Aluminum head reality check.

Diavolo

Diavolo

Member
OK, so I am considering high compression Offy heads for 8BA rebuild but I have to ask...

Just how much actual power will I make over stock iron heads and steel gaskets compared to high compression heads and fiber gaskets. Using roadrunner engineerings chart, it's 2.1 points higher compression but does anyone have real world number differences to justify buying the heads or should I just run it as is.

.040 over w/isky max1 cam.
 
IMO shaving the stock heads will give you as much as the aluminum heads, for a lot less coin. No bling factor tho.

Search on here for how to achieve .050" clearance by measuring with aluminum balls or clay.
 
I'm far from an expert on heads, flow, and compression, but it sounds like compression gained for the cost is your concern. there is a lot of support here for measuring the distance between the piston and the head and then resurface the head for .040-.050 clearance when the gasket is installed and torqued. If you aren't familiar with the measuring process, search the forum for "claying heads" or some such for the process. Someone will come along shortly with a link to a thread that explains it.

There might be some flow advantages to some aluminum heads that you won't get with surfacing the iron heads. Others will help with that.
 
Claying heads simply means filling the area above the pistons and valves with modeling clay, then turning the crankshaft one full revolution, then removing the clay to see if there was any conflict between the parts and the head surface. We do this to check to see if there was any previous work that involved shaving either or both the heads and block surface. If conflict with the valves if found, the pockets must be milled to resolve the problem. We seldom worry about new finned heads, but old ones are often suspect and should be checked. This is true when stock heads are swapped because some need modificationif early or late types are used.
 
You need to read JWL's book Flathead Facts for the REAL dirt on flathead performance claims, and you need to do it BEFORE plunking down any $$$$ on gear.
 
I figured this. I will get the book. IMO, 10 hp for $600 is not worth it. I'm in a mostly stock situation anyway and I would rather clay and shave my stock heads than throw a bunch of money for such a small return.

I increased the valve size to 1.6, so I might just take the stock heads to the machinist and have them shave them down.

Thanks for the heads up!
 
You may have to open up above the valves after you chop the stock heads for 0.040" piston-head clearance, due to the cam. In doing this your gonna loose some of the compression gained by chopping them.
The 8-10 hp gain spoke of above, ain't the whole story. The torque gain in low revs, is much much more noticeable in your pants. Every time you press the loud pedal, you'll be reminded high compression is a good thing. On your engine it'll make a bigger difference due to you already loosing a fist full of low down torque due to that max1.
So real world difference? Yep, a bunch. Depending on car, use, trans, rear gear, tires and such, I'd think your gonna like 55-60cc heads as its a small engine. Can you cut stockers to this small? Don't think so.
Martin.
 
Forgot this, you state a bunch of money for such a small return. A pair of high compression heads is a probably one of the highest bang for buck modification. In real world driving experience.
Martin.
 
Reading Johns book is a must here, especially considering the amount of low speed torque you loose with the cam. Increasing the displacement and milling the heads will increase Cr. you can also use different stock jeads. the smallest are the 81A (39-41) they will fit ALL 24 stud blocks with some simple mods. Now measuring the cc's of the heads and the clearance to the piston, will tell you how much you have to remove from the head. On my 280 ci engine I used EAB heads milled .040". This is actually too much, so I used a die grinder to increase the area in a few spots. This gives me 8.2:1 CR and is a real axle breaker.
 
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I put them on mine because I got a set of used ones in perfect condition for $100 30 years ago when very few folks were even interested in flatheads. If they made any difference I couldn't tell it. BUT. They look so cool!!!!! ;)
 
Dia,
The cheapest HP is added compression per Barney Navarro and many others.
I sure agree with Ol' Ron and JWLs book and EAB heads. Regardless of whether you
go alum or iron I can guarantee you would be unpleasantly surprised to see the mis-
match between the location of the combustion chamber in the head (regardless iron
or alum) and the actual location of the piston/cylinder bore. I've done enough
individual cylinder to comb chamber matching to give me a headache thinking about it.
Is it worth it ,you bet it is !
Charlie ny
 
A lot of the aftermarket aluminum heads were designed for applications where the block is relieved a bit. They really haven't changed much over the past 50-years. The crow foot chambers of a lot of aftermarket heads would probably benefit from relieving but the stock heads likely don't. Back in the day, a lot of hot rodders were big on relieving the block or working with a truck motor that was already partially relieved so that was the in thing back then. A lot of water (and testing) has gone under the bridge since then. JWL wrote a book about testing different ideas that is invaluable for the folks that want to hop these little iron wonders up.
 
Different lengths needed, your head studs will of course have to be changed out. Common to substitute studs for bolts but longer studs will also work. If your studs will come out great. If not, they are really a ***** to remove (If they've been in there for 70 years). Good luck with it. The look of the offy heads is worth the work (maybe).
 
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Thanks all for the additional info regarding the cam and loss of low end power. Some thing to think about for sure. I'm gonna look at my 8BA heads as I have them already cleaned and ready to go. Get some aluminum foil and shims and see where I am at.

Worst case scenario, I do this and get aluminum heads later. Not worried about trying the milling and see what happens with it.
 
If you try chopping some stock heads any chance you could cc them before chopping and after along with how much they were chopped, and a before and after seat of the pants comparison please?
Info like this is real good stuff to have, and can benefit a bunch of folk.
Many thanks,
Martin.
 
I just re read my post and found a miss print caused by bad eyesight. I wrote the heads gave 9.2. THis should read 8.2, sorry.
 
If you think of the 10 HP as a 10% increase, is it anymore worth it.. 10% is a big step on any motor.
 
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