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Dyno time, N/A tuning guidlines?

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S351 R

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Joined
Nov 3, 2002
Messages
66
Taking my 427W, 10.5:1 cr N/A motor to an engine dyno with B2B FAST.

What Im figuring is that best power will be in the 32-36* timing, and 12.5-13.2 a/f range (slightly richer at pk tq).

Assuming most will agree with these ranges, is there a relationship between both as I sneak up on the power, ie. how does timing effect A/F (& vice versa), and does one value need to change along with any changes to the other. This isnt max effort (85% street...) and don't want to need 50 dyno runs to get it right.

Also, should I 'turn off' all my AE tables to keep the added fuel from skewing the % correction to more quickly dial in VE?
Thanks
 
I would actually recommend that you leave the closed-loop ON while you dyno tune. Provided that you have enough time, do the following procedure:

1) Do one pull and discard the numbers. Your first pull will always show more power than subsequent pulls, so the number cannot be used for tuning (but you can brag to your friends).

2) Set your target A/F to 12.5:1 and do a "baseline" run in closed-loop, and do a log that includes the % of WB correction.

3) Note the % correction, and make slight tweaks to the VE table. This should reduce the % correction on the next run.

4) Make a "trial and error" adjustment on the target A/F ratio. For example if you were at 12.5:1, try changing to 12.2:1.

5) After a few minutes of cooldown, do another pull. Now take the GRAPH of this pull (not just the peak number) from the dyno printout and overlay it against the "baseline" pull to see whether you are making more or less torque (which is more important than HP) at each point on the graph. Figure whether torque went up or down at each point.
Note: You *might* want to have different A/F at different RPMs. That's why you look at the whole curve, and not just the peak number.

6) Tweak the VE table again slightly to reduce the O2 correction %.

7) Keep making pulls and overlaying the graphs until you are satisfied that your A/F is making maximum power (and your oxygen sensor is making < 5% correction).

Now move to timing.

8) Starting around 34 degrees, try adding one degree of timing to see if torque increases or decreases.

9) After a few minutes of cooldown, adjust timing by another degree to see if torque increases or decreases.

Note: Optimum timing may or may not be just less than where you don't get pinging. For example if you get knock at 37 degrees but not 36, you might still make optimum power at 34 degrees. (This is especially true for nitrous engines)
Note: Again, you might want different timing at different RPMs. In my car, I run 1 degree less timing above 4400 RPM than below.

10) After you have found optimum timing, try one last run making the A/F ratio slightly richer (i.e. move from 12.2 to 12.0) and see if that helps your torque. If it did help, it means that you were slightly lean when you were advancing your timing, and the slightly richer mixture will help you get a tad more torque.

This whole thing will take you 10 - 15 runs, but you'll get your timing, VE settings, and A/F ratio exactly where you want them.

A few notes about running on the dyno:
- Allow the engine temp to stabilize between runs. At least, you should have a big fan blowing on your radiator constantly. The dyno I go to has my radiator sticking right out the front of the garage door, so the operator lets me spray water from a garden hose on the radiator. (The engine creates of lot of heat during a run, and you want this to fully stabilize before your next pull so you don't have excess heat and get some abnormal detonation.) The engine should be idling during cool-down so that the water gets circulated.
- Run the same fuel as when you run the track (or your illegal street races or whatever). Make sure it is fresh.
- Make adjustments to your transmission if necessary to avoid accidental downshifting during the run. Downshifts can create "spikes" and false readings because of the sudden change in gear ratios (the dyno's torque calculation depends on a constant gear ratio during your pull).
- If possible, do your pulls in 3rd gear (for automatic transmissions) so that you have your most efficient 1:1 coupling.
- If the dyno has a Wb sensor, use it only as a point of curiousity. Since your built-in WB sensor will probably not match the dyno's, and your car will only be using its own sensor in the future, that is the sensor that is most important for tuning.

