To have true zero vacuum and verify it, you have to reference the atmospheric pressure outside of the intake manifold and compare it to the pressure inside the manifold. IE the pressure in the intake would need to equal pressure outside of the intake to have zero vacuum.

To read the pressure inside the intake only and say vacuum inside the motor is XYZ and not compare it to the atmospheric conditions on that day is not accurate. Atmospheric pressure changes with humidity, temp, and elevation. Atmospheric pressure is not always 101kPA. For example, at 500' above sea level, using standard day weather conditions, the pressure would be roughly 99.5kPa.

An easy way to test the theory is to remove the sensor from the intake and read the atmospheric pressure that day, then make a run and compare to the two. If the reading is lower then you have vacuum, if its the same then zero vacuum.

101 kPa is the atmospheric pressure on a standard day at sea level.
A standard day at sea level is:
Pressure: 101.325 kPa (14.7 psi)
Temperature: 15°C (59°F)
Density: 1.225 kg/m³


FWIW dyno'd a couple of my motors with air cleaners and without on 5" toilets and 4 hole accufab. No measurable difference. Even brought the scoop and scoop pan from the dragster, zero change.

quote:

Originally posted by Triple Nickel:
To have true zero vacuum and verify it, you have to reference the atmospheric pressure outside of the intake manifold and compare it to the pressure inside the manifold. IE the pressure in the intake would need to equal pressure outside of the intake to have zero vacuum.

To read the pressure inside the intake only and say vacuum inside the motor is XYZ and not compare it to the atmospheric conditions on that day is not accurate. Atmospheric pressure changes with humidity, temp, and elevation. Atmospheric pressure is not always 101kPA. For example, at 500' above sea level, using standard day weather conditions, the pressure would be roughly 99.5kPa.

An easy way to test the theory is to remove the sensor from the intake and read the atmospheric pressure that day, then make a run and compare to the two. If the reading is lower then you have vacuum, if its the same then zero vacuum.

101 kPa is the atmospheric pressure on a standard day at sea level.
A standard day at sea level is:
Pressure: 101.325 kPa (14.7 psi)
Temperature: 15°C (59°F)
Density: 1.225 kg/m³

I agree with what you wrote about the difference between atmosphere, manifold air pressure and verifying it.

Here’s my N/A EFI 388 using a 1150 cfm 4 hole air horn at a recent race. The difference between Baro and MAP is 5.7 kPa. The 4” (1435cfm) toilet I use was better (less than difference) by about 1 kPa. Moving the fuel map afr recently has improved the difference in the smaller 4 hole air horn. With a few more small changes I’m hoping both 1435 and 1150 will be equal in kPa at wot. This should equate to same ET.

With an N/A engine sucking air at wot, zero vacuum is not attainable imho.

i can see i am proven wrong in my statement but that difference is minute in my opinion

I could probably get away with one but I run dual 4.1" toilets on my 588.

quote:

Originally posted by rusty:
i can see i am proven wrong in my statement but that difference is minute in my opinion

I thought there may be a little but knew it would not be much.

While orignal post was not about most of thread but doea involve it in some way. Good for DRR.

I agree it is better to error on side of big rather than too small. I disagree about not possible to be too big. Kind of like a port. Yea if little big for engone you can get by w/o penalty. If you go too big by good amoun t velocity suffers. In a inductiuon situation as sytem wityh good velocity coming threw air valve or flys and continuing to valve had to better than dead air having to be restarted moving towards valve. Another point of view why grab more air causing a drag, than enigne can use?

New injestor is being designed aroung 30 to 35 sq in with bell mouth entry. Less drag more than enough air and hopefully higher velocity air entering plenum. Working on getting material for injector and new design intake. Even if merical happens and donme before getting ass back into seat,not changing till get good baseline of what I have does. Will ot 100% know effect of intake and/or injector. Will know if combo better or worst. Hell will not be first project to hit trash or be recycled into another project. Figure about 200 bucks and lot of hours. that is intake,injector and bellmouth front for injector. Hell if not working on car watching NEws max and getting pissed off at democrats more.

This message has been edited. Last edited by: wideopen231,

mark where is your map sensor located

quote:

mark where is your map sensor located

thanks

Markemark, did you read baro from your weather station or disconnect the sensor line and read from the actual manifold air pressure sensor? Calibration is everything in these smaller increments. An easy test may be to turn ignition on, open blades fully and read MAP ouput with engine off. That would be the true baseline for this conversation.

quote:

Originally posted by CURTIS REED:

quote:

Originally posted by wideopen231:
Was hoping RPM performance had a vacuum sensor so I could check to see if any vacuum at WOT and maybe get one tha would sense a slight positive to let me know is any ram effect. Looks like no such item exist.

They do

If so not listed on site.

Wow you’re right they aren’t on there anymore. I have one on my system though so maybe it’s a shortage problem or possibly they overlooked putting it on the site.

Hell the older I get more stuff I overlook when its right infront of me. Was hoping you would show me where I had done just that.

They don't have the old style anymore with the push on hose. Call Randy, they have a sensor, it reads -30 inches to +15 psi

quote:

did you read baro from your weather station or disconnect the sensor line and read from the actual manifold air pressure sensor? Calibration is everything in these smaller increments. An easy test may be to turn ignition on, open blades fully and read MAP ouput with engine off. That would be the true baseline for this conversation.

The first pic I what the MAP and Baro looked like engine not running, obviously not the same. There is a calibration adjustment in the software for the MAP.

First I took my weather station and used the absolute BP to determine the Baro in kPa. Then I thought just to be sure my hand held weather station is correct, went to the airfield and compared to their reading. Mine read 0.25 lower. At home the BP adjusted for reading low it was 28.92 . That converted is 97.93 kPa Baro. The Baro is reading correct in this MAP sensor.

Second pic, then I moved the MAP calibration adjustment until it read 97-98 kPa in 0.10 increments. The final adjustment was +2.6 kPa to bring the Map to 97.9 kPa. It only displays in full numbers, and moving to 2.65 takes it to 98 kPa.

I stand corrected when I previously wrote 5.7 kPa was the difference between Baro and MAP. It is actually 3.1 kPa difference. My apologies!

did a megasquirt on mine.

logged the MAP. 100kpa KOEO, and 99 KPA at the finish line. Forward facing scoop on an old ford door car. Half tempted to try to put a stock appearing flat hood back on it.

I KNOW there's some MPH to be found, but I'm not in a position to do aero changes, fuel changes, then go to a wind tunnel to test, repeat etc. It's a bracket car. It is what it is.

With MFI, I think it's pretty much impossible to get too big of a throttle body. I run Ron's dual terminators, each is rated at 2100 cfm. I ran twin 1295 demons when it was on gas, and it seemed like they were too small.....just the switch to the ron's system was worth significant performance....