Author Topic: HO intake problem  (Read 3668 times)

71455formula

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HO intake problem
« on: September 20, 2015, 07:53:27 PM »
I have an issue. I put my HO intake on the car today. It's on HO heads. If you look at the pics the exhaust crossover has a gap between it and the gasket. They are the correct gaskets from felpro. 90123's. Has anyone else ran into this?

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PontGuy

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Re: HO intake problem
« Reply #1 on: September 21, 2015, 07:37:55 AM »
Yup, common issue especially when mixing and matching heads and intakes from different years.

The size of the crossover ports changed after 1972.  Scroll down to the "Exhaust Crossover Port Matchings" table here:  http://www.wallaceracing.com/head1.htm

If your heads have the short square crossover ports then its easy, just get the correct small crossover port gaskets.  If the heads have the tall rectangular ports then it will take some creativity to use the crossover without leaks.
1974 455 TA, blue on red HPP cover car
1969 Lemans Vert - 455 powered sleeper

The best way to show a car is to drive it!

71455formula

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Re: HO intake problem
« Reply #2 on: September 21, 2015, 09:06:28 AM »
No mix match here. Intake and heads are 71 HO.
1971 LS5 Formula. It's on the road finally!
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PontGuy

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Re: HO intake problem
« Reply #3 on: September 21, 2015, 09:44:47 AM »
Hmm, do the heads have the small square ports?  Because it sure looks like that's what the intake crossover is designed for.

I had one of the 69 RAIV factory manifolds on a set of 68 RA heads years back and the crossover matched up fine, but I don't remember the details.
1974 455 TA, blue on red HPP cover car
1969 Lemans Vert - 455 powered sleeper

The best way to show a car is to drive it!

oldskool

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Re: HO intake problem
« Reply #4 on: September 21, 2015, 10:26:29 AM »
Maybe the crossover was milled down for some previous build, in which the heads and deck were milled down a lot. It's best to take equal amounts off both the combustion chamber and intake sides of the heads. But, some guys cut the intakes down instead. In which case, that intake will not be a good fit for a different engine that has not had the heads and deck cut down as much.

This may not be your problem. But it has caused problems for lots of guys. :(

There is a pic at the link below, which shows that the 7F6 '72 HO heads do indeed have the blind hole which causes the mismatch problem. I'm just going by the description of the pic. I have never owned any '72 HO heads. So, is it possible that either the crossover or the heads are '72 ?

https://www.google.com/search?q=pontiac+7f6+heads&espv=2&biw=1052&bih=664&tbm=isch&tbo=u&source=univ&sa=X&ved=0CBwQsARqFQoTCODXovnGiMgCFZcWkgodf2sNcw#imgrc=mVwhajnehVMFuM%3A

http://www.ebay.com/itm/72-PONTIAC-TRANS-AM-GTO-455-HO-455HO-ROUND-PORT-7F6-CYLINDER-HEADS-/370896836778?nma=true&si=70%252FcrQGlC6ixjN6RyN%252BJJADN%252Bbs%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

This article says that the '71 and '72 455HO engines had different crossovers, with different part numbers. Check your crossover # to verify which one you have.

https://books.google.com/books?id=MGzXnpw2xwoC&pg=PA516&lpg=PA516&dq=intake+crossover+for+a+1972+pontiac+455ho+engine&source=bl&ots=fx8Kr_9zwy&sig=-n0OUcwilRWmr__cdwKon7zav-0&hl=en&sa=X&ved=0CB8Q6AEwAGoVChMI-Lz6t82IyAIVRgySCh0ypg-s#v=onepage&q=intake%20crossover%20for%20a%201972%20pontiac%20455ho%20engine&f=false

Reproductions of the crossovers show that they will fit '69 thru '71 round port heads, but NOT '72 heads. So, '72 and later heads have the small square heat riser holes, with the blind hole just above them. That means that the crossover with a large rectangular hole on one side, won't work on '72 heads.

https://www.npdlink.com/store/products/crossover_intake_cast_iron-146960-10248.html

 I assume the crossovers will be like the crossovers in the one piece D-port intakes. The '71 will have a large rectangular hole on one side. The '72 will have small square holes on both sides.

