Trebor,

sorry for the hijack

Delboy,

Using Link ECU with HKS EVC3 boost controller.

Rich

 

We are discussing the Map sensor problem here

Your input Rich, David and Del would be very useful.

Cheers

Simon

[Edited by Jolly Green Monster - 11/13/2003 11:51:40 AM]

 

JGM,

I'm not a member of 22b and to be honest my input wouldn't be much.

All I know is the car runs 1.5 bar on a standard MAP sensor with a Link and an EVC3 and it's as fast as ****. Ask Harvey what the car drives like as he was the one driving it while Bob mapped.

Personally, I'm not going to be shoving syringes and voltmeters into anything

I think sometimes to much "knowledge" can be a bad thing. A lot of people spout bullsh*t on here when their cars have failed to produce anything like decent figures.

It's like the old "380 injectors are maxed at 300bhp" bollox. All theory, no practice.

I'm going to shut up now as this is Trebor's thread and it's not fair.

Rich

 

rich it depends on afrs etc and how many cc's of fuel you need per bhp.... Lets start another thread

 

Rich read this then-

Using a rising rate reg and a 3 bar differential fuel pressure on vacuum, you should have 4.12 bar differential fuel pressure at 1.6 bar boost pressure (you're pretty close at 5.5 absolute, so that's fine). Now work out the new flow rate of your injectors at that differential fuel pressure... (4.12 / 3)^0.5 = 1.17 times the normal flow rate, so 380cc units will flow about 445. If you only had 4 injectors then that'de mean you need to flow 1781 cc in one minute, but you need to take into account any extra injectors you have...

Once you know what your injectors COULD flow at 100% IDC, you need to give yourself a safety margin, I'de recommend at least 20%, so for just four injectors that'de be 2226 cc / minute. Go and find a fuel pressure gauge, and connect it up to the fuel rails, then with the engine stopped, run the pump and adjust the pressure up to 5.72 bar. Now remove the fuel return line from the reg, and attach another piece of hose, and grab an empty petrol can. Put the return hose into the petrol can and then time the pump, to fill the can, if it's a 5 litre can, filling should take no more than 134 seconds. If it does take longer, then your pump is not big enough, and you will need to fit one that can flow that much. If it takes less time then you will be fine. Obviously adjust the figures as necessary given that you may have more injectors and hence the time should be lower.

Just out of curiosity, the pump that I have is rated to flow 208 litres / hour at 8 bar, which is 3466cc / minute at 8 bar. You would get 8 bar fuel pressure at 3 bar boost on a rising rate regulator, giving 5 bar differential fuel pressure, which will make injectors flow 1.29 times as much as normal. The injectors would have to flow 866cc /min at 5 bar differential pressure to max out the pump, so given a 20% safety margin, they'de ideally be no bigger than 693cc at the raised pressure or 537cc at normal 3 bar differential. I'm running 550cc injectors in my car, so it's pretty close, ie the fuel system would be fine up to 3 bar boost pressure, but the engine internals would go south first. At 80% utilisation, this pump will be good for 500 BHP, assuming it's using all 8 bar it's rated to. If it were using a linear regulator and 700cc injectors, then we can forget about the 20% safety margin, because the absolute fuel pressure would be 6 bar at 3 bar boost, and the pump can flow more than 208 litres / hour at 6 bar... so set up that way the fuel system would be good for about 630 BHP.

The moral of this story is that a a rising rate reg CAN dig you out of a hole, if your injectors aren't big enough, but it does make bigger demands of your fuel pump and the entire fuel system (more pressure). Fitting bigger injectors will also stress out the fuel pump but not as much, and it won't be quite as agressive on the puel pipes, but less friendly on the wallet, and result in poorer emissions at idle (maybe slightly rougher idle). I'de say that for people using a linear regulator and higher boost, the stock pump isn't up to the job, and a replacement in-tank pump such as those sold by Lateral Performance will work really well. If you're running high boost AND a rising rate reg, then I'de suggest the larger pump that I'm running, which is also available from Lateral Performance.

As for flow limitations of 380cc injectors, consider that you need about 5.5cc for every BHP, and then do the maths... at 1 bar with a rising rate, you'de have 3.7 bar differential fuel pressure giving 11% more flow (or 421cc per injector, 1687 for the lot). So at 100% IDC that'de be enough for 306 BHP at 1 bar, but ideally you wouldn't want to push them that hard, say 95% absolute max, so about 291 BHP. You could of course raise the fuel pressure to 4 bar at atmospheric, which would make your pressure at 1 bar boost 4.7 differential, thus making the 380s flow 475, and that would be good for 345 BHP at 100% or 311 at 90% which is fairly comfortable. But remember that the pump must be able to deliver 2375cc / minute at 5.7 bar absolute fuel pressure in order to allow the 380s to work like that.

Assuming 1 bar boost pressure, 85% volumetric efficiency, and 1.5 cfm per BHP, you can get about 280 BHP at 1 bar from an Impreza engine at 7000 RPM. Interestingly I got 301 BHP at 7000 RPM at 1.1 bar a while back on the rollers, and theory predicts 307 BHP, which is exactly the figure I got on the first run. With this in mind, you'de be better running the injectors merely on stock fuel pressure with rising rate reg, and not stress the pump out too much, because unless you get some head work done, etc, the engine really can't consume enough air to warrant the fuel requirement...

Obviously if you want to run 1.3 bar then you need to do the maths again... using stock fuel pressure with rising rate you'de get 1735cc at 100% IDC, good for 315 BHP, but your airlfow potential is 362 BHP.. obviously more fuel pressure would be required. You'de need 2000cc / min to satify that airflow, or the equivalent of 500cc injectors (assuming 100% IDC, which is bad). That'de mean a raise in differential fuel pressure of 73%, or 5.2 bar differential at 1.3 bar boost, about 6.5 bar absolute. The pump must be happy flowing 2500cc/min at 6.5 bar. To get 6.5 bar absolute fuel pressure at 1.3 bar boost you'de need to run 4.3 bar at atmospheric, at the very least, probably 4.5 bar to be "safe". But 4.5 bar fuel pressure is really a lot of pressure at atmospheric pressure in the intake manifold, I wouldn't want to run them that hard... it is probably possible to get the best part of 350 BHP out of 380cc injectors, but definitely not with the stock pump, probably not with the uprated in-tank pump, definitely possible with the pump I have, and most certainly not wise to try it, better to get bigger injectors.

For those that are laughing at the concept of 350 BHP from 1.3 bar, consider that there are cars that have done that on the rollers, it just takes some attention to thinks like headers, intercooler, turbo etc.

This was by Pat on another thread.

You must be running massive fuel pressures to achieve 1.5 bar on 380cc's

 

Rich W - Those numbers correspond to the Oem Map sensor which definitely is only ranged to 17.2psig. I fitted a newer model due to this problem which was ranged to 24.2psig. Are you using the ECU's boost control or a standalone controller?

Trebor69 - As you have probably gathered I have a custom mapped scoobyecu in MY96 which was mapped by me with the aid of others you know who you are and thanks for ya help
I am very pleased with the results but It depends really on what you are aiming specifically to achieve. The Unichip is a piggy-back ECU and for 600 squid I would be inclined to go standalone for this type of money. In the end its down to your personal preference

Cheers

[Edited by Delboy2 - 11/12/2003 6:34:19 PM]