WOT Vacuum Issue??

[rio95]

I've been noticing that according to my logs I have vacuum at WOT so I made a few third gear pulls today and thought I'd get some advice. I logged barometric pressure and it was 99 KPA. At WOT my MAP reads 99kpa and then tapers down to around 95kpa as RPMs increase. Is this a problem or is bernoullis affecting the MAP reading?

My car is a 2007 Z06 with heads, cam, fast intake, stock throttle body, and Halltech 107R. I have the MAP installed in the front port and drilled the recommended hole size for the MAP sensor.

MAF tuning.cfg
WOT.hpl

[10_SS]

I've been noticing that according to my logs I have vacuum at WOT so I made a few third gear pulls today and thought I'd get some advice. I logged barometric pressure and it was 99 KPA. At WOT my MAP reads 99kpa and then tapers down to around 95kpa as RPMs increase. Is this a problem or is bernoullis affecting the MAP reading?

My car is a 2007 Z06 with heads, cam, fast intake, stock throttle body, and Halltech 107R. I have the MAP installed in the front port and drilled the recommended hole size for the MAP sensor.

MAF tuning.cfg
WOT.hpl

~95kpa from 99kpa is pretty normal... however that just means there is a bit of a restriction.. Throttle Body, MAF, Air cleaner, ducting, etc. Can try to improve those items if they are stock but may not gain much on an already high flowing motor.

[Higgs Boson]

95/99 = 96%


For contemporary naturally-aspirated, two-valve-per-cylinder, pushrod-engine technology, a VE over 95% is excellent, and 100% is achievable, but quite difficult. Only the best of the best can reach 110%, and that is by means of extremely specialized development of the complex system comprised of the intake passages, combustion chambers, exhaust passages and valve system components. The practical limit for normally-aspirated engines, typically DOHC layout with four or more valves per cylinder, is about 115%, which can only be achieved under the most highly-developed conditions, with precise intake and exhaust passage tuning.
Generally, the RPM at peak VE coincides with the RPM at the torque peak. And generally, automotive engines rarely exceed 90% VE. There is a variety of good reasons for that performance, including the design requirements for automotive engines (good low-end torque, good throttle response, high mileage, low emissions, low noise, low production costs, restrictive form factors, etc.), as well as the economically-feasible tolerances for components in high-volume production.

http://www.epi-eng.com/piston_engine...efficiency.htm

[rio95]

95/99 = 96%


For contemporary naturally-aspirated, two-valve-per-cylinder, pushrod-engine technology, a VE over 95% is excellent, and 100% is achievable, but quite difficult. Only the best of the best can reach 110%, and that is by means of extremely specialized development of the complex system comprised of the intake passages, combustion chambers, exhaust passages and valve system components. The practical limit for normally-aspirated engines, typically DOHC layout with four or more valves per cylinder, is about 115%, which can only be achieved under the most highly-developed conditions, with precise intake and exhaust passage tuning.
Generally, the RPM at peak VE coincides with the RPM at the torque peak. And generally, automotive engines rarely exceed 90% VE. There is a variety of good reasons for that performance, including the design requirements for automotive engines (good low-end torque, good throttle response, high mileage, low emissions, low noise, low production costs, restrictive form factors, etc.), as well as the economically-feasible tolerances for components in high-volume production.

http://www.epi-eng.com/piston_engine...efficiency.htm

That was a pretty good read. Reminds me of engineering school.

I feel a little embarrassed for not understanding this better, but doesn't vacuum in the intake not directly correlate with volumetric efficiency? I guess I'm not understanding the relationship if there is one. My VE table actually has VE values over 100% and aligns very well with my torque curve. If you look at the log above, shouldn't I see a hump at peak torque by your explanation? There is no bump. It is a very linear decline. Explained another way, before I added headers and fast intake, my MAP reading was actually closer to atmospheric at WOT, yet I made less power with the same displacement, hence less efficient.

[1sick_eg]

No need to make it overly complicated. If you're seeing less than atmospheric, your pump(engine) is out pumping it's intake. Whether that is due to your intake design, filter, maf, or intake manifold, you will have to figure out. 95-99kpa is pretty good though. I'm dropping to as low as 94kpa at 4300, yet still make around 550whp n/a. Clearly my restriction is my stock ls3 intake manifold. My heads flow 390/255 @ .700, and I'm running a solid roller setup to match. My only issue is finding a decent intake now that I'm not having to cut my cowl on a relatively new car, or one that doesn't cost 4k.

[Higgs Boson]

That was a pretty good read. Reminds me of engineering school.

I feel a little embarrassed for not understanding this better, but doesn't vacuum in the intake not directly correlate with volumetric efficiency? I guess I'm not understanding the relationship if there is one. My VE table actually has VE values over 100% and aligns very well with my torque curve. If you look at the log above, shouldn't I see a hump at peak torque by your explanation? There is no bump. It is a very linear decline. Explained another way, before I added headers and fast intake, my MAP reading was actually closer to atmospheric at WOT, yet I made less power with the same displacement, hence less efficient.

Ve and maf table also has any variation in injector/fuel system characterization baked in. ideally, the fuel system is properly described in it's tables leaving only airflow values to the airflow tables but that doesn't happen in reality. the overall AF error gets corrected in airflow tables.