comp ratio
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Senior User
Joined: Sep 2003
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From: northwestern missouri
comp ratio
does anyone know what compression ratio a 78 351m with stock heads and guts with a mild cam and aluminum intake would be runing?....thanks for the help in advance
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Senior User
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From: northwestern missouri
need t find out what comp ratio i have to go from there to beable to run my cam and upgrades...going with a comp extreem energy cam w/ 584/588 lift and 110 deg. lobe sep matched valve springs, lifters locks, seals, retainers, port and polished heads matched single plane intake, double rolers timing chain...to start more goodies to come
Tuned
Joined: Jul 2003
Posts: 455
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From: Berkeley
stock compression on '78 351M is around 7.74:1, according to:
http://home.earthlink.net/~bubbaf250...history03.html
and there's good info here, too:
http://www.projectbronco.com/Technic...e_build_up.htm
http://home.earthlink.net/~bubbaf250...history03.html
and there's good info here, too:
http://www.projectbronco.com/Technic...e_build_up.htm
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Senior User
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From: northwestern missouri
i appreciate the info packlet from what i understand the car 351m have the 7.74:1 ratio and the truck block have a slightly higher ratio 8.0:1 which is good for me to do all the mods to my motor i need to be running @ 9.5:1 or higher so going from an 8.0:1 to 9.5:1 wont be all that bad or expensive but once again i appreciate the info....as well if ou know anywere i could pick up a high rise single plane intake for the 351m with rpm range of around 1500-2500 to 7000+ let me know summit sucks and i cant find one there
Posting Guru
Joined: Aug 2000
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From: (near) Denver USA
No one makes a single-plane manifold for the M-block 351M/400 engine.
Back in the late '70s, both Edelbrock and Holley used to make low-rise, single-plane manifolds for the M-block. The Edelbrock manifold was the StreetMaster and the Holley manifold was the Street Dominator.
Check ebay. They show up there on a regular basis.
Back in the late '70s, both Edelbrock and Holley used to make low-rise, single-plane manifolds for the M-block. The Edelbrock manifold was the StreetMaster and the Holley manifold was the Street Dominator.
Check ebay. They show up there on a regular basis.
Posting Guru
Joined: Aug 2000
Posts: 1,127
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From: (near) Denver USA
I've never seen or heard of a commercially produced high-rise manifold for the M-block engines. If you really want a high-rise unit, you'll have to adapt a 351C manifold.
I don't think it makes sense to spin a 351M to 7K rpm, but if you're serious about it, then you have a lot more expensive issues than the intake manifold to worry about.
If you want it to look really cool (until it explodes at 7K+ rpm), there's the BDS #578-3S1/2 blower and manifold kit.
I don't think it makes sense to spin a 351M to 7K rpm, but if you're serious about it, then you have a lot more expensive issues than the intake manifold to worry about.
If you want it to look really cool (until it explodes at 7K+ rpm), there's the BDS #578-3S1/2 blower and manifold kit.
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From: northwestern missouri
well iam not worried about the innerds comming apart iam just wanting to suck the most power out of the cam i can and to do that i need the high rise intake dual or single plane and if it comes apart it comes apart it happens just as long as i was having fun doing it. i mean i built a 350 chevy that would spin 7500 no problem now iam wanting to do it with the new ford beast...how would i adapt a 351c intake to the 351m? blower would be nice but the motor has to look at least somewhat normal for the truck to pass the all mighty missouri inspection. and i dont think blower would accually trip their stingy triggers. i have been thinking about a webber set up as well but i havent really looked into it so much. that would really make the truck look mean with some offset chrome velocity stacks poking out of the hood. but not really economical when iam throwing mud everywere.. know what i mean?
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Senior User
Joined: Sep 2003
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From: northwestern missouri
now on a more serious side i know 351c had 2v and 4v heads did the 351m have these? and if so how do i id them? the motor is damn near brand new i have paper work on it but no specs all the paper work i have is waranty crap.
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Senior User
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From: northwestern missouri
danlee now with the adapter kit does that adapt the 351c intake to 351m heads or do i need 351c heads. as well if i need 351c heads i will go with the 4v how will that affect compression ratio as well any overall performance of the motor?
Postmaster
Joined: Aug 2001
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From: Delaware
The adapter is made to mate a 351C-4V intake of your choice to any 2V head on an 'M' block. However with a little machine work, it can be used to mate a 351C-4V intake to a 351C-4V head.
Tom Monroe's book says that a 351M with a 78.4 cc head is 8.0:1 CR. If you install a 4V Cleveland with a 75.4 cc head the CR is 8.2:1. If you get a set of closed chamber heads with 62.8cc, then your CR will be 9.2:1. That should work well with a mild cam, but don't expect to see 7500 RPM without some exhaust port work.
There is a TRW replacement piston for the 351M that will give you a little more compression. If I were going to replace pistons on a 351M, I would also replace the crank with a 400 crank. Of course then you will need a 400 piston. If you use a flattop piston for a 400, and 62.8cc heads, you will have 10.4:1 CR.
Tom Monroe's book says that a 351M with a 78.4 cc head is 8.0:1 CR. If you install a 4V Cleveland with a 75.4 cc head the CR is 8.2:1. If you get a set of closed chamber heads with 62.8cc, then your CR will be 9.2:1. That should work well with a mild cam, but don't expect to see 7500 RPM without some exhaust port work.
There is a TRW replacement piston for the 351M that will give you a little more compression. If I were going to replace pistons on a 351M, I would also replace the crank with a 400 crank. Of course then you will need a 400 piston. If you use a flattop piston for a 400, and 62.8cc heads, you will have 10.4:1 CR.