Are you talking about static, or dynamic compression ratio? Static compression raito doesn't change. With a stock block and head setup, and a steel shim head gasket, you should be right around 9.9:1. Overlap itself doesn't effect static compression ratio, however different cams will effect your dynamic compression ratio, as the cam timing points and overlap changes.
Yes, the 401 I last built ended up at 9.8:1 with steel head gaskets and only a 0.007" clean-up cut on the heads. The DCR (Dynamic Compression ratio) is around 8.5:1 with the above CR and stock cam with intake closing at 39 degrees (@0.050").
basicly dynamic cr is when the engine is running and the valve timing, ign timing ect have a effect on the cr....
What about this cam,i am looking for silky smooth idle and more torque from down than high RPM HP's,everything stays stock with Q-Jet on top,maybe slight port-matching on the heads. http://cgi.ebay.com/ebaymotors/ws/e...0332293342&viewitem=&sspagename=STRK:MEWAX:IT o No:
Thanks Tom,thats what i was thinking after reading all the threads about cams here. Will this cam work with Your roller rockers?:Brow:
Quesiton Walt - when calculating DCR, aren't you suppose to use the advertised, or seat to seat, ADBC figure?
That is correct, seat-to-seat values should be used......but it depends on which DCR calculator is used. This one from KB-Silvolite ESTIMATES seat-seat times based on Duration @ 0.050" figures. http://www.kb-silvolite.com/calc.php?action=comp This one was recommended by Larry70GS (The Wizard), very informative: http://www.empirenet.com/pkelley2/DynamicCR.html I believe it uses 0.006" lobe lift, which most cam grinders use for ADVERTISED duration....but not Buick..... Buick used 0.002" lift in their published cam specs. I'd like to have the various combinations charted, but having trouble with setting up a spreadsheet....
Re: 425 Camshaft questions. 209-213 for the 091 cam? As my nailhead research continues I came across this post from http://www.teambuick.com/forums/content.php?214-Buick-Cam-Specifications-for-401-and-425-nailheads buickrodder - 01-02-2012, 01:35 PM "I have degreed the late 401 and the 425 cams in to find the spec's at .050 and found that they were = to a 270 aftermartet grind the 401 was 209-209 at .050 on 114 lc lift 431-431.... the 425 cam was 209 213 at .050 with 109 lc lift 438-438 now this was checked at the lifter and x a 1.6 rocker ratio .. The new Mellings cams came out to be 206-207 with 112 lc .. I checked out 13 cams back in the 80's" Does the 209-213 duration make any sense for the 091 cam? It is the first time I've seen any 091 numbers that are significantly bigger than the other nailhead cams so it made some sense to me.
Re: 425 Camshaft questions. 209-213 for the 091 cam? the 091 cam was on a 109 LSA but it had 461 lift
