I've been working with Megasquirt with timing and Fueling. The car has been responding well to the changes.

I had to take a trip to the foothills today and decided to take the 914 and really test the changes. Most of the driving I had been doing had been around town so I wasn't sure how the car would respond to a long freeway trip.

while cruising up hwy 5 the cht's were 340.....I pulled up Tuner studios and leaned out the area around cruise a bit. Suprisingly the CHT's dropped about 5 * and were stable.

I kept the setting there and was wondering how this would be when I started climbing hills, again I was suprised how good the head temps were. nothing over 370(which was for a very short time) on the long climbs.

I don't have my 02 sensor connected yet so I can't say what the AFR is.

At the end of the trip, I drove 176miles and it took 4.5 gallons to refill....39.1mpg......NICE!!!

Nice!

YIKES!! Really risky to change timing or fueling without AFR's....detonation lurks there....especially when leaning it out!!!

No risk at all , I have a Dakota digital CHT gauge. If any ill affect of leaning the AFR were to happen I'd know instantly.

The timing at 26-2700rpm (cruise speed) was 25-26*BTDC,( I think I can go more) well within stock timing range. With MS you can alter how fast the timing comes in, which, I'm finding makes a big difference. You can also alter areas of cruise, which makes a big difference. The only detonation(pinging) that I noticed was at the upper rpm's while having my foot in the gas. Again more tuning needed in that area.

Surprisingly, as I leaned out the cruise areas the cht's got COOLER.

Seems counter intuitive, I have an idea why this is but can't say for sure.

It would be a great question for Jake.

From my combustion chemistry, max combustion tempeerature occurs at stoiciometric A/F, that is wheere exactly the correct amount of oxyger surrounds the fuel molecules , no more/ no less. Either richer or leaner from that and tempeeratures drop, so looks like you're now running a bit lean.
Our modern direct injection gas engines run that way lots of the time, that's how imporved fuel economy figures are emerging.
here's a graph:

http://en.wikipedia.org/wiki/File:Flametemp.jpg


Barefoot

Sweet!!!! When you get your wideband hooked up, post your timing and AFR targets.

So you may be the guy to ask...

Mt theory is, With enough timing and a leaner mixture at cruise, you are not making a hotter exhaust gas which in turn will make for a cooler discharge.

Am I close?

I definitely will. I'm curios also.

My comments are only on mixture strength. Timing may have it's own unwanted temperature consequences.
Sorry not enough theory to go on here.

Where's Jake???

I remember him mentioning a while back that it's possible to lean these engines out more than people think.

There is tons of info in the aviation world about running air-cooled flat fours - Lycoming IO 360 - in the lean of peak ranges (LOP) for EGT.

Google LOP Lycoming IO 360 or go to the Van airforce webpage and you will find volumes.

The bottom line is that EGT's around 30 - 100 F LOP will reduce CHT's with a small reduction in peak power. Detonation is an issue and monitoring CHT is a pretty indirect way to see it.

It works but be careful.

Detonation??

Are you and wndsfr referring to engine failure???

If so, This is not the case here. I think that I "may" be in the area of 15:1 AFR, if that.

My 02 sensor should be done this w/e. I'm going to leave the settings where they are and check it.

From what I recall Jake saying a few years back was, 15:1 is more than doable with these engines.

Your timing was likely the reason you didn't have any issues with detonation. May not want to advance it more until you can monitor AFR.

The reason CHT goes down running LOP is that the internal combustion pressure drop significantly. ICP is highest near peak EGT.

Again do some research in the aviation world. They run engines in labs and measure all parameters, including ICP The situation is not exactly comparable because airplane engines sit a drone away for hours at a constant speed and load. An auto engine is more critical since throttle settings constantly move, but the theory is the same

A short period of intense detonation can ruin your whole day

Also known as knocking, pinging, or spark-knock. Uncontrolled combustion in the combustion chamber; it leads to hot spots and can make the piston push down against the crank at the wrong time. A lot of detonation can melt holes in pistons, heads, or valves.

