Dyno brake slippage?

General engine tech -- Drag Racing to Circle Track

Moderator: Team

Post Reply
rebelrouser
Guru
Guru
Posts: 1938
Joined: Tue Sep 15, 2015 2:25 pm
Location:

Dyno brake slippage?

Post by rebelrouser »

Just need some opinions. I have an old land and sea water brake dyno 14 inch. The company told me it has approximately a 800HP capacity. They did not give me a max torque capacity. 90% of the engine I do are in the 350hp to 600hp range. The dyno gets calibrated and seems pretty accurate. I did a big 580 inch mopar wedge yesterday, Indy tunnel ram with two dominators, and the guy knew up front that I was not going to pull it hard, just enough to check the air fuel and seat the rings, look for leaks etc. He had a no prep race this weekend and could not get dyno time anywhere but me.
My question is the combination was a copy of another engine and they had dyno numbers on it. I pulled it to 6,250 rpm and it made 865hp 5750rpm and 837 ft lbs @ 5000 rpm. Most I ever tried with my dyno, outlet water temps were around 170 degrees. My question is it had a 114 center cam installed at 110, 282//296 @.050 .927 lift this cam should pull way past 6,000rpm the numbers from my dyno agreed almost exactly with the numbers from the copied engine until 5,500 rpm, then mine fell off. I am thinking my brake just could not hold it, and it slipped since I was over capacity. The copied engine made a little over 1,000 HP. It is supposed to have 14.5 compression, set of Indy CNC heads flowing around 400cfm. So the 1,000hp is quite possible. The only thing O2's and plugs looked great, but the exhaust temps were a little low I thought, all very close but barely 1,200 degrees.
billet
Pro
Pro
Posts: 256
Joined: Thu Oct 25, 2007 5:25 pm
Location:

Re: Dyno brake slippage?

Post by billet »

Where you check the outlet temp? a fair ways from the brake where water in the brake may have turned to steam? I would think you would see an large RPM per second increase if that was the case or the brake was maxed out.

Also is it possible the strain gauge won't read that high? I know the bigger 1600HP brake is a dual rotor brake but don't know if it has a different strain gauge that reads higher or it's the same one on the smaller brake you have
rebelrouser
Guru
Guru
Posts: 1938
Joined: Tue Sep 15, 2015 2:25 pm
Location:

Re: Dyno brake slippage?

Post by rebelrouser »

I have about 6 inches of hose coming out of the brake and the water sprays on a temp sensor in the surge tank. And you may be right on how much torque the sensor can handle.
PRH
Guru
Guru
Posts: 1501
Joined: Fri Sep 08, 2017 4:16 pm
Location: S. Burlington, Vt.

Re: Dyno brake slippage?

Post by PRH »

I would think if the sensor was maxed out at 837ft/lbs, that it would have just flatlined that number until the tq output dropped below that point.

But 865hp@5750 is only 790ft/lbs.

If the engine isn’t “running away” from the absorber, then the output and the load should match each other........ no?
Somewhat handy with a die grinder.
rebelrouser
Guru
Guru
Posts: 1938
Joined: Tue Sep 15, 2015 2:25 pm
Location:

Re: Dyno brake slippage?

Post by rebelrouser »

The engine was defiantly accelerating faster than I could hold it. Photo of the pull on the software. Second is what the software calls troubleshooting graph, raw data before it is processed. You can see the hump when I added load to the brake, and I added more but I don't see any hump that it affected the torque reading.
You do not have the required permissions to view the files attached to this post.
PRH
Guru
Guru
Posts: 1501
Joined: Fri Sep 08, 2017 4:16 pm
Location: S. Burlington, Vt.

Re: Dyno brake slippage?

Post by PRH »

It does appear that the tq curve takes a definite downward turn at 5250.
If the motor started running thru the absorber, especially if it was “cavitating” internally, then that’s what I’d expect the curve to do........ or something similar anyway.
Somewhat handy with a die grinder.
PRH
Guru
Guru
Posts: 1501
Joined: Fri Sep 08, 2017 4:16 pm
Location: S. Burlington, Vt.

Re: Dyno brake slippage?

Post by PRH »

I built a fairly similar 572 a few years ago.
14:1, 380cfm Indy heads, Indy TR w-2 x 750’s, .800” cam, 2-2 1/8 x 4 dyno headers......
Made:
811tq@5400/911hp@6300, still 887hp@7100
Somewhat handy with a die grinder.
ClassAct
Guru
Guru
Posts: 1024
Joined: Wed Dec 05, 2018 11:55 pm
Location:

Re: Dyno brake slippage?

Post by ClassAct »

How big are your water pumps? I’m just curious.
quickd100
Pro
Pro
Posts: 398
Joined: Sun Jul 18, 2004 7:34 am
Location: Nielsville, Mn.

Re: Dyno brake slippage?

Post by quickd100 »

Me thinks you need a 13" dual rotor like mine.
[img]http://img.photobucket.com/albums/v514/quickd100/9ff3c690.jpg[/img]
rebelrouser
Guru
Guru
Posts: 1938
Joined: Tue Sep 15, 2015 2:25 pm
Location:

Re: Dyno brake slippage?

Post by rebelrouser »

ClassAct wrote: Fri Jul 29, 2022 4:53 pm How big are your water pumps? I’m just curious.
I am not sure exactly how big the pump is, got it in the pile of parts when I got the dyno. But I have a pressure gauge on the manual control, and it is set to 50 psi, seldom see it drop more than a couple PSI on a pull. I have no way to measure the flow, but in just running the line into a tank, it is like a fire hose.

And as an update to the thread, guy took the car to a race and he called me this morning and said your dyno was not wrong, as it seemed not to pull much more after 6,000 rpm. And the worst news was 4th pass it spit out a rod. I only dynoed the engine for the guy, but now it looks like now he wants me to figure out why it blowed up.
You do not have the required permissions to view the files attached to this post.
rebelrouser
Guru
Guru
Posts: 1938
Joined: Tue Sep 15, 2015 2:25 pm
Location:

Re: Dyno brake slippage?

Post by rebelrouser »

quickd100 wrote: Sun Jul 31, 2022 12:46 pm Me thinks you need a 13" dual rotor like mine.
yes, I got old junk, but at my age don't see spending a ton to update the unit. Only reason I have a dyno is that it was a retirement present to myself. The guy I bought my components from upgraded to a dual rotor. Land and Sea makes a newer brake with helical cut rotor fins, that is good to 1000hp but of course nothing is really compatible with my parts, so it was a big chunk to convert. Plus I have a spare brake and torque arm with the parts I bought.
User avatar
FC-Pilot
HotPass
HotPass
Posts: 913
Joined: Tue Mar 17, 2009 2:23 pm
Location: Springtown, TX
Contact:

Re: Dyno brake slippage?

Post by FC-Pilot »

With the land and sea water brakes, and I would imagine others as well, if they don’t hold it would be at the lower end of the Rpm band as the brake has less holding power at lower RPM’s than at higher. I have only had issues with ours below 4000 RPM’s with big cubic inch engines that made torque very low. That was also without a restrictor and a pre valve bypass open. With a naturally aspirated engine I think at that RPM I think it should have worked just fine, and if it slipped it would have been around peak torque, not peak HP. When mine did it, it was like a torque converter letting it slip to a certain RPM and it held there until the expected sweep rpm matched the holding RPM, then it continued on up the rest of the sweep till the max programmed sweep RPM.

Paul
"It's a fine line between clever and stupid." David St. Hubbins
Post Reply