legacycentral bbs

Just so I can start understanding boost complications, why do you need to retard timing as boost climbs. I understand to prevent detonation but what is the boost doing that causes the detonation then in turn requires the ignition to be retarded?

Thanks.

Also, when using higher octane gas require less ignition retardation? So if you were running 87 octane vs 96 octane, the ignition would be set completely differently?

Thanks

Your first question.......it's really tied to the second about octane.

Higher octane fuels require more energy to be put into them before their bonds breakdown, aka ignition.

Pressure caused by piston and/or compressing of intake air by the turbocharger all add heat/energy to the system, which in turn will cause the fuel to ignite. The higher the boost, the higher the energy and more the chance the fuel is going to ignite.

That make sense......I know that's probably rather simplified......

So, again in a highly simplified question, running 110 octane race gas most people would not have boost/ignition problems? obviously when boosting that is.

The reason I am asking this is when I first get the superchargin working, and if I am having detonation problems, I will probably just run high! octane fuel until I figure out the best module to install to control the ignition.

Thanks

yeah.....in theory that should work.....however there is probably a point that depending on how much the air is compressed and if timing is too advanced.....a higher octane rating may not help. But again.....it'd be a little hard to tell just by looking at what sort of boost you're making.

I'd probably just do the same.....or just run with low boost initially

How long are you planning on being without ignition control? Isnt 110 oct like $5/gal? So you'd get like 200 miles on a tank or something, thats like $60 a tank or something. And how many weeks do you plan on r7unning like this? MOney would be better spent saving for timing control. I mean you've gone how long without boost, and you cant wait another week or something.

Wouldn't a really cold/good intercooler solve the temperature thing?? like if you ran a front mount with a Co2 sprayer?

I did say "in a highly simplified question"

And if you mix 110 octane with regular premium you can get some higher octane fuel with out it being $5 a gallon. 1 gallon of 110 octane mixed with 4 gallons of 92 octane = 95 octane and only costs $2.75 a gallon. If you want to do such a thing.

And just for start up and tuning it to see if it would run, yes, expensive gas would be worth not damaging your engine.

I do plan on getting an intercooler though, and the iginition timing if neccesary if it starts knocking on 5 lbs of boost.

More fuel is actually your best bet to stave off detonation, douglas. It's the air/fuel ratio getting too lean (towards way too much air, with not enough fuel to consume it) that gives the oxygen in the air more and more chance to ignite instead of being consumed = "run-away detonation". You've got a non-turbo model, and you're adding a 'charger, right? Your fuel rail ought to be able to accept some larger injectors without a problem, and I bet your fuel pump could keep up with a few pounds of boost without much trouble... but of course a higher-flow fuel pump will be an inevitable upgrade anyway so plan for that.

It would be easier to do this with a turbo vs. a super charger, though: Increase the amount of fuel delivered, so you run rich - then watch a/f ratio at WOT, and each run increase boost until you see it start to get away from rich. Then you're at least in the right range without being in danger, and can have some fun until you can get some good aftermarket fuel control for actual tuning. You'd need a few pulley sizes for this though.

I just don't think relying on higher octane gas is a good idea, ever. It helps, as do colder spark plugs and timing retardation, but more fuel is the main ingredient needed to support more air...

(and for gods sake... EVERY boosted vehicle should have an intercooler... I don't understand what the hell Subaru was thinking when they released our cars )

I got to say I think the amount of fuel will be more of a problem than the race fuel could fix. Run it on 93 and if you feel the need use some toloune (don't waste money on race fuel) to up the octane. Don't worry about an intercooler for now, if you are running enough boost to need it with no fuel or timing mods, I don't think the engine will last long. With low boost and a turbo FPR you should be ok...

Easy way to max out richness = Unplug the O2 sensor. You'll run at 0.00% Fuel Trim (full rich), which is better than running "well" and risk running to lean.

Free5t1le - It's generally seen that a few PSI can be run un-intercooled safely. A friend of mine has been running like 7psi (making 260whp) un intercooled in his Taurus SHO for quite some time. It's not recomended, but a decently designed engine will put up with the abuse. The EJ22 isn't one of those engines though, so an intercooler is required (at least in my eyes). The EJ22T IS one of those stout engines. That's probably why Subaru didn't see it as a requirement to intercool the whole setup, and could cut costs by not including one.

