hamck

Too high? Cranking pressure is 210, My dcr is 8.15. Statics at 9.56. I was planning a cam change so should I try to lower my dcr or am I good?

427Hotrod

First...are you sure gauge is good? It probably is....but that's some stout cranking compression for a 9.5 motor. Must be an awful tiny cam or it's advanced like crazy.

What are you trying to do with it? Is it currently running? Does it run OK?

Do you want a bigger cam to move the RPM higher and make more power? Or just to make these numbers "better".

DCR is a real thing...but there are so many variables to how it works with respect to what RPM the engine becomes efficient...how the heads flow..the exhaust etc etc. What can run very well at lower/mid RPM on a mild motor could get into trouble if a high flowing set of heads were installed and all of a sudden the cylinders actually started getting filled at higher RPM. With that sort of cranking compression I'd expect it to run very well off idle and lower ranges considering that compression ratio.

JIM

Flyinace3

My combo has a cranking compression of 210psi as well and I was thinking of a can change as well but it runs fine on 93 with 35 degrees of timing.
Going to pull the heads this winter and have a look at the pistons and do a few other upgrades while I have it apart.
My static is about 9.3 and dcr is less than yours .
I question why my cranking compression is 210 with only 9.3 static and a dcr of 7.5.

hamck

I went from stock 882s to dart 180s Didn't change the cam. a comp xe 256. I was thinking a more matched cam for the heads would lower the cranking pres. I have TONS of torque now, but that 210 psi has me a little concerned.

63mako

No problem if it runs on 93 and your happy with the operating range leave it alone.

hamck

I used a calculater on a jeep website, I may be a little off on my calculations

hamck

I like leave it alone... Wallets getting a little lite.

63mako

If you used the Jeepstroker calculator did you figure 4 degrees advance ground in? Great calculator!

Flyinace3

Dart 180 comp 276 hyd roller. Good low end and will pull to 6000. I've been thinking of going with a solid roller and a tad more duration .

hamck

no. I put in intake closing angle of 55 Was that wrong?

63mako

Intake closing point 57.
http://www.compcams.com/Company/CC/c...x?csid=91&sb=2
Or you enter 256 under duration, 112 under LSA and 4 degrees under ground in advance and the intake closing angle (57) will pop up off to the bottom right box

hamck

OH I just looked on the cam card ,it said 55 abdc @ .006 I'll do it again. Thanks

hamck

Static 9.58 dcr 8.06 Thanks Mako

63mako

You are right. For some reason the 112 LSA cam popped up. Here is yours, 110 LSA. 55 is correct.
http://www.compcams.com/Company/CC/c...x?csid=91&sb=2

hamck

Sorry to open an old wound, But I have developed a new problem now. I have oil entering my manifold by way of the pvc system. I put a clear tube between the valve cover and the pcv valve to see if oil was entering there. Oil was in the tube. baffle is in place. I thought it was from switching to synthetic from dino , so I went back to what I was using. Didn't work. I put a vac. gauge on the dipstick tube. I have about 1 in. of vac, plug the vent, and it climbs higher. By changing the heads and raising the comp. ratio, did I damage the rings? If/when I change the cam to lower the cranking pres. and dcr, will the rings survive? Maybe I cooked them from too much heat/pressure. Any ideas are appreciated.

REELAV8R

Did you change to a higher CR without re-ringing the engine?
If this is the case then often times old rings and their level of seal are not sufficient to handle the new higher CR. Now the cylinder pressure at TDC and every where else in the stroke is also higher.
This ends up in excessive blowby from pressure leaking past the rings.
This means that the crank case gets pressurized. The excess pressure/blowby contains oil vapor as well. That is sucked up by your PCV valve and delivered to the intake to be burned by the engine, giving you an oil burning engine.
So it's likely you haven't done any damage to your engine. But it will now burn oil unless you drop the pressure in the cylinders or hone cylinders and re-ring the pistons.
You could try 20w-50 oil and see how that works. It may slow down the oil burning, but probably won't stop it.

This may lower your DCR and your cranking pressure but it will not reduce your CR. Once the engine reaches a certain RPM the full, or close to full, CR of the engine is seen and full cylinder pressure is reached. So you will still see the same oil burning/blowby issue as before.

edit: I went back an read your previous posts. It looks like no one asked about the condition of your rings. Myself included.

REELAV8R

Had another thought on this issue you may be dealing with.
I have read about guys using "catch cans" kind of an oil air separator idea.
So the vent from the valve cover goes into this catch can first, the oil drops out of the air and then the air continues onto your intake via the PCV valve. Or some I think just vent it overboard, but going to the intake in order to keep crank case pressure to a min seems like a better idea. Then just empty the catch can periodically.
It won't solve the root cause of the problem but it may help reduce oil burning to a minimum. Rings are still gonna get carboned up over time due to blowby which can create it's own problems.

hamck

I believe your right. I was hoping for some magic bullet, but I know there's none. I thought of the catch can idea, but that's no way to live, empting that thing all the time. There's not many miles on the engine, maybe 3 years old, 5000 miles at most. I didn't assemble it, the machine shop did. I will need some help selecting a cam later. That will be on a later post.