Yellow Bullet Forums banner

1 - 20 of 32 Posts

·
Registered
Joined
·
487 Posts
Discussion Starter #1
I have lightweight billet Scat 28oz 4.0" crank, I believe it is this one:
"7-351P-4 351 Superlight Pro Comp (45-50 lbs.) $2,149"
http://www.flatlanderracing.com/scat...ordforged.html

It is strange in that it is Billet and external balance, but it was a good deal when I bought it (new 2nd hand back in 2001, custom ordered for 28oz. balance) instead of waiting months for a neutral balance 4340 unit at the time, so I built it ext. balance. I needed an new flexplate balancer/flexplate so I ordered them neutral balance.

I am now rebuilding my 427" SVO block engine to handle 7000rpm/1200hp.
7000rpm will still be MAX planned with hydraulic roller.


My builder called yesterday and to change the crank to neutral balance will require 6 slugs (3 front and 3 back) IF he can do it-- he said the design of the throws may make it difficult to add the mallory.

So, what should I do, I see 3 options:

1) spend about $700 on balancing the rotator if its even possible and have a billet crank with extra metal:
--is that a good idea?
--any problem with doing this for the planned power?
--if try and fail will it junk a very nice crank?

2) sell and put money into a neutral balance 4" crank:
--would a regular 4340 unit be OK at the power?
--any recommendation on company?

3) keep the motor 28oz. external balance?
--is that a good idea?
--any problem with doing this for the planned power?


Good news is the crank otherwise looks fine.
Any help appreciated.
-J
 

·
Registered
Joined
·
1,585 Posts
Balance it neutral and save yourself a whole lot of aggravation down the road. Shouldn't be a problem putting 6 slugs in a windsor crank. And spend the money on a higher end balancer like ATI. External balance and high power/rpm DO NOT mix well.
 

·
Registered
Joined
·
487 Posts
Discussion Starter #5
Thanks guys.
I'm looking into a few options now.
Already have a neutral balance ATI balancer and JW flexplate, so committed to neutral balance.
-J
 

·
Registered
Joined
·
1,290 Posts
i have 12 slugs in my crank and its going on 4yrs.. its a cheap RPM 4340 crank.. my spare motor has 12slugs too... you may ask WHY... well, years ago i had a thrust issue and ruined a good crank. After that, i didnt want to invest in a big dollar crank and weld on it. A $300 crank was OK to weld on LOL.. we make 1200rwhp and spin the motor to 8600rpm.. at 7,000 rpm, you can do anything you want

BTW, when i ran renegade, i spun the motor to 7300rpm with a 28oz balance and 900rwhp
 

·
Registered
Joined
·
49,443 Posts
It'll be fine to add the mallory. Just make sure the wieghts are fully welded in.
 

·
Registered
Joined
·
487 Posts
Discussion Starter #8
Thanks for the real world experience Bob.
Sean, probably going to do that but going to look at a used crank/rod set first.
-J
 

·
Registered
Joined
·
6,100 Posts
I make 1000+ rwhp on 28oz balanced motor
 

·
Registered
Joined
·
49,443 Posts
Thanks for the real world experience Bob.
Sean, probably going to do that but going to look at a used crank/rod set first.
-J
Well if your thinking rods, go olivers. As for the crank pretty much any 4340 crank will get the job done.
 

·
Registered
Joined
·
1,290 Posts
if you decide to go with a 4340 rotator (crank and rods), i recommend upgrading to MIN ARP2000 rod bolts or L19 if you can afford them... we ran 8.20s the first 2 yrs in drag radial with RPM crank and rods... not very light, but strong as hell
 

·
Registered
Joined
·
1,585 Posts
Please explain. Have a 28oz dampner, 1400 to the rear tires, spinning motor to 8800. Bearings look great when I tear down the motor, but I dont want any future problems. Plan on making 2000-2200 next year (flywheel) so any advice appreciated.

Thanks
With an external balance motor, that weight on the balancer is unsupported. Over time the cranshaft will break, usually in the first rod throw if you have a steel crank. Fords are weak here because they have extra width here to allow for the distributor.With a cast crank it will simply break the snout off.

It is not a question of IF the crank will break, but when. May live for years, may break next week. Another thing that can exacerbate this problem is an inferior balancer. The cheaper balancers are made of softer steel and they will deform over time and develop excessive runout where the weight is located. This puts the motor WAY out of balance. Soon after this happens it is game over. I am an engine builder that specializes in these types of engines.
 

·
Registered
Joined
·
49,443 Posts
With an external balance motor, that weight on the balancer is unsupported. Over time the cranshaft will break, usually in the first rod throw if you have a steel crank. Fords are weak here because they have extra width here to allow for the distributor.With a cast crank it will simply break the snout off.

It is not a question of IF the crank will break, but when. May live for years, may break next week. Another thing that can exacerbate this problem is an inferior balancer. The cheaper balancers are made of softer steel and they will deform over time and develop excessive runout where the weight is located. This puts the motor WAY out of balance. Soon after this happens it is game over. I am an engine builder that specializes in these types of engines.
actually its really hard on the thrust bearing as the crankshaft trys to run like a jump rope becuase the balance wieght is even further from center.
 

·
Registered
Joined
·
517 Posts
Scat 4340 SBF 331ci small outside dia crank zero balanced.

This is a blower motor with H beams, trend hd wrist pins and Diamond pistons. The BW was just under 1500 grams.

Adding weight is no biggie for a good shop.










 

·
Registered
Joined
·
106 Posts
dear god thats alot of weight, ill stick with my billet junk
Billet doesn't have nothing to do with it. Thats a hack job on that crank the weights are not even press fit. They also put weight in the slinger LOL... Doesn't look like 1500 BW to me but the throws are short.... And for the others stay away from L-19 bolts they don't do good with moisture or with your hands. I would use A1's before i did this. i've never had an issue with ARP 2000 thats all GRP uses
 
1 - 20 of 32 Posts
Top