BX16V.com Forum

Hi
Is anyone clever enough on here to work how much if any a XU9J4 with the stock compression of 10:4:1 should be de-compressed to run 8psi of centerfugal superharger boost.
I want a simple answer like "yes to....... because...............or no because.........
Ive asked every engine builder in the land and can't get a straight answer.

any help would be appreciated

many thanks

I'd take a look on the 205 Drivers site, I'm sure someone on there will have done exactly what you looking to do:

http://forum.205gtidrivers.com

Mike P

AFAIK you need to swap your pistons and possibly cams for DFW ones (catalysed engines).

The guru on the NZ French car forum has said you can look at simply machining down the top of the pistons a little. The top ring is far enough from the crown and the amount coming off so small that's it's safe enough to do so.

I haven't tested this theory though so I can't verify it, but it's something I've been contemplating. I want to go down the centrifugal blower route in the 4bie.

Kitch wrote:AFAIK you need to swap your pistons and possibly cams for DFW ones (catalysed engines).

That or GTI pistons, I seem to re-call Luke writing somewhere that would lower the CR enough to allow forced induction.

Thanks for your help guys,although just machining a "bit" off the pistons isn't a great deal of help to me, seeing as though an XU9J4 MI16 internal combustion engine is a precision engineered Gem I have the technology to de-compress my engine just not 100% sure if I'm wasting my time doing it due to the science behind cenrifugal Superchargers.
I'm pretty sure i know the answer but i'd love to speak to a guy over on the 205Drivers forum,who seems to know a lot about using Rotrex superchargers.Trouble is they're not taking any new members for some reason.anyone know why?

Jezziebx16v wrote: That or GTI pistons, I seem to re-call Luke writing somewhere that would lower the CR enough to allow forced induction.

Wouldn't the valve cutouts be wrong? Or do they lower the crown height enough to not need them?

badlyworntoy wrote:Thanks for your help guys,although just machining a "bit" off the pistons isn't a great deal of help to me, seeing as though an XU9J4 MI16 internal combustion engine is a precision engineered Gem

I can ask the dude for the exact amount if you like? I imagine you would still want to do the math though to make sure you get it how you want it.

I guess whether or not you need to lower the compression depends on the boost you want to run, fuel you want to run it on and whether you intercool it or not. Again that answer isn't really a huge help

If you were going to do that the only way you can do it is too machine a bowl onto the piston crown.However The easiest way round it is to fit a de-compression plate which is 2 head gaskets with a laser cut stainless steel plate in between,has the same affect as fitting low comp pistons.
Imagine a screaming competition normally aspirated Mi16,they hike the comp ratio up to 12:0:1 to get extra performance.So by adding a low boost supercharger you effectivly doing the same thing by adding more commpression into the cylinders.Obviously the sceince behind it is quite complex although the principle is the same.
I know of a couple of people who have done it but its murder getting hold of them................

here you can buy a de-compression plate.
And all the other stuff you need

http://www.dp-engineering.nl/

And the list and prices of all the plates
http://www.dp-engineering.nl/EN/products/decompression/