Can anyone tell me how much VanAaken were taking off the top of the pistons when doing a high boost kit to a cinq engine? I heard somewhere that it was 2mm but that sounds too much.

Cheers Rich.

to quote VAD when i asked them"a couple of mm"

It's 2mm from the top of the pistons only the piston is uhmmm dish.

so the thickness in the middle is allmost the same.

You also need to grind some of material out of the combustionchambers.

Volume of 1 cilinder + volume combustionchamber (also gasket and dishvolume of the piston / (divide) volume combustionchamber.

That the Compression ratio and novitec is about 8.8:1 fot 0.5 bar (0.6 is also possible)


My old 1.1 pistons


At the left a custom one and at the right a punto 1.2 8V piston.
The custom still has a dish shape only the pistonpin is placed a little higher which causes a lower CR.


And some of engine restore fabriques (don't know the right word) can fix it.

Ok thanks. Im only asking because I have struck a deal with a local engineering company to machine the pistons(hence I needed to know how much material to remove)at a good price. I am doing a 1242cc mpi high boost kit at the moment and when I have it running and tested I am going to start doing more of them(next will be a 16v engine I have in a cinq already if I dont sell it soon).

Rich.

You're best not just machining pistons down by a depth, but rather measure the compression ration and machine to required ratio.

Most VAD hi-boost conversions are about 8.6:1 compression ratio, standard car is 9.6:1, tho when I measured mine it was 8.2:1 so a bit lower and after removing a piston you could actually see the differance in crown thickness compared to a piston out of Emma's turbo Cinq.

You have to remember that if your head has been skimmed the compresion ratio will be higher again to start with, so may need to take that into account.

The pistons that Emma's car as now are dished so should be much better than the flat VAD ones as they are Mahle pistons and notably had a thicker crown and what look like a stronger construction than the Fiat piston did to begin with, hense why it was possible to machine a dish in them.

Aaron.

Hi

Thanks for the info. I investigated having a set made but it was going to be too expensive plus I have too many car needing to be finished to splash out all that on one of them(Dont do more than 1 at a time I hear you say! I didnt intend to it just happened).

Rich.

One thing to bear in mind is that its rumoured that the 1242 pistons dont have enough metal to them to support that kinda skim. Even then, there might be issues with temperature and thicknesses of metal - easy piston melting!!

arseofbox said:

One thing to bear in mind is that its rumoured that the 1242 pistons dont have enough metal to them to support that kinda skim. Even then, there might be issues with temperature and thicknesses of metal - easy piston melting!!

Click to expand...

Yeah think you are right Tom, I remember thinking about a hi-boost 1242 and I came to conclusion after getting info from someone who works for Mahle that for a 1242 you would need custom pistons made for the job.

PS Rich the Mahle pistons are not custom that Emma has but there OEM spec piston (although the larger to accomodate a small overbore to ensure true, think her car is now about 1130cc) that happens to be superior to the Fiat one when you compare them side by side.

When you say they're OEM, do you mean they came off some other car? If so, which make?

Christ, this is an old thread. Made by Mahle, but as a replacement, so to speak. Dunno if there are any still in existence.

But Martin's car is still running (ex Emma, on the Mahle pistons), mine ate a piston (ex Aaron, on FIAT pistons).

There are alternatives to machining the pistons, including a decompression plate, forged pistons, machining the cylinder head to make the combustion chamber larger.