injector cc = what potential power?
 

right bit of a difficult one this probably one for the formula / maths wizards (raunch). 98bhp VTR picco (blue) what cc do they run at and what power (max before over doing the cuty cycle) can they cope with n/a and turbo?

also got some mi16 injectors which I know are 167bhp n/a standard form will cope fine for what I am after but I am thinking more ahead to mapping and how resolution will be like

I've got a formula in a book here - I'll post it up tomorrow morning when I've not had beers.

If you google it there's a few formulas knocking about.

I have it in a book somewhere in my room. I'll have a rumage around for it

I've got the formula in one of my progress threads as I worked out the max bhp for the 65lb injectors.

cheers guys ross, best you work it for me as my maths at the best of times aint that great

http://www.saxperience.com/forum/sho...&postcount=144

Pow :)

I'll do some maths tomorrow - slouching in bed with a cup of tea, The Rock on BBC1 after a few beers isn't best time to be whipping out your calculator and having a play with numbers ;) will pm you some workings 2mo

Happy Birthday btw :y:

I'll do it for you now if you like.
give me a min

Just a thought but if the mi16 injectors cope with 167bhp, then what duty are they running at?

If it's 100%, then they sound a slightly larger cc that the oem Vts injectors (225cc@3Bar) so they will be fine resolution wise easily for around 120bhp? What sort of bhp you hoping for? As ideally you don't want to run them over 80%duty.

As for the vtr injectors, not sure what cc they are, but I think they are around the 180ccmark? I'll have to try and find out before working out their rough max bhp@ 80% duty @ 3Bar on a boosted car

Quick bit of research, the mi16 injectors are 214cc@3Bar.

Making them well past their limit at a true 167bhp@3Bar. Just trying to find the cc of vtr injectors

yeah go for it guys any help you guys give me much appreciated

btw work it out at 3.5bar power wise was thinking 130-150 ish

check the saxo 106 turbo thread you posted mate, someone posted alot of injector info in there, model numbers and duty cycles etc, should have the info you need in there for 98bhp injectors

Right, I thought I'd post it in here so that if anyone else wants to insert some figures for themselves, they can do.

You can work out the injector size needed to hit a certain bhp figure:

Needed Fuel flow (cc per minute) = (Maximum BHP) x (A constant (roughly 5.6 for boost, 4.6 for NA)) / (Number of Cylinders)

So for say 160bhp with boost, you'll need (160 x 5.6)/(4) = 225cc injectors

To work out the size of injectors you'll need to keep a nice duty cycle, it is as follows:

Injector Static Flow = ((theoretical flow (from above formula)) x 100) / (Number of injectors per cylinder x Desired Duty Cycle)

So sticking with the 160bhp boost example, (225 x 100) / (1 x 80) = 281cc/min

Roughly speaking, with a 160bhp target in a turbo engine, you'll need injectors around the 280cc mark to keep a nice duty cycle at the max bhp point.

These are only rough calculations, and have been taken straight from a forced induction and performance tuning book.

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On a side note, you can work out the cc increase you'd get from upping the fuel pressure.

The formula is as follows:

Revised Static Flow = (Injector Static Flow (from formula above)) x (New Fuel Pressure / Old Fuel pressure)^0.5

So for example,

vts injectors at 3Bar are known to be around 225cc@3Bar, but what if we were to increase the fuel pressure to 4Bar?

Well, 225 x (4.0 / 3.0)^0.5 = 260cc.

So by upping the fuel pressure to 4Bar, you're effectively increasing the max bhp of the injectors at a nice duty - you can only up the fuel pressure a certain amount though - I personally wouldn't go above 4Bar.

If you put the above formulas into an excel spreadsheet then you can play about with figures and try and gauge the rough size of injectors you'll be needing.

