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.