stockA4

I finally got around to checking my cranking compression after changing cams on my low mileage J/y 2002 LR4 with 706 heads, motor is untouched save for cam and valvesprings, heads have never been off.

I first ran it with a used 1721 cam out of a good running 2002 LS1. When I first checked the cranking compression I got an average of 165psi with that cam. I only do this test on a hot engine that's just been running.

Now my 4.8 is running a used comp cams 54-424-11 bolted up with the same stock timing set and everything. All I changed was the cam and valvesprings. I never ran the 4.8 or checked cranking compression with the stock cam.

I have to say I'm a little surprised at the result. I got a 170psi cranking compression with this cam! I'm surprised because this cam is supposed to be a 212/218-115+0. Just looking at the IVC @ 0.050 for these two installed dot to dot the 212 cam closes much later(41 degrees)than the stock ls1/lq4 cam (33 degrees) so much so that I thought the cranking compression was going to be significantly less after changing cams and yet it's 5psi higher.

Just wanted to share this with the community. Now I just wonder if maybe the cam actually has some additional advance ground in it or if this is just the normal result of my tinkering. Either way it runs great for what it is
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JoeNova

You shouldn't ever share with the community that you measure compression based on the .050" IVC haha.

stockA4

It would be awesome if a few ppl volunteered the cranking compression of hot 706 headed 4.8s with the stock cams still in them so we could all learn something today

stockA4

The 54-424-11 closes the intake @0.006 at 68 degrees and it got 170psi, 5 more than the 1721 cam. Is that better?

SLOW SEDAN

iTrader: (13)

Give you an idea if you're close: http://www.wallaceracing.com/calc-crank-press.php