Injector Choice For A Given Engine

[Anthony 1,003]

What are the recommended guidelines when it comes to choosing injectors for a given engine?

 

I'm just sorting out the last bits for my new engine (2045cc S16 based) and have come to the injectors. From when the engine was installed in James's car I already know that the standard Mi16 mangement and injectors (214cc) can't cope and runs out of injector flow around 5000-5500rpm resulting in it leaning out - and that was on standard cams and inlet

 

Clearly I need aftermarket management and larger injectors (as I don't like increasing the fuel pressure for the extra strain it puts on the fuel pump) but the question is how large an injector should I spec and what other issues are there with regards to injector choice?

 

The two sets of suitable injectors I have here are some GTi-6 injectors (circa 250cc) and some Saab Turbo Reds (circa 360cc), both of which should flow enough fuel although clearly the Saab injectors will be running at a much lower duty cycle to do so. I know that it's unwise to exceed about 80-85% duty on an injector, but is there any issues with running an injector at a fairly low duty so long as you still have sensible injector pulsewidths at idle/cruise? Logically I can't think of one, but I can't help thinking there must be a reason that most engines are fitted with injectors that don't have a great deal of spare capacity.

 

And then there's the spray pattern of the injector and what effect this has - the standard 1.9/Mi injectors are just a single hole with what I'd imagine is a fairly narrow spray. The GTi-6 injectors have a two hole cap which I'd imagine should give a split spray pattern and spray fuel down both valves on a 16v head. The Saab Turbo injectors have a four hole cap which I'd imagine gives a wide spray patttern. Is one type better than another for a given engine (in my case a 16v NA lump), or does it really make little difference in reality?

[Jonmurgie 2]

Your right about the Mi16 injectors, the standard setup fires all the injectors each time any one pistons fires, therefore they all fire 4 times a cycle and this is how Peugeot get away with using such small injectors in the standard setup.

 

The figure for working out an injectors given 'power rating' at 80% duty is as follows:

 

cc * 4 / 5 = bhp

 

Therefore for the Mi16 injector the calculation is:

 

214 * 4 / 5 = 171bhp

 

So only just enough for standard if they were running on an aftermarket ECU and with sequential firing.

 

So using that calculation you can then work out the 'power rating' for the other injectors you have as follows:

 

GTi6 250 * 4 / 5 = 200

Saab 360 * 4 / 5 = 288

 

So the next thing is to figure out what your expected power is going to be and trying to match the injectors to that power @ 80% duty.

 

Your question about using bigger injectors on a smaller cycle is a good one, but the general answer is your best finding the injector that is closest to your expected power. This is due to an issue on bigger injectors being run on a lower duty cycle and running into problems being given enough time (and we're talking mili-seconds here) to actually open-fire-close. If say your running 444cc injectors for 200bhp then your looking at approx. 40% duty, they are going to struggle to fire in the time the ECU will give them at 40%. Hope that makes sense... it's late!

 

With regard to the spray pattern, again I've been led to believe this is largely irrelevant. Different make/style of injectors have different patterns and unless your getting into BIG power out of small CC engines then it should be very low on the list of things to look at.

[Sam 4]

AFAIK the GTI6 ones are good for ~230bhp @ 3 bar. I'm not sure you'll end up with each of the holes aiming down the throat of the port though because the caps are never on straight, so you could do it but it'd be extra hassle.

[engine killer 6]

i haven't got a clue which is the best but the current set i am using from 306GTi6 is still good enough for my engine. the spec for my engine is: Mi16 block, 85.5mm oversize liners, 85mm JE hi-compression pistons, Schrick fast road cams, Jenvey 45mm tbs, custom 4-2-1 manifold, ported head, Autronic SM2 engine management system. my tuner suggested me unless i go for bv head, otherwise the GTi6 injectors are still capable for any mild modification.

[PumaRacing 2]

Your right about the Mi16 injectors, the standard setup fires all the injectors each time any one pistons fires, therefore they all fire 4 times a cycle and this is how Peugeot get away with using such small injectors in the standard setup.

 

It doesn't make a scrap of difference to the injector size needed for a given peak bhp whether they fire sequentially, all at the same time or in random patterns determined by the time of day multiplied by the colour of the driver's eyes.

 

At 100% duty cycle they're all firing continuously whether they were initially triggered during the inlet valve opening period or not. Sequential only makes a difference at light throttle and low duty cycles when all the fuel can be squirted in while the valve is open. The rest of the time most of the fuel is going in when the valve is closed and waiting there in the port until it opens again. Peugeot just happened to pick relatively small injectors for the Mi16's power but why that is I couldn't say.

