Manometer Test results

Hi Bruce,

 

Wow, good on ya for doing this, and so quickly too!  Here are my suggestions, but I may not be correct in my assumptions.

 

You have measured the pressure difference between the positive pressures at the rear outside fender and the cockpit, at varying speeds.  While that is interesting, I would think you would really want to know pressure differences at rear outside fender and the wheel well, which would be the opposite end of the vent, and the area where you may mount an inlet vent.  You would accomplish the measurement of this pressure differential by connecting a hose from the right side of the manometer to the wheel well area, and leaving the hose connected to the left side of the gauge as it is.

 

Regarding the stand off positions of the tube inlets (3" & 6"), I would think that would only be relevant if air would enter the vent at those distances.  Will you have a vent that sticks out 3" or 6"?  My research indicates that a NACA (forerunner of NASA) duct would better serve as an inlet.  NACA ducts are inset, not even flush, never mind not standing proud, and function to eliminate or lessen the boundary layer of air pressure that runs along the body.  Current Porsche fender vents are a type of inset NACA duct.  You also see NACA ducts on stock car windows for cabin air and fenders for brake venting.  I hope you take these suggestions in the constructive spirit in which they are offered.  My hats off to you for doing this!! 

Thanks Jim.  What prompted me to do the 3" and 6' stand off was the idea that a wide body car does stick out there and i was curious about how much pressure was out there. My thinking tells me that at the juncture of the side of the body where it would curve out to the fender flare may even create more positive pressure such as at the hood/windshield juncture on conventional cars. At the least, I have a little more info what's going on down there.

Your right about the pressure differential measurement between the rear outside fender area and the wheel well area. Easy to rig up with another hose to the other side of the instrument.

Another thing i forgot to mention was that when following a small camping trailer approximately 50 or less feet behind, The pressure went to nearly 0 . It didn't return until i was near a 100 feet behind. I didn't expect that.   Again Thanks.....Bruce

I feel like if I Google 'manometer' the top ten results would be threads from this site. 😛

Bruce,

Did you ever get around to measuring pressure under the car in front of the firewall over the transaxle?  it would also be interesting to know temperature in that same area. I'm wondering what kind of temps are coming into the engine fan intake thru the 6" screened hole.  Thanks, Frank

Frank.....i forgot that you asked me to check the pressure that area in front of the firewall where your oil cooler is. I'll try to do it this next week. On the temperature stuff I can't do it yet. The thermocouples I have are not compatible with the gauges I have so that will have to wait. Probably putting a sender right in the middle of that 6" hole in your firewall and another up in or near the engine grill may give some interesting information......We'll see....Enjoyed spending time with you when you were out here last month  .....Bruce

 

TRP ....You made me laugh ! I guess a lot of people didn't know what a manometer is. I know I didn't for many years but have learned the value and the simplicity of their existence and use since. The one really nice thing about them is that they never have to be calibrated like a gauge. In fact most pressure/vacuum gauges are calibrated to a manometer! They are really simple instruments but very accurate. I guess the term "Manometer" is somewhat intriguing  and could be used to humorously describe a measuring device/ instrument for something else. This is and can be pretty funny if some people way more witty than me get hold of it and go with it. ...I enjoyed your comment......Bruce

"This is and can be pretty funny if some people way more witty than me get hold of it and go with it."

 

Oh I am sure folks on this site can oblige. 

Bruce, I'd also like to know what the air pressure reading would be on the lower and upper inside of the wheel well.

I'm wondering how air would flow, at say 70 mph, from a hole on in inside of the fender (right beside the air cleaner).  I'm sure the air pressure would be low on the inside of the engine compartment at 70 mph, but I'm wondering what the difference would be in the wheel well.

I suspect the air pressure underneath the car is negative, but I curious as to what effect the spinning rear wheel would have.

 

Also, I'd like to thank you for doing all this testing. Much appreciated.

This is all very good information and I'm glad that Bruce is spending the time doing this for the benefit of all of us.  It does make me wonder however.

Some of us with basically the same types of cars, configured in basically the same way don't have overheating problems.  In my case, I have a regular body Vintage with a 2110, with an oil cooler mounted in the standard Vintage location behind the firewall and an external oil filter mounted in the left rear wheel well. It has the standard 6" hole in the firewall and it is to the right of where the oil cooler is mounted.  It has a louvered deck lid and a typical grill, but I have three large badges mounted over it and they take up a considerable amount of space.  I also have a deep sump.  It has an A1 Sidewinder header with no heat exchangers.

