Static Compression Ratio vs Boost?
 

Can anyone tell me whether it's possible to run 1.0 - 1.1 bar boost on an EFI motor running 8.5:1 static compression ratio, fully programmable ECU, full bay intercooler, and twin plugs on pump fuel?

I don't think I'd try it cuz you'd be running at an effective CR of 17.75:1 at 16 psi...

I don't believe that is correct. Combining static comp and boost is not the whole story. A turbocharged engine may only see 20% higher peak cylinder pressure over it's NA counterpart, the power comes from more pressure during the whole cycle compared to the NA motor

I see no issue running 16psi on a 8.5:1 motor

Personally I would not go lower than 8.5:1 with such setup

Much more into it than static pressure from boost + CR .... think about cam and duration overlap for a second in regards to static pressure...then think squish, ignition, fuel, etc etc.. IMO Forget static pressure as argument. It is not static pressure but in the end combustion pressure and detonation that needs focus/concern

Your EFI and twin plug makes it possible to control combustion and detonation in a professional manner on these aircooled engines and thereby skip the old school low CR. I don't understand why anyone that convert to EFI would stay with low CR 7.5:1 ...waste of money and no understanding what is going on IMO.

Porsche, Saab and others (pioneers in mass manufacturing turbo cars) started with low 6.5, 7, 7.5:1 in CR before converting to OEM EFI ...

Jakob

Sure you can do it. Then rebuild your motor when something goes wrong like overheating in traffic or a bad (mis- labeled) load of fuel. You don't have four valves, water cooling, center plug, variable cam and most important knock sensors.


http://forums.pelicanparts.com/uploa...1323474147.jpg

EFI has no magic effect on knock resistance on it's own. What made higher compression ratios on turbo cars possible is the knock control that is integrated into EFI.

I'm not an expert, but the fact you have a fully programmable EFI makes it safe to do from my understanding.

Since you have programmable EFI, I'm assuming you have a wideband to monitor AFR's?

What motor?

If a fully programmable EFI cannot detect knock and pull back the timing, your just as screwed as if you are running an old-fashioned vacuum advance distributor.

So you're saying a fully programmable setup utilizing a wide band is no better than the Motronic from the '80's?

From my limited knowledge, if you use ancient EFI that has simple fuel (and ignition) tables, you will have variation between AFR's during different points of operation.

With modern fully programmable, I was under the impression you can fine tune nearly every aspect of engine operation mitigating risk if you had bad fuel for instance.

Sorry, this is for a project car... 911SC 3.0 motor running a Carrera EFI intake, programmable EMS, full bay IC and potentially a twin GT28RS turbo configuration.

I think we'll retain the 8.5:1 and use twin Tial 46mm 1.0 bar wastegates. The EMS will have WBo2 input, and also regulate boost pressures above 1.0bar if need be.

Was just curious. We are going into the motor to install new rings and fasteners anyway, so we may slip in a 0.5 or 0.75mm base cylinder shim to reduce static CR to ~8.0:1 if need be. We do like the idea of retaining 8.5:1 for the twin setup to make it ultra responsive pre-boost :cool:

Suggestions?

Very wrong IMO. Do you map/tune EFI applications on closed loop knock sensor readings? Try to define knock resistance/control .... Knock sensor is just a sensor input nothing more...many sensor input goes into EFI to tune against detonation.

3D programable load maps that is where you have the single most major difference to knock control (out of many). With EFI your ignition now measure and calculate retard/advance intelligent from MULTIPLE parameters (same goes for fuel), such as:

• Oil/water temperature,
• Inlet charge temperature,
• Exhaust gas temperature,
• Air Fuel Ratio
• Manifold Air Pressure
• Voltage
• Frequency - if you choose to use it (Knock sensor)

Knock sensor is only one parameter out out many way more important.
Newer trust a knock sensor alone. Many don't use it and only with calculated uncertain margins for full stop damage control
A knock sensor measures the FREQUENCY in the block/cylinder/head from combustion. The combustion frequency makes a peak (after normal plug fired combustion) when detonation sets in and varies around 6400 hertz (as I remember for alloy) depending on alloy/cast material and setup! It needs to be calibrated.
I would never trust tuning/mapping on closed loop knock control.
You need same mapping/tuning with or without a knock sensor.
Knock sensor should only be seen as an alarm that you use to set up "damage control" parameters (ign retard, fuel enrichment, boost backoff etc.) Like situations from bad/wrong fuel. Nothing to do with picking your CR.
To say knock sensor alone is the major factor to what makes higher CR possible is totally misunderstanding tuning/mapping IMO.

