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Downsized charged engines, peak cylinder pressures?
5

Downsized charged engines, peak cylinder pressures?

Downsized charged engines, peak cylinder pressures?

(OP)
Hi guys,

Just wondering what typical peak cylinder pressures are for these new breeds of downsized turbocharged gasoline engines we're beginning to see ?

Cheers,

Harley

RE: Downsized charged engines, peak cylinder pressures?

If I were to hazard a guess, the peak would not be that much higher than previous designs.

Average pressure though... much much higher.

RE: Downsized charged engines, peak cylinder pressures?

I agree with k86...gassers are still limited by knock

RE: Downsized charged engines, peak cylinder pressures?

If you read the auto engineering rags, you'll see things like 30bar BMEP. I did read today from one powertrain design team about engine architectures capable of 140bar peak pressure. But these are all development, not production engines.

- Steve

RE: Downsized charged engines, peak cylinder pressures?

I've heard peak combustion pressure numbers similar to what SomptingGuy notes for current SI turbo engines. Knock is obviously an issue, but one other problem that pops up once peak combustion pressures go higher than around 2000psi is the combined thermal/mechanical stress causing fatigue failures with aluminum head materials. As the section thickness of the deck and chamber walls is increased to deal with higher pressure loads, it becomes difficult to adequately cool isolated chamber surfaces such as the narrow bridges between valve seats and the spark plug port.

RE: Downsized charged engines, peak cylinder pressures?

Interesting design space. Aluminum,by virtue of its high conductivity, permits higher compression ratios or otherwise more aggressive combustion recipies, from a knock margin point of view. And then the other edge of the sword is aluminum's lower fatigue performance, relative to ferrous material. Sounds like fun, for those fortunate to be playing in that sandbox.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

RE: Downsized charged engines, peak cylinder pressures?

Interesting article & seems to have good knowledge base. The only part where I raised my eyebrows a bit was the following:

Quote (EPI)

It is worthwhile to note that a contemporary, normally-aspirated CI (compression-ignition) engine can easily make 15 bar of BMEP.

  1. Who these days is developing a high performance non-turbocharged diesel engine?
  2. Are we talking about a smokey exhaust or what? I've visualizing an exhaust plume that a squid would be proud of.
Does anyone know of a case in point?

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

RE: Downsized charged engines, peak cylinder pressures?

Komodo86, when you say average pressure is "much, much higher", do you have an example?

RE: Downsized charged engines, peak cylinder pressures?

"Komodo86, when you say average pressure is "much, much higher", do you have an example?"

The fuel is always going to the limiting factor to peak pressures. With turbocharging however, it is not about peak pressure.

Here's a modelled Otto cycle for comparison for two engines.



The green trace is a NASP engine of 11:1 compression, with 45° ignition advance.

The blue trace is the same engine boosted to 1 bar. Ignition timing reduced to 16° so that the peak cylinder pressure remains the same as the NASP model.

The difference is quite clear. The boosted engine maintains a significant advantage in pressure throughout the power stroke, despite have no gain in peak pressure.

In reality, a boosted engine may be able to handle a small gain in peak as well, but the majority of the gain comes from average pressure.

RE: Downsized charged engines, peak cylinder pressures?

^ Sorry, read off the wrong details there. The boosted engine is seeing 0.5 bar and ignition timing is 28.5°.

RE: Downsized charged engines, peak cylinder pressures?

Komodo86, I assumed we were comparing turbocharged engines. With NA vs boosted, the BMEP of the boosted engine will definitely be higher, perhaps much higher while the peak pressure could be the same or even lower if the intake temperature is higher (the compressed charge autoignites at the about same temperature NA or boosted). The same or lower peak pressure would be from a reduced CR in the boosted engine.

RE: Downsized charged engines, peak cylinder pressures?

