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Old 01-14-2013, 09:44 PM
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adding the 4 deg comp grinds into the cam , ontop of the 44 ICP ABDC + 15 deg the numbers come out exactly the same as the other sites , I hope that was the error , can anyone agree that makes sense ?

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Old 01-15-2013, 12:35 AM
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Finishing up BBC build quench and dynamic compression questions

Jumbo2, Enter all your figures in the KB's calculator except when you get to the intake valve closing enter 70. This is the intake valve closing figured using the advertised duration. This is what all the other calculators use. I got 10.482 and 8.062.
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Old 01-15-2013, 02:52 AM
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Originally Posted by cdminter59 View Post
First unless you have the correct figures everything is a guess. Assume that the 820 heads have 113cc chambers and the pistons are .015 down in the block. Using a .027 compressed thickness head gasket, a 4.375 gasket bore, and 44+15=59 for intake closing point. Your static compression would be 10.561 and the DCR would be 8.826. I am sure you would hear detonation with these figures. On a BBC you don't want to go over appoximately 9.6 static compression with iron heads.The DCR should be in the range of 7.5-8.5 for 91 octane gas. One option to lower the compression is to machine the dome to .016 which will lower the compression to 9.705 and DCR to 8.125. Like I said this is guessing until you cc the heads and measure how much the pistons are down in the hole. BTW I am using the KB compression calculator. United Engine & Machine Co. Incorporated
to many diffrent answers , the KB calculator sucks but I understand the mistake now.. Why do people say not to go over 9.5:1 with iron heads when so many people do ?
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Old 01-15-2013, 04:39 AM
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Finishing up BBC build quench and dynamic compression questions

It is a known fact that if you have the tight quench, temperature within 170-180 range, a good timing curve, and using 91 octane gas and not running lean their will be no detonation at 9.5:1 compression. It doesn't take long for detonation to destroy an engine. This relieves them of the responsibility if you go ahead and set it up at 10.5:1 and the engine beats itself to death from the inside. There is instances that by using aluminum heads you can get away with 10:1 compression. Look at the 80's and 90's 454s from the factory with 8.5:1 compression. Back in the day when it first came out, it had 11.5:1 compression but we had better octane gas back then. We had lead as an additive instead of corn. You do build an engine expecting it to last with regular maintenance, right?
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Old 01-15-2013, 02:19 PM
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If 10.4:1 static and 8:1 dynamic is too much for 93 octane I might as well just sell the engine and go a diffrent route , It hard to listen to people when 15 people are running the same thing or more problem free , this thread has went to **** now and im ready to give up on my project in fear of causing damage and its just not practical to pull the short block apart to change pistons or spend $1000 on rebuilding iron heads , wanted a hot motor for my street strip toy that might see 3000km of street use a year if lucky a 15 pass down the 1320. Im done asking any more questions

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  #21 (permalink)  
Old 01-15-2013, 03:00 PM
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I can understand your frustration. Let's go back to the beginning and start with the basics....
Cylinder cc's 943.0
Chamber cc's 114.5
Piston dome cc's 25.7
Piston deck height cc's @0.015" 3.5 cc's
Gasket cc's (Fel-Pro Q1037) 9.7

Now, we'll take a very sharp knife and cut the dome off one of the pistons and glue the dome into the combustion chamber.
This will make the piston value zero (0) and the chamber value 88.8 cc's (114.5 less 25.7)

Now, total 943.0, 88.8, 0, 3.5 and 9.7 and find and find 1045.0 cc's.
Subtract the cylinder volume of 943.0 from the total of 1045.0 and find 102.0 cc's. Divide the total 1045.0 by 102.0 and find 10.24:1 Static Compression Ratio with a 0.054" squish. I'd be fine with 0.054" squish on a BBC if it was my build. Using a camshaft that closes the intake valve at 44 degrees ABDC @0.050" tappet lift, the KB calc tells me that the DCR would be 8.564:1. If this was my pile of parts, I'd bolt it together and run it.

If, down the road, you can't get fuel that will resist detonation, buy and install a water/alcohol injection kit. That will absolutely stop detonation. You can use distilled water and high-grade Isopropyl rubbing alcohol from the pharmacy section at Walmart.
Snow Performance : Snow Performance Water Methanol Injection Systems. The Best Most Accurate Gas and Diesel Water Methanol Injection Strategies for Fuel Injected Carbureted Turbocharged Supercharged
AEM Water Injection Kit - AEM 30-3000 | FCP Euro
The Best Water injection system and water methanol injection systems at AlcoholInjectionSystems.com
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Old 01-15-2013, 03:04 PM
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Originally Posted by techinspector1 View Post
I can understand your frustration. Let's go back to the beginning and start with the basics....
Cylinder cc's 943.0
Chamber cc's 114.5
Piston dome cc's 25.7
Piston deck height cc's @0.015" 3.5 cc's
Gasket cc's (Fel-Pro Q1037) 9.7

Now, we'll take a very sharp knife and cut the dome off one of the pistons and glue the dome into the combustion chamber.
This will make the piston value zero (0) and the chamber value 88.8 cc's (114.5 less 25.7)

Now, total 943.0, 88.8, 0, 3.5 and 9.7 and find and find 1045.0 cc's.
Subtract the cylinder volume of 943.0 from the total of 1045.0 and find 102.0 cc's. Divide the total 1045.0 by 102.0 and find 10.24:1 Static Compression Ratio with a 0.054" squish. I'd be fine with 0.054" squish on a BBC if it was my build. Using a camshaft that closes the intake valve at 44 degrees ABDC @0.050" tappet lift, the KB calc tells me that the DCR would be 8.564:1. If this was my pile of parts, I'd bolt it together and run it.

