compression ratios

[steer from the rear]

Right here's the question if a renault 1.6 k4m engine has a 80.5 mm stroke x 79.5 bore and the compression ratio was 9.8:1 and you fitted renault 1.4 k4j engine crank and pistons which are 70.0mm stroke and 79.5 bore what would u expect that 10mm in stoke to do to the compression ratio? Bearing in mind I think a c1j engine is 8.0:1 I think

Just a ruff estimate saves me buying two engines and measuring it all lol any one know if a gtturbo box fits these k series engines also?

[Scoff]

Orignal engine must have 45.408cc's in its combustion chambers in order to get to 9.8:1. Add another 10mm's of space (49 and a bit cc's) and your down to 4.7:1 !

[michael tierney]

u could run 4 bar boost with that if it would start!!;)

[steer from the rear]

Off boost would be a nice drive :disagree:
Well there goes that idea next one I once turned down some f7r pistons and ran it at 10 p.s.I quite happy for 1000 miles till it blew up lesson there was don't use a fast chip for turboing :agree: any way what about turning the crowns down on the piston? I know it makes them weaker but surely a properly mapped engine shouldn't get a failure like that? I just need to get the compression down some how? Do piston manufactures do one offs (or 4 lol)????

[Scoff]

CNC cut a spacer plate and use 2 gaskets. Beware of effects on cam timing if its OHC.

Or, cut pistons down like you say, but check that there's enough meat on the deck, you don't want them 2mm thick :D

[Adey aka Ewok]

how much boost do you want to run, thats nice and low to start with

[steer from the rear]

i had a go measuring the squish ratio on the f7r engine with syringe but really got lost with the cc's so how can i really say " this much material removed from my piston crown will give me about x compression ratio?

[Scoff]

I forgot to account for the smaller capacity in the first reply so actually you'd be down at 4.7:1 with the 1.4 crank.

Here goes:

Original engine is 80.5 x 79.5, so thats 399.594cc's per pot, 1598.37cc total.

If the engine has 9.8:1 then you can work out the volume of the combustion chamber with:

Swept vol
------------
CR-1

So:

399.594
----------
8.8

=45.4 cc's. (that includes the volume of the gasket too)

With PIxR2 you can work out that 1mm of piston height is worth 4.96cc's. So if you cut 1mm off the piston then you'd have the original 45.4cc plus the extra 4.96cc = 50.3cc.

New CR with 1mm cut off:

399.594 + 50.3
-------------------
50.3

= 8.9:1

That lot asumes your pistons are flat top to begin with. If they have a shape to them then you'll need to take that into account. If it's only valve cut-outs then it won't make a lot of difference. Dished or raised crowns need some more thinking about :)

[steer from the rear]

sounds like i need to get one of these engines off ebay and take it to bits, just hope a gt gear box fits the block.
If 1mm of material removal removed from the piston (all being well) drops it to 8.9:1 im sure adding another head gasket would it to a gt turbo sort of CR and then its happy day 1.4 16v turbo.

just got to find me a 1.4 clio now.........just sold a 2002 clio sport for 1300 today :(