The other key thing to note in Komodo's diagram is the heat release for the turbocharged case is delayed relative to the normally aspirated case. Generally speaking, this would be due to a combination of reduced compression ratio and spark advance, compared with the NA engine.
The delayed heat release equates to lower indicated efficiency, all other things being equal. Of course, assuming the turbocharged engine is downsized accordance with its higher BMEP, there should be a relative increase in mechanical effiency, and significant reduction in engine mass, which should cascade onto lower vehicle mass, even with the same vehicle interior dimensions and load capacity.
Since we're only looking at one operating point, I can only speculate what the comparison of brake efficiency looks like over a realistic drive cycle, and what the actual fuel economy comparison would look like considering the difference in vehicle mass, not to mention the probable reduction in average pumping losses for the downsized engine.
Getting back to peak cylinder pressures; it seems that the cutting edge for commercial diesel engines these days is around 3000 psi. I think it's fair to assume we're talking about iron heads and steel piston crowns here. In the case of an Otto-cycle engine, neither of these are helpful for avoiding knock, compared to aluminum, but at least they can handle higher levels of mechanical & thermal stress; which might buy some knock margin on the mechanical side, assuming the rest of the vulnerable components (fire rings, bearings, rods, spark plugs, head gasket) are equally up to the task.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

RE: Downsized charged engines, peak cylinder pressures?

Quote (hemi)

I can only speculate what the comparison of brake efficiency looks like over a realistic drive cycle, and what the actual fuel economy comparison would look like considering the difference in vehicle mass, not to mention the probable reduction in average pumping losses for the downsized engine.

In my experiences, turbocharging small block Ford's in 3800 lbs cars, fuel economy usually increases from 22-26mpg N/A to 28-31 mpg under similar cruising conditions

RE: Downsized charged engines, peak cylinder pressures?

Correct with no other changes all else remaining constant

RE: Downsized charged engines, peak cylinder pressures?

Like Greg, I find that amazing also.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

RE: Downsized charged engines, peak cylinder pressures?

Decipha, that result is counter to what I would expect from a turbo installation on a car. Aftermarket turbos are most often installed for performance and are usually not optimized for economy. Can you tell us details such as do you include a wastegate?

RE: Downsized charged engines, peak cylinder pressures?

yes every engine I've ever turbocharged MUST have a wastegate otherwise they will come apart (as in rotating assembly / engine block failure), typically most engines burning 93 octane pump gas don't run anymore than 20 lbs of boost


The more efficient you make an engine at a given state, the more performance and economy you will return at that state.

This is currently one of the primary 'pushes' in the industry and why a lot more vehicles are being manufactured factory turbocharged in an effort to increase economy and as a result performance as well.

RE: Downsized charged engines, peak cylinder pressures?

Quote (decipha)


This is currently one of the primary 'pushes' in the industry and why a lot more vehicles are being manufactured factory turbocharged in an effort to increase economy and as a result performance as well.
Umm, yeah, we all understand how downsizing with turbocharging works to increase fuel economy and performance as well (due to reduced vehicle mass, pumping losses, & engine friction resulting from downsized engine). Question on the table is what is the physical explanation for increases in fuel economy you claim as follows:

Quote (decipha)

In my experiences, turbocharging small block Ford's in 3800 lbs cars, fuel economy usually increases from 22-26mpg N/A to 28-31 mpg under similar cruising conditions...no other changes all else remaining constant

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

RE: Downsized charged engines, peak cylinder pressures?

Yes, this is key. When you replace a 3.8L with a turbocharged 2L you may get greater economy. This is because at zero boost the pumping losses through the smaller engine are less. Also, engine friction is less, the engine package and car are lighter, etc. But, when you take a 3.8L and turbocharge it, you usually get lower economy, especially if the engine is "overboosted" meaning it requires a waste gate to bleed off exhaust back pressure to keep boost under control.
So, if you are getting the kind of gain in economy you say you are getting, your installation would be of extreme interest. Can you please describe in detail?

RE: Downsized charged engines, peak cylinder pressures?

I misinterpreted your question

the gains are accredited to the reduction in pumping losses

In theory you have pumping gains from the exhaust heat energy used to spool the turbine which would otherwise be pumped out of the exhaust pipe with the majority being wasted energy

RE: Downsized charged engines, peak cylinder pressures?

Well... to recover efficiency from the exhaust at cruise is pretty hard to do. Long haul diesel trucks can do it because they don't run engine vacuum. The compressor can make pressure that pushes down on the piston, but the back pressure in the exhaust side has to be significantly lower or you don't get a net advantage. So, these are low back pressure installations.
Auto installations are high back pressure so you can have quick turbo response. They have waste gates to limit boost on top. It's a different approach. Even with diesel auto engines I'd like to see how it's done for increasing cruise efficiency. I bet variable nozzle geometry is where you start.

