Head shim on MPI supercharged Nytro? Why not?

Phyxius said:

I have a MPI supercharged Nytro with the 180hp kit. I'm thinking about bumping it up to 220hp with the upgrade kit but here is the problem. I don't want to run race gas! I want to be able to still run pump gas because it's conveniant so the question is why do MPI recommend not running a head shim? MCX run their 270hp kit on pump gas and they use a head shim. In my mind boost is boost and it's now differende if it comes from a supercharger or a turbo. Am I wrong?

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My first post here! :yo:

It's possible to use a mcx head shim or other pistons to lower the compression. You need to add a intercooler and upgrade your fuel system. Fuel pump and injectors from mcx 270 might do the trick.

I called about the 180 turbo kit and they told me the same thing. Im going to run it at 180 this year but next year Im going to get the upgrade kit which is just basically an intercooler and reprogram of the GEMS controller and they said they would also not recommend a head shim. Theres no way I can run a 50/50 mix so I want to be able to run pump. Im wondering the same thing as you Phyxius about the shim and the fuel pump.

My guess is that lots of guys pick the MPI super over a turbo because the application is different. Supers are beter suited for corner to corner trail riding etc where power at the bottom end is desired where a turbo likes to be taped to the bars and provides it's boost at the top end. By installing a head shim you would lose the bottom end snap that the stock compression provides which would work aginst the point of having a super in the first place. I would think this is why MPI does not recommend the shim, To my way of thinking there is no reason you could not run a headshim on the super other than for the reasons above. It should work fine if you are pinned all the time but for sure it would not have the same throttle response.

All of the low boost kits are set in the range of 8,9,10 lbs max depending on elevation when running pump premium, if you go above that boost you need the octane. The Nytro motor enters the danger zone at around 10 lbs on stock compression without race gas. Your only 2 choices short of a complete engine management system are to lower the compression or raise the octane. The intercooler helps but even with that you will blow up the motor on pump.

One other thing to consider is the MPI turbo kit I saw last year at the show was built with a Mitsu 15G turbo which is a pretty basic turbo. A 15G is smaller and spools slower than a 16T due to the older turbine design so with a shim it would be even worse. When you compare the compressor maps the peaks are quite close but the 15G is old school so it benefits from stock compression. You will be pretty much off the map at 12 lbs with that turbo, it'll make more boost it just won't make any more power.

M5

I added An 80 thou head shim with 2 factory gaskets before I installed my turbo kit. I rode the sled that way a couple of times and can honestly say that the bottom end was not noticeably affected. It definitely lacked power on the top end though. Having said that, I would say go for it. MPI used to trash turbos bad.......guess what they're all excited about now?

Phyxius said:

Sounds like a likley reason to me! When I get the upgrade kit I'm sure gonna run the head shim cause race gas is not an option. Too much hassle.

BTW... Roest, got that tunnel cooler ready soon? I'm probably gonna need one. :face-icon-small-coo

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I'm working my azz off to try and pull everything together so they are available asap.

Roest said:

I added An 80 thou head shim with 2 factory gaskets before I installed my turbo kit. I rode the sled that way a couple of times and can honestly say that the bottom end was not noticeably affected. It definitely lacked power on the top end though. Having said that, I would say go for it. MPI used to trash turbos bad.......guess what they're all excited about now?

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Hmmmm.........someone flamed me for this post?..............

I installed a head shim on my mpi stage 2 S/C at 18 lbs boost and the only difference I notice was the price of fuel lol no performance issues what so ever.

I would find a used GEMS box that's not locked and intercooler, install the shim and have a good time...

Make sure you have a working air/fuel and boost gage for tuning

A.Granath said:

My first post here! :yo:

It's possible to use a mcx head shim or other pistons to lower the compression. You need to add a intercooler and upgrade your fuel system. Fuel pump and injectors from mcx 270 might do the trick.

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If your doing a headshim 2 things ive been told by most in the business.

1-Buy studs
2-Make sure you get your timing right.

You could always run Water meth kit to. Allot of people dont approve of it but its another option to race gas.

Head shim

I was at MPI the otherday and they can flash your sled and make it so you can run high boost on pump gas. If you tell them what your plans are they can make the proper electronic adjustments to accomodate them. I am taking mine up next week.