FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: 1968galaxie on October 21, 2022, 02:54:55 PM
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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.
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You can internally balance it, but it will require a good bit of heavy metal.
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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?)
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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.
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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.
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FT pistons ........ flat tops ??
I saw FT ( 391 ) ..and thought, man , those things are heavy
Ricky.
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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"
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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.
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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.
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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").
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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)
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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.
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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.
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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.
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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?
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Yes, it will all boil down to what the heads are and how well they work. For instance, a TFS head on a 390 will make about 540 hp @ 6000-6200 with a hydraulic roller. I have also made 540 hp with a 390 and ported CJ heads with a hydraulic roller, at 7000 rpm.
The solid roller lifters require more spring pressure because of lash. It takes more spring load to keep things from bouncing around uncontrolled. It also will depend where on the lobe the actual lifter contact takes place as it may accelerate the lifter and that also requires more spring load.
It would be hard to not want to use solid roller lifters if you already have them. It would save you money. However, if I were planning to use solid roller lifters, I'd stick them on a solid roller camshaft with moderate lobe aggression. Comp Cams also has a few lines of hybrid lifters that aren't visible in the lobe catalogs. They kind of bridge the lines between hydraulic and solid. I've used them with both style lifters successfully. If you could sell them and buy a quality set of hydraulic roller lifters, you could hit your horsepower and rpm goals and not have to worry about the lifters down the road.
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You can use solid roller lifters on several of the Comp hydraulic roller lobes. As noted, they run with minimal lash, and can do surprisingly well. Most traditional solid roller cams were designed for racing applications with profiles and RPM bands beyond anything appropriate for a cruiser style street car. These hybrid lobes do fill the hole, although custom stuff is possible that would likely do a better job.
The need/desire for more spring is to keep that solid roller in contact with the lobe as much as possible - rollers do not like impact loads - each roller needle is essentially "point contact". Hydraulic rollers do not share that problem since the preload ensures that the roller is always in contact with the cam. Valve float in a hydraulic roller makes for a bunch of noise and a huge power drop-off. Valve float in a solid roller makes for busted parts.
You can theoretically run solid rollers with far lower tension springs than we normally see in drag cars - but doing so requires a level of research and analysis far beyond that used in a common street/strip application. If we are to believe what's reported on the web, there are Cup engines running 9,000+ RPM with spring pressures that we might find marginal in hydraulic applications.