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Front Subframe Spacers, What Affect Would They Have?

suspension geometry steering goemetry subframes engine swap

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#1 Nix.

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Posted 15 April 2021 - 12:09 PM

So long story short I'm mid engine swap at present and to get the engine to sit where I want it I need to drop it about 15-20mm relative to the engine bay. Unfortunately that would mean the oil pan would sit right where the steering rack wants to live.

 

The way I see it my options are move the steering rack down and forward slightly (probably 10mm forward and about 10-15mm down) but I know that will piss with the steering geometry and seeing as how my car is already lowered quite a lot and suffers from a fair amount of bump steer and whatever else I don't really want to screw with it further if I can avoid it.

 

The second option is to space the entire front subframe down by 15mm. However posts on some forums about this subject suggest that this would screw with the suspension geometry but I cant see how it would. The front Subframe on the MX5 has the mounts for Steering rack, LCA and UCA so they would all move relative to each other, the only thing that changes is the distance between the top and bottom suspension strut mounts and as I'm on coilovers I can compensate for that by adjusting the height.

 

So any thoughts on which route is better and why and also why some people seem to think that spacing the subframe down would affect suspension geometry?

 

Thanks.

Nix


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#2 Zed.

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Posted 15 April 2021 - 12:23 PM

Bumpsteer either way  :popcorn: 

remember, the suspension arms move in an arc, so does the steering-racks trackrod so moving the rack anywhere is not great....

 

lifting the body from the subframe assembly could only work if you're increasing the ridehight otherwise increased bumpsteer due to suspension angles...

honda swap?

Rich.


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#3 Nix.

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Posted 15 April 2021 - 12:41 PM

Thanks Rich, that makes sense, I'd over looked the fact that dropping the subframe but adjusting the the ride height to compensate would mean that the arms are at an even worse angle than they are currently.

 

I think I'll try spacing it for now anyway and see how that goes as I don't really want to move the rack, and my car is low but not slammed (still got like 15-20mm wheel gap at present). I may be able to get away with a 10mm spacer and then drop the engine another few mm before it gets too close to the rack.

 

Not quite, its something a little bigger with a couple more cylinders  :D. Ill update my project thread about it once I've got the engine and box in and the turbo fitted

 

Thanks,

Nix


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#4 Zed.

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Posted 15 April 2021 - 12:46 PM

Not quite, its something a little bigger with a couple more cylinders  :D. Ill update my project thread about it once I've got the engine and box in and the turbo fitted

external oilpumps can allow shallower sumps & lower engines......

Rich.


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https://mighty5s.com...silver-na-eunos


#5 deviator

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Posted 15 April 2021 - 01:51 PM

I was going to suggest modifying the sump. Or if the budget allows, dry sump. Also look at other fitments of the engine you are using. Sometimes you'll find a transverse fitment engine has a more useful sump than the inline sump.
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#6 Shadowraven

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Posted 16 April 2021 - 04:36 PM

Can't you also then space the tie rods to correct?


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#7 Nix.

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Posted 03 May 2021 - 10:07 PM

Yeah unfortunately because the engine leans over at 30 degrees, a dry sump wouldn’t help as the oil pan is flat to the subframe but only sits about 15mm below the block on one side. I ended up spacing the subframe down 10mm (or 3/8 of an inch if your so inclined) and then dropped the rack by 5mm. Hopefully I can space the other tie rods down by the appropriate amount to compensate as Shadowraven suggested.

The engine is a BMW M52TUB25 so no options for other oil pans as it only came in one configuration
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