--DD

Did some reading on the subject and there seems to be some differences of opinions about ROP and LOP. I agree that LOP can create issues BUT I don't think I was even close to being LOP and in the dangerous range.

If I was in danger of being too lean I think I would have noticed lean surging. This was not the case.

Thanks for all the info. when I get the 02 sensor up and running I will post the AFR's.

I'll always remember one of our Thermo lab experiments:
We had a variable compression spark ignition test engine (you could adjust the combustion chamber volume by cranking down the cylinder head onto the cylinder.)
It had a pressure transducer feeding signals to an oscilloscope to watch combustion pressure.
Normal pressure wave is a smooth curve with ignition, but as compression was increased to the point of detonation you could watch very rapid pressure spikes of at least double normal combustion pressure. Neat stuff !
Sorry i can't find a neat graph to show.
Barefoot

This was my first thought....pinging...also known as PRE detonation.

I had none of that going on

What size tires are you running to calculate you MPG?

205/65/16....4% over driven.

With previous calcs. with the same tires I was getting 30ish mpg

hmmm....every pro tuner I know (and we're talking guys that run pro teams, local shops, and big time engine builders) says to keep AFR below 13. I burned up many a piston running near 15 (I still have them).

We just tuned our engine in Papa Smurf. Kept AFR around 12.6-12.8.

This is what happens when you get detonation due to lean AFR...

Click to view attachment

Tuning the entire load range at 13:1 would result in pretty poor overall gas mileage for a street car which spends 80% of its time at low loads. Race motors are a different animal because you're usually at WOT.

My experience has been that generally it's pretty hard to knock at partial load. Different animal, but I've run bike motors at up to 18:1 AFRs (part load) and not had knocking problems. Running WOT is a different story, though generally when you're that lean I don't think you have terribly extreme problems either. I believe this is because the mixture just doesn't burn easily enough to pre-ignite. Going super lean is a really effective means of torque control and is safely used on tons of production cars (especially direct-injected) rather than just pulling timing since it's more effective and less wasteful of fuel.

In any case, the real place where you have problem is WOT with AFR's around stoich and a hot engine because the mixture so readily burns. The plot below has some pressure traces of normal combustion to knock.

At WOT you really need lower AFR's if you are tuning timing for maximum brake torque. I believe AFR~ 13.5:1 is generally best for max power and 16-16.5:1 is generally best for max brake specific fuel consumption; both internal geometry dependent.

When running really lean pulling timing isn't a bad way of preserving motors. With conservative timing I wouldn't be surprised if you could run loaded at 15+:1.

Click to view attachment

Also, Google maps calculated the miles at 85 one way. My total miles driven were 176. Pretty darn close

nevermind, went back a page...

Nasty looking!

What mileage does a 1-7 get with
Stock d.jet

High 30' s. I'm guessing

34 was the best that I heard of.

Nice graph! that's kinda how i remember our thermo lab stuff.
i worked with the Bendix folks in the early days of US electronic FI, driving a test car with a dash control of A/F mixture, as the mixture was leaned out it took more and more throttle to keep up steady low load speed, cause power production was falling off rapidly with leaned out mixture.

I can't recall, but I got near 40 but never made the goal.
Never leaned it out, just changed tires, drove differently etc.
There is an old thread from maybe 8 years ago about it.....we all tried different things.
If you can safely get over 40 , I would love to hear all the details of the setup.
Multi spark ignition may help a bit.

"Did some reading on the subject and there seems to be some differences of opinions about ROP and LOP. I agree that LOP can create issues BUT I don't think I was even close to being LOP and in the dangerous range.

If I was in danger of being too lean I think I would have noticed lean surging. This was not the case."

What indicates to me that you are LOP is that when you went leaner CHT's went down. If you were ROP, leaning would cause CHT's to go up.

Running LOP is a good thing at partial throttle, cruise conditions moderate timing, short of knock. It will bite you at high power outputs.

All sounds like you are OK, just be careful.

Slight hi-jack...

Papa's got some pretty impressive slugs.

