[Joog]

Hello, I was interested in 400 swapping a 55-57 chieftain. But I realized the motor mounts on a 400 are located on the passenger and driver side while a 55-57 are not set up like this.

Are there any motor mounts on the internet or someone else that makes them that will work for this application?

Is there any way I can custom make/weld motor mounts from a GTO, Firebird, or other factory 400 car to fit the 55-57 on the passenger and driver side?

[242177P]

Two examples of what the 55-57 Chevy guys use. SBC/BBC mounts are forward of where the 64-72 mounts are, but the later 400 blocks have other mounting options. You might be able to use a smog-era clamshell block mount with the Chebby pedestals? Dunno. If not, something like the late-to-early Pontiac motor mount adaptor plates might allow you infinitely more flexibility? Again, dunno. Hope this helps

[Joog]

I am using a 69 big body 400. Also, is that mount located on the crossmember or the frame rail? Because on my application the guy deleted the factory cross member and put a new bar further forward.

[Joog]

[QUOTE=242177P;6547396]Two examples of what the 55-57 Chevy guys use. SBC/BBC mounts are forward of where the 64-72 mounts are, but the later 400 blocks have other mounting options. You might be able to use a smog-era clamshell block mount with the Chebby pedestals? Dunno. If not, something like the late-to-early Pontiac motor mount adaptor plates might allow you infinitely more flexibility? Again, dunno. Hope this helps

I am using a 69 big body 400. Also, is that mount located on the crossmember or the frame rail? Because on my application the guy deleted the factory cross member and put a new bar further forward.

[Bill Hanlon]

Wait for Bill Eveland to check in. He'll know. Check out his Pontiac here:

https://forums.maxperformanceinc.com...r.php?u=137381

[Joog]

I’ve contacted him prior on the HAMB, but I was waiting for a response on a picture of how he put together those motor mounts!

[Tom63LeMans]

I copied the basic design of the Hurst 2nd design brackets for use in my ‘56. Since it’s a gasser and I was removing the factory crossover I moved the mount location back and inward from the Hurst design. They can be duplicated very easily with angle and flat steel. I will find a link that details measurements of the Hurst brackets.

[Tom63LeMans]

Here is the link to a Hamb post showing the mounts and also measurements of the brackets.
https://www.jalopyjournal.com/forum/...ontiac.998644/

[Joog]

Originally Posted by Tom63LeMans

Here is the link to a Hamb post showing the mounts and also measurements of the brackets.
https://www.jalopyjournal.com/forum/...ontiac.998644/

Thanks! Did you copy that design from the HAMB? I'm also doing a gasser build. And I think I saw your 56 at Pontiac nationals.

[Tom63LeMans]

Originally Posted by Joog

Thanks! Did you copy that design from the HAMB? I'm also doing a gasser build. And I think I saw your 56 at Pontiac nationals.

Yes that’s me. I used the Hamb post for some of the measurements and the basic idea. I didn’t care for how far forward the mounts were from the engine bolts but understood it was done that way to reach the original crossmember. I originally was not going to add a mid plate so I was concerned about stress on the bellhousing. I did end up adding a mid plate too.

[Joog]

Originally Posted by Tom63LeMans

Yes that’s me. I used the Hamb post for some of the measurements and the basic idea. I didn’t care for how far forward the mounts were from the engine bolts but understood it was done that way to reach the original crossmember. I originally was not going to add a mid plate so I was concerned about stress on the bellhousing. I did end up adding a mid plate too.

Alright, do you by chance have a photo of where and how you connected the bracket to the frame? And possibly a picture of the midplate.

[Tom63LeMans]

Originally Posted by Joog

Alright, do you by chance have a photo of where and how you connected the bracket to the frame? And possibly a picture of the midplate.

Here are a few pictures showing crossmember and brackets for the motor mounts and midplate I used the Speedway biscuit motor mounts but then used aluminum spacers in place of the rubber mounts. With the mounts moved back like I did I might have been ok without the midplate but didn’t want to chance it. I also found a few pictures of my rear crossmember if you’re interested.

