E31 with LS motor swap

[TPIOlds]

I have the L98 im my E31 and would like to do the LS conversion

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[72tpik5]

Hey TPIOlds. What did you use for exhaust off of the engine? I am assuming that would be the toughest part of the swap. Nice job.

[TPIOlds]

I used small block manifolds with custom down pipes to aftermarket catalitic converters and then to the e31 exhaust

Hey TPIOlds. What did you use for exhaust off of the engine? I am assuming that would be the toughest part of the swap. Nice job.

[72tpik5]

I used small block manifolds with custom down pipes to aftermarket catalitic converters and then to the e31 exhaust

I figured it would be too tight on the drivers side. Thanks.

[Dolsey056]

Any other hurdles to consider when doing an LS swap on an E31?

[thelongeride]

I have an E31 840 that I bought for a swap. I have had it for a while. Sweet car, so I am still not moving with the swap as yet. I still have my SC
850.

[Richard454]

I went the opposite...I put a BMW engine in a Corvette!!!

M73 (some m70 parts) in my 71 Corvette that originally had a Chevy Big Block....

[WildKarrde]

I love those trumpets. If they didn't cost close to $10,000 I'd do the same to my 850.

[exalted]

I went the opposite...I put a BMW engine in a Corvette!!!

M73 (some m70 parts) in my 71 Corvette that originally had a Chevy Big Block....

Currently in the planning of an engine swap on my 850 and a Chevy BB (620hp) is my backup plan if I don't find an at least somewhat reasonable hp/$ bmw option (I'm looking into a fun M70/M73 alternative or possibly S38/S85).

How do the two engines compare for size and weight?

[72tpik5]

A complete big block is roughly 700 lbs, an M70 is about 570 lbs. I think your big block is going to be a little too wide. Google is an amazing resource.

M70 Dimensions

total length [end of crank pulley to rear block face] 29.25"
top of motor, widest point at valvecovers 19.5"
bottom of oil pan sump to crank centerline 8.5"
bottom of oil pan sump to highest point on valve covers 25.5"
bottom of oil pan to bottom of sump 3.5"
rear block face to crank end 1.0"
rear of block to oil pan sump 14.5"

Big Block Dimensions

Length: water pump pulley to bellhousing BBC 32.5
Length: water pump pulley to back of distributor BBC 27.0
Height: bottom of stock pan to top of valve covers: BBC 23.5
Height: bottom of stock pan to top of carb: BBC 29.0
Width: across valve covers: BBC 22.0
Width: across stock exhaust manifolds: BBC 27

[exalted]

I've seen a lot of different numbers so was just thinking someone who had actually made a swap the other way might know how well it worked in reality

Went and meassured between the two front beams and there is 30" between them so it should be doable if tight and some things on the driver side might need to be moved but that was in the works anyway.

Also that close in weight with aluminum BBC it would be more or less a dead run between them.

[Richard454]

I had both on the stand...My car originally was a big block. I was going back in with an aluminum headed 502 but decided to go with the V12.

They are about the same length- going with the corvette style short water pump.

You can look at all the measurements all you want- but what's important is measuring from crank line center to get the dimensions

The BMW's bottom half of the engine is bigger than the Chevy-Big help for clearing the frame and steering by going Chevy.

The oil pan on the Chevy is available in numerous configurations as it was used in many different chassis over the years. Unlike the BMW georotor pump that really can't be moved around- You can simply put a different pick-up and you are there. The BMW - I had to mod the pan and go with a Dry Sump system.

The other places where it matters- like the bellhousing- the Chevy is smaller.

Exhaust manifolds- again - there are hundreds of configurations out there- easy to get a pair of "block hugger" type and solve a lot of problems. The V8 is a 90º block and the V12 is a 60º block- but the intakes on the BMW make it just as wide as the Chevy.

The Chevy is taller with a carb- but there are several fuel injection set ups that would put it about the same height as the V12.

The weight? The iron block -aluminum heads is about 40 lbs more than the V12. The Aluminum block and heads weight about 25lbs less- but gets pretty expensive.

I think it is definitely do able


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