I know I'm not a knowledgable source on this, but can we discuss the effect spark dwell has on performance and average MPG?

 

Is dwell adjustable thru tuning? Just curious.

 

Yes, spark is adjustable through HP Tuners. I have played with the dell tables and have adjusted it as much as 3milliseconds (I know, I'm a rebel huh?). I noticed rougher running engine in the lower RPM's and although it felt more responsive, it did nothing but increase engine harmonics, as though it was stressing in a negative way. Gas mileage, well I don't care so I can't tell you if that changed. What I have done since my experiments with dwell is restored it back to the factory dwell settings, but added a multiplier that increases the dwell as RPM's and or MAP readings increase. Increasing dwell on the top end DOES make for some better pulling power. On the low and midrange though I noticed negative effects. Maybe cuz I like to run a lot of timing

 

http://hptuners.com/forum/showthread...ighlight=dwell
https://www.performancetrucks.net/fo...ighlight=dwell

 

Here's some math to help you figure out dwell:

Math done at 6000rpm:

RPM - 6000
Cylinders - 8
Number of combustion strokes per second - 6.25 (rpm / # of cyl / 2)
Total degrees of rotation per second - 2250 (360 x 6.25)
Numbers of milliseconds per degree of rotation - .44

And at 650rpm:

RPM - 650
Cylinders - 8
Number of combustion strokes per second - .667 (rpm / # of cyl / 2)
Total degrees of rotation per second - 243.75 (360 x 6.25)
Numbers of milliseconds per degree of rotation - 4.1

You need to determine how many degrees of stroke you want the spark to burn for....most aftermarket systems give you 20º-30º of spark duration at idle (around 82 -123ms) with that dropping off as RPM's climb to around 5-7º at 6000rpm (around 2.2 - 3.08ms). Factory systems typically aren't designed to the handle dwell times this long but we are in luck as our systems seem to handle pretty much anything we want to throw at them (but coil life is dependant upon usage...the higher the dwell time the shorter the coil life).

Once you've figured all of this out you can set your dwell to whatever you want as determined by the number of degrees that you want the spark to fire for.

I've double checked my math about 10 times but if someone sees an error please let me know. I've attached the spreadsheet I put together to do this math too

 

I think dwell as we are discussing here, adjustable with HPT, is the charge time/dwell of the coil, not a measurement of how long the spark last.
The same as adjusting the contact point dwell on older engines.

I hope I am wrong, it would be great to be able to directly adjust the spart dwell.


Br//

 

Why is it that I can run a modified dwell table but my cousin's tahoe and my buddies 04 Silvy both get detonation? All with similar mods and tunes.

What are some other changes that need to be made in conjuction with Spark Dwell?

 

Thank you !!

I just realized I missed typing a BIG portion of the necessary info above.

Coil dwell directly affects spark dwell, coil dwell is a measurement of the portion of the time the coil is active that it will be charging, how long the coil will provide voltage to the plug is determined by this dwell time. When the coil releases it's stored charge to the plug that charge jumps the gap at the plug creating a spark.....but if coil dwell is too long it can affect discharge and recharge time. typical coil dwell times are about 115% of spark dwell times (on average)

We ARE taling about coil dwell here...I just forgot type that part and give you the math to figure it out

 

could dwell time negatively affect the amount of timing you could run?

 

Soon,

Yes it can. If you have an agressive spark curve such as I run, you won't be able to get away with high dwell settings. I found this out when playing around with the dwell tables on my truck. Just raising the dwell 2ms without any kind of multiplier caused audible knock from 2000-4000 with anything over 30 % TPS. At higher piston speeds as the combustion process becomes less efficient, the added dwell increase made a noticeable difference on the top end. I could putts around with it more I'm sure but that's why I run stock dwell settings on anything under 3500 RPM's, from there I use the MAP multiplier and by the time I'm at 6000 RPM's I have added 2ms of dwell. Another note is peeking at Jesse's (wait4me) tunes he adds about .5 MS to the entire dwell table. If I end up dynoing in the next week or two I will be more than happy to do a dwell experiment for everyone to see what kind of effects it has and how it manipulates the power curve.