260 PSI Cranking Compression !!

[BrutalBronco]

I have a 400 w/ aussie iron heads and flat-top pistons. the block is not decked, and the heads are not milled. they were sqare and didnt need it. The cam I'm running (I thought was conservative 2600-6400 rpm range) is a Crane Energizer 284H12 228 @0.050 .550(1.72 ratio 1411's) intake close event 41 degrees ABDC @0.050. Using the KB DCR calculator i have 9.1 Dynamic compression ratio. The heads have a valve job to accept 2.19/1.71 Race Duty valves, which are unshrouded to 0.140", throat cut (75degree) to 90%intake valve and 85%exhaust valve, blended bowl, untouched valve guide boss, and gasket matched runners. Last mod was deshrouding which helped too much. had to change 28 nozzles to 35's w/o smoke! Even though I've always ran 93-94 octane w/o detonation, and I'm absolutely pushing these rocker arms in spring pressure and lift. I'm thinkin' that I have too much cranking compression. I'm on the 2nd starter, alternator, and 4th solenoid. I like to keep my cam timng due to the awesome and consistant performance. Thanks for any input.

[Lazy K]

Not an expert but sounds like you have a much higher compression ratio than 9:1.

[85e150six4mtod]

Thisy here says 15 to 20 times your CR. You is waaaay high:

Compression ratio - Wikipedia, the free encyclopedia

150 to 200 psi they says....

This article talks about a specific cam and CR and resulting cylinder pressure. Short version: Comp Cams XE268, 9.75 CR and 175 psi.

Tuning Engine Compression - Tech Article - Chevy High Performance Magazine

And yea, it's a Chev, but inside the combustion chamber, the rules are all the same.

You may have a problem here that requires more than a thicker head gasket.....

[BrutalBronco]

My Static CR is at least 10.75:1, while my Dynamic CR as calculated with my cam phasing is 9.1:1

[85e150six4mtod]

Well, 260/10.75 = approx 24--so your pressure is 24 times your CR, a ways out of the "10 to 20 times" range.

You can buy higher torque starters, so if you must keep it that way, that's probably the answer.

I predict blown head gaskets at a disappointingly low mile mark on the rebuild. You only have 4 bolts per cylinder. Did you use ARP studs?

[BrutalBronco]

I blew some el cheapo McCords early in the season. I used them after having the heads of for a valve that fell out. Forensics proved that when the pedestals were milled and tapped the burr, that is supposed to be removed with the last step chamfer, was left under the guideplate, which are hardened, and the guideplate broke. Had to replace an intake valve, and rocker arm. Thanks Derrick Hubbard @ CompCams. The Rocker and guideplate was replaced for the cost of shipping. Knocked 3 sharp burrs off the piston and reassebled with the McCords. Using Fel-Pro gaskets, properly lubed bolts, and triple checked torque. I know, given the RPM envelope with the cam and compression cranking/ratio, this motor is a candidate to have studs on top and bottom, and maybe when I can afford to get them, I'll have another block prepped for a direct transplant of my top-end and balanced bottom-end. Thanks to FoMoCo for making over 1 million of these red-headed stepchild ba$t oops boat anchors.

[doug1222556]

You could get an aftermarket ignition that has a start retard to go with that high torque starter.

[lew52]

Yeah i would put the best battary & starter in it that you can find . MSD makes a timing control box that has a controll knob in the cab so you can change the timing with the turn of a knob , but you need to use there ignition box for it to work . Then you can retard the timing to start it , then after it starts turn it back to where it was ... Lew

[doug1222556]

They also have ignition boxes that do it automatically. I'd have to look again to see, but as Lew52 pointed out, you need their ignition box to make the Timing Twister work, and I think it works out cheaper to get the box alone.