RE: Downsized charged engines, peak cylinder pressures?

no automotive engines are not high back pressure. They are designed for optimum delta pressure, the exhaust is designed to scavenge using the venturi effect, this is how horsepower gains of up to 10% can be ascertained by optimizing the exhaust manifolds which can be seen in the tri-y header design

The same applies for cylinder filling using airflow modeling and valve timinge this is why properly designed naturally aspirated engines are capable of exceeding 110% volumetric efficiency.

While the turbocharger isn't creating positive pressure (boost) during cruising conditions it is still supplying high velocity air. This is evident by removing the compressor discharge piping while the engine is running, you can feel the airflow by placing your hand in the airstream, the turbocharger (if its properly sized) will be moving sufficient airflow to perhaps dry your hands. Some higher horsepower engines have larger turbocharg that do not even spin at idle... how's that for back pressure?

RE: Downsized charged engines, peak cylinder pressures?

"...no automotive engines are not high back pressure..."

This is relative. There are low back pressure systems that work primarily on exhaust gas velocity. These are called blow-down systems. The alternative is the pressure system. I have never seen an auto installation that was not a pressure system. One guarantee that a system has appreciable back pressure is the presence of a waste gate. Waste gates work by bleeding off back pressure and they work best, most precisely and over the greatest range when the back pressure in their absence would be very high. This implies that the turbo itself is a severe exhaust restriction and the combination of turbo, waste gate and associated plumbing is more restrictive than a good NA exhaust system.

"While the turbocharger isn't creating positive pressure (boost) during cruising conditions it is still supplying high velocity air".

This is what is inconsistent. A gas engine at cruise is highly throttled, producing a small fraction of its WOT power. It runs a manifold VACUUM. A turbo producing "high velocity air" is fighting the throttle while costing power in the form of back pressure.
It is very easy to gain power from adding a turbo to an existing NA engine, but gaining mpg? and especially in the amounts you claim? You have not provided details of how this was done.
I believe you would need to do mods to the NA engine, probably including exhaust gas recirculation and direct injection.


RE: Downsized charged engines, peak cylinder pressures?

My android just refreshed the page and caused me to loose a well detailed and thorough reply so ill summarize

Exhaust delta presure is vital to proper engine operation, and turbos are restrictions but the wastegates primary purpose is not to limit back pressure although thats the effect, the wastegates purpose is to bypass exhaust gas from overspooling the turbo to limit compressor airflow, often the wastegate vents to atmosphere

The wastegate only opens when the reference line (typically manifold pressure) exceeds the diaphragm spring pressure (desired boost pressure) this usually occurs at approximately 4000 rpm at WOT for the majority of the engines I play with. Some engines where boost is increased to the compressor maps surge limit, the wastegate never opens. Typically a properly sized turbo should flow at least 300 cfm more than what the engine will be ingesting.

As for throttle angle, a typical 4300 lb vehicle (loaded with typical payload) maintaining a 70mph cruise with a slight headwind of 1-3 MPH and a vehicle drag coefficient of 0.31, final drive ratio of 2.07:1 with approx. 22% drivetrain loss at an engine speed of 2000 rpm, the engine ingests a steady 52 cfm at 20% throttle, this was at 18 ft above sealevel engine coolant temperature of 210 degrees F and aircharge temps of 122* F barometric pressure approx 30.08, humidity of 87% with ambient temperature of 83* F, this was averaged over 24 miles (causeway bridge) on 3 different days of similar weather.

RE: Downsized charged engines, peak cylinder pressures?

engine vacuum of 14 in/hg during these conditions

RE: Downsized charged engines, peak cylinder pressures?

oops I left a lot out, that engine in question is a 231 cubic inch 6 cylinder that averaged 19mpg prior (naturally aspirated) to the turbo and 24mpg after, again that was averaged over the 24 mile bridge.

No other changes were made

That same engine with a supercharger averaged 22mpg

RE: Downsized charged engines, peak cylinder pressures?

If the vehicle in question is tested under near identical part load conditions, the N.A. and Turboed cylinder pressures will likewise be near identical

Since operating the turbo creates a net loss of energy through heat dissipation and the exhaust pressure required to rotate the turbo, yet produces the same cylinder pressure as the N.A. version, how can that loss of energy be improving rather than reducing the vehicle's economy?

I concede such may be possible if the turboed engine's componentry and tune was optimised but, apart from removing the turbo, was left unchanged for the N.A. test - -

Maybe you've omitted key information, such as the N.A. engine was a larger capacity unit than the turboed engine - -

Tekton

RE: Downsized charged engines, peak cylinder pressures?

