[A Schab]

It's a clone.

[alloy indian]

I know but someone went to a lot of trouble to make it believable. It needs the air let out of the rear shocks though! I hate it when they leave a 69 so high in the rear the rake to the back makes them look like there going a hundred miles an hour siting still!.

[bird72]

So are 72 and 71 crossovers not interchangeable? Will repro work on 71? And another puzzle: some 197 heads are drilled for 2 end exhaust bolts and some only one? what I deduce from ebay ads. I just got set that have one hole drilled, and Ram Air Ent manifolds are cast for two bolts, so I should have shop drill end hole when do heads I assume (?).

[njsteve]

71 and 72 crossovers are different due to the exhaust riser opening shape on the 1972 heads. Major exhaust leak if you use the wrong one.

[4birds]

Originally Posted by bird72

So are 72 and 71 crossovers not interchangeable? Will repro work on 71? And another puzzle: some 197 heads are drilled for 2 end exhaust bolts and some only one? what I deduce from ebay ads. I just got set that have one hole drilled, and Ram Air Ent manifolds are cast for two bolts, so I should have shop drill end hole when do heads I assume (?).

Anthony, which heads do you have? If you have 71 HO heads, you must use a 69-71 intake crossover. If you have 72 7F6 heads, you must use the 72 intake crossover, as it is different.

Are you going to use factory GM exhaust manifolds or reproductions? (or headers?) The factory exhaust manifolds on the 71-72 HO's only used 3 bolts to hold them on. That's why the 2 holes are not there in the heads. The reproduction manifolds use 5 bolts (copied from the 73-74 SD) for improved sealing. Therefore you will need to drill and tap the heads if you use the 5 bolt reproductions or headers.

The first picture is of the GM 3 bolts OE manifold. Picture #2 is a R.A.R.E. reproduction round port manifold. Pictures 3 and 4 are 72's. The last picture shows the different long slot for the crossover for 71. (the 71 197 HO heads will match this long slot)

[4birds]

1972 and later gasket on top, up to 1971 gasket on bottom.

[PAUL K]

Originally Posted by 4birds

Anthony, which heads do you have? If you have 71 HO heads, you must use a 69-71 intake crossover. If you have 72 7F6 heads, you must use the 72 intake crossover, as it is different.)

You are correct when using GM parts, however most reproduction crossovers were designed to work with either head.

[bird72]

Just to clarify 71 heads and intake is what we have. I have oversize RA Ent new manifolds. In my prior aborted HO attempt the cracked factory manifold nightmare ensued and this time decided for once repro was a functionally better route. I need a crossover, have offer on repro, so doing detective work on opinion / fit / quality, it looks nice in pic. Slight appearance differences probably would not matter to me. Of course a 71 GM one would be preferred.

I looked on ebay on 71 head pics see some have all holes (?) wondering if some 197 came double drilled and some not. Or are double ones owner modded.... I lean towards drilling head as smart, but if it is of no value and degrades head I guess I would not, but really don't care in this area also as to head "virginity" too much unless drilling is just dumb move stuff value wise. But it does seem smart engineering wise to drill for grins.

[bird72]

That is what I thought Steve, thanks. Do you know anything on the end bolt situation? Should I concern on missing bolts or go with 3... (?) or drill & tap?

[rexs73gto]

You can use both just by installing a thin piece of metal behind the cross over at the port on the head to fill the difference in the gap that doesn't cover it. It's had to be done on a lot of late model heads when changing the intakes . It works fine & if you paint it you can't tell it's there.

[1971WARBIRD]

Originally Posted by bird72

That is what I thought Steve, thanks. Do you know anything on the end bolt situation? Should I concern on missing bolts or go with 3... (?) or drill & tap?

i'll just say I drilled and tapped mine. I liked the idea of more bolts holding, just me.

[Judge273]

Good information. 71 is much different in carb, linkage to carb, choke, the look of intake, and exhaust in configuration and part numbers.

