Automatic Compression Release Questions

Reply Subscribe

Thread Tools

Search this Thread

Oct 17, 2011 | 02:43 PM

harley_jeff

Thread Starter

Road Master

Joined: Aug 2007

Posts: 838

Likes: 35

From: Northern California

Automatic Compression Release Questions

I am researching my winter project - 103" conversion for my '07 Dyna. Couple of questions -

1) Is there a rule of thumb for when ACRs are required in terms of compression ratio? I was considering JE 10.0:1 flat top pistons. But maybe 10.5:1 ?????

2) If ACRs are required, where does the machine shop drill the hole in the head for them? On the top of the head, LH side, RH side?

Oct 17, 2011 | 02:52 PM

wheel752

Road Captain

Joined: Jul 2010

Posts: 675

Likes: 3

From: Newport, Wa

10: 1... use them. they are installed next to spark plugs.. They save the starter

Oct 17, 2011 | 02:54 PM

PistonPuller

Ultimate HDF Member

Joined: Feb 2006

Posts: 5,190

Likes: 5

From: Eastern Washington

Usually rule is anything at or above 10 to 1. However it is cheap insurance to have them done when heads are already off. Sort of a no brainer. I know the manual one are usually driller next to where the spark plug enters through the head.

Oct 17, 2011 | 02:57 PM

harley_jeff

Thread Starter

Road Master

Joined: Aug 2007

Posts: 838

Likes: 35

From: Northern California

Thanks guys. So, if they go next to the spark plugs, does that mean I can no longer use the set of fins I bought from H-D that "fill in" the area where the spark plug is located?

Oct 17, 2011 | 06:15 PM

northeastconfederate

Tourer

Joined: Jul 2007

Posts: 497

Likes: 8

From: New Egypt, NJ

I'm not sure if the Automatic version gets located in the same place as the manual version, but assuming they do, and Wheel 752 says so. That being the case, it DOES mean you can't use those fillers.

Oct 17, 2011 | 07:07 PM

qtrracer

Ultimate HDF Member

Joined: Jan 2008

Posts: 6,532

Likes: 132

From: SoCal

Quote:

Originally Posted by harley_jeff

There are 2 holes to be drilled 1 for the ACR and 1 to vent the compression into the exhaust port, the ACR goes in the top of the head and it hidden from view. They work great. And there is no compression ratio # that is the magic number that requires releases, its more of a cranking pressure number, like 190 or there about. I have 103" motor 10.5 cr with a 42 IVC camset and crank at 195 and I have the ACR's and I have NEVER had a starting issue of any kind. The speed you drive your clutch with the starter has an effect on the starter too, like if you have changed your primary gearing for more engine rpm it will put more strain on your starter.