20 replies to this topic

[bluedragon]

The June 2005 issue of MiniWorld has a breakdown of MPI performance gains per modification. The testing was done by Slark Race Engineering.

 

Base power - 61 hp flywheel, 74 lb/ft torque

 

1) Free flow filter (stock air cleaner housing) + 1 hp

2) Remove catalytic converter - +1 hp, +1 lb/ft

 

Catalytic converter was then refitted, as the +1 hp gain wasn't worth the trouble or the problems failing emissions testing.

 

3) uprated cylinder head + LCB manifold + exhaust = +9 hp over base, +5 lb/ft torque

4) 1.5:1 rockers = +1 hp

5) 52mm throttle body = +1 hp

6) fuel pressure regulator = +3 hp, +1 lb/ft

 

The final total being 75 hp and 80 ft/lb max. The head is the most important part, and then the MPi fuelling limitations come into play. The fuel pressure regulator helps increase fuelling, but it's a crude way to get more fuel into the engine to take advantage of the extra air flow. Going too far with it will kill fuel economy.

 

To get a substantial change, I would bite the bullet and go with an improved head. The rest of it might be good for 4-5 hp and I don't think it's worth the trouble, honestly. The improvement is better than the raw peak numbers because the powerband is broadened, which is just what a street-driven Mini can use (vs. a motor that you have to rev the life out of to get to the increased part of the power band.)

 

Perhaps someday someone will release a plug and play fuel injection controller for the MPi that will allow us to use bigger injectors and truly unlock increased power while keeping the broad torque band of the injection.

 

 

Dave

[Guess-Works.com]

Perhaps someday someone will release a plug and play fuel injection controller for the MPi that will allow us to use bigger injectors and truly unlock increased power while keeping the broad torque band of the injection.

Cough.....

 

http://twinkam.co.uk.../Products/SC220

 

on a secondary note, I've found many mpi's which have been fitted with a 'fuel regulator' have washed the bores and therefore need rebore & new pistons.

Edited by Guess-Works.com, 12 October 2016 - 10:35 AM.

[tmsmini]

I will have to dig up that article. I know there was a lot of talk about an "uprated" fuel pressure regulator to go with some of the kits being offered back then. hard to see how a change in FPR would increase anything.

 

I think you also need to look at the sum of the parts, each one of these may not contribute what is expected until all the pieces are in place. It is really no different than a carb car, putting on a giant carb without other modifications will result is weakened performance.

 

I know people have mentioned their success with the SC throttle body conversion, but it does seem to take some work to get it sorted.

[bluedragon]

The MPi injectors are limited in the amount of fuel they can deliver in a given timeframe. It's exacerbated because the siamesed intake ports mean the fuel has to be injected within a very tight window to get to the right port.

 

Increasing the fuel pressure raises the amount of fuel delivered for a given time period, helping address the fuelling limitation. But it also means that excess fuel could be injected under low-load conditions, since the injection ECU doesn't know that the pressure has been raised. This accounts for the problem of excess cylinder bore wash.

 

Ideally, the injection system would detect if it's running rich (due to more fuel being injected that it expects because of the raised fuel pressure) and it would back off under those conditions, but either the MPi doesn't work that way or raising the fuel pressure excessively exceeds the MPi ECU's ability to adjust.

 

The real upshot is that the MPi system is limited in power output because it can't fuel the engine adequately at high revs (the higher the revs, the shorter the time window is to inject fuel for the siamese intake ports.) Inject too long and you get intake charge robbing, which should be a term familiar to all who look into hotrodding MPi motors before long. The fuel/air mixture gets pulled into the wrong cylinder when the window is exceeded. But gains can be had by improving power beneath the rev limit, which is the main goal of most MPi kits. Products that enhance power at high revs probably will not be that successful on an MPi.

 

The Specialist Components unit is interesting. I don't know a lot about it so I could be wrong with this conjecture, but it looks like a super-SPi injection unit. The twin injectors are concentrated in a central intake, not focused in the individual intake ports, so I don't see how it can fuel each cylinder individually the way an MPi can. Not to say it doesn't work (it seems like many people are happy with it) but it doesn't seem like it works like the MPi injection.

 

The only people I know of who have siamese-injection strategies available to the end user are the MPi Megasquirt folks, but these require fabrication and aren't plug and play. There was a German group that was working on this too, having produced a successful SPi replacement, but I've heard nothing from them in years.

 

Dave

[tmsmini]

I would suggest that the SC unit is not exactly plug and play either. Certainly closer than using a Microsquirt or Megasquirt from scratch, but from my experience, there is substantial tuning required as would be expected for any system like this. On this side of the pond, there are few with experience setting up the Typhoon or Delta ECUs.

 

I think the Rover MPi/MEMS does a great job at what it was intended to do, supply a managed fuel/ignition system for a 60+ year old engine design.

 

To the question, I think you will find a modified head to give the greatest gain and MiniSpares, Mini Sport and CalverST all have them available for the MPi. All the other pieces are very incremental as indicated in the article quoted.

[brivinci]

What they said! The head is key. If you dont mind pulling the motor, the cam is another key part. A good head and matched cam will really wake these cars up.

 

The other thing is the final drive on these. The MPi had the tallest of all the factory final drives. Made for happy (or happier at least) motorway driving. It was an attempt to make the car a bit more refined and competitive in the market. Not so high reving and noisy. If this car is more of a back road barn stormer, switching to a lower FD will add a sizeable about of kick in the back.