Dyno results question

[WBR33]

548ci BBC, Crane, 244/256 .632/.632 HYD roller 114LSA. 10-71 BDS, dart 345 heads, 8lbs boost, pump gas.

Went to a dyno shop to dyno and tune.

Started out with cam installed per cam card at 109ICL. Engine made 882HP at 6300 once fuel and ign tuned in. We then advanced the cam 4 deg per the cloyes hex adjust. Still made 882HP at 6300, and torque went up about 4ft lbs at peak. Then, we retarded the cam, 4 degrees from the original 109ICL, and power dropped to 851HP at 6300, and torque fell off by about 30-35ft lbs at peak.

Normally, I wouldn't question the results, but when we refired the engine after the cam retard, dyno operator noticed the dyno had blew a gasket at the pump, and water was leaking out of the back of the dyno. He said it wasn't a big issue, and proceeded to do the pull. He had to stop the pull, as he said he "ran out of servo". Turned some dial on the dyno to compensate, and redid the pull. Would that have any effect on the readings?

The goal here was to pick up a little power at peak rpm, definitely didn't expect it to drop 30+HP. Also seems odd, that advancing the cam 4 deg from the original ICL, made EXACTLY the same HP at 6300, and torque was nearly identical. With the cam retarded 4* on the pull with the water leak, it also shows the torque peak to be sooner, than it was with the cam advanced 4*!??

[Zmechanic]

If they dyno was still able to maintain the RPM/sec rate that was programmed, then no, it shouldn't matter. In this situation, they dyno essentially has control of the engine, and because of that, all the power is being delivered into the brake. The power gets absorbed into the water and generates torque on the brake which is read out by a load cell (strain gauge). IF the RPM climbed faster than the programmed rate that means the dyno wasn't totally in control, and some of the power went into the motor accelerating itself instead of the brake, which would show a loss. (Note that the motor always has to use some power to accelerate itself but if you run the RPM rate slow enough it essentially looks steady state i.e. no acceleration)

I would highly suspect (or at least hope) that any modern dyno would have a way of knowing or alerting the operator if it was losing control.

[WBR33]

It was a superflow Sf902 if that matters.

[Adger Smith]

That has nothing to do with the actual TQ reading you are getting from the Dyno. Dyno's read TQ and the HP number is not a direct read out. That is the servo that controls the rate that the pull is made and the load the water pump puts on the brake. It is common for them to leak. I have a few spares and have had to change them before on our SF 901. It is also very common for someone that doesn't understand a dyno blame the dyno for lost power. What you experienced with the cam movement is just what I thought should have happened, esp with a hyd roller. The engine just told you where it liked the cam and you were not listening. It is an old wives tale (or BS if you prefer) that retarding a cam makes more peak power. The sooner peak (lower RPM on the retard) is because it fell off in power. I would have tossed a longer ratio rocker on it or tightened the valve lash(if it was a solid) to pick peak up. With the blower deal you are going to have to go to a lot bigger cam to get the peak RPM up. Blowers and NOS always make the BMEP at lower RPM than the same set up N/A. I think the biggest mistake made with dyno testing/tuning is to go to the session with preconceived ideas or expectations. You should read the results of the instrumentation and let that information tell you what is going on & what the engine is happy with.

[bigjoe1]

That pretty well sums it up. I have the exact same feelings too.


\JOE SHERMAN RACING

[bigfoot584]

Bingo X3, well said Adger

[WBR33]

That has nothing to do with the actual TQ reading you are getting from the Dyno. Dyno's read TQ and the HP number is not a direct read out. That is the servo that controls the rate that the pull is made and the load the water pump puts on the brake. It is common for them to leak. I have a few spares and have had to change them before on our SF 901. It is also very common for someone that doesn't understand a dyno blame the dyno for lost power. What you experienced with the cam movement is just what I thought should have happened, esp with a hyd roller. The engine just told you where it liked the cam and you were not listening. It is an old wives tale (or BS if you prefer) that retarding a cam makes more peak power. The sooner peak (lower RPM on the retard) is because it fell off in power. I would have tossed a longer ratio rocker on it or tightened the valve lash(if it was a solid) to pick peak up. With the blower deal you are going to have to go to a lot bigger cam to get the peak RPM up. Blowers and NOS always make the BMEP at lower RPM than the same set up N/A. I think the biggest mistake made with dyno testing/tuning is to go to the session with preconceived ideas or expectations. You should read the results of the instrumentation and let that information tell you what is going on & what the engine is happy with.

