Can you help a brother out?

[88-406]

Ok, here's the story I'm trying to get my engine tune dialed in and I'm all out of ideals. I'm hoping one of you guys more familiar with this type of stuff might see something and/or possibly have a susgestion.

My AFR curve is wierd! You can see it here. The fuel pump was upgraded prior to this pull with a 500HP Bosch unit. Here's a Diacom trace of the pull.

So far all I know is that the curve follows the pulse width changes. Could that mean my pump is still to small? The injectors are FMS 24# units. Are the injectors too small? What would be some examples of the pulse widths in the lower RPM range for a NA 383?

Thanks for taking a look.

KM

 

[JDEstill]

I think we'd need a lot more info. What kind of FI system are you running, what kind of engine is this, etc... You haven't explained much about your situation.

John

 

[Ormand]

??

I agree with Estill. More info would be very helpful. BUT.. it doesn't look like the pump is too small. If the pump was too small, you would go lean near max horsepower, since the fuel consumption goes up as horsepower goes up. The lean spot at 4000 rmp looks dangerous, though! Small fall in torque, but running that lean would seem to be risky. Some engines will hit lean spots like that due to length of intake/exhaust runners, which can cause a "peak" in air flow. Just guessing, though. Give us more info.

 

[88-406]

Ok, the engine is an all forged 383 with the TPIS MiniRam on it. The heads are AFR 210's with the REV kit. It has 10.2 compression with 236/242 hyd roller cam in it. It also has a Vortex rammer on the inlet side and Hooker 1 3/4 Super Comps for the exhaust. The rest of the exhaust system is 2.5" free flowing all the way out back.

This engine is installed in a 1988 Vette with a 4spd tranny!

Would you say the engine needs a lot more fuel below 4500 or so? Are the injectors too small? It's currently using the stock computer with a chip. Do you think an aftermarket ECU would easily solve this problem?

How long does it take a Joe Blow to get an aftermarket system drivable? Is the wideband o2 option essential? How tough is tunning with out it?

Thanks

KM

 

[Chuck Leeper]

HP vs Inj size??

you wrote:

Ok, the engine is an all forged 383 with the TPIS MiniRam on it. The heads are AFR 210's with the REV kit. It has 10.2 compression with 236/242 hyd roller cam in it. It also has a Vortex rammer on the inlet side and Hooker 1 3/4 Super Comps for the exhaust. The rest of the exhaust system is 2.5" free flowing all the way out back.

I assume the "rammer" is a blower??
Given the 368 RWHP, the inj's are too small for the output of the engine.
The math:
368 at the wheels is about a 15% loss. [Given the driveline is a clutch application] That says the FWHP is about 425 FWHP.
The math, using the following, shows the injs to be too small.
[24pph is a stock inj in a 350 N/A application.]

.6 BSFC, duty cycle @ 80%.
This says the injectors should be 34.5, AKA 36# inj's.
There appears to be other issues as this engine w/ that much comp. ratio should easily make 383 HP without the blower. [If my assumptions are correct and a "rammer" is a Vortec blower.]


I would give serious consideration to an aftermkt ECU [FAST] w/ wide band O2.
I would also look at inj pulsewidth and FP at WOT...
You don't mention what boost you are running.[if any.. ]
Timing curve??
Plug readings?
HTH,

 

[88-406]

The engine is normally aspriated and the Vortex Rammer is type of Y-body air filter. So you think 36# injectors are needed aye?

As for the plug readings, they seem normal to me. The timming curve is something I'm not sure about because it's a mail order chip.

The diacom trace shows it's putting in 34 degrees total and has it all in by about 2800-3000 rpm.

KM

 

[JDEstill]

Yeah, running through some math I agree with Chuck. The behavior you are seeing in your AFR curve is due to the injectors being too small. At ~5300 rpm they are probably hitting 100% duty cycle, and as the revs go up things just start leaning out. Absolute minimum injector size for you is about 30 #/hr. Much better would be 36 #/hr, which will give you about 80% duty cycle at 6500 rpm.

John

 

[Chuck Leeper]

My reply?

Looks as tho my reply was either deleted or never made the trip!
I recalculated the numbers when I found that a "rammer" was NOT a blower. Don't see it here tho...
The numbers didn't change much tho as all I did was to lower the BSFC to .5 for an N/A engine...
John's comments mirror mine.. The AFR trace was scary !! I'd get the FP gauge up on the windshield where you can see it and look for pressure drop @WOT...

One added comment:
We have a 406 w/ about the same specs, less cam and GM heads..TPIS, yadda, yadda. Even tho it was a dead player at 6000, due to head flow, we made 605... Could be you can get a significant increase w/ more injector,[we had 42.5's] and tuning.. BTW, those numbers were on an engine dyno, using a stock computer w/ our own chip

 

[88-406]

So you guys think and a programable ECU would yield more HP? I pretty much felt the same way, because I could tell that the AFR was way off for making HP.

At this point I'm leaning towards the GEN 7 without the wideband initialy. How tough is it to tune without the wideband o2?

Thanks

KM

 

[Chuck Leeper]

WB or Not??

I wouldn't get the system without it.. FAR too much info for tuning comes from the WB.. With it, you can make logs and use the WB trace to correct the VE tables and it will also correct the fuel within the parameters you have set while driving.
Also, if you do it later, it gets EXPENSIVE!!
I'd recommend getting everything now...

 

[88-406]

Ok thanks! do you know if the GEN 7 can be made to work with my existing NTK wideand probe? I wonder if I can make up an adapter that would allow one probe to run both the wideband meter and the GEN 7?

Thanks

KM