Piston Squirters
 

Hi

I've been meaning to ask this question for a while now, Piston squirters were installed in the 7R case and are considered mandatory for Nikasil Cylinders, Is this for additional bore lubrication or piston cooling? Because to me it doesn't make sense that an aluminium P & C combination (Nikasil) requires cooler pistons than Iron/Aluminium P & C (Biral) Can anyone authoritively answer this?

Thanks
Neven

Neven,

From the way I understand it, the only way Porsche was able to increase the 2.4L to a 2.7L was to have a smaller cylinder cooling fins to compoensate for the larger piston. The only way to dump the additional heat with the smaller cooling fins was to go to Alum which has much better heat disipation than iron.

The piston squirters were added back aroun 1970 with the 2.4L to take care of the heat that engine produced over the 2.2L. I assume that the change to the nikasil figured that the squirters were already there and were part of the cooling required to handle the additional heat from the bigger p/c.

Don't know how authoritive that is, but I hope it was worth the stab.

I'm no expert but john is exactly right, as pistons got bigger, cooling fins got smaller. Pistons squirter cooling provides lots of cooling where it's impossible to cool any other way, the back side of the piston. Second with cooler pistons, the expansion of the piston inside the bore is less, therefore the pistons to cylinder clearances can be much smaller.

The change in tempreture is dramatic, I think it's somewhere north of 50-75c.

Guys

Yes I understand all this, about cooling the piston, 2.4 came out in 72 with squirters, I was more wondering why they are considered mandatory if you are doing a 2.4 -> 2.7 upgrade with Nikasils, Is it the material or simply the bore change (84mm to 90mm). Because in theory Nikasils could run hotter. or is it that they also require more bore lubrication than nodular cast iron

Neven

Actually Nikasil has a higher lubricity (and lower coefficient of friction) than cast iron. The oil squirters were more for cooling of the piston and not lubrication of the cylinder.

Charles Navarro
LN Engineering
http://www.LNengineering.com
Aircooled Precision Performance

Charles

Thanks for that so what is the reason for piston squirters being so critical when installing 2.7 nikasils? Is it that cooling the piston has some effect on the cylinder temp?

Neven

I couldn't find the best way to explain this, so I got this off google:

"The purpose of the oil squirters is to cool the aluminum pistons. There are two reasons for this. First of all, the strength of aluminum decreases rather quickly as the temperature is elevated. With the emphasis on decreasing the mass of pistons (a reciprocating part) the amount of material is reduced to the absolute minimum, so the margin on strength is not large. Any further decrease in strength due to heating should be avoided to maintain the mechanical integrity of the piston. There is also evidence that cooling the pistons can reduce the likelihood of pre-ignition (and possibly detonation). This can be caused by hot spots (on sharp edges of the piston-top) lighting-off the mixture before the spark plug fires. Rounding off any sharp edges on the machined piston-top can also help prevent this."

http://e30m3performance.com/installs/installs-3/squirters/index.htm for the entire article on oil squirters.

This kind of touches back on the discussion of mahle vs. je pistons and the p/c clearances between both brands of pistons. Since the mahle has a higher silicon content and lower coefficient of expansion, it can be run with tighter clearances. The compromise that has to be made for this reduction in expansion is a loss of strength at higher temperatures. The 2618 forging from JE has a lower content of silicon and higher rate of expansion (so higher p/c clearances), but is stronger at higher temperatures and less prone to loss of integrity under these conditions. Just an observation that explains why the oil squirters are so very important and worth the effort.

Charles Navarro
LN Engineering
http://www.LNengineering.com
Aircooled Precision Performance

Just to clarify....
The piston oil squirters were introduced on the 1971 2.2L (the 1970 2.2L didn't have them)

Regards,
Andrew M

Nikasil = closer clearances = need for tighter tolerance control = need to maintain cooler temps and decrease expansion. Hence the piston squirters...

-Wayne

“Nikasil = closer clearances = need for tighter tolerance control = need to maintain cooler temps and decrease expansion. Hence the piston squirters...” and the 1.82:1 engine cooling fan ratio and a good front cooler.

Best,
Grady