I don't believe I can be of any further assistance, I don't have a definitive answer for you, all i know is the real world results

RE: Downsized charged engines, peak cylinder pressures?

We'll, if you're going to play that card, then can you share your methodology for determining that your observed delta fuel economy measurement is statistically significant?

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

RE: Downsized charged engines, peak cylinder pressures?

decipha,
You have to have done some special and unusual things to get the results you claim. Otherwise, what you say is not credible.

RE: Downsized charged engines, peak cylinder pressures?

Typical PCPs of GDI boosted engines I've seen are like early diesel motors- 110 -130 bar.

Regarding turbocharging increasing fuel economy with no mods-

when did the workshop-mechanics equipped with dremel and seat of the pants dynos invade these forums?

www.auto-scape.com

Sideways To Victory!

RE: Downsized charged engines, peak cylinder pressures?

I gave up on the debate because there's nothing more that can be said, the fact is engines get better fuel economy when they are fitted with turbochargers as well as superchargers, this cannot be disputed its a known fact by millions of racers around the globe, if you disagree you are wrong its a proven fact not for debate

its statistically significant because the vehicle can travel a greater distance without refueling, one of the primary factors of engineering design is efficiency which comes only second to safety

As for not being credible, I'm appalled you would even insinuate I'm being dishonest, what benefit could possibly be ascertained from spreading mistruths?

Perhaps you aren't aware that the knowledge we gain in life is only temporary, when we pass on that knowledge does us no good.

I've tuned several hundred engines I have yet to have a single 1 get less fuel economy than it did prior to being boosted, in other words I have yet to have a single engine not get better fuel economy when boosting abilities were added.

As I said prior there's nothing more that can be said, if anyone cares to elaborate as to the physics behind the increase in economy then go right ahead otherwise your spreading mistruth about something you cannot comprehend.

RE: Downsized charged engines, peak cylinder pressures?

My quiet bet is that you did a bit more than just 'fit' a turbocharger. I suspect you played with the mixture and the timing at least, Normally in order to get a 25% boost in fuel economy you'd have to change the gearing.

At 20% throttle your turbo will not be doing anything much.

Cheers

Greg Locock


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RE: Downsized charged engines, peak cylinder pressures?

Turbos and superchargers are not add-on economy boosters. They are power boosters. Normally you will lose economy from such installations. The simplest example is adding a supercharger with no mods to the engine.
First, the supercharger will increase the total compression of the engine, fully equivalent to increasing the CR. It does this because it increases the air intake per cycle while the combustion chamber volume remains the same. So, it can result in the necessity to use a fuel with a greater octane number. This means that fuel costs may increase and the engine's ability to take supercharging is ultimately limited from this effect.

Assume we take a 3.8L engine and add a positive displacement supercharger (like a Roots type) that increases the breathing capacity by 20%. Now the engine has a volumetric capacity that is 20% greater than before. For all intents and purposes it behaves as a 4.56L engine. That means that at cruise it has the pumping losses of a 4.56L and a pure and unavoidable decrease in economy compared to its unsupercharged state as a 3.8L.

However, there are things that can be done such as what Greg mentions, lowering the gearing. Also, you can declutch the supercharger and bypass it so that the engine behaves again like a 3.8L, but that has a lower gearing. NOW you can gain economy. But, it takes details like that that can make something like this work. The supercharger alone "with no other changes" LOWERS economy.

RE: Downsized charged engines, peak cylinder pressures?

that is incorrect, boosting an engine does not require a higher octane fuel, the higher octane fuel is often used to increase power by the knock suppression it is not a requirement of any internal combustion engine

from your logic you are failing to comprehend the dynamics of a running engine, fuel consumption is not linear to engine size, there are thousands of 350+ cubic inch engines that better 31mpg in a 3800lb vehicle, yet there are thousands more 4 cylinder and 6 cylinder engines less than 200 cubic inches that cannot match that fuel economy in even lighter vehicles

RE: Downsized charged engines, peak cylinder pressures?

"Boosting an engine does not require a higher octane fuel" - Say what? Higher cylinder pressure with higher temperature (particularly if there is no intercooling) means more knock propensity.

RE: Downsized charged engines, peak cylinder pressures?

which means you have to reduce timing to prevent knock, you do not have to run high octane fuel you simply do not get the gains you would otherwise by not doing so, but its not required

RE: Downsized charged engines, peak cylinder pressures?

