'69 911E 2.0 Dyno Pull Results

[jluetjen]

I finally got around to putting my car on a dyno to see how it would do. My biggest concern is that given it's configuration, I was kind of guessing as to the settings. Specifically it is a stock '69 911E 2.0 engine with the stock MFI. The only changes are that it has: "S" 9.8:1 pistons per the previous owner, and I added an MSD ignition module. So going in the ignition timing was set to to the factory setting of 30 degrees BTDC at 6000 RPM, and I had set the injection by feel based on it's road performance. I had half a tank of 93 octane from my local un-branded gas station which I usually use.

Here's the initial pull...



Note the rough sound and the smoke out the exhaust pipe at the top of the rev range. That appeared to be a little bit of detonation based on operator's ear and the roughness of the torque and HP lines. Hopefully that wasn't my pistons blowing out the exhaust pipe!

Anyhow, the results showed maximum power of 135 HP at about 6500 RPM, and maximum torque between 5500 and 6000 RPM. So there were basically 3 things to adjust -- the MFI's part-throttle adjustment if we were really out of the park, the MFI idle adjustment and the iginition timing. Based on the operators (Daryl?) input, we backed off the timing from 30 degrees at 6000 RPM To 26 degrees at 6000 RPM and did another run. That took out most of the squiggles from the curves and filled in the holes a bit at 4500 and 5300 RPM and moved the peak HP up to 139 RWHP. I suspect that the holes are a result of using the "S" pistons with E cams. The A/F mixture was pretty steady at about 12:1, which he thought was pretty good for an older car. I suggested that we do one more run and I backed off the idle-mixture by half a turn (leaned it out), which isn't much.



Now it's running a lot cleaner and sounds much better at peak RPM. The last change knocked 3 HP off the peak, but also smoothed out the curves a little more. Since I use my car exclusively on the road, I figure that I'll leave it there and enjoy the car. I can't complain about the estimated estimated 160 crank HP and the flat torque curve, it's better than I was expecting. I'm pretty happy that the tuning was as close as it was when we started, and now I feel a lot better about it when I do give it "the boot". I can always go back and richen it up by the half turn in the future.



One observation - when I plot the BMEP compared to other E cammed engines, you can see where the "S" pistons appear to make the torque curve flatter both above and below the factory peak, but also have a hole at 4500 which is normally the top of the stock engine's torque curve. If I had a mapped ignition system I suspect that I could get rid of that hole, but it's doubtful with the adjustments that I have right now.



So if anyone is wondering what the extra .8 points of CR will get an early 2.0E -- there you go!

[304065]

John, my 901/05 is going on the Dyno this fall, can't wait to compare. That will be supercup 102 with 9,5 compression and stock webers, but same basic geometry.

26 degrees seems like you really backed it out, do you have a plot of EGT as well?

[jluetjen]

Hi 304065 (John?)

No, unfortunately I don't have any exhaust temps. On the drive home I didn't notice the oil temps being any higher than normal. The other thing to keep in mind is the fuel that I'm running. I bet you that if I had filled it up with a tank of Sunoco 93 or added some toluene it might have been a little better and taken a little more timing. But I figured that I'd tune it to the "worst" fuel that the car might see so that it would always be safe. Like I mentioned, I could richen the mixture by half of a turn of the idle richness which would give me a few more ponies, but for my use I don't see any benefit to this.

[Grady Clay]

Guys; John (jluetgen) & John (304065),

You guys PLEASE be careful with your engines.
Backing off the timing to 26º advance is a BIG sign of too low octane for the situation.

I would never do dyno testing on 2.0s without starting with 114± octane race gas.
Once you have done all of the adjustments, only then carefully return to ‘pump’ fuel.
If you see a (downward) performance change, you know there is a fuel/detonation issue that you must adjust for.
These engines are ‘detonation limited’ and a mistake will put a hole in a piston. Very easy to do on a dyno.

I agree that exhaust temps and exhaust gas analysis will also help here – particularly spotting detonation before damage is done.

You will want much colder sparkplugs for full-power dyno runs.

The ‘Rubbermaid Solution’ was devised for dynoing 930 Turbo engines in ’75 and was extended to all other, including track.

I see progress.

Best,
Grady

[jluetjen]

Originally Posted by Grady Clay

Guys; John (jluetgen) & John (304065),

You guys PLEASE be careful with your engines.
Backing off the timing to 26º advance is a BIG sign of too low octane for the situation.