If, down the road, you can't get fuel that will resist detonation, buy and install a water/alcohol injection kit. That will absolutely stop detonation. You can use distilled water and high-grade Isopropyl rubbing alcohol from the pharmacy section at Walmart.
Snow Performance : Snow Performance Water Methanol Injection Systems. The Best Most Accurate Gas and Diesel Water Methanol Injection Strategies for Fuel Injected Carbureted Turbocharged Supercharged
AEM Water Injection Kit - AEM 30-3000 | FCP Euro
The Best Water injection system and water methanol injection systems at AlcoholInjectionSystems.com
If it was your pile of parts what comp hyd roller would you use ? are you adding the 15 deg the calculator ask's you to add ? does the 4 deg comp grinds in make a diffrence ? every other dynamic engine calculator gives me 8:1-8.2:1 dynamic , your number is .5 higher why ?
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Old 01-15-2013, 03:25 PM
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That's where everyone is gettin' their panties all bunched up, by trying to use 3 different calcs. I have used only the KB for decades, so I know that 8.5 on the KB will work with pump gas. I've seen other guys run as high as 8.9 on the KB calc on pump gas without any problems. You guys are trying to overthink this whole mess. Bolt it together and have fun. Don't worry about the advance ground into the cam at the grinders, they all do that. Again, bolt the parts together and have fun.

The above calculations were made with the XR288HR. I think that's the cam you said you wanted to use?
http://www.compcams.com/Company/CC/c...?csid=445&sb=0

Last edited by techinspector1; 01-15-2013 at 03:30 PM.
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Old 01-15-2013, 03:35 PM
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Finishing up BBC build quench and dynamic compression questions

I won't tell you that your setup won't work as is. I really don't know. There is one thing I do know that with a DCR of 8.1 it is suppose to run off 91 octane gas. If you want a hot street engine do it as planned. Just make sure when you choose your cam you have an ICP of 70 using the advertised duration. Assembly the engine carefully, align the head gaskets to make sure all holes line up. Make sure the intake gaskets fit as close to the port size as possible. Use the Cometic .027 MLS gaskets, they are on the expensive side but will give you a .042 quench. Follow the directions do not use any sealer they are coated. For startup, setup your carburetor to run a little rich. If you are going to use EFI that should help with less chance of detonation. Keep temp at 170-180 degrees. Hold the rpms at 3000 and set total timing at 36 degrees. If you are running a hyd roller cam this is better. You can use the " EOIC" is the easiest and most accurate way I have foundto adjust valves cold. When the exhaust valve on a particular cylinder starts opening, adjust the intake rocker on that cylinder. When the intake valve has opened and is on its way back down closing, adjust the exhaust valve on same cyl. If I can be of anymore help let me know.
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Old 01-15-2013, 04:00 PM
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Originally Posted by jumbo2 View Post
so after checking 2 chambers 2x with a spark plug im very confident to say I got 114.5cc chambers on these 820 casting heads

So if I average the piston down the hole I would call it .015 , so im looking for a head gasket from .025 to .030 to keep my quench in check considering im right at 10.5:1 comp ratio I proabably want to keep the quench as tight as possible to avoid detonation

Looks like the only 2 options are cometic or copper , gmpp used to make a .025 but it looks like its discontinued , can anyone add anything ? feels good to get these measurements finally done !!!
Did you measure the piston dome at its highest point. That is where the installed hieght should come from. Then the piston dome cc number from the mfr is from the top of the dome down to the head of the piston. I would put the piston at tdc and cc them as well all the way to the top of the cylinder. If they dont proturde. Then its a little trickier cause you cant cc the piston at tdc. But you can roll it down a few mm until it will clear the plex and. Then measure how far down they are and move to tdc figure how many ccs account for them being lower and subtract. Assuming they are not full pop ups.

With this measure ment you can do the math alot easier. The dcr calculators do a simple calculation that figure how many mm down in the hole the piston is when the valve closes then does the static cr calc at that adjusted storke length. I think you can find the calc on the net pretty easy. Just trying to take some of the mystery out of the entire process. Best to get the measurement from your engine on final assembly then order gaskets. You may find its not going to be an issue or just the opposit. Best to check and be sure.
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Old 01-15-2013, 05:52 PM
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Did you measure the piston dome at its highest point. That is where the installed hieght should come from. Then the piston dome cc number from the mfr is from the top of the dome down to the head of the piston. I would put the piston at tdc and cc them as well all the way to the top of the cylinder. If they dont proturde. Then its a little trickier cause you cant cc the piston at tdc. But you can roll it down a few mm until it will clear the plex and. Then measure how far down they are and move to tdc figure how many ccs account for them being lower and subtract. Assuming they are not full pop ups.

With this measure ment you can do the math alot easier. The dcr calculators do a simple calculation that figure how many mm down in the hole the piston is when the valve closes then does the static cr calc at that adjusted storke length. I think you can find the calc on the net pretty easy. Just trying to take some of the mystery out of the entire process. Best to get the measurement from your engine on final assembly then order gaskets. You may find its not going to be an issue or just the opposit. Best to check and be sure.
I don't have a clue what this means or how it pertains to my situation , I have my engine measurements and compression calculated ?
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