Mounting an LS7
Discussion
Ooh er missus.
I posted this in here rather than the Major Mods section as its fairly specific to the Challenge chassis and I know there are some folks out there with LS motors in their chassis; and others with more experience and better engineering brains than me.
After persevering for a number of years and 3 major engine failures, I’m swapping out the very broken Small Block Chevrolet motor with an LS7…or at least a motor with an LS7 block.
In my more optimistic moments I imagined it might just drop in to the same space as the SBC and I could just use adaptor plates on the SBC mounts. After much fettling and grinding of block I’ve got it in to the same place as the SBC and even can get the gearbox in exactly the same position. Whoopee.
And in fairness if it was just the motor I could indeed just mess about with adaptor plates and get it all bolted in. Except the new motor has a dry sump pump. It was actually mounted on a very nice bracket on the right of the motor by the engine builder, but assuming I want to keep the car RHD it isn’t going to fit there in the car. The only place it can go is the left, and real tight to the block.
BTW, does anyone know of an off-the-shelf bracket that will mount a dry sump pump real tight to the left of an LS block low down?
But the bigger problem is that the existing chassis mounts I have for the SBC are in the place the pump has to go, so I’m going to have to find some other way to mount the motor. I have 3 ideas, each with merits, each with drawbacks. I welcome your learned comments.
Oh, and this is a BIG horsepower motor with practically zero clearance in the chassis, so it has to be near-as-dammit solid mounted.
So here’s the problem:
So you can see the triangulated upright tube that used to have the SBC mount on the top. It has to go. So plan A is to use the AJP mount plate. I could make up a sort of upside down wide-V bracket that bolts the block (you can see where on the adaptor plates) and then sits on the plate where the AFP sat. I’d put a thin polyurethane top-hat affair in the large hole and bob’s your uncle. So kind of like this:
The advantage is apart from whipping out the SBC mounts there’s no chassis mods/welding. It’s all in the bracket. What worries me though (and why I’ve not just nipped down to the local metal shop and started work) is that the standard SBC and LS brackets put the chassis part of the mount almost directly underneath the mountings on the block so the bolts are pretty much in sheer. The AJP mount on the chassis are further away from the block so I’m thinking the bottom bolts on the block will be in tension and may pull-out. Also it is quite a lot further forward from the mountings on the block to they’re going to get twisted too. And finally, the plate for the mount doesn’t look that substantial. Is it going to buckle with…well…580ft/lb of torque?
I’d really need to be convinced this wouldn’t over stress the mounts on the block itself, and that the mounting plates won’t bend.
So I’m actually a bit happier with Plan B, and that’s to weld on a sleeve for a top-hat style poly-bush to the top chassis rails. I can line it up with one of the vertical chassis tubes and triangulate it to there’s no ‘twist’ on the top rail. And that’s well within the mounting plate zone of the block so I’ve no worries about over-stressing the mounts on the block. Real simple plates with bolt holes for the crush tube on the block. And the poly-bush top hat would seem to give good fore-and-aft location too.
The only downside I can see I’m loading part of the chassis that wasn’t actually meant to take the weight of a motor…but it is at the convergence of 4 different tubes.
Plan C is to use the standard Corvette aluminium mounts.
From the pictures you can see these should sit on a donut/bobbin [bolt at each end, rubber in the middle] mount, and they’re actually not a million miles off being in line with a vertical chassis tube, and the mounting surface they’d have to sit on would be a couple of inches above the bottom chassis rail.
The advantage of this approach is it’s using a standard Chevrolet mount on the block, and being alloy it’s pretty light and there’s minimal welding on the chassis – just a ‘platform’ with some triangular webs on the vertical tube.
The downside is I’m not convinced that the single bolt-each-end rubber/poly mount is going to keep the motor solid enough. Every time I’ve seen these sort of mounts (and I’ve trawled the web) they seem about an inch thick and there’s nothing in there to stop fore-and-aft movement.
With the AJP mount in Plan A and the bush mount in Plan B there would be no more than a few millimetres of polyurethane between the motor and the chassis. Unless anyone’s aware of a real thin and/or solid pancake type mount?
Over to you…
I posted this in here rather than the Major Mods section as its fairly specific to the Challenge chassis and I know there are some folks out there with LS motors in their chassis; and others with more experience and better engineering brains than me.
After persevering for a number of years and 3 major engine failures, I’m swapping out the very broken Small Block Chevrolet motor with an LS7…or at least a motor with an LS7 block.
In my more optimistic moments I imagined it might just drop in to the same space as the SBC and I could just use adaptor plates on the SBC mounts. After much fettling and grinding of block I’ve got it in to the same place as the SBC and even can get the gearbox in exactly the same position. Whoopee.
