No. If it dets, it breaks. I'm sorry to say this, but it doesn't sound like the dyno was operated correctly.

Well, I'll just continue to test my map to make sure I have tuned out all the det. Then I'll pull a little extra so that I know it's safe. I'll assume that my current setup has changed enough that my old tune is no longer valid.

I can say that when I reduced the timing from the areas where I heard det, there is definitely a point where the motor sounds like it is in a happy place. Very smooth sounding.

(zack morris's phone)

I've run the map I posted for over 4 years. Fwiw.

I should just pull timing until I don't hear anything and leave it. For some reason I get hung up on leaving power on the table. Is there a rule of thumb for subtracting timing as you increase kpa. i.e. 2 degrees for every 30 kpa? I think I'm going to just leave my 180 row conservative, and just reduce the advance as I increase kpa based off that row.

It doesn't quite keep me awake at night, but you'd be surprised how much I think about this stuff.

It looks as if perhaps the tuner had started with his small block Chevy map and just dialed in the full throttle portions of the map, leaving the low load sections unchanged. Was this tune done on a steady state dyno, or an inertial one like a Dynojet?

You can say that again.

Did you have any sort of EGT information available to you? That might be the third piece of the puzzle after detonation and power optimization.

double check your base timing for -10*. I helped a guy tune his car once and it was knocking bad because it was -15*.

It was on a steady state dyno. I drove quite a distance because it was steady state. He didn't really tune the spark much in low kpa areas. I checked base timing, and it is good. No EGT info. I'm running the timing on CAS only, no crank trigger. I guess it could be changed slightly at high rpm. I have the hardware latency set so it maintained 10 degrees through about 4500 rpm, I didn't check higher than that.

I'll pull a little timing out and see how Brain's map feels in the lower kpa rows. If it doesn't feel lik it looses anything, then I guess it's better to pull some out. I'm taking a break right now from tapping my IC for the IAT sensor. Hopefully I'll have to retune fuel because my temps are lower. Right now fuel is tuned at 100 degrees.

At this point I'm tired of paying people to tune my car, but maybe it's worth one more trip here in town. The first tune was not on a steady state, but it felt great when it was done. No knocking on the knock sensor I had hooked to my LINK.

I think your problem is you are paying the wrong people to tune your car - either that or not paying them for enough tuning. A good tuner would have dialed in the whole spark map. The low kPa areas are key to good throttle response, drivability, and fuel economy.

Would you go into further detail on the timing values you would relate to gas mileage and throttle response?

I was under the impression that high advance in cruise is good for mileage. I'm not really sure how fast one wants the timing to transition when getting on the throttle from idle. My knowledge is from BB mopar. Timing all in by 2800rpm.

High advance makes for bad mileage - the right amount of advance is what makes for good mileage, and going significantly higher will make pressure rise too fast on the compression stroke, reducing engine efficiency.

Big block Mopars will need a lot more advance for these reasons:

1. They have a bore that's about an inch larger. It takes more time for the flame front to travel from the spark plug to the edges.

2. The cylinder heads don't do as much to promote burn speed. The open chamber wedge heads don't have any squish to speak of, and closed chamber ones can lose their squish on lower compression builds if you don't use a dished piston that mirrors the chamber shape.

Bottom line, optimize the timing in every cell you're in for optimized performance. If you're building a drag car that you only care about full throttle performance, you can get away with only tuning the top cells; if you are actually driving at part throttle, you need to get that tuned too.

Thanks, I guess this is why I seem to get crap mileage and a lot of others seem to get much much better mileage. Thanks

Great info !!!

So from the point where you hear det, how many degrees would you say peak power occurs ?

We've never deliberately bounced a motor off the detonation limit in every load cell to find out. That tuning approach would be seriously dangerous to try.

Thanks Matt.
I don't plan on doing that either but the fact that I will be using a Det can implies that I will be hearing (hopefully) at least the onset of faint detonation.
The plan is to compare a few of those points to my existing table.
I read that there is a relationship between the det point and the optimum point for power. I am just trying to establish a relationship if one exists.

Cheers

P

Only for a single given engine and fuel, and this point will move arbitrarily based on RPM and load. A simple example of why this can't be a single amount: Going from 87 to 93 octane won't move the optimum timing for power at all in most cases... but it'll sure move the detonation point!

So to map that out would require both a full dyno tune and a second tune where one maps out the detonation point across the full RPM and load range, and hoping you don't grenade the motor on the second test.

Gotcha!

Thanks man!

This is great suff and it reminds me of Automotive Technology that I pusued in another life. :cry:

As for my spark able I've played with it and played with it ...
The car runs fairly well. It will ping slightly under heavy load and boost if I uselow ocatene fuel so I don't.
Guess that means I'm at least somewhat safe and not too far off the mark.

The other day I drove a non aspirated Miata equiped with an MS3. It was really responsive down low and very smooth.
I looked at the tiing map and to me it seems that mine is not advanced enough but then again it coud be a fact of the resolution diference between my Ms1 and the Ms3

What do you gus think ?

Resolution shouldn't be a problem with proper scaling and the fact that it uses interpolation.

Post both maps if you can.

Using the knock module I have really had to pull timing in a bunch of places outside of boost.