348 Hub Dyno run at Competizione

Sounds good. What does your fuel/air curve look like over the test run RPM band?

 

His system can probably print it out for you. With it, you can see if having a new chip made would give you a great deal more HP or not.

 

im in . ill be there saturday to discuss.

 

Yeah, you'd benefit from a custom chip based on that graph...but that chart shows you running so lean that you would benefit from simply turning the CO screw on each MAF to reduce the resistance shown between pins #1 and #6 (or #5, they go to the same point).

Some of the hot-rodders and racers could give you a better fuel/air ratio number than me, but you want to be closer to 12.5 than to the 14:1 or so that your chart is showing.


I'd say that a good first guess would be to set your MAFs around 350 ohms resistance instead of 383 (presuming that they were both set to 383 when those graphs were made).

 

Hey Eric, congrats........ We'll have to go drive around when we get some good weather.

Did you get the HP /Trq graph too? I'd like to see that.

 

+1 !!!!!!!

 

Yup. I'd guess that he's got at least 10 foot pounds of torque that he could gain just by using a flatblade screwdriver on each MAF. No chip required.

That will translate into added hp across his RPM band. Enough to feel by seat-o-da-pants!

 

No Doubt - As my car is running decat + X-OST + K&N air filter - should i reset my MAF's to 350 ohm? (mine are currently bang on 383 both sides)

 

Yikes! I hesitate to recommend just guessing at the right ratio without so much as a fuel/air curve from a dyno run.

I mean, that's like something I might try myself! Don't be like me!

You probably are running a bit lean with those mods, but you would be doing yourself a favor to either do a real dyno run first, or to plug in an Innovate LM1 wideband system in place of one of your O2 sensors.





(That being said, you could probably dial down to 370 ohms on both MAFs until you get to the dyno run without risking too much, considering your mods)

 

ND,

Thanks. The only reason i ask is that K&N filters tend to lean off the mixture a little due to extra flow?

Why would the dyno'd car be running a poor AFR with only exhaust and cats being changed? Surely a problem exists elsewhere?

 

Well, my first guess would be that his MAFs are set above 383 ohms. If so, then he needs to drop them down 30+ ohms or so and do another dyno run to see if he's dropped that fuel/air curve down to be closer to 13.6 at mid-range and 12.5 at top-end RPMs.

Of course, every car wears, so fuel/air ratios can change as your fuel pumps put out a little less or your fuel filters get clogged over time or as compression and leakdown ratios change with engine wear, etc.

Or it could just be that's how M2.5's were mapped. For all that I know that's the factory tuning on perfect display.

That's just speculation above, of course.

What's not speculation is that he can gain more HP with a bit more fuel. And his fuel/air curve is off so much that dialing in an across-the-board fuel boost via the MAFs makes sense for a first step to that end.

 

Well, an ideal gasoline air/fuel mixture is at the Stoichiometric ratio (around 14.7 to 1, but gasoline with additives like MTBE stoich at 14.1 to 1, so this ratio isn't set in stone based upon what your region supplies in fuel).

However, maximum power is usually considered to be in the air/fuel range of 12.5 to 13.3. Lower numbers are richer, by the way!

The caveat is that leaner mixtures typically rev faster...so you want to be slightly lean while you're revving up into your power band, then slightly richer than Stoich to make the most power (assuming that your prime goal is to go fast).

Now, where the perfect curve would lay for 348's is best answered by one of the tuners or racers on this board, not me...but the answer is going to be a curve that shows higher numbers than 13.3 in the low/mid RPMs range, and that gets richer (e.g. down to 12.5) into your high RPM band.


Your curve as graphed is too lean (numbers too high) at every RPM, so there's lots of room for improvements...doubly-so if your area makes you consume MTBE-additives for smog control.