cylinder pressure vs power

[efini13]

I recently had a discussion with an engine tuner about cylinder pressure, and what he said has me pulling my hair out. He claims, and I belive him, that the engine power can be dramatically increased without increasing cylinder pressure just by tuning. He actually tunes racing engines by physically measuring the peak cylinder pressure. I have asked many experienced engine builders and tuners about this and they can not give me an answer that doesn't require modifications to the engine. I have read many tech articles on the subject and found nothing. The only thing I can think of is increasing the average cylinder pressure without going over the peak limit. I know reducing pumping losses and stuff would do the trick, but he does it without getting out of the car using a laptop and speedpro(or any engine managment system). He has spark plugs that have a small hole in it that is channeled through a tube into the pressure gauge. Any way does anybody know how this can be done? Am I on the right track? Or am I completely off? Thanks in advance for any input.
Ben

 

[Flowczar]

Ben,

I know of one way to do this, although the method you described sounds much more simple than this next path. Since the pressure will approach approximately 2500 psi for such a small increment of time, or degrees of crankshaft rotation, I'm unclear how a mechanical pressure guage would give an accurate reading. In cylinder pressure measurement is normally accomplished using a piezo-electric pressure transducer, usually mounted in the block to avoid "noise" during valve closing events. There are some special spark plugs for this, but the data I have seen usually includes the spikes seen by the sensor when the valve arrives at the seat. There was a technical paper presented at the AETC Conference (circa 1988/90) on the very subject by Dr. Paul Puzinouscous (spelling), who went on to the Engine Lab at UC Denver. I should still have a copy of this, and could share it if I'm not overrun. As far as equipment, Superflow has a system to do this and I'm sure many of the successful race shops are using it to maximize their engines.

Happy Wrenching!

 

[efini13]

I beleive he mentioned something about the peizo electric sensor. The device is not mechanical, but it reads all of the cylinders individually. Thanks for the reply, any help would be greatly appreciated.
Ben

 

[Retracnic]

Efini13,

Your tuner friend is correct, engine output can be effected without increasing peak cylinder pressure. This is because it's not just a matter of how much pressure you make, but it's when that pressure occurs. Typically, as a tuner, you're trying to achieve peak cylinder pressure around 14-20 degrees ATDC. The exact crank angle is determined by the engine geometry and the timing of the various valve events.

Once you've determined the exact point when you want peak pressure, it’s a matter of tweaking spark and fuel curves to realize that goal. As far as seeing 'dramatic' power increases go… that would depend on how you defined dramatic.

Bryan Carter

 

[efini13]

That makes sense. Thanks for the input.
Ben

 

[ecclestone]

The sensors you describe are available from Kinsler Instruments, I read an article in Circle Track where Robert Yates used this technology which ,then,was obviously fairly "trick". I recall the HP gain by correcting peak cylinder pressures from cylinder to cylinder was 7HP.How you manage to do it ,on a carburettored engine as opposed to one that you have freedom to alter the fuel mapping/injector timing and duration I cant think at the moment. Comments ???

 

[efini13]

7hp isn't the kind of gain I was talking about. But the engines I work on spin 12000 rpm with alot of boost.

 

[Retracnic]

Efini13

The power gains that can be obtained from fuel/ignition tuning are based largely on how far the engine is from the ideal. To give you a real world example, I recently tuned the ignition and fuel curves on a turbocharged Honda engine. The engine in question was a B20/B16 hybrid with all the usual goodies. The tuning had been done by another shop, and though the owner was satisfied with the power output, he was less than happy with the streetability of the vehicle.

After an afternoon on the dyno, the following results were seen:

-Peak boost pressure dropped from 21 PSI to 18.5 PSI
-Peak boost pressure occurred 600 RPM earlier
-Initial onset of boost occurred 400 RPM earlier
-8% reduction in peak cylinder pressure
-Reduction in EGT (exhaust gas temperature)
-Peak HP increased 43 HP (from 371 at 8100 to 414 at 8100)
-Peak TQ increased by 12ft/lb with a 900 RPM range increase in useable TQ.
-Dramatically improved transient throttle response and drivability.


The driver was pleased and said it felt like a completely different car. All this was achieved without turning a single wrench. Laptops and programmable engine management are good friends of mine.

So it is possible to see big gains with a little tuning. But had the engine been tuned correctly before being brought to me, I most likely would not have seen such big gains (if any).

Good Luck

Bryan Carter

 

[massage]

HI,
can anyone give me a hint where I can find such a measurement unit, because I´m looking quite a long time for such a box which can measure the peak pressure of the cylinders.

Thanks in advance,
Ed

 

[Retracnic]

Massage,

Cylinder pressure indicators are available from many companies. I am personally only familiar with the products available from Optrand, NGK, and TFX Engine Technology.

You should be able to purchase one of these units from a local source that sells engine analysis equipment (such as dynos and gas analyzers). Or visit their repective websites for a dealer in your area.

Bryan Carter