And in fairness if it was just the motor I could indeed just mess about with adaptor plates and get it all bolted in. Except the new motor has a dry sump pump. It was actually mounted on a very nice bracket on the right of the motor by the engine builder, but assuming I want to keep the car RHD it isn’t going to fit there in the car. The only place it can go is the left, and real tight to the block.
BTW, does anyone know of an off-the-shelf bracket that will mount a dry sump pump real tight to the left of an LS block low down?
But the bigger problem is that the existing chassis mounts I have for the SBC are in the place the pump has to go, so I’m going to have to find some other way to mount the motor. I have 3 ideas, each with merits, each with drawbacks. I welcome your learned comments.
Oh, and this is a BIG horsepower motor with practically zero clearance in the chassis, so it has to be near-as-dammit solid mounted.
So here’s the problem:
So you can see the triangulated upright tube that used to have the SBC mount on the top. It has to go. So plan A is to use the AJP mount plate. I could make up a sort of upside down wide-V bracket that bolts the block (you can see where on the adaptor plates) and then sits on the plate where the AFP sat. I’d put a thin polyurethane top-hat affair in the large hole and bob’s your uncle. So kind of like this:
The advantage is apart from whipping out the SBC mounts there’s no chassis mods/welding. It’s all in the bracket. What worries me though (and why I’ve not just nipped down to the local metal shop and started work) is that the standard SBC and LS brackets put the chassis part of the mount almost directly underneath the mountings on the block so the bolts are pretty much in sheer. The AJP mount on the chassis are further away from the block so I’m thinking the bottom bolts on the block will be in tension and may pull-out. Also it is quite a lot further forward from the mountings on the block to they’re going to get twisted too. And finally, the plate for the mount doesn’t look that substantial. Is it going to buckle with…well…580ft/lb of torque?
I’d really need to be convinced this wouldn’t over stress the mounts on the block itself, and that the mounting plates won’t bend.
So I’m actually a bit happier with Plan B, and that’s to weld on a sleeve for a top-hat style poly-bush to the top chassis rails. I can line it up with one of the vertical chassis tubes and triangulate it to there’s no ‘twist’ on the top rail. And that’s well within the mounting plate zone of the block so I’ve no worries about over-stressing the mounts on the block. Real simple plates with bolt holes for the crush tube on the block. And the poly-bush top hat would seem to give good fore-and-aft location too.
The only downside I can see I’m loading part of the chassis that wasn’t actually meant to take the weight of a motor…but it is at the convergence of 4 different tubes.
Plan C is to use the standard Corvette aluminium mounts.
From the pictures you can see these should sit on a donut/bobbin [bolt at each end, rubber in the middle] mount, and they’re actually not a million miles off being in line with a vertical chassis tube, and the mounting surface they’d have to sit on would be a couple of inches above the bottom chassis rail.
The advantage of this approach is it’s using a standard Chevrolet mount on the block, and being alloy it’s pretty light and there’s minimal welding on the chassis – just a ‘platform’ with some triangular webs on the vertical tube.
The downside is I’m not convinced that the single bolt-each-end rubber/poly mount is going to keep the motor solid enough. Every time I’ve seen these sort of mounts (and I’ve trawled the web) they seem about an inch thick and there’s nothing in there to stop fore-and-aft movement.
With the AJP mount in Plan A and the bush mount in Plan B there would be no more than a few millimetres of polyurethane between the motor and the chassis. Unless anyone’s aware of a real thin and/or solid pancake type mount?
Over to you…
Are the LS3 and LS7 similar engines? if so,I take it you will be running manifold tubes up and out.If you are, as it happens my motor is out at the moment and i can take a picture of my engine mounting arangement in the morning which because motor is out is very clear in construction in my car.As you say the oil pump is a pain but we sorted mine out with not too much hassle although my dry sump is for the austrailian market which as you know is right hand side driver so pump is on left from standard allowing steering column route,and at the coost of my dry sump i am soooo glad it worked out perfect first time and i had the same issue as you with the AJP mount being in the way.We had a crude solution to that bracket been in the way 
i think you can guess what we did, but i will post a picture of that tomorow as well which will be plane to see.You must not solid mount the engine as tempting as it is, it is a flexing chassis and ally block as you know.I solid mounted my old school iron block SBC before getting into the real world.I have about the same torgues as you which i run in Combe GT but have wound it back alot for the challenge series.Any how back to the friday night Bulmers Pear cyder.i will put my answers up in the morning.I,m sure Andy has done somethink completly different to me and probably Jamie as well.
