Dyno Report

#21

Ranger wrote:

Reasonable? … yes, but what were the BMW engineers’ reasoning when they pick the particular spark plug? How about the BMW accounting guys?

#22

Yep, he’s at O’fest this week.
Sure could use a mentor…

RP

#23

Ranger wrote:

[quote]Steve D wrote:

[quote]Ranger wrote:

[quote]-Replaced plug wires (a colder NGK then our Bosch plugs) and coil.
[/quote]
Re: colder plugs - Since we can’t modify the engines beyond an 020-over, what advantage is there to a colder plug? Won’t a colder plug foul easier?[/quote]

After the first unspectacular dyno effort, you know, the one before the second unspectacular dyno effort, I asked around on a variety of ignition related issues. I had a particularly good talk with an NGK technical guy. There was consensus that race cars like colder plugs then DD’s. At the time I didn’t know what cold and hot meant in the context of plugs, but for everyone’s edification, a cold plug is designed to absorb less heat from the combustion chamber, and radiate heat better to it’s metal surroundings. Therefore a cold plug reaches a colder steady state temp then a hotter plug.

So I figured that I’d try a one step colder plug then the standard Bosch. Bosch didn’t make 1 step colder so I had to go to NGK.

I don’t know much about how different kinds of spark plugs behave differently. I can read marketing stuff as well as the next guy, but I really don’t know spit about spark plugs. All I can say is that there was consensus on the issue and their reasoning (that race cars tend to operate at higher temps then DD’s) seemed reasonable.[/quote]

In the early 90’s, I started racing with a Honda Civic and a Webber carb. We had an air density meter, had to read plugs, use an exhaust gas temp gauge, change carb fuel jetting, change air corrector jets, and use cold plugs.

Thank you fuel injection!

The cold plugs were one factor that kept us from melting pistons and the cylinder head, if we jetted the carb too lean or the air density was too high. The water temp would also go up if we ran the engine too lean. We also used a timing light to set the ignition timing and if we went too far (too advanced), it would do the same.

Our engines are stock or very close to stock so I use the stock plugs. Unless the car is overheating due to a lean running condition, the stock plugs should do fine.

Carter

ps. A cold plug has shallow ceramic and a hot plug has deep ceramic.

#24

My engine does not run hot. But I’m perfectly happy experimenting with different plug types. I’m not sure that I’d see different dyno data based on hot/cold plugs tho. I’m not sure that the motor gets hot enough on the dyno for hot/cold plugs to matter.

Re. lean. That reminds me. One thing I noticed from my dyno reports is that my engine runs a bit lean almost all the way thru it’s rpm range. It gets richer and then too rich at around 4500-5500 and then goes lean again. It’s not super lean, but it is a little leaner then the (non-BMW) dyno guy thought it should be.

This behavior was unchanged thru multiple ECU’s, AFM’s and everything else I could think of.

I haven’t seen other folks fuel/air mixture in the published dyno reports, but how say you guys on our fuel/air mixtures? Do your dyno reports show the same lean behavior?

#25

Ranger wrote:

Here is my AFR curve from the runs just before Nationals. This is a fresh rebuild with a brand new AFM and blueprinted injectors. Don’t know whether this curve is good or bad, though.

#26

14.5-15 to one is dangerously lean under load. That can be improved some by tweaking the AFM, but the real problem is not enough fuel pressure. The rules need to allow an adjustable fuel pressure regulator to protect the motors from meltdown. The AFR line should be as flat as possible all the way across the rev range. Steve, you need to ritchen the motor…it will also improve torque. Chuck

#27

Here’s mine The dyno guy was all hot that I didn’t have a way for him to adjust the mixture such the ratio would stay near stoichiometric (13?) thru the rpm range.

#28

If the motor runs dangerously hot at stoich (14.7), wouldn’t that show up in excessively high oil temps? I don’t monitor exhaust gas temps. It seems like the AFR curve is decent over our useful range (4500-6200 rpm, slightly lower for a 2-3 shift).

I am interested in the data behind the “14.5 is dangerously lean” comment.

With a non-adjustable FPR, stock injectors and the ECU reading from a set map in open loop at WOT, what is there left to adjust to impact AFR?

#29

I think that Chuck’s point is that we have no way to tune the engine. With the current rules all one can do is to try different FPR’s and DME’s in the hope that a better combination can be found.

#30

Jim -

Doesn’t the DME reference a fixed fuel map at WOT in open loop (e.g. at high rpms)? If so, I don’t understand how a different DME will help tune this problem.

That leaves us with trying to find a cherry FPR with the strongest spring (or a nice weak vacuum line that will suck itself shut :laugh: )?

As I understand it, running at stoich is good for minimizing emissions and bad for power. I am trying to figure out if I should worry about a KABOOM-type problem given how my car is running.

#31

PS - Will a significantly stronger fuel pump (think Jones’ biceps) help overpower the stock FPR to get higher fuel rail pressure or will that just blow other crap (think Jones’ tendons) like lines apart?

#32

For max power, you should look at 13 to 1. For max torque, slightly richer, 12.5 to 12.6 to 1.

With cast pistions, you are running on the ragged edge of cooking a motor at 14.7 to 1. I understand that there have not been problems to this point, but as more people get involved and build new motors, this will become a real problem. It should be addressed now: be proactive. Chuck

#33

cwbaader wrote:

This synchs with what my (non-BMW) dyno guy said.

Didn’t Robert Patton do some experiments with fuel pressure a couple yrs ago on a dyno? As I recall he said he couldn’t make more power. It would be interesting to see what was going on with his F/A ratio as he varied fuel pressure. Maybe something got overlooked.

#34

I have spent many hours on the dyno trying to adjust F/A ratio. I am lucky since I run a MegaSquirt and adjustable FP. My F/A line is dead flat at 12.9 to one from 3000rpm to 5500rpm. No bumps, no jumps, dead flat. Consequently, I don’t have a gross loss of power at the engine harmonic, as do the Spec motors. We should be able to adjust the FP. CB

#35

Where do you guys measure the A/F ratio? Tailpipe? Stock O2 bung? Additional bung?

#36

cwbaader wrote:

Maybe we can get our adjustable FP regulators back next year. We just have to coach the issue in terms of engine longevity. Lean mixtures are dangerous mixtures.

I’ve had a lot of success getting changes to the rules. There was the issue of…Ok, well, I can’t think of any successes.

But I would certainly be curious as to how F/A ratio responded to different fuel pressures. Hey Robert, can I borrow your adjustable FP regulator for some testing?

#37

OriginalSterm wrote:

Dyno guy did it at the tailpipe. I’m completely new at this dyno and engine management stuff so I don’t hardly know good ideas from bad.

#38

yea, I bought an adjustable FPR, over $200, just to have it outlawed…rules stability??? Will anyone in the SE care if I run it? I will be running my new junkyard motor on the dyno, possibly tomorrow, will be interesting to see…

Al

#39

FARTBREF wrote:

Only the guys who finish behind you. Which could get tough to figure out at IFU3. :laugh: :huh:

#40

My test with higher than 40psi fuel pressure (test at 50 and 60psi) proved that the BMW engineers were/are/was pretty smart. With the stock Bosch unit the A/F ratio bounced up to 14:1 at times, but the HP and torque numbers were about 2 higher. Or was it cold soak…or hot soak…or dyno burp.

My conclusion is that the money spent for FPRs is wasted money and that allowing them is like allowing a non-spec exhaust or a non-spec intake…another unknown to have to wonder about.

I can bring all of the Dyno test for all to look at. Just say yes and remind me prior to CMP.

RP