14 replies to this topic

[Bean]

Hi All,
Looking for an answer - The geekier the better, really!

I'd like to know the exact difference between the MPi and standard carb subframes.

I know about the mounting holes being further back, to allow for the radiator.

But, were there any other changes to the subframe in the later Minis.


For example - Did they make the openings for the driveshaft that little bit wider, so that you can get the pot joint out ... or not?

Or any additional strengthening?



Trying to work out whether to use an MPi subframe for my car (got an MPi engine in it), or stick with the original & just drill more holes?


Thank you ever so!!

[1984mini25]

The front sections are different, with a kinky front section and radiator mounts (mpi ones), as apposed to the completely straight section on the carb subframes.

Edited by 1984mini25, 17 February 2011 - 12:41 AM.

[Bean]

So, it's necessary to use the MPi subframe, to mount the radiator?

Sorry for the probably daft question - We've run the MPi off a side mounted rad up until now, so I've not had to think about it!


Cheers, Karl!

[1984mini25]

Would be easier for using a front mounted radiator, but then the later mpi front panel is also different.

*I’m tying to find picks to explain, but not having much luck *

[Bean]

Does the rad mount to the front panel, too? The front panel seems to have strengthening bars in a different place - I wondered if it was mounted to the subby and stablized on the front panel?

If so - Imma have to do some more shopping!!

I figured it was just the notch out of the lower lip of the front panel that was different, but I'm not so sure any more!

[Dan]

The altered engine mount position is not an MPi modification, it was to allow the larger HIF44 carb to be fitted easily. It's only the rad mounting cups and altered front member that are MPi parts.

[Bean]

D'oh! Doesn't sound hopeful for using a standard subby, then!

Cheers, Dan!!

[GraemeC]

Wasn't the front member 'bowed' at the same time as the engine was moved forward, then the cups added at MPi time? I'm sure my SPi frame has a bowed front cross member.

As far as I am aware the drive shaft holes never altered.

[wardyxxx]

Isn't the rear subby different too?

[ibrooks]

Rear subby is different but only in that the exhaust hangers are welded to it. You can buy a bracket that goes on the front crossmember (of the rear subframe) that repaces the hanger and you can buy the hanger to weld to the side near where the tailpipe starts. Or you just use an RC40 fitting kit.

The engine moved forwards a fraction when the SPi cam along to allow for the injection gubbins at the rear of the engine but you can get away without moving the engine so long as the mounts are kept reasonably fresh.

The MPi front crossmember (of the front subframe) is quite different to the previous ones. As mentioned it has a bit of a bow to it (similar looking to auto subframes but I've never directly compared them). It also has a bite out of the lower return which is actually folded down into a lip for extra strength. Then of course there are also the holes and cups to take the radiator.

Iain

[Sprocket]

The engine moved forwards a fraction when the SPi cam along to allow for the injection gubbins at the rear of the engine but you can get away without moving the engine so long as the mounts are kept reasonably fresh.

The MPi front crossmember (of the front subframe) is quite different to the previous ones. As mentioned it has a bit of a bow to it (similar looking to auto subframes but I've never directly compared them).

Dan has already explained why the engine was moved forward 1/2" on 90s subframes, it has little to do with the SPI and more to do with the HIF carbs hitting the bulkhead. The 90s subframes used the front stretcher bar from the Auto frame (the one with the bow in it). The MPi subrame was a revision of the 90s frame that incorporated the lower radiator mounts.

If I were putting an MPi engine in a non MPi car, I would bin the front mount rad and the raised alternator, and fit a side mount rad and standard alternator.

[Bean]

Mmmm, interesting - I trust your judgement hugely, Mr Sprocket!

Out of interest - What's the reasoning behind keeping the side-mounted rad?

The reason that I thought about changing to the proper front mounted rad, was to eleviate any anomolies, mainly for maintenance and upkeep, really.

It currently has a side-mounted rad, with an SPi bottom hose setup. The problem we found was with the temperature sensor and sandwich plate - This could be moved onto the head, I presume? (in the old heater-tap recess?)

I have never had an issue with cooling with the side mounted rad. The issue that I have had was with the temperature sensor & getting the correct reading?

As I say, the only reason I thought it was best to change back is that I now have access to the proper full setup, and figured it was there for a reason? Seeing as the gearbox has blown and the engine is out (and the body is in bits) - I thought it best to take the time to look over the best ways of doing things!

It seems that there was no additional strengthening that went into the MPi subframe, then - So I think it might be worth sticking to the original?


Not so bothered about the rear subframe - I'll be using the current 1 1/4 exhaust setup that's on it, so happy with that!


Cheers all!

[ibrooks]

Dan has already explained why the engine was moved forward 1/2" on 90s subframes, it has little to do with the SPI and more to do with the HIF carbs hitting the bulkhead.

There were a hell of a lot of HIF carbs fitted to Minis before the subframes were altered.

Iain

[Sprocket]

Dan has already explained why the engine was moved forward 1/2" on 90s subframes, it has little to do with the SPI and more to do with the HIF carbs hitting the bulkhead.

There were a hell of a lot of HIF carbs fitted to Minis before the subframes were altered.

Iain

And how many of those were fitted by the factory?

I can assure you that the HIF carb sits too close to the bulkhead if you do not move the engine forward 1/2". The SPi Manifold on the other hand has miles of clearance. we could argue this all day and still not come to an agreement and since there is no one around from Rover likely to say for sure, lets just leave it as it is.

[Tommyboy12]

My HIF hits the bulkhead without my engine mount being correctly adjusted if that helps