Here it is, my R4 :)

[23e Heure]

Hi Nik. 3 years later... I wonder how your project worked out. Any updates?

 

[Sandor]

The pistons are also different between the atmo and turbo, it looks you have turbo pistons.

At mecaparts http://www.mecaparts.com/Moteurs/page.php?lang=0&sortie=html&col=R5&page=1#ok you can order the correct parts needed for the specific type of engine

Left: R1223 (R5 Alpine atmo) Right: R122B (R5 Alpine turbo):

When you use the turbo pistons on an atmo you create a lower compression ratio so performance drops, because a turbo or compressor provides the extra power and higher compression ratio.
On the other hand don't use atmo pistons on a turbo to create a surplus compression ratio, good chance that pistons, push rods and more cracks as it ain't made of the wright materials and it isn't designed for mixing wrong parts!

My advice is to rebuild your engine as it was originally designed for, so everything works well.
Either you build an R1223 engine or you build a R122B engine.

Hello JdeW and Nikswe / everyone.



I am glad to join this forum, although I have been visiting these pages for many years for technical help and ideas.

However, now I have a specific question, partially explained by JdeW and Nikswe previously.
I Have R5 alpine turbo engine 840-C-7-26 2nd model quite in a good and clean condition, except the pistons what I going to replace.

Can I equip it with atmo pistons? Do you have any experience ? I will place it into my R4 and I never ever will fit turbo for that.



I know from previous chats;

- Head ; Height: 79.30mm / Chamber volume: 43cm3 / Joint thickness: 1.9mm parameters are the same atmo / 840-C turbo

- Linears are the same

- JdeW; On the other hand don't use atmo pistons on a turbo to create a surplus compression ratio, good chance that pistons, push rods and more cracks as it ain't made of the wright materials and it isn't designed for mixing wrong parts! – do you mean in case you keep the turbo? This would be logical…

- here you see the dimensions I found at Der Franzose; the atmo piston goes 0,5 mm higher then the Turbo piston. ( most probably the circle edge) Can the atmo piston collide with the valves? cylinder head?


Thnaks for support !

 

[Sandor]

 

[Sandor]

correctly; 1,5+0,5 mm

 

[angel]

Yes the Turbo engine can be fitted with atmo pistons, but Turbo head is 0,5mm higher (79,8mm) and combustion chamber volume is bigger (45,3cc) so you will end up with slightly lower compresson ratio than factory 10:1. You can always skim cylinder head by 0,5mm, though.
Also camshafts are different, atmo one has noticeably less duration (244 versus 282 degrees).

 

[Sandor]

Angel, I appreciate your quick feedback !Thanks ! Good news, most probably I will go for atmo pistons and the whole set with liners, smaller compression is not a problem. I also estimated that atmo might fit. I also estimated that atmo might fit.

 

[Sandor]

I keep the original camshaft, anyway I haven't even found an atmo
camshaft on the market