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Not Using A Decompression Plate


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#1 stevemkeen

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Posted 13 July 2019 - 06:09 PM

Hi all,

 

Sorry if this has been covered before, I am going to rebuild my supercharged 1000 cc engine that currently uses a decompression plate and 2 gasket and instead I would prefer to not use the decompression plate and instead lower the compression ratio either using dished pistons or could I consider using the exiting flat topped pistons and machine the the required amount of material to achieve the require lower compression ratio, the supercharger kit I've used to date was from Jonspeed, which as worked ok, but I'm rebuilding the engine to stop the oil leaks.

 

So can anyone tel if this as been done before ?

 

What if any are the issues if I machine material off each piston, I would prefer this method as it wold be much cheaper for me., how much material can safely be taken off the piston.

 

The head I'm using is a standard unleaded 1000cc head

 

Any advice would be vey much appreciated 

 



#2 mini13

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Posted 13 July 2019 - 06:34 PM

Don't just chop a lump off the piston, machine a dish in, you can take the crown thickness down to about 4mm in the middle and leave a band round the outside for squish, also you can enlarge the chamber.

#3 mini13

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Posted 13 July 2019 - 07:08 PM

Don't just chop a lump off the piston, machine a dish in, you can take the crown thickness down to about 4mm in the middle and leave a band round the outside for squish, also you can enlarge the chamber.

#4 stevemkeen

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Posted 13 July 2019 - 08:11 PM

Thanks for reply, does it have to be dished or can it be a square cut with a platform around the piston, could i achieve the required lowered decompression by just machining the pistons, if so anyone have the 

depth and dimension of the cut needed on a flat top piston or do I need to loose metal by enlarging the chamber also.



#5 Turbo Phil

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Posted 13 July 2019 - 10:00 PM

How much volume do you need ? I’m guessing quite a bit if you need to compensate for the removal of two gaskets and the plate.
Taking some material from the chambers would bring benefits not just in lowering the compression, but by deshrouding the valves. Even on standard size valves the chambers cause a massive restriction to airflow, larger valves make the situation even worse.

Phil.

#6 mini13

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Posted 13 July 2019 - 11:09 PM

The dish can be flat bottomed in the piston, as long as you leave a radios in the corner, say 8mm ish

#7 DeadSquare

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Posted 14 July 2019 - 07:10 AM

"radios in the corner, say 8mm ish

 

Tune into short wave "Radio 8", in the corner of your workshop, it's all about tuning a Mini.



#8 mini13

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Posted 14 July 2019 - 07:50 AM

Lol! Radius!

#9 stevemkeen

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Posted 14 July 2019 - 07:22 PM

Again thanks so much for all your responses , can you explain by what you meant by "tune into short wave "radius 8" in the corner of your workshop? where is this info ??



#10 mini13

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Posted 14 July 2019 - 08:23 PM

Basically no sharp corners, somthing approaching this would be good.

https://images.app.g...t97SKJ8wTHgozi9

Edited by mini13, 14 July 2019 - 08:24 PM.





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