AITs and AFRs and ****s

[blaze6]

Originally Posted by paul@1320autos.com

http://www.minitorque.com/forum/f215...ttle-devil-75/

Its a Rotrex kit which is currently in development at RMW, the Rotrex producers lower IAT temps than an Eaton at those boost levels.

i was kinda expecting that answer....can't you just pretend my car has a rotrex and map it....

[Paul Webster]

I'm glad I didn't disappoint you then

[BigShow]

I am not taking sides by saying this as I don't fully understand the AFPR and can only speak from my own experience which is a car making very good power with 440's and a remap.

So if someone could explain how I might benefit from an AFPR it would help me understand more.

[MINIMANIAUK]

Fuel is used as a coolant to offset the high IAT - running rich is deemed necassary
the injectors provide fuel closely controlled by the ECU controlling pulses to the injectors -for this to be accurate the injectors require constant voltage and fuel pressure - with boosted engines the air pressure rises so the fuel regulator is connected to the boost pressure and rises at the same rate a 1;1 ratio this keeps things constant for accurate fuelling
problem occurs when the boost is higher than the regulator maximum - it cannot add presure so fuel leans out (not good as it is used for cooling)
the adjustable regulator has a the capacity to set a new higher value of fuel pressure -in effect an addition to the fuel mapping amount at a constant rate
Potential problem ; the fuel pump must have the flow capability -they have limits and can when asked to increase the delivery pressure reach a point that the flow drops off (not good ) - What is this point ? that is the question the pumps are also voltage sensitive and extra loading can drop voltage and alter delivery ,also the cables to the pump must not drop voltage due the load current -also a drop in delivery flow -
testing under controlled conditions can show the pump limits
If capacity is available and the pump life unaffected then a good cheap way of adding fuelling - usually gets people paranoid about fuel pressure and so the add a bling fuel pressure guage to monitor
As always consideration must be given to items reducing in performance such as injectors ,if relying on these for cooling and they degrade over time then you are back to the potential lean condition -hence a routine check will always be a good idea-all part of the tuning extra servicing costs incurred

[R53mcs]

1320s route is a good one and uses big injectors and then a remap to help keep those injectors fuelling at the correct levels.

GTTs route is another viable option that allows you to keep a stock map, but increase the capacity of the car to fuel in line with up rated boost. I think this is more important on very high boost cars than on 15-17% pulley cars. Fitting a VFPR allows you to change the pressure to stop a big injector from over fuelling, when running a stock map at low revs/boost, while still retaining the big injectors capability to fuel correctly all the way to very high boost.

They essentially do the same thing but using different methods, some might say that a remap is the better option (gets you more power as it tunes the engine as well as just adjusting the fuelling), but for my purposes I was happy enough with the power I was getting, I just wanted to know she wouldn't run lean. My AF readings and temps etc have shown to me (and I believe others) that the VFPR and big injectors does work fine... maybe not gaining you that extra couple of gee gees that a remap would... but I'm not after that just yet.

Basically to retain the stock map and have big boost you have to compensate for the stock maps inability to understand that there is a bigger injector fitted. This is done by altering the fuel pressure (stock fuel pressure is too high for a big injector, I think is the problem). Once you have done that then the stock map will happily fuel as required no matter what the boost or revs you go to as the bigger injector has a high output, but the VFPR stops it over fuelling too much when not having to cope with the high demand created by high boost (mine and other AF reading show that this method does work at tick over and WOT in all gears, all the AF readings stay within tolerable levels, that’s not to say that a remap to help tweak it even more could not help get that few extra gee gees, but it does work well just on its own)

The 1320 route is similar but uses a remap to adjust how the injectors feed the fuel... however I think that because of the variance required to get a big injector to fuel correct at low boost and very very high boost (E.g. on a GTT or even a BBR car with crank pulleys etc) the map might struggle on very very high boost cars as the stock fuel pressure will be too high and it will try to force too much fuel in. I think that once you get to extreme levels of boost thought would have to be given to using something to lower the shear volume of fuel the engine tries to force through in any given cycle.... and eventually a remap might struggle.

All the VFPR does is give you a way of fitting a big injector and then setting the car at a fuel pressure that does not need a clever map to hold it in check.... A remap can then concentrate on getting the best performance out of the car, rather than also having to worry about having to cope with little nuances caused by too high stock fuel pressure.

That’s my limited understanding gained from the forums. I'd say that on moderate high boost cars like those 15% and 17% pulleys etc the remap option is a perfectly good way of dealing with fitting big injectors and getting good fuelling across the range and maximising power. But I think that once you start throwing higher boost, such as 19% pulleys, big oversize cranks etc at things, the vast difference between WOT point A at full boost and point b low boost would be so much that a way of regulating fuel pressure is helpful to the situation as the map will struggle to get you the maximum it could as you'll have to make concessions to ensure low boost fuelling is not too high... Just my feeling though

personally I think the ideal option would be to have nice big injectors and vfpr to get fuelling either bang on or well within tolerable levels on a stock map, and then have Jan or someone do a remap on that to maximise the potential the car has, that the stock map does not give you. Basically I imagine this is what Roland is now offering at GTT with his remaps.

TBH I'd love to have Jan remap my car at some point but it looks like that won't now happen as 1320 and Jan are now dubious of the GTT VFPR ... so I may have to go to GTT to get it done or Superchips or AMD

[Lucky]

Adam your correct BUT the AFPR drops the pressure, just enough, and even the lazy pumps can keep up!

To make an engine run correctly the fuel pressure should rise at a liner rate to the inlet chamber pressure.

in an attempt to explain:

fill a large barrel with water and then drill a hole in the side at the bottom.

How far from the barrel do you think the water will shoot out?

is it more when the barrel is full or empty?

So now we agree that pressure on a fluid does make a differance?

here is a table of results that CAN happen

Boost psi Fuel psi
10 30
11 31
12 32
13 33
14 34
15 35
16 36
17 36
18 36
19 36
20 36

On a high boost car the fuel pressure cannot keep raising in line with the boost.

One answer is to map at the higher boost to open the injectors for longer

but that is just like making the hole in the barrel larger.

during lift off the fuel pressure will build back up in the rail and then on the next wide open throttle movement the injectors will be wide open and the pressure will be up and then back down.

This bouncing of the fuel pressure may not be seen during a rolling road session but on the road with normal on off situations it does happen.
Its very easy to spot if you have a boost gauge and a fuel pressure gauge.

In short the APFR drops the pressure to a level that allows the fuel pressure to track with the boost pressure.
I have never said its better than a map but used with a map it gives all the headroom required for high boost.

[blaze6]

which still leaves with the question i still don't understand the answer to....why can't i have an AFPR and get a remap afterwards?.........

[blaze6]

it's like the end's in sight...but just out of reach.....

[R53mcs]

There you go, a man in the know... thats who you need! I'll shut up now as i was only half right

[R53mcs]

Originally Posted by sayanthan

which still leaves with the question i still don't understand the answer to....why can't i have an AFPR and get a remap afterwards?.........

There is no reason. Roland does live mapping for his VFPR cars now ... the problem is that Jan and Paul are not fully sold on the VFPR and so are not happy remapping them. You could go anywhere else that does live mapping such as AMD or Superchips and once you have a VFPR and they will remap the car for you.