I'm planning my winter project early and I wanted to do some research.
I wanted to switch my 906 heads to a set of 516's I've got. I planned on putting in new stainless valves, increasing the exhaust to 1.74, new springs and gasket matching the ports. Do I need to do anything else? Bronze guides? or just knurl the originals? what about hardened seats?
I also planned on surfacing the heads just to make them true.
I have trw low compression pistons and I thought I might see a nice gain in power by doing this.
Any reason why I should not do this?

thanks for the input
scott

every thing you listed is great ex that the 906 heads flow much better than the 516's & you may end up worse off even w the higher CR from the closed chambers. If you have not purchased those parts/services yet you might consider a set of stealths or another set of 906's(& people have milled them quite a bit) to prep & have em ready to throw on & on the local craigslist there was a set of bare 906's for $50 & no takers so they are out there cheap. I'm considering having my ace metal man weld up the open chambers closed in a set of 906's then milling them flat as the 906 is a fairly good flowing iron head & I have yet to see one that has cracked if it wasn't overheated but those stealths keep looking better all the time.

i think the aluminum head with lower compression would not work very well either. What about a set of 915's built up the same way?
I have several sets of 906's but i thought I would be better off getting the compression higher by switching to a closed chamber head.

thanks
scott

If you want to stick with the iron head,go with the 915.There hard to find a decent set,I know I'm still looking .A member here sent me an offer for some real nice 915 heads fully loaded,but a bit steep for my purpose.If you want his e-mail pm me and I'll give you his info,they may still be for sale.

with the work you mentioned, you would probably be money ahead in the long run to get some eddies.

the whole can't run aluminum with low compression is kind of a myth.

it also might be cheaper to keep your heads, pull the motor, and if it mics out good for cyl taper, do a hone job and get some higher compression pistons.

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the whole "can't run aluminum with low compression is kind of a myth".

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Absolutely!

Whether the head is iron or aluminum makes no never mind with a low compression. If the motor had 8:1 with iron heads and you slap on 8:1 aluminum it'll still run as well - with tuning maybe a little better.

However, where aluminum shines is when you get into higher compression. Compression means power and the heat dissipating ability of the aluminum heads usually allows you to run about a point more compression on the same grade fuel i.e. where you'd only be able to run 9.5:1 with iron heads on pump gas without detonation, you could run 10.5:1 compression with aluminum heads with no detonation.

In a nutshell....a total waste of time, money and effort to make this swap from 906's to 516's!

My 2 cents.

I had my 516 done with 2.14 1.81s.They were totally reworked and new guides and some porting.I had like 900 in them.They worked well on the 440.That was before aluminum was cheap.Now I have the Stealths.You can just feel the difference.They are on the kids 62 300 now and it runs well with them also.I agree get Stealths or Eddys.Just have them checked before you install them.I have 12.5 slugs in my street 440.Rocky

ok the newer aluminum heads sound like a viable option, so which ones are better the stealth or the eddys? Eddys are a little higher, but do they have better parts in them? what would i need to have checked out before installing?
out of the box what kind of horse power gains 20% reasonable?
will they work with stock manifolds or would headers be the way to go?

As always great information
thanks
scott

Eddy's are definatly a better head and have the best flow of the two out of the box. Real good bang for the buck!

It depends for what 400 difference you are 1/2 way to ported and flowed Stealths.Plus they have straight plugs.Mine I changed the springs retainers and locks which I would have done to the Eddys also.My .588 cam and 4 speed I wouldnt trust stock from either.My shop backcut the valves and cleaned them up a bit.Other than that its a toss up.Maniflods I dont know if they fit with the Eddy angle plugs some headers have problems with them.HP gain depends on the motor.Id say 50 horse isnt out of the question for either over stock heads.As far as which flows better OOTB its a toss up.Both probally use inflated numbers and the difference isnt that much.Rocky