Great post here. It seems that there can be significant dyno variations, as Eric may have found between the one at Nationals and the later one used. I had my car dynoed a number of times at the first Miller nationals (5 or 6). It ranged between 127 and 134 on the same dyno over the course of 4 days. I did nothing to the car between dyno runs. Getting that engine up to 141 hp sounds great and mainly from fuel adjustments. What would he have done at Nats with that tune????

BJ makes it sound like different gas can create issues for our cars. Sounds to me like I should put in a A/F gauge system and put it into the Traqmate, as Eric suggested, to be able to adjust for different gas types at the track. In California, our gas changes between winter and summer blends.

Eric, can you please post details of how to log this on a Traqmate system, including where to buy the necessary parts and pieces. Will any A/F gauge system be able to go into the Traqmate. I assume using the wide band version would be better. Is that correct? I also assume that, at the track, the only safe way to adjust for the gas would be to use the FQS on the ECU rather than trying to use the AF method. Again, is that correct? I have never opened up an AFM and, frankly, would prefer not to if I can avoid it.

Jim,

I think Joe made the fuel comment, but it gas can definitely have an impact. Fuel varies greatly from state to state. There is also the issue of E10 vs. plain old gas. Of course humidity and elevation also have an impact.

Really, there is only so much that can be done on a 944 Spec. The FQS lets you make small adjustments to fueling, but nothing else. It also lets you retard ignition timing, but you certainly don't want to do that.

The AFM is the only was to make big adjustments in fuel delivery. Another thing to consider is the early vs. late AFM. I've been told that late ECU ignores the AFM at WOT, but that the early AFM still uses the metering. I'm not sure if this is true, but is another thing to consider.

-bj

I'll get into this in more detail when I have more time, but a few things:

1. The 141 HP was achieved with thinner oil than we typically run - changed d/t 30 degree temps at the event prior, and both cars tested gained about 2 HP baseline, so that equates to about 139 HP - still impressive, as is the 5 HP gain from tuning (this is probably not typical, but shows the potential of tuning).

2. Don't be afraid of AFM tuning, - it's not hard, and very worthwhile, just do it when you can monitor A/F ratios so you don't accidentally run it too lean and cause damage. We've found many Spec cars are running pretty lean after removing the cat., etc. improves airflow over stock. Tuning via the FQS switch is pretty limited, and not the nice step-wise progression that each click on the AFM gives you. AFM tuning only moves the whole curve up and down, but you can get nice, steady A/F ratios if your AFM is in a good state of tune.

3. The late cars respond to AFM adjustments just like the early cars, and fuelling is plenty adequate to make our motors as rich as you could want them.

4. We've found that Dynojet dynos can be pretty consistent if you set things up correctly. Most dyno variation comes in cars not showing there true potential - in large part due to fluids not being up to temp. With the 20/50 oil we use, a car can gain sometimes as much as 8-9 HP as it warms that heavy goo into something slippery. High readings are much more rare, and typically due to dyno operator/input error - using STD correction instead of SAE will results in numbers several HP high, for example. If you have the oil temp up to >160, tire pressures set the same, fans consistent (on), make sure you're using SAE correction, smoothing factor 5, then results fall within a tight range. I now have somewhere around 50 dyno pulls on my car between nationals & testing recently, on a couple of different Dynojets.

5. Innovate, and AEM make good wide band A/F ratio meters. DO NOT use a narrow band A/F meter - it won't read in the ranges we need to make power. The one Neal Agran & I use is here: www.summitracing.com/parts/avm-30-4100/. It has a 0-5V output that the Traqmate can log, and turn into real-time A/F ratios. The how to for the AEM gauge, is here: http://forum.traqmate.com/viewtopic.php?f=26&t=1296

6. Dan would have been significantly more competitive with 5 more HP - that guy can drive! Poor Dan is kicking himself now!

Guys, the early and late AFM's all work the same with regard to WOT (Wide open throttle). This is controlled by the TPS (throttle position sensor or switch).
The TPS has a two state switch. All it knows, and tells the DME, is:

1. I'm at idle.
OR
2. I'm at WOT.

As soon as the throttle starts to move off idle, the TPS sends a ground signal to the DME (pin 2?) and gives over control of the air fuel ratio to the AFM.
When the throttle gets to the WOT point, the TPS is switched the other direction and sends a ground signal on a different path (pin 3?) to the DME. This knocks the AFM ( and O2 sensor) offline and gives control of spark/fuel back to the DME, which understands the command as " Gimme all you got!". Timing is advanced, fuel is maxed out.
So the DME controls your mixture at idle and WOT, the AFM controls everything else in between.

Eric,
1. Did you guys try affecting the mixture by turning the 5mm allen head in the AFM bypass?
2. Why did the fans being on affect the HP measured?

Tim, we did not try altering that. That would presumably fine tune A/F's even more precisely, but probably with less range of adjustment. The steps in AFM "clicks" seems to be a fine enough adjustment to be useful.

I can only presume the electrical loads of the fans. costs the 1 HP loss. Maybe we're imagining things, but it seemed repeatable between the two cars. The fans do draw a lot of amps.