V8 - Change to ITB, find the right Setup

[martin2day]

Hello,

my engine is a SBC 350 in a very light car. (2000lbs)
I change my fuel/air hardware form TBI to ITB. 8 ITB's and 8 Fuel Injectors.

Now it's time to decide how to fire it up with the right setup.
I also have got an MSD Ignition box.

I think for fuel i will use 8 cylinder semi sequential (4 driver) because i only have got an crankshaft VR sender.
So the setup is 2 Squirts per Circle Simultan.

But how to fire the spark's. Do i use my setup with the MSD Box and use the distributor?
Or is it better to change to 4 ignition driver and use wasted spark?
With this question/answer i can decide what ECU i have to use.

Thank you for helping.
Martin

[billr]

My opinion:

Scrap the MSD and single-coil.

Use the dizzy only to drive the oil pump, and later to provide a cam signal if you want sequential injection.

Add a real crank trigger wheel, either 36-1 or 60-2

Use four wasted-spark coils. There are a several different practical ways to do that, both with or without having an MS3X extender board. I do, however, recommend using the MS3X, there are many other features available with the MS3X for a pretty nominal cost (compared to the overall project). I'll outline details of how to get wasted-spark if that is what you want to pursue.

Hmm, I should have mentioned before... buy an MS3 kit, unless you are totally against soldering or have a robust budget that can happily swallow an MS3Pro. Don't even think about an MS2; again, the difference in price between an MS3(kit) and an MS2 is trivial in the overall project. Why scrimp on the very heart of it? Use the latest hardware/software available.

[martin2day]

Hello,

can you tell me why to scrap the MSD and Single-coil.
What is better to use 4 coils or 8 coils?

A build a 36-1 Trigger Wheel... but this is on the Crankshaft, so i have no information if 0° or 360°... a can modify the distributor to get a camshaft signal.
But the cobra is no daily driver... keep it simple... So i will only use the crankshaft trigger.
So i can run wasted spark an semi sequential fuel only.

Can you tell me a good way to modify to wasted spark?
Today i have a MSD (6421) Box and an single Coil (8202) and a MSD distributor with a rotor i can adjust.
The Trigger is in the crankshaft.

Soldering is no problem also 0805... or smaller.
Today i don't need any of the MS3 feature. But a have a look at the MS3.

Thank you for your help.
Martin

[billr]

I'm short on time this morning, but will answer a couple now, the rest probably tonight. A single coil simply runs out of time for dwell (charging the coil) when an 8-cylinder engine gets much over 5000 rpm. The MSD is a crutch to help get past that problem. Adding coils, either wasted (4 for you) or COP (8), eliminates this rpm limitation in a simpler manner; no more wonderment if the MSD box is bad. Also, and not at all trivial, is elimination of any chance of cross-firing in the dizzy cap due to bad phasing of the rotor or bad cap/rotor.

Both wasted-spark (4 coils) and COP have advantages. Wasted-spark (or wasted-COP) has less coils and drivers to buy fuss with, and can run without a cam sensor if you have a missing-tooth crank wheel. COP (8) can have a neater and more reliable install with no high-voltage plug wires, and less chance of EMI, but locating those coils on an older engine can be a real problem. For instance, my BBC plugs are "intimate" with the exhaust headers and I don't think COP could live there. And, I would need special brackets to hold the COPs in a place where they were never intended to go.

Many get around the mounting problems for COP by using CNP (coil near plug); 8 individual coils located where practical and connected with fairly short plug wires. This can help neatness of wiring and maybe reduce EMI problems (if any); but to me it incurs the worst features of both wasted and COP with little gain over wasted (4 coil). Neatness isn't a big priority for me and EMI has never been a problem for me even with the long plug wires snaked in-and-around all other wiring. Got it? I like 4-coil wasted-spark for a V8.

It sounds like yoy will be using a true crank wheel, so poorer accuracy from a dizzy trigger doesn't apply, but I usually pooh-pooh dizzy systems for that reason too. Modifying a dizzy to provide a cam signal is usually a trivial process, and can be done later after the engine is running fine with wasted-spark (or wasted COP) and semi-sequential injection. And will run fine with wasted and semi-sequential.

Yeah, 0805 is as small as I can reasonably go...

[martin2day]

Hello Bill?,

thank you for your answer.
What i now is that the MSD is a cdi ignition. (Capacitor discharge ignition) Up to 10000rpm is no problem i think.
What i now is with cdi you have got more current and this can make some other problems, but rpm's over 5000 with V8 is no problem.
Is this right?

At this time a have a look at the MS3 manual.
I consider not to use the MS3X Board but only a 4-Channel Ignition/Injection Driver Board.
So i can trigger my Injection and IGN direct...

Martin

[billr]

I can believe MSD or CDI can get a dizzy/single-coil system up in the 10K rpm range; I used CDI back in my dizzy days and it helped (both contact point and then VR triggered). Of course wasted or COP can do that, and maybe more. I think a 4-coil wasted should be able to hit 12K with no problem and COP doubles that to, um... 24K. How fast is your 350 SBC going to turn? Performance at higher rpm is certainly a good reason to add MSD to a single-coil system, but is of no relevance to choosing single-coil over dizzy-less. They can both provide all the rpm capability you can use.

The compelling reason for abandoning dizzy/single-coil is timing accuracy. Even if you stuff a 120-tooth wheel into the dizzy to be effectively 60 at the crank (and it can be done), lash in the drive gears/chain/belt from crank to dizzy introduces spark scatter that isn't a concern with dizzy-less. You could, of course, use a real crank wheel with a dizzy to avoid that scatter, but the previously mentioned issues of cross-firing, reliability, and EMI would still be there. Once you add a crank wheel you are well on the way (effort and cost) to a full dizzy-less system.

OK, I've voiced my opinions, I suggest you wait for one of the "MSD/CDI lovers" to present the other side. Then you decide...

PS: Since you can solder, $30-40 buys the BIP373 drivers needed to fire four simple GM wasted-spark coils. Those are widely available in the USA at reasonable cost, either new or used. Look at SMP (Standard Motor Products) #DR-39.

[martin2day]

Hello Bill,
thank you for your hint.
today my rev limiter is set to 6500rpm.
I don't now what rpm my SBC will run if i am ready.... today it run good and fast till 6000rpm.
You are right.
I can only buy the MS3 without the MS3X... all i need is on the MS3... and with 4 separat IGN and INJ Driver i get what i need.
And with an Dual VR Board i can connect my too ABS Sensor to run the Traction Control too.

Martin

[billr]

Yes, you can certainly do without the MS3X, all the functions it provides originate from the MS3 board, on the two ribbon headers. You could build your own circuits for just the functions you want, but the MS3X is just a convenient "buffer" for the I/O from the MS3. All in one tried-and-true package that is fairly economical, I think.

I know little about ABS or traction control, so won't try to comment on that.