Knock resistance/control is the combination of programing several important parameters. You need each 3D load point to (which can be as many as you want) automatically calculate the correct output depending on multiple measured input.

How old do you think that dusty boost chart is??
It is oooold and from times when igntion control was limited to mechanical vacuum advance up to 3000rpm and then a straight "dead" line through out the rpm.
Nice as history memory.

Use it for a guideline if you have old school mechanical ignition distributor (OEM 930 ignition setup)
IMO dont ever use it as a guide line for now days EFI setups / upgrades.

He mentioned going EFI and twin plug.

Four valve - numbers of valves has IMO no effect on knock control (squish has)
Center plug - he use two plugs and you get same flame travel distance (depending on bore)
Water cooling - water or air... use temperature sensor on head/cylinder and EGT to map ignition and fuel against overheating/detonation
Variable cam - for knock control ? Twin scroll setup (true build, not single WG) prevent much of the cam overlab issues (backpressure) and makes it possible to stay "on cam" with NA cam together with proper sized turbo.
Knock sensor - tune engine first and then setup as loop "alarm / full stop" parameter (calibrated and tested) to igntion retard and fuel rich compensation.

A knock sensor is a sensor just like all other sensors. EFI reads all input and you tune to map/calculate output.

Most used KISS and effective amo against detonation when dyno or bench tuning for MBT ... (Minimal Advance for Best Tourge)

http://powerpage.dk.web26.wannafinds...nkesensor6.jpg

Wow, some people are stuck in the past.

Wasn't the world once thought of as flat? Until technology proved that to be false

Same goes for our precious air cooled Porsches.

Take advantage of modern technology to improve your car. Are we still all running bias ply tires?

Richard Clewit says it can be done

case closed ;)

Are you referring to the EFI "hear balls" which almost every professional EFI tuners uses when mapping igntition and fuel against MBT ??

Or the general debate from those still keeping 70/80's low CR when doing forced induction + EFI ??

the latter :)

It's Porsche's, published in 1978 when pump gas was much better than now. See the N.A. motors on the bottom line? Motronic, plus the 3.6L has twin plug, CHT and knock sensor. Sorry, push the chart and blow a very expensive motor. I stand by it because it describes the 40 year old air-cooled motor.

Too many guys on this site paid the price and some have bailed this past year.

I have a stroked motor to 3.5 with 8:1 on CIS with a meth injection kit and I run 16lbs booost with no problem.. with plenty of fuel.. Motor runs so good and no issues so I dont even think about efi the motor..

It is a boost chart! and I trashed it many years ago...properly the first made ever. Now please tell me why you make reference to NA applications on a boost chart ?? Sorry, but you are completely off track. If you want to talk NA CR on a chart then start figure what should be on the Y-axe....

That is exactly the point - you stick to and make reference to 33 year old pioneer turbo chart in a post where the person is not asking to veteran setups however asking about CR using modern technology (EFI). No differences to other 2 valve - try and compare squish if we should stay on track! This is EFI and CR. Making reference to those CR chart figures in this post is basically IMO asking people with EFI to through money and power out of the exhaust pipe. That chart belongs on a museum for veteran forced induction in the days when they started without intercooler, mechanical ignition and loooooow CR to clear detonation.

Jakob

Not the first, but prepared and presented to the Society of Automotive Engineers by Porsche's chief engineer Hans Mezger.

N.A. is not a vacuum, it is pressure - atmospheric pressure. Following your logic where should one stop at C.R vs. boost? Why not go to 11.5:1 and boost it to kingdom come....absurd? yes. You get my point? Besides intake manifold pressure is not the absolute measure of power.

Regarding the chart it has several data points of interest known to many on this site. Both Les-garten and Don E are modern fully built 930 based motors and each is at the edge on pump premium with 12.5:1 effective C.R.

Now you make me laugh....sorry...Come on....talking NA on that chart just expose yourself… Atmospheric pressure is 14.7 psi at sea level....you are talking funny stuff in all different directions...to follow your thinking on this matter you would need to draw yourself a nice chart-painting... put 14.7 psi for sea level in the middle of the y-axe and then paint mountains on top and deep canyons beneath that … only then your argument makes sense and you get reference points to plot from. You are wasting time. Sorry. You can get absolutely ZERO out of that specific boost chart for NA. It tells you have understood very little about CR. If you really think so, and serious, then please…… try and write a post here to us all describing how to determine CR on a NA build application from that specific boost chart... I will read it!