http://www.hotrod.com/how-to/engine/hppp-1301-pontiac-cylinder-head-modification/
« Last Edit: September 21, 2015, 11:51:06 AM by oldskool »

Re: HO intake problem
« Reply #4 on: September 21, 2015, 10:26:29 AM »

71455formula

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Re: HO intake problem
« Reply #5 on: September 21, 2015, 10:42:01 AM »
When I look at the gasket the crossover has the large opening and matches the intake ports of the HO heads. Is there a gasket set designed for the HO heads with the small crossover?
1971 LS5 Formula. It's on the road finally!
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2013 GMC Sierra Denali 6.2 6 speed AWD (sold)

PontGuy

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Re: HO intake problem
« Reply #6 on: September 21, 2015, 11:13:26 AM »
That blind rectangular hole on the 72 heads does not have to be covered so no worries there.  And they do have the small square crossover port.  Here is a link showing that the 71 HO 197 heads also have the small square crossover port, but without the blind hole.

https://www.google.com/search?q=pontiac+7f6+heads&espv=2&biw=1052&bih=664&tbm=isch&tbo=u&source=univ&sa=X&ved=0CBwQsARqFQoTCODXovnGiMgCFZcWkgodf2sNcw#tbm=isch&q=pontiac+197+heads&imgrc=IqkxKRS2Xu1Y2M%3A

Assuming that your heads look like one of those in the pics... regardless of what the catalogs say all you need are the gaskets with the small crossover ports and you will be good to go.  The intake height port height should be the same (or very close) for the HO heads and the D-ports, so don't worry about that.  These will work:

http://www.autozone.com/external-engine/intake-manifold-gasket/felpro-intake-manifold-gasket/pontiac/trans-am/1973/8-cylinders-t-6-6l-4bl/69925_0_0/
« Last Edit: September 21, 2015, 11:15:09 AM by PontGuy »
1974 455 TA, blue on red HPP cover car
1969 Lemans Vert - 455 powered sleeper

The best way to show a car is to drive it!

oldskool

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Re: HO intake problem
« Reply #7 on: September 21, 2015, 12:13:38 PM »
I'm not trying to be disagreeable, but IF his crossover does indeed have the large rectangular hole on one side, as he said, then I don't see how those gaskets, with the small square holes will seal up the large rectangular hole. If you look at the difference in the size of the large hole in the crossover and the small hole gasket, I think you can see what I mean. Those small hole gaskets are made for '72 & later heads. Now, if he has a '72 crossover, I think those small hole gaskets will work. That would be just like using a new Edelbrock intake. They have the small crossover holes on both sides. So, they'll work with either the early or late style heads.

http://www.hotrod.com/how-to/engine/hppp-1301-pontiac-cylinder-head-modification/

I'd like to see pics of the large hole in his '71 crossover, and the 197 casting # on his '71 heads.
« Last Edit: September 21, 2015, 12:34:03 PM by oldskool »

PontGuy

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Re: HO intake problem
« Reply #8 on: September 21, 2015, 12:20:48 PM »
If he does have a large port on either of those heads then yup, those gaskets won't work.  That's where creativity would be needed.  I'd like to see the pics that you suggest too.
1974 455 TA, blue on red HPP cover car
1969 Lemans Vert - 455 powered sleeper

The best way to show a car is to drive it!

oldskool

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Re: HO intake problem
« Reply #9 on: September 21, 2015, 12:46:13 PM »
If he does have a large port on either of those heads then yup, those gaskets won't work.  That's where creativity would be needed.  I'd like to see the pics that you suggest too.

Actually the earlier heads don't have large rectangular holes. It's only one side of the '71 and earlier CROSSOVERS that have the rectangular hole. That's why the aftermarket alum intakes will fit either early or late heads. Those intakes have small square crossover holes on both sides, just as the factory '72-up crossovers do. I've read that the larger crossover holes were used as a "choke stove". It provided more heat for the divorced style choke coil. Then, in '72 because of the blind hole in the heads, the large hole in the intake could not be used anymore. This may have caused the '72 model chokes to not work as well. Anyhow, for '73 models, they moved the choke to the side of the carb. They were called "hot air" chokes. :)

http://www.wallaceracing.com/intake-crossover.html
« Last Edit: September 21, 2015, 01:39:46 PM by oldskool »

PontGuy

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Re: HO intake problem
« Reply #10 on: September 21, 2015, 01:06:33 PM »
That's exactly how I remember it, though its been a while now since I had an early engine apart.  And his crossover certainly looks like it has the small ports.  So my bet is that the gaskets with the small crossover holes will work.

