Wedge 'flapper' sound?
Discussion
Hi
would it be possible to alter the airflow meter (hotwire system) on a 400se to get the banging, popping sound associated with the flapper system on the earlier cars? Previously had a series 1 and a series 2 wedge and loved the sound when stepping off the gas. What would need to be changed, airflow meter, ecu?
would it be possible to alter the airflow meter (hotwire system) on a 400se to get the banging, popping sound associated with the flapper system on the earlier cars? Previously had a series 1 and a series 2 wedge and loved the sound when stepping off the gas. What would need to be changed, airflow meter, ecu?
PokiGTA said:
apologies for my ignorance, but what series had the flapper? Was there a change in the injection system?
I think it is just the later cars that have the hotwire system, I have a '91 400se that is and had an '89 350i that was a flapper.The hotwire system also uses a different ecu and the devices connected to the plenum are different, there is no cold start injector or extra air valve for instance. I think the easiest way to spot the difference is the air valve on the back of the plenum, the hotwire system controls this so there are wires coming out of it. On the flapper this valve is just spring loaded and opened by the differential pressure between the plenum and atmosphere so there are no wires coming out of it.
Edited by Toltec on Thursday 26th November 23:07
Try loosening one of the exhaust manifold joints slightly - where it joins onto the main exhaust - so that there is a slight 'blow'.
Then it will suck air in on the overrun, and the CO will burn.
I find with my flappers that the popping is much more pronounced under these conditions, so you might find it provokes it even with a hotwire.
If you find that it works, a more permanent solution would be to drill a hole in the zorst just after the olive joint, and then you can put a jubilee clip around it for the MOT.
Then it will suck air in on the overrun, and the CO will burn.
I find with my flappers that the popping is much more pronounced under these conditions, so you might find it provokes it even with a hotwire.
If you find that it works, a more permanent solution would be to drill a hole in the zorst just after the olive joint, and then you can put a jubilee clip around it for the MOT.
adam quantrill said:
Try loosening one of the exhaust manifold joints slightly - where it joins onto the main exhaust - so that there is a slight 'blow'.
Then it will suck air in on the overrun, and the CO will burn.
I find with my flappers that the popping is much more pronounced under these conditions, so you might find it provokes it even with a hotwire.
If you find that it works, a more permanent solution would be to drill a hole in the zorst just after the olive joint, and then you can put a jubilee clip around it for the MOT.
A few months ago I had those clamps changed so it wouldn't blow ! Didn't make much noise anyway !Then it will suck air in on the overrun, and the CO will burn.
I find with my flappers that the popping is much more pronounced under these conditions, so you might find it provokes it even with a hotwire.
If you find that it works, a more permanent solution would be to drill a hole in the zorst just after the olive joint, and then you can put a jubilee clip around it for the MOT.
combine said:
adam quantrill said:
Try loosening one of the exhaust manifold joints slightly - where it joins onto the main exhaust - so that there is a slight 'blow'.
Then it will suck air in on the overrun, and the CO will burn.
I find with my flappers that the popping is much more pronounced under these conditions, so you might find it provokes it even with a hotwire.
If you find that it works, a more permanent solution would be to drill a hole in the zorst just after the olive joint, and then you can put a jubilee clip around it for the MOT.
A few months ago I had those clamps changed so it wouldn't blow ! Didn't make much noise anyway !Then it will suck air in on the overrun, and the CO will burn.
I find with my flappers that the popping is much more pronounced under these conditions, so you might find it provokes it even with a hotwire.
If you find that it works, a more permanent solution would be to drill a hole in the zorst just after the olive joint, and then you can put a jubilee clip around it for the MOT.
B@man said:
I believe that you have to create an over lean mixture on overrun which emulates the overrun valve bleeding extra air into the plenum on the flapper.
For flappers, its actually the other way around:When the engine encounters rapid deceleration with the throttle plate(s) shut, otherwise known as Overrun, a very high vacuum occurs in all the inlet areas which encourages any liquid fuel lurking there to vaporise. Messers Boyle and Charles wrote some laws about this!
With throttle shut, a small volume of air enters the engine via the Air Flow Meter (AFM) through the idle air gallery plus whatever sneaks past the closed throttle disc. The ECU responds accordingly by trying to inject correctly matched amounts of fuel at a level similar to the quantity at idle. Unfortunately the Overrun depression felt in the inlet manifold is much larger than that normally corrected for, by the Fuel Pressure Regulator, so the overall pressure differential across the injectors is also much larger than the usual maximum of 36 psi.
This has the effect of sucking even more fuel from the injectors than intended by the ECU, exacerbating the overall richness making it impossible for any resultant mixture ito ignite inside the combustion chambers from where it passes unburned into the exhaust manifold.
Here, the rich unburned mixture encounters variable quantities of air, very hot gasses and piping hot metal surfaces enabling random combustion right there in the exhaust system. The result is loads of popping and banging, typically a very loud crackle, capable of generating spectacular flames from the tail pipe depending upon the state and nature of the silencers.
Apart from the anti-social nature of the associated decibels these random detonations outside the combustion chambers create excess stress and eventual damage to any local exhaust manifold gaskets.
Rover and Lucas' initial elegant solution to this phenomenom was to introduce a valve that responds to the high vacuum generated in the inlet manifold to allow in a more generous quantity of metered air from the air rail which in turn operates the AFM flap resulting in the signal to the ECU to inject an appropriate amount of fuel. A secondary effect of the opening valve is to reduce the pressure differential across the main injectors nullifying the excess sucking forces on them,
This larger combustible volume now combines successfully with the vaporising residual unburned fuel to ignite and burn properly inside the combustion chambers. Thus, the unwanted noise levels and it's associated potential damage generated on Overrun are suppressed.
I say "Elegant" because that simple adjustable valve is incredibly effective, as anyone who has tried adjusting it will know.
In later Flapper Range Rover Efi versions a vacuum operated switch/relay was employed to interrupt the engine running signal to Pin 1 of the ECU thereby cutting off all fuel injection for the duration of high vacuum on Overrun.
A system so enabled could have the vaccy switch/relay disabled to allow loads of fuel to be sucked right thro the system to be detonated in the exhaust system as explained above.
It beats me however, why one would want to do this just to make lots of unsociable popping and banging and spectacular flaming exhaust displays, knowing (as you do now) that such dispalys also cause collateral damage to the manifold gaskets and exhaust system seals.
johntom said:
I guess the sound is a big feature of TVR and the reason we love them
I fully agree with your sentiment (having this up-front)
giving me loadsa growl to go with the grunt. Being an Ex Boy-Racer, I'd even go for "unsociable" but the ill-advised acceptance of collateral damage to a loved one is weird.
Edited by honestjohntoo on Saturday 28th November 12:47
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