Purchased a set of Heddmen Shorty Headers (68476) from Summit apparently designed to work with the third gen 305 Firebird. Installed the headers easily during my 305 rebuild, and they seem to fit perfectly on the engine stand. But now I'm adding accessories (alternator, steering pump, A/C compressor) and noted that the Summit application information on the 68476 says modification to the rotary A/C bracket is necessary. Anybody know what modifications they are talking about, and/or is a modified bracket available? Have e-mailed this question to Summit and also awaiting their reply.

 

Heard back from Summit. There are two different types of Rotary A/C brackets for 8 cylinder third gen FB's (both shown in diagrams in the FB shop manuals). One fits the Heddmen 68476 with no modifications at all, and the other just requires some minor notching out of the bracket with a grinding tool. Doesn't sound like a big deal. Most important is that I'll still be able to use my A/C with my Heddmen headers......yeah baby!

 

Knowledge gained from fundamental understanding breeds confidence to challenge the unknown.

 

OK, job done, but not at all the simple matter of "grinding" as suggested by Summit's e-mail tech line. The issue, apparently with most aftermarket headers (including my Heddmen) is that the factory 85 FB 305 a/c bracket bolts to threaded extensions on the rear ends of header studs #1 and #2, as they exit the factory headers about 1 1/2 inch away from the head. Also the factory bracket is contoured to straddle exhaust header #1 about 1 3/4 inches from the head. Thus, the factory a/c bracket will only correctly line up the compressor and power steering pulleys if positioned and bolted tight about 1 1/2 inches away from the head. Unlike the factory headers, however, aftermarket headers bolt directly to the heads using their 1/4" steel base. Thus the factory A/C bracket has nothing but air to bolt to. Even worse, aftermarket exhaust header #1 protrudes several inches outward and backward, and thus gets seriously in the way of the rear portion of the factory A/C bracket. Simply grining the rear portion of the bracket will not remove enough of the bracket to ever allow it to clear exhaust header #1 when positioned 1 1/2 inches from the head. In fact, the entire rear portion of the bracket needs to be ground off (or much more easily, simply cut off with a metal blade saws all). This modification completely frees up the rear portion of the bracket away from the exhaust pipe #1, but eliminates its ability to fasten to header bolt #2. And then, of course, the forward portion of the bracket still needs to be bolted up to the #1 header bolt about 1 1/2 inches from the aftermarket header's base. So I just yanked one of the old factory header bolts which had a built in nut (to torgue down the header) and a threaded extension (used to bold various accessories), and installed it upside down. Then I created a metal spacer sleeve by stacking oversized nuts/washers over the bolt's threaded extension so that the factory a/c bracket front portion could bolt on at exactly 1 1/2 inches. This same #1 bolt also supports the base of the power steering pump lower bracket under the factory A/C bracket. And even though that single header bolt holds the base of both brackets, each is also secured by several other bolts to various places on the block, heads and manifold, holding the net assembly quite tightly. After adjusting V-belt tightness and bolting the power steering pump and the a/c compression to their factory and modified brackets, the belts lined up nicely. And the entire assembly seems pretty strong even though using only the forward bolt of the original A/C bracket. While I haven't actually tested it yet, I found old postings in this same thread (unfortunately after I had already figured it out on my own) that suggested doing exactly same thing (i.e. cutting off the rear of the bracket), and claiming that the end result works nicely. The only other option I can think of if this fails, is to weld a short piece of 1/4'' steel to the amputated rear base of the factory a/c bracket and route it over to bolt hole #3 in front of the driver side exhaust pipe #2. While this would clearly provide support approaching that of the original a/c bracket, it would be a much more substantial modification which I don't really think will be necessary. I suppose only time will tell. Hope this is helpful. Have taken a couple of pictures which I'll try to post.

 

This is Extremely helpful! thanks for the write up.

 

Well friend I'd like to thank you for the pictures and advice. Just performed surgery on my 84 Z28 A/C bracket. Got it back together just fine.