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| Thicker (than stock) cylinder head gasket needed https://slantsix.org/forum/viewtopic.php?t=45346 |
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| Author: | lgu32 [ Sat Jun 18, 2011 7:52 am ] |
| Post subject: | Thicker (than stock) cylinder head gasket needed |
After installed a new MP268 degree camshaft to an engine with 0.09" milled the block I have measured 200 PSI compression pressure. This is absolutely too much for the regular fuel available here. This means I have now pinging problems when engine is hot. I cant put more than 28 degrees mechanical advance at all - I am loosing performance!!! I have a standard (I assume 0.02") head gasket. To get compression down I like to get a THICK cylinder head gasket. Are these available or do I have part the engine again to mill the pistons or engrave heads for some additional volume... |
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| Author: | Fopar [ Sat Jun 18, 2011 8:30 am ] |
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Felpro or some other aftermarket composit style head gaskets are about .042" to .045" thick Richard |
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| Author: | Joshie225 [ Sat Jun 18, 2011 10:17 am ] |
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I think the cam timing is off. What's the installed intake centerline? Also, 28° total mechanical and initial timing is all you want and need. More timing advance will hurt power. What is the calculated static compression ratio? |
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| Author: | Dart270 [ Sat Jun 18, 2011 10:29 am ] |
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I agree with Josh - something wrong there. Also, 28 deg is about perfect for max power. Slants do not like a lot of timing. Felpro - 0.034" thick ACL or Permaseal (Aussie) - 0.046" thick I think the Corteco and Victor gaskets are 0.045" or thicker as well. Lou |
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| Author: | lgu32 [ Sat Jun 18, 2011 11:42 am ] |
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Even the 28 degrees will ping when this engine is really hot. I am waiting for a new bigger radiator to avoid this "really hot". Here these parts are not always available at the shop. I did the cam chain and -wheels installation with a tools. I did also measure TDC and 32 degrees advance marks as my engine god not new, but better vibration damper from another slant. I am pretty sure the cam is as the Mopar Performance said it has to be done. Cant remember the degrees but I had the numbers when I did it. There is Clifford Performance timing set (roller chain set) and it is at "zero" setting. The head was milled before but I measured head volumes to be 54cc. The block was at stock height as there were factory "225T" stamped to the block before milling. Stock style, .06 OS pistons were about .175 deep before milling. Now thy are .09 closer at .85 After milling I had to order custom made short pushrods. There is a std Felpro gasket. As I have now informed, it is .04 thick. So the compression could be between 9.5 and 10. Not that much? Could it be something sharp edges at cyl head casting which causes pinging? This engine will typically "run without ignition" after shut down if is hot (just loaded or city driving at a hot day). I dont know the correct term of this "feature". I handle this keeping the transmission setting "D" until engine is stopped. How about installing 2 head gaskets together? I have ARP studs for head, I think I can handle the torque and head gasket compression. |
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| Author: | Joshie225 [ Sat Jun 18, 2011 12:10 pm ] |
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OK, it sounds like you have an overheating problem. Fix that before anything else. If you degreed that cam according to the instructions it's retarded for best performance, but that also means it's bleeding off cylinder pressure which will make it less likely to ping. Again, fix the overheating. Two head gaskets together will fail. "Run-on" with the ignition switched off is also a sign of overheating. A high idle speed makes this condition worse. |
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| Author: | Dart270 [ Sun Jun 19, 2011 3:59 am ] |
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My guess is your cam is advanced significantly, giving the high cylinder pressure readings. I agree with Josh you should make sure the engine is not too hot. I had a similar issue (too high cyl pressure) in my '68 Dart, on the street. I successfully stacked 2 Felpro head gaskets together for a total thickness of 0.074". I sprayed each gasket with a light-to-medium coat of Ultra Copper permatex (spray can) on the surfaces where they met and installed them. I never had a problem (20-30k miles) and the compression was dropped down from about 11:1 static, to just above 10:1. I was running a MP 276, 0.490" cam at about 100 deg centerline. This 3300 lb car ran high 15s with a 2.94 rear gear in full street trim. Lou |
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| Author: | lgu32 [ Mon Jun 20, 2011 12:47 am ] |
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Quote: My guess is your cam is advanced significantly, giving the high cylinder pressure readings. I agree with Josh you should make sure the engine is not too hot.
Ok, its worth of trying, thanks!!! I assume VHT SP 21 COPPER GASKETI had a similar issue (too high cyl pressure) in my '68 Dart, on the street. I successfully stacked 2 Felpro head gaskets together for a total thickness of 0.074". I sprayed each gasket with a light-to-medium coat of Ultra Copper permatex (spray can) on the surfaces where they met and installed them. I never had a problem (20-30k miles) and the compression was dropped down from about 11:1 static, to just above 10:1. I was running a MP 276, 0.490" cam at about 100 deg centerline. This 3300 lb car ran high 15s with a 2.94 rear gear in full street trim. Lou spray which is available here could to the same. I will open this engine, double check the timing. Sure I double double checked it during installation as the multi position Clifford chain (+8 to -8 degrees) was a new component for me. I have a degree wheel and the "clock" for measurements. If it is in centerline I will try your method. If it blows the gasket I will go to injected E85 later. This is only a partially "daily driver". Depends of a day, as my Harley which also have some engine problems just now. |
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| Author: | Dart270 [ Mon Jun 20, 2011 6:22 am ] |
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Be aware that I have only done this once, so anything might happen. That said, I would do it again... 9.5-10:1 should not be too high with that 268 cam degreed correctly and 28 total advance and good AFR mixture. Of course, dropping the comp will make things safer and easier to tune for no ping. Lou |
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| Author: | Brussell [ Mon Jun 20, 2011 9:36 pm ] |
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I didn't get too read through much of this^ in a rush. But before you do anything fix the overheating problem as josh said. If you are running something around 10:1 compression do you need to have a double gasket? I would have thought that would indicate that you have issues somewhere else as suggested^. Thanks |
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