High end power lacking

[zx2yetti]

Hey guys,

I'm new to the site, but I've had my zx2 for a little over three years now. I have always noticed that my top end seems weak. Basically, the car stops pulling at around 5500 rpm, and just starts to make a lot of noise all the way up to 7k. This really sucks, cause it isn't any fun to take it above 5.5k. Why does my top end suck?? What mods would help most??

I do live in Colorado, and drive at altitudes from 6 to 9 thousand feet (some pretty thin air).

I have a couple of little mods done, like a K&N, removed the lower resonator, replaced the muffler with a glass pack, and a couple others that don't have to do with power. And I'm planning on some others this summer. Just curious as to why my car doesn't pull all the way to the fuel cut off.

Thanks in advance for any help!!!!

[iceracer]

Engines lose power at higher altitudes.

[chasingsafety]

I found that by pulling my knock sensor, I got much more top end power

[zx2cambo]

my i have some things done to my car and i still have sucky power from the same RPM ranges..... im hoping my 4-1 header im getting should help that out a bit. only thing i can think of that could help out is SCT and cams possibly.

[zxtuner98]

get a cam gear and advance the timing.

[joshalabama]

my i have some things done to my car and i still have sucky power from the same RPM ranges..... im hoping my 4-1 header im getting should help that out a bit. only thing i can think of that could help out is SCT and cams possibly.

You will love the 4-1 header ;)

[zx2cambo]

You will love the 4-1 header ;)

ya im def. looking forward to it. im gonna run it with trubendz piping no resonator or cat... should be rediculously loud

[joshalabama]

Muffler?

[zx2cambo]

ya i have a focuz racing CF muffler

[joshalabama]

It is going to be really loud, but honestly...it will sound so good between 1000-2000 rpm

[zx2cambo]

ya and i was also thinking i can also cut out a section and install a resonator later on if i needed to

[joshalabama]

You probably will, it will be raspy I believe.

[zx2cambo]

o well...we'll see in about 2 weeks

[zx2yetti]

I know engines lose power at altitude...but i would expect a somewhat linear pull from the engine, not a noticeable drop off up high. My buddie's bimmers all pull all the way to the redline at 8500 ft, so is it just the motor from the zx2?? Am i not getting enough air to the engine?? Are the reciprocating parts too heavy to turn up high??

I'm gonna try and pull the knock sensor this weekend, if my fat arm can fit back there ;P Hopefully that will help.

I was also hoping to get a Kami header and an MMI intake sometime this summer (btw, is that a good combo)... and if i'm really lucky (money wise), i want to get the trubendz 2.5" SS with a resonator, no cat, and i'm not sure which muffler....is there any difference between the mufflers performance wise?? i know the site says the aeroturbine muffler is supposed to be the best, but is it?? (i know there are sound differences, i care more about performance.) I have more plans in my sig.

As for the cam suggestion....i'm still not sure what i want to do motor wise. i have a spare engine (a blown thrust bearing from an '03) that needs to be rebuilt, so i have to decide how much power i want (either mild N/A, (20 hp or so), or turbo for any more power than that), but the motor wont be worked on till next summer. I just wanted to do some bolt ons for some more power, make it handle better, and make it stop better.

One last thing (wheezing....) sorry for the long winded response. i have limited access to the internet through the week (a little at work, and dial up at home :( ) Thanks for all your suggestions.....and keep them coming if you got them!!

[joshalabama]

The MMI+Kami will make a huge diff. but your stock exhaust will become a major restriction. Pull the knock sensor to smooth out power band. Then start your upgrading. This car has potential to be a moderantly fun ride to an unreliable sex bucket. Good luck.

[zx2cambo]

lmao....sex bucket.....nice wording :bangnana:

[iceracer]

get a cam gear and advance the timing.

Advancing the timing would reduce the top end. retard it.

[iceracer]

Higher compression helps at high altitude. The stock Zetec runs out of power at around 6500 rpm.

[zxtuner98]

Advancing the timing would reduce the top end. retard it.

man i must have read this article wrong lol.

[Beodude123]

Pulling the knock sensor won't help about 6K, since the engine doesn't look at it after that point. It will help with the midrange though.

