How the boost feels in the high rpms

[Jookmasta]

so this past week i took some friends in my car for a ride and the car acted really weird after about 4500 or 5000 rpms. This occurred after the one good boost pull but mind you it was like 90 or so outside. Nonetheless, the car would pull like normal going thru the powerband fairly quickly until about 5000 where it would slow up like it was NA. now i asked one of my friends about it and he said that it is due to my use of an mbc. It bleeds off the boost pressure which causes that response to occur. I thought that my need for new plugs could also be the culprit as well as the gap of the plugs. And the heat probably didnt help either. So is there anything else that could explain this or am i hovering over the solution? All opinions/comments would be greatly appreciated

[Florida240sx]

What size is your turbo?Is it choking at that high rpms?Got any a/f ratio?Did it pull to redline before?

[Jookmasta]

well my turbo is a str8 T3. doesnt really choke at high rpms (well at least in first and second). Also my a/fs were elevens and twelves but that was with an exhaust leak. now i really dont know what my a/f's are but im goin to retune after this hurricane does its thing. it would normally pull but i see the boost fluctuating after the peak is hit due to it being an internal wastegate. so basically it goes up and down (not by much) when the 12 psi is hit.

[fabio420]

The mbc can be your issue, but if you have the same size turbo I do, than that's common. My t3 is small (.42 trim, .48a/r) starts to loose boost at 5000 rpm. At that point it drops from 14 psi to 9 psi. Has your turbo never had this prblem before? How big of a t3 do you have?

[Structure240sx]

does the car feel like it falls on its face? does it sputter at all?

[skatanic28]

what plug gap are you running?

[Florida240sx]

I think it's the turbo.....But changing other factors might make your turbo better like plug gap.

[fiznat]

Sounds like your ignition missing to me. That happened to me for a while untill I got my MSD box and coil set up correctly. It would pull just fine till 4000-4500 or so and then start to sputter and lose power like crazy.

Anyways, pull your plugs and see how fouled they are (they will foul quickly if you are running rich). Check your gap (.030" or so should be good for your boost level, maybe even a little tighter) and either clean the plugs or replace them. If that doesnt work, then start looking into more complicated problems...

[KATwo40]

Sounds like your ignition missing to me. That happened to me for a while untill I got my MSD box and coil set up correctly. It would pull just fine till 4000-4500 or so and then start to sputter and lose power like crazy.

Anyways, pull your plugs and see how fouled they are (they will foul quickly if you are running rich). Check your gap (.030" or so should be good for your boost level, maybe even a little tighter) and either clean the plugs or replace them. If that doesnt work, then start looking into more complicated problems...

WTH???

Why plug gap at .030" ? I'm running 10-11psi and .044" with no problems. I doubt he's blowing spark out. He's probably within 15-20whp over what I'm making.

[Florida240sx]

Your running stock gap?

[KATwo40]

Yes...somewhere between .040 and .044.

[nissanfanatic]

What is yoru setup?

[KATwo40]

s13KA24DE (stock, unopened, 140k, original headgasket)TD04H-13C (Too small...soon to be replaced)10-11psi370'sWalbro 255stock fuel psi reg.stock ecustock MAFSAFC2FMIC 30x6x3Custom methanol intercooler sprayer (designed by me)base timing approx. 15* BTDC2.5" custom turbo back with flowmaster dual chamber (LOVE the sound, but the exhaust has to be 3" soon)plug gap on .040 if I remember correctly.

Makin' like 235ish whp.

Next week I'm bolting the 50-shot on it. We'll see how that holds up. Should show some decent upper end spooling if it doesn't essplode!

[fiznat]

WTH???

Why plug gap at .030" ? I'm running 10-11psi and .044" with no problems. I doubt he's blowing spark out. He's probably within 15-20whp over what I'm making.

Well it depends. Honestly I have no experience with the 12 psi range, but I know from experience that at 20 psi with a MSD 6a and Blaster II coil, I will lose spark unless I'm gapped down to .025". I figured he wouldnt need to be that extreme, but it seemed like a decent place to start. Hey, its only spark plug gap-- if it doesnt work well its simple enough to adjust. It is just my experience that once you start getting up into the boost, you're gonna need to seriously tighten down that gap.

