whatsamerc??
Well-Known Member
I have a 77 motorhome 440 that has dished .060 over pistons in it. The only numbers i can find on them are 1886 inside of the skirt. I cant find any info on them and was someone might know what they are.
Its already .060 over though. The bores are in really good shape but i hate to put new pistons in old holesThrow those cast pistons in the trash. They were junk before they were installed. And they didn't get better over the years
I'll get a measurement this friday. I dont mind fairly low compression because its going in a driver and id like to run cheap gas but 7.5 to 1 is pitiful.Do you have a deck height or a compression height measurement?
Agree with toolmanmike. Likely way under 8 to 1, unless an over two inch compression height.
Then hone it and run new pistons. You don't have to bore for new pistons.Its already .060 over though. The bores are in really good shape but i hate to put new pistons in old holes
Do you have a dial caliper? You can measure comp.height of the piston and figure out what the expected deck height should be.Compression height is the distance from the center of the pin to the flat area at the top of the piston.
Measure the pin diameter. Measure from the bottom of the pin to the flat of th top of the piston, then subtract half of the pin diameter.
Over two inches, you might have some compression. Zero deck, if I remember right, is somewhere around 2.06" . Too lazy to calculate it exactly right now.
Around 1.9" to 1.95, you might be looking at 7
Yeah, ill get it measured friday. ThanksDo you have a dial caliper? You can measure comp.height of the piston and figure out what the expected deck height should be.Compression height is the distance from the center of the pin to the flat area at the top of the piston.
Measure the pin diameter. Measure from the bottom of the pin to the flat of th top of the piston, then subtract half of the pin diameter.
Over two inches, you might have some compression. Zero deck, if I remember right, is somewhere around 2.06" . Too lazy to calculate it exactly right now.
Around 1.9" to 1.95, you might be looking at 7 to 1.
Comp height is 1.98. The piston is .050 down from the deck. The dish is .30 deep and the dish starts .500 in from the edge.Do you have a dial caliper? You can measure comp.height of the piston and figure out what the expected deck height should be.Compression height is the distance from the center of the pin to the flat area at the top of the piston.
Measure the pin diameter. Measure from the bottom of the pin to the flat of th top of the piston, then subtract half of the pin diameter.
Over two inches, you might have some compression. Zero deck, if I remember right, is somewhere around 2.06" . Too lazy to calculate it exactly right now.
Around 1.9" to 1.95, you might be looking at 7 to 1.
Comp height is 1.98. The piston is .050 down from the deck. The dish is .420 deep and the dish starts .500 in from the edge.
Wow! So basically what you are saying is ..... high sixes to one?Does the block appear to be decked?
The nominal stock deck height for an RB block is 10.720”.
With an uncut block, pistons with a C/H of 1.980 should be close to .100” down the hole at TDC.
If the top of the dish is 1” smaller than the bore, and the bottom of the dish is .750” smaller than the top……. And you average those two bore sizes it’s a hole 3.905” …….. x .420” deep.
Which would be a dish that’s about 82cc worth.
Whereas a .060” over flat top piston that’s down the hole .150” is “only” 37cc’s.
It is a remanufactured motor so it could be decked. I re measured the dish and it is .300 deep 3.380 at the top and 3.88 at the bottom. The formula i found put it at 43cc. I used summits compression calculator and came up with 7.15 to 1 with a steel shim head gasket.Does the block appear to be decked?
The nominal stock deck height for an RB block is 10.720”.
With an uncut block, pistons with a C/H of 1.980 should be close to .100” down the hole at TDC.
If the top of the dish is 1” smaller than the bore, and the bottom of the dish is .750” smaller than the top……. And you average those two bore sizes it’s a hole 3.905” …….. x .420” deep.
Which would be a dish that’s about 82cc worth.
Whereas a .060” over flat top piston that’s down the hole .150” is “only” 37cc’s.
It has 906 headsIf your thinking about spending money on the original motorhome heads, don't, limited potential
I can’t really imagine me reusing those big dished 440 pistons in anything I was hoping to make any kind of power with.
See post #22. lolIt is a remanufactured motor so it could be decked. I re measured the dish and it is .300 deep 3.380 at the top and 3.88 at the bottom. The formula i found put it at 43cc. I used summits compression calculator and came up with 7.15 to 1 with a steel shim head gasket.
Ive been thinking seriously about a turbo. I wonder how much boost a cast crank can stand.See post #22. lol
I don't know, but I can tell you in horse power terms. The Chrysler nodular iron cranks are good for 500HP in stock trim. They can be lightened and balanced to the Nth degree and run a GOOD quality balancer and take more than that. What you're gonna have to be careful with are the pistons. Do NOT run it lean. I would run it a little on the fat side and you'll probably never have an issue under 10PSI. I'd run the 6-71 though. lolIve been thinking seriously about a turbo. I wonder how much boost a cast crank can stand.