I have experimented with MAF in my boosted application. What I have found is that MAF fueling alone it is difficult to get the AFR's reliably that most people want to run under boost. MS allows you to "fudge" fueling by adding a component of speed density while under boost to allow you to get to your target AFR's.

Good to hear I wasn't crazy. I've read that even with lower air temps (although still higher than ambient) from an efficient IC, you still need lower AFR's for boost vs NA.

Tippy,

The very first calculation done on AirFlow is to divide it by RPM/2 so that we know exactly how much of the air is injected by 1 engine cycle. This removes RPM and time from the equation. Once we do this we know exactly how much air is ingested by 1 cycle. We also know the the amount of air a cyl can injest without boost and this theoretical value is known as VE=1.0 the ign and fuel tables in a turbo motor have a row for 100% load so the first set of rows run 0-100% and these can be assumed to be just like normal aspirated motor. But in the turbo application we build the maps with rows beyond 100% for example 100-150% it's these extra rows where we add extra fuel and remove ignition respectively. We don't have WOT maps at all since they make no sense in a turbo setup, we simply have rows that are indicative of cyl filling ability, and any row above the 100% indicates boost conditions.

Or think of it this way, a cyl not under boost has a theoretical max ingestion ability usually calculated like this: 3.2L engine with 6 cyl - each cyl will ingest how much air per cycle assuming VE=1?

3.2L / 6cyl / 2revsPerStroke = 0.267L/cyl

so anything higher than 0.267L can only result under boost.

Unfortunately it is much more complicated than that. Each engine has many more dynamics involved which makes each one require far different tuning. Things such as cylinder efficiency, air flow dynamics, combustion chamber heat (hot spots), valve timing, plug temps, fuel content/formula, day to day air density, etc....

I guess one example of how complicated this can all be is with an engine I tuned a few years ago on an engine dyno. It was a 964/993 based block with 3.9 ltrs displacement, individual throttle bodies and twin turbos. It was a road race engine and made 550HP at 1.8BAR of boost which was already showing signes of detonation at that level.

I removed the Electromotive junk and installed EFI TECH (the Italian version), and started tuning. Once she was basic tuned (overall fuel and ignition maps) we were making 625HP with the same boost levels but 100 lb/ft TQ more in most the mid range power band. This could have been just the difference of how we tuned vs the other shop that did the Electromotive but that is debatable (we never even looked at what they were doing).

The fun part is this...we then did individual cylinder by cylinder tuning of fuel/ignition map called trimming, then also cyl to cyl fuel timing as well (when the injector started to open, not just open time). These are things that average EFI cant do. End result was that even with individual and identical throttle bodies there was significant tuning differences from cylinder to cylinder in both what they needed for fuel as well as timing (imagine what you average intake manifold is doing). Why? Well even with seemingly perfect air flow per cyl. there are many more dynamics involved such as cyl to cyl temperature differences, cross engine air pulses, exhaust dynamic back pressure pulse differences etc...

End result was the ability to run 2.0 BAR of boost, and power now at 800HP and 200 lb/ft TQ more almost everywhere in the power band with zero detonation.

Of course the EFI system, sensors, and install/tuning was $20K ;)

"That's all we tuners really do, is validate or correct stock ignition on the dyno. It's not snake oil, it's a science that's used by OEM tuners."

"science" - what a joke! It's just engine basics - more timing = more torque.
"validate or correct stock ignition" Right, "correct", i.e. 'push' the timing!
Now how much science is involved in that? Like I've been saying for many years now,
'tuners' are like snake oil salesmen, i.e. It's all in the hyperbole (BS for many)!

Bottom line: Any engine management system (EMS) which doesn't include knock control
as ALL present day OEM EMSs do, belongs in a high school auto shop class for teaching
engine basics!

Loren,

Let me ask a question: Your 88 Carrera you show in your signature you run it bone stock? You have absolutely no performance changes?

"Your 88 Carrera you show in your signature you run it bone stock? You have absolutely no performance changes?"

My 88 3.2 has a number of mods. The best one is the carbon fiber shift knob.

Loren,

I'm asking specifically about engine mods your not an easy person to communicate with. Hello SmileWavy

Sal, This has been an informative thread. Please don't take the bait. I know it's low hanging fruit, but it takes this whole thing in another direction, and we have all been down that road before. :cool:

Jon,

Yup, I've seen this before.

Thanks for the advice.

