Injector Angle for Bandit 1200

[ColinH]

Afternoon All,

I am working on a design for intake runners I intend to machine. I am working on a design that injector enters body at 30mm from mating face on head as that's where VFR throttle bodies and others seem to add up with rubbers to mount etc.

I'm going for injection port on each runner close to head and single throttle body on plenum for the challenge of machining billet runners, sizing plenum for response etc.

When I measure angle to hit back of valves it comes out 20˚ which is very steep to machine and causes clashes with plenum etc. I'm probably overthinking as lots of different throttle bodies have been used on bandit and those angles spray onto floor of inlet port rather than at back of valves.

Any thoughts on injector angles relative to the valves please? 

[peter1127]

Imo it doesnt matter that much. Like batch injection: theoretically you will inject  while inlet valves are closed which doesnt sound good. In reality it works fine. I can imagine if you are looking for that last bit of efficiency and emissions like automotive, this is important. For us, not so much.

[ColinH]

3 minutes ago, peter1127 said:

Imo it doesnt matter that much. Like batch injection: theoretically you will inject  while inlet valves are closed which doesnt sound good. In reality it works fine. I can imagine if you are looking for that last bit of efficiency and emissions like automotive, this is important. For us, not so much.

Thanks for that, when you explain it like that, it really doesn't matter that much. The 20˚ angle is causing all sorts of either machining or welding issues so will go to steeper angle so I can mount fuel rail easier and also clear plenum at rear of runner.

[peter1127]

FYI this is OEM GSXR600 throttlebodies. Sprays definitely not on valves.

 

[ColinH]

Just now, peter1127 said:

FYI this is OEM GSXR600 throttlebodies. Sprays definitely not on valves.

 

That's a great drawing. Did you do this yourself? I found gsxr1100 engine online for free which really helps with layout. I am still check a few dimensions though

[dupersunc]

13 minutes ago, peter1127 said:

FYI this is OEM GSXR600 throttlebodies. Sprays definitely not on valves.

 

Is that your own throttle linkage?

[TLRS]

Some modern injectors spray at an angle. Maybe it offers a small refinement over more simple setups. Wouldn't worry about it too much.

[Arttu]

Yeah, ideally you want to point the injectors towards the valves but in reality it isn't that critical. However, further down to the port you can get the spray before hitting the walls the better.

All this matter quite little at full throttle and high rpm when the air flow is strong enough to keep the fuel moving. But at lower rpms it may have noticeable effect. Especially during throttle transitions. More "wet" intake wall surface you have more you need acceleration enrichment. And excessive acceleration enrichment will cause all kind side effects that can be difficult to compensate.

But as said above, don't worry too much about this. Do what you can to get them at good angle but compromises are fine.

[peter1127]

1 hour ago, ColinH said:

That's a great drawing. Did you do this yourself? I found gsxr1100 engine online for free which really helps with layout. I am still check a few dimensions though

Yeah I measured them, put them in CAD and changed spacing and linkage to be in the center instead of at the outer end.

[Duckndive]

For Whats it worth the mechanical Fuel Injection Nozzles 

On Blown Nitro , Methanol or Petrol Engines used in drag racing are all at 90 Deg to the direction of flow  

[TLRS]

1 hour ago, Arttu said:

Yeah, ideally you want to point the injectors towards the valves but in reality it isn't that critical. However, further down to the port you can get the spray before hitting the walls the better.

All this matter quite little at full throttle and high rpm when the air flow is strong enough to keep the fuel moving. But at lower rpms it may have noticeable effect. Especially during throttle transitions. More "wet" intake wall surface you have more you need acceleration enrichment. And excessive acceleration enrichment will cause all kind side effects that can be difficult to compensate.

But as said above, don't worry too much about this. Do what you can to get them at good angle but compromises are fine.

Any insights about the fuel rail? When injectors open the fuel pressure changes and with that the amount of fuel they inject changes. Are compensators always a good idea?

[ColinH]

Here is first stab at the inlet. In reality the round injector bung will be square as I'm machining out of solid on manual machines but still trying to get that detail right.

