I have a 59ab block sitting at the machine shop ready to be machined. Hasn't been bored yet but it's sitting at a .040 over right now. I was going to keep the stock 3.750 crank and just go maybe .060 over on the bore. Then this good deal comes around.... 600$ for a Scat rotating assembly everything from pistons to crank. 304ci with a 4.25 stroke. Brand new from speedway. My question is... is this safe for my flathead? My build was going to consist of alum heads and intake. Probably run a 4 barrel for the ease of tuning. I know flatheads don't breathe very well would I be able to use this assembly without porting? Would it be streetable? I'm not trying to race it or anything just drive it around and have fun with it. It was going to be stock but this sounded like a good deal. Pick this up or keep her tamed down?
What is the bore of that, 3 3/8?? Good blocks are getting scarce, and that bore is on the edge of risky, made more risky every year as rust advances. Risks include actual failure of a bore and the heating potential with thin walls. I would tend toward 3 5/16, big but not very risky, and I am a little suspicious of strokes beyond 4 1/8...I have observed oil consumption issues on seemingly well prepared long strokers, and I worry about piston rocking from increased rod angles possibly being the cause. I don't like the idea of taking a good flathead block to the ragged edge.
Actually I mis read the posting. It is a 3 5/16 bore so I believe that would make it about 296 ci. I was wondering about the rod angles as well. Also then the piston speeds increase. I feel like it may be too long of a stroke to be considered "safe" but i have no experience as this is my first flathead build. I was definitely going to go with a full flow oil filter and high volume pump. You think the pistons rock so much they wear out the bores prematurely? If it's not going to be a reliable Streeter I may end up passing on it. Just figured it would end up being cheaper than using my parts that came out of the engine. After resizing rods, pistons/rings, and getting the crank ground. Not to mention the cost of full floating rod bearings.
A 304 would be a 3 3/8 bore and 4 1/4 stroke. As with any block, the safest way to determine a safe bore is sonic testing. 3 3/8 was very common in the old days and very few blocks would not go that far out. What with rust aging, it is best to test them now, even with a .060 bore. Cheap insurance. Heating is never a problem if you have the block acid stripped and have an adequate radiator. The combination should work fine with no porting or relieving for the street. You will be absolutely amazed at how much neck snapping low speed torque you will have with the 4 1/4 stroke. Oil consumption will be no problem what with modern ring and piston design. I turned out an engine with a one inch stroke awhile back and it uses no oil in a complete race program.(70 laps)
I don't know. I saw a lot of oil burning by a very hot motor that had been machined by an excellent machinest and run by a sophisticated and experience racer. He too suspected rod angle. No autopsy, engine was still hot stuff and was supercharged, so when it went into boost there sure weren't any problems! it would have been interesting to look over the pistons after it had some mileage to see. Speedway makes multiple setups, I think, I'd just dial back to 4 1/8 or 4...
if its .040 over now I would go with the least bore you can do to true her up, and no problem on the 4 1/4 and Scat rods if you use Eagle Rods there will be some clearance work to be done on the cyls. Since you have her down for all of this I would spend a little time on porting and matching the intake to block. But that's just me, and for just a street engine you won't be spinning the shit of it anyway I very rarely run my blown truck over 3500......... now the dragster that's another story................. and like Pete says gobs of torque. Just make sure you take your assy to a good balancer they do need some work!
i've said it before, but i'd be leery of those inexpensive aftermarket cranks. had a chat with the local crank grinder over the winter and he told me how he gets many that aren't straight and that are a bear to balance. the real ford pieces may cost more, but it's good stuff. 4-1/8 x 3-5/16 with the 38-42 ford rods is the way to go imo.
What should the minimum wall thickness be if you have the block sonic checked? Is 0.100" thick wall safe for a mild street motor with compression lower than 8:1 or thereabouts?
.100 wall is fine. I have run race engines at .090. As for aftermarket stroker cranks, I have had good luck with them in street engines if you keep the hp under 200. Sometimes they need straightening and regrinding right from the vendor. They are all hard to balance, meaning they are way too heavy on the throw side. I machine the weight off rather than use heavy metal in the counterweights. It's cheaper.
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