I know that Bosch 803 injectors have a flowrate of 382 cc/min and are good to about 350/360 bhp. The Siemens 55lb should do 570 cc/min, but what power are they good for? And the same question for Siemens 72lb and 83lb. Can you simply scale the power linearly with the flowrate?

 

The injectors are only one part of a Cosworth YB power upgrade. Camshafts,cylinder head modifications, ecu, chips, inlet and exhaust manifolds and turbochargers etc can all vary and 2 cars using the same injectors could have widely different power levels.
Unfortunately you cant say by fitting say Siemens 55lb injectors I will get 400 bhp or 83lb injectors will give me 450bhp it all depends on the rest of your modifications.

 

I know that you need to improve the breathing of the engine by fitting a larger turbo/different camshafts/porting the head/etc. to make use of the higher flowing injectors. And that your chip must match the total engine configuration. But that is not my question. I just want to know to which power levels the different injectors are sufficient.

If the power scales linearly with the injector flowrate I would expect that Siemens 55s would be good for about 520 bhp, Siemens 72s would be good for 680 bhp and Siemens 83s would be good for 780 bhp. But I have the feeling these numbers are very high so the real numbers are probably a bit lower. But how much are they?

 

It can be calculated from basics if you know the b.s.f.c of the fuel. Its something I do for all the fuels I use. I can go into the maths but most just glaze over & think im some sort of gimp. For instance pump fuel has a a bsfc of .6 a decent race fuel .8 & the FTW Purple I will use is 1. It means the Purple will use 67% more fuel so you cant just assume what you say above.


Done a google search this may help- Use .65 for pump fuel & .8 (80%) for duty cycle.


http://injector-rehab.com/shop/Injec...Selection.html

 

You would be way out with the figures you have put.Why not ask some of the tuners what sort of power levels you can expect ? From other peoples cars I think the 83lb injectors can produce over 500 bhp but 680 or 780 bhp will require much bigger injectors like 1100cc ones.

 

Thanks!

I've used the link and used a BSFC of 0.65 and duty cycle of 80%. In that case 350 bhp would require 71lb / 746cc/min injectors. But in practice 350 bhp is possible with the 803 injectors which are only 382 cc/min. I understand you'd be able to go above the 80% duty cycle, but this is almost a difference of a factor 2.

@Cossynut, tuners are also allowed to answer my questions here. But I don't want to bother them with generic questions.

 

The Bosch delivers its 382cc/min @ 42psi according to Bosch. On a YB you are probably running 50psi static + 20psi of Boost so that's 70psi. Find a chart to see what the 803 deliver at 70psi . The maths wont be wrong you are not comparing the same thing.

 

The Bosch indeed does the flow at 3 bar and the cosworth is running 3.5 bar fuel pressure. So if you scale the flow rate linearly with the pressure it would do 446 cc/min at 3.5 bar. The boost pressure isn't important as the flowrate depends on the differential pressure over the injector, and that's is kept constant by the fuel pressure regulator. But even the 446 cc/min doesn't give enough to get 350 bhp.

I've also seen a reference to the 803 injector being 523 cc/min instead of 382 cc/min (all at 3 bar). http://www.cosworth.hu/content/haszn.../injectors.htm
If you scale that flowrate up to 3.5 bar it would be 610 cc/min. And when you enter that value in the calculator you get a maximum power of 358 bhp at a 100% duty cycle. I guess that kind of matches with what it does in practice.

So if I now do the same for the Siemens injectors the flowrates at 3.5 bar would be (all at 100% duty cycle):
55s: 570*7/6 = 665 cc/min --> max 390 bhp
72s: 756*7/6 = 882 cc/min --> max 517 bhp
83s: 890*7/7 = 1038 cc/min --> max 608 bhp

Does this sound correct for the different Siemens injectors?

 

Its only 3.5 bar at idle if you have 2 bar of boost it will rise to 5.5bar that's what im trying to say. Stu explains it better in his articles .
So you have the rate at 3 bar from Bosch & you run 5.5bar it will be vastly different.

 

The way I looked at it was to build in a future proof redundancy and Mark agreed / advised. We put in 1000cc injectors as I needed to buy bigger so instead of buying again if I upgrade again then at least they are there and ready?

 

I understand what you mean, but it's not correct. The fuel pressure regulator has a hose connected to the plenum to increase/decrease the fuel pressure based on the pressure in the plenum. The reason for that is to keep a constant pressure difference over the injectors of 3.5 bar. If you run 2 bar boost the fuel pressure goes to 5.5 barg, but the pressure difference over the injectors is still 3.5 bar (5.5 - 2.0 = 3.5 bar).

 

That makes sense. But I'd still like to known how much power those injectors would be capable of (roughly).

 

Fuel pressure regulators on turbo cars are "rising rate"
It means that the fuel pressure rises along with the manifold pressure(boost)
So what Rod is saying is right
I think you may be getting confused with a n/a injection system

 

No he isn't confused with a nasp, on a nasp the inlet wouldn't be filled with boost pressure.

The fuel pressure rises 1:1 with boost pressure to compensate for the pressure on the injector nozzle.It also drops the fuel pressure in vacuum for the same reason.

if you had 40 psi of fuel pressure and 40 psi of boost, how much fuel would you inject?

