VAUXHALL ASTRA GTE MK1 CAR PERFORMANCE SPORTS TURBO
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Engine Tuning

 
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glenn
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Joined: 17 Mar 2005
Posts: 2095
Location: Chelmsford

PostPosted: Sat May 28, 2005 10:59 am    Post subject: Engine Tuning Reply with quote

The FSE boost valve is a useful engine protector. If you look at the fuel/air map for almost any standard ECU you'll see that they all go very lean in the higher revs.

The reason for this is partly fuel consumption and the fact that most road cars aren't going to spend a lot of time at high engine rpm so the map isn't considered so critical.

By fitting a 'boost valve' in place of the standard fuel rail's regulator you can artifitially maintain a higher fuel pressure delivery for any given engine rev. This will give a better throttle response and marginally increased BHP (PS) as most engines produce their peak power at high rpm, just as the standard regulator would be leaning off the engine.

The boost valve is simply a diaphram, whose resistance to return fuel, is varied using a spring adjusted by a screw. As you screw in the resistance on the spring it increases the pressure on the diaphram and so prevents so much fuel returning to tank via the return port on the side of the casting. This effectively holds the pressure in the fuel distribution rail artificially high. Given the choice, it's safer to have an engine running a little rich than lean. Engines that go lean at sustained high revs go pop due to bore wash.

As for K&N filters you have to bear in mind that K&N owns Ram Air and possibly Pipercross as well. I think the company was bought by them a couple of years ago. With that in mind it's unlikely that K&N would want their filter range to be beaten by the companies 'lesser' brands. I'm not sure if that is strictly true of the performance of the newer Vector and B2K cone filters that have the cone contained within it's air feed pipe.

If you don't want one of these, as they are bloody expensive, then go for a panel filter in place of the standard paper element as cone filters tend to absorb a lot of the heat soak from the exhaust manifold, which is so close. It doesn't look as cool as there is nothing to show for the expense but if you're interested in bang per buck then a new panel filter will give you more BHP.

You can increase the air volume into the air flow meter by removing the restriction immediately before the sprung door of the meter on the upper side of the airbox. Cold air feed would also be improved by removing the small diameter feed pipe and fitting a larger diameter flexi pipe extending down to the intake in the front valence where the high pressure air is.

Fitting a high air flow filter will have the effect of leaning off the engine as you have increased the air volume per rpm without increasing the fuel delivery. This takes you back to the boost valve as you can now re-adjust the fuel/air mix by adjusting the valve. I'd recommend taking the car to a rolling road as they will need to run the engine, under load, and observe the co2 using an exhaust gas analyser.

One last thing, whilst I'm ranbling, is the tension spring on the air flow sensor. I can only speak for the C20SEH but it may be possible with the 1.8. On mine it's possible to take the cover off the top of the airflow meter to reveal the door's tension spring. The meter's door is opened by the airflow being drawn into the throttle housing. By reducing the tension on this spring it allows the door to snap open wider, earlier and so allows the ECU to provide more fuel as it takes it's signal from a swash plate on the meter. This has the effect of improving throttle response. Be aware that the primary reason for the adjustability of the spring is to maintain sufficient tension on the door as the spring ages and becomes weaker. Be careful to make sure there is still sufficient tension to close the door firmly when not under load.


thanks to Pag1 for the information.
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