Altnerative coil setup for Saturn 4cyl wasted spark?

[ChevelleFan]

I'm looking to add MS2-Extra/3.57 board to our Saturn SC2 track car, Saturn 1.9L DOHC, 7000 rpm redline. From my reading, the GM DIS setup doesn't seem well-supported or widely used. The manual calls the GM DIS section "for reference only" (pg 117/186). Is there a more well-known/well-documented 4cyl wasted spark coil setup that someone would recommend? I'm planning on still using the factory GM 7x crank trigger wheel for RPM input. Not interested in doing COP, as I'm trying to keep this simple/reliable.

Open to suggestions/critiques.

Thanks,

-Dave

[Drew442]

Wasted spark and coil on plug can be mutually exclusive. Do you mean you don't want to run cam angle for sequential? Or do you want to run a coil with 2 HT's on it?

I'd go for 36-1 crank trigger kit. I'm not a Saturn guy but it shouldn't be hard to set something up and some logic level coils like LS coils.

Running high current triggered coils like a Ford 4cyl (or half an 8cyl) would also be easy enough to set up.

Sent from my MI 5 using Tapatalk

[Six_Shooter]

The GM DIS works fine with MS, at least the 60 degree V6 version which IIRC is very similar to what the Saturn uses. The 60 degree V6 DIS is what I'm currently running on my turbo LX9 and MS2 without any issues, along with GM HEI dizzy in another car on both MS2 and MS3.

I'm not sure why the manual states "for reference only", since the information has been confirmed AFAIK...

[ChevelleFan]

The GM DIS works fine with MS, at least the 60 degree V6 version which IIRC is very similar to what the Saturn uses. The 60 degree V6 DIS is what I'm currently running on my turbo LX9 and MS2 without any issues, along with GM HEI dizzy in another car on both MS2 and MS3.

I'm not sure why the manual states "for reference only", since the information has been confirmed AFAIK...

So are you actually using GM DIS now? Are there any additional resistors or pull-ups needed? How do your settings look compared against the manual? Is it really just a matter of sending the tach signal out of the DIS into pin 24 and hooking up Spk A to the EST wire & 5v to the Bypass? Do you have an MSQ you'd be willing to share?


Drew442,

Correct, I do not want to run a cam sensor. This engine doesn't have one and I'm not interested in retrofitting one.

I'm talking about wasted spark, from the manual:
"Wasted spark - double ended coils (or a pair of coils) that fire twice per cycle"
As in 2 coils for a 4cyl. (Not sure what HT's mean?) And Non-sequential, batch-fire fueling.

Looking at the manual on page 83, the "032 905 106B - 4 tower wasted spark logic coil" used on VW/Audi vehicles looks like a nice option.

We do endurance racing with this car, everything from 7 hr "sprints" to 14hr and even 24hr races, so whatever I do needs to be really robust. The goal is to end up with a tunable setup, because there is literally nothing we can adjust with the factory ECU.

thanks for the responses!

-Dave

[Six_Shooter]

Yes, I'm using it now, in fact I drove the DIS/MS2 car today.

The hardware setup is exactly the same as the HEI 7 and 8 pin, where inputs and outputs are concerned. V3.57 hardware setup is a little different than the V3.0 that I use, but should be easier on the V3.57, by simply using the jumper pins available and the HEI "mod kit" from DIYAutotune.

My settings differ slightly in that I'm using fixed dwell type, set to 50%, since I found standard dwell to have issues at higher RPM..

[ChevelleFan]

I'm running a 3.0/HEI8 on my small block Chevy and I used the fixed dwell as well, but I'm using a MSD 6A to drive the coil. Been working well for several years now.

I guess I'll give the DIS a shot. What RPMs do you run with yours?

If anyone wants to chime in on the other options, it would be good to have a backup plan.

-Dave

[billr]

The S-series Saturn doesn't have a cam sensor, but the ICM synthesizes a cam signal; so you will be losing the stock sequential injection, "going backwards" from OEM. I think the Saturn ICM has simple logic-level inputs for firing the two coils, but not sure. I have several of these cars, but none 'squirted.

There are a couple of Saturn-specific forums that may have the info you need:

<saturnfans.com> ask in the S-series "tech" or "mods" forums
<sixthsphere.com> not familiar with this one, but seems more oriented towards racing

[slow_hemi6]

If they are the GM twin tower coils they are easy to drive with a couple of BIP373's. I used 4 of those on my small block.

[Drew442]

HT = high tension = 'towers'

Batch might be going backwards but if fuel economy over the 7/12/24hrs is the concern then it can be gained back in other ways with the MS. Duel maps for fuel/spark for example, cruise and compete maps.

For reliability, especially 24 hour events I'd be trying to get that 20 year old piece of GM electronics out of there...

Sent from my MI 5 using Tapatalk

[billr]

"If they are the GM twin tower coils they are easy to drive with a couple of BIP373's. I used 4 of those on my small block."

Yeah, if the stock ICM doesn't have logic-level inputs, I would gut it and use two BIP373s; retain enough of the old ICM to easily mount and connect to the coils. It should be an easy conversion, but you would lose the CMP signal.

They are "twin tower", but not quite the same as the DR39 type that is so widely used in other GMs. They are very similar, but I don't know if the mounting is the same, and no clue as to the primary inductance/resistance, turns ratio, good stuff like that.

[Roofy]

Billr is correct, the cassette waste spark setup that the SAAB's, Saturn's and newer L61 Ecotec engines use, uses an ion sensing method to simulate a cam sensor signal. Basically, when the ICM commands say, cylinder #1 to fire, the coil will fire that cylinder with the matched cylinder on the opposite stroke. For this example, say cylinder #'s 1 and 4 are paired. When it's commanded to fire cylinder 1 on TDC compression stroke, cylinder 4 will also spark, but it will be on exhaust stroke. The higher compression cylinder #1 takes more time to fire due to the compression of the fuel/air mixture. So the ICM is able to determine the resistance difference between cylinders 1 and 4 by sensing which side of the coil is fired first. The low resistance side will be on exhaust stroke, and the high will be compression stroke. It's programmed to simulate a 5v square wave signal which is a replica of a high/low or half moon style cam wheel, based on the difference between the 2 sides of the coil firing. It actually works really well, but as far as I know, nobody has used it in a Megasquirt system yet. I am running an Ecotec, but decided to use a cam sensor and go COP ignition. I've had some theories on how to make the ICM play nice with the megasquirt, using the simulated cam signal for full sequential, but never got around to it. Maybe the next one I do with that style ICM, I'll play with it and put my theories to the test.