From 350 to LS1 on Granny's mount

[383mazda]

This is just an FYI post.  I was always confused on what was needed physically to take my "old school" 350 block out of my car and put in an LS1.  Grant at Granny's said it would take some grinding and bending; but overal it was pretty simple to modify Granny's old small block chevy mount to accept the newer LS1 motor - rather than buying the LS1 style cradle.
(I'm actually putting in an LQ4, but an LS1 / LS2 / LS3 / LS7 / LM7 / LQ4 / LY6 and on and on would be the same). 
To avoid too much confusion, from here on I will refer to the Gen I motors as "350" and the newer Gen III / IV motors as "LS1."

Here goes...

First is the actual motor mount bolt patterns on the two different motors (LS1 vs the 350):


Obviously you can't bolt the 350 motor mounts to the LS1 block, so you have to buy an adaptor plate that bolts to the LS1 4-bolt pattern and then will let you bolt on the 350 3-bolt motor mount:


It's pretty simple, just a 3/16" thick plate with both patterns drilled into it (you only count 6 holes because with this plate one of the bolt holes is being shared by both motor mount patterns.  With this plate the motor mount will sit closer to the front of the LS1 engine relative to where it sat on the 350 block - Granny's mount accounts for this by having two sets of holes, a forward set for 350's, and a rear set for LS1's)

Yes Granny's sells these adaptor plates, or you can make your own (the measurements can be found online).  The ones I have I think are a copy of the Granny's plates.  I did a few things to mine to make them easier to work with.

Here is how the plate sits on the LS1 motor:

You can see where the shared bolt hole is (where the 4th bolt is missing), and how the 350's motor mount will now bolt up to the plate.  Originally the plates came with nuts and bolts for the motor mounts; I didn't want to fumble with a handfull of wrenches to replace a mount so I welded on the nuts that the mount will bolt to:


I also gound down on the back of the nuts so they would sit down on block:


(sorry for the fuzziness, but you can see where I had to make room for the nuts to clear the ribs on the motor)

I also went to the local hardware store and got matching allen head bolts (8mm) to bolt everything up - so one tool will get everything out - here's how it all looks put together:

(pay no attention to the color of the plates - I powdercoated them as I was putting everything together)

So that's how you "retro fit" a newer LS1 engine to fit where an old 350 used to go.  Now I'll get onto what I did to Granny's cradle.
The LS1 oil pan is wider than the 350's pan, so some webbing on the cradle needed to be removed:

The cradle is resting on the oil pan in this shot, you can see the gap in between the cradle and motor mount, time for some cutting and grinding...

I just used a paint marker and my calibrated eye for most of this...


Cut the first row out and then eyeballed where the second row needed to be cut:


Now back on the motor for a test fit, plenty of room on the left side, but a little tight on the right side... no big deal, just needs a little more ginding:


After I had good spacing on both sides I took an angle grinder to smooth out / blend in my cutting (so it didn't look like I just cut out notches in the cradle to make things fit):


And on the motor (it looks like I have plenty of room, but the back side of the cradle is actually very close to the oil pan):


Here's where the bolt holes lined up with the cradle just resting on the mounts (notice the two holes on the cradle, this is the LS1 set vs the 350 set - obviously I'm lining things up on the rearward, or LS1 set):

You can see it's not quite a perfect alignment, I just had to put a little pressure on the cradle to push it down on top of the motor and I was easily able to thread that bolt in by hand (I remember trying to get the 350 in my car the first time a few years ago... getting that motor mount bolt in was a royal pain.)  The mount fits great and I didn't have to do any bending / spreading the towers apart to get everything to sit perfect.

And just for your pleasure, here's a before and after of the cradle and adaptor plates when I powder coated them: 


color is called cosmic grey, it' pretty cool looking (eventhough no one will ever see it, lol).

[dream36realms]

pretty cool. didn't you worry about structural integrity of the cradle? For my builf I was told it will need a bit of custom work as well. If this works out for you I may just do it a similar way.

[bikedad]

Thanks.
I was wondering if I was going to be able to use my cradle if and when I go the LS1 route.

I'll be doing this as well.

[digitalsolo]

pretty cool. didn't you worry about structural integrity of the cradle? For my builf I was told it will need a bit of custom work as well. If this works out for you I may just do it a similar way.

That's one of about 100 pulls in my car with a cradle modified the same way.       FWIW, this mod basically converts the cradle to Granny's newer style LS1 ready cradle, which is just the old cradle with the reinforcement laid out like the one above.

[sciff5]

Honestly just get pez's mounts.

I dealt with modifying grannys mounts and it was more of a pain than it was worth

[bluethunder]

I also have an LQ4 with the older 350 SBC cradle.  Just trimmed up the webbing also and cut the middle of the mount out completely so I have two mounts. Works really well to line everything up when you bolt it in.And for those who think it's not strong enough, I have numerous 1/4 mile runs and it has not moved one  bit. The weakest link are those old syle rubber mounts that Granny's sell with there kits. I have that covered with a turnbuckle motor to frame mount to limit twist while at the track.  Good luck with your car!

[383mazda]

The cradle is bolted down in 5 spots, it's not going to move.  And even so, the "weak" spot would be the middle where the wasn't any webbing to begin with.  I'm not worried at all about this not holding up to any ammount of power I'll have on it.  And I will be replacing those rubber mounts.

As shown above, it wasn't that tough to modify at all - granted I do have access to a metal shop and it's tools, but this could have ben done with a dremal and lots of patients.

[RX7V8Builder]

Good information here.  I will certainly do this when going the LS1 route too.
Have you dropped the motor in yet?  How is the firewall clearance with these plates?

[dream36realms]

thanks for clearing that up for me. I am looking around for my setup but all I been able to find is the granny mount for the first gen and to make it work with the LS they said wouldn't be cheap I think sourcing parts instead of buying from one spot is my only option.

[383mazda]

Haven't dropped themotor in yet.  I assume the clearence would be the same as another car with granny's mounts (since it's his mount and a copy of his plates...)

I've actually decided to sell this mount and grab some of Pez's mounts... rumor is they're easier to work with when doing a turbo.  I'll be running C6 manifolds pointing backwards... I'd have to do some more grinding to get the pass side exhaust to fit by granny's mount.

[FCs Rule]

i took my LT1 kit and convert it to LS1 but i am changing over to pez kit just because i want power steering now and the granny kit is no fun for power steering

[Copper280z]

I did the exact same stuff, the firewall is tight when using the rear holes. It was a major whore to line up the last motor mount hole when dropping the motor in, I had to loosen the cradle almost all the way, pry on it in all sorts of weird ways until I could finally get that damn bolt started.