Piston cooling

[Mark911]

I’m tying to figure out had to add full time piston squirters to my block. In theory, it looks pretty easy. Just drill a small galley from the main bearing webs directly into the main bearings oil supply groove, just like a Porsche. The two end webs would handle the front and rear cylinders while the center two webs would need to service two cylinders each. This works out fairly well as the front and rear webs feed the OHV and V-Tech already so the center webs can afford an extra cylinder each.
Specialized oem spring loaded check ball squirters can be used from many different model cars and threaded into the new galley to direct the oil under each piston crown.
Anyone experimented with something like this?

 

[swerve2007]

how did you determine a need for additional skirt cooling? wouldn't added oil pressure draw/drop possibly mess with v-tec and top-end lubrication? need for bigger oil pump? just curious.

 

[titaniumdave]

Mark,
Isn't there already an oil hole on the rod squirting on the bottom of the piston skirt?

 

[ScienceofSpeed]

There are oiling holes in the factory rods that feed from the crankshaft already that are designed to lubricate the pin. It does not produce a spray pattern like factory jets on other cars though as I believe the factory intended them for lubrication, not cooling. If you are going to increase oil flow into free space, it's probably a good idea to modify the oil pump to bleed off less pressure through the bypass valve.

Cheers,
-- Chris

 

[Mark911]

Chris is correct, the small passage in each rod doesn't do very much cooling. The oil only ejects once a revolution when the crank and rod holes align and due to the spinning is deposited over a wide area. Anyway, it's a far cry from the dedicated systems used on many new HP OEM NA cars and most circuit race engines, including F1.
As you can see, it's an easy mod to tap into the main's oil circuits. Most spring loaded valves don't allow flow until a given pressure is reached (more or less based on RPM). I would hope that the stock (in my case Comptech) pump has enough capacity to maintain pressure even with this additional demand. A ceramic coating on top of the pistons is another option but in my opinion I'd rather have the pistons absorbe more heat out of the charge during compression so I can run higher CR or higher boost.
I'm looking at my CAD model for a way to provide a dedicated circuit fed by an external pump, that way I don't need to worry about pressure loss due to the stock pump.

 

[titaniumdave]

Nice concept Mark.

The stock or Comptech pump usually is by-passing oil volume and pressure at about 6,000RPM so you should have plenty of capacity. I can see the by-pass valve open on my mechanical gauge from the seat pressure being released. I was wondering about using the the by-pass oil flow to run through an oil cooler so there is no main pressure drop for oil delivery, plus the cooler will only be operating when the car is running high RPM. Presumably when it is really needed. This is the way our MR2 is set up from the factory.

Any thoughts?

 

[Mark911]

Dave. Yea, if you can tap into the bypass and get enough flow to make it worthwhile why not! Unless there's some restriction downstream or some major flow you could probably go with a low pressure cooler as well.

 

[Mac Attack]

With my engine build, I was doing a lot of reading and thinking about this too. Especially since my B-series rebuild book talked about squirters :biggrin:

But, I've come to the conclusion I'm not going to modify the block for this. Even for pressure-dependent squirters and then increasing the oil pump bypass spring rate to compensate. The reason being, without some trial and error in oil squirter location, flow area and pattern, and actual data (besides piston temp to measure effectiveness you'd want oil pressure data at the head at constant engine RPM's before/after is my best guess), I wouldn't want to be the guinea pig for something like this. Sure, the stock oil pump bypass relief spring rate could be increased to compensate, but if you don't know the oil squirter flow rate and knowledge of the oil pump head/flow and RPM curve, it could be a costly mistake. There is a lot of iteration required for a spray pattern that is effective yet doesn't unnecessarily increase windage losses, as well as bypass oil needed for other areas of the engine.

As mentioned, the OEM rod has a hole that will squirt oil when aligned with the crank once per revolution. What's odd is that this hole is the same location for every rod, which means it alternates spraying at the intake side of the piston, or the discharge side of the piston - depending what bank it's placed in.

It would be cool to align this hole on the intake portion for each piston. This would correspond with OEM and aftermarket piston squish zone design, as well as keep heat in the exhaust area for a better burn.

Another thing is our OEM rods have two slots milled on each big-end side of the rods, again to help direct discharged bearing oil to cool and lubricate the piston underside and walls. The B-series rods are like this, and Cosworth rods are like this too. OEM B-series rods don't have the oil hole though, but the VTEC blocks have real oil squirters. Maybe Honda wanted to reduce windage losses at high RPMs and free up a few ponies for their halo engine at the time? OEM NSX rods with oil passage locations:

So, instead I tried to optimize what I could. I have the standard SOS-spec Wiseco 10.2:1 CR pistons with the 2618 alloy. To reduce piston temperature fluctuations (and maybe run a slightly tighter piston-to-wall clearance than what Wiseco recommended with this hypoeutectic alloy), I did the following:
* Ceramic coated the piston heads
* Coated the skirts with dry film lubricant
* Polished the underside of the pistons such that the oil is shed and dispersed easier. Some put oil-shedding coatings on the piston undersides and even on the rods....

All of these options should help control piston temperatures.


The other thing is that the new Wisecos have eight oil ring holes per piston compared to the OEM's ten, but I estimate the Wisecos have over twice the total flow area then OEMs, and the oil inlets are even chamfered :smile: So, hopefully, the oil that does make it to the piston underside with the OEM arrangement will make it's way quicker to the oil rings!

OEM:

Three of the eight Wisecos (before piston radiusing and polishing):

Bottom line is that I can't afford to mess with my engine's oiling system given the stock oil pump capacity, but this would still be a neat mod to do if you had a robust oil system like a dry sump arrangement (ahem) :wink:

My $0.02.

Dave