Fuel cut or boost cut???

[I`m Batman]

that basically means u got rid of KR w/ the Denso plugs which is what the hesitation would be, so a good thing.

still need to clarify tho if those AFR's are WOT or part throttle.

It's not quite WOT... maybe about 3/4 throttle. I guess I should try WOT...

[tbot]

try WOT and let us know what ur AFR's are.

[I`m Batman]

So, I did a few WOT run in 4,5 and 6th gear over the weekend. (not to redline in the higher gears obviously) The AFR was at low 12s... about 12.0x - 12.1x. Is that good enough or something that I should worry about?

[erod550]

That's fairly close to where mine are with a pro-tune so I'd say you are ok, though you could be a little safer with AFRs more in the 11s. It's really strange that you are running that lean on the stock map. Normally the stock map will have you in the 10s through most of the power band and down into the 9s by 6k.

[tbot]

check your fuel pressure...

if it were me, i'd be worried about it. But could be your fuel pump isn't holding a high enough fuel pressure for the afr's that the engine is asking for.

[I`m Batman]

I'll take a look at the fuel pressure. What should it be around?

[~Barn~]

Not to muddy your thread Metha, but I've been datalogging myself and for what it's worth, at WOT between 5300rpm and 64000rpm:
fuel PSI (averages) at 1675.xx
AFRs (average) 10.41.

These numbers are with an off-the-shelf map from Cobb. (Stage 1 tuned for 93oct but I use 85 in it out of principle.)

For comparison sake though, without any tune, but under nearly the exact same engine parameters (WOT, 5400-6400rpm):
1677.xx (average) fuel PSI.
AFRs (average) 9.34.

Boost averages during the above range:
15.88 tuned
8.50 stock

And no more of that violent boost-cut symptom I was describing earlier, by the way. The off-the-shelf map that was causing that was Cobb's Stage 1 tuned for 91. I never left it installed long enough to datalog anything off it.

[tbot]

fuel pressure should be 1650 or higher

[I`m Batman]

Oh, I guess I better go higher than 5k RPM then. I usually let off around there. Lets see what happens. I'll let ya'll know.

[I`m Batman]

So I took 470 home and try WOT in 3 and 4 th a few times... And it looks like my AFR is in the 11s once I get close to 5k. I guess it didn't hit that in 5 and 6th because I ran out of room before I can get the rpm high enough or didn't give it WOT.

I'm still getting the cut though once I get up there.

[erod550]

Yea the cut will be there until you get an AP or something else to trick the ECU into not seeing how much boost you're actually running.

And Barn did I read that right that you're using 85 octane gas??

[~Barn~]

And Barn did I read that right that you're using 85 octane gas??

Oh yeah. 85 octane FTW.

After having this discussion ad nausem on the CO Sportbike forum, the consensus of some very brainy folks, is that high-octane gas is only needed if, in fact, you are experiencing the symptoms of knock.

Adding higer octane fuel to a vehicle that doesn't even have these issues, is essentially causing horsepower loss, as you are removing the combustable ingredients from the cocktail. To compound this, being at the altitude we are here in Denver, we already have less oxygen and less-dense air going for us.... So by virtue of those geographical physics, we are less prone to knock anyway.

This is why you will see many varieties of "race gas" that are 80some octane. The super-high octane fuels are for already built engines, that would otherwise not run properly w/out them. And again... We were talking about sportbikes here, which are already running a very high compression ratio, compared to cars.

Here is a snipit from somebody who I consider a local authority on the subject. But yeah... it make sense to me that there is no need to address an issue, if it really isn't even happening.

High octane *inhibits* combustion. In high compression or high performance engines this can be necessary to avoid pre-detonation, however increased elevation (like Colorado) has the same effect of reducing compression due to less air density (less air+fuel means less mixture being squeezed, so while the ratio is the same, the tendency to pre-ignite is reduced). You should therefore use the lowest octane possible, which will give you the most power, best mileage, and reduce carbon buildup.

If you're pumping premium into a stock sportbike motor (or even a mildly tuned one) at this elevation, you are not gaining a thing (and in fact spending more money to reduce HP).

There are exceptions to this with race fuel blends that might need higher octane because of the chemistry (note: VP U4e is actually in the mid 80's I believe), but pump gas is not anything special, so just buy the cheap stuff and be happy.

[erod550]

But we don't drive sportbikes or have high compression, naturally aspirated motors. Turbo motors are a whole different story when it comes to premium gas.

Oh well, I will continue to use 91 and would use 93 if it was available. The extra $2 per tank I'd save isn't worth it to me when I've spent as much as I've spent on this car.

[~Barn~]

I can appreciate that. =)

[tbot]

I agree w/ erod...we don't drive NA sport bikes. And even looking at your logs you ARE getting KR, so therefore should be running higher octane. You also have to look at the tune the motor has. Yes there's less chance of knock w/ higher octane, but that also means you can advance your timing to get more power. Mazda does that in their stock tunes for our car. More knowledgeable people with our cars have stated the highest octane is required for our cars.

Basically you're comparing apples to oranges in this scenario and it does NOT apply. But I can see where they are coming from on ur sport bike forum, but again, does not apply to our cars.