I'm pretty sure 0.00% fuel trim means no fuel trim, not maximum fuel trim...

The simplest way to increase fuel is to use a high-flow pump and a rising rate fuel pressure regulator. This is the approach that a lot of aftermarket forced induction setups use.

howsabout maximum pressure tolerances for our injectors? If I go and get me a big walbro fuel pump and a rrfpr, whats an absolute maximum fuel pressure I'd want to keep a safety margin from before something (fuel lines, injectors, etc) can't handle it any longer?

I know some VWs run on like 95psi fuel pressure, I always thought that was friggin high...

O-rings like those used with fuel injectors are incredibly robust seals, and properly-used fuel injection hose with fuel injection clamps is very strong, but it's really hard to imagine what a reasonable limit would be.

I seem to remember several RS-T setups using 6:1 RRFPRs and running about 6 psi of boost... that should put peak fuel pressure somewhere around 72 psi, right? I'd feel uncomfortable going much higher... 100 psi might be an upper limit, but I'm pulling that number out of the air.

Remember, though, that flow increases with the square root of pressure, so increasing pressure yields diminishing returns. 100 psi only yields 18% more fuel than 72 psi.

95 psi does seem pretty high... Germans tend to use very high quality fuel line and stuff though, so I guess they have it figured out.

Is that for VW's direct-injection engines? They require very high fuel pressures.

Steve

Direct injection pressure is way higher... close to 12000 psi if I recall. That's the pressure between the injection pump and the injectors though, not in the lines up to the injection pump.

I think VW probably likes using high pressure because it aids in fuel atomization.

direct injection sounds insane. So do whipple-style 'chargers, for that matter.

Anyway, if our fuel pressure at 0psig is 36.3psi, that means to reach 72psi of fuel pressure we would need to be running 72-36.3= 35.7psi of boost...!

I'm interested to know at what level our 390cc/min injectors would cease to be able to compensate for the boost levels. It sounds like we don't have any imminent fuel pressure worries until way after our engine would explode.

With a larger turbo (VF-23, 16g), the same boost levels will yield higher airflow... that will also affect how much boost the injectors will be able to compensate for.

I suppose what I'm trying to get at is, where's the math to determine at what point we need a different fuel rail/larger injectors/RRFPR with 1. the stock turbo, 2. the VF-23, and 3. the 16g?

Every time I try and do engine math I end up doing it wrong...

free5ty1e wrote:Anyway, if our fuel pressure at 0psig is 36.3psi, that means to reach 72psi of fuel pressure we would need to be running 72-36.3= 35.7psi of boost...!

Or about 6 psi of boost with a 6:1 RRFPR.

I'm interested to know at what level our 390cc/min injectors would cease to be able to compensate for the boost levels.

Keep in mind that when you increase the pressure differential between the fuel rail and the manifold, you increase injector flow.

To use the above example again, if you were running 6 psi of boost with ~72 psi fuel pressure, you'd have a ~66 psi differential instead of the usual ~36 psi differential. Injectors which flowed 390 cc/min at 36 psi flow around 530 cc/min at 66 psi.

ahh, I see... The need for larger injectors and maintaining stock fuel pressure differential becomes clear in this case. RRFPRs sound as if they would seriously tax our fuel lines and fittings' abilities to hold the pressure.

Are we really really freakin' sure there's no larger injectors that fit into our stock rails? Who makes our injectors... Bosch? Don't they make all import injectors...? Theres got to be an alternative to swapping over to the n/a fuel rail, other than a RRFPR...

There probably are some Nissan-application injectors that would fit in our stock rails; they'd have to have the same shape as our injectors:

http://bbs.legacycentral.org/viewtopic. ... 6556#63549

But swapping fuel rails isn't really that big a deal...

Our injectors are not made by Bosch. I know later non-turbo injectors are made by JECS; I would imagine the others would be made by either Hitachi or Denso.