Bbc SC deck height
02-03-2017, 08:01 PM
#21
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You can get flat tops that are blower pistons. But, I do agree. A blower piston will have the Top ring down .300+, thicker piston, etc. Also, the wrist PIN. Most forget about the pin. I have JE blower pistons, with upgraded .180 wall , series 52 High Carbon steel through hardened pin. I believe the standard JE pin, is a series 51, low carbon steel pin.
02-03-2017, 08:11 PM
#22
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You can get flat tops that are blower pistons. But, I do agree. A blower piston will have the Top ring down .300+, thicker piston, etc. Also, the wrist PIN. Most forget about the pin. I have JE blower pistons, with upgraded .180 wall , series 52 High Carbon steel through hardened pin. I believe the standard JE pin, is a series 51, low carbon steel pin.
02-03-2017, 08:46 PM
#23
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What about the deck height and gasket height with over all quench scinereo? I know you have researched this and have info that could potentially help. Amazing how much you can research this and still be lost. You've obliviously got a good thing going on with your builds so why not use them as an example of what's proven to work. Btw both blocks are identacle.
Its not nearly as critical as a N/A engine, and even N/A engines, its not do or die like some make it out to be. Some guys will chase a super tight quench, thinking anything over .050 is horrid. Theres tons of marine BBC's running around with pistons .02 in the hole, with a .040 fel pro gasket, just fine.
I'd prob shoot for .050-.060. A little more, little less is fine.
As far as the static compression goes, on a traditional roots build, I like between 8 to 8.5:1 for the most part. If youre blower limited, with a small blower, then you want to keep the static up, and the cam small (minimal overlap). If you have enough blower, the lower static, more overlap, and more boost, will walk all over a small cammed , low boost, higher compression deal.
Meaning, an 8:1 engine, with a healthy cam, and 10lbs of boost, will generally outperform a 9:1, 5lb boost, small cam setup on the big end. Big torque numbers in the low end from short cams and high static, are nice, but also leads to big cylinder pressures that can cause detonation. Lots of ways to skin the cat.
High static compression, can make high PEAK cylinder pressures. But high PEAK cylinder pressures, aren't what make supercharged engines make big numbers. It high AVERAGE cylinder pressures that get it done. Its why a 565 thats 12:1 NA, still wont make the power that an 7.5:1 565 will make, with 10lbs of boost. Although the final compression ratios both may be 12.5:1, and both be limited to a particular octane level before detonation occurs.
02-03-2017, 09:02 PM
#24
Geronimo36
Gold Member
I'm surprised that piston to wall clearance, piston material, bore size and rpm aren't talked about in this thread when considering compression distance. Its all a factor.
02-03-2017, 09:18 PM
#25
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What about the deck height and gasket height with over all quench scinereo? I know you have researched this and have info that could potentially help. Amazing how much you can research this and still be lost. You've obliviously got a good thing going on with your builds so why not use them as an example of what's proven to work. Btw both blocks are identacle.
Last edited by mike tkach; 02-03-2017 at 09:26 PM.
02-03-2017, 11:25 PM
#26
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I personally wouldn't get too wrapped up in it. Fel Pro's MLS gaskets, are avail in .041 and .053 if I recall. Cometics, you can go much thicker if desired, but the price also goes up a good amount. If you're truly .010 in the hole, I'd go with the .041. IF you're 0 decked, I'd go .053.
Its not nearly as critical as a N/A engine, and even N/A engines, its not do or die like some make it out to be. Some guys will chase a super tight quench, thinking anything over .050 is horrid. Theres tons of marine BBC's running around with pistons .02 in the hole, with a .040 fel pro gasket, just fine.
I'd prob shoot for .050-.060. A little more, little less is fine.
As far as the static compression goes, on a traditional roots build, I like between 8 to 8.5:1 for the most part. If youre blower limited, with a small blower, then you want to keep the static up, and the cam small (minimal overlap). If you have enough blower, the lower static, more overlap, and more boost, will walk all over a small cammed , low boost, higher compression deal.
Meaning, an 8:1 engine, with a healthy cam, and 10lbs of boost, will generally outperform a 9:1, 5lb boost, small cam setup on the big end. Big torque numbers in the low end from short cams and high static, are nice, but also leads to big cylinder pressures that can cause detonation. Lots of ways to skin the cat.
