Dyno results!!

[shadrach74]

Originally Posted by manolo

They're not likely getting a good exhaust sample on the dyno at lower RPM's. The car wouldn't actually run if it was at 18:1. The probe is probably too short and getting reversion at lower RPM's. They could put the dyno O2 sensor directly in the exhaust if you have a spare bung in the headers or bypass tubes.

Are you guessing or have you seen data to support this? 18:1 is not really that lean in terms of efficiency ratios. I run a large displacement flat four with a fuel and ignition system far less sophisticated than those in our Porsches at efficiency ratios approaching that level. Some of the new direct injection engines run at 60:1 or more under certain conditions.

[Squiden]

Is there a stock Boxster S run on this same dyno to compare? I've seen too much variation between different dynos to hold too much faith in the power gains (though I hope they are real!)

[Topless]

Originally Posted by shadrach74

Are you guessing or have you seen data to support this? 18:1 is not really that lean in terms of efficiency ratios. I run a large displacement flat four with a fuel and ignition system far less sophisticated than those in our Porsches at efficiency ratios approaching that level. Some of the new direct injection engines run at 60:1 or more under certain conditions.

Ummm, not if it's running gasoline. 18:1 is way to lean to be safe for full power applications and would not be making good hp numbers. I suspect the exhaust sensor was fouled. Ultra lean burn on direct injection motors is useful at idle or cruising down hill, not making max power on a dyno.
http://en.wikipedia.org/wiki/Gasoline_direct_injection

[jaykay]

Hmmm well you learn something everyday.....I had thought anything approaching 16 was way too lean. Perhaps I am over "conditioned from blowing up 2 cycle motor cycle engines

[shadrach74]

Originally Posted by Topless

Ummm, not if it's running gasoline. 18:1 is way to lean to be safe for full power applications and would not be making good hp numbers. I suspect the exhaust sensor was fouled. Ultra lean burn on direct injection motors is useful at idle or cruising down hill, not making max power on a dyno.
Gasoline direct injection - Wikipedia, the free encyclopedia

I never said that his number was accurate. What I said is that it's unlikely that his engine would not run at an AFR of 18:1. If it was a carbed engine then yes (because of the uneven fuel distribution that is typical of carbed engines) 18:1 would be difficult to attain without rough running or missing.

And yes, I do much leaner than stoichiometric (14.7:1) all the time when running a 360CI, magneto timed (fixed @25BTDC) air-cooled flat 4 with the throttle wide open. Can you guess the application?

What do you think happens to the combustion event as the mixture goes lean of Stoic? Given that Stoic is the theoretical perfect mix of O2 to fuel. Is having having more O2 some how more combustible? The fastest burn of the most fuel happens just a tad rich of stoic as does the highest internal cylinder pressure thereby giving the lowest detonation margins (not good). At full throttle, this is not where you want the mixture to be. You want to be richer or leaner, but since we are limited by atmospheric pressure with N/A engines and turbine inlet temp with turbocharged engines, it's far easier and practical just to puke gas through it to slow (relatively speaking) the combustion event and cool the exhaust gasses thereby increasing detonation margins.

BTW the whole reason behind direct injection is to improve fuel distribution to allow very lean mixtures. In theory this will eliminate the need for a throttle body and the suction losses associated with partial throttle operation. Imagine sucking through a straw with partially cocked butterfly valve; that's what your engine is doing whenever it's not at full throttle. With lean burn engines, the engine management system will just reduce fuel flow, the mixture will get leaner and the engine will produce less power, no suction loss from choking off the intake. Another benefit is little to no unburned hydrocarbons, meaning we may have catless road going cars in our future.

I could go on, but I'm digressing! So to come back to the original point, an injected otto cycle engine should run still run at an efficiency ratio of 18:1, whether or not it will grenade in the process depends on throttle position, timing and compression ratio. The ratio in and of itself is not a death sentence... 14.7 to one is actually a hotter, higher pressure place to run

[Topless]

Originally Posted by shadrach74

I never said that his number accurate. What I said is that it's unlikely that his engine would not run at an AFR of 18:1.
With an 11:1 compression ratio and pump gas, an m96 motor will ping like a big dog at 18:1 A/F ratio under full load on a dyno. Narrow tuning window. It may run.... for a little while.

And yes, I do much leaner than stoichiometric (14.7:1) all the time when running a 360CI, magneto timed (fixed @25BTDC) air-cooled flat 4 with the throttle wide open. Can you guess the application?

Sounds like a Lycoming 0-360 variant. A fine aircraft engine with a very wide tuning window. With an 8.5:1 compression ratio and avgas it will probably purr like a kitten at 18:1 A/F ratio. It won't be making max power though. My father was an aerospace engineer and certified aircraft mechanic. We rebuilt a few of these in our garage when I was a kid. I am guessing you still prefer to do your sea level takeoffs at full rich.

[shadrach74]

Originally Posted by Topless

Sounds like a Lycoming 0-360 variant. A fine aircraft engine with a very wide tuning window. With an 8.5:1 compression ratio and avgas it will probably purr like a kitten at 18:1 A/F ratio. It won't be making max power though. My father was an aerospace engineer and certified aircraft mechanic. We rebuilt a few of these in our garage when I was a kid. I am guessing you still prefer to do your sea level takeoffs at full rich.

IO 360-A1A (8.7CR) to be exact, Most carbed 360s don't like lean ops. I've experimented with full throttle "lean of stoic" take offs and had no issues, performance takes a bit of a hit obviously, but it runs quite cool that way. I prefer full rich take offs because the work load is lighter... but again I digress, this is for another forum!!!

Incidentally the big Turbo'd Continentals will run 90% power all day long when lean of stoic running 34 to 35 inches of manifold pressure.