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Discussion Starter · #1 ·
I just picked up my new hypertech pistons from Speed Pro today. They are an awsome sight. They are made for a 302 with a cleveland head. they are .030 and have a nuckle just like the original Boss 302 and the skirts sre even coated. $170 plus shipping from my local speed shop, I tink I gota good deal. I know I could have gotton them from Highlander(i think thats right) but with TRW goin out they said it could be a problem.
Anyway what I am planing on doin is puting these bad boys in a 351W block with a scat 3.85 crank and the stock 351W rod. It makes sense to me that if you can use a stock 302 piston and make a 393 then it should work with these because they was made for the stock 302 rod in a 302.
I have made out of 3/16 x 3.5 inch steel plates my intake adapters so I can run a 351W intake on it with the Cleveland 2V head.
Does anybody see any problems with my math here? I think it will work......Bob
 

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I hope they have a descent dish unless you want 13:1 compression. That is how KB makes all of the money on the 393 pistons, no one else makes a 302 piston with that big of a dish. This is just what I found. If you play with the compression calculator on the home page you can figure out what you need.
Chris
 

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Some of the pistons made for a 302 will not work in the 393 stroker. Seems that the skirts of the piston will come in contact with the crank at the bottom of the stroke.
You might want to do a search in the archives about this.
 

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I purchased Speed Pro #273 302 pistons for use in my 393. Some preliminary calculations show that with a 64cc chamber I will have around 11:1 compression which is way too much for pump gas. I have measured the valve reliefs in these pistons to be 9cc. I am waiting for my block to be finished so that I can do a mock installation on one piston and rod to verify the volume. I have a milling machine and rotary table so I plan to cut a dish the necessary size to end up with around 9.5:1, which should mean I need to take out an additional 11cc or so. I have heard of some people who have experienced skirt clearance problems with these pistons while others say it is a drop in. Only time will tell.
Danny
 

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Discussion Starter · #5 ·
The pistons are high compression. They have a .100 dome just like the original Boss piston. This is not for a street machine. With a 76c cleveland 2V head I should have at most 10 to 1 but more likely 9.5. I have run into the piston skirt issue and I dont think it is an issue here. it is piston number h557p and can be found at flatlander(not highlander as in previous post)but I got mine here locally.....Bob
 

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I hope they work for you.
If you have a pop up with valve reliefs that nets you the equivalent of a flat top, then with the 3.85 stroke and the 76cc head you will have 10.5:1. If the pop up is mellow and the reliefs large and the net is say -5cc, then the cr will be 10.0:1.
Good luck.
 

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I hope this isn't a problem but...
In doing the math, those 302 boss/clevor pistons have about a 7cc dome. That means with 76.2cc head and a 302's 3" stroke the comp ratio is 8.93:1.
However, when you lengthen the stroke to a 393's 3.85" the compression jumps to 11.22:1
 
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