Loren,

If "tuning" a Carrera 3.2 is frowned upon, what does a person do when they have significant mods done to the engine, ie. turbo/supercharging?

Sal and Loren,

Where do you place the knock sensor on a 3.2 Motronic car that does not have one stock? There are no cylinder bosses like the 3.6 variants. Are there certain locations that work better than others?

The most accessible place is the linkage console stud by cyl#3. It may not be the best choice but it is located away from the valve train (noise) and directly on a crank journal boss.

This will be useful for those who are installing aftermarket systems to meet the needs of internal modifications and have to tune the motor to match.

Thanks

Tippy,

A simple exhaust change can benefit from a revisited tune. Anything that alters air flow can benefit.

Most folks interested in this thread fall into this camp, this i why Loren's comments can really derail these threads.

I totally understand, but Loren always says to leave the factory stuff in place.

So I posed the question to Loren, what do you do when turbo/supercharge a C3.2?

Leaving everything stock Motronic wise boosting these will have a jug dragging the ground in no time at all.............

How do meet his criteria of leaving the Motronic stuff alone but still making big power???

You dont....

I know......it was rhetorical :)

I know, I was emphasizing ;)

Loren,
I respect your vast knowledge, but could you please tone down the rhetoric?

Thanks

"what do you do when turbo/supercharge a C3.2?"

My comments were with regard to basically stock engines which most here on
Pelican Parts have and where AFR tweaking yields little to no improved torque.
Major changes, e.g. cams, turbo/supercharge, CRs, major intake/exhaust, etc.
are another story.

Most/all 'performance' tuning posts for stock engines claim AFR tweaking yields
torque improvements which is not factual when the initial AFRs were in the
11 to 14 range. The real results come from the 'pushed' timing which anyone who
has basic engine knowledge knows that increasing the timing advance always
'wakes-up' the engine, i.e. takes no great science or expertise there.

"The most accessible place is the linkage console stud by cyl#3. It may not be the best choice but it is located away from the valve train (noise) and directly on a crank journal boss."

Right. But the difficult part is getting the proper algorithm designed, which is a very
difficult task and is specific to each engine. One would need to characterize the
actual knock/pinging/detonation signal from engine noise and convert it digitally,
(a digital filter), e.g. using the Fast Fourier Transform.

Since the late '80s starting with the 959, Porsche used knock control to allow maximum
advance timing while avoiding detonation. The 928/964/993 can selectively retard problematic
cylinders in three degree increments to a max of nine. That way the overall engine torque is not
compromised because of a few cylinders. So using knock control allows more aggressive timing
to max torque and not compromise engine reliability to the same extent as what 'tuners' do with their 'pushed' timing on the 911 3.2 engine.

Thanks Loren. I too, remember reading (here) knock control on an air-cooled is a major feat to get right due to the inherent noises that are not dampened through coolant, thin, single walls of aluminum vs thicker, dual walls that water-cooled engines have, etc., which create a lot of false readings and noise.

Knock control should only be a safety net, a well tuned engine should not hit the knock limit while running even at WOT. If a EFI system hits knock it normally simply pulls ignition out and this yields to less than best max Torque. A good Tuner looks for knock to stay away from it, they should not tune a engine intentionally to hit the knock limit.

Also worth mention is that a tuner looks at several factors for IGN. For example most EFI systems have ign compensation tables for IAT and CHT, as either of these increase the maps pull ign out as well. Knowing howto properly set these allows a engine to run more ign adv if IATs are cold, like in cold Winter weather. It is very dangerous to tune a engine in cold weather and not understand these concepts, this is a major mistake made by first time tuners.

Yes, the difficult part is getting the proper algorithm designed. You are describing a "brute force" approach that must be mapped for each engine type.

Of course, there are other ways to do this. I came up with an elegantly simple method over twenty years ago.

Tippy:

It sounds reasonable that an air-cooled engine would be noisier than one cooled by water, but that is not the case.

The SafeGuard has no problem working on VW, Porsche, or Corvair.

Partial list of some on pelicanparts that are using it:

spuggy
Nize
Steve@Rennsport
Cloggie
smurfbus
sjf
Louie928

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I run low-15 AFR's at cruise easily. It's not until I see low to mid-16's before I get lean surge. Might be I get away with it due to pretty advanced timing at part throttle.

Yes, If you can not advance timing, your call will be unhappy under lean conditions.

