Cylinders, oil and heat loadings

tadd · 11-03-2006, 04:35 AM

Ok, so I am sorting out the last few pieces of the engine puzzle and I need some advice...

The motor: 2.1 longstroke (80x70.4) using Titanium rods, 2.4L crank, WEVO ultralight flywheel, ported (39/37) and twin plugged 67S heads (42/38) with C6 cams and a GT3 oil pump. The case is a magneisum 3R with turbo squirters and oil bypass mod. Pistons will be 906 for a final CR around 10.7:1.

Questions:
With that ginormous oil pump do I really need nickie type cylinders (charles or henry) or can I just bore a set of 80mm birals to 81? If I have a DLC applied to the underside of the pistons for improved heat transfer and oil a la 935 thru both the cam center and spray bar can I get the heat out that would have gone thru the cylinders? I realize oil is a poor heat transfer fluid, but suzuki did a fine job with the early GSXR series.

If I do add a DLC coating to the pistons it isn't that much more for a few additional items. I was thinking of the head studs. It seems that the boogyman for divlar studs is corrosion leading to breakage. The DLC would take care of corrosion and the divlar is a really nice solution to the expansion problem if I do need totally aluminum cylinders.

Thoughts are appreciated!

tadd

304065 · 11-03-2006, 11:36 AM

Tadd:

It's like wearing white socks with a suit, unless you are the lead singer for a Ska band. Titanium rods with biral jugs and dilavar headstuds?

You would be far better off to go with the enhanced cooling capacity of the aluminum cylinders and use steel rods. Oil is a decent cooling medium but not as good as water.

tadd · 12:00 PM

OMG that was funny.

I guess I should be insulted

?

I've already got the rods, so too late there.

The divlar stud would be for use with aluminum cylinders. That is what they formulated the alloy for, right? They just don't use them cause they break. So if there is a solution to the breaking, is it wrong to use them as they were intended (stud pulling due to expansion differences)? It was my assumption from reading that the ultimate cause of the breakage was from weakening due to corrosion. Is that actually correct?

As for the birals... well, I would rather spend my money on ultralite 906 clone pistons in birals rather than 906 Mahles in custom nickes. Any reduction in reciprotaing (pardon my french) mass is good for more safe rpms in my mind. If I need the heat transfer of nickes then actual assembly gets pushed back a bit more. I was just curious if I needed the 'full solution' as I might not really have the full problem.

I will agree that water has a better heat capacity than oil by a longshot. But consider the crappy interface - hence the temperature drop from using Redlines 'water wetter' which is nothing more than a surfactant and some dye (SDS I would bet) to nuke the surface tension. Oil would wet the underside of the piston with a DLC coating much better, and if you have enough oil to handle the thermal loading thanks to the big pump... Why buy what you don't need?

tadd

Eagledriver · 11-03-2006, 06:12 PM

I would try to keep biral cylinders and steel studs. Your mag case will last much longer that way. If you use all aluminum cylinders then I would indeed use Dilavar (you'll get other opinions on this) studs. The coating is worth a try as far as the studs go. I don't see how a coating on the bottom of the pistons can help keep them cool but it's your money to spend as you see fit (don't think it would do any harm).

I would use a 7R case with that set-up. It's stronger behind the flywheel where these cases like to crack. Better yet would be an aluminum case.

-Andy

tadd · 11-03-2006, 07:27 PM

Eagledriver:
Every joule removed into the oil is one less joule that needs to be disapated from the cylinder/head fins. If I get the heat into the oil from the underside of the piston thanks to the squirters, that is less heat that must be delt with by the cylinders.

Diamond, like graphite is very hydrophillic, so is the oil. Oil will coat out on the coating much better than the raw aluminum. Water on diamond beads, which is one of the quick ways you can tell diamond from cubic zirconia where the water does not. Aluminum typically has a very thin layer of oxide on the surface and is somewhat polar so oil will bead (not interact well) but not so polar that water interacts really well (hence the improvement with a surfactant). Poor interaction between the liquid and the solid interface reduces heat transfer. You really need chemi-absorption to get the best heat transfer. A good wetting surface will promote better heat transfer from the piston to the oil. How much better? That is the question.

As far as I can tell, porsche didn't use squirters with the 906, so they had to go chromal with the cylinders. Who knows if they would have if they had tried oil cooling first.

tadd

cnavarro · 11-04-2006, 07:52 AM

How about nikasil plating a biral, it's been done before :-) Then you get the superior oiling and friction reduction. I would most definately use oil squirters if you use the birals. The question of the century is by the time you do all this work to put coatings here and there, if you have more or less spent that much equal to a set of aluminum cylinders. Either way, you'd be very close and personally I would save up and go all the way on an engine like you've got planned and with the quality of the parts already sourced.

tadd · 03:17 PM

cnavarro:
Yes, I concur that prices would be atleast within 70% of your fine product with the coatings so the cost difference would be minimal. Becides, you make a beautiful product. I keep one on my desk just to touch and marvel at

.

I'm just kind of dog with a bone about this chromal vs biral thing. Clearly, 160hp was the magic number for porsche since they put squirters on the 2.2 - as the S was rated at 180 hp. I've read thru the sports-rally info sheets and there is no mention of adding squirters for 170-180hp engines with the stage II kit. It does mention cylinders for the C6 option, however. Were the 72 2.4 S models nikasil? Those were rated at 190.

Steve@rennsport made an interesting comment over on the early 911 board about the 993 divlar studs having a coating that just works. What was interesting is that he said the 2.0s can use steel studs just fine because they don't make the heat of the larger engines.

So that brings me back to a resuppsition of my earlier question:
Did porsche go to the trouble of chromal cylinders because some clever engineer hadn't thought of using squirters yet? Oil squirters were added in 71 and nikasil in 73 on the 2.7s from the 917 so one could assume that the heat problem was first. I've looked at a some pictures of 906 mag cases and I don't think they came from the factory with squirters. BAs book lists several 71 year racing engines 901(20, 21, and 22) making well over the 906 hp. Were these biral, chromal, or nikasil cylinders?

I guess the bottom line is that the 180-200 hp range (33 per cylinder - which I think I have seen before) is the grey area on what can be done with the heat loading with birals.

Nikasil on steel. Now that is interesting. How thick is the coating? Could you save an undamaged (just out of spec) cylinder that way?

As always, thanks for the input you folks are great!

tadd

cnavarro · 11-05-2006, 05:39 PM

Nikasil on steel. I have done it to bring a cylinder back into spec, since you treat it just like an aluminum cylinder, with a slight overbore then replate and hone to final bore size. More common is where the customer wants performance better than cast iron without the cost of Nickies and head studs to go with the cylinders. Like I said, better oiling and reduced friction.

Good question on what Porsche was using for bores and where squirters where first implemented outside of production vehicles.