Compression and cooling

neilca · 02-09-2004, 05:31 AM

What is the highest compression people use without running into cooling problems on the six cylinder? Consider I am going to run a 2.0 (80mm bore x 66 mm stroke). I will be running piston squirters (the smaller ones) and a front mounted oil cooler.

Additionally, I have been thinking that I could use a 5 blade fan because if the higher RPM's (4500-8000) I will be using under racing conditions.
This car will NEVER see the street it is only a race car. Any thoughts on this?

Thanks,
neilca

304065 · 02-09-2004, 06:59 AM

Hmm, you plan to rev to 8000 RPM, I would recommend dual front fender-mounted coolers and -12AN or larger lines. I have such a setup in my "E" (which used to be an "S") it does a great job cooling. With a 2.0 liter displacement you need all the power you can get, the engine will make best power between 180F and about 220F oil temp.

Grady Clay · 02-09-2004, 07:31 AM

neilca,

John is correct, the engine needs 180-210 and must use the oil thermostats (engine and oil system). There is a safety oil relief valve that was used on 911RSRs that is worthwhile and can prevent burst coolers at starts or in long yellow-flag situations in cool/cold weather.
To get power out of your 2.0 you are going to need to get as high compression ratio that you can, 11:1 and more. While the oil likes the 180-210 temp, the heads absolutely need to be as cool as possible. That is a limiting factor with an air cooled engine. Unless you are ice racing in the Arctic, do not use the 5-blade fan. In hot weather you can rev the fan ratio up a bit to get more air cooling. In cold weather, block off some of the air to the coolers so they actually run hot to the touch (say 120). The oil will flow properly. Do you have a cooler at the engine or the oil filter assembly?
What series & class are you racing?

Best,
Grady

neilca · 02-09-2004, 08:14 AM

I am not going to use the stock oil cooler but put an oil filter in its place. This is going into a 914 chassis and will be vintage raced with the HSR. I believe the class is 3L.
neilca

bpick84 · 02-09-2004, 12:46 PM

You are correct on the class. 2 liter 6s and 4s are both 3L in HSR. When will the car be ready? Sebring is just a few weeks away.

neilca · 02-09-2004, 12:55 PM

The car won't be done for about 2 more years. Work and family keep getting in the way of real progress. I already have 3 years invested and the chassis is still on the routesserie. I just recently decided to change from a 4 cylinder to the 6 so some of my previous work is for naught. Additionally, I have to educate myself on this new engine. I must say Wayne's book has been a great help.
neilca

Vintage911Racer · 02-09-2004, 03:29 PM

I suggest you keep as many coolers going as possible. Even the engine mounted cooler. I have pretty mcuh the same set up. 2.0L 11:5 - 1 compression, to fender mounted 930 Oil coolers, engin cooler, later engine shroud with ducting to engine cooler, 11 blade fan and aftermarket oil tank. All my cooler ducted to allow maximun air flow through them.
On hot days I still see, 220 and on cool days I do have to block the cooler off. but my point is. Go for the best cooling. You can always block them off.

neilca · 02-10-2004, 09:54 AM

You guys have talked me into keeping the stock cooler. Now how am I going to get a filter in the system. Do you think it is a good idea to put the filter on the scavenge side before the front cooler?

Thanks,
neil

304065 · 11:51 AM

Neil,

For guidance you should check out the factory oil system diagram. Basically, the scavenge pump picks up the oil from the sump, sends it forward through the cooler, then back through the oil filter and into the tank. So the factory put the filter AFTER the front cooler and before the oil tank.

So if you blow the engine, you have to replace the lines and coolers. Some have had success having them ultrasonically cleaned, but they are much cheaper than a new engine.

What I have seen a lot of guys do is put an Oberg mesh-type filter in line with the -16 hose for the coolers. This helps with filtration and also radiates some heat, although it's typically mounted inside the trunk.

If you are using a front oil tank, I would put the filter ahead of the tank, so you don't end up getting sludge/contaminiation buildup in the bottom of the tank, that would get pulled aft into the pressure stage.

There is an EXCELLENT diagram on the Smart Racing products web site, in the installation instructions for their front oil tank.