Going to much lower octane, need to change VE #'s??

[Bobo]

I assumed I'd need to go higher on all my ve #'s when going from 118 octane to 93 for the street, but I have been told yes and no What do you guys think? If so, isn't there a way to highlight more than one VE cell when changing them? Can the whole range of cells across the screen be changed all at once? Seems like you hit "shift" and something else and you change the #'s as a percentage? Thanks for any help!

 

[fast4d]

Regarding selection of multiple cells in a table keep the shift key down while you drag the mouse/key arrow. Then you can press "*" to enter in a percentage multipler.

ea. to add 20% to all selected cells enter 120 or to subtract 20 percent enter 80.

As for the other question you should richen it (depends where you're at already). More important will be timing.

Hope this helps.

 

[Bobo]

Thanks for the response Alan. I hope you can get your fuel pump problem figuered out cya
Bobby

 

[Craig Smith]

You can also use the % key rather than the * key. When using the % key, entering 20 will increase by 20%, -20 is -20%, etc. Can be simpler than the multiplier value.

 

[Bobo]

Thanks Craig

 

[J. Lubrant]

Thought the question was does he need to change his VE tables when changing from 118 octane to 93 octane??

I may be wrong but I never change VE with lesser octane.
I change to a lower timing--i.e. 25-26 deg. with 116-118 to 16-18 deg with 93-94 octane.
I also enrichen the Air/Fuel ratio (Target).
Lastly I do not run as much boost!

I don't really think the VE of an engine changes that much due to octane.
Timing, boost (cylinder pressure)& A/F will be the major factors with changing octane?

Just my 2 cents worth.

 

[Bobo]

Thanks Joe, that's kinda what I had heard at first. Harry tuned my SP, I was gonna call him up and pick his brain a lil about this. I'm running 11.2 a/f, most guys have said that is very conservative, I'm not sure if it needs to go lower for the street and 93 octane.

One more thing, do you work @ PT? I am considerin upgrading from my T76 to a PT-88 4 bolt. I am not sure it'll bolt right up, I've heard "yes" and "no" lol. Got any clue? Thanks

 

[JDEstill]

In response to the original question, here's how I see it:

The fueling as figured out by the FAST is a 2 step procedure -

1. Figure out how much air is coming in, and then

2. Figure out how much fuel should be added to match that air flow

The VE table (among other things) is part of item 1, used to figure out the air flow coming in.

The a/f ratio table (again, among other things) is part of item 2, figuring out how much fuel is required to match that air flow.

If you want to add fuel, you can trick the computer by changing the VE table and making it think there is more or less air coming in, which will then result in more or less fuel.

It is "better", and more direct, to just change the a/f ratio table instead. If the VE table is all dialed in, leave it alone, let the computer know what the correct air flow is, and change the a/f ratio desired to get the amount of fuel you want.

John

 

[Bobo]

Thanks for that explanation John, but I got a question. Excuse me if I'm a lil ignorant

This is what I thought was going on. Say if I have the target a/f @ 11.2, then the VE #'s have to be adjusted to get as close to 0% correction factor for that 11.2 ratio. Now if the weather gets cooler, the VE #'s need to go up a little and the computer will show a + correction factor if I don't take the VE #'s up, right? I haven't tried changing the target a/f, but I assumed when I did the correction factor would go either up or down depending on which way I sent the target a/f. So I guess me question is, how do you ever know when the VE #'s are right? I guess it may not matter a whole lot, maybe as long as the ecu doesn't have to use a very high correction factor, but I'm just a lil curious. Thanks for all the responses guys!

 

[TurboTR]

re:

No. In theory at least you don't try and compensate for a change in air density (the colder air) by changing the volume flow factor There is air temperature correction already; if it's all working correctly then you should not have to change the VE table in response to outside air temp changes. In an ideal sense anyway...

FWIW the research I've seen (Heywood?) suggests that fuel octane would have a minimal effect on VE. Similar for spark timing. Air density changes will have a small effect.

Plus, you paid for a system that you can command target a/f ratios directly. Sounds like that is what you are looking to do- change the a/f ratio. So why not use it? ;-)

JMO.

TurboTR

 

[Bobo]

Yeah I definitely plan on changing the target a/f for either race or street. I have only raced the car a little so far but if I remember correct, the O2 correction was adding fuel when the weather got cooler. I had the O2 correction at almost 0% after playing with VE #'s. Maybe the O2 correction wasn't much, maybe only like 5-7%, but that's what I remember. My memory isn't the best though haha. I need more play time to get more of a grasp of all this

 

[bobc455]

The VE table has nothing to do with octane.

It sounds like your VE numbers are very close. Leave them alone now.

If you're running too lean, fix your target A/F ratio. And if you're reducing octane, you might want to back off the timing.

I have three different programs that I use- one for 87 octane, one for 89 octane, and one for 93 octane. The only differences are timing at WOT, target A/F at WOT, and a few other boxes that needed the timing retarded (heavy load / low RPM). The VE tables are identical for all three.

Remeber that VE tells the ECU how much air is going into the motor under various conditions- the airflow won't change because of octane levels.

-Bob Cunningham
bobc@gnttype.org

 

[Craig Smith]

I agree with Bob - once the VE table is set I would leave it alone. If correction values are small while running closed loop, you are in good shape. Things like octane, timing, etc. may have a small impact on what the "correct" VE numbers will be, but probably not worth recreating a fuel map for. I would use the target a/f table to richen or lean the motor.

 

[Bobo]

Cool, thanks for the info guys

 

[J. Lubrant]

Originally posted by Bobo
Thanks Joe, that's kinda what I had heard at first. Harry tuned my SP, I was gonna call him up and pick his brain a lil about this. I'm running 11.2 a/f, most guys have said that is very conservative, I'm not sure if it needs to go lower for the street and 93 octane.

One more thing, do you work @ PT? I am considerin upgrading from my T76 to a PT-88 4 bolt. I am not sure it'll bolt right up, I've heard "yes" and "no" lol. Got any clue? Thanks

I believe most of the fellows echo'ed what I had said in my earlier post about leaving the VE alone.

I feel, if the VE table has been tuned at all loads of operation, you basically have in effect the "Finger Print" of your engines efficiency(VE).
No further adjustment of VE table should be necessary.

As suggested just lower timing to compensate for the lower octane. I'm am also sure you will not be able to run the boost levels that were obtainable with Race gas, so you will have to lower the boost.
A knock detection device and/or egt gauge should help in tuning etheir with pump 93 or race gas for that matter.

The PT-88 4-bolt will bolt up, but it will actual be higher and further foward, which means you will have some fabricating to do with your inlet and exhaust system on the outlet side.
The PT 76 and PT 88 are totally two different animals, I mean you can't make a PT 76 into a PT 88. The 88 uses a totally different bearing housing, tubine housing etc. etc.
The PT 88 will definitley support about 200hp more than the PT76.

Give Harry a call, I'm sure he will fill you in on your options.

I am no longer working at PTE on a daily basis, although I am still doing some consulting work for them.
I have re-joined a previous employer of 14 yrs, as their Quality Assurance Mgr, engaged in Power Plant Construction.