Dropping CR
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Postmaster
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From: Spokane WA
Dropping CR
Hiya All, I just found out that I have a 429 thunderjet, curious how to find a thicker set of head gaskets to drop the CR a hair, anyone know a brand or specific part number, or have any information that will help me out, I wanna just squeeze in under the radar of 92 octane, dont mind having to buy premium, and am really excited to get this thing on the road, suggestions?
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From: So Cal
Haven't modded this model engine, but a couple ideas from way back when I used to play with engines a lot more than I do now.
You might stack some flat copper head gaskets together. I used a set I think from Victor way back. The copper was expensive but supposedly gave a really good seal. They were a bit thicker than they usual stell gaskets. I think I read that using two would drop the compression a bit. If you did this, I would recommend using a spray on copper based gasket sealer, I think the brand was Copper Seal, looked like copper metalflake paint when sprayed on. Another brand might be KW, I think they also make a spray version of their copper sealer. Last time I bought these products was at least ten years ago so don't know if they are still out there and may be a different name now.
Another idea if you are handy with a grinder and have some time is to polish your chambers. This will lower the compression a might and eliminate any potential hot spots which could contribute to detonation.
Good Luck,
Jim Henderson
You might stack some flat copper head gaskets together. I used a set I think from Victor way back. The copper was expensive but supposedly gave a really good seal. They were a bit thicker than they usual stell gaskets. I think I read that using two would drop the compression a bit. If you did this, I would recommend using a spray on copper based gasket sealer, I think the brand was Copper Seal, looked like copper metalflake paint when sprayed on. Another brand might be KW, I think they also make a spray version of their copper sealer. Last time I bought these products was at least ten years ago so don't know if they are still out there and may be a different name now.
Another idea if you are handy with a grinder and have some time is to polish your chambers. This will lower the compression a might and eliminate any potential hot spots which could contribute to detonation.
Good Luck,
Jim Henderson
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From: Pryor
Polishing the chambers is a great idea. You can unshroud the valves a little while you're at it. Just make sure to do all of them the same. You can get solid copper gaskets although most are pretty pricey. Check out http://www.paeco.com/gasket.htm http://www.magnumforceracing.com/sto...ad_gaskets.htm
http://www.scegaskets.com/pdf/page%2032-36.pdf
The last link is probably the best. Their Titan self sealing copper head gaskets are around $130 from Jeg's.
http://www.scegaskets.com/pdf/page%2032-36.pdf
The last link is probably the best. Their Titan self sealing copper head gaskets are around $130 from Jeg's.
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From: Pryor
9.5:1 is about right for 92 octane gas. You shouldn't have any problems with that CR. You can use full timing. If you go much higher it becomes a tightrope.
Personally I'd stick with the heads you have. They will outflow the D3's. I'd polish and unshroud as well as get a 0.060 or 0.080 thick gasket and be done with it. I did all of those calc's when I was building my engine. I can't say for sure, but I think a standard bore gasket that is .080 thick will drop your compression by just over 1 full point vs using a standard gasket.
Personally I'd stick with the heads you have. They will outflow the D3's. I'd polish and unshroud as well as get a 0.060 or 0.080 thick gasket and be done with it. I did all of those calc's when I was building my engine. I can't say for sure, but I think a standard bore gasket that is .080 thick will drop your compression by just over 1 full point vs using a standard gasket.
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From: Spokane WA
Thanks you two 
I really appreciate it, when the time comes Ill bump this thread and let you know how it went
I really appreciate it, when the time comes Ill bump this thread and let you know how it went
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From: Spokane WA
okay you guys...one more.....I have access to 101 octane racing gas, I can mix it with premium to achieve the octane I need to make this run until I can afford to have this head work done....that said....
what octane do you think it needs at its present 11:1 to run EFFECTIVELY with the timing the way it should be
this is the last ? and ill leave ya' alone, promise
what octane do you think it needs at its present 11:1 to run EFFECTIVELY with the timing the way it should be
this is the last ? and ill leave ya' alone, promise
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From: Spokane WA
Brandon are you sure? I get So many conflicting statements from people I know on this board that I KNOW have a clue whats going on that I guess Ill just have to wait and see, I guess we can put this thread to rest now and Ill bump it with an update when I get it figured out.
I respect all your opinions, and we'll see what happens in a month or 2
I respect all your opinions, and we'll see what happens in a month or 2
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With my moddified EFI 460 I am running 9.2:1 with base set at 16 deg. total around 32 deg. on 91 and it does fine. Will run decent on 89. Of course every motors differnt But you should be able to go an easy 10:1 on straight pump.