Crankcase Pressure Levels

In a serious blown alcohol deal (screw or roots) has anyone ever monitored their net crankcase pressure values during a pass? Or even better, has anyone ever monitored their blowby gas volume rates?

I would be really interested to hear more, either online of offline, if you don't mind.

I'm curious about your values and flow rates, but I'm just as curious to know whether the typical twin 1.25" breathing tubes might be causing a net restriction or not ??

I kind of gather that the current rules were written to suit typical chassis tube diameters. That's not a terribly scientific approach, but it has obviously worked.

Got some ideas, but need some real world data to bounce them against.

Thanks in advance !.........

 

Case in point is this one ........

I'm currently designing the ventilation circuits for my new/own block design.

I have allowed for about 6.28 ^2 of external crankcase ventilation flow area inside the block, connecting the sump to the outside world. My interior airflow is not contra to any oil drain back flows. I'm just handling vapors and oil/fuel entanglement.

Two 1.25" tubes on the other hand (typical of modern day breathers) is only about 2.45 ^2 of breathing area. Obviously there is a disparity here that I could take advantage of. I doubt IHRA/NHRA would balk at bigger diameter breathing tubes if so desired.

I am wondering whether the normal twin 1.25's cause any appreciable back pressure (crankcase pressure) or not? Or are they just fine & dandy as long as there is not a catastrophic/explosive event (think nitro down the road)?

It would be neat to draw a vacuum, or a near vacuum, but the baddest vac pump that I am aware of is only 100 cfm at max rated speed. I kind of doubt it would be up to the job. At 8 pounds each I would not want to run two or more.

Thoughts ?........

I'm thinking (and please chime in here to correct me) that it might be best to just simply freely vent the crankcase and get the tip of the puke tank into a low vacuum aero zone ? I'm mainly curious about the effect of the twin 1.25" current conventional breathers as a restriction.

Open to ideas.

Thanks.

 

If your short block is correct... you do not need more than the 1 1/4 tubes. I would see from zero to 1 lb @ 6500 stage and zero right after the foot swap and then a bit negative at the top of low to minus 1 1/2 to minus 2 at the finish line with our T/AD. A big legal volume puke tank takes a bit of time to equalize pressure; I had the exhaust vent in the air stream so that it would help pull a vacuum @ 270.
Jeff Johnsen

 

Hey Jeff just want to make sure I am reading you correct. When you say minus 1 1/2 to minus 2 at the finish line, do you mean psi or inches of mercury? Where are you measuring pressure? Any chance you could send me a typical trace from one of your runs? Thanks.

 

I was referring to PSI when I said minus 1 1/2 to 2 at the finish line. I used a pressure transducer at the front of the lifter valley to get clean data on pressure without another line on a valve cover and both covers are not the same either.
We last ran through the 2013 season and I have the log book here but not the laptop. I am looking through the run sheets for the data but have not seen it noted yet in my book but I did look at it every run as one of my checks on the health of the engine. Hugh, the car owner has the computers and is close to me so I can get at the Race Pac files when I see him next. The traces are interesting but what I took away from your posting was that you are looking for something big here. In my opinion, the big deal is to not have a leaky short block; sealed up puts all the push on the piston dome although there is no doubt a bit of vacuum in the base helps the rings to seal and particularly at high rpm, which the alcohol cars have to run. Jeff Johnsen

 

Thanks Jeff !.......

 

I picked up the computer and only had time to pull up a couple of files so I did Q1, we were #1 qualifier @ Norwalk 2013 and 2 weeks later Q1 and we were #1 qualifier @ Seattle 2013. I will show you the RPM and Pan pressur @ stage, top of low, top of 2nd and finish line. I have blanked out the other data. The pan pressures were higher than I told you on these particular runs, luck of the draw but they are very low anyway. I have some where a cyl was hurt and it immediately spikes pan pressure which is what I used it for. The Norwalk run was 5.349/269.08; we went 5.341/269.94 the next pass. The Seattle run was 5.263//268.81 with the #3 plug wire off @4.5 sec. I hope I can attach the screen pictures I took. Jeff Johnsen

 