EDIT: I just saw that you said you don't want to run 50 times on the dyno- therefore just adapt the above procedure as best you can during your limited runs. I think you'll end up around 34 degrees of timing and 12.2 A/F ratios, but every engine is different. I'm guessing you'll also want 96 - 98 octane because of your 10.5: compression ratio, but this depends on a bunch of factors (like cam design).

-Bob Cunningham
 
Wow! Great write-up, thanks Bob!

Good to know I can do one part at a time. I will definitely leave it in closed loop, but should I zero-out or at least minimize the three AE table so that throttle input won't skew the VE requirements?

FWIW, this will be on an engine dyno so I wont have to worry about cooling the radiator/motor down - dyno electric water pump can keep the water flowing to recool quickly between runs.

Also, I will have to "re-tune" a bit once its in the car to account for shifting etc.
Putting it on the engine dyno is more for peace of mind that everything is working well, no leaks, making the power it should, etc, rather than having to mess with repulling if something is wrong.
Thanks again.
 
This sounds like a tuning session on a fresh engine without a base tune? If so I'd take it SLOW.

On my dyno with a new combination that is run for the first time I load a base program in that I know will get the engine started. I setup the fueling rich and the timing VERY safe. I break in the motor as normal and will dial in the VE table so it's somewhat close.

On my dyno I can load the engine to hold in any cell range I like. After break in I will do the normal inspections and then start tuning the VE table in while loading the engine. I try to do as many cell areas as possible. I keep A/F ranges safe and again timing very low. If I think an engine will like 36 I'll keep it down to 30 for total timing. Watch the timing when the motor has a load of say 150 HP and it's turning 2500 RPM, keep the timing LOW to avoid potential detonation. It's VERY hard to load an engine on the street like this but VERY easy on the engine dyno. So again, window pane the VE and timing maps next to each other and keep a VERY close eye on both to make sure you don't have "poor choices" in those cells.

After I rough out the fueling and timing I then make a few lower RPM pulls. Dial in the accel maps so that you have crisp throttle response. Sisnce the dyno will load the motor the hold it for a second prior to the pull being made it's not affecting the VE. Datalog these pulls and make corrections.

If I think a motor will max at 6000 I may start the first run at 3000 or 3500 and pull to 4500, maybe 5000. I won't make a hard pull until I know the fuel map is fairly close and slightly rich throughout the RPM range.

The lower you start the pull the HARDER it will load the engine. You will also see on an engine dyno the loading on the VE map will occur in areas you will NEVER see on a street car. You need to be VERY aware of where the dyno is loading the engine and where you are on the VE map as it's quite easy to think you are safe and you are DEAD LEAN.

Once the fueling is in good shape after it's logged with a decent pull from say 3000 to 6000 I'll slowly creep up on timing. You can't hear detonation on the dyno but you can see the affect both in torque output as well as in major cases old faithful out the breathers. So be careful. Optimizing the tming map will have some affects on your VE table so you will want to go back and datalog the fueling and correct as needed. I would not get too anal about this until you get the car on the road.

On the road you are correct, there will be some fine tuning you will need to do but the car should go down the road and run OK. On the road it should take you about an hour of driving around with another person to get the car running real well. Again, I make sure there are no weird numbers in the timing map and start with the VE and A/F table first, get the throttle respose clean with TPS and if needed MAP tables then try to dial in some timing under part throttle conditions and then full throttle conditions.

Of course there is the battle with starting and idle that you'll just have to play with on your own to get right once the base maps are set.

Without a doubt on a new tune like this I'd use 110 race gas just to be safe. Once the tune is close you can cut it down some just to see if there is any change in the tune.

Plan on 2-4 hours of solid running dyno time messing around with things.
 
Thanks! Another great post!!

Well I have my start up program sorted out. It is very similar to what Im using for a N/A 393, so Im hoping it'll at least start, but this has a much more radical cam. Guess I'll just give it what it wants.

I'll post results by this weekend barring any disasters.
Thanks again.
Kirk
 
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