Testing on a dyno

[Bud Kaiser]

The shop owner said to test at rated 1600 rpm = 540 on pto and got 54hp but when we loaded it down to 1400rpm was about 59hp .Where do you yall take the hp reading?

 

[Dblair]

I'm sending the Nebraska test to answer your questions

 

[mEl]

(quoted from post at 19:59:11 04/30/10) The shop owner said to test at rated 1600 rpm = 540 on pto and got 54hp but when we loaded it down to 1400rpm was about 59hp .Where do you yall take the hp reading?

It depends on the dyno, there are a lot of M&W hydraulic brake dynos out there and these are only accurate at the calibrated check points--540---1000 RPM marks on the tach. HP readings taken at other points are meaningless and used only for misguided bragging rights. If correct HP readings at other than calibrated points are to be got with this type dyno there is a "nomograph" which calculates true HP from the pressure and shaft rpms. This is why I am very sceptical of HP figures posted as there are few that understand these types of dynos. If those inflated power readings were correct don't you think the manufacturers would have advertised that as the true HP for sales purposes. These high readings at lower than rated rpms would be less than rated if "corrected" by the nomograph. There are other dynos that do correct via computer so it does depend on the system used. BTW all tractors are not rated at 540 so for those a conversion is necessary to get HP at proper manufacturers pto speed. mEl

 

[The Dukester]

Most dynos I've seen and pulled my tractors on, both PTO and belt pulley, have had a book with 'em that told you what speed the dyno should be run to get the horsepower figure comperable to what the manufacturer's rating was arrived at. Otherwise you run it out to get the highest torque at the highest speed the tractor engine can hold just like they do at a prony brake set-up. For example my "little bit souped up" John Deere G (still stock stroke) will put out about 10-12% more horsepower at 10% overspeed which is about 600-620 rpm on the PTO versus 540 rated speed, or 1050-1100 rpm at the pulley versus 975 rated speed. The engine actually overspeeds about 10% in either case at no load wide open throttle speed. Either way the tractor puts out "a little more" than it was factory rated..ah, quite a little more actually. But nothing like some of the "radically modified" jobs I've seen.

 

[Anonymous-0]

Test rpm from 540, and pull it down to about 400 rpm on the pto dyno.

Open er up and pull it down,,,,,,, it should rev up to about 650 pto rpm,,, then pull it down to 540,,,, adjust the timing, then the carb, then recheck both after improvements are seen. Then take it from 540 to 450,, then to 400 pto rpm.

Tune in these pto rpm ranges, you will have better low end lugging power. If your getting beat by inches,, then it should lug ya out a couple more,,,, if your getting beat by feet,,,, then you better rethink the class. JMHO.

Governor springs,, Yep, I got em. 15 bucks. ChadS

 

[james rumph]

Well spoken but the dynos are not calibrated at 540 and 1000.

The presure gauge is calibrated to read oil presure from the pump. I have a M&W P-400 that i went threw all the crap of having it calibrated and certified by the U.S goverment dept of weights and scales.

We have a formula to figure out H.P at any rpm.

Who's to say if the numbers are accurate but it gives you something to work with.

I do have to say that we have had very repeatable results and good results based on the info we recieved from it .

The H.P numbers are really only referance to see improvement or damage ..

Just my thoughts.

 

[buickanddeere]

Sad to say your dyno operator failed high school math and physics class. Then again so did you.

HP= torque X RPM / 5252.

At 1400rpm the engine is making 51.6HP.

 

[james rumph]

The most important formula is

Torque= 5252 x horsepower/ rpm

This formula gives you the torqe #s that are so important.

Chad is so right about tuning down around 400 pto rpm on the dyno.

Anyone can make big numbers at 540 but down at 400-540 is ware you really tug.

This was great advice Chad past on one night that changed everything.

 

[mEl]

In deference to Mr. Rumph, I should have said designated instead of calibrated check points. B&D,s math proves what I stated, once the designated check points are left the HP on that gage means nothing. As Jim said it is just a point of reference and good for tuming only. Our PB400 is very good in repeatability also. The above discussion is why I take HP readings posted on here with a grain of salt. Tune for maximum meter reading at any rpm you'd like , just don't post it as any kinda accurate HP reading if you are useing a Hydraulic brake dyno. More sophisticated dynos have the computerized capability of reading hp at any given rpm, just look at the computer screen and there it is. This technology is beyond most of us "hackers". mEl

 

[A.P.]

The HP number on the gae (calibrated for 540 rpm) needs to be multiplied by 74% for the actual horsepower number. Without this correction, all anyone is looking at is the torque rise of the engine as it is lugged down. Chad's suggested tuning regimen is still valid, but you are tuning for higher torque values; i.e. the ability of the engine to lug.

 

[Anonymous-0]

Cam lobe wear, broken or extremly worn cam key and cam gear (in SMTA-450) wrong distributor advance, equals alot of power loss.

If it still has the live pump, 50-57 hp on a pto dyno is pretty common on a 281ci 450.

If you did not "R&R" the cam gear from the cam,, and just dropped the old cam back in,,, there is no telling what kind of disaster is awaiting when it comes apart,, if its worn out.



Ever see a valve lash adjustment gain 25 psi of cyl pressure???

ChadS

 

[Anonymous-0]

We are never gaining torque in a dyno tune calibration session.

Were merely "enhancing" whats given and peaking it to a certain rpm range by making repairs and recalibrations as the engine breaks in.

Its amazing what can be done to enhance another 20ftlbs of torque in certain situations. ChadS