MG 1098 Supercharger
Turbo Mini Forums

I have been following this forum for a while, and also am an active member of TMF, the question I now have, I felt would best be answered over here, rather than Facebook or TMF.


I have an MG 1098 Engine has recently been rebuilt and has not yet been fitted to the car. This was previously fitted to an MG 1100, and was running fine before rebuild.

The engine spec is as follows:

MG 1098 Block
295 head w/skim of .60 thou

Standard pistons as fitted to MG 1100

I believe with this spec and build the CR as current stands at around 9/9.5:1, but I am only going from what I have been told on this one.

I have recently been gifted an E45 Supercharger kit, that is ready to fit to an A' series, come with the manifold, pulleys, belt etc.


Will I need to carry out any more modification to my engine, or will I be able add this supercharger straight up, and be away with some correct tuning adjustments?

I have been told in other places that I could need to fit a decompression plate between the head, probably around 4-6mm?

***Edit***

The suggested boost levels are between 8-10psi based on the 65mm pulley.

Thanks in advance to all that can shed some light on this matter!

Ps: I don't wish to be told that I am fitting this to the wrong engine etc, this is a weekend car and will not be racing around race tracks or such like, it will visit shows a few times a year.

Edited by Albino_Hedgehog on 8th Nov, 2019.

I run 8.8:1 with about 11 psi using a Toyta charger.

You don't mention the expected boost, the "kits" are often 12psi.

If you want to get the CR down a decom plate isnt the best option you could use a cometic gasket, but you need to accurately measure the C/R. Phil is the man that can help with heads.

i would also recommend a simple water injection system and a run a mapped injection like megajolt, proper fuelling and it should hold together with some mechanical sympathy.

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Yeh, first thing to do is whip the head off and see what the c/r actually is. From there you can decide If you need to lower it further or maybe just run a bit less boost.

I have updated the original post with expected boost information.

At current time I don't wish to invest in a MegaJolt system, and will be staying with the Accuspark Amethyst system.

Well... IMO the CR that you quoted is too high. I think some accurate measuring is required or the result could be liquid pistons.

Can the accuspark change the timing based on MAP signal?

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

No, I can be pre-mapped and switch between a couple of options, fuel economy mode/sport mode haha

I'll best be looking into lowering the CR either via a Decompression plate or some work on the head,,

Any recommendations as to what the CR should be?