Air/fuel Ratio's And Good Old Knock!

[siksII]

In my gtst, i have hit the limiter several times since i have owned it, with a regular power fc.

A few things i have noticed.

1. Its not accurate, as others have noted, i have my limit set at 6900, and i have seen ~7100 as peak rpm

2. It has NEVER showed a higher than normal ping reading after hitting the limiter, my ping readings are very low, usually around 10.

3. The only odd thing i have noticed when hitting the limiter is plenty of popping(rich pops) and i dont understand how that happens when there is meant to be no fuel.

(i dont know what my afrs are, i need a retune its very rich)

[williamsf1]

well Im still in search of a commercially aval. rev limiter...

and I think you will find a harder or more fine tuned car will get more knock at the limiter... that is what I have been told, so maybe the RB25 doesnt stress much anyhow...

[Duncan]

Hang on this thread is about AFRs not rev limiters I'm very interested since there have been a few tunes lately that I thought were a bit close.....but like I said in those threads I'm not a tuning guru and I am interested in other people's thoughts.

What does worry me in a road car is old dirty injectors (get them tested! I checked about 4 sets before I found 1 that were within 10% of factory spec), dying fuel pumps (likewise check fuel pressure), turning up the boost and not retuning etc etc.

[Mik]

well Im still in search of a commercially aval. rev limiter...

and I think you will find a harder or more fine tuned car will get more knock at the limiter... that is what I have been told, so maybe the RB25 doesnt stress much anyhow...

<{POST_SNAPBACK}>

Yep...fair enough, I was't disagreeing with you, I just can't undertsand how they pop and belch black smoke and flames when bouncing off a rev limiter that supposedly cuts fuel???

[Duncan]

I'm pretty sure that is all the unburned fuel from when the cylinder does not fire due to insufficient fuel

[williamsf1]

I think they pisss and fart as the rev limit is doing just that... holding it at the limit by cutting and re-adding the fuel... so suddenly the fuel is off.... then on.... then off.... and is going very lean, high RPM, very rich, high RPM... etc etc so there are your flames and soot

I'd still love to see say a V8 supercar AFR and my side issue is the rev limter

[Duncan]

BTW the other thing I forgot to mention is that most tuners will use headphones to listen for knock while on the dyno, the PFC and standard computer just use a mic and an algorithim to guess if a sound might be knock. All other ECUs miss out on that altogether.

[gtst25]

Hang on this thread is about AFRs not rev limiters   I'm very interested since there have been a few tunes lately that I thought were a bit close.....but like I said in those threads I'm not a tuning guru and I am interested in other people's thoughts.

What does worry me in a road car is old dirty injectors (get them tested! I checked about 4 sets before I found 1 that were within 10% of factory spec), dying fuel pumps (likewise check fuel pressure), turning up the boost and not retuning etc etc.

<{POST_SNAPBACK}>

Got to agree there,

As I'll be installing/getting tuned my 2835 pro s soon I'd like to learn as much as possible. I don't think too many tuners will say much as they wouldn't like to give anything away.

Also just purchased a wide band oxygen sensor, and although I'll be getting it tuned professionally I'll use it to check things out every now and again.

Interestingly I also had issues with my stock injectors when doing my first tune with the stock turbo - shouldn't be a problem now though with new nismo's.

[Scooby]

most tuners will use headphones to listen for knock while on the dyno, the PFC and standard computer just use a mic and an algorithim to guess if a sound might be knock. 

<{POST_SNAPBACK}>

Since when does PFC have an input for engine knock? I'll fit mine right now if it does.

[Beer Baron]

Jaycar have a kit?

EDIT: Indeed they do which cuts ignition (with another kit) - http://www.jaycar.com.au/productView.asp?I...x=&SUBCATID=347

So for $50 or so, you should have a ignition cut rev limiter

<{POST_SNAPBACK}>

sweet, i will give it a go.

[Mik]

sweet, i will give it a go.

<{POST_SNAPBACK}>

From memory, that kit just uses a relay to cut igntion. And you think the Power FC is slow to catch the 8000RPM rev limit

[williamsf1]

yeah well I'll buy something that is quality.... any ideas?

