A neat injector sizing tool!

[kenmosher]

I've asked Craig is we can get this incorporated into the GN/TType site for all of us to use. It's pretty cool!

Anyway, Playing with Craig's handy dandy tool... http://home.att.net/~cbwatson/airflow.html

I'm getting some neat info out of it! It's really interesting to see what effects raising and lowering fuel pressure, injector size, efficiencies, etc. have on the whole equation...

Just a brain dump of what I was playing with ... pretty neat stuff!

Default values for efficiency, turbo, gear ratios, etc....

2 psi drop for stretch intercooler
11.5 A/F ratio
45 psi fuel pressure (static)
42.5 009 injectors
22 psi
5200 RPM shift point
28 inch tall tires
0.47 BSFC

Calculations show that we are at about 82% duty cycle. 378 g/s of air flow and about 507 HP. NOTICE THE 5200 RPM SHIFT POINT. Makes a big difference (no surprise). Also, notice the 11.5 A/F ratio ... on the "safe" side.

Some tweaks ...

5% more efficient intercooler, requires ~2% increase in duty cycle (to
84%)
5% more efficient turbo, requires another ~2% increase in duty cycle (to
86%)
90% VE (assuming ported heads, probably optimistic?) results in 100% duty cycle (static) 24 psi of boost results in 108% DC

E.T. Ends up in the 11.24 @ 121+ (pretty much my level) ... keeping E.T. the same, let's see what fuel pressure does?

Add fuel pressure (and put boost back at 22 psi) ...

47 psi = 98% DC
50 psi = 95% DC
52 psi = 93% DC

Up the injector size to 50s...

43 psi = 88% DC
45 psi = 85% DC
47 psi = 83% DC

Now 55s ...

45 psi = 77% DC
43 psi = 80% DC

No surprise to Bruce, I'm sure (or me for that matter)... definitely shows that bigger injectors are controllable at the high HP level. The interesting thing is that the 009s hold up pretty good and the fuel pressure "crutch" works to a point.

A couple of other interesting things (at least to me)...

Put the RPM at idle (650 RPM) and 15"Hg and 14.7 A/F ratio ... 55s @ 43 psi are at 5% DC (about 9 ms)
50s @ 43 psi are at 5% DC
42.5s @ 43 psi are at 6% DC
36s @ 43 psi are at 8% DC
29s @ 43 psi are at 9% DC (about 17 ms)

Makes pretty good sense, the 55s are almost 2x the size of the stock 29s, so it takes half as much pulse width to deliver the same amount of fuel. How fast does an injector react? 2 ms? 4 ms? Reason I ask, I'm wondering at what point it's almost too small to control?

Very cool tool !

 

[bruce]

Originally posted by kenmosher
I've asked Craig is we can get this incorporated into the GN/TType site for all of us to use. It's pretty cool!

Anyway, Playing with Craig's handy dandy tool... http://home.att.net/~cbwatson/airflow.html

0.47 BSFC

378 g/s of air flow and about 507 HP.

5% more efficient intercooler, requires ~2% increase in duty cycle (to 84%)
5% more efficient turbo, requires another ~2% increase in duty cycle (to 86%)
90% VE (assuming ported heads, probably optimistic?) results in 100% duty cycle (static) 24 psi of boost results in 108% DC

definitely shows that bigger injectors are controllable at the high HP level. The interesting thing is that the 009s hold up pretty good and the fuel pressure "crutch" works to a point.

A couple of other interesting things (at least to me)...

Put the RPM at idle (650 RPM) and 15"Hg and 14.7 A/F ratio ... 55s @ 43 psi are at 5% DC (about 9 ms)
50s @ 43 psi are at 5% DC
42.5s @ 43 psi are at 6% DC
36s @ 43 psi are at 8% DC
29s @ 43 psi are at 9% DC (about 17 ms)

Makes pretty good sense, the 55s are almost 2x the size of the stock 29s, so it takes half as much pulse width to deliver the same amount of fuel. How fast does an injector react? 2 ms? 4 ms? Reason I ask, I'm wondering at what point it's almost too small to control?

Yes, it can be useful, but like any any tool, you got to get the stuff right on the input end to get valic info out.

I just don't see a .47 BSFC happening with a Buick turbo motor when in boost.

The airflow numbers line up with the HP to grm/sec stuff I've been posting.

The actual VE numbers of a turbo engine can get to 140%. Alan Locheed has done some interesting work on looking at what goes on in a turbo motor. I'd think 120 is a fair number for a well tuned GN.

While I'll admit to having done some experiments, the 55s will idle down to 1.7 msec at idle just fine, and my math shows a 72 would be at 1.3 msec.
The 9 msec idle PW for the 55s is really different from what I'm been seeing.

going sub 1 msec is getting real tricky on some injectors.

the 1% enrichment per 1 PSI, is again crutching things.

What do you click on to run the computations?.

 

[kenmosher]

It automagically computes stuff when you make a change in a field and then click on another field.

The idle stuff I think has it a bit confused, since it is still subtracting stuff out for the turbo. I was expecting to see <2ms times and it returned the bigger times. Maybe it's just a breakdown in the model?

I'm not sure how you'd adjust for the VE? If you put 120% in for VE, it shows that the stock injectors are maxed out at 12 psi of boost. (by a LOT!)

 

[turbo buicks]

what would the manifold temps be @ say 22 psi w/alky? could the intercooler efficiency be boosted to compensate for the lack of and alky field?

 

[bruce]

Originally posted by kenmosher
It automagically computes stuff when you make a change in a field and then click on another field.

The idle stuff I think has it a bit confused, since it is still subtracting stuff out for the turbo. I was expecting to see <2ms times and it returned the bigger times. Maybe it's just a breakdown in the model?

I'm not sure how you'd adjust for the VE? If you put 120% in for VE, it shows that the stock injectors are maxed out at 12 psi of boost. (by a LOT!)

OK.
Looks like, if you want I can run some numbers on the bench and give you some actual answers

They are, with enough breathing changes to really let the engine breath. I guess I need to clarify that 120, that's for a good breathing Turbo motor. A stock type exhaust or 6" K+N won't let you do that. Blowthru MAF, 4" pre turbo, THDP, 14" K+N, straight thrus, etc will prolly get you close. The TTA heads are an instant big plus with them good exhuast ports.