Losing puff after about 5,000rpm

jordy · 13-08-2006, 07:22 PM

So my '91 Astina GT (Japanese BG) goes absolutely awesomely and I love it, and it has plenty of power (below those revs), except I feel I am missing out on a good 20kW or so.

It seems as if it pulls harder at 5,000 rpm as it does at say 6,000 or 6,500. Now it's an old car so I don't expect it to be perfect, but I've seen dyno sheets and Jap BPs are meant to peak at 99kW at 7,000 rpm. There doesn't seem much point reving my engine past about 5,500.

Really the only thing I have done to it is replace the airfilter, which made a small amount of difference to low end power but nothing noticable to the upper end. Oh and I have had the middle resonator removed because it rusted out, it's straight pipe in there now.

Since I have just landed myself a cushy new job I will be getting new plugs, fuel filter and CAI after a while. But the thing is I understand these cars have what's called VICS which opens a butterfly valve at around 5,000 rpm give or take. Now if this wasn't opening as it should, then I would expect this exact symptom.

What's your ideas?

mazdamanik · 13-08-2006, 09:47 PM

generally from my experience before 5000 is just teh sweet spot of the bp engine, like for example the wrx sti is faster if you shift before readline because of the powerband, i dont tihnk theres mch u can do to stop it short of having to remap ur ecu

LordWorm · 14-08-2006, 11:16 AM

I'd think that if the car is running out of puff right when the VICS is spose to be opening, then thats where your prob is.

Other things could cause it i spose...restrictions in the exhaust, restictions with the cams, restrictions in the tune, spark fade, limitations of the injectors, etc etc...

But i'd think if the problem is occuring right when something you know is spose to be opening, then thats a good place to start looking.

jordy · 14-08-2006, 08:59 PM

Ok thanks.

Can anyone suggest an easy way to check if it's opening or how to have a look in the inlet manifold without ripping it too much to bits?

Do BPs normally keep on pulling hard right to the redline or is fairly commonly noticed thing?

mazdamanik, the WRX being faster before the redline will be because the turbo loses efficency at higher revs, that shouldn't be so much of an issue with an NA engine, only restrictions, mostly the cams, and the BP not reaching it's max HP on the dyno till 7k suggests it has fairly agressive cams already.

13-08-2006, 07:22 PM	#1
jordy Junior Member Join Date: Oct 2004 Location: New Zealand Car: '91 BG Posts: 230 View Photos By: jordy	Losing puff after about 5,000rpm So my '91 Astina GT (Japanese BG) goes absolutely awesomely and I love it, and it has plenty of power (below those revs), except I feel I am missing out on a good 20kW or so. It seems as if it pulls harder at 5,000 rpm as it does at say 6,000 or 6,500. Now it's an old car so I don't expect it to be perfect, but I've seen dyno sheets and Jap BPs are meant to peak at 99kW at 7,000 rpm. There doesn't seem much point reving my engine past about 5,500. Really the only thing I have done to it is replace the airfilter, which made a small amount of difference to low end power but nothing noticable to the upper end. Oh and I have had the middle resonator removed because it rusted out, it's straight pipe in there now. Since I have just landed myself a cushy new job I will be getting new plugs, fuel filter and CAI after a while. But the thing is I understand these cars have what's called VICS which opens a butterfly valve at around 5,000 rpm give or take. Now if this wasn't opening as it should, then I would expect this exact symptom. What's your ideas?

13-08-2006, 09:47 PM	#2
mazdamanik Senior Member Join Date: May 2004 Location: Rathmines Car: Was an Astina now a Commohore :-( Posts: 903 View Photos By: mazdamanik	generally from my experience before 5000 is just teh sweet spot of the bp engine, like for example the wrx sti is faster if you shift before readline because of the powerband, i dont tihnk theres mch u can do to stop it short of having to remap ur ecu __________________ You can't race what you can't catch!!

14-08-2006, 11:16 AM	#3
LordWorm Senior Member Join Date: Feb 2006 Location: . Car: . Posts: 1,689	I'd think that if the car is running out of puff right when the VICS is spose to be opening, then thats where your prob is. Other things could cause it i spose...restrictions in the exhaust, restictions with the cams, restrictions in the tune, spark fade, limitations of the injectors, etc etc... But i'd think if the problem is occuring right when something you know is spose to be opening, then thats a good place to start looking. __________________ Need parts? Contact sales@b3motorsports.com

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Losing coolant & oil and blowing white smoke	X-Lead	Performance & General Maintenance	21	08-08-2006 07:36 PM

14-08-2006, 08:59 PM	#4
jordy Junior Member Join Date: Oct 2004 Location: New Zealand Car: '91 BG Posts: 230 View Photos By: jordy	Ok thanks. Can anyone suggest an easy way to check if it's opening or how to have a look in the inlet manifold without ripping it too much to bits? Do BPs normally keep on pulling hard right to the redline or is fairly commonly noticed thing? mazdamanik, the WRX being faster before the redline will be because the turbo loses efficency at higher revs, that shouldn't be so much of an issue with an NA engine, only restrictions, mostly the cams, and the BP not reaching it's max HP on the dyno till 7k suggests it has fairly agressive cams already.