Cylinder heads, injector size , type & Set up

Been looking at Injector size and type of manufacture and come across some interesting informtion , also following my trip to the Berg Cup the position of the Injectors in the intake system.

Make of Injector seems to be a wide topic of dicussion.

Size calculation is very important.

http://www.rceng.com/technical.aspx

Position of the Injector in the intake system.

150mm from valve


300mm from valve

 

A really interesting topic.

As I mentioned the other day, it seems there are 2 schools of thought on this one.

Jenvey DTHs are able to position the injector very close to the valve and the feedback appears to be that this is good for throttle response, whereas it seems the more money people seem to spend (works, or Berg), then the more we see of injectors in the trumpets & twin fuel rails. Edit: Mk3/4 Golf exception, but we still see the outer rail quite far out, drilled into the top of the inlets.

Stating the obvious for those who know, but worth putting down early on: all cars with bellmouth injectors have to have 2 injector rails, the inners being requried to get the engine to idle, since the butterflies are shut.

Reference points on this are invariably works stuff (as usual) where 8 injectors across the board is the rule (Golf/Seat/Audi). I've got conflicting stories on which injectors are used at what stage in the rpms/throttle pot positions, with some suggesting the inners are used only at idle and switch off as soon as the throttle moves off zero, and other input which suggests that there is a transition period.

 

There is a wide range of engine specs and injector positions.





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It would definitely be good to get more technical input on what is happening with the fuel mixture, when it is sprayed in, towards butterfies, from far further out. Part throttle must see the fuel bounce off the butterfly, meaning it drains down the inlet and then gets picked up in the airflow again.

Mind boggling!

 

At low airspeeds fuel sprayed that high up the inlet tract would, as you say, just drop out onto the floor, so small injectors with a fine spray are used close to the head to avoid this.

At higher airspeeds though, big droplets/coarser spray coming from the larger, higher-flowing injectors needed to fuel for the top end, need a better chance to atomise. The extra distance from the inlet valve gives the fuel time to atomise. Sometimes injectors perpendicular to the airstream, or even backward-facing injectors are used to mix the air and fuel more effectively.

X-tau correction is a technique used to estimate the thickness that layer of fuel which drops out onto the inlet floor, so adjustments can be made to take account of it being sucked into the engine later on (mainly for emissions control on road cars).

 

WOT would make sense with no butterflies in the way, but part throttle seems a bodged job, bouncing off the butterflies.

Although there is an argument that race cars spend a lot of time at WOT, it won't hold all the time.

 

If my mk1 ever gets done, i'll be running 8 injectors on a standard ABF. You need a clever ECU to manage them properly. I'm using DTA which is fairly simple, switching between inners and outers. I may switch to outers before engine comes on cam i.e 4k, to prevent any glitches or hic-cups in the drive.

Anyone else running standard engines with ITB's ??? I wonder what a standard ABF would peak at??

 

I believe the thoughts regarding injector position date back some time... to an age where injectors did not spray as well as modern injectors do.

the pooling effect I suspect is older injectors

Infinity: 8 injectors on a stock ABf.. I cant see what having enough flow to justify the 2nd set.

 

With correct selection of Injectors type and cc i wouldn't see a benefit in the 8 injector set - up .

But the idea of injectors mounted at the front of the intake trumpets is an interesting one for the maximum atomisation.

For this reason i would probably understand that the inner set of injectors would be used just for idle, but for a race engine that doesn't need good idle maybe the inners aren't required.

 

I forget where I heard it, but the high tickover of a (say) BTCC engine was attributed to open butterflies allowing it to idle. It was chat, rather than gospel.

This could easily be an engine spec oversight, cams/mapping dictating higher idle.

If anyone has seen a BTCC engine on 4 injectors (trumpets only), that would confirm it is real.

 

mute point given no one on here runs a comparible spec motor to BTCC

for the few who have, outboard secondaries, I believe will contribute, but only once the motor is up on song, and will very much depend on motors spec and the tuned length of the intake..

 

On tuned length, it would be useful to see what happened to the injector positions once the FIA castrated the kitcars in 2001 and (AFAIK) added a restrictor to the TBs themselves. This came about after a few WRC events where Citroen in their pre-WRC F2 cars were beating the WRC turbo cars on tarmac events.

It's all in the homologation documents - work in progress this end.

 

I was told in past by few people who knows what they talking about that injectors positioned in common place such as in Jenvey set up is ok for most engine specs reving up to about 7.5-8 K revs

Only on very high reving engines does this become an issue due to poor fuel attomisation as there simply isnt enough time for fuel to mix with air

 

That expains the Berg Cup Boys running the high revving CBR Heads with the outboard injectors

 

I agree, running 8 will be way over the top, DTA won't let me do that anyway. I'm just moving over to the outer set at higher RPM, as far as I know no ones tried it yet so just gathering data really

 

on what blocks

 

1 litre / 1100cc (poss 1300) blocks

 

Red Polo has a 1300cc 16v block 246bhp @ 10500rpm (torque ? probabley very little 50lb/ft)

Blue Polo has 1400cc 16v block 178bhp

 

I think there will be at least 120 lb/ft from a 1.3 engine running that much power

 

i know i was only putting a figure up for that one

Injector Types is an interesting one.

Bosch/RC/Genesis the video is Genesis Bias so i don't think is a true demonstration

www.youtube.com/watch?v=VfynoxL2RZI