Problem with a new header on a CRX

[lundgren]

Geek and I are helping a friend, who is more knowledgable about honda's than I, but we are totally at a loss.

It's a 91 CRX. It has an Electomotive Coil/ECU with individual throttle bodies, RC 245 injectors, with a custom air box, exhaust, and now a new CUSTOM header.

The rev limit on the car is set at 8500. The car WILL NOT rev past 7500. As soon as you hit 7500, it feels and sounds like a rev limiter.

So we take off this new header, and put the old one on. With the old one, it revs freely all the way to 8500. (the new header however, makes a lot more power). The new header is a 4-1 with a merge collector and megaphone.

We've added fuel, taken fuel out, changed plugs, plug gap widths, just about everything we can think of and nothing but putting the older header back on removes this problem. The new header is much better, and we want to use it, but this problem at 7500 rpm is a really pain in the ass!

Any suggestions?


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http://www.groupbuycenter.com/

[Ho_Train]

If the engine makes a lot more power with the new header, I don't see the problem. If the engine makes the car run faster with the new header, isn't that the idea?
I assume that "much better" does mean more power, or does it mean that the new header looks "much better". There is a difference.

[grippgoat]

Do you have adjustable cam gears you could play with? Perhaps changing the exhaust timing would make a difference? Or is it a single cam?

Are there any sensors associated with the headers? I don't think there are... Hrm... Are they causing different vibrations or something that might be interfering with another sensor? Is there a knock sensor? Perhaps it's incorrectly sensing a knock and doing something bad.

I'm willing to bet you all know more about engines than I do, but I figured I'd toss out a couple ideas.

Does it feel and sound *exactly* like a rev limiter or *kinda* like a rev limiter. If there was some strange airflow characteristic that was hitting at 7500 rpms that caused destructive interference leading to really high backpressure, could it totally choke out the engine?

Does it do it in neutral? What if you remove the exhaust system, what happens then?

-Mike

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'95 GS-R Sedan Dark Green
Injen intake, DC Ceramic 4-2-1, Greddy SP
GC Coil-overs f/r 380/250 lb/in, KYB AGX f/r 2/3
soon: GC 25mm rear sway

[zip]

Hmmmm...a CRX problem, you should ask Shawn from VTEC.net
He's pretty knowledgeable about the CRX since he owns that Zdyne SC'ed rex.

[lundgren]

Modified the timing and no effect.

To answer the question, yes it is faster with the new header, but you cannot rev past 7500. It starts to go POP, BURP, POP .... and that's it.

Something is not right.

[redline]

sounds likes a misfire

[lundgren]

But it doesn't misfire (if that's what it is) if the old header is in.

[This message has been edited by lundgren (edited May 04, 2000).]

[Holden]

I'm pulling this idea out of my ass, so buyer beware...

To test Larry's idea, shove some steel wool or muffler packing down each of the primaries.

It'll run like crap, but the steel wool will interfere with any back-waves. If it revs over 7500 with no problem, I think Larry's opinion would be proven and your friend will be in the market for new headers!

Don't some expensive headers have a short lead pipe into the primaries that is of a smaller diameter, so any waves coming backwards get killed by the diameter change?

Greg

[sjoback]

Maybe car is making too much power and injectors are being maxed out?
If with the new headers the car makes more power, there is obviously more fresh air availble, so you obviously need more fuel.


spark plug gap too wide and not able to ignite the mixture properly at higher rpm?

couldn't say its not enough spark energy with an electromotive, at least I don't think.

That's all I got.

[lundgren]

We added more fuel. Also updated the fuel pressure 25 psi, no change at all, not even a little.

We tried different plugs, and at different gaps

The electomotive has 2 coils, I doubt it's a lack of spark.

Larry (TOO) thinks it may be some sort of reversion effect with the header design.