Thank you for answering. The only reason I had any doubts, was on a couple things. First pull on the other engine we dyno'ed, also a hyd roller roots supercharged combo, 468ci, which in a previous form, had made 800hp on pump gas, anyhow, the first pull, the engine made 650hp. The dyno operator thought everything looked ok, and thought that was a decent pull. I was like "ya, it all looks great, but the power is in the gutter". I insisted something had to be wrong, and I went in the dyno cell looking over the engine. he likes to call his dyno the "heartbreaker", and assumed that because he had recently had a blown 468 that made 675ish hp, that this 468, was where it should be. i asked him if he checked to see if his throttle cable was opening the carbs all the way, and sure enough, it was not close to opening the carbs all the way. Fixed that issue, re-pulled the engine, 761HP with 6lbs of boost. Did some tuning, changed pulleys, and did another pull. This pull, the engine got way lean at the top end, AFR's went to high 13's-14 range. Cause? He forgot to plug in the supply fuel pump on the dyno. Fixed that, engine made 817hp with 8psi peak. Also, he was doing sweep pulls, starting at 2,800RPM, lugging the engines from 2800-6500. While he says that is better data, I wasn't comfortable pulling an engine like that out of the box, without an unknown state of tune. The engine would never accelerate that slow in real world. The dyno pull was nearly 30 seconds long.

Sorry, but I paid for dyno time, and If I didn't "question" anything, I'd be leaving there with a sheet that said my engine was making 650hp. As far as changing to 1.8 rockers, I did not want to do that. I paid careful attention spec'ing the springs out to run reasonably close to stack, as these are endurance engines. I'm also not sure how I feel about a cam designed for a 1.7 ratio, and slapping on 1.8s in an endurance engine that sees 6000-6500RPM for minutes at a time.

I admit, I did not expect retarding the cam 4 degrees, to cause the peak tq to come in sooner, than when it was advanced, nor did I expect the power to drop off sooner. Then again, I have never done a back to back comparison like that, hence the question. Sounds like that's to be expected. I know nothing about dyno's, and was just curious if the fact the dyno was spraying water out of the back of the pump would have had any effect on the readings. Doesn't seem like it, so the cam will go back in advanced.

[WBR33]

Update. Buddy whos engine this was, pulled the timing cover access panel off to set cam back to straight up, and found the cam bolts loose! The cam went to full retard.

We had adjusted it on the dyno to go to 4 deg retard. We re set the igntion timing, and made the pull. After the pull, rechecked ign timing, just to see if a mistake was made. I put the light on it, and it was 5 deg retarded from where we wanted it. I gave them chit about knowing how to use a timing light joking around. Anyhow, my guess is they timed it right, but the cam actually moved during the dyno pull, hence the ign timing retard.

I never used a hex a just, i need to put a degree wheel on it to see just how far it moved. Basically the cam bolts are what kept it from moving any further.

[F-BIRD'88]

I had a very similar thing happen.. Cam bolts came loose soon after install.
Like you I got lucky and caught it just in time.
Noticwd the strange noise of the cam gear rattling aroubd and the bots rubbing on the cover...
Tore it down and found a very loose cam gear and cam bolts just about to fall out...

Cam lobe got nicked bynext lifter...

Trusted a friend to stick the cam in..

Lucky all it cost me was a new cam and lifters set.