Brian, you are correct. Combustion engineering is a science, not an opinion and especially not an uninformed opinion. There are text books that cover this subject in great detail.

RE: Downsized charged engines, peak cylinder pressures?

and all those text books are wrong because you can simply reduce ignition timing to prevent knock

for example, lets say we have a 9:1 static compression ratio engine boosted making 18lbs of boost (which will return twice the horsepower the engine makes naturally aspirated), lets say this hypothetical engine reaches MBT at 36 degrees of timing at maximum pumping capacity, at 18lbs of boost we can only safely run 25 degrees of timing with the same 93 octane gasoline, the engine should return 320hp and 640hp respectively.

Now lets say we run that same engine on 87 octane gasoline, at maximum pumping capacity we can only push 28 degrees, anymore and the engine starts detonating, at 18lbs of boost we can only safely run 17 degrees of timing, the engine should return 280hp and 560hp respectively.

the octane rating of the fuel is its resistance to burning, by increasing the resistance you can run more ignition timing without detonation. A faster burning fuel can not run as much ignition timing.

disagree and you are wrong just like your text book

RE: Downsized charged engines, peak cylinder pressures?

Diesel engines do not have spark plugs. When you increase compression above a certain point, a spark ignition engine engine become a compression-ignition engine. Pre-ignition and detonation are related but not the same. Both can be described as knock.

RE: Downsized charged engines, peak cylinder pressures?

Applying turbocharging and then retarding the ignition timing will reduce power output and efficiency below what would be seen if fuel of appropriate octane rating (generally higher than the non-turbo engine wants) were to be used. Running the engine at high load with retarded ignition timing will raise exhaust temperature and exhaust valve temperature (that's where the power loss and reduced efficiency is going - it's getting thrown down the exhaust pipe, and to some extent into the oil and cooling systems, as heat). Do that extensively enough and long enough, and the hot exhaust valve will become the (pre)ignition source. When that happens ... ka-BOOM.

Just because you can control detonation (up to a point) by retarding ignition timing to later than MBT doesn't mean it solves all of your problems. The right solution is to run ignition timing close to MBT with minimum retard for detonation control, and use the octane rating that the engine wants!

By the way, I own and occasionally race a street-legal vehicle with a port-injected spark-ignition engine, non-turbo, that has high-13's compression ratio (it's not stock). I'm uncomfortable using any less than 94 octane, and when it goes to the drag strip, racing fuel. Retarding the ignition timing to try to make it run on regular is NOT happening. I prefer having the exhaust valves stay together and the coolant and oil temperatures stay in an acceptable range.

Some modern direct-injection engines, notably Mazda SkyActiv, are handling this by careful control of the spray pattern and careful design of the combustion chamber so that detonation either does not occur or remains manageable. Mine is not that sophisticated. Those engines are something of a halfway-house between gasoline and diesel engines - and Mazda is not using turbocharging in those (yet).

RE: Downsized charged engines, peak cylinder pressures?

Compositepro, Pre-Ignition cannot be described as knock. Preignition is early ignition by any other means except a timed spark that normally initiates combustion. Preignition can lead to detonation and if you are that lucky then yes there is some audible knock but real preignition is silent most of the time and often leads to thermally induced damage.

RE: Downsized charged engines, peak cylinder pressures?

pre-ignition is more of a design flaw and not so much a tuning fault

the amount of heat required to split an exhaust valve is significant, it will take a significant amount of retard to do so not to mention the engine will have to maintain that load for an extended period of time, the only real concern you have for damaged exhaust valves are in truck applications that see heavy loads during towing for extended periods of time, otherwise its null and not even worth mentioning

brian your 13:1 SCR engine shouldn't be ran on anything less than high octane fuel, but its not typical for a gasoline engine with that much compression to be turbocharged, in fact, the upper limit for boosting that i recommend is 10:1 unless you have direct injection which allows you to go higher safely

in any case, you just reiterated what i stated previously, you CAN run your engine with a lower octane fuel but it will require you to pull timing, it IS NOT required that you run higher octane fuel but you do so for safety, regardless of the fuel octane you run, you can typically reach MBT below approx 25% VE then thats when you wreak the benefits of the higher octane

i don't recommend you run your engine with low octane fuel, im just stating that you can

i've ran 450+ rwhp supercharged engines on 87 octane fuel with over 16lbs of boost

RE: Downsized charged engines, peak cylinder pressures?

