does anyone know what effect on tuning the cylinder size has? if i change it, will it affect the a/f, ltrims, etc? I just got my 422 in, and although the car seems to run very well now, it still has the stock cylinder size numbers.

 

I have been asking about this too. There are two or three threads on HPtuners.com that you may want to look at. There is also a calculator attached to one of the threads if you need to recalculate CV.

 

Anyone else? I cannot find any info.

 

Did you read this thread?




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Posts: 59
Re: Stroker motor ?
« Reply #1 on: Oct 20th, 2004, 10:22pm » Quote | Modify

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If your cylinder volume has changed (which it has since you stroked it, or even bored oversize) then you should definately accuratly remeasure the actual volume of the new cylinder in litres and enter this mumber in the cylinder volume location. I measure the volume with liquid, cylinder head on, rings sealed with light grease, fill through spark plug hole until full to bottom of threads (this only works with engine on build stand so you can lay it on its side).

here is some info Chris posted elsewhere on forums

you need to understand what VE is guys. VE is just the amount (volume) of air you are getting into each cylinder versus the amount you could theoretically get in there under ideal conditions. Hence the name *volumetric* efficiency.

So you get:

VE = CylAir Actual / CylAir Ideal

if you have a MAF and you trust its measurement then to work out the amount of air going into each cylinder on average for a V8 engine is just:

CylAir Actual = MAF(gm/sec) *15 / RPM

now to work out CylAir Ideal you need to go look at the gas equations PV = nRT and plug in the atmospheric (barometric) pressure for P, the cylinder volume for V, the Air Temperature (in Kelvin) for T and the values of R etc...

you get something like:

CylAir Ideal = (BARO * (Displ/ * 28.96) / (8.3145 * (IAT + 273))

then divide the two values to get the VE or:

VE = (MAF(gm/sec) *15 / RPM) / ((BARO * (Displ/ * 28.96) / (8.3145 * (IAT + 273)))

which reduces to your equation once you adjust for units etc.

If you put MAP in instead of BARO you will get the theoretical airmass at the current throttle position (ie. you are removing the effects of intake tract loss). True VE is compared against BARO.

 

I understand how to change it, but I'm wondering why I should, if the engine seems to run fine, etc.

IE Does it have an effect on power?

 

Using http://www.c5frc.com/calculators/Com...Calculator.htm, I found the cylinder size to be 0.86526, using default deck (its a new 5.3 block) and default gasket thickness.

I will compute the VE using formula above.

Again I ask, what are advantages to doing this if the car appears to run ok? IE, will there be any power gains?

 

If you adjust just the Cyl Size and don't touch touch the VE tables, how does changing that affect the car?

 

This is the response I got from HPtuners when I asked about this,

Re: Cyl Volume
« Reply #9 on: Sep 26th, 2004, 7:32am » Quote | Modify

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it is used in the cranking airflow calcs and in the misfire code to determine the cylinder VE% (the top axis in the misfire tables).

I have been trying for weeks to get someone form HPtuners to chime in on the cause and effect of Cyl volume value. I have had no luck getting a response other then above. If you find the info please pass it along...

 

I was told by the tuner tonight that it has zero effect on anything.

 

If that is true, then why is it even there for the changing........

Keith

 

There are a few things that are like that, example rev limiter by gear (for 6 speed cars).

 

Just Curious who the tuner was in Il?

 

This was done at ARE. I have autotap'd the engine, and the LTRIMS are dead on, slightly negative. I have yet to put it on the wideband, however. It runs very well.

 

I wouldn't mess with it. Just out of curiosity, does your VE table have any values over 100% in it?

 

You have a theoretical Limit of air you can force into a cylinder w/out boost (at WOT you should ideally be at atmospheric pressure... no vacuum no boost)

w/HPT should have no negative affect... and if they say it is used for cranking air and misifire calcs... I'd believe them

You can tune your car w/out changing these values, but changing it really has no affect ... makes it easier to tune VE in HPT from my experience

 

I know, but that's not what I'm getting at. A 422 with 100% ve flows the same amount as a 346 at 122% ve, so instead of changing cylinder size they could have changed ve instead. But if cylinder size isn't used with ve in the speed density calcs, then it doesn't matter and ignore everything i just said.