Compression and Pistons
Senior User
Joined: Aug 2001
Posts: 250
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Compression and Pistons
You were right on the cup size. It is 13cc. I spoke with the engine builder this morning to get a little more info. The number is KB148 on the pistons. his B looked like 13. He also said "0" deck height means that. The highest point on the piston is the same as the deck.
So my queston is does the 13cc cup mess up the quench of my Aussie heads?
So my queston is does the 13cc cup mess up the quench of my Aussie heads?
Senior User
Joined: Dec 2001
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From: space city
Compression and Pistons
[updated:LAST EDITED ON 05-Aug-02 AT 02:22 PM (EST)]no - the dish on the KB's is shaped to work WITH quench heads .
but even with flat-tops, the whole quench thing (regardless of what kind of engine) won't work if there is more than .060 between the flat top part of the piston and the flat part of the head, and it works better the less clearance there is, with .040 being a good compromise between GOOD quench and not banging pistons into the heads - according to speed-pro, KB, and other web pages.
if they milled your block down .047, which is what it takes to get zero deck with the KB's on a 400, then you should have about 11:1 with a 12 or 13cc d-cup. i think it takes about 24cc to get 9.8:1 - IF the block has been cut down to 10.250 deck (.047 off).
if that .047 mill was done, then you're running around on 91 octane with 11:1, and only slight knocking!
but even with flat-tops, the whole quench thing (regardless of what kind of engine) won't work if there is more than .060 between the flat top part of the piston and the flat part of the head, and it works better the less clearance there is, with .040 being a good compromise between GOOD quench and not banging pistons into the heads - according to speed-pro, KB, and other web pages.
if they milled your block down .047, which is what it takes to get zero deck with the KB's on a 400, then you should have about 11:1 with a 12 or 13cc d-cup. i think it takes about 24cc to get 9.8:1 - IF the block has been cut down to 10.250 deck (.047 off).
if that .047 mill was done, then you're running around on 91 octane with 11:1, and only slight knocking!
Senior User
Joined: Aug 2001
Posts: 163
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From: Florida
Compression and Pistons
Hey guys, I've read all the posts on this topic, and some of it is another language to me! I'm trying to research parts for my engine, being the first truck and engine I've ever restored, things get confusing and difficult at times. I have a 1979 351m with stock heads (78.4cc i assume) which I'm turning into a 400. I dont know how to pick out the pistons. I want to use 351 cleveland pistons. Can anyone tell me what Cleveland pistons will give me 9.5 to 9.9 compression. My goal was 9.7. I dont want anything under 9.5, and I want to stay under 9.9. If any of you know can you tell me what piston to use, and even what part number they are if you have it. Can you tell me what CR they would give me.
I came to ya'll cause I talked to a shop, summit, and a long time mechanic and no one really wants to help, everyone tells me something different and what they say is a better idea.
Help me please,
Gabriel
I came to ya'll cause I talked to a shop, summit, and a long time mechanic and no one really wants to help, everyone tells me something different and what they say is a better idea.
Help me please,
Gabriel
Freshman User
Joined: Jun 2002
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Compression and Pistons
>actually the highest octane we have here in the u.s is 130
>octane. ita called turbo blue and is about $4.50 a gallon
>last i checked.
>
>any how the highest pump gas i've seen is 94 octane and it's
>usually carried by exxon. some places have it some don't.
>guess it depends on your locale.
>
>
>later.......:P
sorry about the typo on the 130 octane turbo blue. i meant 104 octane. must of been half asleep. but i still stand by exxon carrying the 94 octane. i filled up there yesterday and there it was big as life on the pump. so maybe it's just in my area or you need to check for an exxon in your area.
later.......:P
>octane. ita called turbo blue and is about $4.50 a gallon
>last i checked.
>
>any how the highest pump gas i've seen is 94 octane and it's
>usually carried by exxon. some places have it some don't.
>guess it depends on your locale.