Should have done it myself... Another lesson learned..


You probabily will need to repeat your tests to get a difinative answer..

You got very lucky.

[Chris1]

548ci BBC, Crane, 244/256 .632/.632 HYD roller 114LSA. 10-71 BDS, dart 345 heads, 8lbs boost, pump gas.

Went to a dyno shop to dyno and tune.

Started out with cam installed per cam card at 109ICL. Engine made 882HP at 6300 once fuel and ign tuned in. We then advanced the cam 4 deg per the cloyes hex adjust. Still made 882HP at 6300, and torque went up about 4ft lbs at peak. Then, we retarded the cam, 4 degrees from the original 109ICL, and power dropped to 851HP at 6300, and torque fell off by about 30-35ft lbs at peak.

Normally, I wouldn't question the results, but when we refired the engine after the cam retard, dyno operator noticed the dyno had blew a gasket at the pump, and water was leaking out of the back of the dyno. He said it wasn't a big issue, and proceeded to do the pull. He had to stop the pull, as he said he "ran out of servo". Turned some dial on the dyno to compensate, and redid the pull. Would that have any effect on the readings?

The goal here was to pick up a little power at peak rpm, definitely didn't expect it to drop 30+HP. Also seems odd, that advancing the cam 4 deg from the original ICL, made EXACTLY the same HP at 6300, and torque was nearly identical. With the cam retarded 4* on the pull with the water leak, it also shows the torque peak to be sooner, than it was with the cam advanced 4*!??

The SF902 is adjustable for low power all the way up to 1500hp. To do that they have a capacity valve on the back of the housing that is operator adjustable to adjust flow for the engine being tested. If for example you're going to dyno a 600CC snowmobile engine it's going to take less water than a blown BBC. With the capacity valve set the servo valve then takes over and manages the load on the engine through the pull. With the water leak I'd guess his capacity valve needed a tweak to compensate to get the servo back into a range of control. Bottom line... as other stated if in the end the accelleration was managed through the pull then the servo did its job. The torque isn't measured by the servo or capacity valve, it's measured by the strain gauge. Hope this helps!

[WBR33]

548ci BBC, Crane, 244/256 .632/.632 HYD roller 114LSA. 10-71 BDS, dart 345 heads, 8lbs boost, pump gas.

Went to a dyno shop to dyno and tune.

Started out with cam installed per cam card at 109ICL. Engine made 882HP at 6300 once fuel and ign tuned in. We then advanced the cam 4 deg per the cloyes hex adjust. Still made 882HP at 6300, and torque went up about 4ft lbs at peak. Then, we retarded the cam, 4 degrees from the original 109ICL, and power dropped to 851HP at 6300, and torque fell off by about 30-35ft lbs at peak.

Normally, I wouldn't question the results, but when we refired the engine after the cam retard, dyno operator noticed the dyno had blew a gasket at the pump, and water was leaking out of the back of the dyno. He said it wasn't a big issue, and proceeded to do the pull. He had to stop the pull, as he said he "ran out of servo". Turned some dial on the dyno to compensate, and redid the pull. Would that have any effect on the readings?

The goal here was to pick up a little power at peak rpm, definitely didn't expect it to drop 30+HP. Also seems odd, that advancing the cam 4 deg from the original ICL, made EXACTLY the same HP at 6300, and torque was nearly identical. With the cam retarded 4* on the pull with the water leak, it also shows the torque peak to be sooner, than it was with the cam advanced 4*!??

The SF902 is adjustable for low power all the way up to 1500hp. To do that they have a capacity valve on the back of the housing that is operator adjustable to adjust flow for the engine being tested. If for example you're going to dyno a 600CC snowmobile engine it's going to take less water than a blown BBC. With the capacity valve set the servo valve then takes over and manages the load on the engine through the pull. With the water leak I'd guess his capacity valve needed a tweak to compensate to get the servo back into a range of control. Bottom line... as other stated if in the end the accelleration was managed through the pull then the servo did its job. The torque isn't measured by the servo or capacity valve, it's measured by the strain gauge. Hope this helps!