I would never do dyno testing on 2.0s without starting with 114± octane race gas.

Hi Grady. Thanks for the input. I appreciate your caution, but my scenarios were bound a little bit on the downside. By this I mean that I've been driving the car with the current engine (including I assume the S pistons), using 93 octane from this service station (and others) since I bought the car 10 years ago. I did use 94 octane until that went away. I've never taken a head off the engine, and have only opened the engine to fix a leak behind one of the cam sprocket housings. So whatever I did on the dyno couldn't be that much worse than what I've been doing to the engine on entrance ramps for the last 10 years (only up to 65 mph mind you! ). What I wanted to do was...

1) Get a baseline of the engine's performance
2) See if there was anything within the range of the available adjustments that would improve the situation.

I think that I achieved both of those goals. Since I only drive my car on the street, and 93 octane is the best that I can find, I really only have two choices:

1) Rebuild the engine with lower CR pistons
2) Adjust the engine to live with the gas that I have access to.

All along my philosophy for the car is to drive it while fixing it -- emphasis on driving. If the engine blows up -- I'll rebuild it. But since it no longer leaks, runs strong, gets 24 MPH and sounds fine -- I'm going to drive it until an issue arises. My next big investment for the car will be to have the body fixed. I'd rather not detour down the path of an engine rebuild if I don't have to.

By the way -- do you see anything in the dyno graphs that would suggest an issue with the way that the engine is running?

[Grady Clay]

John,

I guess my only dyno observation is the first run may have had the rev-limiter ‘kick in’ or something.
It might also be lifting the throttle with or without the overrun solenoid (micro-switch) operating.
Whatever, it ran out some soot and unburned fuel.


With ‘E’ cams, your torque peak (maximum cylinder pressure) should be at about 4500 rpm.
If detonation occurs, that is where it first becomes apparent.
Perhaps this is the cause of the ‘dip’ in your BMEP graph.

Your BMEP graph is ‘normalized’ but the gain at high rpm may be real and due to the CR but ‘protected’ from detonation by the cams (rapidly falling volumetric flow).

It is such a simple and easy operation to swap fuel from your pump 93 octane to some 114 octane race gas.
If detonation isn’t an issue, there is no change and you just have some nice high octane fresh gas.
I’m not suggesting you regularly use race gas – only as a test to see if detonation is an issue.
Having your maximum timing (6000 rpm) set so low (26º) makes me wonder.

The ‘good news’ is that this inertia-type dyno is relatively low stress on the engine.
Depending on the instrumentation (and operator skill) it may or may not be particularly accurate, precise or repeatable.

Did you inspect the spark plugs after the runs?
Any sign of detonation? (Unlikely due to the short runs.)

I don’t want to get ‘over the top’ here.
I just don’t want you rebuilding the engine when you want to follow John’s (304065) chassis rebuild.

Best,
Grady

[Plecostomus]

My biggest concern would be it grenading, lol.

[jluetjen]

Originally Posted by Grady Clay

John,

I guess my only dyno observation is the first run may have had the rev-limiter ‘kick in’ or something.
It might also be lifting the throttle with or without the overrun solenoid (micro-switch) operating.
Whatever, it ran out some soot and unburned fuel.

The only rev limiter on the car is the MSD's "soft-touch" at 7000 RPM.

Originally Posted by Grady Clay

John,

With ‘E’ cams, your torque peak (maximum cylinder pressure) should be at about 4500 rpm.
If detonation occurs, that is where it first becomes apparent.
Perhaps this is the cause of the ‘dip’ in your BMEP graph.

Agreed. In the original run, the peak torque occurred at 5000 RPM (just). If you look at the factory 2.0E HP graph, you'll see that the peak is graphed at about 4750 RPM, even though the text says 4500. So it's a bit confusing. The wild-card here is the affect of the extra CR on the intake and exhaust tuning. Does the extra CR result in the changing of the phasing to the point of there being a bit of reversion at 4500? This is a bigger deal with carbs because it will spit the fuel back up the stacks as well as not draw as well -- MFI is less sensitive to this issue because the fuel is injected no matter what the pressure in the intake. I've done some models in the past that suggest that the difference between being in-phase (ie: low pressure in the cylinder with the intake valve open, and drawing mixture into the cylinder) and out-of-phase (ie. high-pressure in the cylinder while the intake valve is open, and not drawing mixture into the cylinder, or potentially pushing mixture back into the intakes) can be just a matter of 500 RPM. So the extra CR combined with the E cams may have resulted in the system being out of phase at 4500 RPM, and being in phase at 4000 and 5000 RPM, as opposed to the standard E where everything is in phase at 4500 RPM, resulting in the peak that you normally see. This could explain the difference in the torque curves.

