# Installing h.o. exhaust manifolds on non-h.o. engine



## Popof4 (Aug 13, 2021)

I am installing a set of h.o. exhaust manifolds on a non-h.o. 400 in a1967 GTO convertible. It is a factory 4-speed car. The manifolds are from Ames. I have the engine on a stand. The heads are not drilled and tapped for the end bolts and it looks like there will be interference with the head bolt cavity if I do drill it. I have the means to do the job and I've made some bushings to keep the drill bits correctly aligned, but I would like to get some input from others that have run into this in the past. What has been the SOP for this project.


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## Baaad65 (Aug 29, 2019)

Popof4 said:


> I am installing a set of h.o. exhaust manifolds on a non-h.o. 400 in a1967 GTO convertible. It is a factory 4-speed car. The manifolds are from Ames. I have the engine on a stand. The heads are not drilled and tapped for the end bolts and it looks like there will be interference with the head bolt cavity if I do drill it. I have the means to do the job and I've made some bushings to keep the drill bits correctly aligned, but I would like to get some input from others that have run into this in the past. What has been the SOP for this project.


There are brackets out there I had to use because my 7K3 heads were not drilled, paid about 55.00 I can try and look up the manufacturer or you can interweb it.


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## Popof4 (Aug 13, 2021)

Baaad65 said:


> There are brackets out there I had to use because my 7K3 heads were not drilled, paid about 55.00 I can try and look up the manufacturer or you can interweb it.
> View attachment 148886


Thanks for the reply! I saw those in the Ames parts book. I wasn't sure if that is the only option, or if someone has tried to drill/tap the heads.


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## GTOTIGR (May 3, 2020)

Hi Popof4,

Are you attempting to install the HO exhaust manifolds on OEM “670” heads? If so the holes in the heads are the same for the HO manifolds and non-HO manifolds. 

While there are holes in the heads that you cannot access when installing HO manifolds, this was done by design, versus the standard exhaust manifolds utilizing all of the head bolt locations. 

I cannot speak to the situation Baaad65 addresses with the later model heads.


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## O52 (Jan 27, 2019)

And your exhaust head pipes will need replacement or modification.


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## Popof4 (Aug 13, 2021)

] lb


O52 said:


> And your exhaust head pipes will need replacement or modification.


Thanks Ed. We are going back with a new exhaust system.


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## Lemans guy (Oct 14, 2014)

I had Butler drill my #15 heads for HO manifolds, bolted up real nice and tight. You might call and just ask for any tips on that they are very helpful on such stuff.


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## Popof4 (Aug 13, 2021)

Lemans guy said:


> I had Butler drill my #15 heads for HO manifolds, bolted up real nice and tight. You might call and just ask for any tips on that they are very helpful on such stuff.


Thank you! I'll give them a call tomorrow.


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## lust4speed (Jul 5, 2019)

Brake lines were moved to the front of the cross member with an H.O. engine, and battery cables come from the front of the engine instead of dropping down around the #5 sparkplug. Pontiac used a horizontal tube attached to the driver side engine mount for the cable and wires to go through, but the wires really can't move very far out of place if you don't use the tube.


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## Popof4 (Aug 13, 2021)

lust4speed said:


> Brake lines were moved to the front of the cross member with an H.O. engine, and battery cables come from the front of the engine instead of dropping down around the #5 sparkplug. Pontiac used a horizontal tube attached to the driver side engine mount for the cable and wires to go through, but the wires really can't move very far out of place if you don't use the tube.


Thank you for the information.


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