Thanks for the link and information. I'll have to do the CR calculations to see if that would work. No valve reliefs may be a problem, but not insurmountable
318 Connecting Rods and Crankshaft
- Thread starter Grumpyoldman
- Start date
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Do you have personal experience with this Scat cranks? I would like to hear from those that can speak to the quality of their products, please.
dartfreak75
Restore it, Dont part it!
I already did it because I'm curious too! It came out at 9.2 with 70cc heads
one 408 with a scat one 408 with a K1...both engine very a like....scat crank engine is a tenth faster so far....plus I got probably 4 scat crank new in boxes waiting .....
both K1 and Scat cranks are made in china...
both K1 and Scat cranks are made in china...
Wyrmrider
Well-Known Member
way overthinking this
Scat 4" crank (no Eagle)
at your rpm the rod ratio makes no real difference
and besides you are still better than a 383 or 400 chevy with a 6" rod
pick a popular combination
if you have to use stock heads use the KB pistons
power Is in the heads but you do not have to go nuts with that combo
find ones that flow well at 300-400-500 lift
at that rpm short cam with lots of lift
sort of an "engine masters" build
long tube headers
dual plane manifold with q jet or AVSII
with your build cubic inches really matter
Scat 4" crank (no Eagle)
at your rpm the rod ratio makes no real difference
and besides you are still better than a 383 or 400 chevy with a 6" rod
pick a popular combination
if you have to use stock heads use the KB pistons
power Is in the heads but you do not have to go nuts with that combo
find ones that flow well at 300-400-500 lift
at that rpm short cam with lots of lift
sort of an "engine masters" build
long tube headers
dual plane manifold with q jet or AVSII
with your build cubic inches really matter
Which Weiand manifold do you have(name or P/N) and what is your grind number on your Lunati cam? Secondly, with a four inch crank the rod ratio is going to be close to the same as a 454 Chevrolet. The best near daily driver example I knew of that was an oval port standard deck engine in a C50 tow truck. It still runs, has been going on the stock short block since the early eighties. What is your projected or required power output and vehicle weight? It sounds like your pretty well dead set on a stroker, and I won't argue against it, but a well built 318 will probably do everything you need it to. You don't need to find new parts. Look for a 318 donor engine from a 67-79 truck. A lot of these still had a forged steel crank that was shot peened, flame hardened, and then nitrided. Unless the PO's were horribly negligent, the most it will need is a good cleaning and the journals miked to confirm they are round and true.
nm9stheham
Well-Known Member
Look into the rod materials for Eagle vs SCAT, OP for the I-beams. (I have not compared the H beams.) The Eagles are a 5140 material and the SCAT's are a 4340.. stronger. Your app is not stressing the rods so maybe no big deal. For total weight, they are nominally the same: 605 gr for the Eagle I-beams vs 602 gr nominal for the SCAT's. I have been able to call Summit and ask for the lightest set of SCAT's they had on the shelf and got some that were 30 grams lighter than nominal to help with a challenging balance setup. Which leads into balancing.....
The non-standard combination is gonna require balance work on the crank. With a 3.58 stroke, lighter rods are going to put you a long way towards being able to balance internally without adding weight to the crank, just removing it. (Adding weights drives up the balance price.) So the aftermarket rods and the 3.58 stroke are a good thing here. Going with lighter hyper pistons like the KB's plus light rods will almost guarantee being able to balance a 3.58 stroke crank internally by just drilling out weight... you just pushed the 'easy' button LOL. A 4" stroke makes it very hard to impossible to balance internally without adding weight to the crank.
Not a show stopper in any case, but with a 4" stroke, the 318 block may need a bit of notching by the pan rails; I'll venture to guess that the 3.58 stroke setup with SCAT rods will easily clear the pan rails as cast with no issues. For either stroke, the SCAT rods will help with that clearance versus stock rods, by 1/8" or more from direct measurements. I have not measured Eagles for that.
