high comp?

[allanr5gtt]

i have an msm engine that has higher compression than std? i haven't stripped it down yet but was interested to see how the compression had been raised ? the easy way would been is to skim the head loads. but i remember reading on the old site that the compression chamber has to been modified at the same time .
has any stripped one of msm high comp engine and seen what was changed?
or have an a idea how it can be done?

thanks allan

[Markey Mark (BD)]

I've had an MSM high comp engine before, the block is skimmed as is the liners, pistons are then machined and depending on the comp wanted so was the head.

To be honest i don't know why it was done that way (been a long time since i had it) but do remember it being done this way

[Scoff]

i don't know why it was done that way

It ment you could keep the thick uprated type gasket and improve on squish effect.

[allanr5gtt]

but to make any difference i would of thought that you would have to skim loads off the block and liner's?

[Scoff]

but to make any difference i would of thought that you would have to skim loads off the block and liner's?

Why do you think that ?

[Markey Mark (BD)]

From what i remember it was no more than 1mm that was skimmed off the block and liners

[allanr5gtt]

i just thought that to make any difference in the compression you would have to skim a good 2-3mm off the block and liners to raise the comp. but i may be wrong as i'm no expert. and is why i'm asking how is the comp raised as i don't really know?

[allanr5gtt]

From what i remember it was no more than 1mm that was skimmed off the block and liners
did you know what the compression was with 1mm skimmed off?

[Markey Mark (BD)]

1mm was skimmed off all the engine's i believe, it was the amount skimmed off the pistons and the mods to the chambers that determined the compression ratio. They also had to take into consideration how much the original head had been skimmed too when machining the bits so at a good guess no 2 engine were identical

[Woznaldo]

I understand that high comp will make the engine more responsive on and off boost and reduce lag but do you need mappable ignition to get the most out of a high comp motor?

[philr5t]

if i can remember and i maybe wrong but i thought the msm engines were around 8.1-1 i am running alot higher compression ratio but yet to see what the engine will do hope this helps mate

[Sparkie]

gordini turbos ran 8.7:1....:agree:
with no intercooler....:laugh:

[James5]

I know my old MSM engine was High Comp, the liners were slightly shorter when compared to a set of standard ones only know this when I changed the rings to the total seals I thought I would take a look @ one steel liner compard to a standard liner and yes on a flat surface. I only had a look after a few things I heard on RTOC about the MSM engines being high comp so it was more of a curiosity thing, but I also noticed my pistons were standard type and not skimmed, but I know the chambers on the head had a fair bit of work done.

[Woznaldo]

For those of you that are or have run MSM high comp engines, what was done to the ignition? Was it just an adjustable timing sensor or something more comprehensive?

I would imagine the Gordini Turbo didn't run the same advance as a GTT?

[Scoff]

You can't really compare the crossflow head with the C1J, they're different things entirely. I'm pretty sure Mike would have left the ignition alone in most cases. At say 8.5:1 things will start to get a bit sketchy at about 18psi so if it was a low boost motor then standard would have been fine. For more than that he would probably have to pull a few degrees. My old C1J ran 8.7:1 and 2 bar or so, that took -4deg and some octane boost in the fuel occasionally to keep it happy. If you are playing with high compression you need to be very aware of the likelyhood of detonation.

[James5]

For those of you that are or have run MSM high comp engines, what was done to the ignition? Was it just an adjustable timing sensor or something more comprehensive?

I would imagine the Gordini Turbo didn't run the same advance as a GTT?


I know my MSM engine was running fully retard on an adjustable TDC, I did move it back to standard position once and I then blew the Head gasket, after which I put it straight back to retard and never had a problem again.

[allanr5gtt]

I know my old MSM engine was High Comp, the liners were slightly shorter when compared to a set of standard ones only know this when I changed the rings to the total seals I thought I would take a look @ one steel liner compard to a standard liner and yes on a flat surface. I only had a look after a few things I heard on RTOC about the MSM engines being high comp so it was more of a curiosity thing, but I also noticed my pistons were standard type and not skimmed, but I know the chambers on the head had a fair bit of work done.


what was done to the chambers in the head? do you have any photo's?

[James5]

what was done to the chambers in the head? do you have any photo's?


I have been looking for pics as I did take some when I blew the H/G to due to the fiddling with the TDC but am able to find them as yet:(


I was running 21psi manifold on the VNT and had to run full retard was seeing 12.1's @ WOT (I know others went a little leaner for more power) :)

[Woznaldo]

So from what I can gather, STD ignition timing is ok for a mild increase in comp as long as boost doesn't go too high but, some kind of ignition adjustment would be desirable to make it work.

[rs250nut]

An ignition only system would be worth while on something like this, megajolt lite, dta s40 and run it with an oxygenated fuel, turbo max or something similar:devil:

[Rob@Backyardracing]

An ignition only system would be worth while on something like this, megajolt lite, dta s40 and run it with an oxygenated fuel, turbo max or something similar:devil:

Q16 ....helll yeahhhh :D

[rs250nut]

Q16 ....helll yeahhhh :D

Damn right, I bet that ganni santi guy runs something like that to produce the numbers he does. Makes me want to build a c1j now:laugh:

[Woznaldo]

I think it's an area that hasn't been fully explored on the C1J outside of a select few (Scoff, MSM etc) and would make for a nicer more responsive and tractable engine. In the Mini (classic) world, this sort of machining to raise comp is more common, being documented in some detail by Dave Vizard, although mainly N/A applications.

Is it the cost of this work that holds people back, or the complexity?