Best to find correct piece. Tapping and drilling for nom makes its a molested part....

[Brewster]

Originally Posted by Judge273

Good information. 71 is much different in carb, linkage to carb, choke, the look of intake, and exhaust in configuration and part numbers.

Best to find correct piece. Tapping and drilling for nom makes its a molested part....

Altered might be a better term Mike

[PAUL K]

Most of the reproduction exhaust crossovers are designed to work with either 197 or 7F6 heads.

[The Boss]

Mike made that sound a little dirty didn't he?

['ol Pinion head]

Originally, 197's, whether early style with no dates, or the later production style cast in early Dec after the strike, only had 4 holes on the flange area to attach the exhaust manifold. I looked at heads on my '71's engines, as well as extras I have, and pics of both styles that have been on original engines that I've had in previous cars, also pics of ones Ive traded off, all only had 4 bolt holes, not 6.

In the late '80's, there was a fellow from the San Antonio area that at Tx swappers was buying up cracked roundport manifolds and I can remember him telling me, he was providing them to Delfield. Shortly there after Delfield had his version of the A-F body roundport manifolds recast. When he did, he used the later SD manifolds as the model. The SD manifolds have more attaching holes in them. From owning several 71 HO cars & quite a few pairs of 197's, what I believe you are seeing is heads that have had two bolt holes drilled and tapped so typical thin flange headers could more effectively seal. I don't see how a very rigid exhaust manifold, ESP the repro's from RARE, are not going to seal up with the right steel gaskets. Of course, several empty holes with no bolts in them is going to look odd, but some will probably see an oddity of viewing a roundport headed engine in the car. It's your choice how to remedy the problem, it's not like you are in several of our shoes and will get dinked in Concours judging at Nats for having the wrong exhaust manifolds, or get told the oversize manifolds are wrong for the car at Purestock events. just my.02.

[FrankieT/A]

When they reproduced the crossover, they reproduced the 69-71 one I'm sure is because of the year coverage. However, you can use a 72 crossover on earlier years but not vice versa. In my case the only 72 crossover I have is original to my 72 455HO Formula. The rest of my factory aluminum manifolds are Ram Air IV and when I aquired them over the years I was never able to secure the crossovers to go with them. So, what did is bought the the reproduction crossover and I mig welded the area in question and ground it smooth and finish it off with a file. Of course you can't weld to cast iron but in this case it's not structrual, the weld has enough bite to stay in place, it does burn away and is undetectable. I have over 50,000 miles with no issues.

[bird72]

thank you everyone for all the great input. OPH I agree on sealing part and will drill for basically appearance. Also agree on illogical car. I did get RARE gasket also. BTW, the big bottom angle cut flange is razor sharp on their manifolds. Not too much blood, but in the handy part of hand no band aid works Getting repro xover from member (THX) so the world keeps spinning. this is great thread, lucky.....

[bird72]

Don't any of you HO guys want to run an unpainted manifold just a little bit? Looking at my new acquisition on the workbench, I will really have to resist not painting, but I will paint no doubt. Keep picturing a patina'd aged aluminum atop the motor. I know it is a felony though. Although if anyone has a car to commit felonies on...

[4birds]

Originally Posted by bird72

Don't any of you HO guys want to run an unpainted manifold just a little bit? Looking at my new acquisition on the workbench, I will really have to resist not painting, but I will paint no doubt. Keep picturing a patina'd aged aluminum atop the motor. I know it is a felony though. Although if anyone has a car to commit felonies on...

Been there, done that. I had a bare aluminum intake on mine for 30 years! And chrome stuff everywhere too. What was I thinking? Well, that was then, this is now. I put it back a lot closer to the way it came, although there are MANY things that are still not 100% correct and probably never will be. That's OK, because I am happy with it the way it is.

The thing is, it's your car, and you can do whatever makes YOU happy with it. Go bare with the HO intake, and if you don't like it after a while, paint it.

Its the journey and stories with these cars that make it fun. Enjoy it the way YOU want it.