ok so what the hell ! i get the car off the dyno 2 weeks ago (made 623 rwhp ) went and beat it up a little that nite and parked it for 2 weeks in leu of running at our drag day. of course drag day gets rained out and it pours all week. i take the car this weekend and now she has a misfire-pop.

it started when i was on my way to race a 04 gsxr 750. i gave her some pedal and at about 15psi, she starts to miss... now here is where it gets odd. at 10 psi, it will run beatifully, pull strong and long all the way through the RPM range, turn it up a few psi and she crackles.

the sound it makes is like some one is lighting off salutes under the drivers side front. the sound is only present at 13 psi or more at WOT above 3k rpm. it is intermittant, and does not have a pattern. the car slows with every pop.

things i did:

changed header gaskets
fresh plugs at .035 (NGK b9es)
changed over to my old MSD wires from taylor 409's
welded header due to some minor cracks
fresh gas
lowered timming with AEM to 17* total
A/F is 10.5


combo:

stock bottom end
stock cam
holley heads
cometics torqued to 85-75ft lbs with ARP studs (new)
holley systemax intake torqued to 15ft lbs
DIY turbo kit
67mm p trim
50lb injectors
255 hp intank pump
AEM with 5bar map
crane ignition

i think it may have eaten another HG on the dyno it was pushing a lil water above 15 psi. nothing to be concerned about. i drove it around after that and it would only push water over 15 psi. if i left the controller at anything below, it wouldnt push water. there is some water seepage from the cometics around the front and back of the head. but some say this is normal

my best guess is that under boost (13psi or more) the head rattles and it lets some combustion gasses out and this is whats making these pops. or maybe its blowing out the spark? i dont know what that sounds like nor have ever expieriance it.

so can anyone point me in the right direction where i should look? i am out of ideas


thanks
dave

 

my guess is either spark blow out, or plugs. I dont liek the NGK's never had luck with them

 

:withstu:

Are you running any ignition box. Try closing you gap a little on the plugs. It sounds like spark blow out. The pop could be the unburnt fuel igniting in the exhaust from the plug not firing.

 

How old is the gas in it?

 

What are you EGT's like when you get above 13psi? Probably a head gasket like you think. Since you stated that you changed all the obvious possibilities.

 

i'm with tunty maloney from conneticut


spark blow out, close that gap change back to taylor wires.

 

At 623 hp the single 225 lph pump seams kind of small. Maybe you are running out of fuel.

 

i'm on the head gasket idea too.

my turbo buick did that... over a certain boost pressure it made this funny noise, i thought the dp was vibrating against the frame or something. almost sounded like when i used to tape playing cards to the spokes on my bicycle to make the motorcycle sound.. turned out to be headgasket

 

Its seems evenly split. Tighten the gap on your plugs and see what happens.

 

ayeeeeeee.... here we go again. i am gunna try the gap first, letcha know in a lil bit

 

So? Resolution?

 

.035" is too big of a gap. Drop them to like .028" and go from there.

 

Hmmm putting new R5671-A9s in tonight, Ill gap them down tight like Dan said.

 

actually i go down to .026" but i think anything bigger than .029" is too large for high boost.

 

yup dropped to .025







































DIDNT FIX IT ! FUCK @%^()#@*

this cars plays more head games with me then a fuckin girl. ayeeeeeeee so i am gunna do some more HG's...... this time around i am doing a 9333 pt1 with yama-bond 4. this sucks... gotta get it together before the 28th... i got time i hope

 

What were your EGT's like above 13psi?

 

what is yamabond?

 

Is that the same as hondabond? That stuff works awesome

 

My nonna uses that stuff on her teef

 

dan, its like a super duper RTV for heads. from what i gather, this stuff is soo strong, the only way to get the head off after it has been applied is to keep the plugs in, remove the nuts, and crank the motor over. the compression will pop the head off. i have heard that yamaha racers do not use a hea gasket, just this shit inbetween.... so who knows. at this point anything is worth a try for me


and bags, i am sure its the same junk


and canadia coupe, i do not have an EGT meter