Going back to the mi16 injectors, from looking online they look to be 214cc@3Bar so,

215 x (3.5 / 3.0)^0.5 = 232cc

Boost
232cc = (Max BHP x 5.6) / 4
which gives Max bhp = 165bhp

BUT ideally at that BHP, you'd have 290cc injectors at 80%duty cycle

NA
232cc = (Max BHP x 4.6) / 4
which gives max bhp = 201bhp

BUT at that bhp, you'd have 290cc injectors at 80%duty cycle

REMEMBER THESE ARE ONLY GUIDES AS TO THE INJECTOR SIZE YOU'LL NEED

legend thanks Ross :) so

140bhp x 9psi / 4 cyl = 280? either way I know I will have a decent safety margin on specs I wanna run

Going off this (http://mrinjectoruk.auctivacommerce....7-P598732.aspx) the vtr injectors are 154cc@3Bar (not sure if these are the 90bhp or 98bhp ones) , therefore:

Change the cc to a 3.5Bar FP:
154 x (3.5 / 3.0)^0.5 = 166cc

Boost
166cc = (Max BHP x 5.6) / 4
which gives Max bhp = 118hp

BUT ideally at that BHP, you'd have 147cc injectors at 80%duty cycle

NA
166cc = (Max BHP x 4.6) / 4
which gives max bhp = 144bhp

BUT ideally at that BHP, you'd have 147cc injectors at 80%duty cycle

you looking to run around 140bhp, but leave scope for future 'improvements' ;) ?

Also, I've updated the calc for the mi16 injectors for rough figures at 3.5Bar as opposed to 3Bar.

They are only meant to be used to spec up injectors that'll get you in the ballpark region size wise - the mi16 injectors look to be fine for boost upto around 150bhpish before the duty will get high.

It might be worth trying to check the spray pattern of the injector too - as the vtr injectors look to have a single spray pattern for a single port on an 8v head - whereas say vts injectors have more of conical spray pattern which I assume is for the 16v port setup in the head. Not sure how much difference it would make but every little helps, and it's worth considering before buying injectors

yeah 140 as solid and more for future :) I think mi16 ones will do for now and then I will use either clio 182 ones in the future if it gets spicey

I like the sound of spicey ;) pics or gtfo :cool:

Yeh the mi16 look like they'll be fine for now, but try and get a god spray pattern depending on what engine they are going on. 8v vs 16v

would you be able to do it for gti-6 injectors?

Ross, you should become a teacher or something :y:

lol, i wouldn't mind it if there wasn't so much red tape nowadays with teaching - i'll stick to finance for the time being :hug:

for sure - the gti6 injectors are rated at 265cc but Sandy has measured them as equivalent to around 300cc ish. As a result of this I'll use a mid point for the workings (283cc) and do it at 3Bar fuel pressure. He did note that they have a nice spray pattern.

Boost
283cc = (Max BHP x 5.6) / 4
which gives Max bhp = 202hp

BUT ideally at that BHP, you'd have 350cc injectors at 80%duty cycle

NA
283cc = (Max BHP x 4.6) / 4
which gives max bhp = 246bhp

BUT ideally at that BHP, you'd have 350cc injectors at 80%duty cycle

Desired Injector sizes will change depending on your injection type - sequential etc too

You really don't want a large conical spray pattern if your using a 8v head. Your afr will be all over the place as fuel collects on the port walls and de-atomises.
The reason carbs are so unpredictable

also some 172/182 injectors are not what stated... had my test and cleaned and was only 244cc!!! :S

what would they be at 3.5 bar for boost, its what ive got in mine at the min so need to know how far they can go before there know good

Injector Static Flow = ((theoretical flow (from above formula)) x 100) / (Number of injectors per cylinder x Desired Duty Cycle)

and then plug the injector static flow back into my equations above for NA and boost.

just bookmarking.

