Car: Impreza Hawkeye WRX (2.5l)
Mods: After-market exhaust (pipe and rear box) - CAT in place

I changed the air filter element for a Cosworth one (following a recommendation from another Scooby owner) and the engine developed a "flat spot" around 3k revs on hard acceleration, lasts a few milli-seconds (seems like an age) and then accelerates fine

I changed back to the original "Unipart" one today and the flat-spot has gone but acceleration doesn't seem as powerful as with the Cosworth

I know the obvious solution is a remap but I don't have the funds to do this yet. So in your expert opinion do I keep the Unipart filter and "slower" acceleration or stick with the Cosworth and accept the flat-spot until a remap?

Am I going to do any harm running with a flat-spot ?

Advice/thoughts please

 

I "think" the hawk eye 2.5 engines are abit of a pain, and very sensitive.

That flat spot if I remember correctly is a lean point.

Like I said, I'm not 100%. There's some thing like a different map for normal driving then a another for BOOST. Or something along those lines. Ie when Accelerating, something changes over that's different from oem set up causing Tito run dangerously lean for a few milli seconds.

I think a remap is the answer. But I'm not sure if you need an after market ecu.

A guru will be along shortly to clear it up. Hope you find the problem mate.

 

Thanks.

A lean point would make sense as they'll be more air coming in with the Cosworth filter in place therefore the lean point would be more noticeable as it would be even more leaner (and less noticeable with the Unipart filter) - if that makes sense.

Yes I know a remap is definitely the thing to do but it'll be a good few months till I've enough cash to do that (new baby and a new car are expensive things) so need a "safe" solution for now but would prefer not to "lose" the extra power the Cosworth felt like it gave me.

I'm aware it may only be an "Phantom" increase rather than a real one as I was "hoping" for more - if someone can clarify that there's naff all difference with standard or Cosworth in place I'll just stick to the standard one for now?

 

Its probably a different induction sound makes it feel quicker. The filter alone will make very little difference.

More importantly if theres a lean spot. It could result in major failure. The sensible head says stick with the unipart filter until you can afford the remap. Then have it all done at once and enjoy a safe car

 

tick tick tick booooooooooooooooooom

 

OK will go for the "sensible head" solution - many thanks for your input chaps

 

Standard filter is as good as any until it gets blocked.

 

This is very strange.

You certainly don't need a remap for a freer flowing panel filter, the changes will be minimal.

 

All I can say is that with the standard filter I couldn't get it to "hesitate" yet with the Cosworth I could make it happen.

Maybe I dislodged something (the MAF sensor for example) when I put the Cosworth filter in.

I'll have to swap it again to re-test....this could be a never ending story, lol

 

Lvc do a quick test & remove airbox scoop go out & see if that cures it , clean your airbox & Maf tube of any oil film whilst your at it / see if that cures it

 

OK will give that a try - thanks.

What's the idea behind removing the scoop (I get the cleaning of the other bits) ?

 

Less induction pressure
Curious to see if it alters it may well make it more lumpy further up the band
If it cures your flat spot at 3k but pushes throttle issues higher up then I would go back to stock ( with scoop attached) until you were actively seeking more power with a package modification & remap

Regards

 

OK thanks - will give it a go and report back

 

Progress report:

Took out the Unipart filter (again), cleaned the airbox, found some carb cleaner and cleaned the "sensor thingy" (MAF I think), found a spare clip that I think the Sensor wire should be held with so re-routed the wire via the clip, put in the Cosworth filter, let the engine warm up gently and went for a spirited drive and .......................no hesitation and lots of lovely acceleration

So it looks like the sensor was possibly a bit mucky and didn't like being disturbed when I swapped the filter the first time

Many thanks to all for your help and input - most appreciated

I'll definitely going to get a Re-map done but am now happy to use the car whilst I save the pennies