DRAG RACERS - How do you calibrate your leakdown guage?

Seems I've read that a Hilborn nozzles should "leak" it's rating - meaning a 18A nozzle ought to leak 18%. When I calibrate my leakdown guage to a 27A nozzle I had laying around and then check it against a 7A nozzle it says the 7A nozzle is leaking 10%.

Normally I just use the guage as a reference - not caring what the "real" value is, but in the case of leaking down my Barrel Valve on the digger - I was wanting to have a set standard to reference each time. I suppose I can still just use my "standard" and go from there, but I was curious what the RIGHT way to do this was.

I heard of the 80-80 rule, but again this is at the opposite end of the spectrum and I wondered if there was a way to calibrate it closer to some known standard closer to where I am actually operating at - 20% or so.


TIA!!

 

I have only set the barrel valve (metering block) with a leak down tester, not the nozzle. Or are you saying that you want to change your barrel valve setting when you change nozzles?

 

Leaking down a nozzle from small to big or vice versa is not linear from a flow standpoint. In otherwords a 14 will not flow twice what a 7 flows.

We always have our nozzles flowed, and than calculate total nozzle area (total oriface size) as a baseline. None of this has anything to do with leaking down your barrel valve, or the accuracy of your gauge.

 

joemarsicano, Yes - I use a leakdown guage - the question is HOW do you calibrate your leakdown tester. I have tried several and they all read different. So what I was planning on doing was to "calibrate" my tester prior to each use so that I can ensure X% change is really X%.

DaveyJonez, I agree. The barrel valve "leaks" ; a Nozzle "leaks" - I'm trying to establish consistency. I "heard" Hilborn nozzles "leak" what they are stamped - I found for myself that isn't true - but I suspect there may be some point at which the 2 curves intersect (meaning coincidently a certain nozzle may actually "leak" the same as it is stamped - that may be a pipe dream, but was what I was really wondering.

So may I ask you guys - What do you do to CALIBRATE your leakdown guages? I followed the same procedure on 2 Sun guages and when in use - they both read differently - hence the origional question.

Thanks for your thoughts.

 

Make sure that you have a presure regulator coming off of your compressor. This will keep the incoming air at a constant rate (or somewhat close).

 

Hopefully this answers your question....

Leakdown testers (gauges) are also just burden tube gauges and the only way they are calibrated is with another certified calibration gauge.
All of certification has to be done in a controlled environment also with constant temp, barometric pressure, etc., etc.

You will hardly ever find any two gauges that read the same psi within 5-10% as the cheap ones (made in China, auto store, mail order, etc.) are not claibrated after manufacturing and the more expensive ones (aircraft type) are claibrated and are quite expensive but will still have <1% margin of error.

I am a drag racer also and set my barrel valve with a leak down tester. You have to use the return pill that is your base line tuneup as changing the "pill" will also change the leakdown %. Each motor and fuel injection system wants something a little different so no two are quite the same....

My engine (sbc) likes the barrel valve set at an intial 20-23% leakdown and the idle speed is very consistent over the minor tune-up changes I make during a race. I race in the Midwest where ADR is 90 at best and corrected al***ude is >4,000 ft during the summer. This changes slightly from spring into summer as the weather quality (ADR, Corr Alt, etc.) deteriorates.

Hope this helps......

 

HR Cant answer Youre question for sure but ,maybe I can help some.
When I called Hilborn I asked what pressure they started with to leak My barrell valve
they said around 80 lbs. Around ?? Yea He said 80-90lbs. Incoming pressure changed the leak reading so I just chose 80 as a standard. As You mentioned not all gauges read the same. So if You buy one new calibrated gauge say 120 lb that could be the gauge You use for Youre standard. Use this gauge as cose to Youre leakdown tester as possible. Now You can compare the incoming pressure going to Youre leakdown gauge and also at Youre compressor. Good chance the gauge on the compressor will be low because of the hose length. Then adjust both ends as needed. Remove the calibrated gauge and keep it safe and secure.
I have done alot of air testing with calibrated gauges for the Navy and a couple things I learned is gauges are fragile. Dont spike them with air. Gradually bring the pressure up and down . This alone will let Your gauge live a long accurate life.
You could remove the leak side gauge and compare the pressure against the calibrated gauge. Hope this helps a little, Good luck ---FEDER

 

OK I have done some digging around and while I have read (again) that a Hilborn nozzle &#8220;leaks&#8221; it&#8217;s rating (meaning a #16 nozzle will leak 16 %) HOWEVER - THAT is definitely INCORRECT!!!!! &#8211; and I believe a misquote of what they REALLY do flow which is (according to my research) is that a nozzle FLOWS it rating in GPH so a #16 Hilborn nozzle will flow .16 GPH AT 30 PSI. THAT explanation makes a heck of a lot more sense &#8211; especially when you look are the nozzle areas.

I still want to use a nozzle as a &#8220;standard&#8221; as it makes sense to me to be able to calibrate my leakdown tester each time I use it &#8211; but I will have to do some more research to see what actually makes sense &#8211; value wise.


