9 replies to this topic

[300bhp/ton]

Ok, I know that SPI is Single Point Injection and MPI is Multipoint Injection.

But what exactly does this mean?? :'(

Is the SPI using a single injector into the throttle body, alla TBI (throttle body injection) or is it meaning somthing else?

I know other Rover cars (200, 400) and Discovery also went SPI to MPI but I don't recall any having an injector on the TB though.

So a little clarification would be appreciated.

Also I know MPI should be superior, but what's the concensus on this. What real world advantages (HP or mpg) does it offer.

Thanks.

[Jimmyarm]

MPI injectors are in the manifold rather than the throttle body I believe (ok there are pics in one of this months mags !).

Hopefully Mini Sprocket will post up, he seems to know the injection systems like the back of his hand !

[Sprocket]

Ha Ha

LOL

The only difference between the SPi and MPi engines (other than the physical differencies in the block) is emissions and a little more mpg, though the the MPi gained a little more torque but still boasted the same power figure. This enabled rover to get away with fitting the 2.7:1 final drive without loosing too much of the drivebility, which along with the front mount rad, reduced driveby noise levels and increased driver comfort, especialy motorway crusing which has become a big part of some peoples lives.

The SPi uses a distributor, but not in the normal sense that most mini owners would think of. Its an empty shell containing a solid, fixed shaft, convential rotor arm and cap, attatched to the cam in the normal way. It is mearly a distribution of spark device and will not advance ignition with centrifugal force or vacuum as a carb distributor does. The Injection manifold is, as you say, throttle body injection, also sometimes called electronic carb as thats baisicaly what it is.

The MPi uses the distributorless ignition system also known as wasted spark ignition.

The MPi block is completely different to any of the blocks gone before. The cam is slightly different for the cam position sensor and the second gear on the box is also a new ratio never seen on boxes before, though similar to the Cooper S or 1275GT ratios. The injection system on the MPi is sometimes called port injection as the injectors squirt the fuel straight at the back of the valves. There are two BIG injectors on the Mini. This has to do with the port robbing that five port heads suffer from. There is a very complicated program in the ecu that requires the cam possition as well as the crank position to get the right amount of fuel into the right cylinder at the right time. This is known as sequential injection, where as most multipoint systems prior would have been batch fire either all four injectors at once or in pairs alternately. Fine on an 8 port head, useless on the aging 5 port.

Sum it up like this. MPI complicated for only a small improvement in emissions and torque. SPI simple, its baisicaly a carb.

Rover K series engines did have the SPi manifolds but for short period only. The K8 1.1 and 1.4 had SPi only, K16 1.4 had SPi for a very short period, but you mostly find them to be MPI. K1.4 SPi is rare as hens teeth!

Edited by Mini Sprocket, 28 November 2006 - 08:36 PM.

[fikus01]

i have a spare 1.4 k-16v gti spi system going spare/for sale if anyone wants to make me an offer pm me!!

if memory serves it was the biggest spi injector they used!!

[300bhp/ton]

Mini Sprocket - Thanks

[Jammy]

If we're all finished with this topic I'll move it to the FAQ section?

[AlexM]

In my opinion for the home mechanic spi is better as it is simpler and less expensive to fix than the more complicated mpi system. Previous to 92 minis had always run with a carb, and all the spi system does is replace that carb with a fuel injectior (as well as the various sensors which go with it) and thus the engine remains very similar to how it does before.
An mpi system does not work as well as it normally would on any other car because of the siamesed port configuration of the mini engine. And the charge robbing effect that mini sprocket described.
An spi sytem maintains the proven layout of the carb system whilst adding the benefits of fuel injection. Ie economy, drivability, emissions etc.

[vasi]

Indeed summergnu, this is why I've chosen Spi as my route for FI. Although this will be running a complex custom ECU with a wideband O2 sensor.

I do challenge Sprockets notion of Spi K's being rare though, they're plenty round here! In fact the GTM project TT (don't ask) obtained a few from spi k's as we blew some up, oops

[Sprocket]

Well i found one after a LONG search. Just cant seem to find them up Noorth, maybe im looking in the wrong place. It does have to be the 1.4 16v one though. theres poo loads of 1.1's and 1.4's 8valve

[vasi]

Thus proving that the rover 200 is the shed of choice around stooork on trent tee hee.