Quote (decipha)

its statistically significant because the vehicle can travel a greater distance without refueling

Assess Statistical Significance

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

RE: Downsized charged engines, peak cylinder pressures?

for a factory honda k23 which was fitted on the acura rdx (2.3L Turbo) the max cylinder pressure was about 1400psi at 2500rpm (peak boost). subtract ~300psi when the boost started tapering off at 6000rpm. It was just a conventional 2.3L I4 with MPFI and 8.8 compression. Not sure about the newer ones with direct injection and everything.

RE: Downsized charged engines, peak cylinder pressures?

I have found that most OEM on board fuel economy gauges work off of injector pulsewidth. When fitting larger injectors the fuel economy numbers will show higher (better MPG) numbers due to the reduced injector pulsewidth at cruise. Perhaps this is where these fuel economy numbers are coming from?

RE: Downsized charged engines, peak cylinder pressures?

LateApexEE, this is very interesting speculation and might help to explain the apparent violation of the laws of physics that has been claimed.

However, using the on-board fuel economy gauge to calibrate fuel use instead of a professional rig or at least calibrating the gauge or the pulse width vs amount injected and then thinking you have certifiable data to support extraordinary claims would be naive. Besides, the firm claim is that there were NO changes, so NO larger injectors.

On the other hand, applying substantial supercharging without changing injectors in several hundred cases would also seem incompetent. The risk is leaning out the engine under high power leading to catastrophic damage -guaranteed to happen in at least some of the hundreds.

RE: Downsized charged engines, peak cylinder pressures?

Decipha, were the economy figures you quote calculated by filling the gas tank with known volumes of fuel, which were then divided into known distance covered - - or from dash guage readouts?

Tekton

RE: Downsized charged engines, peak cylinder pressures?

All modern EFI systems are closed-loop, which means that the fuel injector PWs are constantly adjusted to deliver a specific mass flow of fuel based on feedback from the oxygen sensor, the knock sensor, the air mass flow sensor, etc. As long as the PW commands are within the limits of the ECU software maps, then there should be no problem for the ECU to adjust to the higher flow rate of a larger injector.

RE: Downsized charged engines, peak cylinder pressures?

(OP)
Going back to my original post, I have now finished Uni and am working in powertrain at a high-end OEM.
Peak cylinder pressures are in the region of 120 Bar.

Reading Race Engine Technology this month, Mahle have said peak cylinder pressures for the new F1 engines next season are seeing peak cylinder pressures of 200 bar, and are running in knock conditions.

RE: Downsized charged engines, peak cylinder pressures?

tbuelna, that is precisely the point!!! The ECU will deliver the correct amount of fuel using a diminished duty cycle for the injectors. A meter that reports the duty cycle as a measure of fuel use will falsely report better fuel economy.

The emphatic claim by decipha of better economy in ALL installations would be more credible if he gave full details of what he did. To be thorough in making such a claim (that overturns the textbooks and the science to date on vehicle fuel economy) decipha had to have done calibration runs on roads, before and after, on each vehicle. These runs, if properly done, would not have relied on the unverified reporting of the vehicles' internal gauges. Such a procedure would have been extraordinarily expensive for the installers and burdensome in time on the customers. Short of that, dyno runs would give an inferior estimate and had to have external fuel use measuring or a recalibration of the internal mpg meter. Again, this is not an inexpensive procedure tacked onto the cost of the installation.

For these reasons, LateApexEE's observation is tantalizingly suggestive of a VERY easy mistake. On the other hand, decipha is clear that he did not change injectors "no other changes".

RE: Downsized charged engines, peak cylinder pressures?

HarleyE30, how did you measure the peak pressure?

RE: Downsized charged engines, peak cylinder pressures?

(OP)
@140: in-cylinder pressure measurement

RE: Downsized charged engines, peak cylinder pressures?

Thanks Harley, I meant what transducer did you use? There are spark plugs with this capability and it's possible to modify a plug putting a transducer in a drilled hole. Also possible to put one in a drilled hole in the head.

RE: Downsized charged engines, peak cylinder pressures?

(OP)
Im in design so am not sure of the exact method of measurement. I remember using the spark plug type transducers at uni; they were supplied by AVL. I will find out what we use on Monday!

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