How much fuel (VE) is too much? (FAST)

[carbuff]

Hi guys,

This may be a naive question, but that's ok... I'm still learning.

I'm starting to finally tune my motor for WOT, and I'm finding myself adding more and more fuel. I've been as high as 120 in some VE entries in the FAST tables. And it's still reporting lean in those areas.

The motor is a SBC 377ci, strongly built (252/268, .672/.672, 114 LS cam), with the FAST B2B system and WBO2 option. I'm running 36# injectors and no power adder.

I'm willing to keep adding fuel, but I'm also going to put the car on a dyno soon, so I'd like to know if there is a point where I should stop adding to the VE entries.

Thanx!
Bryan

 

[HYPER-6]

Originally posted by carbuff
Hi guys,

This may be a naive question, but that's ok... I'm still learning.

I'm starting to finally tune my motor for WOT, and I'm finding myself adding more and more fuel. I've been as high as 120 in some VE entries in the FAST tables. And it's still reporting lean in those areas.

The motor is a SBC 377ci, strongly built (252/268, .672/.672, 114 LS cam), with the FAST B2B system and WBO2 option. I'm running 36# injectors and no power adder.

I'm willing to keep adding fuel, but I'm also going to put the car on a dyno soon, so I'd like to know if there is a point where I should stop adding to the VE entries.

Thanx!
Bryan

There are no magic numbers. Keep adding until
the target and actual air/fuel parameters match.
Try to get the the 02 correction as close to 0%
as possible.

 

[JrTuner]

Your VE numbers should never exceed 100 especially on a naturally aspirated engine. You might want to make sure you do not have a fuel delivery problem. The FAST system being "true" speed density, calculates VE (volumetric effeciency) based upon you entering CID (cubic inch displacement), injector flow rate (based upon 43.5 psi static fuel pressure), rpm, air temp., etc. If any of they values are off in your software compared to what is actually happening on your engine, your calculated VE numbers will be off.

 

[RickWI]

I agree there could be a fuel delivery problem but I have my motor tuned pretty well at WFO and run in the 110-115 range. That matches what I got for VE's pretty well on the dyno. I run a pretty radical street motor though Question though, at what point in the map is it running lean?

 

[bobc455]

Possible that your fuel pump might be inadequate.

Also, your cam sounds very healthy - are your injectors big enough? What is your highest injector duty cycle (inj DC)?

-Bob Cunningham
bobc@gnttype.org

 

[carbuff]

One fear that I have is that my fuel pump or lines may be too small... I'm headed to a chassis dyno tomorrow to watch the fuel pressure (gauge in the engine compartment) which I go through the RPM's. If I see a fuel pressure drop, then I get to start looking for problems...

I haven't watched the injector constant Bob. I'll add that to my log capture and see what it says. Thanx!

Rick, it's appearing to be lean around 4500-6000 rpm at WOT. That's the areas I've added fuel. I can't remember off the top of my head if it were the 1st 2 lines , or the 2nd 2 lines where I added fuel though. Have to go back and look..

I did notice my air temp sensor was reading pretty warm the other day (about 138 degrees) when it was 95 or so outside. I have the ATS Correction table all 0's, but I would expect the ECU is still using this value for some calculations...

Thanx!
Bryan

 

[RickWI]

Well having it go lean in the mid and upper would indicate you may have a fuel delivery problem. That is why I asked the question, to try and narrow the possible causes down. If I remeber correctly the AFT can be left at 0 as the compensation for temps will be taken care of if you are running in closed loop. The dyno will tell you what you need to know. One thing to make sure of, are you sure the fuel filters are clean. Check those prior to making any radical upgrades to the fuel system.

 

[carbuff]

Follow-up

Hi guys,

Well, I made it to the dyno today. And unfortunately, I saw pretty much what I expected to see...

At about 5000 rpm, my fuel pressure dropped off like a brick. It went from about 45psi to about 20psi where it stayed until the end of the run. Hmm... Not good. The ECU kept adding fuel, as it was in closed loop, but it didn't matter.

At the point where the pressure dropped, the Injector DC % was about 70-something. It did go over 100 once the pressure dropped, but I think they would have been ok with enough pressure.

So, my first plan of attack is a new fuel pump. I'll glad accept any suggestions. My plan is to install it close to the pump, and use the intake pump I have to feed it. If that solves the problem, great! It not, and I lose pressure again, I'll upgrade the size of the fuel lines (currently -6AN front to rear). And if I then get pressure but still go lean, I'll look at the injector constant for static injectors...

