I recently dynoed my comptech s/c 7lb pulley no aftercooler. I pulled 287 whp and 172 lbs. The odd thing is that after 7500 rpm the dyno plot becomes very wavy - if someone would host the pics I'd be happy to post them. Anyways - I'm using the emanage to tune.

I might have hit the upper 290's if I wasn't misfiring - that's what someone thinks the wavy lines represent. I'm using the NGK copper 1 step colder gapped at .035 I think I'll try and gap it down to .030 but do you think I should be going 2 step colder? Would being too hot cause misfiring?

 

I think you're probably on the right path. I had a problem with spark plugs and swapping to NGK Iridiums with the correct gap fixed it.

 

Is the wavy line like spiked up and down over a limited width on the graph? Did your S experience any symptoms from it? Audible backfire or miss?

 

On my first dyno pull, i experienced the same thing, my dyno showed wavy lines, like very rapidly going up and down. Gapped them down to .028 and got rid of the problem

 

Yes, after 7500 rpm the lines were rapidly going up and down. Also, I noticed the a/f became richer - prob from not really igniting the a/f mixture. No audible noise but the engine was kind of shaking/ vibrating more than usual.

I just gapped my plugs down to .030 and see if that helps. Does the iridium have a larger spark compared to the NGK copper glugs? I assumed the only advantage with Iridiums were that they lasted longer than the copper plugs.

Ray

 

What kind of air/fuel ratios are you hitting at 7500 and above? I'm thinking your plug gap is a little too big. Gap the plug smaller in steps until it stops misfiring. Running too hot of a plug will not cause a misfire, but it could cause detonation. Since boosted applications run higher combustion temps., the plug can retain enought heat to the point where it could pre-ignite. Running a colder plug is insurance. If you run too cold of a plug however, your plugs will tend to fowl up. I think the problem you're having is the plug gap. Gap the plugs in small increments until it stops misfiring. Check the wideband readings on the dyno and pull a plug to check what it looks like after a run. Good luck.

 

Thanks for the reply.

My a/f ratio is about 13.0 at 7500 rpm and drops to 11.0 at 9200 rpm. If someone can post my dyno plots I'd be grateful.

I have my gap down to .030 and that is hopefully enough. I'm positive I'm not detonating but with the misfiring - I never noticed that I was misfiring when driving up to redline. I'll try what you recommended and let you know how it turns out.

Thanks everyone for all of your help.

 

13:1 is a little high for a boosted motor. I'd feel much safer at 12:1 on the dyno, because that would work out to around 12.5:1 on the street.

 

Here is a link to my dyno plot. I set Vtec to 4800 and after adding some more fuel - up to 10% more fuel on the emanage - my a/f curve didn't really change. Either I am not doing it correctly or perhaps I maxed out my injectors and need to install my 500 cc injectors that I have laying around.

https://www.s2ki.com/forums/index.php?showtopic=237378