With a base pressure of 40PSI
Idling at 20inHg, the nozzle is exposed to 20 inHg vacuum causing fuel to be sucked into the intake manifold. This combined with the 40 PSI base pressure would equated to a theoretical spray pressure of 50 PSI which is above the desired fuel pressure of 40 PSI. Since the top of the valve in the FPR is also exposed to 20 inHg, the valve in the reg is pulled up which opens the outlet port up increase the fuel being bled from the fuel rail which reduces the pressure by 10 PSI. This then gives you your desired fuel pressure of 40 PSI.

At a boost pressure of 10 PSI, the nozzle is exposed to 10 PSI of pressure. This pressure is acting against the base fuel pressure which would mean that the spray pressure would be 30 PSI which is below the target fuel pressure. By also providing the top of valve in the reg with a reference boost signal of 10 PSI, the FPR now has a combined force to provide 50 PSI of fuel pressure which can overcome the force exerted on the nozzle to give you your 40 PSI target pressure.

 

I understood that all wrong then,
I was always under the impression that the actual fuel pressure would rise at the same rate as the manifold pressure
When i said about n/a i was meaning vacuum not boost pressure obviously
This is why its always best to just ask the experts

 

it does, it rises 1:1 with boost, so for every lb of boost you get a lb of extra fuel pressure.
BUT, the extra fuel pressure is only there to compensate for the pressure in the manifold, you don't actually inject any more, the reg is designed to always give you your base pressure, if the manifold is in vacuum or boost it adjusts the fuel pressure accordingly.

so on a YB at 2 bar of boost, you would have 5.5bar of fuel pressure, but still only be injecting your base pressure of 3.5 bar because you have a 2 bar opposing pressure in the inlet manifold.

 

you can get regs that have various rates like 1.2:1, these will give you more actual fuel delivery as it sees pressure, but i think they are a little happy shopper, and would rather just use the right size injector for the job in hand, and if you run out of duty, fit bigger ones rather than fudge the pressure ratio.

 

I was in the right line, just didnt pick up on it quite right
Thanks James

 

Cheers for taking the time to explain it better than I did James! Do you also have some input on the max power levels for the various injectors?

 

The best way to understand it, is that the fuel is always delivered at the "Differential Pressure".

So take fuel pressure, subtract the inlet pressure and you have delivery pressure.

In escense, to ease understanding... if you take a drink from a glass of milk through a length of say, 4mm pipe (this is now your injector) and then blow that milk gently out into the sink, it flows out nicely.

Now do the same, suck up your milk through that spare dump valve pipework your wifes been telling you to move out of the kitchen for 9 months but this time, place BOTH ends of the pipe into your mouth and try to blow the milk through the pipe (injector) with the same pressure. You wont feel any flow through the pipe as the differential pressure between the Injector pressure supply (your lungs) and the inlet manifold (your mouth) is Zero... both ends of the injector are subject to identical pressure so flow = nil.

To expand on this, now do the same but have your wife put the other end in her mouth and blow harder than you are blowing and you will see why we need to run a 1:1 reg that increases pressure as the inlet manifold pressure (your wife) increases.

Without it, the flow gets less and less as inlet pressure (which is technically a restriction) rises and in some cases where cars run very low fuel rain pressure, we can end up with no flow at all and even backflow.

Now please go and put that pipe in the garage before you wife sites me as the reason it is there for another 9 months, pending future technical experiments. ROFLOL

 

Cheers for explaining the reason of the fuel pressure regulator being there. But I am still hoping for an answer on what power levels are possible with the different injectors. I understand it depends on several other factors too, but giving a rough number should be possible, right?

 

Rod has already very kindly done that and his link will provide you with all the info you need to get your "rough value".

The problem is, the BSFC of each engine differs.
For example, pop a set of 803s in a CVH and see if it will do 350bhp on them like a YB does.
It wont, as it has a lower BSFc than a YB which, for a tractor, is surprisingly efficient, even by quite modern standards.

The only way to get an accurate BSFC is a dyno cell with an accurate fuel delivery monitor and work out how much horsepower your making from any given input of fuel. This drops as engine efficiency increases.

 

Cheers for explaining that!

One last question. Is the flow of 382 cc/min at 3 bar correct for the 803s? Using the link Rod has given proves to me that the 382 can't be right.

 

Marc as everyone has said it all depends on what else you do to the engine. Here is an example Escort Cosworth----Bd 14 cams, GT30 turbo, ported and polished head, Siemens 83lb injectors etc made 480bhp. Another Escort Cosworth----- slightly different specification but again with Siemens 83lb injectors made 503bhp. If that is the sort of power you are after go for it!

 

my YB made 415bhp on 55's if that helps?

 

Thanks, that all helps! It already shows my last estimation for the 55s was on the low side. I guess the 72s and 83s are then also capable of more than I estimated.

 

hes not asking how much power can a yb make with xxx and xxx modifications, hes simply asking how much power will they support on I assume v power.


cams and head work have no relevance on how much fuel the injectors can supply and how much power they can support

 

I think your close enough there with those calcs tbh.


my old yb ran 83lb siemens at 480 hp and I seem to remember stu saying they were around 70% duty.


I remember the car well it ran great live mapped, no closed loop control, good on fuel and ran fine good fueling at all cruise points, go for some 83lbs if you can get them for future proofing imo

 

Cheers for understanding my apparantly not so well formulated question and also for giving the answer I was looking for!

 

I ran 590bhp on a set of 83lb Siemens but I believe they were pretty much flat out.

Rich