Author Topic: 3.98 stroke Scat cast steel or forged crank balance  (Read 1592 times)

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1968galaxie

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3.98 stroke Scat cast steel or forged crank balance
« on: October 21, 2022, 02:54:55 PM »
I was looking at getting a Scat 3.98" crankshaft.
Can these be internally balanced ?
Or does weight have to be added to counterweights?
4.09" bore block.

blykins

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Re: 3.98 stroke Scat cast steel or forged crank balance
« Reply #1 on: October 21, 2022, 03:49:26 PM »
You can internally balance it, but it will require a good bit of heavy metal.
Brent Lykins
Lykins Motorsports
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1968galaxie

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Re: 3.98 stroke Scat cast steel or forged crank balance
« Reply #2 on: October 21, 2022, 05:00:34 PM »
Thank you Brent!

Correct me if I am wrong - The 4.125" stroke and the 4.25" stroke Scat cranks can be internally balanced without adding heavy metal.

I have a few options - would like most cost effective.

1. Using factory 3.78" crank, regrind and balance - and purchase 0.040" FT pistons - cost of grinding, balancing and new pistons.
    The rods I have are low mileage set that have sat for 30 years - fitted with Boss 351 bolts (years ago)
2. Purchase a stroker kit (4.125" or 4.25" with pistons, rods, and balanced. (Are bearing clearances checked on these assemblies?)

blykins

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Re: 3.98 stroke Scat cast steel or forged crank balance
« Reply #3 on: October 21, 2022, 05:15:24 PM »
It depends on what the rest of the parts consist of, whether it's a cast or steel crank, etc.   Obviously, heavy pistons and rods would put you in a worse spot than the opposite, and there's a big difference in piston/rod weights out there.  A Mahle piston and a Molnar rod on a 4.250" cast crank would put you in a really nice spot...

Bearing clearances are not checked on the stroker kit assemblies. 
Brent Lykins
Lykins Motorsports
Custom FE Street, Drag Race, Road Race, and Pulling Truck Engines
Custom Roller & Flat Tappet Camshafts
www.lykinsmotorsports.com
brent@lykinsmotorsports.com
www.customfordcams.com
502-759-1431
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Barry_R

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Re: 3.98 stroke Scat cast steel or forged crank balance
« Reply #4 on: October 21, 2022, 05:47:39 PM »
We end up with at least one or two pieces of metal in almost all of the aftermarket cranks we balance.
The steel cranks sometimes get away without.

As noted by Brent - there is a good bit of variance in pistons and rods.

winr1

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Re: 3.98 stroke Scat cast steel or forged crank balance
« Reply #5 on: October 21, 2022, 07:45:10 PM »
FT pistons ........ flat tops ??

I saw FT ( 391 ) ..and thought, man , those things are heavy



Ricky.

1968galaxie

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Re: 3.98 stroke Scat cast steel or forged crank balance
« Reply #6 on: October 21, 2022, 08:24:28 PM »
Thanks guys.
Flat top pistons yes.
I may just freshen up the crank I have - and rebalance with new pistons.
The TRW pop up skirts look great, but the 0.085" clearance is too much.
Looking at Autotek pistons or DSS racing pistons.
DSS does list a +0.040 piston. Autotek would be a custom at +0.040"

winr1

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Re: 3.98 stroke Scat cast steel or forged crank balance
« Reply #7 on: October 21, 2022, 09:30:02 PM »
I have a set of these .... they are around .013 in the hole ( factory deck height )

I will weigh one with and without pin

https://www.summitracing.com/parts/slp-l2291f40/make/ford

What kind of pistons do you have in your mill at the moment and do you know what they weigh ??

Seems the aftermarket cast pistons are around .030 in the hole but much cheaper than forged

You could go cast pistons and deck your block to .00 , perhaps break even

What vehicle is the mill in and what do you do with it ??



Ricky.
« Last Edit: October 21, 2022, 09:44:42 PM by winr1 »

1968galaxie

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Re: 3.98 stroke Scat cast steel or forged crank balance
« Reply #8 on: October 21, 2022, 10:34:41 PM »
The TRW pop ups I have are quite heavy.
I will replace them with a more modern piston.
The cylinder heads are being finished up - porting/flow bench testing underway.
Will use a hydro roller grind with solid roller lifters.
Not too aggressive - aiming for 500+ HP.
The race built 502" 385 series in the car now is honestly way too much for the street.
Half throttle in second gear is nuts.


blykins

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Re: 3.98 stroke Scat cast steel or forged crank balance
« Reply #9 on: October 22, 2022, 05:03:51 AM »
Will use a hydro roller grind with solid roller lifters.

I see guys doing that, but what it means is that the camshaft was not designed correctly in the first place. 

If a hydraulic roller cam can't be used with a hydraulic lifter, then it means that the lobe was too aggressive, the valvetrain was too heavy, or a combination of both.  FE's have some of the heaviest valvetrains of any engine family and it takes a certain combination of parts to get them to work easily.  When you get the right combination of cam lobes, lifters, spring loads, etc., then it's very easy to hit 7000-7500 rpm with them. 

