need help with pistons...Please!
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Senior User
Joined: Aug 2001
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From: Florida
need help with pistons...Please!
Hey guys, I've read all the posts on this topic, and some of it is another language to me! I'm trying to research parts for my engine, being the first truck and engine I've ever restored, things get confusing and difficult at times. I have a 1979 351m with stock heads (78.4cc i assume) which I'm turning into a 400. I dont know how to pick out the pistons. I want to use 351 cleveland pistons. Can anyone tell me what Cleveland pistons will give me 9.5 to 9.9 compression. My goal was 9.7. I dont want anything under 9.5, and I want to stay under 9.9. If any of you know can you tell me what piston to use, and even what part number they are if you have it. Can you tell me what CR they would give me.
I came to ya'll cause I talked to a shop, summit, and a long time mechanic and no one really wants to help, everyone tells me something different and what they say is a better idea.
Help me please,
Gabriel
I came to ya'll cause I talked to a shop, summit, and a long time mechanic and no one really wants to help, everyone tells me something different and what they say is a better idea.
Help me please,
Gabriel
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Joined: Feb 2001
Posts: 829
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From: Porterfield
need help with pistons...Please!
OK here we go .. I don't know if you'll end up with your goal of 9.6 to 9.9 Comp. but here's what one of my truck pulling buddies run in his truck and with closed chamber heads he's getting 11 to 1 with a zero deck height. If you leave a .020 deck you should get a better comp. ratio.......
He uses the 12 to 1 351C and bushes the pin on the rod. do your math to get the right deck height for your comp. ratio.
I'd also get a set of Aussie 302C 2V heads that well make this a great setup.
I tell everyone that thinks you can make any horsepower out of a smog 400 engine this ....
Just think of the 400 as a Stroked out 351C and use all the 351C hipo parts to make a kickass Motor. Most 351C Parts well bolt right up and just the intake needs intake spacers to make them work, there's more intakes for the 351C so take your pick .And there a lots 351C cams out there in Flat, Hyd., and roller grinds...
He uses the 12 to 1 351C and bushes the pin on the rod. do your math to get the right deck height for your comp. ratio.
I'd also get a set of Aussie 302C 2V heads that well make this a great setup.
I tell everyone that thinks you can make any horsepower out of a smog 400 engine this ....
Just think of the 400 as a Stroked out 351C and use all the 351C hipo parts to make a kickass Motor. Most 351C Parts well bolt right up and just the intake needs intake spacers to make them work, there's more intakes for the 351C so take your pick .And there a lots 351C cams out there in Flat, Hyd., and roller grinds...
Thread Starter
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Senior User
Joined: Aug 2001
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From: Florida
need help with pistons...Please!
Thanks for the help Billp, I will see what I can do. I have another question. Can anyone tell me the center to center rod length and the actual deck height a 400ci. Thanks in advance,
Gabriel
Gabriel
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Senior User
Joined: Aug 2001
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From: Florida
need help with pistons...Please!
Can someone check my calculation. If i were to go with KB108 pistons +2cc on my 400 i would end up with 9.4:1cr, and if i were to deck the block .020 i would get 9.8:1cr. I dont know if im doing this right, just wanna make sure. I might be way off!
78.4cc heads
Gasket thickness is .041
gasket bore is 4.100
cylinder bore is 4.030
deck clearance is .045
stroke is 4.00
If this calculation is correct and it is 9.8:1, can anyone tell me pros and cons to going with this option?
Gabriel
78.4cc heads
Gasket thickness is .041
gasket bore is 4.100
cylinder bore is 4.030
deck clearance is .045
stroke is 4.00
If this calculation is correct and it is 9.8:1, can anyone tell me pros and cons to going with this option?
Gabriel
Freshman User
Joined: Feb 2001
Posts: 40
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need help with pistons...Please!
I think you're right. That's the piston I figure on using when I rebuild the 400 I have sitting in the garage.
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Thread Starter
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Senior User
Joined: Aug 2001
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From: Florida
need help with pistons...Please!
OK, what I calculated seems to be right. I talked to a guy at Keith Black and he said it would work. Since thay are Cleveland pistons what do i need to ask for to make them fit my 400? Floating pins or something?
After Ya'll tell me what i need to make those pistons fit my 400, my engine should be done in a couple months. Which is very exciting, my friend put my specs on the desk-top dyno and it is outputing 420hp and 477 lbs torque.
Im sure I'll have other question so I'll talk to ya'll later!
Gabriel
After Ya'll tell me what i need to make those pistons fit my 400, my engine should be done in a couple months. Which is very exciting, my friend put my specs on the desk-top dyno and it is outputing 420hp and 477 lbs torque.
Im sure I'll have other question so I'll talk to ya'll later!
Gabriel
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need help with pistons...Please!
Actually when you re-surface your block and heads you will be taking about .010 of of each surface for a total of .020 so you shouldn't have to take any extra off the block. Your compression at 9.8 would seem to be pushing the margins for pump gas. The open chamber heads are prone to detonation also.
As far as the pistons go you will have to bush the piston rods and machine the piston for a floating pin. Why don't you just buy a set of Ertel or Ohio Piston 1282P's, any machine shop can get them for you. With those flat top pistons you won't have to bush the rods or machine for floating pins.
As far as the pistons go you will have to bush the piston rods and machine the piston for a floating pin. Why don't you just buy a set of Ertel or Ohio Piston 1282P's, any machine shop can get them for you. With those flat top pistons you won't have to bush the rods or machine for floating pins.
Thread Starter
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Senior User
Joined: Aug 2001
Posts: 163
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From: Florida
need help with pistons...Please!
If i go with ohio or badger pistons compression will only be 9:1. I will probably not surface to much off me heads or block, just enough to achieve 9.7:1. My friend has a 73 ch-vy c-v-tte and he run 9.9:1 on pump gas...he does fine.
Gabe
Gabe