Back to reality on this thread ... Time has moved on and what 35 years ago was 6.5-7.5 in CR is now days 8.0:1 > 8.5:1 > 9.0:1 with EFI (two valve twin plug depending on application). Back then some also learned that cooling inlet charge air could improve combustion control and CR and porsche started using intercooler OEM and left CR 6.5/7 behind. Yes, believe it or not a "CR milestone" was moved forward. We are now in 2011. Among others we now have EFI at our disposal. To me you clearly haven't understood what has moved and limited CR TODAY with proper EFI tuning and ignition setup. That is why you IMO are off target and back in history in your answer to this persons question in regards to EFI + Twin Plug = CR.

Anyway looking much forward to a “in depth” description from you how you use and determine CR on a NA engine builds from that specific boost chart...maybe you could post that picture with reference points to the y-axe.

Inspiration for your mountains Y-axe painting - Look at this video The BEST rally video you will ever see(No music, RAW sound) - YouTube

That is pikes peak 0-4000m

That ECU has 1 bar internally atmospheric pressure sensor mapped to correct ignition, fuel and boost on its way to the top (by the way +2 bar forced induction)
Such internally 1 bar atmospheric pressure sensor is standard in all professional aftermarket ECU EFI today for such use among others.

Ok, this is really getting old, and your closed mind makes me laugh.

I know what altitude is, I lived the entire month of August working turbo issues at 4300METER in the Antamina Mine in the Peruvian Andes. Look it up. I didn't go 4300M on YouTube, I lived there.

Take the time to open your mind and read the chart. Pressure is pressure, this chart starts at atmospheric pressure so it is valid to set N.A. engines on the bottom line. By doing this you have additional data points reflecting the effective compression Porsche found gives reliable engine usage. It shows gains made by their addition of EFI, knock sensors, CHT and twin plug.

Besides there are some on this site who know boost isn't everything. They set their intake pressure at a reasonable level then start working down exhaust backpressure and intake manifold temperature. This is the correct method of producing reliable turbo power. EFI has it's place but better spark advance and A/F ratio control cannot replace inadequacies in the basic engine architecture and systems.

Now you go the funny direction again. Now you say you work in a Mine and argument that this chart tells you how to set CR 4300m beneath sea level on what would be expected to be industrial turbines. I dont think any porsche ever been down there or set up as turbo engines in Mines. Or do you have a NA race track down in that Mine? Totally BS.

By saying so you leave out that no NA Porsche is ever driving above sea level AS no less than 14.7 psi is on that boost chart. That is why I asked you to do the painting. I repeat, no less than 14.7 psi is on that boost chart. Go figure...

Going up hill means less than sea level atmospheric pressure (and big surprise it is not figured on the chart) As 99% of all roads are above sea level it equals quit easy up that you are talking diffuse BS and Porsche did not make that boost chart for you to plot NA engines as answer to CR on forced induction application.

Now please I kindly ask you again....do the magic and try and show us all in a post how you would plot on the Y-axe for NA engine above sea level.

Show us...

An Internet dialog with you is pointless and futile. To show you I will need to determine what you have learned in you life experience before I can proceed. From what I have as a starting point I decide to end this here.

A little background info; copbait has a lifetime of experience as a turbo engineer for one of the most prolific turbo manufacturers on the planet. The chart applies to the basic technology of the engines' 40 year old design. It's a great tool. I think the point copbait is trying to make is you can throw all the EFI technology you want at a 40 year old engine design and it won't do a thing to change the basic design contraints.

Sure it will, because the basic design restraints were based on knowledge back then. Modern EFI has proven over and over that what we once thought impossible is now common place. There are many old school engines making 300-400hp per liter using modern turbo and EFI technology. I see and deal with this on a daily basis.

I hate to hear " it can't be done". The person making that statement assumes he knows everything which in turn proves he knows little.

I respect the thoughts and opinions of everybody on this board, but forward thinking is what pushes technology not looking back

@Copbait... that was expected

The point is -> You can NOT use that boost chart to determine NA CR applications. Period. And second, that chart is for ooooold veteran forced induction setups. This post is (or was) about EFI + Twin plug. CR are not to be compared when using such different instruments to control detonation. Totally different ball game!

@Copbait.. quit the funny talk ... you now ask for others background before you expose the NA nonsense futher.
I have (just as many others) a long history within NA and forced induction both commercial and in practice and besides that, articles (not in english) and speaking of CR ... I did a "Configurator" to easily set up individually ignition startup maps. It has it purpose to drive from EFI garage to the dyno/bench for tuning against MBT. It has been used and proved working in real life by EFI customers, competitors and users on EFI forums for many years (http://powerpage.dk.web26.wannafindserver.dk/tuning_ignition-filer/Ignition_timing_konfigurator_opstartsmap_v106.xls). You wont run "dry" on experience here.