Tried to upload screen pictures but it says the file is too big for even one.....so I guess data is the best I can do. Will????
Norwalk Q1 stage: 6236 rpm / pan pressure 0.74 psi
top of low gear: 10627 rpm / pan pressure 0.37 psi
top of 2nd gear: 10556 rpm / pan pressure 0.37 psi
top of 3rd gear: 10252 rpm / pan pressure 0.55 psi
Seattle Q1 stage: 6775 rpm / pan pressure 0.44 psi
top of low gear: 10879 rpm / pan pressure 0.15 psi
top of 2nd gear: 10813 rpm / pan pressure 0.13 psi
top of 3rd gear: 10293 rpm / pan pressure 0.33 psi
Jeff Johnsen

 

Thanks !.......

 

what does the pressure go to if you get a cyl at 90%leak down

 

Well, you should not be running it with leakage like that but that said, a static leakage test at say 100 psi is not the same as with running pressure. It will not leak 90 * of the running pressure but you will see elevated pan pressure and some performance loss.
I could only give you some numbers for a blowup run as a reference:
Pomona Finals 2013 Q2, hurt #7 piston @ top of 2nd and kicked the rod right @ the finish line........
Stage: 7450 rpm Pan Pressure 0.35 psi
Top of low gear 9968 rpm Pan Pressure -0.33 psi (that is a vacuum)
Top of 2nd gear 10655 rpm Pan Pressure 0.28 psi (just zooming up)
Rpm laid over in high @ 9850 ish and Pan Pressure maxed the transducer @ 14.98 psi indicated from 5.08 sec till it boomed @ the finish line.
The low first gear shift RPM was because it shook @ 1.3 sec and laid the rpm flat for 1/2 second and he shifted.
***Note that the early part of this run is what I was talking about as typical of what I would see; a bit of pressure at stage (0.35 psi) and this run was down to zero @ .2 sec and then slowly building a vacuum on the run till it started to eat itself. This run showed a max of -0.44 psi @ 1.288 seconds in low gear @ 9508 RPM just before it shook.
Jeff Johnsen

 

Jeffj, curious as to what you are running on the scavenge section of pump. Is is a roots type pump or gear? Some of the pumps now have a roots type scavenge section(S) that supposedly work very well. I understand some will pull a vacuum in the pan.

 

Well I used to run TA/FC with a Pluger dry sump pump which has the pan scavenge section and the pressure section. I did not monitor pan pressure with that system.
The setup I was describing was on a TA/D, Psi blower/Alcohol. We used Faria wet sump pumps as there was adequate oil pan room without the extra dry sump apparatus. It is very hard to make weight without adding any extra parts. The vacuum achieved was from air flow across the puke tank exhaust in the air stream. There was no vacuum pump on the car.
Jeff Johnsen

 

I've been working with this for 15 years now, and ill tell you that with two legal burn down tubes, the best blown alcohol engine builder in the country has always had 2 to 2.5 psi at the finish line. Thats a PSI Screw Blower BAE engine that is always at the head of the pack. Cars that have average pressure is about 3 to 4 psi. Anything more and there are issues with the total package. An oil pan wil start showing signs at about 6 to 7 psi.

 

We have bugged Scott for many years for bigger and badder alcohol vacuum pumps.

 

What were you hoping to gain if it came to pass?........

 

They are not allowed in TAD-TAF

 

Yes. I wonder why?......

 

Let's try this again. Is it not allowed because there is something to be gained, or is it not allowed because it induces too many problems to deal with? (Sidenote: Wouldn't it be nice if rules makers left little footnotes for what they were thinking at the time !........).

 

I was looking at the discussion on this thread and was interested by it's direction and it served to remind me that I had not been able to load shots of racepack screens, only data.
So I took pictures of the screens for a Q1 run @ Seattle, 2013; 5.263 #1 qualifier and one that hurt a piston @Vegas 2013 showing vacuum till it zoomed up due to the piston.
I included shots for Stage, top of Low, Second and High Gear/ Finish Line RPM, Drive shaft and Pan Pressure for both runs.
I hope that looking at the data will be interesting for you all. I am personally very interested in air flow generally.
I emailed the info to Will yesterday asking him to post it all to this thread as I have not been able to do so. Jeff Johnsen