Hello to everyone on the forum.
I really enjoy reading the posts here. There is so much information and knowledge that cannot be found so easily elsewhere.
I have a problem and hope that someone can make sense of it all.
I have a 400 0.030" oversize, 2V open-chamber aussie heads ported, 4V stainless valves, Crane Energiser roller rockers, screw in studs, guide plates, double valve springs, set of Tim's 1.72 compression height Badger pistons, Gas Research dual carby set up flowing 840cfm:

http://homepage.mac.com/kionga/PhotoAlbum8.html

Recently fitted a Crow cam with the following specs:
Solid cam, Adv Duration I: 278, E: 282, Dur @0.050" I: 238, E: 244, Gross Valve lift I: 0.55, E: 0.56 (roller rocker lift ratio 1.7), lobe separation 108.
The motor now pings under load. Had the distributor recurved for propane. This has reduced the problem but not entirely eliminated the problem.
Can anyone calculate the CR of this motor? Is it also possible to DD the torque and power made as well? Why should the new cam cause the motor to ping?
The previous cam was a hydraulic one with the following specs:
Adv. Duration I: 284, E: 290, Dur @0.050" I: 218, E: 224, Gross valve lift I: 0.49, E: 0.53, lobe separation 110. Used the same heads/valve springs/valves combo. Had no pinging at all.
All comments greatly appreciated. If I have left anything out then I'll do my best to provide the answers.
Cheers
Craig

 

You raised the dynamic compression ratio. There is a program out there to calculate dynamic compression ratio. Some of the users here have it also.

 

What was the Intake Centerline of the 2 cams and what was the valve lash on the new one? Are you sure about the advertised duration figures?

 

Thank you for taking time to reply. I figured the dynamic compression was raised. I'm guessing the old cam would bleed off compression due to the extended duration on exhaust.
Not sure Brian about intake centreline of both cams? Will get back to you with those numbers. The advertised duration is listed online.
Thanks again

 

"The advertised duration is listed online."

Yes, I know. I guess that means the cam wasn't degreed or dialed in. The IC will tell how much advance is built into the cam. I'm guessing it was installed straight up. Dynamic compression is about when the intake valve closes.

The cam seems to have a short advertised duration compared to it's duration @ .050. Mechanical cams have about 8 degrees less duration than listed compared to hydraulics because of valve lash clearance.

Try some of the detonation reducing tricks listed in the link below. If all else fails, you may try running slightly less intake valve lash ( no more than .004 tighter than recommended) to increase duration or you could retard the cam a few degrees. Sometimes only a little bit is needed to get you out of detonation.

http://popularhotrodding.com/enginem...power_squeeze/

 

Some of the information in that article is great for racing but not good for a daily driver or fuel economy. Other than that it is a great article.