[Beer Baron]

From memory, that kit just uses a relay to cut igntion. And you think the Power FC is slow to catch the 8000RPM rev limit

<{POST_SNAPBACK}>

i don't know wtf i'm doing but can someone explain to me how it can be worse, or better than say the bee-r kit? mmm beer.

I just assumed it's like a shift light, but instead of lighting an LED as it's out put, it cuts ign. the other question is how do these systems function on a multi-coil engine? do the just cut every cylinder at once or what?

if it's a bit lazy i can just set if for say 7800 knowing it will allow more like 8000...

like i said i don't mind spending say 200 bux, but any more than that and i'd rather just buy a PFC pro and not have to f**k around wiring up another bloody module in the car.

[Mik]

It actually is jaycar's shift light kit.

A relay would do a terrible job of controlling RPM, it won't be able to switch on and off quick enough to regulate the RPM. If you were sitting on the rev limiter, instead of say bouncing between 8000 and 8100RPM like the power FC does, it might bounce between 8000 and 9000RPM.

It wouldn't be too hard to make something I guess. Just a frequency comparator circuit that looks at the tach output and then switches say the CAS (will cut fuel and igintion) to regulate the RPM.

You could also have an input from the speedo sensor to have two limits, a lower one when the vehicle is stationary (for launch control) and a higher one as soon as it starts moving.

[Beer Baron]

A relay would do a terrible job of controlling RPM, it won't be able to switch on and off quick enough to regulate the RPM. If you were sitting on the rev limiter, instead of say bouncing between 8000 and 8100RPM like the power FC does, it might bounce between 8000 and 9000RPM.

<{POST_SNAPBACK}>

ahh, thanks mate. that makes sense to my simple brain now ok, so the jaycar kit is off the menu...

not hard to make eh? well if you can make one, you will have my money I don't want any fancy gizmo either, just as long as it does the job, cause i will just stick it behind the dash and forget about it c'mon mik, you know you want to!

[Busky2k]

The rev limiter may not 'keep it' at the exact RPM beacuse of inertia. Imagine spinning up a bike wheel with your hand really hard and letting go.. It'll still accelerate, even when you've taken the force away. This much like an engine. Its accelerating, you cut the fuel and due to inertia it'll keep accelerating for a couple more hundred RPM. Thats why the peak RPM may a lil higher than the set limit. Ive noticed with my lightened flywheel it doesnt overshoot as much, presumably due to the less inertia the lightened flywheel has.

[Mik]

The rev limiter may not 'keep it' at the exact RPM beacuse of inertia. Imagine spinning up a bike wheel with your hand really hard and letting go.. It'll still accelerate, even when you've taken the force away. This much like an engine. Its accelerating, you cut the fuel and due to inertia it'll keep accelerating for a couple more hundred RPM. Thats why the peak RPM may a lil higher than the set limit. Ive noticed with my lightened flywheel it doesnt overshoot as much, presumably due to the less inertia the lightened flywheel has.

<{POST_SNAPBACK}>

Not really. The inertia will make the wheel tend to maintain its rotation when a force (torque) is removed, but it won't increase it's rotational speed.

If it did, energy would be coming from nowhere!

[GunMetalR33]

Not really. The inertia will make the wheel tend to maintain its rotation when a force (torque) is removed, but it won't increase it's rotational speed.

If it did, energy would be coming from nowhere!

<{POST_SNAPBACK}>

Makes sense to me

[midnight]

get one of these Bee Racing rev limiter

Im running one, it cuts ignition and you can wire in a switch for lauching.

mines wired to my clutch so when my clutch is in, it limits to 4500rpm, means if I keep my foot on the floor and drop the clutch, it drops right back into 4500rpm..

mmm powerband...

you can also set the frequency of the cut between fairly descreet, to huge loud backfires.

Edited September 22, 2005 by midnight

[Busky2k]

Not really. The inertia will make the wheel tend to maintain its rotation when a force (torque) is removed, but it won't increase it's rotational speed.

If it did, energy would be coming from nowhere!

<{POST_SNAPBACK}>

Well, thats how I explain it, based on the observations of the flywheel differences. I'm no physics pro haha..

But try this. At idle, give it full throttle to like 4000rpm and back off real fast. The revs dont die straight away do they? It still goes up a couple more hundred RPM after your foot is off...

Edited September 22, 2005 by Busky2k