is it possible to put 347 pistons in a 331? imean they would both be for a .030 over bore. but would they fit and what wouold it do to the compession ratio??
347 pistons
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faststang90
10 Year Member
a 347 is a 3.40 stroke and a 5.400 rod.
a 331 is a 3.25 stroke and a 5.315 rod.
a 331 uses a 5.315 rod and a 347 uses a 5.400. so the piston would be down in the hole .085 because of the rod and then u would be another .150 down in the hole because of the stroke. so that .235 down in the hole. im not a motor person but i dont think that u can do that. i was doing a bbf and i needed a rod like 6.800 and i was not thinking and i got a rod that was 6.700 and was told by bennett that it would not work because the pistons i had was for a 6.800 rod. they said .100 was way to much.
a 331 is a 3.25 stroke and a 5.315 rod.
a 331 uses a 5.315 rod and a 347 uses a 5.400. so the piston would be down in the hole .085 because of the rod and then u would be another .150 down in the hole because of the stroke. so that .235 down in the hole. im not a motor person but i dont think that u can do that. i was doing a bbf and i needed a rod like 6.800 and i was not thinking and i got a rod that was 6.700 and was told by bennett that it would not work because the pistons i had was for a 6.800 rod. they said .100 was way to much.
ok it makes sence. the reason i ask is that since putting a crate motor in i ask the buider which pistons he put in and he said P3471F-030. and i then emailed him back and said that i recieved a 331. i have been have spark knock and it has been to 2 diffenert dyno here in north carolina and they both are saying that it has a higher compression ratio.
Actually a 331 is a 3.25" stroke, 5.40" rod and a 1.175" or 1.165" CH piston, depends on brand.
A 347 is a 3.4" stroke, 5.40" rod with a 1.09" CH piston or you can build it with the 5.315" rod and a 1.175" piston (same as you would use in a 331)
P3471F-030 is a Probe FPS series piston (its the cheapest piston Probe makes) its a flat op 4cc with a 1.09" CH and a .927" pin.
Your short answer is if that piston was used you have a 347 or your piston is way down i the bore, so I would belive you have a 347. Compression ratio with a 58cc head is around 10.7:1, with a 61cc about 10.2:1. Both are very managable witht he correct cam, I actually like stuffing as much compression as possible on pump gas in the motors I build....cam is crucial.
Hope that helps...
A 347 is a 3.4" stroke, 5.40" rod with a 1.09" CH piston or you can build it with the 5.315" rod and a 1.175" piston (same as you would use in a 331)
P3471F-030 is a Probe FPS series piston (its the cheapest piston Probe makes) its a flat op 4cc with a 1.09" CH and a .927" pin.
Your short answer is if that piston was used you have a 347 or your piston is way down i the bore, so I would belive you have a 347. Compression ratio with a 58cc head is around 10.7:1, with a 61cc about 10.2:1. Both are very managable witht he correct cam, I actually like stuffing as much compression as possible on pump gas in the motors I build....cam is crucial.
Hope that helps...
ok but to really find out i need to see that part number ont top of the piston. is there anywhere to get like a flexable scope or something to look down on top of teh piston with the spark plug out
Yes, Snap-on has a bore scope that is awesome, im sure there are other companies that make them, but i do know the snap-on one will take pictures and video, it uses a roughly 2 foot flexible line with a LED light at the end and a LCD display. It is rather pricey though, like $4-500 i do belive. I would see if you might know anybody that has a bore scope or if a local machine shop has one rather than buy it. I do agree though with the other posts that it sounds as though you have a 347 and may need to look into other issues for the spark knock problem, such as timing. Hope you get it figured out with relative ease.
faststang90
10 Year Member
guess it matters what kit you are tring using. i was looking at the dss kits and there kits are the way i posted so you need to get all the parts checked to make sure they work
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