5 replies to this topic

[welshdan]

hi, ive recently moded my mpi mini. currently running ported head, standard valves reseated, double valve springs, standard bottom end, 1,5 roller rockers, lcb, straight through exhaust, engine compression ratio of 10.7:1, k and n induction, 52mm alloy throttle body


it goes really well. however the bottom end is tired and needs rebuilding.uses oil (smokes a little), oil pressure not the best. not using a power boost valve at the moment, though it goes really well, and showing no signs of fueling issues.


have a spare mpi engine. am thinking about building bottom end up with 73mm overbore, taking it to 1360. will use standard crank with new bearings. also wondering what the best cam would be to use. was thinking swiftune sw5i (i already hasve one of these in the garage), along with duplex lightened timing chains. would also centre strap the crank.

i have worked out the compression ratio, and the pistons im looking at would give me a compression ratio of 11:1. would the car be able to handle this, if i fitted a power boost valve? will be using same head/rockers.

gearbox will be checked, centre oil pickup, maybe hardened diff pin, with final drive of 3.1 or 3.2, as i do a fair amount of motorway miles.

does this engine look to be a decent spec?mainly will the ecu handle it (bearing in mind that people said it would struggle with 10.7:1 cr), with power boost valve?. is the swiftune cam the right one to use?

many thanks

[KLAS]

you have to match the CR to the camshaft used.
squeezing the hell out of the air fuel mix doesn't make sense and you will have trouble with detonation.
the power boost can not help there, it just can give correct fueling, but that won't help with detonation at all.

with the SW5 i would stay just below 10:1CR, but the best would be asking Swiftune for advice

[minicooper1.3i]

You also might want to bear in mind that with those kind of mods, you're going to be hitting, if not exceeding the limits of the Rover ECU. Which will almost certainly give you unwanted results as the standard is only good for around 80-85 bhp. Also, if you're changing the diff to a lower ratio, then I suggest you change the whole box to a decent / recon earlier model type, as the MPi boxes are probably the worst around, at coping with above standard horsepower.

Good luck with it all!

[welshdan]

yes, it will be an earlier box that i recondition. was hoping for around 80-90 bhp, due to the ecu. plus this spec isnt the most performance orientated.

the cr wouldnt be of choice, its what my current head and the pistons i am looking to buy would equate to. would ideally go for 10.6:1, am just wondering if the nearer to 11:1 cr is going to be a disaster?

if thats the case i need to look for another mpi casting, redo all of the grinding work, get it skimmed again, so a lot of work again. as i said, car seems to be getting on well with cr of 10.7:1

cheers

Edited by welshdan, 08 June 2009 - 11:25 AM.

[bigmotherwhale]

11 to one is achiveable, the sw5 cam is a mild camshaft with a low duration so the dynamic compression ratio wont be too high, i used to run very high compression on my mpi with the sw5 cam it was extreemly fast, i managed to blow up a compression tester doing a check, after i bought a new one i was running@ about 210psi not sure what it actualy was because i never measured it with a burrette, i never had any problembs with detonation, if you do have any problembs you can change the timming by either getting a pick up wheel on the crank damper for the hall sensor, or using a resistor on the air intake sensor, you can also run a mappable water injection system to prevent detonation like on a turbo supercharged engnine, the fueling requirements wont change all that much when you increase the compression, the mpi ecu should be able to cope, after all it copes with running a performance air filter on 1380cc engnines, saying that a few extra psi might help on the fuel rail, ive heard that 2.7 - 3.2 bar is about right for the mpi engine. dont be put off go for that high compression engnine! after all most petrol contains ethanol these days which has a higher octane, must be why tesco has just released 99 octane fuel, try some of that with octane booster and 5ml acetone per gallon

if it doesnt work you can always take the head off and grind the chambers out a little.

Edited by bigmotherwhale, 08 June 2009 - 12:06 PM.

[welshdan]

anyone else have views on this engine spec?cheers