[tharkun8]

Hey all,

I just picked up a 70 GMC C2500 ( for pretty cheap ) with the SBC350.. the engine has issues
and I dont know how much effort I want to put into fixing it..

I have a 67 pontiac 400 engine newly rebuilt that Id like to swap in and I need some help with
figuring out the motor mounts to put a Pontiac in there. I already know I need a tranny bolt
pattern adapter etc.. just need some help with motor mounting. The setup that some say can
work is the stock Chevy mounts with the F body brackets from the early 70s.. but it seems thats
more for the later Pontiac blocks with 3 or 5 holes.. Not sure if it will work on earlier blocks with just the 2 ..


I did refresh a (very) old thread in the Non Pontiac engine section but I figured this section gets
a lot more eyes. I know this isnt the most common swap but I know someone on this board
has to have the info Im looking for.

Does anyone have pics of the motor mount setup needed to put a pontiac into a Chevy motor mount truck ?

Thanks all

John

..

[hurryinhoosier62]

A standard BOP pattern TH400/TH350 will bolt right up to a Pontiac block, as will a BOP pattern TH200R4.

[tharkun8]

Yeah.. the t350 in it now seems to shift fine actually the issue
is just the engine..

The engine originally was blowing back through the carb... I found that #2 exhaust
valve rocker was extremely loose and not letting out the full exhaust charge.. so
when #2 intake was opening it was blowing back.. After fixing that
I was hoping that was the only issue but there are still running/operating issues..

Rather then spend more time trying to get a SBC to work.. thought id
rather just drop in a Poncho that is already ready..

Im trying to get this truck back on the road as quick as possible with the
least outlay as possible.. I have a few of the 200r4s but the only one
ready to go is earmarked to go into my 64 Cat Safari.. I also have
a few spare T400s but they are all longtails and need rebuilding and
I dont really want to get into trying to figure out how to modify the 2
piece driveshaft with a diff length trans..

so.. just want to swap engines.. i could just buy a crate SBC but I dont
really want to spend another 2k when I have a pontiac 400 ready to go in..
I just need some guidance on the motor mounts..

Not to mention... Id rather have a Poncho then a SBC in my truck and I dont
really want to sink more money/time into an engine Im really not interested in..

John

..

[cdrookie]

Bolt the frame mounts to the engine mounts and lower it onto the crossmember. Then bolt the motor to the tranny and make sure the motor is straight and level. Next, mark the holes, or outline the mount, or tack weld the frame mount in place. Remove the engine and drill the holes in the crossmember, then bolt the frame mounts in place and drop the engine in.

[1965gp]

As cool as this sounds- you will probably be $$ ahead to just drop a small block Chevy back in it. You can find a good running 350 for $500-$700. Your built 400 is worth much more than that. Add the cost of the adapter for the Trans and figuring out the motor mounts, accessories, etc I think I would just find a good replacement motor.

I went through this with my 73 Blazer. I heard a knock from the original motor (turned out to be the fact that there was only 1 bolt on the torque converter) so I looked around for a decent motor. Found an early 70’s 350 for $500. Detailed it and dropped it in. With all of these LS swaps there are a ton of decent 350’s out there for little cash.

[SRR]

Originally Posted by cdrookie

Bolt the frame mounts to the engine mounts and lower it onto the crossmember. Then bolt the motor to the tranny and make sure the motor is straight and level. Next, mark the holes, or outline the mount, or tack weld the frame mount in place. Remove the engine and drill the holes in the crossmember, then bolt the frame mounts in place and drop the engine in.

Since I don't think any adapters are made for this swap.

[66sprint6]

I'm helping a friend right now with his square body. We picked up a low mile mid-nineties Vortec motor for cheap, dropped it right in and the thing runs like a dream.

[Stuart]

Yes, but...putting a Pontiac engine in a GMC is cooler.

I remember someone here on the board had a 1960s era GMC with a Pontiac engine in it but don't recall who - hopefully they'll see this and chime in with how they did it.

[1965gp]

The Pontiac mill is definitely cooler.

[sdbob]

When I swapped 71 400 into my 74 2500 the torque increase was noticable.

[Sirrotica]

You're probably not going to find any parts that are going to be a direct bolt in for motor mounts. If you can't weld or fabricate the mounts you might just be further ahead to put another chevy in it.

You're also going to run into exhaust fabrication needs, and rewiring the starter (on the opposite side) and alternator wiring (extending the wires usually). You also have the option of using a BOP trans or buying an adapter plate to use the chevy transmission, usually $50-75.

I've swapped a lot of Pontiacs into many chassis, but being I'm able to weld, and fabricate everything I need, it's just a matter of setting the components into the chassis and making up what I need. You also have to decide what set of the Pontiac mounts you want to use also, Pontiac has used quite a few different mount systems over the years. There is the early and late styles that are different in relation to the later ones are further to the front of the engine and the early system is right around the middle of the engine.

I'm not trying to discourage anyone from getting rid of a chevy for a superior Pontiac Stratostreak engine, just being realistic on what you will run into when doing a swap. I used to drive Jeeps and have done 3 engine transplants of Pontiac Stratostreak engines into the 4X4 Jeep chassis and didn't delete the 4X4 running gear in them, many people just make them 2X4 because keeping the 4X4 is a bit more difficult to adapt everything to.

Below is my 1973 Jeep 3/4 ton wrecker/snowplow with a 455 Pontiac in it. I did the conversion in the late 70s and by the late 90s the frame and body had rusted too badly to make it feasible to keep driving it. After 20 years it owed me nothing, and making the swap from AMC 360, to 455 Pontiac was a huge step up in reliability and power.

[tharkun8]

Thanks for the responses all..

