911 aircooled developments

[PeteKz]

Although we call the se engines "air cooled," the majority of heat gets removed by the oil and cooler. I know that many of you know that too, but I'm reminding the others that these engines need more oil flow than just enough to keep the bearings from wiping out. Perhaps a split oil system would accomplish both lubrication and cooling with reduced drag by having a high pressure/low volume circuit for lubrication, and a low pressure/high volume circuit for the oil squirters and cam housings?

[Henry Schmidt]

I hesitate to venture into these waters but here goes.

Originally Posted by PeteKz

Although we call the se engines "air cooled," the majority of heat gets removed by the oil and cooler. I know that many of you know that too, but I'm reminding the others that these engines need more oil flow than just enough to keep the bearings from wiping out. Perhaps a split oil system would accomplish both lubrication and cooling with reduced drag by having a high pressure/low volume circuit for lubrication, and a low pressure/high volume circuit for the oil squirters and cam housings?

Accurate but simplistic.
Cooling the air-cooled engine is a combination of air and oil to be sure but "more oil" is hardly the cure. Cooling the heads is the issue and the fins on the cylinders provide the cooling necessary for these engine to survive.
Cam tower spray bars supply oil to lubricate the valve train and some oil cooling but in the late eights, Porsche decided that too much oil was detrimental.
In the early 964 engine development they concentrated on control fan speeds to increase air flow over the cylinders and reduced the oil to the cam towers.
To compensate for the reduced flow to the cam towers they massively increased the piston squinters volume.
The synergy of thermal dynamics, pulling the heat out of specific areas to allow for increases in horsepower output. Limitations in head cooling is why building a high horse power air-cooled engine is limited.
By running an over sized oil pump [one that produces a greater volume than necessary] you end up sending hot oil back into the oil pump through the oil by-pass system.
Balance always seems a better strategy the "more".

[Neil Harvey]

My reasoning for more Oil pump is not for more supply volume but more scavenging volume. These engines like more scavenging and more crank case "vacuum".

We can only achieve negative pressure with a sealed crankcase. With the open breather on these engines, just lowering the case case pressure helps.

As some pump pressure sections are larger than others, the difference in supply volume is not huge but it is different.

Like a lot of the stuff we do, its a modification to a stock engine so there are always limitations. With the mods like we are trying here, every time we do, its never known if it will work. But you have to keep trying or you will never know.

If we could gain some torque lost in turning the pump with less resistance, and not have any other detrimental effects, I'll take it. What could be gained here along with less Valve spring pressures, less friction etc, all could add up to some real gains. Lowering the friction will lower the temps too.

These engines that make low torque numbers and only rev to approx.6800 RPM, will always benefit from some gains.

As Del Boy says in my favorite UK TV comedy, "he who dares wins".

[PeteKz]

Henry, let's dispose of the straw man argument and stipulate that simply more oil does not necessarily equal more cooling. Done.

That said, I can point to examples of other engines that rely greatly on oil for cooling internal parts and heads, in particular, several motorcycle engines. Obviously, more oil CAN be used for increased cooling, if it flows to the right places. What are those places in the Porsche engine?

[Henry Schmidt]

Originally Posted by PeteKz

Henry, let's dispose of the straw man argument and stipulate that simply more oil does not necessarily equal more cooling. Done.
.......

"straw man" suggests an argument. I am offering facts not debating arbitrary theory. If that bothers you, I apologize.

[ChrisHamilton]

Originally Posted by PeteKz

Henry, let's dispose of the straw man argument and stipulate that simply more oil does not necessarily equal more cooling. Done.

That said, I can point to examples of other engines that rely greatly on oil for cooling internal parts and heads, in particular, several motorcycle engines. Obviously, more oil CAN be used for increased cooling, if it flows to the right places. What are those places in the Porsche engine?

It sounds like Henry described it fairly well in his post. The top of the piston gets the most heat removed by oil, and the cylinder itself relies on the fins and airflow over them. Only way you could increase the cooling effect of oil on an air cooled head would be if there were internal passages in the head near the chamber to help absorb heat. Mr Schmidt would be eminently more qualified to speak on that but air cooled Porsche heads have never had that feature if I'm not mistaken. I know that heads like that exist though with off road stuff, some BMW motorcycles as well. But that's a moot point.

