302 vs. 351 Pistons

[Nathan in MI]

Just a quick question...are stock lopo 302/351 pistons dished or flat top? And if they are, is the amount of dishing different between 302 and 351 pistons?

Thanks guys.

--Nathan

[DuceAnAHalf]

I believe they are notched flat tops. The also have different compression heights. You can use 302 pistons in a 351 with a special crank and 351 rods to make a 396

[Nathan in MI]

The also have different compression heights.

Are you saying that in a 302 the pistons come to the tops of the bores and in a 351 they don't?

[DuceAnAHalf]

No, they should come to about the same depth in the block, however the distance from the centerline of the wristpin to the top of the piston is different.

[1987cp]

My original '87 302 pistons are dished, as were those from my '79 351. Just remember that the 302 and 351 use different rods and such along with the different crank stroke, and I don't doubt in the least Duce's claim about the dimensions from the crown to the wristpin. It's possible the wristpins don't even interchange, though they might. My personal opinion is that with SpeedPro/Federal Mogul parts for either engine being relatively cheap, it'd be silly to mix-and-match without a good reason. If you must mix-and-match, make some VERY careful measurements of the assembled short-block to avoid breaking stuff or ending up with 7:1 compression.

[Nathan in MI]

I'm not planning on mixing and matching anything. Guess I should have been more specific on what I was asking. The reason I asked in the first place is that I'm wondering how compression ratio will change when I put E7 heads on a 351W engine. Assuming all other things are equal, the CR should come out higher on the 351, however if the 351 pistons have a greater amount of dish, then that would negate it.

If anyone can shed any light on this specific issue, I'd appreciate it. And I apologize for not being more specific from the beginning.

[DuceAnAHalf]

My original '87 302 pistons are dished, as were those from my '79 351. Just remember that the 302 and 351 use different rods and such along with the different crank stroke, and I don't doubt in the least Duce's claim about the dimensions from the crown to the wristpin. It's possible the wristpins don't even interchange, though they might. My personal opinion is that with SpeedPro/Federal Mogul parts for either engine being relatively cheap, it'd be silly to mix-and-match without a good reason. If you must mix-and-match, make some VERY careful measurements of the assembled short-block to avoid breaking stuff or ending up with 7:1 compression.

The wristpins are the same, you can put 302 pistons on 351W rods for a 396.

[1987cp]

The wristpins are the same, you can put 302 pistons on 351W rods for a 396.

I did not know that. Is that what's used in the retail 393-stroker kits?

[DuceAnAHalf]

I did not know that. Is that what's used in the retail 393-stroker kits?

yea they are 302 pistons with 351W legnth rods with a custom 3.85" stroke crank. There might be kits out there that use a different rod/piston combo though.

[Nathan in MI]

Yeah, I was looking at those stroker cranks on eBay tonight. Don't know if the $400 eBay special cranks are worth buying or not, but it's tempting. Just buy the crank, a set of 302 pistons, put it together and I'd have a 393. w00t

[1987cp]

I'm not sure I would pay $400 for something off eBay when you can go to summitracing.com and get an Eagle crank for $300 or a Scat crank for $400 ... but I suppose you're thinking the same thing.

http://store.summitracing.com/partdetail.asp?part=ESP%2D103513850&autoview=sku

http://store.summitracing.com/partdetail.asp?part=SCA%2D9351W10&autoview=sku

[Nathan in MI]

Well, I've heard less than favorable things about Eagle products, so I probably wouldn't go that route, but $400 for a SCAT crank from Summit sounds like a good deal. I hadn't checked on prices for them through the performance catalogs yet, so thanks for the info.

[DuceAnAHalf]

a local guy bought a SCAT crank, his engine builder (who used to build NASCAR motors) said that it was of comparable quality to a $3000 (yes three thousand, thats not a typo) Callais crank he had there.

[Nathan in MI]

Sounds like the thing to use, then.

But why such a severe discrepancy in price? If they're of comparable quality, what's the difference?

[1987cp]

Perhaps the Scat crank in question was a forged model? Especially if it's a non-twist forging, those run quite a bit more than the cast-iron one I saw. Of course, cast cranks are said to be *usually* good enough for most anything we really need on the street.