Does that sound like a logical progression at this point?

Thanx for the input everyone!
Bryan

PS: Even with losing fuel like that, I made 419rwhp and 376 rw-ft-lb of torque. It was a beautiful flat torque curve, but I know it has more in both! The curve was still rising until the fuel dropped off..... I have much tuning to do!

 

[Chuck Leeper]

Fuelin around!

Staging fuel pumps is a risky deal, in that if 1 fails, you stand a good chance of toasting the motor..AND, if the current pump can't outperform the new pump, you have the new, higher flow pump, pulling thru the orig pump.. NOT GOOD!!
I'd suggest you do a single pump w/ sufficient capacity to handle the HP you intend making. [I use AEROMOTIVE stuff]
The number crunch shows that at 500 FWHP[20% driveline loss] and .5 BSFC and 85% duty cycle, you are already out of injector..[calcs show 36.76PPh required]
As for lines, I'd want to see a -12 to the pump, w/ a 100 micron filter B4 the pump, the pump, a -8 [at minimum], to the engine w/ a 10 micron filter after the pump. Once up to the engine, using a "Y" block and feeding both rails assures good fuel supply. The return should be a -6 from the rear of both of the rails to a remote reg and then -6 to the tank.
The return should be at the side opposite the supply to cut down on areated, [and hot] fuel getting back to the pump..
DON'T forget a vent line w/ a roll over check valve in it!!
" " a GOOD electrical supply to the pump!!
" pull the fuel out the top of the tank..

Have fun! it ain't cheap!!

 

[carbuff]

Chuck,

You would probably hate my fuel system then...

I wish I had done more along the lines of what you suggested originally, but I didn't. I have an in-tank pump (that is supposed to be a Holley unit, but I don't know for sure). I'm running an inline filter between the pump and the rails. I'm using -6AN line for both supply and return.

I originally routed the rail lines the way you suggest, but it was a pain to route the lines effectively for me that way. So I changed and have the regulator at the end of one line with a crossever in the middle connecting the two. I realize it's not idea, but it was a much cleaner install for me.

The one question I have is: can the large aftermarket pumps actually pull from the tank? It was my understanding that they needed to be on level or below the tank to work effectively. If I remove the intank pump I have and replace it with a pair of pipes for the supply and return, will the new pump pull through one of those lines? There are currently on the top of the tank, as seen here:

Rock Valley Gas Tank

Thanx!
Bryan

 

[Chuck Leeper]

PUMPS AND LINES??

Most all aftermkt mfgrs suggest the pump be below and in back of the tank outlet. However, some situations don't allow the space for this w/out a fuel cell, lots of "cuttin and choppin".
My system is as I described B4.. w/1 exception to the rule. The pump is in front of the tank and slightly higher than the tank outlet..The tank is a stock GN tank w/ my own pickup and returns welded into it..
I am using -12 and -10 lines.. The pump is an AEROMOTIVE Eliminator series, as are the filters, etc..
This seems to do a good job.. Engine makes about 700HP..
Am going to "let it all hang out" tonite at the track.. So damn hot tho, may not be impressed w/ the results..


One of the problems plumbing that way is the hot fuel is next to the pickup and the return fuel has air in it.. MUCH better to return as far away from pickup as possible.. Also return under the fuel level helps keep aeration down..

 

[carbuff]

New pump is in!

Well, I have the new fuel pump in. The good news is it appears to be doing the trick to keep my pressure up! I haven't put it back on the dyno, but I was extremely rich on my first log run. I leaned things out, and now I can pretty much set the desired VE and AF and it attempts to hit it.

And it's doing this with about an 82% injector duty cycle!

The bad news is this thing is LOUD! Ugh! Loud enough that it's going to bug me I'm afraid... When the car is running it's not terrible, but if I'm cruising or idling, it's pretty loud. I used some rubber to try and isolate it from the metal floor, but I might need to add some more... We'll see...

Now I can really start tuning the big end. This thing pulls like crazy now!!! I can't wait to get back to the dyno...

Thanx for the help guys!
Bryan

 

[bobc455]

That's the reason I won't get that pump.

From an engineering standpoint it's great (flow #'s, PSI, etc.) but when your car is 99% streetdriven then there's no way I could live with that.

If you just have a weekend warrior, then it could be more livable.

When you go to sound-proof it, make sure you insulate it properly so that it can still dissapate heat to the air (which unfortuantely probably means dissapating sound to the air as well).

-Bob Cunningham
bobc@gnttype.org