Going for solid mount with O ring on face as plenum etc will all be mounted to this and not bike body like airbox is.

Rear will be gasket / ring to plenum plate.

 

[Arttu]

26 minutes ago, TLRS said:

Any insights about the fuel rail? When injectors open the fuel pressure changes and with that the amount of fuel they inject changes. Are compensators always a good idea?

It depends heavily on injector size. With relatively small injectors, like up to around 500cc/min, you can use even a dead head rail without any major issues. Like most of the stock EFI bikes do. But with bigger injectors the fuel pressure pulsing gets stronger and may start causing all kind weird tuning issues.

Flow through fuel rail is the first and most important improvement. When fuel is flowing through the rail back to the regulator the flow in the rail doesn't need to stop and start moving again when the injector pulse. This reduces pulsing a lot and usually it's good enough even for pretty extreme injectors if the rail ID is big enough. 

Pressure compensators / accumulators can improve situation even further but like said usually they aren't necessary. Only cases where I really had needed them are nitro engines with 7000+cc/min injectors...

[ColinH]

3 hours ago, TLRS said:

Some modern injectors spray at an angle. Maybe it offers a small refinement over more simple setups. Wouldn't worry about it too much.

Yeah it’s trying to work out what is for emissions, manufacture cost and drive ability over performance 

[ColinH]

3 hours ago, Arttu said:

Yeah, ideally you want to point the injectors towards the valves but in reality it isn't that critical. However, further down to the port you can get the spray before hitting the walls the better.

All this matter quite little at full throttle and high rpm when the air flow is strong enough to keep the fuel moving. But at lower rpms it may have noticeable effect. Especially during throttle transitions. More "wet" intake wall surface you have more you need acceleration enrichment. And excessive acceleration enrichment will cause all kind side effects that can be difficult to compensate.

But as said above, don't worry too much about this. Do what you can to get them at good angle but compromises are fine.

Thanks for the detailed reply. As I’m matching these runners I have placed the injector at 45deg and moved close as I can to inlet port so shouldn’t hit walls until inside inlet so hopefully that reduces wet walls.

 

[Gixer1460]

Stop overthinking! There is optimal positioning and there is - it works!, positioning. I used twin injector TB's by Jenvey - one in top, one in from below, neither of which point at valves - they just work acceptably well! One point to watch it positioned too close to head a) they can get heat soaked and b) there is a cam chain tunnel in the way of the fuel rail so other things influence where things can go!

[ColinH]

6 hours ago, Gixer1460 said:

Stop overthinking! There is optimal positioning and there is - it works!, positioning. I used twin injector TB's by Jenvey - one in top, one in from below, neither of which point at valves - they just work acceptably well! One point to watch it positioned too close to head a) they can get heat soaked and b) there is a cam chain tunnel in the way of the fuel rail so other things influence where things can go!

I like to know to know how to do it perfectly first, then completely ignore it 

thanks for pointers on head distance, I’m  only slightly closer than a stock setup so hopefully OK.

 

[Gixer1460]

12 hours ago, ColinH said:

I like to know to know how to do it perfectly first, then completely ignore it 

thanks for pointers on head distance, I’m  only slightly closer than a stock setup so hopefully OK.

 

They are much closer as you are omitting the rubber AND it's an aluminium inlet which soaks up heat! Suggest you get it working first then try to 'improve it' or it could end up as a dogs dinner and get parked, never finished - happens too often!

[ColinH]

1 hour ago, Gixer1460 said:

They are much closer as you are omitting the rubber AND it's an aluminium inlet which soaks up heat! Suggest you get it working first then try to 'improve it' or it could end up as a dogs dinner and get parked, never finished - happens too often!

It certainly does but I am a stubborn old git nowadays. Spent a year hand scraping my lathe back into as new tolerance powers by pure spite 

Good points about the heat soak, distance etc thanks. I’m going to cast these now rather than machine solid so less material cost and easier to change.

I think welding up a tube set to start might be better for testing etc.