45 High Compression heads - revisited

[RvP]

I had posted this question before about using the high compression (#6) aluminum heads on my WLA engine instead of the medium compression (#5) heads and if there would be any improvements. Since that posting I have changed the venturi in the M88 from the stock 7/8” to 1 1/16” (modified with an internal vent). This has made an improvement with increasing the useable RPM range and I actually was able to comfortably cruise at 65mph using a 33 tooth engine sprocket at about 3/4s throttle solo.

What I am still lacking is power between 45mph and top speed for going uphill and riding 2 up. Last time the answers came back with no clear direction except for Kurt who felt the #6 heads would only generate heat with no apparent power increase. Is this still the consensus now that I have the rough equivalent of a M51 carb with the 1 1/16” venturi?

As an added note, I am half way there because I found in a pile of parts from a basket case what I think is a high compression front WLD head. There are no numbers on this head but has under it a 3 finger casting which I have read identifies a 1939/1940 high compression WLD head.

Before I search for a #6 rear head, is the consensus the same, lots of extra heat with no gain? Thanks again for the help.

Ronald V. Papasso
#3129

[Chris Haynes]

Generally sidevalves get more boost from porting and relieving than most other things. Sure compression helps but ya can't go very high on flatties.

[Sargehere]

Hi, Ron,
What's the underside of the head you found look like? A high-compression head would be basically flat across the top of the piston, with only the minimum recess for the valves to rise up into on one side, with a sparkplug hole in it. Your quest now will be to match it!

[Chris Haynes]

I am half way there because I found in a pile of parts from a basket case what I think is a high compression front WLD head. There are no numbers on this head but has under it a 3 finger casting which I have read identifies a 1939/1940 high compression WLD head.

Just for comparison this photo shows the heads with two bars or fingers. I belive the more bars the higher the compression?

[RvP]

3 finger front head

I have never posted a picture before and I hope I did this right. I have attached a picture of the front head with the "3 fingers" on it. The part number I got off with a pencil scraping is "19-39" which I am guessing is a 1939 WLD high compression head. This head looks slightly different than the one in your picture with the location and type of 3 fingers. The height of the ridge between the cylinder and head is about 1/4 the height of my #5 head. I need to find a #6 high compression rear head and give it a try.

[Ohio-Rider]

That 119-39 number may be just a casting number.
The #5 heads on my 1945WL say the same as yours.