-3750-6000 400 mains, 2pc rms, 3.75 stroke, 6.0" rods, forged, internal balance.

Local shop will do balancing as opposed to buying a balanced assy from someone in CA or TN and not having any protection if not done well.

I already have a good new set of 6.0" H forged rods, clearanced for stroker and using ARP 8740 cap screws.

Best laid plans of mice and men......:yesnod:

Once the shop tells me the actual bore I will be using 4.155 or 4.165, I can do my hunt for the pistons....