[jluetjen]

Here's the factory HP and torque chart that I referenced earlier. Someone was nice enough to post it the Pelican site a while back. Curiously it doesn't seem to be included in the graphs which are in my shop manual.

[jluetjen]

John and Grady;
What would be the downsides to having the ignition retarded to 26 degrees?
- Elevated EGR's -- so what?
- Lost HP as heat goes out the exhaust? -- I think that this is quantified
- Elevated emissions? -- The car is a '69 -- It doesn't matter.
- ???

[304065]

John (other John here )

Consider the following variables

Duration of combustion event. Varies with mixture and cylinder pressure
Timing of ignition event
Peak pressure point (16 degrees ATDC for best mechanical advantage, varies with rod/stroke ratio)
Rod/stroke ratio and its effect on the "top" half of engine rotation and the "bottom" half.

Ignition timing curve is intended to center the peak pressure point at 16 degrees ATDC. If you have too much advance, you have a smaller combustion chamber at the time of peak pressure. Too little advance and you have a larger combustion chamber, for reduced BMEP.

Delaying the combustion event moves it into a larger combustion chamber with lower average pressure. Of course this steps on the power becuase it moves it later, but I also think it will put more heat into the exhaust. Do you still have nailhead valves 39/35 with a sodium filled exhaust like I do? I would be concerned about overheating the exhaust side. A comparatively longer rod will pump better on the exhaust or "bottom" side of the engine, but your 130mm/66mm =1.97 ratio isn't as good in this department.

[db_cooper]

Just a note from my own experience with fuel octane, ignition timing and the same engine (not Porsche) since 1976. Its a motorcycle..Laverda 1000 that I used to production race thirty years ago..with success. I now use the same engine on the street.

Back in the good old days..using high octane pump fuel (I was fond of the old Sunoco 260)..I ran the timing on the engine at 28*total advance..maybe a little more or less dependent on the weather conditions at the event.

Using the best available pump fuel now...anything above 25* total advance..and the engine needs very flat advance curve now.. or it will induce detonation.

I think the timing specs as written years ago were using a better fuel than we have today. I wish I could find 100+ octane at a pump..rather than the racetrack.

[jluetjen]

db; Didn't I see your picture recently in the news?

[jluetjen]

Originally Posted by 304065

John (other John here )

Consider the following variables

Delaying the combustion event moves it into a larger combustion chamber with lower average pressure. Of course this steps on the power becuase it moves it later, but I also think it will put more heat into the exhaust. Do you still have nailhead valves 39/35 with a sodium filled exhaust like I do? I would be concerned about overheating the exhaust side. A comparatively longer rod will pump better on the exhaust or "bottom" side of the engine, but your 130mm/66mm =1.97 ratio isn't as good in this department.

As far as I know the engine has the original valves, including the exhaust. So I assume that it is sodium filled. So you're suggesting that the extra heat could fatigue the exhaust valve causing a failure? But isn't that what the sodium was supposed to address? I thought that it was to dissipate the heat from the head half of the valve down through the stem?

[304065]

John- of course you have deduced what I was suggesting- that the delayed combustion event will put a lot of heat into the exhaust, backfiring as the burning mixture sets off the oxygen in the muffler, and will give you poor fuel mileage and reduced power.

The exhaust ports are small and the valves are sodium filled to conduct heat away from the valve face up the stem to the guide and into the head and out into the air. 75% of the combustion heat goes through the valve seat, the remaining 25% through the valve.

Making it hotter probably doesn't help from a longevity perspective. I don't know whether you are watching CHT, this is easy enough to do.

I guess my fundamental issue is this: with an otherwise healthy motor you should be able to operate on 93 octane pump gas with reasonable timing and still have a detonation margin. If that is not possible, I would look for the root cause somewhere and try to address that, rather than compromising power with reduced timing (and the side effects noted above)

[db_cooper]

Originally Posted by jluetjen

db; Didn't I see your picture recently in the news?

