I see that Racing Beat install there fuel injectors in the rotor housings for there turbo PP engines. Has any one here got there PP turbo to run well with there injectors mounted in a more conventional position ie in the throttle body or even above there 'trumpets' .

 

Ok does this mean no one out there has a PP turbo?-maybe it cant be done.

 

Oh it is done all right

 

Wow neat to see thats it done some where -just waiting for a sensible reply to my question. do you have one of these peejay?

 

10k2 I have a personal photo from the RB dyno room from 1997 that shows a tripple rotor with T51 turbo and 6 methanol injectors mounted in the intake runners.

They have done both types (locations) and either works.

Location near the ports gives best responce and economy but higher up near the trumpets gives better power. On PP's either turbo or n/a the biggest thing is you need a richer mixture on transient throttle (bliping & initial accel pump functions) to get a stable combustion (no misfire).

Injector location at the rotor housing is a economy thing at the expense of power. Its not a functional thing that will stop a PP & turbo working together at all so you need not worry Now go build it

 

I've personaly always made more power in the midrange and higher rpm's by placing the injectors higher on the intake track. The torque curve tend to be broader as well. I've also noticed lower intake temps and less detonation with the injectors mounted higher.
There are a couple of possible reasons why RB placed the injectors in the housings. Only testing would be able to answer that. I'll guess it had something to do with exhaust temps or probably it was the safest and only place available to mount them. Your guess is as good as mine!

 

I think it depends on what your computer and fuel system are capable of.

Like Crispeed said, if you have lower end conventional stand-alone computer and conventional fuel system you will have definite gains in having the injectors upstream as this is provides more time for the evaporation of fuel to cool the intake charge. Throttle response and fuel economy will suffer some due to the whetting of fuel against the manifold runners at lower intake velocities.

But, if you have a complex stand alone w/ multiple sequential injection channels and a direct injection fuel system you can gain even more cooling effect AND better throttle response by injecting a short pulse of fuel just as the port opens to cool the intake charge and then inject a longer pulse as the mixture is being finished compressing (requires seperate direct injector locations on the rotary) to provide a fuel dense "pocket" that is easier for the spark plugs to ignite.

What Mazda did on their side port engines when they put the primary inj. close to the port and 2ndary inj. upstream was a good idea to minimize whetting at lower rpms and provide good intake cooling at upper rpms. This could be replicated for a P-port set-up rather easily (staged injectors) w/ a conventional stand-alone and fuel system.

 

Thanks for your informed reply guys. My thinking was with the injectors in the rotor housing you could stop the 'fuel overlap', but still have the 'air overlap'- if you know what I mean. It looks like it will be a better idea to mount them in the intake further away from the engine. Now off to the garage

 

Well, at a guess, RB may have been putting the injectors at the rotor housing because that's what Mazda came up with? The R26B had injectors right at the housing, for reasons of throttle response.

 

The 26B still uses an injector in the intake, at the base of the manifold. The RB PP turbo has the injectors in the rotor housing which I think would squirt once the port had closed?. A bit like direct injection.

 

Injector timing is a falicy on rotary engines !

If you do a "normal" injector sizing equation, you will quickly see that under mid to high loads you need the injector to remain open for a long time. If you break it down into a "duty cycle" as is referenced by almost every type of aftermarket ECU you will see that the injector feeds TWO rotor faces in any one given injector cycle with an overlap period of 50% on any more than one injector per rotor (i.e. primary and secondary).

In basic language, the injection/injestion cycle of a rotary is almost constant there are no massive amounts of time that are dead like in a piston engine at low speeds.

Injector location is more to do with transient drivability and responce and fuel economy in PP engines. It is not an issue of the engine not working with any other injector location as Racing Beat have proved by doing turbo PP's with many different injector locations.

A racing engine believe it or not is a delicate balance between outright power and efficiency (especially the R26B) BSFC is all important that is why Mazda choose this close to port injection location, if you look around there is a good SAE paper describing this in quite some detail.

For power go for the higher injection point and use the energy of evaporation to further cool the charge and make more power, at the expence of bit more fuel use and a bit "grumpier" engine.