740P pistons for a sbc 307
 

I was taking apart my chevy 307 the guy I bought it fron said it was 30 over but then the piston where not stamped so I had a .040 piston from a 283 an of course the share the same piston size but the 307 piston is bigger so now the only number I found was 740P feb 92 can some one help me

Your post is very confusing, and a run-on sentence/post. I don't know what your reference to the .040 piston thing is, or the 283 piston. You know they have different strokes, right? Can you explain?

I don't believe the 283 and 307 share the same piston, they're different strokes and different compression height (pin location) pistons.

Well I was told that a 307 shared the same bore as a 283. And the motor was suppose to be .030 over and the piston I tried was from a 283 bored .040 over but the pistons are not marked or stamped but I did fine a 740P on the inside of the piston

So I am trying to find out what 740P means?

The do share the same bore, but not the same stroke. The 283 stroke is 3.00", the 307 is 3.25".

I'll give you a start in your search, the 740P piston was manufactured by Ohio Piston & Pin, now out of business, and sold under the brand names Nytel and Ertel. They were once associated with Dynagear, but not sure in what capacity.

Maybe some here from back in the day can shed more light.

Yeah the 307 has the stroke of a 327 but the bore of a 283. But I'm just wondering what size it is, I am thinking probably .060 over. Thanks for the info

Just found out my 307 is bored to a standard size 327. Planning on running camel hump heads and a small mild cam around a 210 or 212 duration. Anyone got some opinions on that? I would like more help on my build

Makes sense- the 740P is a 327 SBC slug. So your 307 is now a 327.

Nothing wrong w/that cam duration and cylinder head- keep the quench tight, the CR might be a bit low, but w/a short cam that's OK. Might want to run the dynamic CR numbers just to be sure you're in pump gas territory.

Long tube 1-5/8" headers, a dual plane intake and a Q-jet would make a pretty sweet street engine.

Yeah I think my cr would be around 9.5 or 9.75 to 1 but I also have a 260h cam I am thinking about using? What do you think?

the cam i have is like a 204 to 208 duration not a 210 or 212.

According to the Badger Pistons website:

I have to wonder whether 72chevy's engine is in fact an original 327 or a 307 overbored .125". Can a 307 be safely bored .125"? No matter, if it's using a 740P piston it must be a 327. If it is in fact an original 307 with a .125" overbore I would be very leary of doing any further overbore for this build.

Cobalt327 made a good suggestion to run the compression ratio figures. I ran the compression ratio using 4" bore, 3.25" stroke, 5.7" rod, standard .025" deck height, a .015" thick by 4.1" bore head gasket (Fel Pro #1094), 7cc for piston dish (flat top with 4 valve reliefs), and 64cc heads (the double hump heads). I got a static compression ratio of 9.43. Using the specs for a Comp Cams 260H I got a dynamic CR of 7.99 so your build is well within range for pump gas use.

Ed

No I am not going to do any more bore to it. But the casting numbers on the block are infact a 307 from 1969. But I am still deciding to use the 260H cam or the 268H cam still undecided.

Since my compression will be close to 10:1 do I need to change my converter?

With the 268H your dynamic CR will drop slightly to 7.78. Comp Cams literature shows the 270H as "Biggest cam with stock converter but better with 2000+ stall" so both the 260H and 268H are mild enough to work well with a stock converter, but both would show increased performance with a slightly higher than stock converter. On Comp Cams free simulator software, CamQuest.com, the recommended TC for the 260H in a 327 is 1500-2500 rpm. The recommended TC for the 268H in a 327 is 2000-3000 rpm.

thanks for the info i feel better with using the 268H cam without changing my converter.