Police Head, Bored, Performance Questions

B

Banky

Senior Member
Hi all,

I recently put a Police Hi-Compression head on my 30 tudor. The pistons each had a "40" stamped on them, assuming they were bored out at some point. Modern points installed. Everything else is stock. RUNS GREAT!!!

Would the above modifications change the customary GAV 1/4 turn open until warm, then close?

I also seem to not have to pull the timing lever down as far. Thoughts?

Lastly, this concerns me the most, at higher RPM's the "chug chug chug" sounds like it hits a little harder. Not like anything is breaking or anything, but a noticeable sound. Not sure I'm making sense at all, but I'm asking anyway.

thanks all!
Banky
 
Banky,
You're hot on a subject that I was discussing today with some friends regarding higher performance add-ons for our four-bangers. I did read in the instructions from AER for my newly built engine that he feels advance higher that 28 degrees is a point of no return and hard on the main bearings. I purchased a NuRex timing kit a while back and will be checking my timing now that I have the engine running to see what the range is. The degree indicator mounts near the crank pulley and allows the use of a timing light at the crank.
If I remember correctly, the spark advance range is near 40 degrees of difference from top to bottom, so setting TDC with zero degrees advance with the lever all the way up could still mean trouble at full advance.

Looking forward to other comments regarding
 
high compression heads require less advance. The Lion head seems to take more advance than the others. My Brumfield, the Snyder and the Ford B ( police) head will ping under a hard load at about 25 degrees. I set my timing so full advance is 28 degrees, which means with the lever up its very retarded, but that's no big deal, I just don't run it there. I did not notice a difference in the GAV setting, but that is something that varies with temperature, speed, fuel quality and elevation, so its not impossible in your circumstance that it could have changed. I do not know what noise you are referring to, but loose pistons and bearings will generate more noise with higher compression. The engine will sound and feel rougher too, as the higher compression causes a stronger impulse when the fuel explodes.
 
I have an aluminium Winfield head atop a Model B motor that I 'rebuilt' with the best second hand parts that I had to hand. Very sensitive to timing - a fine line between losing all the power and pinging at the top end - although I think I have now found the sweet spot.

I've done about 400 miles in it now just pootling about locally. On returning from the first long trip I tried some premium 95 octane gas. It liked that a lot. Noticeably stronger running, much smoother and no hint of a ping.

Model A'ing just got 4 pence a litre more expensive.
 
This is great! Happy to hear my questions are not completely off the wall.

I believe I am experiencing the "pinging" under hard load described above. Is is OK? Or should the timing lever be adjusted to smooth it out?

thanks all!
 
Banky said:
This is great! Happy to hear my questions are not completely off the wall.

I believe I am experiencing the "pinging" under hard load described above. Is is OK? Or should the timing lever be adjusted to smooth it out?

thanks all!
Click to expand...

Pinging is very bad for the engine. Retard the spark as needed to get rid of it.

My engine had pinging with a stock head and 50 lbs. compression when I gave the throttle just a little push. Turned out the engine had an accumulation of rust flakes around #3 or #4 cylinder and it caused a hot spot that caused the pinging. After I got rid of the rust the pinging went away.:)
 
I never run with the GAV closed as the reduction in performance is not worth the minimal savings on gas. If I must do a cold start and immediately drive off I'll run 1/2 turn open for about a mile and then I can get normal performance at about 1/4 turn open. Of course that is tailored to the performance of my particular cars.

As far as the timing advance goes, you've been given good advise already. However, you are already "ahead of the game" as you obviously can hear and feel when it's too far advanced. Many folks cannot. Trust your instincts. It's much like feeling when you need to downshift. Keep in mind that cars with automatic advance do so directly proportionate to engine speed. The higher the compression, the more critical it becomes to properly use the advance.
 
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