Is it bad to have VE values over 100%?

nickturner22066 · Post by **nickturner22066** » Fri Jan 12, 2007 10:06 am

I have a 2.0L 16v 4cylinder VW engine with BIG cams and 10.8 compression. Running 24lb injectors, 50psi fuel pressure, my VE at 100kpa and 7000+ was upwards of 115%. I was still able to hit AFR values in the 12's and 13's at those RPMs though. I was just wondering if running that much VE% can cause problems.

I just ordered ITB's, and brand new 30lb injectors to go with them, so it won't be a problem in the future. I just wanted to know if you guys think it could have been causing a loss in performance. Thanks,

-Nick

Dr.Hess · Post by **Dr.Hess** » Fri Jan 12, 2007 10:24 am

It isn't the VE of over 100% that can cause a problem. That just indicates that (providing the required fuel amount is correct) the motor is more than unitary in air pump efficiency. 4AGE 20v's do that, among other high strung motors. Now, if your injector duty cycle starts to approach 100%, then you have a problem.

nickturner22066 · Post by **nickturner22066** » Fri Jan 12, 2007 11:48 am

I see. The VE is also a function of your base Req_fuel. In other words, maybe I just have my set Req_fuel a little low. But it doesn't matter, so long as I'm hitting my AFR targets and my duty cycle is within good ranges.

Dr.Hess · Post by **Dr.Hess** » Fri Jan 12, 2007 12:55 pm

The VE is not a function of your Required Fuel, but what values you put in the buckets will be effected by your Req Fuel. You could change the Required Fuel value to a larger number and tune your VE table to lower numbers and it would all come out about the same. That's my understanding of it all.

VE stands for Volumetric Efficiency, and on a 2L motor, that would be 2L of air being pumped at 100%, or 2.2L of air moving at 110%. As long as your duty cycles are OK and your AFRs are where you are happy, then you don't need to worry about it, and may not need to change your injectors from 24 to 30 lb, if you aren't changing anything else. And I doubt that going to ITBs will change the efficiency of your motor enough to need 25% bigger injectors. Bigger injectors also can mean giving up some idle quality if you can't get the pulse width down low enough.

wes kiser · Post by **wes kiser** » Sat Jan 20, 2007 12:54 pm

Keep in mind with MS, that you also must add extra enrichment via the VE tables to achieve lambda values of less than 1. This means even if you engine is only 90% volumetrically efficient, that in order to run 12.5:1 AFR at high loads, you will likely have to enter something on the order of 105% if the VE tables. My 250 kPa VE entries are as high as 124% in order to get my AFR to the 11.5:1 I desire under high boost.

Polux RSV · Post by **Polux RSV** » Sat Jan 20, 2007 3:01 pm

Having high VE numbers should permit to better fine tune the AFR. A change of 1 on 115 makes less differences than 1 on 80, for example.

Angelo

chadr · Post by **chadr** » Tue Jan 23, 2007 11:55 am

Polux RSV wrote:Having high VE numbers should permit to better fine tune the AFR. A change of 1 on 115 makes less differences than 1 on 80, for example.

Angelo

yea, I changed my reqfuel number so that my highest ve number was close to 200. This still gives plenty of room for fine tuning since 255 is the max value that can be entered.