I have a couple of questions for discussion after the current 350 build on the main page:
1. Are second injectors allowed in the 450 class of Pro Motocross?
2. If they are, could teams develop a start map that uses the second injector to boost start power? I suppose it’s a moot point if every team does it, but a team with the technical resources to dial in a setup like this could significantly improve their starts—if the rider can keep the front wheel on the ground.
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Yeah they are allowed.
Twisted has a dual injector setup paired with a different throttle body that some guys are/were running. Pretty sure Nicoletti was running it his last year on Club.
I don’t think it really works as a “boost” on the start, just helps overall responsiveness and power.
I haven’t ridden with a dual injector setup on a 450, but on a 250 it makes the engine spool up quicker and gives it more power everywhere.
As far as I know, yes. As for the second question, would you not want more power all the time anyways?
The best way i can describe it on the crf450 is rode that had one is for 1 it depends on how you want it set up.
You basically can use the 2 injection points to make things more linear, more quick pickup snap or with a little work like they did on that bike they wanted it to have more straight low end slow tractor grunt.
I would love to try a rmz450 or kx450f with one on it.
Lots of pros aren’t necessarily looking for more power with a 450. More usable power where you need it, yeah. More power everywhere is not the goal for most though.
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Lol my joke didn't land. I get that. I would think having a second injector gives them more control over where the power is which would help someone who know how to tune it
The bikes are fuel injected so this second injector shouldn't be required for fueling. Are they using it to cool the air via fuel evaporating before it gets down the intake? I know this is pretty big on carburators, my boat intake spacer sweats because it gets so cold.
I don’t understand the 2nd injector thing. I’m not an expert tuner but why don’t we just increase the fueling in the injector or size up if needed?
Closer to the engine is good for one thing, further away is good for another, helps with atomization and response etc
From what I understand, the second injector and throttle body add top end power and response. I thought HEP was running it as well.
Until they start running 3 injectors I'm out
Upstream injectors cause the intake air column to become cooler. Its also fuel in the future, which is necessary at very high rpms. Direct injectors struggle with having enough time to deliver fuel at high rpm even moreso than port fuel injectors ,hence why coyotes, ecoboosts, and the upcoming gm small block all have dual injection. Port fuel injection has excellent low rpm response and atomization at lower rpm, but having enough injector on time(measured in the milliseconds) to get the mix right is easier the further back/ more injectors available. Fuel that is still droplets(liquid) doesn't burn until it becomes mixed with air and is a gas. Which the upstream injector excels at producing. Ever used an airtool or can of hairspray that got real cold? The upstream injector also maximizes this effect, and even moreso direct injection also cools. Enough that compression ratio is able to be raised and or/ lower octane fuel can be used without having to lower compression to fight preignition. Thats why you can run 87 in your ecoboost. (You shouldn't but) it at least doesn't break immediately like an 80s or 90 turbo engine will.
I feel like some ppl imagine the dual injector feeling like a turbo boost. It really doesn't "kick in" or anything, as far as feel to the rider.
Also, I am far from a tuner and could totally be wrong here. But I do own a 250F w a dual set up and I feel like the bike needs to move through the rpms quickly for it to really have an impact. 450s seem to kind of live in a certain rpm range way more than a 250F. If I ride my 250f mellow and try to lug it around, the bike feels docile. But the more aggressive you ride it, the dual injector makes the bike very lively and aggressive (don't mistake it for a burst though.) And that way of riding really doesn't make sense on a 450, to me. So I assume that's why it's not common.
More power is good, CONTROLLABLE power is better.
"More fuel" means more fuel
"More power" means more power
"More fuel" does NOT mean more power.
Most of the start map trickery is done via ignition timing, that is, placing the spark how ever many degrees before, at, or after top dead center, at a given:
I'm also pretty sure they are using, or have developed a way to utilize RPM threshold tuning, meaning: if wheel speed is X, and TPS value (where your wrist is) is Y, and X increases without an increase in Y, thst indicates a wheel spin condition, which triggers a timing and fueling change.
That's how you do it without having to use a Hall sensor (illegal) and/or the ol JGR James Stewart Erin Bates "must be mud" traction control sensor.
Listen to them Hondas off the starting gate. It is immediately noticeable how they have adjusted the mapping on those 450's. A 450 revved to the moon off the start wouldn't be good for joe blow. But boy oh boy, them hondas retard that timing and that thing pulls like a tractor in 2nd gear and when they click 3rd it is a rocket ship
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