[KATwo40]

Best way to tell for sure if it's blowin' out is to use an oscilloscope with data logging while on the dyno. Then you can study the algorhythms and see if it's blowing out.

[fiznat]

Ok or you could just change the plugs and gap for less than $10 and see if it helps. KISS

[PapaSmurf2k3]

or take the old plugs out, clean them up, and gap them tighter for free.

[S14tat]

i was blowing out spark at around 13 psi. the car felt like it hit a rev limiter or something. the studder was very very obvious. it basically felt like a major mis fire once you hit high boost. i had to gap them down to .027"

[Jookmasta]

well on one of the pulls, the car felt like it fell flat on its face. on the third run, it sputtered. So the sputtering could definitely be solved by gapping down the plugs more and changing em. My turbo is a 60 trim with a .63 a/r str8 T3. It didnt do this when i had the boost leak problem. It would hold 9 psi all the way to redline like an animal. I do think an MSD box would benefit the setup and definitely eliminate this but as fiz said, ten bux vs. 200 if not more bux. Now the more i think of it, the more i think it really could be the plugs since they are still gapped for 9 psi. But it definitely doesnt feel like i hit a rev limiter but it did do the sputter thing like structure said. What should i bring the gap down to?

[WDRacing]

Make sure your not suffering from mild detonation. I used to street race ALOT on Okinawa. Before I had any real idea what was what with turbo's, I would just add booost and roll. I blew up alot of RB's that way. But I would hear the ping somtimes, somtimes I wouldn't, but it would get slower then fall on it's face when it happened.

Not saying it's happening, but you should re-check your AF's now before you un-*** your motor.

[virus77]

There is so many variable that you can assume one gap will work for all cars. Like everyone said, knock down the gap a little and see if the problem goes away. My car couldnt pass 12 psi with a .035 gap so I took it down to .028 and I was good till 17 psi on a t3t4 50 trim. I just put an SR in and I didnt even bother with the big gap, gapped them down to .028 and called it a day, I know Im gonna be upping the boost to 18 anyways so...

[Craving4Boost]

is it ok just to gap it even if im not going to make that much power? just so i wont have to worry about it no more?

[KATwo40]

Just crossed my mind:

We've also overlooked a major roleplayer in this "blown spark" conversation.

Using crappy A-Zone wires will also determine spark strength. Maybe one of the reasons my stuff doesn't blow out a .040 gap @ 10psi is because I run a $100+ set of NGK wires. There's no arguing how good those are. I've seen cars come into my shop with misfires and the A-Zone wires had less than 5k miles on them. We'd yank those off, put some NGK wires on and they never had another problem.

This is for Jap cars, anyhow. A-Zone wires work fine for domestics.

[virus77]

I had NGK as well and it blew out, but a good set of wires is a good thing to have.

[mkory]

Hey... I'm just curious, but what's the point of having a big gap at all? Why not just sell the car (or new plugs for that matter) with a tight gap?

[WDRacing]

The larger gap yields a larger spark, in turn giving a better ignition of the AF mixture. Added boost increases the pressure so much that the spark has a hard time completeing the circuit and igniting the mixture.

[Florida240sx]

I keep getting distracted....I still need some plug wires and plugs for that matter by Wednesday.Where can I go and what is it one step colder than stock? part # would be appreciated.

[Jookmasta]

well i will definitely look into that WD. i havent been pushing the car since that occurence so when i get to my friend's house this week, ill report back the a/f's. i would sincerely hope its not detonation. The car doesnt drive weird and i dont feel loss of pressure or misfiring everyday. It was just that one instance. Im gonna replace the plugs b/f the tune so yall think a .028 gap should do?

and for florida 240sx:NGK-BKR6E-11

thats one step colder. its either BKR or BRK, dont remember exactly. but just go to advance, tell em u need spark plugs for ur 240 and when they bring up the NGK V Power plugs, it will say 5E so tell em u want 6E but the rest of the info/letters are the same on the model number.