[Dream Weaver 2]

I have the Saab reds but just couldn't get them to work well enough on my system, it would miss and backfire like mad with them on. They were unknown and not cleaned though which may make the difference.

 

Mine's running on std Mi16 injectors, which may explain my low power run last week of 173bhp, that or the 20psi front tyres that I forgot to check beforehand.

[petert 586]

Peugeot just happened to pick relatively small injectors for the Mi16's power but why that is I couldn't say.

 

As Puma said it doesn't make any difference whether you squirt 2 x 7.5ms per engine cycle, or 1 x 15ms per engine cycle, the end result is the same.

 

The Mi16 and the 1.9L 8V run the same injector. So it was obvious to run the same part in both. The std. injector hits 85% at 180hp, so that's the end of them.

 

If you're making a really horny engine you might consider running "staged" injectors. One bank of four fires at low-med. rpm, then when it's needed the second bank of four fires, doubling the possible capacity. That way you can get away with eight Mi16 injectors rather than four big ones, that might dribble at idle. As your injector size increases, so does your ability to control them at low rpm. An Mi16 has a 2.8ms pulse at idle, so theoretically, if you doubled to a 428cc injector, you'd need a 1.4ms idle pulse. Theory isn't always correct however, as injector dead time becomes a variable. Injectors are difficult to control under 1.6ms.

 

There's plenty of injector capacitor calculators on the net, but as a guide, 270cc would be the minimum you'd get away with

[Sandy 191]

I'm using GTi-6 injectors on the TB'd 1.8 16v. They shortest duration with the GTi6 pressure reg (can't remember what rate it is), is 1.7ms on the overrun, (batch), idle is around 2.7ms. They work fine so far.

[jimbean 0]

What are the recommended guidelines when it comes to choosing injectors for a given engine?

 

I'm just sorting out the last bits for my new engine (2045cc S16 based) and have come to the injectors. From when the engine was installed in James's car I already know that the standard Mi16 mangement and injectors (214cc) can't cope and runs out of injector flow around 5000-5500rpm resulting in it leaning out - and that was on standard cams and inlet

 

we use green injectors out of cossy`s they seem to be able to cope with high power as they should

[PumaRacing 2]

What are the recommended guidelines when it comes to choosing injectors for a given engine?

And then there's the spray pattern of the injector and what effect this has - the standard 1.9/Mi injectors are just a single hole with what I'd imagine is a fairly narrow spray. The GTi-6 injectors have a two hole cap which I'd imagine should give a split spray pattern and spray fuel down both valves on a 16v head. The Saab Turbo injectors have a four hole cap which I'd imagine gives a wide spray patttern. Is one type better than another for a given engine (in my case a 16v NA lump), or does it really make little difference in reality?

 

I'm not convinced spray pattern has much effect at all other than possibly a small one on emissions and fuel consumption at low rpm and/or low throttle openings. You see, regardless of the type of injector or firing sequence, at high load/rpm any system is going to be firing half or more of the fuel into the port when the inlet valve is closed. It then sits on the port walls and the back of the valve until the next induction cycle vaporises it again and draws it into the cylinder. So how it sprayed in the first place is irrelevant.

 

To put some numbers on this. The four stroke cycle occupies 720 crank degrees, two revolutions of the engine. Seat to seat cam durations for modern road engines fall mainly into the range 250 to 275 degrees. Obviously race engines run longer cams but we aren't much concerned with emissions on those.

 

These durations would represent duty cycles of only 250 to 275 / 720 = 35% to 38%

 

An injector running at anything above those is clearly injecting fuel when the inlet valve is closed regardless of when or how it was triggered.

 

What supposedly can be of benefit is having the injectors mounted further away from the engine. This means there is a larger column of air downstream of the injector waiting to fill the cylinder on the next stroke and perhaps more of the fuel injected into this during the valve closed period stays in suspension rather than dropping out into liquid form on the port walls as it would with injectors mounted in the inlet ports or close to them. That might account for why 8 small injectors with 4 of them in the ram pipes is alleged by some tuners to help peak power in some situations. I'd like to see more definitive test results on this before making my mind up though.

 

However there may well be a completely different explanation. Who can think what this is and what it therefore tells us might be a possible way of investigating it using only four injectors?

[petert 586]

Have a look at two bits of usefull software on this page:

http://www.autronic.com/page_files/software.htm

 

Injector Range - for determining injector phase angles for sequential injection

 

and

 

Injector Size - as the name suggests

Edited August 21, 2006 by petert

[petert 586]

However there may well be a completely different explanation. Who can think what this is and what it therefore tells us might be a possible way of investigating it using only four injectors?