Thanks to everyone who took the time to post their thoughts!! Much appreciated.

 

That had better be incorrect. I've got four 104A injectors on my four port. 104 % leakdown?

 

I hope you find something consistent to calibrate to. I would question the accuracy of the Hilborn nozzels though. I have flowed my set, and they are all close, but not exactly the same. In fact I stamped them with numbers so I can put them back in the same hole each time, for some consistency.

Check this site out for some more info on leakdown testers.
www.kenlowe.com.au
Specifically this page:
http://www.kenlowe.com.au/LFS-leak check info.htm

Eric

 

I also run "flow" checked nozzles from Hilborn and do the same as you.
At best, they are within 1-3% flow volumes.
What ever works, works just do it same every time.

 

Kerry, That's EASY - you're SUPERCHARGED so cleary there is a FACTOR for that!! ha ha ha. Kerry, seriously - I think that "80 at 80" rule is what is being misconstrued as a Hilborn nozzle flows what they are stamped - clearly - there's alot of grey area here.

1bad67, I am fully aware of the accuracy of the Hilborn nozzles - my plan was to use the same one each time to recalibrate my tester before each use. The question was - whicn nozzle and what value. I reallly like the Ken Lowe link - that was the second time I saw the "80 at 80" rule being mentioned. The only thing I don't like about that cal point is that it is QUITE far from where I am at. A supercharged motor uses ALOT more B/V leakage than a aspirated injected motor - so for the vast majority the 80 at 80 rule is pretty close to where they are gonna USE the guage. I'm in the 18-28% range so I am quite far from that. I think I may have to just wing it as I suspect the 80 at 80 cal point may not repeat very well at the opposite end of the spectrum. I'd check tomorrow but I think we're gonna head to the racetrack instead.

 

Is your meter single or dual gauge?

 

I do mechanical calibration for a living. Have each pressure gage calibrated on a certified dead weight tester. Look for a NIST certified calibration company in your area. Do not over pressure the gages, it may damage them. PM me if you want me to do them for you.

 

I would switch to Enderle nozzles. Easier to set and control fuel flow

 

The way a leak down tester works, there are two "air leaks" in series.

If both "leaks" are exactly the same size (same exact air flow area) then the second pressure gauge will ALWAYS read half the pressure of the first gauge, or 50% leak down.

Now the standard for the up stream calibrated leak orifice is usually 1mm or 40 thou diameter. So if you can drill a 1mm hole, or find a 1mm/40thou carby jet, you can build your own leak down tester with two identical air pressure gauges.

Now the figure you get, depends on how much your rings and valves leak. But it also depends on the type of engine. A chainsaw motor being very small, should not leak much air volume even if the rings were completely rooted. So 95% might be pretty bad on a tiny toy motor.

But a m***ive big bore engine might leak enough air volume to really worry you, but the engine might actually be in pretty pristine condition.

So take leak down figures with a bit of caution, and understand what it is really telling you.

A fresh built motor should read very good because the rings and valve seats are still full of ***embly oil.
Start it up and run it, it will then leak worse.
But when run in it should come back up a bit.
Find out what is normal for your sized engine in good condition, and jut be happy if all cylinders read about the same, and what you are used to seeing for YOUR engine.

All this nonsense about 98+% being good, and 88% requiring a complete rebuilds are ********. It depends on the size of your engine, the volume of air it should normally and reasonably be expected to leak, and the diameter of your calibrated orifice in your leak down tester.

In fact you can make a leak own tester read any value you want just by changing the size of the calibrated leak orifice.

It is rather like a cranking compression gauge reading. In that if 150Psi is normal for your low compression supercharged engine, 220+ Psi might also be normal for a high compression alcohol engine. If you get a reading of 148 Psi, that could mean your engine is fine, or it could mean trouble, depending on what is normal for your particular engine.

 

Thanks for all the replys!!

Let me back up for just a second. My initial reason for asking this was to be able to "accurately" leak down my BARREL VALVE in my Mechinical Fuel Injector. Is this a NECESSARY thing?/ Well not really, but I am curious - moreso I wanted to make sure whenever I check it that I am actually checking it IDENTICALLY to the way I last checked it - so I wanted to CALIBRATE my Leakdown checker - reason I asked for input was that I noticed that 2 different SUN leakdown checkers I had read differently even though I calibrated them as instructed by Sun. I also did some research on the method the supercharged guys calibrate their guages (the 80 at 80 rule of thumb) but I shied away from that method since it was at the opposite end of the spectrum of where I am leakign down at - (18-24 or so %). After some checking and fooling around it seems that my "standard" (a #27 Hilborn nozzle) leaks 22% - so I wrote this down on my checker and will "calibrate" the checker to 22% with this same nozzle each time I check the barrel valve. As for teh motor leakdown- I never considered the guage accuracy as an important consideration - my motors are consistent - then I deem them OK.

So there it is in a nutshell. I don't know if my "conversion" is correct, but is it what I will use and so long as I am consistent - it will be fine. thanks for all the input!!!