Z32 Maf, injectors, programming, etc..

[NeedForSpeed]

Michael,

I understand you to say that the hp is not the limiting or deciding factor with respect to stock injectors, it's the rpm necessary to make the hp?

So, a charged engine could make 330 hp at 6500 rpm with stock injectors easily enough, but a NA engine cammed to make the same 330 hp at 7800 rpm would push the stock injectors closer to the edge?

Originally Posted by longassname

ya, this is a hijacking allright...... lol

you are correct about the bsfc on a supercharger being better than on a turbo. You are also correct that the stage 2 software will let you run higher duty cycles on the injectors. There is also a third factor that lets the injectors handle higher power--well for most of us: the automatic transmission. RPM is the largest contributor to when the fuel injectors will max out. The higher the rpm the less time the fuel injector has to deliver the fuel. At 6500 rpms there is a lot of time to deliver fuel, something like 18 ms. I don't remember the # for sure off the top of my head but I believe I calculated the base injector pulsewidth on a stock svx with factory injectors and software at max load to only be about 8ms. The stage 2 software further reduces the base injector pulsewidth calculated at higher load levels allowing you to achieve the correct fuel delivery by raising the fuel pressure rather than driving the injectors to higher duty cycles where they would overheat. Stage 2 does well for higher load levels from superchargers, turbos etc and stage 2 allows na cars to runner higher rpms to get more power. The limits of the injectors will most easily be reached by those attempting to run turbos at high rpms (so don't do that).

[NikFu S.]

Originally Posted by NeedForSpeed

Michael,

I understand you to say that the hp is not the limiting or deciding factor with respect to stock injectors, it's the rpm necessary to make the hp?

So, a charged engine could make 330 hp at 6500 rpm with stock injectors easily enough, but a NA engine cammed to make the same 330 hp at 7800 rpm would push the stock injectors closer to the edge?

The interval in which the injectors have time allocated to inject fuel is reduced with increased engine speed.

Higher rpms = more strain on the injectors trying to keep up in an on/off sequence.

According to LAN's guess, the injectors are completely maxed at whatever rpm causes them to sequence every 8 milliseconds, which is not far off from the 18 ms at 6500.

[longassname]

While the 1st statement isn't right on the numerical example you gave is correct and I bet you will understand completely if we run with it. For illustrative purposes I see you have chosen the same hp, 330, at two different rpms. The same hp at higher rpms is harder for the injectors to accomplish because they have less time in which to inject fuel.

6500 rpms
3250 rpms available for fuel intake
60 sec/3250 rpms = 0.01846 seconds = 18.46 ms available for fuel delivery

7800 rpms
3900 rpms available for fuel intake
60/3900 rpms = 0.01538 seconds = 15.38 ms available for fuel delivery

Originally Posted by NeedForSpeed

Michael,

I understand you to say that the hp is not the limiting or deciding factor with respect to stock injectors, it's the rpm necessary to make the hp?

So, a charged engine could make 330 hp at 6500 rpm with stock injectors easily enough, but a NA engine cammed to make the same 330 hp at 7800 rpm would push the stock injectors closer to the edge?

[longassname]

Your statements are correct except for how you took my use fo #'s. I said the calculated base injection quantity for the highest load levels a stock svx is able to obtain is only something around 8 or 9 ms. Base injection quantity is what is calculated to reach a stoichiometric 14.7 ratio before adding enrichements. To that is added whatever the fuel table says to reach the desired lower afr and then enrichments for things like ac, coolant temp, throttle position, etc. So the actual pulsewidth is something like 10-11ms. The duty cycle at 6500 rpms is comfortably low--there's lots of time left to deliver fuel.

If you were to use one of these online injector size calculators it would assume a higher rpm and less injection time like the 7800 rpm example given before and say hey.....11/15 is already 73% 250 hp will bring you to the magical 80% therefore we recomend you get a larger fuel injector if you want more than 250 hp.

When you come back to doing the actual math instead of using an online calculator you see you actually have a lot of time between 11ms and 18 ms to deliver fuel for higher power outputs.

Originally Posted by NikFu S.

The interval in which the injectors have time allocated to inject fuel is reduced with increased engine speed.

Higher rpms = more strain on the injectors trying to keep up in an on/off sequence.

According to LAN's guess, the injectors are completely maxed at whatever rpm causes them to sequence every 8 milliseconds, which is not far off from the 18 ms at 6500.

[SVXRide]

Michael,
So, doing the precise math versus an on-line calculator, what's your educated guess as to what the upper limit of Hp is that the stock injectors can support (assuming we've got an adjustable fpr and don't go above 60 psi) - given that the engine has the z32 MAF and 2v5 chip?
Thanks.
-Bill (thinking that the 7ms between 11 and 18 ms is like a lifetime, injector-wise....)