My gauge does not have numbers so I don't know what the actual oil temperature is but it rarely gets past the center even on Fresno's 100+ degree days cruising in town or on the freeway.

This very same car originally had a standard Vintage 1915 motor that ran so hot that my gauge would go all the way to the little white square within about 20 minutes of driving.  It was basically undriveable until I swapped out that motor with this one.

I guess what I am saying is that there seems to be adequate airflow to cool our engines and the problem is more likely with how the engine is setup.

In the case of my original 1915 engine, it had a thermostat and flapper in the shroud that was frozen. It was removed and that engine ran fine afterwards.

Again.  I applaude Bruce for all the work he is putting into this, but it just doesn't seem to me like that is where the overheating problems are.

Good observation Troy.....I guess I never mentioned that my car runs great and isn't heating up. It's a VS with a 2110 built by me. The original VS temp gauge suggests that the engine is running cool and my guess is that it's fine but it's still a guess. I have a Dakota oil temp gauge reading the oil temp in the sump. This gets to 250+ but it's the oil that just circulated thru the engine and i expect it to be hot. I just never realized how hot. I'm currently making a new oil pressure regulator plug with 1/8 pipe threads in it so I can put my Dakota sender in there an measure what the VS gauge is reading. I expect it to read OK since it's the first place the cooled and filtered oil hits on it's return to the engine. BUT right now, I don't know. I'll let all of you know what that is when I know. I have sealed off the VS hole in my firewall and the area in the rear where you can see the tail lights from inside the engine compartment. The engine compartment can now only get air thru the grill on the engine lid. In this arrangement my engine does not heat up but I do record a 1 inch vacuum in the engine compartment over 3000 rpm and at fwy speeds. This goes away when I take the cover off the "VS firewall hole". So I know now that the "hole" provides a fix for the vacuum in the engine compartment at fwy speeds. Since I didn't have a heating issue (at least up to fwy speeds) i can't say it helps eliminate a heating problem. My guess is that if I go faster I may have a heating problem.

So you can see that I like to have both feet on the ground before making any changes. Doing these little tests in a logical order helps a lot in this process plus I really like doing it. It's the discovery that keeps me interested. I don't mind sharing the data I get with all of you either and I appreciate  the guidance some of you have offered.

A long time ago in a land far far away Ha Ha, I used to participate in the testing of various cars for potential use as black and white patrol cars for Los Angeles County Sheriff Dept. From the data collected i wrote the specifications to go out to bid for new patrol cars. This was an annual process and I always looked forward to it. We used a lot of test gear and strip-chart recorders to collect the data in those days.The car manufacturers always had some of there engineers present to see what we were doing and to offer assistance/guidance as well.

Needless to say I had a lot of fun and interesting days. Now I'm having fun with these Speedsters. As they say...information is power........Bruce

I am really interested in your test to see what temperature the VS temp gauge is actually reading in degrees. On a 20 mile run mine creeps up to about center of the sweep or maybe slightly past on a 90+ day. I'm assuming that the center is OK but I have been told by Pat Downs that oil temps shouldn't go past 200 degrees so we will see what your Dakota gauge reads. Thanks again, Bruce.

I was tested by a man o' meter once.............    IT BROKE!!   lollol

 

tebs

Bruce,

 

Pat has built lots of engines, including a 2110 for me years ago, so I know he is a knowledgeable guy.  However, most VW a/c engine builders will tell you that 220 is the sweet spot, since any water in the oil won't even burn off until the temp gets to 212.   

And remember, if you have an aluminum engine case your oil temperature reading is going to be higher.

 

Tebs, I think you're confusing the Man O' Meter with the Stud Finder! 

I knew you guys wouldn't let us down.

The software couldn't handle Teby's hardware!!

 Troy:  When you swapped your 1915 for the currently installed (and cooler) 2,110, did you also swap the temp sensor over to the 2,110 as well?  If not, you would be comparing apples to oranges.  The different sensors alone could be responsible for the difference in indicated temps.

Uhhhh?  Robert?  How would you know that?  Did you look under his hood?

Good point Gordon.  No I did not, but trust me, you couldn't touch the dip stick on that engine and after removing the flapper and thermostat the engine ran at normal temps with the original sensor.