25 replies to this topic

[Cian 'the pain' MPI]

Hey there, i am in the process of getting my MPI engine rebuilt, and ive heard many different opinions on changing to a sportier cam ECU cant take it etc , i will be keeping the original ecu, the spec will be 1275 ported head, standard valves, rebiult box with 4 pin diff 3.4 final driva nad possibly straight cut drops. Just wondering has anyone experience with changing MPI cams etc many thanks !

[jaydee]

These are the figures of a standard mpi cam:
Duration 238/252
Overlap 0,04
Lift with standard rockers 0,329
Lift with 1.5 rockers 0,395
Its very common to add 1,5 rockers on mpi engines instead of changing the cam itself, piper do a cam for mpis, probably kent do a version of the 276 suitable for mpi engines, surely they do for spi engines, so worth ask them directly.

[welshdan]

hi, put a sw5 in my 1360 rebuild.

it definately isnt a race cam! however before its shot down, it has improved torque and the rev limit of the car. the car revs much more freely and along with the other mods it feels much quicker

am waiting to get the fueling set up properly on a rr, so dont have power/torque readings for what i have built.

[jamesmpi]

i've got the swiftune SW5-07 CAM in my 1380 mpi too. Very good CAM. Pulls and rev's up very well.

[Cian 'the pain' MPI]

Are you guys running with the original ECU? Heard the standard ECU cant cope with the fueling

[shpoom23]

I have 1380 mpi with Stage 3 head, 1.5 roller rockers, 3.44 dif, adj fuel regulator, lightened flywheel and rods, 52mm throttle body etc etc and run a Swiftune SW5i cam which in my opinion is excellent, I also retain the standard ECU and the car performs with no problems at all.

[welshdan]

mini is 1360, ported/polshed head with double springs and bronze guiides, cr or around 11:1

standard crank/flywheel assembly.

sw5i cam, piper verneir gears, 1.5 roller rockers

also running 52 mm throttle body with KandN induction kit.

exhaust is lcb, decat pipe and 2 inch backbox

gearbox is a close ratio gearset with 3.2 final drive

seems to run fine with the standard ecu. am limiting it to around 4k revs at the moment, will be fitting and getting the car set up with adjustable fuel pressure regulator when i get chance. will also be nice to get a power printout etc

[Cooper1999]

Let us know how you get on, welshdan - thats a similar spec to what I'm looking at, only 1330. I'd like to see 100bhp / 100ft/lbs as a target but I am thinking of using megasquirt/canems ecu!

[Cian 'the pain' MPI]

When it come to MOT are you guys fine with the emissions?

[Cooper1999]

When it come to MOT are you guys fine with the emissions?

I've got a home ported head on mine at the moment, with lcb, K&N and 52mm throttle body but stuck with 1.3:1 roller rockers as I have heard these make a big difference to the emissions on some cars but not others. There was no problem with the emissions on the RR, but the MoT is due in a couple of weeks - I guess that'll be the ultimate test!

[jaydee]

(As long as you're keeping the cat)
Its the overlap of a cam which makes more emission troubles..
A long duration cam will have consequently more overlap, which could lead to MOT problems when it comes to gas testings.
With a cam like like the SW05, developed to give more lift retaining quite a standard duration(just few degrees more), you have less emission problems; also adding 1,5 rockers will increase lift and not duration, so they have a mild influence on emissions.

[sirweste]

Cian,

The common choice for a "hotter" cam for the MPI is the swifttune sw5i. This will give you more torque, not loads more but some, and it will keep the car fairly drivable for around town in jams etc as well as passing the mot!

The things you heard about the ecu are probably correct, the ecu it's self can only adjust fueling and ignition parameters to a certain extent and so once your at the stage you are with your engine "stage 3" as its commonly called, the ecu becomes the main restriction on torque.

I would say that the straight cut drops are not something i would personally opt for as they will create alot of added engine noise for little relative gain. The straight cut option tends to be taken on much higher tune engines where every last ounce of power is sought.

The 1.5 rockers will do nothing but make your engine less drivable and reasonably significantly shorten the cylinder head rebuild life. The act of opening the valves further and at a faster rate causes the torque curve to shift up the rev band - removing lower down grunt at ~2500. Meaning that you will miss out on some power thats near and beyond the rev limiter, and always be reving the nuts off the engine for the same power you could have had at 1000rpm less if you hadn't a 1.5 lift rocker assy on it!

The other thing to do with out is double valve springs, which put unnecessary load through the valve train. These are required for high reving engines, and the mpi is limited to 6500rpm.......

[Cian 'the pain' MPI]

Great advice thanks man! So i could put the swiftune cam in but forget about the double valve springs? and will the cam make a noticible increase in the way the car performs? The only reason i am goin for the straight cut drops is purly for the noise as i think it sounds great

Edited by Cian 'the pain' MPI, 12 January 2010 - 07:28 PM.

[sirweste]

Fair enough on the drops decision - just dont go doing any long trips in it!
Yes double valve springs on a mpi are a utter waste of time. Coopers just fitted them to make the spec sound more sporty, mine are sat in my tool box where they can't do any further damage.

When I did my engine i changed a few things so i couldnt honestly tell you what difference the cam made as there were several contributors to the engines new characteristic. But it should indeed give the car a bit more torque from about 2K upto 4.5 - 5K. I have not studied the difference in standard cam profile vs. the sw7i so i cant comment on the theory of it.

The "stage 3" head will make the biggest impact on performance change - the 3.44 final drive will make the biggest change of drive ability.

[rick.spi]

sorry to butt in but pretty much all cam companys and other companies recommend stronger or double valve srpings with high lift cams... i dont know why so dont ask but thats what they say.

Edited by rick.spi, 13 January 2010 - 10:14 PM.