Engine builders, Tuners, chime in! DYNAMIC COMPRESSION SITUATION ADVICE NEEDED!

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Oct 15, 2012 | 02:46 AM

LT1STROKER

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Engine builders, Tuners, chime in! DYNAMIC COMPRESSION SITUATION ADVICE NEEDED!

So
I was forced to freshen up a current setup and in the process I made the jump and purchased a LSX block.
I reused the rotating assembly minus the pistons. I purchased the pistons to make this a 454.
The Situation : My new setup has a dynamic compression of 9.967 and is put together and actually in the truck it will live in. The setup use to be a 427 LS3 based block that with this same cam had a DCR of 9.5 : 1.

The Question:
Can this be handled by tuning well, or do I need to change some cam timing.

Will actually retarding the cam change the intake closing point to help with dynamic compression, or is it only in the actual advance buuilt into the cam.

I am gonna try it probably because it is in the truck, but if i am getting too much knock retard I would like to know what all my options are.

Funny how this change in bore can create such a possibly big situation.
Thanks for all the help you guys can render.

Oct 15, 2012 | 09:15 AM

Grr

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From: Fargo ND

could you post up more info? what are the cam specs, ICL valve events and more of the setup. My setup in my sig is 9.65DCR running E85 with no problems, I cant see you running that on pump gas very effectively. You can move the cam around a little depending on how much room you have in there
If you are on E85 then no problem, my new setup has DCR of 10.1!

Oct 15, 2012 | 02:37 PM

LT1STROKER

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The engine is a LSX block with 4.125 stroke crank 6.125 rods and a 4.185 bore. The pistons are Manley flat tops with a 7cc valve reliefs. I am using a Cometic head gasket 4.200 bore with a .040 thickness. The heads are a set of TFS 245's with 70cc combustion chambers. The cams specs are 281/289 231/239 .617/.624 lift on a 111 LSA with 4 degrees advance. Fast truck intake and nick williams 102mm. At .050 the intake valve closes at 42.5 degrees. This same cam in the 429 had a dynamic ratio of 9.5 and it ran on 93 octane, in my truck, here in my area with no adverse problems or consequenses. The truck is a 08 GMC 1500 crew cab. I would love to have a readily available supply of e85 but they took the only pump that carried it away from me in the area.
Hope this helps you help me.

Oct 15, 2012 | 08:52 PM

Grr

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From: Fargo ND

holy crap, that intake lobe is tiny as hell for that engine. The cam as a whole is tiny. your IVC is 42.5*, you need to add a few degrees to that man should be over 45 at a minimum, i would go 47-50 myself. That has to sound like a completely stock vehicle with that cam in there
IMO a 242/248 114+4 would be a cam that is still relatively small but would make a **** load more power and get rid of some compression for you

Oct 15, 2012 | 09:05 PM

S10xGN

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From: Port Neches, TX

You could back that 4° out and center it, that would help a bit if you do have problems.

Oct 16, 2012 | 12:52 AM

LT1STROKER

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Quote:

Originally Posted by S10xGN

You could back that 4° out and center it, that would help a bit if you do have problems.

That is the actual point I wanted to hear. That may be my option if I have problems.

Oct 16, 2012 | 01:00 AM

LT1STROKER

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Quote:

Originally Posted by Grr

The idea was to keep all low speed torque high, and with the big heavy truck it definitely worked with the 429, and it was a detonation free setup. Of corse it was also 9.5 DCR also. The truck had a very nice noticable idle, it was much the attention getter, especially for its platform. The truck is a Denali GMC and I diid not want to be tooooo wild, more tame warmed over surprise attack.