Loren, a much better post I must say!

Jeff

Good point - those motors did indeed have eletronic ignition and two separate ignition systems (mandated for airplane engines).

Pinging can often be heard under load at WOT throttle, not necessarily off-the-line acceleration...

-Wayne

So in relation to this I'm thinking about installing an ECU for ignition on my Hi compression 2.4. I've heard that aircooled engines are "noisy" and won't work well with the detonation sensors. How well would a ECU with anti-detonation control work with this motor?

A very good post and is one of the reason I hope to go with an ECU for ignition.

I've given a little thought to the preignition issue myself, particularly in light of the louder intake/exhaust on my car. While I don't think I've ever heard the car knock, I'm not sure with those mods I would. I am religious about using 91 or 93 octane and not using large throttle imputs at low rpm/high gearing.

This post is one of the reasons that this forum is so great.

The effectiveness of your system will depend entirely on the effectiveness of your knock sensor. Tim is right - it's difficult to sense knocking on these engines. You might want to ask Rick (www.clewett.com) what sensor he uses on the earlier cars - I don't know the answer to that off the top of my head.

-Wayne

If you rely on your ears to detect detonation (sub-audible or the audible kind), your bank account is at serious risk. :)

I cannot tell you how many SC, Carrera, and Turbo engines I have opened up to find broken rings and trashed pistons from detonation. The owners' all told me they NEVER heard a thing.

Air-cooled engines require a margin against detonation as that threshold is dynamic, not static.

Amen, a well written, informative thread.

As Steve has said, a "MARGIN" is required. This means that you just can't
"push" timing arbitrarily to get a desired throttle response. For those that
fail to understand, I'm sure he'd be more than willing to re-do those motors
that had lacked the "MARGIN".

Even better, in the case of the NBD 3.6 chip, is that you can move between stock settings and performance settings by reaching under your seat and toggling a switch. That way, if it's hot or you're running plain old 91 octane gas, you can run on the stock setting. But on days where you want more, you can mix in five gallons of 100-octane, and switch over to the more aggressive side of the chip. I think it's a smart way to engineer a performance chip, since it adds a little insurance on top of the knock sensor.

Great thread, by the way. :)

i'm a little confused here guys so help me out. i thought this was common knowledge.

i thought the whole point of the aftermarket chips was because usa cars and row cars ran different chips and some gains were there to be made. i also thought they were used to match engine mods to fuel/ignition - like swapping out the cat or something.

Well, the USA and European cars did run different chips. Why? The only reason I know of is because of smog regulations. So, whereas the European chips were designed and mapped with a less restrictive set of requirements, the USA chips had to restrain the engine under certain circumstances in order to satisfy smog requirements.

You're right - there are gains to be made by switching, however, they are somewhat minimal in the grand scheme of things. You're forgetting on the 3.2s that the Euro Pistons & Cylinders were higher compression than their USA counter parts. While not a major difference, it does help account for HP differences between the two types of engines.

On your second question, you're also right. The chips can be used to modify the computer to match certain modifications to the engine, like changes in the exhaust. However, again, these gains are many times incremental, not monumental. Most chips get most of their "throttle response" from advancing the timing, which then (as we have mentioned) increases the risk of detonation.

-Wayne

wayne, thank for that. yep, i unknowingly bought a usa spec car - in europe!!

noone has claimed monumental increases in hp with a chip. i would think anyone that has taken any interest in the chips on pelican would have realised that the gains came from ignition and fueling changes. surely its down to the chip supplier (their responsibility) to ensure that detonation/pinging isnt a problem, and to advise if high octane fuel is required.

i am sceptical of "seat of the pants" claims made by a lot of people around here (but if they feel it good luck to them!) but still dont see anything new here.

There is a tremendous leaning towards the placebo effect when you measure by the seat of your pants. I've sold Bursch mufflers to 914 owners who swear their car is 15 HP faster with it installed. In reality, the muffler is heavier than stock and offers no performance improvement (beyond a better sounds). But I don't try to convince them otherwise.

I once tried to explain the truth to a friend of mine who insisted that his car was faster on a full tank of gas. Technically, it's the other way around, but the mind is a strange thing that way.

-Wayne

Wow, what a revelation.
You mean to tell me that if I advance my timing I will get more horsepower but I'll have to run a higher octane? Who would have thunk.

Am i also to understand that instead of an engine running between 14.6 and 15 to one air to fuel ratio by weight I can get more horsepower if I map the fuel injection so that it goes closer to 12.8 to one at full throttle but my fuel economy will suffer?
That is just too much to absorb. How come no one has ever come up with this information before now? (yes, I am being overly sarcastic, it's been a long night shift).

I once listened to a guy who tried two different grades of gasoline while his 3.6 was on a dyno. Predictably, the engine made a little more power with the high-octane gas. His conclusion was that high octane gas releases more power. More BTUs. I did not have the heart to tell him that the additional power came from the increased ignition advance that the engine automatically applied when it noticed that the high octane fuel was more detonation-resistant.

Another reason the stock Euro chip is different from the US chip is that in the 80's high octane gasoline was not as readily available in the US as it was in Europe. Porsche dialed down performance to account for the probability that high octane gas would not be used.

Running a stock chip with a stock exhaust on 91 octane or lower makes perfect sense. The factory did their homework to achieve performance in this scenario. The point of changing a chip is to recognize the fact that 93 octane is now readily available in most places (allowing for changes in timing as the risk of detonation decreases) and to match engine characteristics to other modifications (i.e. exhaust).

Factories have to produce a one-size-fits-all solution, tuners don't. I appreciate the friendly tone here, but hasn't this all been covered here before?

An additional "danger" with some of the aftermarket chips is the less than responsible rev limit reprogramming. I've used a few different chips over the years and some chip makers actually eliminated the limiter. Not good.

Some posters consider this thread somewhat trite info. The reason for initiating
this thread was to inform the many, it appears, that really don't understand the
basis for the performance improvement from most performance chips and the
caveats associated with those chips.

Most may think that Porsche/Bosch lacked the wherewithal to really gain max
performance and some computer whizs have been able to "hack" the DME
and "discover" some hidden horsepower. As this thread should now convey,
this is not the case. For those that already had this insight, I apologize for
posting something that seems obvious to others.

Not more peak HP, just more lower end torque, or throttle response...

-Wayne

With more torque comes more HP, as HP = Torque X RPMs. If at the same RPM
the engine produces more torque, you get more HP at that RPM. We're all basically
talking about the same things and trying to apply a little reality to performance
improvements.