 

The time that it takes to inject relative to the incoming speed of the column of air. There was an article in mag. a few years ago with some back to back dyno tests on an alloy Mi16 in a 205. They claimed 8hp with staged injectors over the std. setup, from memory. I've been looking for the ZIP file of the article. I'm sure it was posted on this forum. Perhaps someone else will remember.

[16v205 9]

Ive got them articles, if you send me your email address then ill forward it through to you. Its about 8mb at the minute but could be made a bit smaller.

 

Rich

[James_R 3]

Just use the saab red's. I ran 240cc/min injectors on my 1.4 16v vx engine, idle as fine for both quailty and fuelling. plus it good pub talk

[Sandy 191]

The time that it takes to inject relative to the incoming speed of the column of air. There was an article in mag. a few years ago with some back to back dyno tests on an alloy Mi16 in a 205. They claimed 8hp with staged injectors over the std. setup, from memory. I've been looking for the ZIP file of the article. I'm sure it was posted on this forum. Perhaps someone else will remember.

That was my friend Colin's. 83.5mm, 11.5:1 CR, Mark Shillaber head (standard valves), John Read cams (adapted 20XE rally profile), maniflow exhaust manifold, 360mm inlet length and twin injectors. 229bhp @ 7000rpm on Emerald's rollers. One seriously grunty engine, still going strong one rebuild and several seasons later.

[Shevy 4]

That was my friend Colin's. 83.5mm, 11.5:1 CR, Mark Shillaber head (standard valves), John Read cams (adapted 20XE rally profile), maniflow exhaust manifold, 360mm inlet length and twin injectors. 229bhp @ 7000rpm on Emerald's rollers. One seriously grunty engine, still going strong one rebuild and several seasons later.

 

 

Hi Sandy do you have any Power and Torque graphs for this engine.

229bhp @ 7,000rpm sounds good considering it is only a 83.5mm bore.

I would have expected peak power to be higher up the rev range fro a 1.9 bottom end.

Was it running a dry sump ?

[Sandy 191]

I've asked Colin to dig them out, but he's not really bothered! it's going in the rollers tomorrow for a health check, so i'll look at what is does then hopefully. It was running baffled sump and solid lifters. Never had an oil pressure issue, even at places like Castle Coombe sprint. It still stuns me with its low down performance everytime I see it. The secret lies in the way the cams worked with the headwork from what I can gather! John Read's cam profiles and Mark Shillaber's headwork seem to work very well together. They have produced some amazing engines, recently a 204bhp@8300rpm 1.4 Vauxhall 16v with Rally profiles!

[Batfink 201]

Colin doesnt really like to retread old ground does he lol

I can't wait to see what his new car will be like Its certainly inspired me to get similar stuff done to mine when it goes down to him in a months time

 

Will he paint this one white Sandy to inspire Graeme to make the right colour choice lol

Edited August 24, 2006 by Batfink

[kate205gti 4]

im using rover 220 turbo injectors on momo 193bhp on emerald and doesnt lean out at all after mapping (still pops thou so possibly over fuelling if anything!)

 

ive got a chart somewhere of the flow cycles for most injectors will dig it out

[Sandy 191]

Colin doesnt really like to retread old ground does he lol

I can't wait to see what his new car will be like Its certainly inspired me to get similar stuff done to mine when it goes down to him in a months time

 

Will he paint this one white Sandy to inspire Graeme to make the right colour choice lol

His probably won't happen for a long time, but he's building a new lump for the black and red one that was at coombe last year, which will be 87x88mm, 1.8 16v head by mark, new JRE profiles. Should clear 260bhp all being well. (Sorry for the off topic, but there's some lovely XU engines kicking around down here at the moment!)

[Shevy 4]

I've asked Colin to dig them out, but he's not really bothered! it's going in the rollers tomorrow for a health check, so i'll look at what is does then hopefully. It was running baffled sump and solid lifters. Never had an oil pressure issue, even at places like Castle Coombe sprint. It still stuns me with its low down performance everytime I see it. The secret lies in the way the cams worked with the headwork from what I can gather! John Read's cam profiles and Mark Shillaber's headwork seem to work very well together. They have produced some amazing engines, recently a 204bhp@8300rpm 1.4 Vauxhall 16v with Rally profiles!

 

Hi Sandy,

 

Did you get to see what sort of power and Torque the engine is making now ?

[Sandy 191]

Yes, thread is here: http://forum.205gtidrivers.com/index.php?showtopic=63823&hl=