[longassname]

Tom has 2v5, an adjustable rising rate fuel pressure regulator, a supercharger running 9 lbs, and a select monitor. Have him check his pulsewidth with the select monitor, compare that to 18.5ms, and then you'll see how much or how little comfort zone you have at something around 370hp.

I'm hessitant to make an "educated guess" by rolling #'s from memory along with interpolations from current data through a formula.

Originally Posted by SVXRide

Michael,
So, doing the precise math versus an on-line calculator, what's your educated guess as to what the upper limit of Hp is that the stock injectors can support (assuming we've got an adjustable fpr and don't go above 60 psi) - given that the engine has the z32 MAF and 2v5 chip?
Thanks.
-Bill (thinking that the 7ms between 11 and 18 ms is like a lifetime, injector-wise....)

[NikFu S.]

I see now. I skipped over the part where you said 18ms is a lot of time to deliver fuel.

Twice now I've been caught not reading a post word for word.

[mbtoloczko]

Originally Posted by Chiketkd

Matt,

I don't think you need to adjust the fuel pressure, as the Stage 2v5 chip will richen the afr similar to the stage 1v4 (or is it v5). With your mods and the Z32 MAF, your afr will probably remain nice and rich in the upper rpms.

If you ever add a mod such as performance camshafts, then bumping up your fuel pressure will be needed.

-Chike

Chike, that's not necessarily correct. If the MAF is not near its limit, and the fuel injectors are not near their output limit, then further performance mods will not necessarily require richening the afr. NA motors generally work best at around 12.5-13.5:1. OTOH, certain mods, such as a turbo, work better when at a richer afr, and in these instances, its reasonable to presume that richening the afr will be helpful.

[SVXRide]

Originally Posted by longassname

Tom has 2v5, an adjustable rising rate fuel pressure regulator, a supercharger running 9 lbs, and a select monitor. Have him check his pulsewidth with the select monitor, compare that to 18.5ms, and then you'll see how much or how little comfort zone you have at something around 370hp.

I'm hessitant to make an "educated guess" by rolling #'s from memory along with interpolations from current data through a formula.

Michael,
I didn't realize the SSM could read out pulsewidth We'll have to see what Tom has to say...
-Bill

[longassname]

Oh ya,

The select monitor can read out all the goodies about fuel.
f08 maf voltage
f09 calculated load
f11 injector pulse width
f19 alpha1
f20 alpha2

Originally Posted by SVXRide

Michael,
I didn't realize the SSM could read out pulsewidth We'll have to see what Tom has to say...
-Bill

[SVXRide]

Originally Posted by longassname

Oh ya,

The select monitor can read out all the goodies about fuel.
f08 maf voltage
f09 calculated load
f11 injector pulse width
f19 alpha1
f20 alpha2

Nice!
We'll have to use it in conjunction with Mychailo's wide band when we hit the dyno!
-Bill

[Chiketkd]

Originally Posted by mbtoloczko

Chike, that's not necessarily correct. If the MAF is not near its limit, and the fuel injectors are not near their output limit, then further performance mods will not necessarily require richening the afr. NA motors generally work best at around 12.5-13.5:1. OTOH, certain mods, such as a turbo, work better when at a richer afr, and in these instances, its reasonable to presume that richening the afr will be helpful.

Mychailo,

I fully understand what you're saying. I was still making assumptions in my reasoning that MAF was being maxed out...

So, if I understand what you and LAN are saying correctly, with his stage 2v5 software & the Z32 MAF, it won't be necessary to upgrade my fpr even with the performance intake cams???

-Chike

[longassname]

That's a question that can only be answered by trial and error. At 42 psi stage 2 keeps the afr between 12.5 and 12.9 through out the entire rpm and load range. At stock fuel pressure it will be a little bit leaner. Which is better? You'll have to try each to see.

Originally Posted by Chiketkd

Mychailo,

I fully understand what you're saying. I was still making assumptions in my reasoning that MAF was being maxed out...

So, if I understand what you and LAN are saying correctly, with his stage 2v5 software & the Z32 MAF, it won't be necessary to upgrade my fpr even with the performance intake cams???

-Chike

[TomsSVX]

Thats why i got my MR. Dyno. I need to perminantly mount it somewhere besides the windscreen to begin taking measurements... Try one run with a certain fuel pressure... then adjust and see where that leaves you... A dyno would be nice... but I don't have over $500 to blow taking a ton of pulls on a dyno

Tom

[Chiketkd]

Originally Posted by longassname

That's a question that can only be answered by trial and error. At 42 psi stage 2 keeps the afr between 12.5 and 12.9 through out the entire rpm and load range. At stock fuel pressure it will be a little bit leaner. Which is better? You'll have to try each to see.

Thanks Michael. That info will definitely be very useful in my tuning...

Btw, what do you see as the most accurate bsfc value to use for an n/a EG33? I'm using 0.50 in my calculations, but I read somewhere that the LS1 corvette motors had a bsfc of 0.45...

-Chike