The non-standard combination is gonna require balance work on the crank. With a 3.58 stroke, lighter rods are going to put you a long way towards being able to balance internally without adding weight to the crank, just removing it. (Adding weights drives up the balance price.) So the aftermarket rods and the 3.58 stroke are a good thing here. Going with lighter hyper pistons like the KB's plus light rods will almost guarantee being able to balance a 3.58 stroke crank internally by just drilling out weight... you just pushed the 'easy' button LOL. A 4" stroke makes it very hard to impossible to balance internally without adding weight to the crank.
Not a show stopper in any case, but with a 4" stroke, the 318 block may need a bit of notching by the pan rails; I'll venture to guess that the 3.58 stroke setup with SCAT rods will easily clear the pan rails as cast with no issues. For either stroke, the SCAT rods will help with that clearance versus stock rods, by 1/8" or more from direct measurements. I have not measured Eagles for that.
Interesting... I was looking for that example..... a small fraction of a % difference in the rod/stroke ratio of a SBM with 4" stroke 1.534 versus 1.531....I don't think that 454 bores wear out particularly fast. 1.50 is considered the lower limit of 'normal' engine design for rod-stroke ratio. FWIW, with the OP's lower RPM range of 5000 RPM max and interstate cruise RPM of 2500, it seems like a good match. But that is probably academic at this point.
MOPAROFFICIAL
Oogliboogli
Ohio crankshaft h beams also.
They are very good rods.
Stock rods with arp bolts should work.
I will give you a set of stock 318 rods, just pay shipping.
Pm me
Pm me
Sireland67: Thank you. Sent you a PM
I did see them and forgot to mention Ohio
Thanks for the information. I had looked at both Eagle and Scat and have been leaning toward the Scats just for the material. Honestly I had not paid attention to weight.
Balancing: Unless I bought a balanced rotating assembly form someone, which as far as I have found is limited to a 4" stroke - 390, I was going to have to balance anyway. An expense already accounted for in the budget.
Clearance at the pan rails is a concern, but not so much with a 3.58 stroke. I do not think anything will have to be done there. But mockup and measuring will tell the tale.
Krooser
Building Chinese Free Engines since 1959...
You won't have any clearance issues with a 3.58 stroke.
I'd use a 360 crank turned down to fit. Good American steel.
Stock rods are tuff...more good steel. One of my engine shops is Chevy oriented but he admits he's never seen a failed crank Mopar crank that wasn't caused by another part.
All this rod/stroke talk is meaningless in your application IMHO.
Have fun.
I'd use a 360 crank turned down to fit. Good American steel.
Stock rods are tuff...more good steel. One of my engine shops is Chevy oriented but he admits he's never seen a failed crank Mopar crank that wasn't caused by another part.
All this rod/stroke talk is meaningless in your application IMHO.
Have fun.
Speed-O-Motive carried a .030 over 318 350 kit for years based on a 318 with a 360 crank. Indeed, it would be pretty easy to do the Silvolite pistons with stock rods and the Scat crank, but I would just use a 360 crank worked by someone trustworthy. No reason to spend the the extra on a forging at this level. The 1978 up 360 crank is slightly stronger than the earlier ones. The fel-pro 8553 PT permatorque head gaskets compress in at .052 actual, but are only about $13 apiece and work well. The 1.658 compression height will put it down .029 in the hole or deeper if the block is taller. You mentioned you had ported 318 heads, what casting number and what do they cc in at? Have they been surfaced? Most come in at 62-63 ccs after a .010 cleanup. This comes in right at 9.9:1 compression. I'm really starting to like this build, the 360 crank I have laying around is starting to look really attractive to me right now!
I agree with you. All I wanted when I started this build was a nice strong 318. Did not want a stroker at all. I have had this block for many years. Had all the rotating assembly also. Sometime over the years I strongly suspicion one of my boys sold the crank, rods, pistons, etc. to one their buddies either to make a few bucks or to help someone out. I do know when I asked my oldest son to ship the crates, all he could find was the bare block and main caps. It was when I tried to find a stock stroke aftermarket crank, and all I could find was an eagle, that I realized I would have to build a stroker. And I still prefer a 3.58 or a 3.79 over a 4.00.
