L89 vs L71 heads

[Jack O.]

Does anyone know if the exhaust ports of the BB aluminum heads (L89) are different from the cast heads (L71)? What has me suspicious is that the Hedman hedders application chart for a BB '69 with sidepipes indicates that they will not fit if the car is fitted with aluminum heads which is puzzling since both motors take the same exhust manifolds.

Thanks in advance,

Jack Ottofaro

[Jerry Clark]

Re: L89 vs L71 heads

I have a set of 392 aluminum heads on my 67 L71 they are, to the best of my knowledge identical
jer

[Joe L.]

Re: L89 vs L71 heads

Jack------

There was a very slight difference in the configuration exhaust manifold mounting surface of the 1969 L-71 heads, GM casting #3919840, and the L-89 aluminum head, GM #3919842. This configuration difference did not affect the installation of exhaust manifolds or exhaust pipes. I do not understand why it would affect the installation of headers, either. But, apparently Hedman thought that it would (or MIGHT). So, why take a chance for a very small number of potential installations?

[Craig S.]

Re: L89 vs L71 heads

Jack - as Jerry and Joe mention, differences were minor. The rectangular intake port iron heads mostly had square exhaust ports, while the aluminum rect intake port heads usually had round, D, or Cport exhuasts. the bolt flanges were all the same. I have noticed some aftermarket headers form the round tubes square near the flanges, and this may have been why Hedman stipulated the difference, since the gas flow would not be as smooth with a round style port....Craig

[Chas Kingston]

Re: L89 vs L71 heads

Might I suggest that the torque required to seal the headers might have been sufficiently high that Hedman did not want to take the risk of someone stripping an aluminum head.

Geezer

[Wayne M.]

Re: L89 vs L71 heads

If they don't list the same restriction for '68, then I'm with Craig; the addition of the D port design "...6041" head for L88's only in June (?) 1969. I believe the L89's continued with the "...842" until MY end.

[Bill Stephenson]

Re: L89 vs L71 heads

-------Maybe also possible that Hedman(in the business of building headers for race cars)could be referring to the many aftermarket raised-port aluminum heads that are available.Ports on my race motor are not raised much but,boy,does it throw off the fitment of the headers.Just a thought..........Bill S

[George Daina]

What the manufacturer was referring to.....

if you use aftermaket heads with the raised exhaust ports, aka Edelbrock or Dart, the headers will interfere with the frame. If you use factory GM heads, regardless of 077, 074, or iron, the headers will fit, just prefit them.