Yes,, there are some tech challenges but not big ones..

to go down some of Sirroticas list..

wiring changes arent that big a deal. Wiring is on my follow up list
anyway. I can splice in any wiring fixes for the reroutes.. I was also
thinking on adding the long branch manifolds..
( put those on all my engines when I do them) then its just a dual
straight pipe..

the engine currently has some cheap headers on it and they are directly
welded to the dual straight pipes to the rear.. I was figuring on just cutting
the welds and adapting the long branches onto the existing pipes as a short
term solution.

The Bop block to bowtie trans adapter is about 65 bucks.. not a killer expense.

I do have a bare 64 block that I can use as a mock up test bed I guess.. Do
as CD said and mount the mounts and brackets to a bare block .. set the block
in and connect to trans with adapter plate.. get it lined up straight and then
mark the new bracket locations and drill.

Im going to put a few more hours on the SBC and see if I can get it
running to my satisfaction.. or Im going to make the call..


John

Originally Posted by Sirrotica

You're probably not going to find any parts that are going to be a direct bolt in for motor mounts. If you can't weld or fabricate the mounts you might just be further ahead to put another chevy in it.

You're also going to run into exhaust fabrication needs, and rewiring the starter (on the opposite side) and alternator wiring (extending the wires usually). You also have the option of using a BOP trans or buying an adapter plate to use the chevy transmission, usually $50-75.

I've swapped a lot of Pontiacs into many chassis, but being I'm able to weld, and fabricate everything I need, it's just a matter of setting the components into the chassis and making up what I need. You also have to decide what set of the Pontiac mounts you want to use also, Pontiac has used quite a few different mount systems over the years. There is the early and late styles that are different in relation to the later ones are further to the front of the engine and the early system is right around the middle of the engine.

[455Grandville]

Originally Posted by Sirrotica

Below is my 1973 Jeep 3/4 ton wrecker/snowplow with a 455 Pontiac in it. I did the conversion in the late 70s and by the late 90s the frame and body had rusted too badly to make it feasible to keep driving it. After 20 years it owed me nothing, and making the swap from AMC 360, to 455 Pontiac was a huge step up in reliability and power.

Were AMC 360s not so good engines ?
I’m looking at a few nice Grand Wagoneers at a place out of Arizona (they do rust) but it seems there’s a lot of mixed opinions of the engines.

[Sirrotica]

AMC inline 6 engines will run forever, not so much with their V8s in my experience. Mine needed a timing chain and I just decided to cut my losses and go with what I knew to be a good engine. The truck was the third Jeep I converted to Pontiac power, 2 Wagoneers previous to the truck so I already knew what it took to do the conversion.

[77 TRASHCAN]

i have seen a couple of Pontiac conversions, did not know what parts were used. The one I saw were 73 and up, though.

The 73 and up frame brackets can likely be adapted to a 67-72 pickup. The 73- up Chevy pickups used the clam shell type mounts. The engine brackets for a 73- up would need to be used, also.
1972 big block (only big blocks) use clam shell mounts. The fame brackets from a 72 big block might be able to be used. I believe these frame mounts are being reproduced.
Some combination of these brackets/ mounts should make the swap happen, with possibly just some hole drilling needed!!!
I truly don't believe any fabricating will need to be done.

These would need to use a 70 and newer, 5 hole per side block. I'm don't know how an earlier block could be adapted...

[se428bandit]

A friend of mine Dad put a Pontiac 455 in a '66 Ford truck. I use to have pictures somewhere.

[Tom Vaught]

The Kansas Boys around Wichita have done several of those Pontiac Engines into GMC or Chebby Trucks. Not that difficult once you make the first set of mounts for the installation.

A really nice swap if you have a fresh Pontiac Engine to go into the vehicle.

Tom V.

[tharkun8]

Thanks Tom..

Would these Kansas Boys be an actual club or just a bunch of guys you know of ?

It would be nice if someone already had a setup worked out that I could copy/buy..

Working on replacing the power steering box ( which was leaking as fast as you could put
fluid in it ) and really looked at the frame mountings.

the current brackets have 2 bolts on each side.. about 2 3/4 " apart...
there is a third hole on both sides 2 3/4 inches to the rear of the current
mounting points..

The brackets are currently mounted to the forward 2 pairs of holes which
puts the brackets to the front of the SBC block where the mounts are..

It looks like the brackets can be moved back about that same 2 3/4" which would put
the brackets in about mid engine on the small block. I have no idea if Chev Big Block
mounts are centered but I would presume this setup was done to allow for small block
or big block installations in the model..

I would think moving the brackets to the position further rearward
would put the mounts pretty close to where the Pontiac block would need
them.. Ill have to do some measuring to find out..

Thanks

John

..

Originally Posted by Tom Vaught

The Kansas Boys around Wichita have done several of those Pontiac Engines into GMC or Chebby Trucks. Not that difficult once you make the first set of mounts for the installation.

A really nice swap if you have a fresh Pontiac Engine to go into the vehicle.

Tom V.

[77 TRASHCAN]

Originally Posted by Tom Vaught

The Kansas Boys around Wichita have done several of those Pontiac Engines into GMC or Chebby Trucks. Not that difficult once you make the first set of mounts for the installation.

A really nice swap if you have a fresh Pontiac Engine to go into the vehicle.

Tom V.

LOL, Would Tom Wilhite be one of them??? He puts Pontiac engines in every kind of vehicle. A few years ago he was planting a 455 into a mid 60's Buick, couldn't think of a better swap myself...LOL

[sdbob]

Back in the late 70s I wanted a light,wood ,fibreglas Pontiac block just for this reason. Never made it.