Increasing dwell time?
 

Hi All,

Basically I still seem to be getting what I think is ignition breakup around peak torque. I have a brand new leading coil, new leads and new 9's leading and 10s trailing.

After reading information some information by chuck I have calculated the pfc values and worked out my coil dwells in milliseconds -

Rpm........dwell (ms)...........pfc value
400........ 3.1 ...............9
1000 ........ 2.8 ...........17
2000........ 2.8 ........... 34
4000........ 2.9 .............70
8000 ........ 2.3 ...........108
10,000 ........2.1 .......... 123


I always thought the spark needs to be at its strongest at peak toque, so I am suprised to see it tail off so much with higher revs.

I am considering ditching the 10,000 rpm column and adding a 6000 one in lower down, then trying to pick up the dwell about in the sort of 6000ish area, maybe something like:

RPM....... Dwel.......PFC Value
480....... 3.1 ....... 9
1000....... 3.0 ....... 18
2000 .......2.8....... 34
4000.......3.3 ....... 79
6000 .......3.5....... 125
8000 .......2.8 ....... 135


So before I go out and blow something up, has anyone ever tried anything like this before or does anyone have any information on what sort of dwell times the mazda coils can handle without getting too hot?

Thanks
Daniel

I guess a picture speaks a thousand words:

This graph shows how I'm proposing to up the charge time around peak torque:

http://i75.photobucket.com/albums/i3...ps29d8cf06.jpg

I cant see any need for me to keep the 10,000 row as I do not rev my engine that high :rolleyes:

I've also picked up the dwell a bit around 1000rpm to maybe help idle smoothness, but I left it low at 2000rpm as I do not want to put tonnes of extra spark into the cruise range.

Also, I thought I should mention my spec:

Pineapple Medium Streetport,
GReddy Style FMIC,
T04r,
550 + 1680 Injectors +
044 Pump,

Break up occures at around 1 bar, this is mostly on my p18 row and I tune this row to about 11 to 1 afr

A little update, when I actually looked at my datalogit I realised I cannot rescale the rpm column.

So I went ahead and used the settings as per the red line on the graph, this increases the dwell up to a maximum of 3.5ms at 4000, so around my peak torque point (around 6250 to 6500) I've got a dwell of 3ms compared to 2.5ms as standard.

The result - no missfires, I did some late night testing around midnight last night, I got quite a few clean runs in 3rd and 4th with no signs of missfire/splutter/powerloss which I have been assuming was spark blowout.

My only worry is by how much the additional dwell time will affect the coil life...

Daniel

The stock setup works well with the stock coils.
Last week I did a test with my HKS Twin Power disconnected and ran 18 psi with WA injection.
No problem for me.

Maybe your AFRs are way too rich. Even with the Twin Power, my setup will start to misfire at around 10.2 -10 AFR at 18 psi running 500cc/m WA.

Hi and thanks for the reply.

My AFR's on my p18 row are around 11.2 and on p19 more like 10.8, I could bring them up a bit higher, but I am a bit worried about detonation as I have no water injection.

May I ask, what sort of AFR's would you would like to see on a single turbo rx7 running around 1 bar of boost?

I have been running 16 psi without any WI or WA for years with a GT35R FD at 11.1 AFR.
But I have all the correct supporting parts: large FMIC with Koyo N pass radiator and proper air flow ducting, upgraded fuel system, relocated air temp sensor, proper gauges for monitoring the engine, and took my time tuning.

I run 11.2 AFR at 14 psi. Only have 18 psi tuned for WA as my 16 psi has been safe since 2005.

Maybe you have bad ignition wires, bad plugs, bad coils, or bad crank angle sensor.