[Joog]

Originally Posted by Tom63LeMans

Here are a few pictures showing crossmember and brackets for the motor mounts and midplate I used the Speedway biscuit motor mounts but then used aluminum spacers in place of the rubber mounts. With the mounts moved back like I did I might have been ok without the midplate but didn’t want to chance it. I also found a few pictures of my rear crossmember if you’re interested.

Thank you! If I understand this right, you just welded the bracket along the sides of the frame facing the motor, and maybe welded some on the bottom side of the frame?

[Tom63LeMans]

Originally Posted by Joog

Thank you! If I understand this right, you just welded the bracket along the sides of the frame facing the motor, and maybe welded some on the bottom side of the frame?

I went back and looked at the pictures and then recalled how big of a job it really was to patch the frame after removing the crossmember. I removed the complete crossmember where it was riveted to the frame rails. Then I plated the insides and also the bottom opening for the springs. The new crossmember is notched so it’s welded inside the rails and underneath like you mentioned. It was the new plates that strengthened what was left of the frame and gave me a good surface for attaching the cross rail for the motor mounts

[Joog]

Originally Posted by Tom63LeMans

I went back and looked at the pictures and then recalled how big of a job it really was to patch the frame after removing the crossmember. I removed the complete crossmember where it was riveted to the frame rails. Then I plated the insides and also the bottom opening for the springs. The new crossmember is notched so it’s welded inside the rails and underneath like you mentioned. It was the new plates that strengthened what was left of the frame and gave me a good surface for attaching the cross rail for the motor mounts

Thanks for the info! And I saw your headers, I'm guessing you custom made those yourself? I was thinking about trying to find SBC fenderwell headers and cutting the flange off, then bending the tubes and tweaking them to work with a 400 flange. Since I don't have the patience or skills to do a whole custom header myself.

[Tom63LeMans]

Originally Posted by Joog

Thanks for the info! And I saw your headers, I'm guessing you custom made those yourself? I was thinking about trying to find SBC fenderwell headers and cutting the flange off, then bending the tubes and tweaking them to work with a 400 flange. Since I don't have the patience or skills to do a whole custom header myself.

I used BBC Patriot headers for tri-5 Chevies to build mine. I think they are 2” primary tubes. That worked great for these since I’m running round port Edelbrock heads. If D-ports and not heavily ported SBC 1-3/4 tubes should work. Since I kept my original steering box and location the upward turns have to happen quickly.

[Joog]

Originally Posted by Tom63LeMans

I used BBC Patriot headers for tri-5 Chevies to build mine. I think they are 2” primary tubes. That worked great for these since I’m running round port Edelbrock heads. If D-ports and not heavily ported SBC 1-3/4 tubes should work. Since I kept my original steering box and location the upward turns have to happen quickly.

You think the 1-3/4 chevy headers would work fine without modification?

[b-man]

The Chevy headers are your starting point.

You will have to finagle a way to weld them to Pontiac header flanges, above average fabrication and welding skills definitely required.

The only way Chevy headers can be used without modification is to use a Chevy engine.

[Tom63LeMans]

Originally Posted by Joog

You think the 1-3/4 chevy headers would work fine without modification?

No they would require cutting the flanges off and attaching new flanges with tubing bends. All I was saying is that SBC headers with 1-3/4” primaries would be of sufficient size for standard D port heads.
This picture shows what part of the BBC headers I used and how far off they were from my stubbed flanges. All of that gap was made up with tubing bends of various angles

[Joog]

Originally Posted by Tom63LeMans

No they would require cutting the flanges off and attaching new flanges with tubing bends. All I was saying is that SBC headers with 1-3/4” primaries would be of sufficient size for standard D port heads.
This picture shows what part of the BBC headers I used and how far off they were from my stubbed flanges. All of that gap was made up with tubing bends of various angles

Alright, that’s what I was thinking. Did you just buy extra of straight tube and bend it yourself? Or did you get one of those pre bent kits?