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  #11  
Old 11-02-2004, 01:57 AM
AKWRX AKWRX is offline
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(con't)

After banging my head against this wall for too long now, I have come to the conclusion, "To hell with A/F." The answer is to tune directly from peak cylinder pressure (PCP), just as Top Fuel, NASCAR, Formula 1, and Indy cars do. Those cars generally are not dyno tuned. It is better done on the road/track. Just run the highest PCP the engine internals will comfortably survive, adjust the postiion of the PCP in the power stroke with ignition timing (knock free), and hold EGT within safe levels. The optimum A/F ratio will appear by default. Then, just monitor that A/F for safety purposes to detect any changes in intake air flow, and fuel delivery.

The trick is to figure out an affordable (DIY) cylinder pressure tuning system...
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  #12  
Old 11-02-2004, 02:23 AM
hotrod hotrod is offline
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Default Peak cylinder pressure

I would tend to agree. I think folks are getting so wrapped up with the new technology they are just confusing the issue.

In effect you already have a peak cylinder pressure indicator.
Engine torque is directly related to the MEP in the cylinders. In theory all you need to do, is run a delta dash log and sit down with a calculator and figure out the engine torque at key rpms in a specific gear. Then you use those reference points as a measuring stick. If you make a change and the index for that rpm goes up you did good, if not go back one step and try something else.

If I had the money you could also use the same concept to do the same thing in real time. Put a pressure transducer in the right front motor mount and a second transducer with a free weight on it near by. subtract the vertical enertial signal from the free weight from the signal generated by engine torque loading of the right front motor mount. Poof instant real time engine dyno.

In concept it is trivial, if it would work in the real world is another question. It is essentailly what a chassis dyno does anyway so the hardware should already exist.

As long as you limit yourself to a specific test location and vehicle weight you could also do the same with either the time rate of change of engine rpm, or road speed, or with a G meter.

If your making more torque, (ie higher cylinder pressures) and your gear ratio and vehical weight is known, the rate of change of engine rpm should increase. From the delta dash logs I've seen I think there is fine enough time resolution to make that approach work. This of course assumes no wheel spin so would be best done in 3rd gear or higher.

Larry
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  #13  
Old 11-02-2004, 10:15 PM
AKWRX AKWRX is offline
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Default Re: Peak cylinder pressure

Quote:
Originally Posted by hotrod
In effect you already have a peak cylinder pressure indicator. Engine torque is directly related to the MEP in the cylinders. In theory all you need to do, is run a delta dash log and sit down with a calculator and figure out the engine torque at key rpms in a specific gear. Then you use those reference points as a measuring stick. If you make a change and the index for that rpm goes up you did good, if not go back one step and try something else. Larry
Yes, computing torque and HP from average cylinder pressure (MEP) is a very accurate method to get "at the flywheel" values. Peak cylinder pressure can also be infered. However, a grapical plot of actual PCP vs crank position is what is needed for tuning purposes, especially to adjust timing. There is lots of software available that will do just that, also plot torque, HP, etc. A possible complication is how long (total degrees of crank) that the cylinder pressure is at work. Fuel burn time comes into play. Slower burn, such as with higher octane fuel, and especially when injecting alcohol, will spread out the energy (as much as 100 degrees of crank rotation). As far as computing wheel HP, it is easy enough to do because drive train losses are reasonably constant over a wide range of RPM and load.
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  #14  
Old 11-02-2004, 10:34 PM
AKWRX AKWRX is offline
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Default Re: Peak cylinder pressure

Quote:
Originally Posted by hotrod
If I had the money you could also use the same concept to do the same thing in real time. Put a pressure transducer in the right front motor mount and a second transducer with a free weight on it near by. subtract the vertical enertial signal from the free weight from the signal generated by engine torque loading of the right front motor mount. Poof instant real time engine dyno.

In concept it is trivial, if it would work in the real world is another question. It is essentailly what a chassis dyno does anyway so the hardware should already exist. Larry
That's a novel concept, and a very interesting idea. It might be doable with a horizontal boxer 4 engine. Extraneous vertical accelerations should be absent. Don't know if it would work with a convential straight 4 cylinder engine, since there is a net upward force from the rotating parts. That's why a balance shaft is required to counter-act the extra upward acceleration forces. A transducer system that requires measuring the vertical force component might be fooled.
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  #15  
Old 07-01-2005, 02:14 PM
TurboGTi TurboGTi is offline
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Wow great reading.
Do you guys have any more information on this discussion?
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  #16  
Old 27-02-2006, 08:27 PM
meansrt meansrt is offline
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Default Maybe I'm confused ... but ,

If you are getting det from pulled timing , the straight methanol would naturally help prevent the detonation , due to it's being 117 octane. However you could be getting the detonation from timing pulled due to excessive intake temps. Rule #1 of course , is it's the water that kills detonation , which should allow you to run more timing.
You guys know WAAAAY more than I do , but I would think you are chasing your tail by depending on the methanol to stop the detonation. Why wouldn't you use a higher octane fuel in your gas tank to prevent the timing being pulled , and garner the benefits of a 50/50 water/meth mix which should also lower your intake temps more ?
Sure , straight methanol will make more power due to it's higher octane rating than when you mix it with water , but running high octane gasoline AND using water injection to lower intake temps should make you waaay more power.
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  #17  
Old 27-02-2006, 10:25 PM
JohnA JohnA is offline
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You did notice that this thread started two years ago, right? :smile:
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  #18  
Old 28-02-2006, 02:50 AM
meansrt meansrt is offline
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Default He he he .....

Quote:
Originally Posted by JohnA
You did notice that this thread started two years ago, right? :smile:
Ughh ... Oops :roll:
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  #19  
Old 12-05-2006, 02:48 AM
TurboGTi TurboGTi is offline
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re-kindling an old ppost is always better than starting a new topic about the same thing...

Plus i've been out for a while
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  #20  
Old 03-07-2006, 03:53 PM
sdminus sdminus is offline
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After a few months of running methanol i noticed that my tune was going crazy. AFR's were all over the place. I was also getting huge flames from the tail pipe :lol: .

This is the chain of events.

Tuned for methanol as WI. tune went like this. 9 deg adv at 0.78 Lambda running 38 gph of petrol and 5.5 gph of methanol.
The car seemed really strong in this tune. After every hard run the inlet plenim was so cold. Like it had just been removed from the freezer. I will attach a pic of the plugs.

[/img]

On the way down to a race i decided to have a mild remap due to a change in weather conditions. ( it got colder ) The ignition was breaking up like crazy whilst adding and subtracting fuel. It seemed to have a very fine balance between to rich and too lean. On race day the temp went back up again and the car drove well again.


We decided to add a few degrees to the ign a few weeks later. ( i basically got a EGT for my datalogit )
We found my egts to be very low. about 700 deg C post turbo. I eventually managed to get 17 deg of advance in before the power started to drop off from the tune. egt was in the 750-800 mark.

As well as this we leaned the car out at peak tq to 0.80 L and up to 0.84 after ( anybody that knows rotaries will be violently sick at the thought of going this lean )

So on to race day again. I had a disaster by crunching my LSD changing in to second gear. How eva the datalogs from the run show the car at 0.70 Lambda across boost. A 14 % change in 24 hours... how is this ?

I have now striped down the system as well as the tranny and found the nozzeles to be giving poor atomisation in free air. I have now cleaned them and the spray pattern is much better. I have also found bits sitting in the bottom of the tank. I know of 2 other people running a similar set up using differant Meth suppliers who have had similar problems.

Any ideas. I thought meth would have kept the nozzeles clear if anything.


Scott :?:
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