Hi at all, I want to use the DCR calculator to calculate my cylinder head gasket. I want a static compression of about 9.5:1 and a dynamic compression of about 7.5 I have determined a gasket of 0.070 with the calculator from Pat Kelley. (SCR 9.46 / DCR 7.59) If I enter the same data into the 396maro.com calculator, I get a SCR 9.47 and DCR 8.94 If I set the ABDC from 34 to 65, I get a DCR 7.55 What am I doing wrong? I have attached a picture of my cam card and the 396maro.com calculator Regards Michael
Michael, try this one: Wallace Racing: Dynamic Compression Ratio Calculator Are you using connecting rod length of 6.385? You need a different cam or maybe lower compression ratio pistons. That's a pretty big swing. I dropped static compression ratio to 8.5 and have 8.03 Dynamic. Why do you want such a low number ? To run cheaper regular grade gas? With tuning you may run mid grade at higher number.
You could do a gasket sandwich. Steel shim, composite, steel shim. Probably around 70 something compressed.
I've seen over 9 DCR without pinging on Premium pump gas if you run at 180 degrees, slow your distributor advance curve to all in at 3500RPM and limit to 32 total. Vacuum advance can should be limited to 12 degrees and use manifold vacuum.
I have a cylinder head kit from amp Mike Philips and also the camshaft. He calculated it with comp cam on DCR 8.1. I had a pinging and a blown gasket. The heads had to be ground and I now have a 52cc combustion chamber. With a felpro gasket 0.040 I have a SDC 10.5 and DCR over 9 That is too much for me. For me this should be a dailydriver
You are using the Intake closing point off the cam card. That is at .050 duration.. You need the IVC with advertised duration. I'm getting 7.97 DCR, and 57.5 IVC with your numbers and Pat Kelley calculator. That should be fine.
Larry, if you don't know, the IN valve close at ABCD at advertised but you do at .050, you can add 24 degrees if at .004 or 26 degrees at .006 , I think.
Larry, thank you. I recalculated it straight away and it looks good. But still different from yours. I would like to drive us 90 octane. Is that ok or should I take a thicker gasket as a precaution?
https://www.v8buick.com/index.php?attachments/screenshot_20231203-170152_gallery-jpg.626566/ 34 +24 = 58. Close, Kelley calculator says 57.5. Intake valve open and closing Math, Simple math to find the closing point.. To find the timing events for the intake: Divide the Advertised Duration in half and subtract the Intake Center Line from the remainder. That will give you the opening event. Intake Opens Before Top Dead Center (BTDC) For the closing event subtract 180 from the duration and then subtract the opening number from that sum. That will give you the closing event. Intake Closes After Bottom dead center (ABDC) 263/2 -106 = 25.5 263-180 - 25.5 = 57.5
I’m going to agree with Jim that you need a different cam to achieve what you’re looking for. You probably also have too little a torque converter and rear gear which is lugging engine with the bigger cam. Again causing extra detonation. .070 thick gasket? Is that a special thing? As mentioned the fel pro is about .040 so that would further increase compression. Also are you sure you don’t have an over temperature condition ? Or a lean issue? I don’t think stacking gaskets when you already have issues that can cause a blown gasket is such a good idea. Did you get pistons from Mike also? He is pretty good with his math so it’s hard to understand how the engine is having trouble.
Cometic gaskets for the 455 are available, https://www.cometic.com/applications/automotive/buick/big-block-v8/455--455ci75l-v8 Not for the SBB AFAIK.
Or gasket sandwich like I mention above. Shim/composite/shim. Deck and heads were milled so good flat surfaces.
Yes, Mike got me the pistons. They are from TA Performance. The block and the heads were milled. I emailed cometic directly about the gasket. Here is the answer: Hi Michael, Following up with your inquiry for a Buick 350 head gasket. Our part number C15267-040 for a Buick 350 '68-'81 3.890 bore is available in different thickness from .027 up to .140 let me know what thickness you are looking for. There is also a .070 MLS gasket in the TA Performance catalog for the 350 TA1724 For this reason I have calculated with this gasket.
Here are some more information about my Buick Cylinder head kit from Mike with larger intake valve Converted from 2bbl to 4bbl 1977 quadrajet from everyday Performance Th200r4 from extreme automatics with 1650 stall 3.42 gear with truetrac Okay, I was running 90 octane gas......that may have been a mistake. But here in Germany the 93 octane gasoline is very expensive.......but maybe I have to do that in the future.
I am sure that Mike has calculated everything correctly! He told me that I would have a DCR 8.1. What he and I couldn't have known is that the cylinder heads have been milled so much that I now have 52cc instead of stock 58cc. If I do the math on the DCR with 58cc and a .040 gasket, I get a DCR 8.01 and SCR 9.52
The octane ratings in Germany are not the same as here in the States. Your 90 octane is equivalent to about 86 octane here. Our Regular gasoline is 87. Our octane ratings are the average between Research octane and Motor octane. You can't expect to run that engine on Regular.