Just remember the stock cams reach peak torque at 4,200 or so RPMs. Peak hp is somewhere around 5,500. So yeah, power is going to start dropping off pretty rapidly after that point, especially with the intake manifold designed as it is.

[joshalabama]

Does porting the manifold help at all? Or is the change still too miniscual?

[zx2yetti]

Pulling the knock sensor won't help about 6K, since the engine doesn't look at it after that point. It will help with the midrange though.

Just remember the stock cams reach peak torque at 4,200 or so RPMs. Peak hp is somewhere around 5,500. So yeah, power is going to start dropping off pretty rapidly after that point, especially with the intake manifold designed as it is.

I remember seeing that the peak power was at 5500 rpm....but I have read a few places where people say that shifting anything short of redline is slower than shifting at the peak power. I feel that my car is faster accerlerating if i shift at 5500 rpm than if i wring it out to 7k. So i guess the overall question is: is the redline/fuel cutoff (6500/7000) determined by valve float (i think that is how it is determined sometimes :s), or where power starts to fall off??

I want a bimmer bad.....i know they pull all the way to redline :twisted:

[mechtech]

Your HP peak is at about 5700 RPMS - just about where you lose your butt dyno feelings.
Perfectly normal,.

[iceracer]

The fuel cut off is determined by rpm or road speed. This is set in the PCM.

[zx2yetti]

Your HP peak is at about 5700 RPMS - just about where you lose your butt dyno feelings.
Perfectly normal,.

The butt dyno definitely says its slowin down, lol....i was just checking to see if it was normal because I haven't heard of anybody else really complaining about it. I'll just start with some of my mods (hopefully soon) and hope it helps.

Maybe my first mod should be my porky ass lossin some weight!! :sheep: LOL

[Beodude123]

Does porting the manifold help at all? Or is the change still too miniscual?

It does a little bit, but it's not really all that much. 1-2 WHP above your peak, and that's about it. It helps fuel economy a bit, but not a whole lot.




I remember seeing that the peak power was at 5500 rpm....but I have read a few places where people say that shifting anything short of redline is slower than shifting at the peak power. I feel that my car is faster accerlerating if i shift at 5500 rpm than if i wring it out to 7k. So i guess the overall question is: is the redline/fuel cutoff (6500/7000) determined by valve float (i think that is how it is determined sometimes :s), or where power starts to fall off??



Valve float won't really occur until somewhere around 8,000 rpm. I know Vit was shifting at 7,500 multiple times on a daily basis with the stock valve springs, and never destroyed his engine.

As far as shifting, the optimal shift points for each car depends on it's power curve and gearing. The reason people take first gear up to 7K is because first is wound up so much more than second, that when you shift into second, you go down a lot of rpms. Say you have 60 pounds of torque at 7,000 rpm is first. You multiply that by the total gearing (final X gear ratio), we'll say it's 13 total. So 60X13 is 780 pounds of torque at the wheel. Say that you go into second at 4,500 rpm. Your torque there is 105, and your total gear ratio is 7.5. So for second, you would be shifting into 105 X 7.5, or 787 pounds of torque.

For this theoretical engine, we would want to be shifting right around 7,000 rpms from first to second. Basically, you want to shift to the next gear when the total torque to the wheels is equal in first (at 7K) to that of what you will shift to in second (4.5K).

ZX2s have a really short first, so that's why it's best to wind it up that high. The gap between second and third isn't as bad, so taking it up to about 6,500 is pretty close.



Hopefully that made sense. There was a great explanation on here a while ago. Maybe I'll write a new one. I'm not awake enough right now to do it though.

[silent_1999]

what if his timing belt was stretched? or floppy?

[Beodude123]

ZX2s aren't interference engines, so unless you have upped the compression, or have some wild cams, you should be just fine.

[silent_1999]

ZX2s aren't interference engines, so unless you have upped the compression, or have some wild cams, you should be just fine.

Some mechanics say that they are, probably to up the labor charges...

[Beodude123]

All of TeamZX2 says it's not. Who do you trust more?

[silent_1999]

Ive tried it myself,its not, plus TeamZX2 is the shiznit!