More timing or a more lean a/f?

[Hiitman]

I've finally got my meth situation fixed so now I'm able to make some real power. So what I was wondering is, which makes more power, more timing or a more lean a/f ratio? These aren't accurate numbers, just an example. Would 18* of timing and a 10.5:1 make more power then 17* of timing and a 10.8:1? Or should I just shoot for a steady a/f ratio and up the timing until I see knock? Should my target a/f start at full boost? I'm not too worried about anything before 4500 since after 1st gear I won't be dealing with anything under that.

 

[Kevin Jewer]

When it comes to both power and knock, timing is a much bigger lever. In your example that 1 degree of timing could be 10-15 whp depending on where you are in the curve, while the .3 change in AFR is unlikely to even make a noticeable change. Go for a normal AFR and adjust timing as necessary. When you first reach full boost is when cylinder pressures are typically highest (better VE at lower RPM. With DSMlink, watch airflow/rev) so you definitely want to be fully richened up by that point. I like to go a touch richer around the torque peak and let it go a little leaner at high rpm where airflow/rev is falling off. Using pump gas as an example, something like 10.8 from the boost threshold to 4500 rpm or so, then 11.0 or 11.2 up through redline. This won't generally affect tuning for the dragstrip, since you'll never be below 5500-6k.

 

[Hiitman]

Thanks for the input. Here's my latest log. 3rd and 4th gear. I pulled those timing sliders up top just to be safe. I think the knock in that run was just from the high coolant temps. I was idling for about 10 minutes before I did that pull.

 

[2gGSX]

That looks like a great log actually--that knock is negligible IMO. If you wanted more power I'd suggest starting to up the boost and dropping timing to deal with knock.

 

[awdfun]

Agreed w/2gGSX - up the boost, drop timing where you have to (if you get knock).

And get some ducting up front to keep your coolant temps lower. I'm guessing with Meth injection you should be able to get a bit more boost and timing...if you can keep intake and coolant temps down.

I saw your post on the 'Link forum and noticed your 70-90 time is 2.1 sec...that is moving, nice work!

 

[Hiitman]

My coolant temps are alot better then they use to be. Those were high because I was doing some hard pulls and then idled for 5-10mins. A typical pull will show temps of 180-190. I'm going to up the boost once I get the PTE 60 trim on here. I don't want to blow the seals before the March 8th track meet.

 

[Black_Bullet]

Agreed w/2gGSX - up the boost, drop timing where you have to (if you get knock).
I saw your post on the 'Link forum and noticed your 70-90 time is 2.1 sec...that is moving, nice work!

Dropping timing for boost and leaving a nice fat afr worked for me.
With meth you should be able to get a little more timing out of it.
Rule of thumb, boost makes the most power, then timing.

On an efficient meth kit, me personally im going to shoot for 25psi ( evo3)
w/ 15-22 degs timing ( starting 15 going up of course.) and a 11.5 afr after torque peak for a daily tune.

Right now on straight 93 octane i run 24psi with 11.0 afr and 11 degs timing slowly ramping up to 18-19 by redline. The low 11 degs comes from the initial hit thru torque peak when the boost is spiking its highest, and then as it begins to drop you add more timing and slightly lean it out some the further the pressure goes down. Pressure = heat. At least that is what ive found to do so far.

BTW. What gear are you guys using to get your 70-90mph times, 3rd or 4th?
Im starting to wonder what mines are, but my mmcd program on my laptop doesnt have that option, nor do i have dsmlink...

 

[turboglenn]

The way i tune is just like stated above. But i'll elaborate more. The basic rules are as follows. (assuming the car is mechanically sound enough to tune/run hard)

Set you timing VERY LOW

Turn your boost into your compressor's peak efficiency range, then start tuning AFR's (working from a lower boost at first to get an idea of where your map is headed pulse width wise anyway) till you've worked your way up to your "peak efficiency boost"

Once your AFR's for each boost boost are dialed in start advancing timing untill you start to see knock, then pull 2* in that area and repeat. you can play with AFR to try adn get rid of pinging, but for now leave it alone

Now you're dialed in and ready to race right? NO

Now go out and do repeated pulls, back to back and allow the parts to heat soak (unless she's a drag/trailer queen car) Now you should be seeing a little more knock with all the heat build up. AT this point you can either turn on your meth and fine tune the AFR, or try adn play with the timing and fuel curves. I recomend turning on the meth if you're above averrage pump gas levels (20psi or more)

Now that the meth is on, see if you're still getting knock, you shouldn't be if you've got the proper nozzle in it. If there is no knock, at this point you can either dial in more timing on the same tune knowing that it went a half point richer from teh meth alone or you can lean it back out to say 11:1 and see if you cans till add timing then.

Using these methods and monitoring what you're doing should yield you the best compromise of running the most power you can while still being able to safely to daily drive and beat on the car.