Looking for advice on 402 Big Block motor swap in my 64 C10

[64shortboxchevy]

I am swapping a 402 bb into my 64 c10 with the inline six cylinder and needing some advice on motor perches and mounts etc. Currently I have the motor in the truck, I moved the perches that were in the truck with the six cylinder ahead to the front bolt holes to allow room for the big block (picked that tip up on here) I then removed the rivets holding the manual 4 speed cross member to the frame rails and slid it forward to bolt it up to the 402 (after some modifications to the trans hump to allow it to slide forward).
I have the motor bolted to the perches (from the 6 cylinder) using the center bolt style motor mounts. Everything seemed fine until I tried to install the exhaust manifolds... they hit the perches. My question is, do I need to get different perches and motor mounts for exhaust clearance or do they make a set of headers that will work with my setup? I can provide pictures of clearance etc. if that helps.

Thanks in advance

[64shortboxchevy]

Here are a few pics of the motor how it sits in it now with the original motor perches and mounts from inline six.

[IMG][/IMG]

[64shortboxchevy]

[IMG][/IMG]

[64shortboxchevy]

If you need me to take any other pics and post I can do that also.

[Captainfab]

Those original motor mount brackets are not designed to be used in the forward location. They will raise your engine up, plus you will have to drill holes to bolt them to the crossmember. The '67-'72 small block motor mount brackets are designed to be used in the forward location. Next, in moving the bellhousing crossmember forward, that also raises your engine. I have no idea is it is the same amount as the motor mount brackets are raising the front. I have never used this combination of parts in installing a big block. Raising the engine is the front and/or back is important in keeping the trans output shaft parallel to the pinion. If those two are not parallel, you will have driveshaft vibrations.

As for the exhaust manifold to motor mount bracket interference, that is to be expected since you are not using the big block motor mount brackets. The '68-'71 big block motor mount brackets are shaped in such a way as to allow clearance for the exhaust manifolds. It may be possible that the '73-'87 big block headers will clear those motor mount brackets. There again I can not say for sure, not having used those motor mount brackets with a big block. You will also have to trim back the top flange of the frame for the manifold or header clearance.

The next issue you will find, is that the original clutch linkage assembly will most likely not work. At best you will have to do a good bit of fabricating and modifying of the original linkage. IMO it will be much less work to just convert to a hydraulicly operated clutch.

[argonaut]

As was said use 69-72 bbc mount brackets or the aftermarket style tubular mount brackets.

Either swap to a hydro clutch or swap to an automatic to make life easier on yourself.

[64shortboxchevy]

Thank you for the replies guys. I did some searching on the forum and found the tubular v8 motor perches and mount kit you are talking about so I will be ordering that this week.

I have a question about staying with the manual 4 speed or switching to an automatic. I guess my thought was that if I stayed with the 4 speed my highway rpm may be a bit lower than if I switched to a turbo 400/350 3 speed auto? Or would they be about the same since 1st gear in the manual is "granny" gear? I plan on using the truck mainly for cruising, daily driving etc. but an occasional trip to an autocross or 1/8th mile drag strip to play may happen as well. A built 700r4 or equivalent is out of my budget at this time so would I be best to just swap rearend gears to something a bit more suited for my application? I believe these trucks came with 4:11 gears from the factory? Atleast that's what I was told when I bought it.

Any input on this would be helpful.

Thanks

[mikie 1954]

There will not be any difference between the 4 speed or the turbo 400/350 as the all are 1 to 1 in high gear ,so your rpm's will be the same going down the highway. I think it will cost about as much to put higher gears in the rear end as a 700r4. Some others will chim in with more and probably better advice, but if you can get an overdrive trany.

[Captainfab]

Keep in mind that you will definitely need to trim the top flange of your frame. Those aftermarket tubular motor mount brackets will not bolt up if you don't. Plus as I said, you will need to for header clearence with a big block.

As mikie 1954 said, your trans high gear will be 1:1 regardless if you keep the SM420 4 speed, or switch to a TH350 or 400. That SM420 will not be condusive at all to any autocross or drag racing. Most guys that really don't know say that a given truck has 4.10 or 4.11 gears, when in reality the gears are most likely 3.73's. The 4.11's were available, but in my experience, not nearly as common as the 3.73 gears. I'm not saying that 3.73's aren't a little low, because they are a bit low for highway cruising with the average tire size found on a C10. If you want a comfortable cruiser, DD or the occasional autocross or 1/8th mile, I would coinvert to a TH350 and a 3.07 rear gear. The 3.42 gears would be a good comprimise between the two, but your rpm's will still be 3000+ at about 70 mph, depending on tire size.

Originally Posted by 64shortboxchevy

Thank you for the replies guys. I did some searching on the forum and found the tubular v8 motor perches and mount kit you are talking about so I will be ordering that this week.

I have a question about staying with the manual 4 speed or switching to an automatic. I guess my thought was that if I stayed with the 4 speed my highway rpm may be a bit lower than if I switched to a turbo 400/350 3 speed auto? Or would they be about the same since 1st gear in the manual is "granny" gear? I plan on using the truck mainly for cruising, daily driving etc. but an occasional trip to an autocross or 1/8th mile drag strip to play may happen as well. A built 700r4 or equivalent is out of my budget at this time so would I be best to just swap rearend gears to something a bit more suited for my application? I believe these trucks came with 4:11 gears from the factory? Atleast that's what I was told when I bought it.

Any input on this would be helpful.

Thanks

[Chevy Fleetside]

I used he tublar monts. I also knotced the firewall so the engine would sit back. As you can see in the last picture, you have to trim the top of the frame just a bit. and the last picture is when it was almost done. http://www.67-72chevytrucks.com/vboa...d.php?t=259536

[64shortboxchevy]

Thank you all very much. That is some great info! Good to know the 4 speed and the TH400 etc. would end up being the same rpm in high gear. I will definitely be swapping the manual for an automatic afterall.

Chevy Fleetside, I ordered a set of the tubular V8 mounts yesterday... it looks like you trimmed about 1/2" from the top of the frame so they would reach the holes? My motor is currently sitting in the front set of holes, do you have to drill your own holes with these or can I use the holes already in frame?If so I think I will keep it there for rear clearance. I currently have enough room to run a manual fan, if the new mounts make it tough to run a regular fan I will use an electric fan I guess.

[argonaut]

I think that if you want to use the forward set of holes, then you need a motor mount bracket made for a 67-72 model pickup (used forward holes for 2wd trucks) instead of ones for a 63-66 (used rear holes for 2wd trucks). I'm not 100% on that though.

I used factory mount brackets from a 71 big block when I put a 402 in my 64. I also had to cut the top frame flange. I used stock exhaust manifolds though. I also only had clearance for an electric fan.

[par4tom]

Another options would be to go with an NP440/MY 6 4 speed. It has 1:1 ratio in third gear and .73:1 in fourth. I recently put this in my 61 and the first 3 gears are almost identical to the TH350. The 4th gear overdrive is a Godsend...what a difference.

There are several articles/posts on this tranny. Good luck with whichever route you go.

Tom

PS - I spent about $450 to $500 bucks on mine...

[Chevy Fleetside]

There was no drilling with the tubular mounts. I did use the rear holes though and I have a built 700R4 behind the Big Block.