Hello
I've been trying to get a answer about a question I have with waste spark systems. Would running a large duration cam with a tight LSA ie a LE2 cam with a waste spark setup the delteq cause the cylinder on the exhaust stroke to fire when the intake valve is open? I know that the cylinder on the exhaust stroke shouldn't have much fuel in it....but what happens when your spraying a 250 wet shot via direct port into that cylinder. This could cause a nitrous backfire into the intake correct? How could I check the valve timing events and point of each cylinder firing to make sure that this wont be a problem? The timing advance on the PCM varies but sometimes as much as 42 degrees at WOT. Any help or ideas would be great.


Jason

 

Not sure what you’re really asking.

The delteg ignition is basically just a multi-coil ignition and uses the standard opti optical sensor so your timing remains the same regardless. Large duration cams and overlap is a very relative term, most on this list would probably not consider a LE2 to be a "big cam." I wouldn't sweat that aspect but the nitrous guys seem to perfer a not so tight overlap cam.

If your running nitrous especially in the 250 hp range, you'll need to retard the spark either from pulling out timing through programming or adding a device that pulls out timing under WOT. Believe the rule of thumb is 2 degrees for every 100 hp of nitrous.

My delteg seems to be working great but don't expect any hp gains on a N/A system. Maybe on juice, but I'd say you need to post on the nitrous list to see what experiences they have as it sounds to me like your down to basics.

 

Maybe I didnt make what I was trying to ask clear. The delteq fires each cylinder 2x on one rotation once on compression stroke once on exhaust. With a large duration cam when it fire the cylinder on the exhuast stroke could have the intake valve open causing the nitrous and fuel in both the cylinder and intake manifold to ignite correct? How can I check timing events of the cam vs the timing events of the spark firing per cylinder? IE when the #8 cylinder is on the compression stroke and it fires at 36 degrees advance cylinder #5 is also getting a spark at this timing event where would its valve's be?

Jason

 

Jason,

The issue is you would need something left in the cylinder to burn at this point.... When the Delteq fires on the dead stroke the exhaust valve is on it's way closed and the intake valve is just starting to open up. The old fuel and air have already been used up and there is nothing left for the Delteq to spark off, so you don't have anything to worry about.

BTW if you can run a larger cam like a GM847 or any of Joe O's larger cams the LE2 is not going to have any problem at all. Those have a lot more overlap.

What you are really concerned about here is the intake valve opening point. You are going to have less than .050" of lift on the intake valve from 40-10° BTDC, and a REALLY small amount when the plug actually fires. We're talking under .010" of valve lift from the intake valve letting air/fuel/N2O charge into the cylinder in the worst case when the Delteq fires the plug that second time. There is nothing new in the cylinder to light off at that point.

I would expect that someone would have had a bad N2O backfire with this system IF there was going to be a problem, but obviously there is not.

42 degs at WOT is excessive timing on a LT1 motor, especially with N2O. Hell it's more than what you would run on old slow burning cast iron OEM heads.

Bret