Piston/compression height?

[dorin48]

Problem: Want a forged piston but nobody manufactures. TRW used to make a piston but it ups the compression, which I dont want. (trying to work all the details out of a turbo build, 1977 Ford 351m)

Possible routes: Custom = $$$$$
Sister engine= different compression height

Basically I need to figure out which piston will work but I am not sure how the math works.

I have a 351m which is identical to the 70's 400 except for the crank(more stroke) and pistons(shorter compression height). The difference in the height is .3 inches. If i were to just put the 400 pistons in I would end up with a 5.5=1 CR.

So the 351 cleveland's pistons are almost identical to the 400's and there are many forged piston options.

Pistons are sold by CR and bore, not compression height. I need to figure out which 351c piston will work in my 351m while keeping as close to the factory compression as possible.

Picking a 351c piston with a higher CR will obviously counter the compression height problem but how much?

Also, will this ruin my quench area?

Important numbers

Bore = 4.00"
Stroke = 3.50"
Combustion Chamber = 78.4cc
Deck height = 10.297

Reps+ around for valid responses. :goodjob:

[teh_mugen18]

Wow that compression is extremely low, 5.5:1?? That motor will barely move when its not in boost!

[TommyD1919]

you can buy an off the shelf high comp. piston like the trw ones and have them milled to meet your comp. needs... However I would have some custom ones built. if you need a number to a guy that would know PM me.

[dorin48]

Wow that compression is extremely low, 5.5:1?? That motor will barely move when its not in boost!

.... read the whole thing. I was not going to run that setup.


you can buy an off the shelf high comp. piston like the trw ones and have them milled to meet your comp. needs... However I would have some custom ones built. if you need a number to a guy that would know PM me.

Once again, read the whole post. I am not buying custom pistons and there are no high comps avail for my engine directly anymore. TRW stopped making them.

[BABY J]

Waits for Init2winit to chime in.

[Init2winit]

Problem: Want a forged piston but nobody manufactures. TRW used to make a piston but it ups the compression, which I dont want. (trying to work all the details out of a turbo build, 1977 Ford 351m)

Possible routes: Custom = $$$$$
Sister engine= different compression height

Basically I need to figure out which piston will work but I am not sure how the math works.

I have a 351m which is identical to the 70's 400 except for the crank(more stroke) and pistons(shorter compression height). The difference in the height is .3 inches. If i were to just put the 400 pistons in I would end up with a 5.5=1 CR.

So the 351 cleveland's pistons are almost identical to the 400's and there are many forged piston options.

Pistons are sold by CR and bore, not compression height. I need to figure out which 351c piston will work in my 351m while keeping as close to the factory compression as possible.

Picking a 351c piston with a higher CR will obviously counter the compression height problem but how much?

Also, will this ruin my quench area?

Important numbers

Bore = 4.00"
Stroke = 3.50"
Combustion Chamber = 78.4cc
Deck height = 10.297

Reps+ around for valid responses. :goodjob:You're shit out of luck for a shelf piston.

[Da_unknown]

damm

[dallasb84]

why are you so afraid of custom pistons.......


je pistons custom makes all orders if you buy direct...... it just so happens that i bought a custom slug from them a few months back when i built my motor....

there really isnt a price issue...


as far as trying to find a high compression piston you will need the to know stroke and deck height of the 351c and m. you will need to find the specific measurements of each 351c piston available and compare them in a compression calculator....

one thing to be aware of is dome design on the high compression pistons you might use... high compression pistons sometime extend past the deck height and into the combustion chamber..... if you use a raised dome piston to accomodate the difference between the stroke of the 351c&m it might put more stress from combustion to the edges of the piston and towards the cylinder walls...... might not work so good.

call je and see what they have in options as far as pistons go for the clevland...


i think it would be more realistic for them to go ahead and cut you a proper set of slugs for what ever it might be that your building....

[SPOOLIN]

custom pistons are not that much more expensive than shelf pistons.

[smote]

just junk the 351m and build a windsor. they are cheaper to build, have a ton of aftermarket support and will make more power.