I think 40 is doable with MS. There are areas I can adjust to make it run a bit better. I don't have my fuel cut set so on decel its still injects fuel.

Also, the CHT temp sensor is jumpy and when the temps get low it jumps into WU enrichment. This injects a touch more fuel off and on.

I was in the throttle hard in some areas and climbing hills.

With flat roads I think 40 would have definetly happened.

That's outstanding. I go thru 4-5 gallons in 20 minutes...not sure what MPG that is...

Joe Sharp had Linda's 1.7 running over 40mpg with duel 34ict carbs when we went the Portland WCR.

Stock 1.7 will get mid 30's on the freeway. So 39 is not too far out for a more efficient metering system. However, if you truely want to tune it you need EGT. CHT is good as a trend, but EGT tells you whats happening at that moment. If you want to get every last MPG you would need a probe for each cylinder. Take the temp to peak and back it down about 50-75 degrees for each cylinder. If you could do that, you would reach the limits of the MPG, also run a higher octane, as it with be less prone to detonation.

I get mid to high 30's with my '71 - 1.7 on the highway without trying. It's all stock FI and tires are 195x65x15 on 2.0 fuchs. Gotta love these cars.

(I'm using gps to calculate the mpg but this tire size is within 2mph at 60)

This is intriguing. Since the FI is not individually adjustable I could not adjust each cylinder.

I could monitor cyl.#3 and adjust accordingly.

My 75 is a stock d-jet, and in about 1200 miles going up to Octeenerfest and back last year i had a whole trip average of just under 35mph. that included the driving in the mountains; / My a/f meter on the highway was reading about 13.7-14.2, .
my speedometer is right on and odometer reads right at 1 mile according to milage markers on the highway.

I now have a different MPS, car has been re-timed and tuned, it is running much better and cooler now so it will be interesting to see what my new numbers will be. I think they will be better wbut we will see. .
- oh, also my transmission is not stock. i changed gear ratios of #4 and #5 so my RPMs run about 750 less at freeway speed than a stock motor. .

What gears are you running in the 4th and 5th position?

I effectively did the same thing with my tires. got 4%overdrive with 205/65/16's

I have a project I'm thinking of that I may want to change the gear ratio's.

i think what we put in was an HA flipped, and X - did it at Dr. Evil's clinic at Scottyb's 2 years ago. i think it ends up making 4th like 4.3 and 5th like a 5.5.

Now i can tell you that i live in the flat land. If i were in the mountains like driving the tail of the dragon i would prefer the stock gearing on those hills there were times when i was wishing the 4th gear was lower, closer to stock.

just checked my milage from driving the 914 the past 5 days. ended up being 230 miles, 36.4 mpg. most of that was 55-65 highway but some 35-45 in town.
also, with the regearing of the transmission, at 65mph im at 2500 rpm in 5th, and its really hard to stay there since the car really likes to cruise between 70-75 which is that sweet spot of 3000- 3200 rpm (speed limit is 60 so i have to be careful)

41 MPG today!!!!

I thought 39 was a fluke but I confirmed it today( and a bit better)

When I first posted I had 205/65/16's. This gives about 4.3% overdrive. The rpm's at approx. 65-70mph were about 2750.

I've since changed the tires to 205/60/16's. this gives a 1.1% OD. I did not have my computer hooked to MS for this drive but, I've calculated approx 100ish rpm's more at the same speed.

Today's drive was flat as opposed to the first drive which was a bit in the hills.

Head temps were running in the area of 335- 340 at 65-70mph.

I'm hoping to connect the AFR gauge tomorrow and I will post the readings.

37.87MPG today!

I did the same drive as in the first post, 178miles. This time I had the 02 sensor hooked up. At 65-70 AFR's are 14.5-14.7 timing advance at 2900rpm was 25-26*

Heads temps were cool at 315-325 with a spike to 360 climbing a hill.

There is still work I can do, so far the last three times I cahecked, 36-37, 39, and 41mpg, pretty consistant

It is amazing what these old school engines with a little tuning!