351M/400 Pistons
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Joined: May 2003
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351M/400 Pistons
I am in the process of rebuilding a 351m to a 400 and have seen numerous articles and forum posts about Ohio Piston and Dynagear having pistons for this engine in 9.5:1 compression ratio. After just about sending my parts man over the edge during a 3 week period the best he could come up with were 8.4:1. I was told that Ohio Piston is out of business and could not find a part number for Dynagear in 9.5:1. Ross Racing Pistons seems to be the only company that will get me where I would like to be.
I have considered bushing the rods and using 351C pistons but was concerned about the downside (spinning a bushing) since I race Dirt Oval in Truck Class. Also the cost of bushing the rods and getting 351C pistons is comparable to Ross, within a couple hundred bucks anyway.
The bottom line is:
Are there Dynagear 9.5:1 for a 400 and what is the part number?
Is Ohio Piston no longer an option?
Thanks
I have considered bushing the rods and using 351C pistons but was concerned about the downside (spinning a bushing) since I race Dirt Oval in Truck Class. Also the cost of bushing the rods and getting 351C pistons is comparable to Ross, within a couple hundred bucks anyway.
The bottom line is:
Are there Dynagear 9.5:1 for a 400 and what is the part number?
Is Ohio Piston no longer an option?
Thanks
Tuned
Joined: Jul 2003
Posts: 455
Likes: 3
From: Berkeley
351M/400 Pistons
There was a set of .030-over dynagear/ohio flat-tops (1.64 c.h., 4cc relief) on ebay the other day... (those are mine now :-)
The same guy(s) had a set of .060-overs, but those sound kinda scary, as i understand one shouldn't bore a 400 block out more than .030"... (or am i confused? do .030-over pistons require increasing the bore RADIUS by .030"? or does one increase the radius by .0015, resluting in .030 increase in bore DIAMETER?)
anyways, my point is that they do seem to turn up on ebay every so often. just gotta keep an eye out... good luck!
The same guy(s) had a set of .060-overs, but those sound kinda scary, as i understand one shouldn't bore a 400 block out more than .030"... (or am i confused? do .030-over pistons require increasing the bore RADIUS by .030"? or does one increase the radius by .0015, resluting in .030 increase in bore DIAMETER?)
anyways, my point is that they do seem to turn up on ebay every so often. just gotta keep an eye out... good luck!
Senior User
Joined: Apr 2002
Posts: 155
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From: KC Metro
351M/400 Pistons
You are correct, 60 over IS a scary overbore.
When I took the old block out of my 78 bronco to get rebuilt, it had previously been rebuilt and bored .060 over with the pistons that matched. Needless to say, we dumped that block off and got a hold of a fresh 71 block. We bored it 20 over, had all of the rest of the work done as well. Still waiting to fire up the new engine though.
It is said that .040 is the very maximum size, so I would say to be safe, stay at .030.
That is just my opinion though.
-Daniel
When I took the old block out of my 78 bronco to get rebuilt, it had previously been rebuilt and bored .060 over with the pistons that matched. Needless to say, we dumped that block off and got a hold of a fresh 71 block. We bored it 20 over, had all of the rest of the work done as well. Still waiting to fire up the new engine though.
It is said that .040 is the very maximum size, so I would say to be safe, stay at .030.
That is just my opinion though.
-Daniel
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