Flat Spot Around 5500rpm

[nuffsaid]

Hi all

I have a R34 GTT and have noticed a rather flat spot between 5500rpm and 6000rpm when flooring it in gear.

Its not missfiring I dont think, and it doesnt pop or stutter, it simply doesnt accelerate as hard in that rev range. You feel the power kinda just drop off, but then pick up again after 6000rpm.

I noticed that this has only happened since I put on the full turbo back exhaust (spit dump, cat etc). Even before I put on the pod, it was pretty much the same. Last dyno run, boost was at 10psi. boost increase to 10psi is only because of the exhaust increasing boost, I have not played with boost at all.

Is this rich and retard? which is causing the flat spot?

I currently have NGK copper plugs in there, gapped at 1.1mm, heat range 6.

SydneyKid recommends 0.8mm gap at the same range to fix the problem.

Anyone have any ideas?

Thanks

Edited May 1, 2006 by nuffsaid

[TTT]

SydneyKid recommends 0.8mm gap at the same range to fix the problem.

Anyone have any ideas?

Thanks

I recommend 0.8mm gap at the same range to fix this problem.

[nuffsaid]

I cannot seem to find heat range 6, 0.8mm, platinum plugs for the RB25DET NEO.

I would rahter get platinums to avoid changing the plugs often, its a pain changing them on a RB.

Note: boost increase to 10psi is only because of the exhaust increasing boost, I have not played with boost at all.

[Guilt-Toy]

What you do is get your normal plugs (or the existing ones) and get some feeler gauges and gap them down to .6 or .7 (or .8 but i have used .6) and that may fix the problem.

you would be running more boost with the free flowing exhaust and your boost would be putting out the spark. Common problem.

I cannot seem to find heat range 6, 0.8mm, platinum plugs for the RB25DET NEO.

I would rahter get platinums to avoid changing the plugs often, its a pain changing them on a RB.

Note: boost increase to 10psi is only because of the exhaust increasing boost, I have not played with boost at all.

[nuffsaid]

Are there no such iridium/platinum plugs though that come pre-gapped, I want to go for this option coz it will mean I wont have to replace my existing plugs for a long time.

Common problem, thats good then, hopefully a plug change will fix it, thats IF I can find em! ahah

[TTT]

I've got news for ya dude... in a stock ECU'd skyline, copper, iridium, platinum, gold or whatever is going to foul up just as quick as one another.

Copper is also a better conducter of electricity than the other options.

if you had an aftermarket computer and your a:f ratio's were tuned to be spot on, then you wouldn't have fouled plugs as often, but at 10psi on a stock ecu on an RB motor, you will find that once boost is on and ecu goes out of closed loop cycle, you're a:f ratios are going to go waaaaaay south.

and they are going to get fouled up.

What I did was use copper plugs at 0.8mm.

when I was putting the engine bay back together, I left the coil cover off.

now All I have to do to change plugs is remove the cros over pipe and bov attachment and I'm ready to remove the coils and plugs.

This is on an RB20 but same deal for you.

plus you have that other engine cover on the NEO which I'd leave off too.

better cooling for the coil packs anyway.

[nuffsaid]

Fair enough, I guess my AF ratios are gones now aye. And now that they are, it means fouling of plugs right? Well since my car will foul plugs more easily now, I guess theres no point in platinum.

I was under the impression that my plugs arent being fouled so figured that platinums were a good way to go.

Even coppers for an RB gapped at 0.8 are hard to come by right? self gapping it is then

[TTT]

Fair enough, I guess my AF ratios are gones now aye. And now that they are, it means fouling of plugs right? Well since my car will foul plugs more easily now, I guess theres no point in platinum.

I was under the impression that my plugs arent being fouled so figured that platinums were a good way to go.

Even coppers for an RB gapped at 0.8 are hard to come by right? self gapping it is then

no there are some already 0.8mm... I don't remember the number though..

but the spark plug gap feelers (I think that is what they are called) are only about $30 from supacheap I think.

they look like a swiss army knife but each blade is a feeler of Xmm thick..

you just tap the plug gap closed and keep feeling it till the designated feeler touches both sides of the gap and that's it.

[nuffsaid]

Yeap got one of those. Just figured if I already needed to buy new coppers, maybe Im better off getting them pre gapped, then Ill just check.

[Abo Bob]

I think your plugs should be gapped to 0.8 and Iridiums are the new platinums and you can buy them already gapped to 0.8.

As others have said you can gap your current plugs down.

As for fouling your plugs straight away... hmm I don't think so. Yes your car will be running richer but it is not going to foul the plugs unless something else is actually wrong with the car. Don't go buying copper plugs for that reason.

All that said, I don't think this is your problem. Assuming you are right when you tell us there is no stuttering or misfiring type behaviour, this is R&R and there is not much you can do about it except get a piggyback ecu like a SAFC or an aftermarket one like PFC.