Well, Speak of the devil.

Sunday I was at the big track at LasVegas playing with God awfull fast road racing bikes. My boy went through MC school at Pheonix and worked in that industy for a few years. Some of his friends are still in it and we were invited to a test day. Watching these things just scares the hell out of me. I cannot watch some of it when two or three guys are fighting over the same apex. I just look away.

No more carbs anywhere. All injected. Hook up the connector, pop in a different  curve and go again.  I have no clue  about it any more.  I can change a tire which is more than some of these people, but that is about it.

OK, TB and injection is very nearly completely different than a carbed engine. Even more so if you are talking about downloading the computer  into your laptop and and pushing that lean spot up a bit and pushing the new curve back into the bike in about 3 minutes. The rider has just enough time to get a slug of water down before the crew chief engineer and owner are looking at him like he was gone for an hour.

Some of these guys have never had a carb apart or are even sure why they ever existed.

The big carb (Large diameter choke) close to the intake valve is a nightmare. The fuel may be spraying out of the vent hole one second, and the float bowel empty the next. If everything is going just right, they lean out at the top, and the trick bag must be opened, to cure that, hopefully without screwing up anything else. Or, the inside carbs are OK and the outside carbs will not come in, because after three weeks you find the intake cam has two different  grinds on it. Or, one two and three must be vented  to the air filter housing but four must be faced forward to get it to work. And every stupid thing that ever happened to an engine will be worse with a carb than with fuel injection. It will be worse with  a  bigger choke than with a smaller.  Worse with  the intake valves within  sight of the butterflys than with a bit more length. Worse if the rider is squeezing the ram tube shut with his knee, better without. and so on. Worse if the original air filter is still in it two years later than with a new one.

With the injector closer to the valve, there is great lattitude in intake design  with no fuel mixture  changing the weight of the flow from  this to that  from this to that RPM,  the engines seem more like electric motors.

With a TPS and manifold pressure talking to the computer, they can cover a poor gear choice off of a certain corner. The suits have carbon back plates for spine protection and streamlined cowels to fair in the helmet turbulance.

With a big TB close to the valves in a bike the TB diameter is nearly the sole control of velocity. So (in a bike,
close to the valves) there is a rather dramatic difference between any two diameters of TB. So, you might get a higher top speed and have no midrange at all from a big one, and have a great engine with power everywhere but the very end of the longest straight with a smaller TB. And this the because the TB is making up nearly half of the tuned length of the inlet. And very well desighned inlets they are.

In the aircraft application, the TB is normally feeding a log style manifold, and in most cases, the TB is on one end of the log, far removed from the last runner into the engine. Equil lengths are out the window, and a rather dull state of tune is more likely the rule at the best of times. However tuning is possible to a great degree, compared to a carb in the same application. It would be great if the common plenum could have semetrical even length runners into the engine, and even if so, how about being able to taylor each injector pulse width for each runner. It is possible but surely expensive.

The TB is so far removed from the intake port that changing its size will have little affect on wide open throttle and near wide openthrottle. With a set of injectors close to the ports that can react to rapid TB movements, and  at various positions below that there may be some benifit to the smaller diameter TB. But I bet with a well taylored fuel curve, that the pilot will be very hard pressed to tell me which I have mounted if the flight has not included a top speed run. When I jump into this, I will jump in with both feet, and we will go fast.

Lynn E.  Hanover