High static compression, can make high PEAK cylinder pressures. But high PEAK cylinder pressures, aren't what make supercharged engines make big numbers. It high AVERAGE cylinder pressures that get it done. Its why a 565 thats 12:1 NA, still wont make the power that an 7.5:1 565 will make, with 10lbs of boost. Although the final compression ratios both may be 12.5:1, and both be limited to a particular octane level before detonation occurs.
Its not nearly as critical as a N/A engine, and even N/A engines, its not do or die like some make it out to be. Some guys will chase a super tight quench, thinking anything over .050 is horrid. Theres tons of marine BBC's running around with pistons .02 in the hole, with a .040 fel pro gasket, just fine.
I'd prob shoot for .050-.060. A little more, little less is fine.
As far as the static compression goes, on a traditional roots build, I like between 8 to 8.5:1 for the most part. If youre blower limited, with a small blower, then you want to keep the static up, and the cam small (minimal overlap). If you have enough blower, the lower static, more overlap, and more boost, will walk all over a small cammed , low boost, higher compression deal.
Meaning, an 8:1 engine, with a healthy cam, and 10lbs of boost, will generally outperform a 9:1, 5lb boost, small cam setup on the big end. Big torque numbers in the low end from short cams and high static, are nice, but also leads to big cylinder pressures that can cause detonation. Lots of ways to skin the cat.
High static compression, can make high PEAK cylinder pressures. But high PEAK cylinder pressures, aren't what make supercharged engines make big numbers. It high AVERAGE cylinder pressures that get it done. Its why a 565 thats 12:1 NA, still wont make the power that an 7.5:1 565 will make, with 10lbs of boost. Although the final compression ratios both may be 12.5:1, and both be limited to a particular octane level before detonation occurs.
So would we want a 650 hp motor with 5 lbs of boost/200 hp minus parasitic or would we rather have 600 hp with 10 lbs of boost, ie a extra 400hp?its actually not quite that simple though as parasitic loss goes up exponentially.
Personally i ran 8.5-1 , 10 in hole w .042 head gaskets and 14 lbs boost (blown 540).
I did switch once to diamond pistons that were pretty much zero decked w head gasket compressed to .039 i had a few pistons touching heads enough to knock ring seal out of motor (.0065 wall) Im surprised to see another poster saying he successfully ran .027s .010 in hole blown. If i had zero decked pistons i would run .053 minimum head gaskets after my last experience,fwiw, Smitty
02-04-2017, 08:39 AM
#28
This has been discussed before however what is the magic number on the piston below deck? This is debatable question and can ask 10 different people and get 7 different answers so the question is more directed toward SC builds with hands on experience. At the same time what is considered a good target quench. I have my own experience with such however on lower hp builds and mostly NA builds. 555 SC 8.5:1 comp build.
NA I'd typically be btwn 005-008 in the hole with .040 gasket with a total of .045-.048 quench. seems like many engine builders try and end up with 0 to .010 deck height to help avoid detonation. SC being a little more forgiving??? Forced induction and chambers can change things up but how much?
NA I'd typically be btwn 005-008 in the hole with .040 gasket with a total of .045-.048 quench. seems like many engine builders try and end up with 0 to .010 deck height to help avoid detonation. SC being a little more forgiving??? Forced induction and chambers can change things up but how much?
02-04-2017, 09:18 AM
#30
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[ATTACH=CONFIG]564430[/ATTACH]
Here is a little 540 that I built many years ago.
8.2-1 compression, 10 pounds of boost. ran for years
My current 509 is going on 230hrs without having the bottom end apart. Makes a little over 700hp with 5 pounds of boost.
Currently building a pair of 555's with blowers. The one thing that they all have in common is that they all have JE -20cc blower pistons
Here is a little 540 that I built many years ago.
8.2-1 compression, 10 pounds of boost. ran for years
My current 509 is going on 230hrs without having the bottom end apart. Makes a little over 700hp with 5 pounds of boost.
Currently building a pair of 555's with blowers. The one thing that they all have in common is that they all have JE -20cc blower pistons