Just me but when a guy with Mr. Schmidt's knowledge and experience speaks I listen. Pete in no way am I chastising you BTW. Just speaking for myself.

[PeteKz]

Okay, I'll take the chastising.

Let me start over: If you had extra oil flow to use for cooling, where would you direct it?

[Neil Harvey]

All of this is good info for many who may be interested.

Just to steer this back to my original post, we are not changing the pump or the flow potential here. Only looking at controlling the pressure where its needed and where its not.

If we can gain some Torque here along with what we have already gained with lowering Valve Spring pressures, coatings etc, we will have proven this can be done and hopefully help these smaller displacement engines make a little more performance.

This has all come about for Project 24. This little 2V NA engine will need all the help it can get to make the performance figures we are hopeful of producing. This is requiring us to look at everything. High RPM engine demand special attention and parts. Its fun back dating some of the development and parts we have for the later water engines. The requirements become the same and the results if not addressed are the same as well.

A lot of new parts are been developed for this engine. Crank, Rods, Pistons, Cylinders, Heads, Camshafts, Valve train parts etc.

Probably our biggest hill to climb. If it works great, if it doesn't we may learn something we can use in the future on other projects.

[Old H2S]

My question for the Motor Gods is ..
If the savaging is important to maintain good ring seal, and the CIS engines had various venting back to the intake manifold to increase internal vacuum as shown by removing the oil cap and having the rpm change as an indicator of a closed system how to duplicate that in with Weber carbs?
Just running a hose to the closest manifold is going to make one dirty, fouled cylinder and pull way to much oil from the restrictor hose.
Is there a level you are trying to achieve or is this an unknown and some is good but more can be problematic.

[PeteKz]

On CIS, the breather goes to the intake boot. There is very little suction in the intake boot (where the stock breather hose routes to) because it's upstream of the throttle body. On some models, the breather hose goes into the air cleaner housing, which has virtually no vacuum. Engine intake manifold vacuum occurs downstream of the throttle body or carbs.

Removing the oil cap allows false (unmetered) air into the intake boot, not the manifold. This leans the mixture, which results in the rougher running and slight increase in RPM when the oil cap is off.

If you wanted to install a real PCV valve with CIS, you would want to put it into the vacuum side of the airbox so that its fumes get more or less evenly distributed to all the cylinders. FYI, one way to stop or reduce engine oil leaks is to draw a vacuum in the case.

For carbs, I would try to gang together the vacuum ports from both carbs, then to a PCV valve, then to the breather nipple on the top front of the case. Or install vacuum nipples on the intake manifolds and go from there.

[Old H2S]

Pete, the breather nipple on the TOD is way to oily to use directly. The long hose tapers uphill to the oil cap allowing time and distance to drain back oil into the case. At RPM the oil is impressive at the TOD from internal pressure. The top hose going to the top of the "peanut" has the brass restrictor in it. When the hose is attached to manifold vacuum both hoses collapse. So a good designed PVC system would be variable not worrying about recycling dirty vapor but getting the right ring seal on light tension ring packs common now.
Maybe going from the TOD to a catch can to a PCV valve that is adjustable to both sides?
Having adjustable bleed off of the PCV might affect the brake master vacuum?
As we have all experienced any TINY air leak in a CIS system will drive you nuts, and a leak on manifold nipples 3 & 6 with carbs for PCV might be problematic?
It was so much easier when we just ran a hose from the case to the exhaust collector and made some more smoke..

[stownsen914]

I’m not very familiar with CIS vent routing, but the case should vent to the oil tank, and oil tank should vent to atmosphere. You should really only get vapor from the tank vent if the engine is healthy and oil level is correct.

For a carb conversion, I believe I’ve seen people vent to the carb air cleaner, but id probably vent to a catch can. Make sure the catch can has a vent, like one of those little filter thingees, this is important.

As for a PCV valve, there’s no harm, but I’m not sure why it would be necessary either. PCV valves keep flow from going back to the engine from the vent, which shouldn’t really happen due to the positive pressure from the engine case.

[Neil Harvey]

Back with info more about engine parts.

We have 2 special projects underway, Project 24 and another that is even smaller. Both use the Magnesium 7R case. I did speak to a Customer who has purchased a new Mag case but it has issues.
I have not seen one yet but one is on its way to use to inspect. I wanted to know the differences between the cases. The engines overall weight plays a huge part in the total weight and the cars performance. Anything we can do to lower component weights we are doing.

