CRANKING COMPRESSION

Posted By: MIKES_DUSTER

CRANKING COMPRESSION - 12/01/10 08:33 PM

Whats the "GOOD,BAD AND UGLY" of cranking compression??? It was suggested by Rick(aarlucas) that I do it,so I did.
I checked #1,#2,#7 and #8 and all were between 180-200.

Posted By: maximum entropy

Re: CRANKING COMPRESSION - 12/01/10 09:02 PM

cranking compression is a good measure of the compatibility of a given combination. beyond that, it's not very useful as a diagnostic procedure. in school we had a 327 shivvie mule on a dyno that we conducted all manner of horrific and cruel experimentation. one of the pistons had a hole drilled in it (i think it was about 1/4 inch?). that cylinder had almost the same compression as the rest of them. learned a lot on that engine.

Posted By: Dads426

Re: CRANKING COMPRESSION - 12/01/10 09:11 PM

I would be more concerned about consistency between cylinders. Cranking pressure will depend on cam design and compression ratio. You can have 14-1 pistons and a ton of cam duration and the cranking compression will be low. Properly matching the components will result in the best combination. Don't know much about your combo, but 180-200 psi is very good.

Posted By: MIKES_DUSTER

Re: CRANKING COMPRESSION - 12/01/10 09:37 PM

Thanks guys!!!! Hers the run-down on my combo.

360 balanced
.040 (368")
stock crank/rods
ARP bolts
KB-191's
12.3:1 comp.
Ultradyne roller cam
.556/.556 .285/.295 .249/.259@50 (1.5 rockers)
J-heads flowed 284@.525
2.02/1.60
1.6 Crane gold roller rockers
M-1 ported
1" 4-hole spacer
worked 850dp

Posted By: Labratt

Re: CRANKING COMPRESSION - 12/02/10 02:25 AM

Mike..sounds like a NICE combo to me!!!

Posted By: bp27

Re: CRANKING COMPRESSION - 12/02/10 02:40 AM

12.3:1 comp.
Ultradyne roller cam

I do like Ultradyne Cams

Posted By: MR_P_BODY

Re: CRANKING COMPRESSION - 12/02/10 02:48 AM

Quote:

I would be more concerned about consistency between cylinders. Cranking pressure will depend on cam design and compression ratio. You can have 14-1 pistons and a ton of cam duration and the cranking compression will be low. Properly matching the components will result in the best combination. Don't know much about your combo, but 180-200 psi is very good.

Yep.... I have 14.1:1 and only have 175 cranking compression
mainly due to the 112 lsa... but my engine never
see's lower than 5600 and thats the launch rpm

Posted By: MIKES_DUSTER

Re: CRANKING COMPRESSION - 12/02/10 04:36 AM

I dont have the best gauge so it could be closer than what it read today. Not sure what the LSA is,looked on Bulletcams.com and it dont say.

Bob...Ultradyne cams ARE good cams!!!

Randy....Thanks!!!

Posted By: Labratt

Re: CRANKING COMPRESSION - 12/02/10 04:44 AM

Mike,a while back I checked 4 cylinders on the 440,and got readings of 180,182,185,and 182 again! Not too bad!

Posted By: MIKES_DUSTER

Re: CRANKING COMPRESSION - 12/02/10 04:50 AM

So,you think I can run pump gas(93-94) or will I have to mix race fuel with it?? If/when I race it,I will run straight race fuel. Was just asking for around town.

5600rpm launch????? LOOK OUT!!!!!

Posted By: MR_P_BODY

Re: CRANKING COMPRESSION - 12/02/10 04:57 AM

Quote:

So,you think I can run pump gas(93-94) or will I have to mix race fuel with it?? If/when I race it,I will run straight race fuel. Was just asking for around town.

5600rpm launch????? LOOK OUT!!!!!

Would depend on temp, quench, timing and IF you
truely get that octane... if you truely have 200
that MAY be a bit much... JMO

Posted By: MIKES_DUSTER

Re: CRANKING COMPRESSION - 12/02/10 05:13 AM

Quote:

Would depend on temp, quench, timing and IF you
truely get that octane... if you truely have 200
that MAY be a bit much... JMO

Kinda thought that. Gonna recheck tomorrow.

Posted By: bp27

Re: CRANKING COMPRESSION - 12/02/10 01:41 PM

12.3:1 comp and iron J-heads You will need better gas than 93

Posted By: mopar dave

Re: CRANKING COMPRESSION - 12/02/10 03:03 PM

with aluminum heads,.039 quench and 195 cranking pressure i ran 93 no problem. cast iron heads may be a problem on pump gas.