Subscribed

After reading Sal run 50+ degrees at part throttle, low loads and "psalt" stating the same for good MPG's, I'm going to try this soon and see how it goes.

Hey eporsche you need to answer your PM's

This is an excellent article written by OEM engine management expert (Allen W. Cline) in Detonation and Pre-Ignition I thought folks may enjoy the detailed read:
Engine Basics: Detonation and Pre-Ignition by Allen W. Cline

This article explains Detonation and Pre-Ignition in very clear easy to understand terms. Pay very close attention to his points about Cyl Temps throughout the article because in our air cooled engines these tend to rise extremely quickly. You'd be very surprised to learn that CHTs rise very quickly without being at WOT. The biggest offender is lugging a 911 engine, where lugging is a term meaning that you are applying moderate to heavy load at low RPMs like 4th gear at less than 2500RPMs. I have a CHT monitoring system in my 3.2L and you can see CHTs rise amazingly fast under this condition especially in HOT 90F+ weather. Do this to our motors then pull a WOT run and your in big trouble! I never run my car below 3000RPMs in hot weather.

Yep this is a common misconception that by running at lower RPMs you are putting less load on the engine and creating less heat. The opposite is true especially on aircooled engines with a direct drive fan. More RPMS = more air cooling, more oil flow through the cooler and lower load per firing event in the cyls.

X Load/Y RPMs = load per revolution

Good stuff!

Very interesting article. Thanks

I am nothing but a rookie that wonders, but here goes...

On the turbo side of the pelican forum, there has recently been a thread about auto tune features in modern efi systems, and wether this is possible or not.

My question is regarding ignition timing and tuning.

Wouldn't it be possible to use a combustion pressure sensor, I.e. one of these:
https://www.avl.com/pressure-sensors-for-combustion-analysis

Based on the peak pressure and cam/crank position sensors, have the efi adjust ignition timing so peak pressure occurs at 14 degrees after tdc, optimum?

In theory you could use autotune but it's not that simple. The very best way is to use a load dyno to determine Peak Torque for a given condition. It simply turn out that peak torque occurs around that 14deg peak pressure range.

The other much more dangerous issue is that peak torque can't always be done because detonation prohibits it.

In the past I've also mentioned how important it is to understand the effects IntakeAirTemp has on peak torque. A common mistake is to tune on a cold 30F day, dial in WOT ignition and call it a day. Huge mistake! The ignition values that can be used with cold IATs won't work once IATs get hot like 90+F! Good ECU systems have IAT and CHT Ignition comp tables, the stock DME has these built in. Knowing howto properly setup these tables can really help get some extra torque at cold temps. But you must dial back ignition as IATs and/or CHTs rise.

Wouldn't the pressure sensor also be able to pick up detonation? Not only would we be able to see an abnormal rise in pressure, but it could also be identified as being "out if timing" when analyzed in relation to cam timing etc. together with regular knock sensing this would further protect the engine as well.

I am not a proponent for complete autotune, I just find this an interesting discussion enabling me to understand a little more based on your feedback - thanks.

Yea I guess you could use these devices to help find Peak Pressure or Detonation whichever comes first. I do think this type of device would be very useful tool to help tune and help ID detonation. I suspect this type of sensor and it's related processing hardware is expensive. Plus keep in mind that the conditions from cyl to cyl differ and you could have detonation conditions in one cyl and not the others. Some cyl run leaner or richer than others, for example I've found that the RHS (cyl 4-6) in my 3.2L run leaner than the LHS, I suspect it has something to do with the distance intake air needs to travel through the intake to the RHS which has slightly longer travel? The difference is not much but it is noticable by like .1 to .2 AFR.

FYI

Spark plug combustion pressure sensors for tuning - Engine - GT-R Life

This would be cool to transfer to a 911:
Trionic - Wikipedia, the free encyclopedia

I think I remember pelican BeepBeep mention this on the turbo forum earlier. Pretty cool.

Very neat article - thanks!

For the tuning crowd. why not just install a knock sensor? After all, that's what all the OEMs currently use.

There are a few reasonably priced aftermarket knock sensors available.

I would love to have a knock sensor and MS II has the capability to use one but it takes an amplier that cost more than my entire ECU to make it work.

No affiliation, don't currently have one installed on my car, though I intend to do so and then get a SW chip. Price is not unreasonable, internet search suggest it does what he claims it does.

J&S Electronics SafeGuard Indivdual Cylinder Knock Control