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Post Info TOPIC: SBC vs. BBC vs. LS Engine Mounting Dimensions



- Erik -
Snohomish, WA


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Posts: 446
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SBC vs. BBC vs. LS Engine Mounting Dimensions
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Dealing with my custom install of an LQ4 in my 1991 Crew Cab has generated lots of questions about why various companies all make slightly different conversion mounts.  Using CAD everyday at work makes designing things before work, during lunch, or after work FUN! :D

So...I have been scouring the internet for definitive information about the location of the various engine mounts and have had some success, but still can't seem to find some of the information.  I thought I would post it on our board to see if you all can clear up a few things...

 

1) SBC engine mounts:  It seems there are plenty of drawings out in the Interwebs that show the location of the 3 point mounts for the small block.  No problem there!

2) LS engine mounts:  I can't seem to find great information about the dimensions other than the dimensions of the pattern, but I do have a pretty complete CAD model of an LS engine block, so I can get those mounts in position.

3) BBC engine mounts:  Here there is a little confusion.  There seems to be not as much drawing information out there that establishes the engine mounts on a BBC.  The one drawing that I can find shows a basic Mark IV Big-Block.  On one half it shows the Short Deck and on the other half it shows the Tall Deck.  The dimensions for the engine mounts are only on the Tall Deck side and they are NOT the same as the SBC!!!

        a) I have always been under the impression that the BBC and the SBC had the engine mounts in the exact same place!  Is this correct?

        b) Does the Tall Deck BBC have different engine mount locations?  It seems in comparing them, that the Tall Deck has the engine mounts raised up, but it is possible that the dimensions shown are not actually to the motor mounts.  The drawing is not clear, but it is typical in how the engine mounts are shown on other drawings.

 

The reason why I ask all of this crap is that I find that stuff posted out on the internet is sometimes wrong! Shocking I know!  I also have found over years of designing stuff that small little errors get compounded and in the end when you correct the small little errors, everything fits so much better and issues tend to go away!  I am dialing in my engine in the Crew Cab and I am getting closer and I am finding that the issues that I am dealing with are slowly getting fixed!

 

Big Block Drawing: ?ref=?ref=http://photobucket.com/gallery/user/slonomo/media/bWVkaWFJZDo3NDg2NzU2MA==/?ref=

 Small Block Drawings: http://www.pdani.it/public/ciampone/v8_sbc_drawing_4.jpg

http://photobucket.com/gallery/user/tjs69_photos/media/cGF0aDovU0JDLTJmcm9udF96cHM2OTk4MjI3Yy5qcGc=/?ref=

 



-- Edited by ehjorten on Thursday 3rd of August 2017 09:42:18 AM

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Erik
'69 Chevelle Sport Coupe, EFI355, TH350
'68 Chevrolet C10 Stepside Project, 292, t-56, C4 IRS (project)
'77 Chevrolet K20 Silverado LWB, 400CI, TH400
'91 Chevrolet V3500, TBI Gen V 454, 4L80E, Lifted



- Mike -
Puyallup, WA


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Posts: 2591
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Guessing at what you mean here exactly...in space where the block ends up fore and aft should be the same between small and big block.  On a later Chevelle there is no differentiation between engine frame stands (unless it's a 307ci) so vertical placement of engine mount block holes should not be an issue either even though a big block is technically wider...it could be the rise of the mounting pads is different on the big block casting and final machining allowing the big block to fit where a small block was first(in '64).  The trans mount ends up in the same place, especially important on a car like a Camaro with a single set of trans crossmember mounting holes.  The angle of the engine/trans assembly in the car should also be the same based on the bellhousing to engine mount relationship giving the same driveline angles and carb mounting offset machined position to be level.

Sliding type adjustable aftermarket engine mounts that raise the Gen III/IV engine 1/4" are not very trivial IMO because trans mount and rearend nose up or down angle can be changed easily enough with adjustable parts.  Not to mention most people keep the fuel injection so no carb level issue.

As for the tall deck OEM having different mounting hole position, I think the internet is flinging poo.

 

For anyone wondering, I based my measurements for my LQ4's position in the Camaro off the 454 block I had before I sold it.



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'67 Chevelle -- 383ci, Jerico DR4, S60 3.54

'70 Camaro -- In the works TT 6.0L, 4L80E, 12 bolt ??? ratio




- Erik -
Snohomish, WA


Status: Offline
Posts: 446
Date:
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Here is how I am laying it out...crank centerline to crank centerline with the Rear Face of Case (RFC - AKA Bellhousing mounting flanges) lined up!

bTvNEclFcHtWZCLsbfT6FWNFzuVanoTILJG1d5cZ

Since I am dealing with small clearance issues, I am CADing it all out and making changes to my brackets so that I only have to make one last set to get it on the money!  This layout shows that the Advanced Adapter brackets are pretty close and there is a difference in height between the two that is about 5.9 mm or somewhere between 3/16" and 1/4", which accounts for the thickness of the adapter plates, but...my truck had plates between the motor mounts and the block that provided for the attachment of the stabilizer rods that bolted to the aluminum converter housing.  Another layer of stackup to account for.



-- Edited by ehjorten on Thursday 3rd of August 2017 11:06:18 AM



-- Edited by ehjorten on Thursday 3rd of August 2017 11:07:42 AM

__________________
Erik
'69 Chevelle Sport Coupe, EFI355, TH350
'68 Chevrolet C10 Stepside Project, 292, t-56, C4 IRS (project)
'77 Chevrolet K20 Silverado LWB, 400CI, TH400
'91 Chevrolet V3500, TBI Gen V 454, 4L80E, Lifted



- Erik -
Snohomish, WA


Status: Offline
Posts: 446
Date:
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So I confirmed some stuff last night on my quest for modifying my LS conversion brackets...some of you may have already known this, but I do find it interesting:

As we already knew, the bolt pattern on the small block and big block for the engine mounts is the same. What I confirmed last night is that the location of the bolt pattern on the block is in the exact same location from the bellhousing surface, or Rear Face of Case (RFC), and it is the exact same height from the pan rail as the small block. The extra length of the Big Block is pushed forward from there.

The weird dimensions on the Big Block drawing I referenced in an earlier post are to the two bolt holes near the front of the block that are up high. I assume those are used for various front accessory brackets like alternator and/or AC pump.

The extra couple inches of length of the big block is at the front of the engine.

__________________
Erik
'69 Chevelle Sport Coupe, EFI355, TH350
'68 Chevrolet C10 Stepside Project, 292, t-56, C4 IRS (project)
'77 Chevrolet K20 Silverado LWB, 400CI, TH400
'91 Chevrolet V3500, TBI Gen V 454, 4L80E, Lifted
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