Egge versus “Offenhauser” Pistons

[Fortunateson]

Egge versus “Offenhauser” Pistons

I’ve reached out to a couple of Ford Barn gurus but I thought I’d ask the general group. I’m rebuilding a ‘49 Merc engine and I’ll be using original Eddie Meyer heads. Speedway offers Egge as well as their licenced “Offenhauser” pistons. While doing some research the question of the tops of the pistons appeared to be relevant. So any experienced info regarding which brand to use?

Thanks in advance!

 

[Bored&Stroked]

Re: Egge versus “Offenhauser” Pistons

I have not used either of them in years, but I know that some of the Egge cast pistons had a piston crown that was similar to some of the Ford pistons -- with more of a "pointed" center (actually used a multiple radius/ellipse shape - see the last sketch).

Given that most after-market heads used a consistent radius dome, sometimes these cast pistons would want to hit the heads in the middle of the chamber. Due to this issue, I've seen engines where somebody took a file or grinder to the piston crowns to get the heads to fit (crude solution).

The solution was that I made a 3D CAD design and we had to CNC the chambers of the heads to match the piston shape (expensive operation). I would review my heads (which I believe you'll find to have a consistent radius like Ross pistons uses). If so, then make sure your pistons are made with the same shape.

You really want your piston shapes to match your head combustion chamber shapes, such that you can achieve a consistent .040 to .045 "squish" above the piston. I can't stress enough how important having a tight and consistent squish is for flathead performance. I've seen plenty of poorly running flatheads - due to having a too big of a squish above the pistons. Did they run . . . "Yes" . . . did they run as they should have . . . "No". To achieve this squish, it requires the right parts (piston crowns and chambers that match), some measuring with aluminum foil balls or clay and typically some work (milling) of the heads. Make sure you check your valve-to-head clearances while you're at it.

The following diagrams will help you see the issue - you might want to review it with your sales folks at Egge:

Egge Cast Profile - notice how the center is deeper and more pointed:



Ross / Edelbrock Heads Profile



Ross / Edelbrock Heads Sketch



Egge Sketch (Parametric - used to drive the profile for CNC)

 

[Charlie ny]

Re: Egge versus “Offenhauser” Pistons

Guys I've detailed how I keep things happy between the crown and comb chamb...no
5 min job.....
Hang the head on 3 studs , no gasket in place.

I do a rough determination using clay or alum balls how much to mill each head.
Apply prussian blue to the piston crowns then hang the head on the 3 studs
and rotate the motor few times with hand pressure on the head. When you remove the head you will clearly see the points of contact in each chamber. Very carefully remove those
contact points , I use a die grinder. The more judicious grinding you do the more proficient

you become. During this labor intensive process it becomes clear that major contact
on one bank is at 3 o'clock the other bank 9 o'clock. What is happening of course is the chambers are being absolutely mated to the crown.
Any way
When done and the head torqued in place the collapsed head gasket gives the req'd .038/.040 squish
10 to 12 hours/ head.
Charlie ny

 

[Ol' Ron]

Re: Egge versus “Offenhauser” Pistons

Excellent information here. I often thought that Offy pistons were made by Janns. If so, this is a heavy piston with poor expansion characters. For bore sizes in the .020./ .060". I'd use stock pistons, these can be fit very tight.
Gramps
PS Van Pelt has them
G

 

[supereal]

Re: Egge versus “Offenhauser” Pistons

Be cautious about any pistons ordered. At our shop, we have received two shipments that contained mismatched sets, even from regular suppliers. It seems that the current upheaval in the available market is responsible, according to the sellers.

 

[Ronnieroadster]

Re: Egge versus “Offenhauser” Pistons

I always go with Egge and never use Speedway when buying them. Order them directly from Egge you will be glad you did. So far I have never experienced any issues with numerous brands of new and used aluminum heads using Egge pistons.
Ronnieroadster

 

[Fortunateson]

Re: Egge versus “Offenhauser” Pistons

Thanks for all the replies! I’ll contact Egge directly as well as You van Pelts. I don’t want to screw This up. Part of the problem is that I’ll order out of the states and cross the line to my mailbox in Blaine Wa. to pick them up. Now my machine shop who have done some preliminary work says that it may be late summer before they can get back on it. So I have to be aware of return policies as to length of time before returns are accepted. Perhaps I’ll order everything except the piston and rings for now.

Now, what are your opinions regarding centre dump headers on this engine which is going into a ‘32 5W coupe with either a F1 steering box or an upgraded ‘32 box. (Which is another question/debate). I’ve read that the centre dumps exit just above the wishbones when they are not split which mine will not be.