Head Gasket opinion for GT-40 clone aluminum heads + 351W

[foothilltom 33]

Hey guys, my apologies if my explanations are ambiguous as I'm not entirely savvy on this stuff yet.  For what it's worth, I have no idea if my 351W block was decked.  The PO said it was stock, but it was a craigslist deal and you never know.  I never did have it examined nor do I know how to confirm.  The aftermarket GT-40 clone, Chinese manufactured, heads I got at a speed shop on eBay.  As I may have mentioned, that seller gets horrible reviews on Yelp for his engine builds, but nobody seems to have maligned the heads themselves.

My original Edelbrock Performer was an unknown quantity as well.  It fit great on the original block with the cast iron heads (at least visually) as it was a running motor (again according to the PO).

When I said the "rails of the manifold", what I meant was the top of the sides of the manifold did not adequately cover the top of the ports on the heads, essentially exposing a tiny amount to the atmosphere. :)  This obviously didn't go well when I got it running for breakin.  My measurements revealed that the ports on the aluminum heads were "situated higher" off the deck than the cast iron heads (that's where .2" came in).  The Performer was never going to cover this gap w/out some kind of serious machining.

Fate stepped in and my friend had a Weiand Stealth that was new (if not dirty).  I've since installed that and -- yesterday -- re-fired up the motor.  Huzzah!  As of this moment, I can report initial success.  I need to do some tuning today (timing, idle-mixture, float-adjustment, etc.) but the motor actually idled yesterday, so that's an indication that my vacuum issues are resolved.

When I called Weiand (Holley) tech support, they said the Stealth was just manufactured "taller" than the Edelbrock and they just happened to work better with the GT40 style heads.  I took it as a design-consequence, not a design decision.

Anywho, I'm super grateful for the help here.  I think I'm a big step closer to a driver.  To 1969_Mach, I did take the time to remove the lifters, inspect, and re-install with assembly lube.  Same for pushrods and rockers.  Re-adjusted the rockers carefully as well.  I lost a number of hours to my original bone-headed mistake of not looking hard at the fit of the Performer during original assembly, but that lesson is now hard-learned.

Tom

[barnett468 418]

1 hour ago, foothilltom said:

Hey guys, my apologies if my explanations are ambiguous as I'm not entirely savvy on this stuff yet. 

When I said the "rails of the manifold", what I meant was the top of the sides of the manifold did not adequately cover the top of the ports on the heads, essentially exposing a tiny amount to the atmosphere. :)

Not to worry, you did a great job, and nothing that you in particular wrote caused any issues whatsoever.

[barnett468 418]

1 hour ago, foothilltom said:

When I called Weiand (Holley) tech support, they said the Stealth was just manufactured "taller" than the Edelbrock and they just happened to work better with the GT40 style heads. 

That explains why I thought your weiand was likely "taller" than a stock manifold based upon all the info you posted. It was really a matter of simple deduction along with around 45 years of experience doing his stuff for a living.

[DocWok 30]

20 hours ago, foothilltom said:

My measurements revealed that the ports on the aluminum heads were "situated higher" off the deck than the cast iron heads (that's where .2" came in).  The Performer was never going to cover this gap w/out some kind of serious machining. 

Tom

Your original heads had probably been milled by some unknown amount ,certainly not .200"  but a substantial amount none the less in the past, for whatever reason (raise the compression, bad machinist, who knows.)

Whatever it was cut, it was much more the a light surfacing and this in turn moves the position the inlet manifold bolt hole inwards , so then the standard Edelbrock manifold bolt holes would no longer line up with the corresponding holes in the heads, and so the manifold would have  to be cut as well to allow it to sit lower in the valley to allow the manifold bolt holes line up again.

This would explain the loose fit of the Edelbrock manifold in the valley when you fitted the alloy heads (returning it to stock bolt hole locations) and the Edelbrock now not quite covering the inlet ports of the new heads.

Machining of the original heads would make the inlet ports on the aftermarket head appear to be situated higher from the deck compared to the original milled head.

In my 47 years of working on cars I have seen this a couple of times and it would be easy to see why someone with lesser experience would become confused.

Your on the right track now and I wish you the best of luck with the rest of your build.

[barnett468 418]

Glad it wasn't me that was confused, and between me, you, and 1969 mach 1, we figured out the mystery behind your taller than stock weiand intake, so one mystery solved.

If you are curious,  I can tell you how to easily determine reasonably closely how much your heads were milled, because I also ran the cylinder head rebuilding department for a local high end shop for a while and rebuilt countless Ford and Chevy heads as well as BMW, Porsche and Mercedes heads etc, and determining how much stock heads have been milled is obviously something that most people that have less experience in this area can't do, unless they happen to find the info by doing an internet search or something.

As far as the top of the ports on your chinese heads being .200" higher than the ports on the stock heads are, this is absolutely no indication that your stock heads were milled at all, thereby lowering the ports, which again, an experienced person would know. The ports in your chinese heads should be significantly lager than the ports in your stock heads anyway, and they most likely did in fact, make the top of the ports higher than a stock windsor head, so there is no "smoking gun" evidence there either that suggests the stock heads were milled at all, although my guess is that they have been. In addition to this, if they had been milled a lot and the intake had been milled a lot to match them, as one person here suggested several times now, you likely never could have even bolted the intake up unless the bolt holes in the intake were enlarged, because when heads or blocks are milled, it moves the intake bolt hole in the heads inward, and I have in fact run into this exact problem a few times. Also, if the intake bolt holes in your chinese heads are in the correct location, and the bolt holes in the intake lined up well with them and those bolt holes were not enlarged, it strongly suggests that your intake was milled very little, if any at all.

I may also have a stock 351 intake in my 54' trailer of Mustang parts that I can measure then give you a dimension of that you can compare to your eddy intake to determine if it has been milled, and if so, approximately how much it has been milled.

Your block may have been milled as well which hasn't been mentioned, but even if both the block and the heads were milled, the combined amount would still be far less than  200".

[1969_Mach1 333]

I thought it was something more simple like a slightly different intake port location on the imported GT40 clone cylinder heads.  I will add, I have tried many intakes on the 351W in my 69 Mach 1.  The Edelbrock Performer RPM and Torker II both sat down lower than the Weiand Stealth that is currently installed.  They all sealed just fine, but the fitment was a little different.  In the end, of all that I tried the Weiand Stealth provides the best performance for a street driver.  At least for my motor, trans, and rear axle combination.