>
>
>later.......:P
sorry about the typo on the 130 octane turbo blue. i meant 104 octane. must of been half asleep. but i still stand by exxon carrying the 94 octane. i filled up there yesterday and there it was big as life on the pump. so maybe it's just in my area or you need to check for an exxon in your area.
later.......:P
Senior User
Joined: Aug 2001
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Compression and Pistons
Teamwizaed there is a great article in here on building a 400. A friend of mine used it to build his. His truck has gobbs of torque and runs really good. You might check it out. Do a search in the tech section.
New User
Joined: Aug 2002
Posts: 2
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Compression and Pistons
I am using KB 351C Flat top pistons part #UEMKB 177030-8
and stock 400 78CC heads. When I CCed every thing I came
up with 9.83 to 1 compression. I have been checking around
to see how accurate I am. Would someone please let me know
if I'm close.
1978 Ford Bronco
David Jarvis
and stock 400 78CC heads. When I CCed every thing I came
up with 9.83 to 1 compression. I have been checking around
to see how accurate I am. Would someone please let me know
if I'm close.
1978 Ford Bronco
David Jarvis
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Elder User
Joined: Sep 2001
Posts: 887
Likes: 1
From: Jax FL
Compression and Pistons
[updated:LAST EDITED ON 19-Aug-02 AT 00:31 AM (EST)]back to the gas issue
ron 98 - uses in austrailia is the same as 93 used in the states
ron 95 - uses in austrailia is the same as 91 used in the states
this should calm some people dwon a bit.
also, i know a lot of people that just put aussie heads on their stock engines, and no pinging that i have heard. i live in jax fl and we are like 15ft above sea level
rule of thumb i have always gone by is; you will start to ping around 9.5-10.0
i think a lot of are worrying over nothing.
ron 98 - uses in austrailia is the same as 93 used in the states
ron 95 - uses in austrailia is the same as 91 used in the states
this should calm some people dwon a bit.
also, i know a lot of people that just put aussie heads on their stock engines, and no pinging that i have heard. i live in jax fl and we are like 15ft above sea level
rule of thumb i have always gone by is; you will start to ping around 9.5-10.0
i think a lot of are worrying over nothing.
New User
Joined: Aug 2002
Posts: 2
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Compression and Pistons
You should have a litte more than 9.5. Because 351C with
with 78cc heads has 9.5 and the extra stroke and bore of
the 400 will give you more compression. I'm using bore,
stroke,deck height,head cc,3cc valve relief in piston,
head gasket volume, and volume sweep. The TRW catalog
gives the comp. of the 351C with a flat top and 78cc
heads.
78 ford bronco
D. Jarvis
with 78cc heads has 9.5 and the extra stroke and bore of
the 400 will give you more compression. I'm using bore,
stroke,deck height,head cc,3cc valve relief in piston,
head gasket volume, and volume sweep. The TRW catalog
gives the comp. of the 351C with a flat top and 78cc
heads.
78 ford bronco
D. Jarvis
Junior User
Joined: Nov 2002
Posts: 98
Likes: 0
From: Connecticut
Compression and Pistons
I have been wondering these same questions myself about max compression vs octane rating and im going to try and give 10:1 a shot and see what happens, hey i could always put in a thicker gasket...
Anyways, one of these posts raised a question in my mind. Someone mentioned earlier that having a low rpm cam makes it more difficult with high compression, i assume making it more likely for detonation. If your camshaft throws a lower intake duration, less volume will be inhaled, thus the dynamic compression is lower than something like a pro street cam. So why is this a problem? I must be missing something.
And, how about timing, can it be retarded enough to still have good driveablity and no detonation?
Anyways, one of these posts raised a question in my mind. Someone mentioned earlier that having a low rpm cam makes it more difficult with high compression, i assume making it more likely for detonation. If your camshaft throws a lower intake duration, less volume will be inhaled, thus the dynamic compression is lower than something like a pro street cam. So why is this a problem? I must be missing something.
And, how about timing, can it be retarded enough to still have good driveablity and no detonation?