Try and get serious - Just try do the chart plotting of an real life "above sea level" NA on that boost chart.

Jakob

I don't think anyone said "it can't be done". There is a big difference between "can't be done" and "probably shouldn't be done if you expect your engine to live a long life".
I fail to see how EFI is going to change the piston/head design on a 930 or turn air cooling into water cooling. Those are the design constraints I am talking about.

Jakob you are probably not going to get an answer. One of the things that is great about this board is that most folks are not hostile or confrontational. That type behavior runs off good folks who are long on knowledge and short on patience when it comes to abuse. They share what they know as a courtesy and have no reason to stay and take any crap. Everyone has the option to take the advice or to not.

Brian, what usually is so great about this board is non-confrontational knowledge sharing where no one is placed on a statue spreading repeated mistakes without people at some point start question it. It might be (not intended) understood as confrontational from those seeing them self up on such statue.

I agree on focusing on backpressure rather then manifold inlet pressure, temperature etc. I personally look at and plan forced induction engines as near NA setups as possible in order to have the boost vs. backpressure positive. Only by that you have an effective reliable and "cold" running turbo engine. That is why you should never build your twin scroll manifolds with one open wastegate due to backpressure issues on cam overlab (I know you offer two seperate WG solution and looks good). Anyway...to say one can determine CR on a NA engine from that boost chart is nonsense.

My posting ends here with the requested NA vs. pressure plot on that specific boost chart above sea level. It will expose no way possible and the talking nonsense in regards to that specific argument. It is very simple and easy, just try and plot it...nothing confrontational in that.

To get "back to the future" on track on the original CR twin plug efi question -> this thread hold most of the simple answers and opinions to that question by now. If you want to study further about using full potential of squish design, then there is respectable books available out there about squish and combustion behavior controlled by modern engine management.

The problem our engines have is not much squish, because the squish band is almost nonexistent with the shallow hemi design. Now if we had access to a more modern combustion chamber design similar to the gen III Dodge Hemi, we could make better use of squish and turbulance.

http://forums.pelicanparts.com/uploa...1323658505.jpg

IMO 8.5:1 is safe under normal circumstances for this 3.0L 95mm bore twin plug + EFI

Sorry guys, I didn't mean for this to become a full on argument. I was just after some opinions from people who've BTDT :confused:

I think what we'll do is start with wastegates preset with 0.8bar springs, and then use the Engine Management System to regulate the boost up to the highest and safest limit to see exactly where it's happiest at 98 Octane.

I would think with twin plug, full bay IC, and very fine/granular control over the fuel and ignition maps, we should be able to push it to ~1.0 - 1.1bar at that CR whilst maintaining excellent pre-boost responsiveness. Thanks for ALL your input and advice.

According to Car and Driver's cutaway of a modern Hemi, Chrysler looked to a 993 for head architecture.

Exactly. I was on the engine design team for the Hemi engine when it was being designed by people from Ricardo and Chrysler. And they had a 993 cylinder head sitting on the cylinder head engineer's desk. They knew enuff to learn from the best ------ie Porsche when they set out to design their new heads.

Fredmeister

Factors influencing maximum dynamic CR in order of greatest effect:

1. Cylinder head design - on the "33 year old" 911 engine, there is a spark plug off to the side so the flame front has farther to travel, not much quench (squish) area so swirl during compression isn't the best and an intake port that doesn't swirl real good either (that's why there's bowl pistons in the SC/Carrera n/a engine).

2. Fuel - a higher octane rating is a measure of a fuel's ignition temperature. Higher ignition temperature is better because it's the end gas (an ever-changing fraction of unburnt gas during combustion that's being squeezed by the combusted gas, changing chemical composition and becoming a compound with a lower ignition temperature) that will auto ignite and damage the engine.

3. Combustion chamber heat rejection - not the best on an air cooled engine; certainly not in the same league as a water cooled engine.

and way down in 4th place is EFI.

EFI will allow tuning very close to the ragged edge of detonation, closer than CIS, but it's ability to allow a cylinder head that was designed without the aid of CAE to run compression ratios seen on contemporary engine designs is just about nil.

Since we're discussing dynamic compression ratios on 930 series engines, the chart is valid IMO. Stray from it at your own risk.

I've heard Juan Ruiz runs 1.4 bar+ on his Carrera motor with 930 P&C's. He's way off the chart :confused:

I've run 1.25bar on my turbo Carrera with 930 P&C's too!