stickmantijuana

iTrader: (1)

so after recent loss of my prior tune, I've been trying to tune the car myself. I got hang of getting AFR dead-on with my handset which I realize is the easy part, but the car runs 10x better now. I can drive it around with ease without constant buckling.

Having had some success with AFR tuning and seeing how engine reacts so dramatically so some key strokes, I have gotten hooked to the process of tuning. I now want to get into tuning timing. I know this is a dangerous territory, but my current timing is so retarded that my downpipe glows red just after a short vacuum cruise.

There is a local dyno I rented for fairly cheap this weekend, and I want to try to tune this myself. I have wideband. I don't have EGT yet.

Here's my current timing map.
t_rpm MAP
500 15
1000 15
1500 15
2000 15
2500 16
3000 17
3500 18
4000 19
5000 21
6000 23
7000 25
8000 27
9000 28

t_map MAP
30 Hg 6
24 Hg 6
16 Hg 6
8 Hg 5
0 Hg 4
2 psi 2
6 psi 0
9 psi -4
13 psi -7
17 psi -10
21 psi -12

t_gap MAP
500 15
1000 15
1500 13
2000 12
2500 11
3000 11
3500 11
4000 11
5000 11
6000 11
7000 11
8000 11
9000 11
10000 11
11000 11
12000 11

What should my approach be? My tuner says find MBT, but I feel that rotarys would usually predetonate on the way to the MBT. Thanks for any help in advance.

Aaron Cake

iTrader: (1)

Do not tune to find detonation then back off!

First, are you sure that you have set base timing properly? As in, with the Microtech locked at -5, the leading mark lines up?

What are your AFRs when the downpipe glows?

Looking at that map you need to pull a LOT more timing out once you start to hit boost. You're still adding timing at 2 PSI. You should set those numbers so you don't see much more than 12 degrees advanced in boost.

But also bring timing in more in vacuum. Add 5 degrees to 0 - 30 HG.

Here we run into the limitations of the stupid Microtech timing model. You're limited as to what you can accomplish by applying stupid corrections to a "virtual distributor".

Increase your split under boost. 15 degrees.

stickmantijuana

iTrader: (1)

thanks aaron!

my pulley isn't marked currently. I haven't done the timing light on it yet. I set the CAS timing with the oil pan down with direct visualization of the CAS marks while the keyway was pointing at the passenger side, so I'm pretty certain I got TDC right on the money. but marking the pulley is something I plan on doing in the near future.

Howard was kind enough to provide a base timing map, and I converted it to Microtech timing map. PowerFC map is on a chart, and Microtech map is on correction scale, but I made it into a chart for ease of comparison for other members.

My AFR was around 11-13 at vacuum cruise when the pipe was glowing red. After I tried new map by Howard (more advanced timing), the downpipe doesn't glow anymore, so I think the original map was too retarded in timing. I just ordered EGT, so I'll report on that shortly.

The car now feels much much better. There is a flat spot around 4000-7000, but "flat" with 3 rotor is a relative term. it's still enough to smoke my tires. My current boost is 3psi with whimpy 5psi spring without controller while I get ignition timing sorted.

Attached are the microtech timing I worked on today.

My big question is how do you fine tune timing? Do you do it by EGT or MBT? or do you just go off base map? Adjusting AFR is simple... I would appreciate any help in tuning timing safely. Thank you.

Aaron Cake

iTrader: (1)

STOP! STOP RIGHT NOW! DO NOT DRIVE THE CAR INTO BOOST UNTIL YOU HAVE VERIFIED THE PROPER ALIGNMENT OF THE CAS WITH A TIMING LIGHT

You MUST, absolutely MUST, sync the CAS to what the Microtech thinks it is seeing. Lock the timing on the Microtech and then put a timing light on L1. Adjust CAS position until timing pointer lines up with leading mark on pulley. ALL factory pulleys are marked. The paint may have worn out, but there will be two notches, one for leading and one for trailing.

If you don't do this, the timing can easily be 5 - 10 degrees off from what the Microtech thinks it is. A small movement of the CAS translates to a large timing change.

This is a required, non option, cannot be skipped step. Period.

Well if those were your cruise AFRs, then no wonder the downpipe was glowing. Timing would have little to do with it.

I personally don't chase power with timing on a rotary. I don't feel like ending every tuning session with an engine rebuild.

In boost I drop timing to 16 degrees advanced around 1 PSI then quickly taper down to 10 degrees by 10 PSI, adding about 2 degrees from 5000 RPM to redline.


If you look at the timing maps I provide on my Megasquirt writeup, those are what I consider a good economical map for cruising and a safe map for boost.

http://www.aaroncake.net/rx-7/megasq...on_table_1.gif

Obviously you'd have to translate that to the crazy Microtech virtual distributor model. You won't be able to get an exact translation. In the Microtech timing world, generally you will default to the safer option.

stickmantijuana

iTrader: (1)

ok. thanks for the special emphasis. Point taken. It's been dyno'd already, but I will check the timing before I do anything else.

if I just take the pulley out and mark the timing mark myself with a degree wheel and a tap, would this be okay? I have an aftermarket aluminum pulley without timing mark. I'm going to take it out and put the center of keyway 90 degrees to the passenger side and mark TDC at 0" (top) with a degree wheel. engine is 20b. thank you.

Aaron Cake

iTrader: (1)

You're going to need a degree wheel to accurately mark it. Or, line the keyway up with a stock pulley and transfer the mark.