Flat Spot In Power Curve

[JAP033]

Hey guys I have been on this page for a little while but only used it for a reference sort of thing. But now I thought I would try my luck asking a question. I recently got my 33 gtst tuned and it has a flat spot in power curve. I basically just want to see if someone has had a similar problem and what they did to resolve it.

Mods are.

•Haltech platinum pro plugin.

•Hypergear atr43g3 on standard exh mani

•Nismo 740cc injectors

•Ebay intercooler kit

•3" bellmouth single piece dump pipe to 3" delete pipe and steps up to 4" before rear muffler.

•Standard plenum

•3" intake to pod filter and 2.5" cooler piping.

•Tomei fpr

Car makes 255.7rwkw on 20psi with bp98 which seems low compared to other peoples results.

Have checked for boost leaks with none found.

Tuner said that he thinks restriction is exhaust manifold but have heard of standard ones still getting 300kw etc.

Has anyone had something similar?

Regards Spencer

[Ben C34]

That is a whack result. Scottynm35 has seen huge power through stock mani, Not sure what your issue is, many things to check but I hope you can get it sorted out.

[scotty nm35]

I saw 430kw through the stock exhaust and intake manifolds the other day, I doubt that is the restriction.

Did you drop the exhaust anyway?

[JAP033]

Na I didnt drop the exhaust because I was pretty confident it wasn't a restriction at the time. Might do it once I get it back on the dyno after I change induction pipe to 4" and maybe see if there is a pressure drop through intercooler

[scotty nm35]

I have seen over 400kw through a 3 inch intake too, infact the 430kw 33 had a Z32 afm... No point going bigger than the AFM unless you ditch it and go MAP sensor.

Just looking at the graph, it seems you are missing a chunk of boost in the midrange, did you get a boost plot by chance?

[JAP033]

Sorry forgot to mention that its running haltech inbuilt map sensor.

[scotty nm35]

I would try a different tuner perhaps, nothing like a second opinion...

[JAP033]

Didnt get a print out of boost plot but spikes to 20.7 psi and holds 19.8 to 20.1 psi and doesnt drop

[ARTZ]

yeah ebay intercooler doesnt explain much,....there are good kits and really bad ones.....could be an issue depending what you have..

[JAP033]

A good way to tell if its cooler is to check pressure drop though right?

[Lithium]

That is a whack result. Scottynm35 has seen huge power through stock mani, Not sure what your issue is, many things to check but I hope you can get it sorted out.

E85 is a hell of a thing. Can't compare a car which is tuned on petrol with one which is tuned on ethanol - the nastiness which is the stock manifold gets covered up a bit if using a very knock resistant fuel.

[scotty nm35]

E85 coveres up 200kw... Yeh right.

Anyway, 250 isn't it's limit surely, not to mention, where is his midrange? It either has no boost in the midrange, or no timing, probably due to a big restriction somewhere. Cam timing?

Did I mention my closed 1.5 inch Varex exhaust makes more than 250?

[Lithium]

I wasn't referring to the 250kw thing specifically - so much as how ridiculous comparing a big turbo high octane combination with a small turbo pump gas setup... there is an issue there, but mentioning a 400+kw ethanol setup is probably not being helpful for perspective.

[Blackkers]

not to mention alcohol fuels much lower EGT's probably let you get more power through a restrictive manifold anyway

[mark33gtst]

I wasn't referring to the 250kw thing specifically - so much as how ridiculous comparing a big turbo high octane combination with a small turbo pump gas setup... there is an issue there, but mentioning a 400+kw ethanol setup is probably not being helpful for perspective.

It proves the standard manifold can flow a lot more than the power he is making. Many people (myself included) have made much more than 250kw through standard manifolds on 98. Why argue against scottys valid point that in this case manifold flow is not the restriction?

[simpletool]

Loses 20% torque in 600rpm. What happens between 5000 and 5600rpm?

Ignition timing reduction? Boost drop?

[simpletool]

It's not the manifold doing that.

[Lithium]

It proves the standard manifold can flow a lot more than the power he is making. Many people (myself included) have made much more than 250kw through standard manifolds on 98. Why argue against scottys valid point that in this case manifold flow is not the restriction?

Because I was bored at home with manflu and brain wasn't working very well - my bad! Forgot I even posted that. There is clearly an issue that isn't the exhaust manifold causing it.

[JAP033]

I changed my induction pipe to solid 4 inch yesterday instead of it stepping down to 3 inch. Tuner is going to print me out a picture of boost plot so will show that when I get it. Also going to change actuator to 14psi and run an eboost street to have high and low boost and get retuned.

Here is a photo of my timing map

[r31 25t]

That timing map is pretty average. Looks like a huge reduction at around 5krpm-20psi drops like 3-5deg then back up at 6k. I'd imagine that'd feel pretty flat through there.

Did the tuner say anything about the engine wanting to knock?