I'm with Andysaxouk, we watched them test some "283" cc injectors and they were found massively wanting

Andy

very complicated to spec injectors exactly --apart from the fact that different companies test their injectors with different viscosity fluids --which will make a big difference in what the quoted size is .

the formulae quoted above must always be taken as a guide --not gospel ,the way your head burns the fuel --ie how it scavenges will make a differnce as will alot of other things ,and once you start adding accel fuelling in as well ,and how rich you want to run the engine --it all makes it a bit hard to use any formulae as gospel ..
rasing fuel pressure will also have a big effect not only on flow but of the atomisation ,especially at low engine powers. clio 182 --does notsuprise me at all that the injectors are not as big as some think --
smaller they can run the better it will be for emissions at low rpms .changing from 3 bar to a 4.5 bar reg will usually give you another 12-15% --but again this is only a rough guide

On an NA clio they are usually swapped out when venturing past 200bhp, so that is a good indication of their limit.

and that will not be at high rpm --duration window gets smaller as rpm increases

Sorry to pull this up John, but I'm rather interested in the the effect of increasing the fuel pressure in terms of increasing efficiency - as I'm guessing there would be better atomisation with increasing exit velocity (through an increase in fuel pressure). My worry is that it will run rich in open loop conditions (idle is my biggest concern for MOT emission regs). You mention 'will usually give you another 12-15%', is that power I'm assuming?

I've got standard injectors, and the usual intake and and exhaust modifications so I know that increasing the fuel pressure would be overkill in my case if I'm pursuing hp although I'm not thinking of it increasing it to even 4 bar - is it viable or am I barking up the wrong tree?

Cheers,

Ads

In regards to increased fuel pressure and atomization this is an interesting read on the effects in an inlet manifold

http://pdfserve.informaworld.com/57444__778649592.pdf

If a little brain ache inducing!

link doesn't work dude!

a std ecu is in closed loop control at most times except for certain conditions decided by the ecu designer ,
std vts ecu is in closed loop at everything but fullthrottle up to around 4k ,after that it is open loop from around 70% --these are not exact figures -but your worry about raising fuel pressure and mot is unfounded ,the std ecu is adpative and will correct quite happily when using a 4.5 bar reg ,but yes it will make it richer on WOT.
I,m not sure what you are trying to achieve ,but if by effiency you mean economy ,then there is a lot more to it than making car run lean .
a stand alone ecu with full w/band will allow yopu to decide where it is controlled and allow you to decide at what lambda level you run at at any given throttle /load setting .
economy + emission are not the same lambda level for cruise --

too deep a subject for a full reply

Thanks John,

ok so (and there is a sale in it for you depending on what you say but I'd like your honest opinion), based on what you're saying, a 4.5 bar fpr on my engine, standard internals, induction kit and lower restriction exhaust, will be fine - but what about 70%-T to WO-T how rich are we talking? too rich and kill the top end? or is there top end power gains to be had? Although it's not my priority (see below).


You're correct about my desire to improve the economy when I was referring to efficiency. but I wasn't referring to running the car leaner at part throttle or any other running condition. I'm referring to better atomisation of the fuel, through a higher fuel exit velocity at the injector that would occur with a higher fuel pressure.

So essentially I'm after a better burn from a fixed amount of fuel - which would be the case if we're at part throttle, closed loop, but comparing a standard fpr (3 bar isn't it?) to a 4.5 fpr. The system with the 4.5 FP will have a shorter injector pulse duration - which means the fuel has to exit the injector with a higher velocity to ensure the correct mass flow (to maintain the ECU's required AFR).

If the gains are negligible, or there is something I've overlooked which means it'll scupper ecomony then don't worry. If the gains are minimal but there are gains to be had, then I'm interested.

Thanks!

Ads

you can get gains but not by using std ecu +narrow band --you are stuck with the preset lambda values .
std ecu runs WOT too rich to be honest -
it is quite normal for customers to remark on the better economy after having fitted t/bodies --when cruising back home --thats because we have better control of fuelling than the std ecu .
you can run 16-1 or 17-1 on LIGHT cruise ,but NOX levels rise --thats why 14.7 is lambda 1 and what std cars are set to--for emission regs

cheers man I'll have a read of it now :)

Thanks again John, really appreciate your thoughts. So you're saying even with the standard FPR and ECU that the AFR is still too rich at WOT? blimey.

Yeah I forgot about the rising NOx for leaner conditions! There's a graph somewhere showing the variation of HC's, COx, NOx with AFR which is interesting. Ta!