Spark Dwell w/ different coils

[99TransAmls16spd]

I have a '99 trans am w/ a 11.7:1 416 in it. I've got a set of D585 truck coils w/ heat sinks I'd like to replace the factory coils with

However, when I pull up a stock tune for say an '01-'03 5.3/6.0 truck, I notice the dwell times are signifigantly lower than that of my stock '99 tune (or modified one for that matter).

Is there a reason for this? Should I still consider inreasing the dwell time in my Trans Am tune, and if so by roughly how much?

It's an N/A motor set up for nitrous, only ignition upgrades are the NGK plugs and MSD wires besides the coils.

Thank you

[SweetS10V8]

I would love to pull a tune out of a truck with the D585 coils as well. I run them on my S-10 and dont have any problems, but that diesnt mean they are correct.

From what I understand with the d585 coils is that if you dwell them too much they will "time out" and fire on their own to keep from burning up, which means random spark timing. Just from that, it sounds like the tunes with the lower dwell are for the d585s

Anyone have a vehicle with the d585s??

[whackem04]

And does increasing or decreasing dwell time have anything to due with getting better mileage or power?

[TX Tahoe Z71]

And does increasing or decreasing dwell time have anything to due with getting better mileage or power?

Digging this thread up, I would like to know this as well. I have heard arguments for and against, but nothing concrete. Any insight is much appreciated.

[99TransAmls16spd]

Well, I have the D585s installed on my 416ci trans am, and factory on my GMC.
I upped the dwell times on my 06 GMC by 20%, thinking I may get a better burn for better MPG - I haven't seen any gains however. Did not feel any either. Will be putting them back to stock, or at most 10% over factory.

The throttle on the TA feels a little better with the D585s and longer dwell times. I attribute this to the fact it is a manual tranny and cable driven TB. It would probably not be noticable if it was an auto. Again, no SOTP gains in power (or trap speeds). Gas mileage is, well impossible to tell in that car - it hasnt seen a full tank in a very long time.

Hope this helps

[TX Tahoe Z71]

Not what I was hoping to hear, but thanks for posting up.

I'm at 9.5/11 city/hwy on E85 right now and it's killing me, I can barely take a road trip without rolling in on fumes, haha. Luckily I have a flex fuel, so I can put in 93 if need be and be fine, but the extra 40-50rwhp from the extra timing is too much fun!

[1slow01Z71]

From the people Ive talked to who have messed with a longer dwell, it didnt increase mileage in itself, rather it allowed more timing to be added at part throttle inputs without encountering knock. Has anyone tried this? The main guy Ive talked to about this was able to get over 40*s at cruising rpm on the highway and netted quit significant gains in mileage in his yukon xl 4wd. I plan on messing with this combo at some point in time but it is difficult as I do very little highway driving where I could get a low enough load to work with higher timing and leaner cruise AFRs.

[99TransAmls16spd]

I have the lq9 in the truck - and though I havent been able to do much logging or tuning (besides the basics) due to the awesome chicago area winters (owned the truck for 2.5 months now), I have noticed in the few logs I have done that it's had zero knock since increasing the dwell time. That's on mid grade, not premium, with fueling and spark tables completely stock. So maybe there is something to what you are saying, but to be fair I have also made some simple tweaks to my TCC and shift points to "hide" what I think is a worn PWM solenoid/bushing in the trans, which may have also been triggering the knock sensor in prior logs.
But I do not think it would lean the A/F ratio - just make more tq at the same MAP/RPM, making for better mpg.
When it gets warmer, I will start dialing in my tables and post results. I'll try to work with premium fuel as well, and see if it makes for better $/mile gains.

[1slow01Z71]

Im basing my post purely off what Ive read in a few posts and from talking to a couple of people who have done some tinkering with dwell timing. The only one Ive got specifics from said he was running 8.8ms dwell at ~41*s timing and 18.5 AFR which in turn netted him mid 20s on the highway running 70 in his yukon on 93 which I believe to be pretty nice if I could get even close to that. The only mods he had was no cats, magnaflow catback and of course his tune. Im hoping that with some attention to the tune I could break the 20 barrier and Id be happy.

[99TransAmls16spd]

Is he running a COS? 18.5 AFR would really concern me.

I will not be running a COS, and will be tuning 14.7 AFR at cruise and post my results. Currently getting between 14.5-15 mpg in the cold weather mostly country back roads driving and a little in town. This is in a crew cab 1500hd.

[1slow01Z71]

Im not sure on the COS deal, he never mentioned running one and he was tuning with HPT if that makes a difference. Here is a quote from him:

"With the lean cruise mode I aimed for 18.5:1, only at speeds over 60mph, and under 24% throttle. If I exceded those it would go out of lean cruise. My timing was around 32* cruising with some ping till I increased the dwell, then I was able to go all the way up to 41* with no KR or audible ping. My dwell if I recall correctly was set around 8.8ms. I immediatly knoticed better throttle responce."

He was running an 05 yukon xl 5.3 4wd with 3.42 gears, Id say he was loading that engine pretty good so if there were going to be problems with it being too lean I figure it shouldve showed up on his setup. I think the 24% throttle is a big key there too with not melting his engine. I just got my V2 lined out after screwing it up upgrading the firmware and boot blocker crap and now its really cold so once it warms up Ill start playing around with it. I refuse to be out there installing my wideband in 15* weather and a 20mph wind.:bad:

[TX Tahoe Z71]

For a point of reference to compare his mid twenties mpg in his 05 Yukon XL 5.3 4wd, when I was just CAI, Wheatley 93 tune and magnaflow muffler (so pretty much the same setup as his), I would get 16-17mpg at 70 and 18-19mpg at about 63 on premium gas. And my tune was dialed in, Wheatley spent probably an hour cruising on the freeway adding timing and leaning it out. I have an 03 Tahoe 5.3 4wd and was running Michelin tires and am pretty religious about changing plugs, fuel filter, cleaning air filter, changing oil, and general maintenance.

[TX Tahoe Z71]

Anyone else have any experiences with working with spark dwell?

[Aloicious]

I've adjusted my LS2 coils a little bit. I can't really say if it helped or too much or not. but have you watched this video? its pretty good if you're patient for the camera guy to work the camera, it shows some interesting tests and shows some differences in dwell changes on his home made bench tester. according to him the truck coil and LS2 coil like "5ms" of dwell, however his bench isn't really made to replicate the engine environment, so I'm not sure how accurately the numbers translate to real life, but at least you can physically see the difference a change in dwell makes.

http://video.google.com/videoplay?docid=-6218245369765754251&hl=en#

[DrkPhx]

Here's a little more information that may help. I run the truck coils on my TA and have also adjusted dwell without a noticeable difference.


http://www.yellowbullet.com/forum/showthread.php?t=337602

[Highlander]

Very informative thread...

[TX Tahoe Z71]

Indeed, thanks for posting up the video and the yellow bullet thread. Seems like there is much more to tuning dwell time than I had originally thought.

[DrkPhx]

You're welcome. What I found interesting was user 427 (He used to own Wheel to Wheel in MI back in the day) commented that the square truck coils were better than the more popular round truck coils. Either way, a good read.

[TX Tahoe Z71]

Yeah, bummer that I have the round ones