i think you can guess what we did, but i will post a picture of that tomorow as well which will be plane to see.You must not solid mount the engine as tempting as it is, it is a flexing chassis and ally block as you know.I solid mounted my old school iron block SBC before getting into the real world.I have about the same torgues as you which i run in Combe GT but have wound it back alot for the challenge series.Any how back to the friday night Bulmers Pear cyder.i will put my answers up in the morning.I,m sure Andy has done somethink completly different to me and probably Jamie as well.Edited by wadsapple on Friday 16th November 19:47
Willie - I used your option C, the GM ali mounts. My engine is solid mounted along with my gearbox. I welded up box like platform on each side (so it is welded to the the bottom (horizontal) and vertical tubes. The engine with mounts sits on top of those and bolts through.
I also have a 35mm thick adaptor plate between the bellhousing and gearbox. This is bolted to a crossmember to provide support at the rear of the engine. There is a further cross member with a mount that picks up into the back of the box.
The diff is still mounted on bushes as I wanted some give in the transmission. However I have a bracket/crossmember which fixes into the lower bolt holes in the diff. Without this the torque tries to rotate the diff and destroys the mounting plates or worse, pulls the mounting tabs off the chassis.
I'll e mail you some pictures.
Cheers
Andy
I also have a 35mm thick adaptor plate between the bellhousing and gearbox. This is bolted to a crossmember to provide support at the rear of the engine. There is a further cross member with a mount that picks up into the back of the box.
The diff is still mounted on bushes as I wanted some give in the transmission. However I have a bracket/crossmember which fixes into the lower bolt holes in the diff. Without this the torque tries to rotate the diff and destroys the mounting plates or worse, pulls the mounting tabs off the chassis.
I'll e mail you some pictures.
Cheers
Andy
Thanks for the info folks. I cut the old SBC mounts off the chassis today and that gave some more space around the motor to see what’s what. Room now to get the scavenge pump in, but I’ll have to make some brackets up.
Took a while to realise the size of the mount/bush in the pics, but it looks like nearly half the height of the vertical tube. Much like my ‘Plan B’ and confirms the uprights are strong enough.
But without the old mounts in the chassis now I put the Chevy mounts on the block and that does indeed look the way to go as it all fits in – and if it works for Andy….
Still not too keen at solid mounting though, but equally don’t like the idea of the big standard rubber mounts. Found these babies and I’m guessing that would mean the mounting plate on the chassis would be around the level of the top of the lower rails.
So I think that’s the way I’ll go – a flat ‘plate’ on/near the bottom chassis rails, these pfadt bush-style mounts, and the standard Chevy alloy brackets to the block. Unless anyone thinks it’s a particularly bad idea.
I had planned to replace the steel bellhousing with an alloy one, but I couldn’t find one that would work. But by keeping the steel one I had already welded mounts onto it for the SBC, and there are Ford Fiesta engine mounts between it and the chassis. I can get the LS in the same position as the SBC so I’ll have mounts on the bellhousing as well as motor and end of the box.
Interested to know what you’ve done with the diff though Andy. I’d already ripped the standard diff bracket apart with the SBC so made up a stronger one…which then pulled out of diff cover so I had to helicoil the holes…so far so good but the LS will be making even more power.
Took a while to realise the size of the mount/bush in the pics, but it looks like nearly half the height of the vertical tube. Much like my ‘Plan B’ and confirms the uprights are strong enough.
But without the old mounts in the chassis now I put the Chevy mounts on the block and that does indeed look the way to go as it all fits in – and if it works for Andy….
Still not too keen at solid mounting though, but equally don’t like the idea of the big standard rubber mounts. Found these babies and I’m guessing that would mean the mounting plate on the chassis would be around the level of the top of the lower rails.
So I think that’s the way I’ll go – a flat ‘plate’ on/near the bottom chassis rails, these pfadt bush-style mounts, and the standard Chevy alloy brackets to the block. Unless anyone thinks it’s a particularly bad idea.
I had planned to replace the steel bellhousing with an alloy one, but I couldn’t find one that would work. But by keeping the steel one I had already welded mounts onto it for the SBC, and there are Ford Fiesta engine mounts between it and the chassis. I can get the LS in the same position as the SBC so I’ll have mounts on the bellhousing as well as motor and end of the box.
Interested to know what you’ve done with the diff though Andy. I’d already ripped the standard diff bracket apart with the SBC so made up a stronger one…which then pulled out of diff cover so I had to helicoil the holes…so far so good but the LS will be making even more power.
Gassing Station | General Motorsport | Top of Page | What's New | My Stuff