If the goal is to use a very aggressive lobe to make more power, then by all means do it, but why not just use a lobe that's specifically designed for a solid roller application?  There's a risk involved with running solid roller lifters on the street.  If that risk is going to be taken on a 5500-6000 rpm engine, then I don't see the need in specifying a "hydraulic roller" camshaft.   A hydraulic roller lobe with a solid roller lifter will still need a lot more spring load than it would have required with a hydraulic roller lifter and unless it's a "hybrid" lobe, the lash requirements will be much different as well, usually much tighter (.005-.006").



« Last Edit: October 22, 2022, 05:40:41 AM by blykins »
Brent Lykins
Lykins Motorsports
Custom FE Street, Drag Race, Road Race, and Pulling Truck Engines
Custom Roller & Flat Tappet Camshafts
www.lykinsmotorsports.com
brent@lykinsmotorsports.com
www.customfordcams.com
502-759-1431
Instagram:  brentlykinsmotorsports
YouTube:  Lykins Motorsports

1968galaxie

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Re: 3.98 stroke Scat cast steel or forged crank balance
« Reply #10 on: October 22, 2022, 10:05:58 AM »
A HR camshaft designed for an FE would have very gentle lobes (lower acceleration rates).
I agree people choose HR cams that are too aggressive for use in an FE.
One can either choose a gentle lobe cam and run the hydro roller lifters, or for better performance with
the more aggressive HR cam, run a solid roller lifter.
Even the more aggressive HR cams are nowhere near the aggressiveness of most SR profiles.
Coupled with tight lash (~0.006") the lifter lifetime is increased substantially.
I would trade lifter lifetime for higher power output using a slightly more aggressive profile.
I have discussed a mild SR with Jones Cams - that is not off the table yet.

(I also have a "free" set of Crower SR lifters from my 385 build inventory)

blykins

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Re: 3.98 stroke Scat cast steel or forged crank balance
« Reply #11 on: October 22, 2022, 10:15:59 AM »
A HR camshaft designed for an FE would have very gentle lobes (lower acceleration rates).
I agree people choose HR cams that are too aggressive for use in an FE.
One can either choose a gentle lobe cam and run the hydro roller lifters, or for better performance with
the more aggressive HR cam, run a solid roller lifter.
Even the more aggressive HR cams are nowhere near the aggressiveness of most SR profiles.
Coupled with tight lash (~0.006") the lifter lifetime is increased substantially.
I would trade lifter lifetime for higher power output using a slightly more aggressive profile.
I have discussed a mild SR with Jones Cams - that is not off the table yet.

(I also have a "free" set of Crower SR lifters from my 385 build inventory)

I don't think I'd call them all "very gentle" because it depends on the valvetrain.  I have some pretty aggressive hydraulic rollers for FE's that do just fine because of the valvetrain part selection.  They are not the "all-out" hydraulic roller lobes that are used for small block stuff though. If you're stuck with a 3/8" stem valve, then yes, you would need to be more on the "gentle" side than aggressive.  If you're running 11/32" stem valves, or even smaller, then you can get away with quite a bit, and I would favor the hydraulic roller lobes that I use over a "mild" solid roller lobe.  Unless you're planning something over 7000 rpm, I don't think the difference in power would be enough that it would make much difference.  Remember, you lose duration to lash. 
Brent Lykins
Lykins Motorsports
Custom FE Street, Drag Race, Road Race, and Pulling Truck Engines
Custom Roller & Flat Tappet Camshafts
www.lykinsmotorsports.com
brent@lykinsmotorsports.com
www.customfordcams.com
502-759-1431
Instagram:  brentlykinsmotorsports
YouTube:  Lykins Motorsports

1968galaxie

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Re: 3.98 stroke Scat cast steel or forged crank balance
« Reply #12 on: October 22, 2022, 12:08:06 PM »
I agree again, one does lose duration and lift to lash.
A hydraulic lifter loses duration and lift due to compression of the lifter and bleed rate.
I recall many instances where hydraulic lifters (FT) were replaced with solid lifters (flat tappet) and substantial gains were made - even with
the solid lash taking away theoretical duration and lift. In a dynamic running engine there is far more than 0.006" lift lost in a hydro lifter.

blykins

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Re: 3.98 stroke Scat cast steel or forged crank balance
« Reply #13 on: October 22, 2022, 12:32:31 PM »
Sure, but that was because the correct components were not used to begin with, or the correct measures were not taken with the components that were used.  Even something as simple as excessive lifter bore clearance can cause issues.

Again, it all boils down to what valvetrain components are being used and what the rpm/horsepower goals are, which have not been discussed yet.

Brent Lykins
Lykins Motorsports
Custom FE Street, Drag Race, Road Race, and Pulling Truck Engines
Custom Roller & Flat Tappet Camshafts
www.lykinsmotorsports.com
brent@lykinsmotorsports.com
www.customfordcams.com
502-759-1431
Instagram:  brentlykinsmotorsports
YouTube:  Lykins Motorsports

1968galaxie

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Re: 3.98 stroke Scat cast steel or forged crank balance
« Reply #14 on: October 22, 2022, 03:05:43 PM »
Thanks for your input Brent.
(I did very much like the 302TP you built!)

Regarding the 390, power goal 500+ HP. I believe the duelling 390's showed over 500 is very possible - even with a smallish duration HR.
I would like peak power 6300 to 6500 rpm.

The solid roller lifters I have weigh 270 gms (set of 2 with tie bar).
HR lifters seem to be quite a bit heavier - 335 gms.
Not sure why SR lifters on a HR profile require higher spring pressures? Perhaps the higher top end rpm range?