I finally got around to weighing all of the cases and one of the new 992 Engine blocks.

Magnesium 7R case 38 lbs

3.2L 911 Aluminum 54.5 lbs

964/993 Aluminum 56.75 lbs

992.1 GT3 79.25 lbs ** This block has its Cylinders integral so the added weight
must be considered.

[Bill Verburg]

Porsche has a breather that increases cc vacuum
996.107.491.91

first used on 996 GT3RSR
RMS also needs to be replaced w/a reinforced RSR version, apparently the fms is fine as is

worth ~5hp for a street car

and increases oil leaks

[LukasM]

Originally Posted by Neil Harvey

Back with info more about engine parts.

We have 2 special projects underway, Project 24 and another that is even smaller. Both use the Magnesium 7R case. I did speak to a Customer who has purchased a new Mag case but it has issues.
I have not seen one yet but one is on its way to use to inspect. I wanted to know the differences between the cases. The engines overall weight plays a huge part in the total weight and the cars performance. Anything we can do to lower component weights we are doing.

I finally got around to weighing all of the cases and one of the new 992 Engine blocks.

Magnesium 7R case 38 lbs

3.2L 911 Aluminum 54.5 lbs

964/993 Aluminum 56.75 lbs

992.1 GT3 79.25 lbs ** This block has its Cylinders integral so the added weight
must be considered.

Good data Neil, that really is quite a big difference! The magnesium valve covers are good for another 3 lbs by the way, compared to the ribbed early aluminum covers, and about 1.5 lbs vs. 964 covers. 915 mag case saves about 15 lbs as well. Titanium bolts instead of the steel studs is another pound.

It all adds up for a car where it really matters!

Project Heavy Metal - an all steel classic, remastered

Originally Posted by Bill Verburg

Porsche has a breather that increases cc vacuum
996.107.491.91

first used on 996 GT3RSR
RMS also needs to be replaced w/a reinforced RSR version, apparently the fms is fine as is

worth ~5hp for a street car

and increases oil leaks

Interesting Bill, we used a similar check valve from Thumper Racing on our big bore single cylinder dirt bikes (500-600cc piston moves a lot of air when compared to the tiny crankcase) after seeing it in Moto GP, however never measured on the dyno if it actually makes a difference on the power.

Why is that with the leaks though? I would have thought that crankcase vacuum helps with those compared to crankcase pressure? Or is it because the sealant will have "conformed" somewhat to outward pressure, and is now being sucked in instead?


Cheers,
Lukas

[Neil Harvey]

Yes, weight savings is an often over looked performance adder.

[winders]

Originally Posted by Neil Harvey

Yes, weight savings is an often over looked performance adder.

Pretty much EVERYONE you might ask says one of the best ways to improve the performance of a car is to reduce its weight. Removing weight is well known to be one of the cheapest ways to improve a car’s performance so it gets a lot of attention.

I would go as far to say that “weight savings” is a rarely overlooked way to improve car performance.

People’s effectiveness at achieving the goal of less weight is another discussion…

[JoeMag]

Regarding the check valve... Think you'll need need to get a better oil pump than gt3. I tried on my latest race build and at WOT no vacuum. Partial throttle a bit, but that doesn't matter. Even had the Cup RMS and without constant vacuum, that thing leaks. ...Maybe Auto Verdi pump would do the trick.

Have others achieve vacuum?

[Neil Harvey]

Just to update here, Project 24 is moving along. Lots of new parts and changes to make this all happen. Still all theory at this point as the first engine has yet to be assembled. It all could turn pear shaped. Hope not. Lots and lots of my $$ invested in this one.

Seems there is a lot more interest in these earlier engines than I suspected. We have been focusing on these large + 4.0L 964/993 engines and forgot about customers who spend huge $$ restoring the earlier cars.

If this does work, we have many customers anxiously waiting on the results. If it doesn't, it won't be the first time I have tried something that failed.

[PeteKz]

Neil, thanks for the update. Still watching this thread.

IN addition to weighing the different cases that you listed above, have you or anyone else weighed the cranks? Is the 70.4mm crank in the 2.4/2.7 engine the same as the 3.0 engine? Or were those cranks beefed up too? Does 74.4mm/3.2 crank weigh more? I'm pretty sure the 3.6 crank does.