Rotary injectors in piston engines?

[Tripharn]

Hey guys,

I've heard from a friend that this is generally not a good idea? But I've seen a number of people do it? The reason is, I have some 550cc injectors from a RX7 that are a direct fit for my car, so I was hoping that I can use them.

Basically it is something to do with the spray pattern.

So, has anyone on here used any rotary injectors, and have you had any problems with it?

Thanks,
Tripharn

[Spac]

550cc injectors from a S4/5 13B Turbo are a quite common 'upgrade' into up-stop-down-stop engines.
They're a fairly old injector nowdays (close to twenty years!) and I imagine that the spray pattern / atomisation is probably lousy compared to a modern injector, but they still work fine - as well as any other twenty year old injector anyhow.

The spray pattern is probably pretty poor also due to their relatively large size (it's generally easier to get good atomisation and spray pattern from a smaller injector if everythnig else remains the same).

None of this is because they're "rotary" injectors - they're just reasonably large, old injectors that happened to be originally fitted to a real motor.

[Zac]

Spac summed it up. I have those injectors myself in a 4 cylinder. I had them spray tested and cleaned though.

[Tripharn]

Yea, ok... I've had mine reco'd as well. I just know of a guy who is having trouble making any decent power from his engine, and can't figure out why. Someone suggested that it was because of the injectors he was using.

I guess what you are saying is that the design is 20 years old? Not that the actual injectors are 20 years old Well, since they are a direct fit I'll see how they go....

Hey Zac, what setup are you running (and what car etc)... and power etc, because I'm looking for close to 300hp ATW or so with those injectors if I put them in.

Thanks,
Tripharn

[Spac]

The first S4T RX-7 was released in 1986. It will be 2005 tomorrow. You do the maths...
Hell, even the very last S5T is nearly fifteen years old...

[Tripharn]

Ok, I thought they were only in Series V since that is what I was told they were out of. Plus, I keep forgetting it is almost 2005....

[Spac]

There's an extra vertical ridge on the S5 ones, compared to S4 (or maybe its the other way around, I can never remember...).
But everyone wants to claim s$%t that simply isn't true in rotary land... S5 sound better 'cause it's newer, so lots of S4 injectors suddenly morph into S5 ones...

[IMOA]

Where "rotary" injectors tend to be different is they are a single pintle design rather than the quadjet design used on most modern DOHC engines. The two theories I have been given regarding the atomisation issues are that the since the quad jets are spraying from 4 individual holes you get better atomisation than spraying from one large hole and also that in the dohc the injector tends to be spraying straight at the divider between the ports so it's better to spray into the ports themselves (quad jet) rather than at the divider (single pintle). In my experience where you notice this most is not so much peak power but at low rpm/throttle openings where the velocity of the intake charge is much lower.

[Zac]

They all have different part numbers written on the side. This is the best way to distinguish them.
http://www.rotaryresurrection.com/ro.../injector.html

[Busky2k]

The two theories I have been given regarding the atomisation issues are that the since the quad jets are spraying from 4 individual holes you get better atomisation than spraying from one large hole and also that in the dohc the injector tends to be spraying straight at the divider between the ports so it's better to spray into the ports themselves (quad jet) rather than at the divider (single pintle).

So you're saying that actually the 'alignment' of the injector in the port is pretty important? Ie if you rotate the injector 45 degrees, then 2 of the holes will spray into the divider and 2 into each port instead?