I had one of the 69 RAIV intakes years back but can't remember what the crossover ports looked like on that one.  And don't know if any changes were made for the later versions.

Hope we hear back and find out!



1974 455 TA, blue on red HPP cover car
1969 Lemans Vert - 455 powered sleeper

The best way to show a car is to drive it!

71455formula

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Re: HO intake problem
« Reply #11 on: September 21, 2015, 01:38:28 PM »
I'll pull things apart sometime this week and show yall.
1971 LS5 Formula. It's on the road finally!
2013 GMC Sierra 5.3l 6 speed Diamond White(sold)
2013 GMC Sierra Denali 6.2 6 speed AWD (sold)

71455formula

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Re: HO intake problem
« Reply #12 on: September 21, 2015, 04:32:05 PM »
Talked to Butlers and they said this is the fix.

http://www.summitracing.com/parts/fel-1233/overview/make/pontiac
1971 LS5 Formula. It's on the road finally!
2013 GMC Sierra 5.3l 6 speed Diamond White(sold)
2013 GMC Sierra Denali 6.2 6 speed AWD (sold)

PontGuy

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Re: HO intake problem
« Reply #13 on: September 21, 2015, 07:40:18 PM »
Those gaskets will work as long as you don't have the tall crossover ports on the heads.  There are two pairs of inserts that come with them, one pair to block off the crossover and one pair that turns the gasket into the small square hole type.  I've seen those but always just used the regular blue gaskets that have the correct size hole for the head/crossover combo.

If you have tall rectangular crossover ports on the heads that aren't completely covered by the crossover then the extra gasket material won't help exhaust gases from blowing out.  I once used some JB Weld to fill in the top of the rectangular port on a pair of later heads so I could use an early intake.  It was just a beater engine so figured I would give it a try.  It actually held up good, several years and many miles on the engine without any problems.  Not so sure I would recommend that on a nice engine, but then again you should have the small square holes so you should not have that problem.

I never ran the crossover on my RAIV intake.  The manifold got too hot during summer weather here in the south and caused vapor lock problems.  I pulled it and installed blockoff plates.  No more vapor lock and it looked really cool that way.
1974 455 TA, blue on red HPP cover car
1969 Lemans Vert - 455 powered sleeper

The best way to show a car is to drive it!

71455formula

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Re: HO intake problem
« Reply #14 on: September 21, 2015, 08:18:51 PM »
Mines got the small ports. I live in Montana so I need the crossover.
1971 LS5 Formula. It's on the road finally!
2013 GMC Sierra 5.3l 6 speed Diamond White(sold)
2013 GMC Sierra Denali 6.2 6 speed AWD (sold)

Re: HO intake problem
« Reply #14 on: September 21, 2015, 08:18:51 PM »

1971WARBIRD

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Re: HO intake problem
« Reply #15 on: April 16, 2017, 06:43:47 PM »
I guess you have figured this out by now, but here was your problem. you have a 1972 crossover, the 1971 crossover has a bump up that would cover that hole.  if you look at yours it is flat across the top, and here is a picture of a 1971 HO crossover.https://www.thepartsplaceinc.com/images/productphotos/CB6288Z.jpg

71455formula

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Re: HO intake problem
« Reply #16 on: April 16, 2017, 08:12:38 PM »
Didn't realize the crossovers were different. Guess I need to fine one. What I have will work till I do. Thank you for the info.
1971 LS5 Formula. It's on the road finally!
2013 GMC Sierra 5.3l 6 speed Diamond White(sold)
2013 GMC Sierra Denali 6.2 6 speed AWD (sold)

Re: HO intake problem
« Reply #16 on: April 16, 2017, 08:12:38 PM »
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