The heads I have are 70's (I cannot remember the casting number and they are not readily available to check). They were rebuilt some years ago and a check of my records says they cc'd at an average of 68. I must not have recorded the cc of each chamber. At the time they were port matched to (I think) an Offy intake and some casting irregularities smoothed out. Not really ported, just cleaned up some. No longer have that Offy intake.
pishta
I know I'm right....
" A 4" stroke makes it very hard to impossible to balance internally without adding weight to the crank."
An Eagle forged 4340 360 mains 4.00 crank has a bobweight of 2050g (same as their cast). Stock balanced rods and cast stroker pistons were 40g under this bobweight, that's lightening the crank, no metal added for internal balance. Not hard, and I used 'heavy' stock rods.
>>> a 360 with 318 mains and 318 pistons is only .170 out of the hole. I heard there is a low compression 318 truck piston that actually is a zero deck on a 360 crank! Someone pointed this out to me when I was researching this as I have a cast 360 with turned down 318 mains already. Fedex chipped the flange between 2 holes in shipping so I never used it. <<<
An Eagle forged 4340 360 mains 4.00 crank has a bobweight of 2050g (same as their cast). Stock balanced rods and cast stroker pistons were 40g under this bobweight, that's lightening the crank, no metal added for internal balance. Not hard, and I used 'heavy' stock rods.
>>> a 360 with 318 mains and 318 pistons is only .170 out of the hole. I heard there is a low compression 318 truck piston that actually is a zero deck on a 360 crank! Someone pointed this out to me when I was researching this as I have a cast 360 with turned down 318 mains already. Fedex chipped the flange between 2 holes in shipping so I never used it. <<<
One thing to keep in mind with all this, if you use a shelf compression height piston NOT designed for the 3.58 stroke, the skirts have to be clearanced for the counter weights.
A friend of mine did this deal. We used Magnum block and heads. There were two different compression height pistons. The ones we had were the taller ones. Piston and rods came out of a very low hour marine 318. The rods were the small beam floaters. He got scared of the compression. Think it came out to about 10.5. Anyway, we machined the skirts down to mimic a 5.7 Hemi piston. Then had the tops turned down, too. These were the flat top 4 relief. Ran an old DC Hemi grind cam and lifters. Only spent money on new parts where absolutely needed. Damn slapped together junk ran pretty good.
Thanks for reminding us! That's one of those details that I've forgotten about along the way that sneaks up to bite during building this type of stroker. One advantage is it lightens the pistons and therefore the bob weight even more having to do that. With 68 chambers and the aforementioned parts and clearances, dead on at 9.5.
nm9stheham
Well-Known Member
Clearancing skirts removes a very small amount of weight from the piston so not much help there. BTDT.... Cast 318 pistons and stock 318 rods (heavy or light) are going to require a considerable amount of weight to be added to any stock 360 crank to internal balance if that is what is desired. An option is to go with the 360 external balance parts at the damper and TC/flexplate to get much closer.
So just be aware....
Pishta's roughly 100 gram drop in piston/rod bobwieght from stock is all in the much lighter stroker piston weights that he used. Stock 318 cast pistons have very thick and heavy crowns and their bobweight with stock heavy rods is going to be around 2160 grams.
The 2050 gram design bobweight number of the Eagle 4" crank number is pretty amazing; the SCAT 4" cast crank has to have under 1760 grams bobweight to internal balance without added weight. (I doubt the SCAT forged crank will be that much higher.) Not sure WHERE Eagle is putting all that extra counterweight..... I'd like to an actual pix of the Eagle crank to compare to my cast SCAT 4" crank. I've been skeptical on the Eagle target bobweight number for a 4" stroke.... but I may be all wrong on that.
I think @j par is running a cast scat crank. My plans for my 360 build call for a cast scat 3.580 throw crank.
I already have the scat ibeams, got them here for around $200-$250. I can't remember, and don't want to look it up on how much I've spent on this hobby... But, that's what money is for.
nm9stheham
Well-Known Member
IIRC.... the Eagle cast crank have reportedly had some breakage issues in the past that the SCAT's have not had..... but who knows how the parts may have been abused. The OP is not pushing this engine so I'll bet you will be OK either way.
70aarcuda has used a number of SCAT cranks IIRC.
70aarcuda has used a number of SCAT cranks IIRC.
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