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mark houghton mark houghton is offline
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Join Date: Jul 2008
Location: Central Washington State
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Originally Posted by DonE View Post
I didn't notice any difference cylinder to cylinder or top to bottom. Yes, I can disable top or bottom, but I didn't.

When I changed from wasted spark to CDI, I immediately noticed a smoother idle and better throttle response - it was amazing to me because the change was so noticable.

When I got down to tuning, I left the fuel alone and started playing with the gaps first (major pain in the ass with 12 plugs). When the gaps were too much, the engine would stumble and miss, especially at higher rpm. That's when I found the best gap was .032.

Then I tuned the timing - I didn't need as much mid to top, but low end was improved big time (I think it's equal to any 3.2L NA car now). By backing off the timing (a couple degrees), adding some more fuel (because it's now being burned completely), I could take the boost up to 1 bar safely (I have 8.0:1 CR).

Once this was dialed in, I started tweaking the fuel tables throughout to achieve a nice tan color on the plugs, proving I had the right AFR for the majority of my driving. In fact, I use the AFR meter to confirm what my plugs are telling me, not visa versa. To be clear, over 120 kpa or .2 bar, I start adding fuel fast and start moving timing back to 18 degrees at 6500 rpm at 1 bar.

Another indication my CDI and plug combination was working well, was when I floored it and there was no more puffs of black smoke (like when I had wasted spark using the same fuel table values). I found I could add more fuel which gave me more power.

Sorry to be so long winded on this, but I think the ignition system is sometimes overlooked in favor of turbos or headers. All components have to work together, but not much beats getting the fire lit quickly and completely while jamming as much fuel and air into the cylinders.

By the way, Neil Harvey at Performance Developments recommended the NGK plugs after I spent a couple hundred bucks experimenting on my own. He sold me the M&W CDI. Listen to the experts.
Don, lots of good info there. Thanks for sharing. Although I don't have EFI and have no experience with wasted spark ignitions, I don't use CDI and instead use MSD's ignition and gap my plugs at a tight .040. It doesn't miss a lick all the way to the top with NGK R5671A8 plugs and I'm running about 16 degrees timing advance at 1.0 bar boost....advanced 12* at idle for low/mid grunt and shaved off as boost builds. Not near as sophisticated as EFI I admit, but the net results are good. Outside of recurving the distributor and going with a digital WUR, it's about as good as we can get with add-ons.

Oops...sorry, off the plug topic! Dual plugs and EFI; well, that's a pipe dream for me. Did I say I like the NGK's?
Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 03-03-2010, 07:55 PM
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