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kiwicar
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Post by kiwicar » Tue May 15, 2012 12:49 pm

Hi Chris
As a follow up, I am sure Al will correct me if I am wrong, with mechanical fuel injection on methanol, as I said you run an AFR about 4.5:1 for best torque, for best power about 5.3:1 so from peak torque to peak power you blead off fuel to lean out the enging, Al's referances to the top end being "fat" you control this with a poppet valve and a calibrated blead back (pill) to the fuel tank, the spring and shims in he poppet valve control the opening revs (load on the poppet valve seat) and the spring rate controles how quickly it opens, the pill controls the ultimate leaning out.
Another issue that comes up is when having staged and you have the trans brake on, you are holding the engine at the stall revs of the converter and have a spark cut rev limiter stopping you bursting the converter. You are pumping so much un-burnt fuel through the engine that it starts to cool everything down too much, often they fit another lean out set up to take about 5-7% of the fuel away to stop the engine becoming too cold, even though these engines have no coolent.
Best regards
Mike


poppet valves rule!

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ChrisJC
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Post by ChrisJC » Tue May 15, 2012 4:08 pm

Interesting, thanks Mike. That would have never occured to me.
Carburettor icing eh.

Chris.
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Series IIA 4.6 V8
R/R P38 4.6 V8

bigaldart
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Post by bigaldart » Tue May 15, 2012 6:13 pm

it is de-icer in the spray bottle, although the first bottle is petrol to actually get the engine running and allow the mechanical pump to get fuel up to the injectors. As to the air fuel, the poppet valve description is nearly right, rate of opening is irrelevant as the poppet is either open or closed. The spring is chosen from a selection and shimmed to give a cracking pressure, as the engine revs increase the pump supplies more fuel being driven either by the cam or a belt drive like we use. At higher rpm the engine loses a little volumetric efficiency but the pump speed and hence fuel delivery is still increasing. So we bleed a little off to correct the air fuel ratio. In real terms methanol is pretty unfussy and will make pretty much the same power anywhere from 4.5-1 to 6-1 air fuel. The trick is to be in the middle of the band so the engine is not sensitive to atmospheric conditions. Fuel pressure rises along with the flow as the orifice size is fixed by the jets and the return pill. The poppet is set to a pressure which is directly related to engine rpm, another return pill or jet is attached to the poppet to meter how much fuel you want to take away.

Now as for adjustment for different engines the pumps are available to supply anywhere from approx 1 gallon per minute at 8000 rpm engine speed or 4,000 rpm pump speed all the way to a Top Fuel pump which can move an incredible 100 gallons a minute at 4,000 rpm pump speed!

Our pump will flow 6.1 gallons at 4,000 rpm pump speed, we currently have around 3 gallons a minute going to the engine and the rest gets returned to the tank, this is controlled by the ratio of areas between the individual cylinder nozzles and the bypass area. Turn up the blower, change the bypass pill, one jet and you are done! How simple can it get!

Not sure if this video or the other one on You Tube but you can actually see the throttle blades slightly open after the finish line, then he blips the throttle and they close properly. Driver says it is nerve racking as the car is still pulling and he has to take his hand off the wheel to put it in neutral before he blips it.

Alan

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