I'm sure some of you are thinking... so what if the fuel pressure is changing by 6psi total... the AFR is still the same?

the widebands we're using are VERY slow, they take an average of 4 cylinders, and they take an average of several combustion events.

Think sampling rate of the wideband... now think about getting the AFR of EACH combustion event at 9k RPMS for each individual cylinder... yeah. No way in hell you're going to get an accurate measurement on a sensor that is reading THAT slow and is the average of all four cylinders and an accumulation of several combustion events.

It makes a difference.

 

If I recall correctly VP Import and Q16 uses MTBE as one of the main oxygentates. It has a very noticeable smell. Love it! When the highly volatile components evaportate the MTBE leaves behind a very thick, sticky, nasty residue/gum. This can clog injectors, fuel lines, etc.

Before I got into EVOs I raced quads. I ran VP Ultimate4 fuel - which has a large amount of MTBE (so sweet smelling! ). I left it in the tank for about a year and when I went back to it - the tank, carb, cylinder head - ALL were covered in a think spooge that was really hard to get off. That may be what VP is warning about when they say not to leave it in your tanks. . . ? I guess to some it may seem like "corrosion". . .

 

I'm not sure anyone disputes less pressure at the injector means less fuel. But one thing to consider, I think, is that these pressure waves will effect the injectors somewhat randomly. Therefore, one injector might fire and have 85psi, and the next time it fires it might have 82psi, and then back to 86psi the next fire.

What I wonder, is what are the real effects of such variations? Running lean is bad obviously. But running lean for one combustion event? And then back to normal the next event. I don't think that would be that bad.

We could do a dyno test, with an Evo without a fuel damper and then add one. How much power would be picked up? Of course the test would be run with the same net AFR on both tests.

 

You effectively have to tune for the worst case scenario.

Say AFR varies by +/- 0.5 AFR due to this issue and let's say under a given set of operating conditions, the engine can run at TRUE (in cylinder) 12:1 AFR without detonation and get good stable combustion.

Worst case, the engine goes lean 0.5AFR and now the cylinder sees 12.5:1, leading to detonation/unstable combustion. To account for this, you richen up the mixture across the board until that worst case situation no longer causes detonation. Your measured (average) AFR is 11.5:1 but the actual in cylinder AFR varies from 11:1 to 12:1. On the events where the actual AFR is 12:1, it's making best power. When the in-cylinder AFR is 11:1, it's low on power due to being overly rich.

Now add adequate pulse damping and now AFR only varies +/-0.1 AFR. You can now tune for an observed 11.9:1 AFR and now every combustion event is much closer to the ideal AFR. Better power through better consistency.

This has to do with some of the response you get when tuning a car. The car usually picks up a lot of power going from very rich to rich conditions. Say like 10.5:1 to 11.5:1. But then the car pretty much stops picking up power from 11.5:1 and leaner. It's not because the leaner AFR isn't making better power, it's because of the really lean combustion events experiencing unstable combustion. Some cycles pick up power because the true AFR is closer to ideal, but other events experience unstable combustion/detonation and lose power.

This whole thing applies to ignition advance too and it's why crank triggers are better then cam triggers. The more accurate and repeatable the AFR and ignition is, the closer you can push the tune to that optimal point without running into engine damage.

 

bingo bongo!

I like to make the comparison to a RRFPR tune... but 03whitegsr explained it quite well.

 

I drilled the siphon on my full blown setup that I had in my 2g AWD a couple years back. You want to ensure you don't open it too wide, because it makes it more difficult for the siphon to pull fuel from the other side of the tank.

 

The more of this I read the more I am getting more certain the fuel system is working much better than some of you may be thinking it is.

 

You are pre-supposing that the motor will det if it goes to 12.5 for one combustion event. What evidence do you have that this is the case?

 

Detonation has a part that is historical based due to residual heat left in the combustion chamber and piston. But then it's more pre-ignition than detonation.

But for the most part, it's just dependent on that one ignition event.

It's not like you build up an "almost detonation" storage that finally causes detonation as the scale finally tips. The ignition event either burns stably or doesn't. The 12.5 would just be the stable limit of combustion in this theoretical engine.

Cylinder turbulence and fuel atomization also affects how stable this detonation point is, along with other things. The ide though is to make everything as stable as possible, so you can get as close to that ragged edge as possible while still having a reasonable margin of safety.

 

I always looked at ignition timing as being something that might be a per combustion event concern, since it directly correlates to peak cylinder pressure.

But AFR's, and why we run so much to the rich side of stoich, I thought was more of a heat management concern. I'd have thought even a single combustion event here and there could burn out a stoich fine, provided the average AFR of the cylinder was where you wanted it.

Would be cool to see some test data on this. As I think both of us our theorizing.

 

Does it help for me to say that while running E85 and measuring on gasoline AFR's that I've run my car at 13.2:1 AFR's for full pulls with no increase in detonation and no damage? That tells me the fine line from cylinder to cylinder probably doesn't vary as much as some may think it does.

 

Did the car make power at that AFR?

It's not just about detonation. It's also about burn efficiency.

I ran 13.5:1 or so on 110 leaded because I was out of injector. Didn't hurt the motor, but I put larger injectors in and got AFRs down and went faster.

Crcain, there is no question things are much more sensitive to ignition advance. You change AFR though and the ideal timing advance changes too.

There was a video I came across a while back that was pretty crazy though. It showed an F1 engine on the engine dyno without the intake plenum on. Even with the fuel spraying directly down the runner, there was fuel ALL OVER the place. You could see a plume of fuel vapor above the runners. Pretty badd *** really, I'll see if I can find it again.

 

Yes, actually I've found that they will make about the same power there as they do at 12:1, so there's no reason to run them that lean. My point was, if there was a large variance from cylinder to cylinder because of pulses or anything else, I'd think running them that far on the edge would put a cylinder over the limits and show signs of detonation, burning off a plug etc.

 

Not to get too off-topic, but is there a part out there where I could install a FP gauge at the rail, while maintaining the stock rail and regulator? I guess it would be between where the rail and regulator bolt up at.

Oh yeah, I just wanted to say that I got my BR dual setup a couple of days ago, and I must say the fit and quality of the product is excellent. I was telling my buddy that someone that didn't know that these cars came with single pumps, could possibly believe that this is the factory sending unit. Alot of props to buschur racing!

 

Thanks lilley, glad you liked it and that is how we wanted it to work, just like stock. Other can copy but they can't innovate.

There are fuel pressure adapters made to do what you are asking, we have one here from Snap-On.