16-17:1 on highway

[72Hardtop]

What's been your experience Colin regarding the following:

"all i can say is, you HAVE to understand the difference between LOAD and NO load or LIGHT load.
If your jetting is correct you can and will run 16s and 17s on the freeway at the right throttle and load.
Coupled with an SVDA.
Soon as more load creates the need for more throttle you should see the AFR change with the load.

The 2085 i built that has a thread on here, has been running at 16s and 17s AFR on freeway for 4 years now.
Every part of it is clean as a whistle. runs perfect.
Gets 25 mph pushing a straight axle bus and he drives 80 mph everywhere despite me always saying SLOW DOWN.

We just hopped in it and drove it to kelly park and then all up through yosemite and back to vegas without a hiccup. Tune is spot on. "

From the wideband thread on the samba.

[luftvagon]

It gets easier with a computer.... Yes.. 16:1 or close to 17:1 is possible, and not dangerous at LIGHT LOAD...

Here is my current AFR target:



Current timing in degrees BTDC:



I'll be approaching 16-17 AFR with next drive....

[72Hardtop]

Define 'Light load'

Clearly in a VW bus/Vanagon that not only weighs 2+ tons but has the aerodynamic efficiency a bread-loaf anything above 50mph isn't/shouldn't b defined as a 'Cruising zone'. The 'Cruising zone' in a bus is more likely between perhaps 35-50mph tops. Trying to lean cruise adjust to at anything above 50mph is likely going to end very bad for someone.

The below graph illustrates that:

[luftvagon]

One way to measure load is through the manifold absolute pressure.. that graph means nothing.. At 65mph, I am seeing about 60kPa/100.5kPa with about 40kPa of vacuum or 11.812 inches of mercury.. that's slightly below idle.. That can be considered very light load. These engines are not as brittle as you think...

If you have the technology to do it.. do it.. I am sure they would've done it if they had the technology back in the day, or if it was cheap enough to produce.

[Amskeptic]

Define 'Light load'

Clearly in a VW bus/Vanagon that not only weighs 2+ tons but has the aerodynamic efficiency a bread-loaf anything above 50mph isn't/shouldn't b defined as a 'Cruising zone'.

I see too much thinking and analyzing all across the net, we have these lovely new toys that allow us to peer into the workings. That graph, where did that come from? The load on a Beetle, like everything else in the Universe, goes up quadratically, not linearly.

There is NO conclusion to be made about "anything above 50". For example, Chloe, with a 57 gross/48 net horsepower engine, gets to enjoy as many slight downhills and nice tail winds as anyone else. A Vanagon is totally easier on its engine than the bay bus out on the highway, it has decent aerodynamics. It is over-thinking to declare that a bus is under load all the time above 50. When I am cruising in any car, there is an obvious steady-state homeostatic "cruise" where the engine is hardly puking its guts out.

I don't know how to communicate the simple intuitive true relationship between you and your car out on the road. I can't seem to communicate the spirit of driving a happy little Volkswagen. It gives me a headache to convolute over test numbers that block out the gorgeous and serene reality of another day on Earth. It bleaches the fun out of it. What is the purpose? I am going 20,000 miles this summer come what may, and my engine will be healthy and happy through it all. I keep it tuned, I pay attention, I enjoy the day.
Colin

[72Hardtop]

The chart came from the 'Wideband results' thread here: http://www.thesamba.com/vw/forum/viewto ... &start=820

John (Aircooled.net) stated:

"In a bus any sort of "lean cruise tune" is usually done by 45mph. Guys trying to do a lean tune in a bus at 65mph just isn't going to happen successfully. All cars have the same issues, but webers/dellortos have progression and main circuits, you can and SHOULD tune them differently if you are using vacuum advance. If you have only centrifugal then they are tuned the same. But most guys try to tune both types of engines the same, and this is sometimes a mistake."

End quote.


Agreed, there will be times when the engine isn't working hard under load such as having a tailwind or downhill grade. But compared to a Beetle, Ghia, 914 the load will be higher in a bus on a flat level highway with no headwind. In my videos you can see the vacuum gauge is nearly at atmospheric pressure at 65 MPH which means I'm in the power zone not cruise zone and the AFR should be in the high 12s - low 13's with no vac advance.

At lower speeds and lower loads I can see getting away with a leaner mixture and more timing. Generally with more manifold vacuum at a given speed one could get away with more timing less fuel. But also there are likely areas where it's not a good idea. Such as low RPM's which could/would make the engine unstable.

In a nutshell I'd say no, one isn't in light load "Cruising speed" in a bus at 65mph. Or generally anything over 50+ mph flat level highway.

Or at least that's how I'm seeing it.

[Amskeptic]

In a nutshell I'd say no, one isn't in light load "Cruising speed" in a bus at 65mph. Or generally anything over 50+ mph flat level highway.

Or at least that's how I'm seeing it.

I find maximum power via fuel mixture to be around ~ 12.0:1 under full throttle, and most efficient power at medium throttle to be ~ 13.6:1

[Bleyseng]

Hmmm, that is the Porsche spec for setting the MPS on Djet-12.0:1 at WOT and 13.7:1 at Partload/medium throttle....Works for me.

[luftvagon]

I can't wait for Colin to test drive my van.. i think you are in for a surprise.

[Amskeptic]

I can't wait for Colin to test drive my van.. i think you are in for a surprise.

We are doing 50-60/50-70mph acceleration runs.
If you want to empty out the BobD (so I can dust under the floormats), we can see how a loosened-up factory L-Jet compares . . .