So if I'm understanding correctly, and doing the math right, a 408 stroker can be built utilizing a stock 351w block and the stock rods. I've been doing some research, and can not find any threads anywhere talking about this. But the math seems to add up, so please correct me if I'm off somewhere. The trick is to use Boss 302 pin height pistons (1.53"). (Block height) - (stroke/2) - (rod length) = (piston pin height). Sooo, 9.503 - 2 - 5.956 = 1.547". If compression ratio is an issue, could a domed piston or thicker head gasket solve that? Please help or guide me in the right direction.
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With a 3.85 stroke.
408 uses 4.00 stroke..(edited)
The 408 also uses a 6.2" rod length as opposed to the stock 5.956 length.
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Yes, but i said "BOSS" 302, which have a pin/compression height of 1.53" as opposed to regular 302 pistons with a pin/compression height of 1.605" i think.
The rod length and piston compression height can change inversely within a wide range, as long as the math adds up. I know what the rod lengths are in pre-made kits, and they are matched up to pistons with compression heights that fit the equation as shown above.
Not meaning to sound like a d!ck, but I'm looking for someone with engine building knowledge, not just experience assembling.
Well if the math works, then There shouldn't be a problem. Thicker head gaskets can be used to lower compression some.
Although I guess I'll keep quiet. I just assemble them. You may try the Corral, there's a few builders that post frequently that can answer for sure.
Although I guess I'll keep quiet. I just assemble them. You may try the Corral, there's a few builders that post frequently that can answer for sure.
I appreciate the input. I just build 'em too, that's kinda why i need the help. Don't wanna put in the work just to spend $2000 more for whatever thing I'm not seeing. Everything seems right, but then why isn't this a coming build? Maybe Boss pistons are hard to come by, or more expensive? Either way, thanks for the direction.
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Fair enough, but if you don't mind me asking, what are you trying to accomplish? By that I mean, are you trying to hit the 408 number with parts you already have, or looking for better rod angle??
Why reinvent the wheel? I could understand stand if you have parts laying around and just need pistons...
I have a 351 from my old 91 F250. I'm trying to keep parts that are still usable. The truck rods are a bit more beefy, so I'd like to be able to use them with new ARP bolts. My original plan was a 393, for that reason. I noticed that the 4.00" crank is usually a bit cheaper (not a big deal, just a bonus). And then I happened upon the nugget of info that the Boss pistons had a shorter pin height than regular 302s. Longer stroke is more torque and at lower rpm, plus the old adage, "no replacement...". Everything came together in my head and so i tried the math. I know the 6.2 rods would produce a better angle, but all my research says that it will be negligible since this motor will probably never even see 7000 rpm. But if i can pull it off I'll only have to buy the crank and pistons, plus the uniqueness of a 408 with stock rods and Boss pistons. Hell of i threw some Cleveland 4v heads on it, it would be a proper retro Boss 408. But I'll probably go with AFR 225s.
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I was going to respond with that, but got called over to the machine shop before I could. If you look at Summit, you can find those cranks for pretty near the same price, believe me, I've been eyeing them myself. And.. those rod journals are smaller "Cleveland" size, which equates to lower surface speed and less friction... At least that's what I've read, I'm not an "engine builder", just an assembler.
Oh, and FYI, your math does look right, albeit you'll be about .013 low on your piston face, which like @hoopty5.0 pointed out, you can fix with a gasket, or mill your deck a little. That much won't hurt.
Obviously you have put in a lot more research than I have. However, it seems that you may be making it harder on yourself by trying to save the stock rods.
If you add arp bolts to them, they will need to be resized. You will probably be within a $100 of an aftermarket rod that will still be much stronger.
I think in the end, you are better off going the conventional route. This may be why you don't see this build often. I have been in your shoes before. You are trying to work around one part that MAY save you a few dollars, but the cost savings probably won't be worth it.
Joe
If you add arp bolts to them, they will need to be resized. You will probably be within a $100 of an aftermarket rod that will still be much stronger.
I think in the end, you are better off going the conventional route. This may be why you don't see this build often. I have been in your shoes before. You are trying to work around one part that MAY save you a few dollars, but the cost savings probably won't be worth it.
Joe
And even if you can make it all work out,...and source Boss 302 pistons, What are you gonna do about the hollow dome that'll stick up w/ valve eyebrows cut for canted valves?
Yeah, i concur and have admited defeat. The piston being in the hole didn't concern me much, use a .020 or .030 head gasket, and you have the ideal 0.040 quench distance. Either way, a kit seems the way to go. Especially since that means i won't have to have a builder put it together and balance it. That cost savings alone seems to balance it all out.
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You can still use your stock rods and build a 393. Everyone I've talked to that built one loved it. What are your plans for the car? I've put together several engines that I didn't have balanced and they did well. Is this a car you plan on racing, or a street car?
Really? I always thought a rotating assembly had to be balanced, especially once you get into such a long stroke. I would actually be happy to hear the contrary. Plan is just for street use with a good grunt that can make babies cry and young women swoon.
Personally, I wouldn't trust my recip assy to be even close to being in balance as soon as a Chinee stroker crank enters the equation.Now throw in a piston of unknown weight that could be heavier (like Collins) or significantly lighter (like Mike's) depending on alloy, and I think you got the perfect recipe for a annoying vibration at XXX rpm.
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