Stuttering engine on high boost
 

Former honda clown on da board O0

Currently I own a 1992 Mazda 323 GTR, this is a Group A rallyecar. One of the reasons I sold my B18R CRX is because I wanted 4WD and a car that was prepped very well from factory. EVO's are too expensive on this side of the ocean :(

3" downpipe and exhaust
BKR7EVX plugs
KN filter
new leads
new rotor and cap
stock manangement and injectors, this is good up to 22psi
stock FMIC (good up to 280ps)
Zeitronix wideband, EGT, boost

Up to 5000rpm I get up to 14psi of boost, above 5000 rpm I get another 3 psi and this is when the ---- hits the fan: At first the engine used to cut in hard, like a boost cut, but this is not possible this kicks in at 24-25psi, then I thought it could be de knock control, not possible since I have 12.5-12.8 AFR and I only use 98RON and sometimes an octane booster. FMIC isn't too great but will be swapped for an EVO FMIC before the summer.

Then I changed plugs to BKR7, stock is 6

Now the engine start to sputter like it just doesn't get a full burn or ignition is too late

I called a respected engine builder and hey said the spark plugs might stick to deep at factory specification and I should use plugs with a shorter shaft like the race series from NGK ($$$$) or the less expensive Champions

Any thoughts guys?

Re: Stuttering engine on high boost
 

Well this may not be the problem at all, but don't disregard the knock sensor because your AFR is good and you use good gas. If your ----'s too advanced it can still knock. I'd say take a good look at your timing first.

Re: Stuttering engine on high boost
 

true.
You can also try to gap the spark plugs....that tend to solve the sputter problem most of the time.
Gap to 0.75mm

Re: Stuttering engine on high boost
 

Thanks so far,

I'll gap the plugs to .75mm tomorrow, they are on 1.1 right now

Timing should be ok, it's bloody hard to get it right, on my Honda it was easy as 1-2-3 but on this car it's hard to see the actual timing with the strobo. It's currently set at 10 degree advance , that's the stock ign.timing

Re: Stuttering engine on high boost
 

Retarding it a couple degrees couldn't hurt... Let us know how gapping the plugs works, then try slightly retarding the ignition timing and see how that goes.

Re: Stuttering engine on high boost
 

Sounds like weak spark. Did you try replacing the wires/rotor/cap/coil?

I had a slight miss last year, I dropped the exhaust and just ran the downpipe. Became very obvious that the problem was spark, the explosions were really loud.

Re: Stuttering engine on high boost
 

may very well be that gap on the step colder plugs...are they gapped the same as your stock plugs? if so, take them down a bit.

Re: Stuttering engine on high boost
 

Thought about the coil as well, Mazda uses external coil, a time ago I left the lead off and it got really hot. Not sure if it took a blow. Normally Denso parts just completely break down.

I could measure coil's resistance primairy and secundairy but how exactly how do you measure this?
New coil costs 40$ maybe I should just replace, I already have new leads and rotor+cap

Re: Stuttering engine on high boost
 

afr's are a hair lean in my opinion for running higher boost, but that's definitely not yoru problem. more than likely yes, you're blowing out the spark on the plugs, close the gap up a bit and see how that works.

Re: Stuttering engine on high boost
 

Narrowed the gap to .8mm and set ignition to 8 degrees BTDC, normally it is set at 10 +-1 degree.

No sputtering now, it actually is a LOT faster on the highway, from 100-160 is just insane!! however, above 5000rpm I notice less response and revhappiness. Before the sputtering started it actually revved as fast as the Integra engine!

Anyway I also ordered a new coil, just to make sure

I'm getting the Greddy Emanage and boostcontroller , I'll be able to set the ignition more versatile instead of this crude manner, sadly stand alones are crazy expensive for this car. Maybe Allgo might be willingly to build a safm for me ;D I'll send him my gf :P