Thanks for that info. Makes sense.

Sounds like the info from that pull, was prob right on. Now, how far that cam went retarded with the bolts loose, is the new question. Buddy said the bolts were so loose he could wobble the cam gear. Scary. Good thing we didnt do any more pulls after that

[Adger Smith]

ouch, How lucky!!! I quit using the hex adjust after I had a couple fail in operation on mild bracket engines and lake race boat engines. Of course, the question is Why were the bolts loose? I would call the dyno parts breaker instead of heart breaker. I've seen more problems with making pulls below peak Tq than making pulls above peak power. Hard pulls below BMEP can cause detonation(esp with a bad tune) and we all know the harmonics of detonation can knock things loose and break parts. I always assume the tune up is junk with anything going on the dyno. I Do a real quick pull to find peak Tq and then work AF ratio and timing around Peak Tq on fast acceleration pulls. You will not hurt the customers parts that way. Highest cylinder pressure is usually at or around peak Tq. If the engine is tuned for that, right AF ratio and correct timing, it shouldn't hurt it's self. I might make one pull starting 1,000 below peak Tq just to see how the curve comes up. If I were a customer I would be pissed if a dyno operators methods hurt good parts. I feel one of the reasons for going to the dyno is to do tuning you can't do in the car and do it safely where parts are not abused. I have used my methods about the RPM and load in making the EMC rules. We don't want to program in failures at EMC. I know there is always several ways to accomplish a given goal, that is just my way. I'm sorry if I have stepped on any dyno guys toes.

[statsystems]

ouch, How lucky!!! I quit using the hex adjust after I had a couple fail in operation on mild bracket engines and lake race boat engines. Of course, the question is Why were the bolts loose? I would call the dyno parts breaker instead of heart breaker. I've seen more problems with making pulls below peak Tq than making pulls above peak power. Hard pulls below BMEP can cause detonation(esp with a bad tune) and we all know the harmonics of detonation can knock things loose and break parts. I always assume the tune up is junk with anything going on the dyno. I Do a real quick pull to find peak Tq and then work AF ratio and timing around Peak Tq on fast acceleration pulls. You will not hurt the customers parts that way. Highest cylinder pressure is usually at or around peak Tq. If the engine is tuned for that, right AF ratio and correct timing, it shouldn't hurt it's self. I might make one pull starting 1,000 below peak Tq just to see how the curve comes up. If I were a customer I would be pissed if a dyno operators methods hurt good parts. I feel one of the reasons for going to the dyno is to do tuning you can't do in the car and do it safely where parts are not abused. I have used my methods about the RPM and load in making the EMC rules. We don't want to program in failures at EMC. I know there is always several ways to accomplish a given goal, that is just my way. I'm sorry if I have stepped on any dyno guys toes.

I have NEVER understood pulling the engine below the actual needed engine speed. Like you said, it kills parts and tells you nothing. If the engine has a shift speed of 6000 you know it will drop to 3500 or so, probably less. So start pulling at 4000. No sense or need to kill everything to try and find power in a part of the curve that doesn't matter.

[user-23911]

I have NEVER understood pulling the engine below the actual needed engine speed. Like you said, it kills parts and tells you nothing. If the engine has a shift speed of 6000 you know it will drop to 3500 or so, probably less. So start pulling at 4000. No sense or need to kill everything to try and find power in a part of the curve that doesn't matter.

But, but , but........isn't the purpose of dyno tuning to tune?
If it's not tuned right it breaks.
If it breaks it's because you didn't do your job properly?

Road engines pull from 1000rpm so should be tuned from 1000RPM.
Swapping parts around for comparison show losses as well as gains.
Losses from upgraded parts usually show up in the lower RPMs.

[WBR33]

https://youtu.be/OeJ_7-hpzq0

Heres the second pull on the 468