Eddie Meyer aluminum heads
 

Hey Guys,

I have a 21 stud flathead with Eddie Meyer heads.
My research shows that the heads are rated 8.25:1 CR but my heads are about 89-90 lbs at each cylinder. If my math is correct, this comes out to around 6:1 compression.
The engine was built by H & H Flatheads and has about 800 miles on it.
Any ideas why such a discrepancy?

Richard

Re: Eddie Meyer aluminum heads
 

There are a few things that affect compression readings in addition to the heads, a big one being camshaft selection. Are you running a stock cam or a performance cam? The later intake valve closing of a performance cam will lower the cranking compression readings.


The distance the piston is below the deck at TDC is also a big factor. That's one reason why getting the piston tops within .040"-.050" of the cylinder head domes is important.


I'm sure you're aware, but the throttle needs to be held open when checking compression so the cylinders can fill properly or test results will be low.


Terry

Re: Eddie Meyer aluminum heads
 

If your engine has flat top pistons and the heads are for dome top your going to lose a lot of compression.

Re: Eddie Meyer aluminum heads
 

I don't think it's the heads. Mabe the rings haven't sealed yet?? ro??
Gramps

Re: Eddie Meyer aluminum heads
 

Hey Guys,

Cadillac, I bought the car last year with this engine in it. It has an aftermarket cam but I don’t know what it is.
Terry, again, I don’t know what kind of pistons it has.
Ron, how long does it usually take to seat the rings?

I’m no expert but it looks like any or all of these things could possibly be the culprit. I’m still surprised that there is such a big difference between the advertised CR 8.25:1and mine at 6.0:1.
Richard

Re: Eddie Meyer aluminum heads
 

Hi Richard-


Your actual compression may be higher than 6:1. Cylinder pressure starts building when the intake valve closes as the piston passes bottom and begins its way up. Shortly after bottom, the valve closes...but a performance cam delays this closing and thus gives less piston travel to compress the air, so the pressure at cranking speed is less. When the engine's running this also happens (and is one reason the low speed power suffers with non-stock cams) but when engine speed increases the pressure rises due to better flow dynamics of the cam grind and the power increase is realized.



Terry

Re: Eddie Meyer aluminum heads
 

Thanks Cadillac, that’s a good description that even I can understand.
So a cam designed for low end torque instead of high end power will yield higher compression figures?

Richard

Re: Eddie Meyer aluminum heads
 

Absolutely. Given the same engine, the cranking compression numbers are all about when the intake valve closes, and a stock or near stock cam closes the intake valves earlier than a performance cam does.



Terry

Re: Eddie Meyer aluminum heads
 

Rings should seat in a few hundred miles when properly lubricated. Ring break in is a crul way to out it, but accelorating onand off the engine on a back road is the easiest.Put it in 3 gear at around 30mph and accelorate tp 50. do this a dozen or so times and the rings will be seated. Now change the oil!!
Gramps

Re: Eddie Meyer aluminum heads
 

If engine was done by H & H I would be going to them for some assistance on whats actually been put into this engine. If at all they carry records of what assembly is used.
Phil NZ

Re: Eddie Meyer aluminum heads
 

Phil,
I would desperately like to know what’s inside this engine. I have the name of the person that H & H built the engine for but so far they have refused to give out any information on the build.
Richard

Re: Eddie Meyer aluminum heads
 

That's just weird. :confused:


Terry

Re: Eddie Meyer aluminum heads
 

I would suspect that H&H maybe didn't build the engine but the previous owner did, since he/she isn't forthcoming about the info. Easy thing to say for a selling point.
When cranking the engine for a compression check did you have WOT (wide open throttle)? You might try putting a little oil in the cylinders and re checking which might give you an idea about the rings.
I think the most likely answer is what TerryOH gave. Maybe this winter you should tear it down and check everything or at least pull a head and look at the top of the pistons.
Aluminum heads need to be retorqued regularly also.

Re: Eddie Meyer aluminum heads
 

It is really weird and makes no sense that H&H won't give you the build sheet. I'd call them and lean on them a bit.

Re: Eddie Meyer aluminum heads
 

Thanks everybody for all the information.
B & S, I’ll contact H & H again and see if they will give me the information. It would be really helpful to have.
Richard

Re: Eddie Meyer aluminum heads
 

Thats the approach I would take also then you know for sure what you have instead of guesswork. Good money would have been paid out if from H & H and the build sheet should be part of the deal!! Lean on them!!!
Phil NZ