Anyone hear running 11.25:1 or higher on Pump Gas DD?
12-21-2009, 10:33 PM
#11
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Moderate duration wide LSA cams work better than narrow lobe sep cams in High DCR motors for sure, Wide LSA cams close the intake valve later and the closing of the intake valver determines when the piston can start making compression and is probably the Key component IMHO, look at dude above with that cheater cam 215-230 at 50 117lsa with 11.65:1 !! i guaranty if you tried that same engine with a say 228-232 at 50 cam on a 106lsa you'd be out a set of pistons!
12-21-2009, 11:48 PM
#12
I disagree, a cam with more overlap bleeds off cylinder pressure. A narrow lsa has more overlap. My buddy was running a 224/228 110lsa cam and it ran quite well, just finicky on cold starts but that was tune related most likely(long story).
12-22-2009, 10:47 PM
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take 2 identical cams except one has a 114lsa and the other has a 110 the 114 will close the intake valve 4 degrees later as long as Both are straight up, if you advance the 114 cam 4 degrees it will close the intake valve at the same point as the 110, its not a matter of argument its a Fact and it will bleed off More Cylinder pressure at a lower rpm But of course its all one big compromise, loose some here gain some there ect
12-26-2009, 07:30 PM
#16
take 2 identical cams except one has a 114lsa and the other has a 110 the 114 will close the intake valve 4 degrees later as long as Both are straight up, if you advance the 114 cam 4 degrees it will close the intake valve at the same point as the 110, its not a matter of argument its a Fact and it will bleed off More Cylinder pressure at a lower rpm But of course its all one big compromise, loose some here gain some there ect
In order to run that high of compression in a heavy truck(on pump gas) you need a lot of overlap to bleed cylinder pressure otherwise you wont be able to run very much timing at all. The heavy load on the motor due to the trucks weight along with the high compression will make the motor detonate MUCH easier.
Thats how my buddy blew up his motor, one of the first cool summer nights and possibly a little too old 93 octane gas and he lost a ring land at 7000rpm.
Now if youre willing to run a safer tune(he wasnt, it was on the ragged edge) then I believe youre on the right track. All depends on what you want.