Not me.....

[jluetjen]

Originally Posted by 304065

I guess my fundamental issue is this: with an otherwise healthy motor you should be able to operate on 93 octane pump gas with reasonable timing and still have a detonation margin. If that is not possible, I would look for the root cause somewhere and try to address that, rather than compromising power with reduced timing (and the side effects noted above)

Agreed. But to be honest, in retrospect the 2.0 heads were not an optimal design. I suspect that they were somewhat modeled after the the 804 motor -- which hindsight has shown to have suffered from too large of a valve angle. As a result the combustion chamber in the head is too large, which forces the pistons to have large domes to fill the combustion chamber. The result is that with the piston near TDC, the combustion chamber is very spread-out -- leaving lots of nooks and crannies for detonation to start. This design was improved starting with the 1970 motors.

To put it differently, a high-CR 2.0 engine is compromised from the start on street fuel. Grady alluded to the same thing. But that is what I've got. Back in the day (ie. the 70's) putting S pistons into an E was considered a hot upgrade (especially for autocrossing), and from a purely power perspective it does seem to be the case. Is it perfect? No. Is it workable -- it seems to have been, at least as long as I've had the car (not to mention the miles put on it by the previous owner after he rebuilt the motor).

Now when you say "pump gas... and reasonable timing". What do you mean by "reasonable" timing. Porsche spec'd 30 degrees -- for a motor with E cams and E pistons, or S cams and S pistons. That's not my motor. I've got an E motor with S pistons -- which means that right off the bat the static CR will jump by .5 to .8 points(?). As I mentioned earlier, if you look at the static CR based on when the valve closes -- E's and S's have essentially the same CR. This is one reason why they can get away with the same ignition timing. But when I combine S pistons with E cams, you'll have a situation where pressures inside the chamber are significantly higher than either an E or an S. There is just no way that you can expect to get away using the same ignition timing as an E or an S assuming the same fuel in each case. It's just not going to happen.

My understanding is that when engineers define the ignition timing for race engines on a dyno, they start with a very conservative setting. They keep bumping it up and rechecking the results until they no longer gain HP. At that point they stop adding ignition timing. Apparently there is a plateau where you can add a little more timing, but no HP is gained until the onset of detonation when the HP will drop. On the flip side, if you lose HP when you retard the ignition, then you're getting into a bad zone where the heat and power are going out the exhaust (and toasting the valves) and heating the cylinder walls -- which drives up the engine temperatures.

I'm not seeing any of those symptoms in my case. The torque curve didn't drop, and I made two 45 minutes drives today on the highway, and the engine temperatures were right at 180 degrees both ways -- which is what I was seeing previously. The only thing that I'm missing is the EG temps as you pointed out, but 2/3 of the indicators do not suggest any problems.

I agree that retarding the ignition from it's ideal setting on a stock engine is not a good thing -- and you will risk the issues described above. But I don't have a stock engine. Keeping the ignition timing at 30 degrees in my high CR engine is a mistake. If it runs better and is a happy engine* at 26 degrees -- let's let it be a happy engine rather than try to tell it what it should be happy with.

* Note, a spread-out compression chamber is bad for emissions, which is why most cars today have compact penta-roof combustion chambers (Thank-you Keith Duckworth!). So chances are my engine's emissions are worse than a standard E's or S's when it comes to unburnt hydrocarbons. But since it is a '69, it doesn't need to pass any emissions tests. Since it's not tested, we don't know how dirty it is, and I'm not going to ask!

[jluetjen]

Ahhhh! Here's the table that I was referring to. I suspect that I have a copy of this spreadsheet around myself, but you can see what I'm referring to. All of the engines from humblest T up to a 906 have a static-dynamic CR of about 7.5:1. The total spread from highest (E) to lowest (906) is only 6%.



Bingo! Here's the spreadsheet tool courtesy of Kenek!

Using the same spreadsheet, my engines static-dynamic CR is 8.3:1 -- significantly higher than the standard E's 7.72:1. That is why I need the extra 4 degrees of ignition retard.

[304065]

I hear you. You mean Dynamic CR is same between E and S given the intake closing timing. I haven't done the Dynamic CR calculation to see if the intake timing makes up for 0.7 points of compression.

[jluetjen]

Sorry John, was making updates when you posted. I calculated my situation and the ratio is .6 points higher than a stock E's.