Are all dynos the same?
 

Just had my engines run on the dyno. I was wondering if all dynos would come back with the same results? Is it a function of the dyno or the person operating the dyno? How many hp or ft lbs of torque might it be off? I am new at comprehending the dyno and trying to understand if these are comparable numbers to what Mercury publishes for their engines? Thanks.

Re: Are all dynos the same?
 

In a word, NO.

All dyno's are supposed to be referenced to an SAE standard in theory. In actuality a dyno test is only repeatable with the same dyno and operator if you want back to back comparisons.

Two of the better dyno shops here in Houston dynoed a small block motor on the same day in the morning for just this reason and came up with a 20hp difference at 400hp. Same brand of dyno also. They eventually were able to get them to read fairly close with some input from the manufacturer.

Edit: this comparison was done with uncorrected data

Re: Are all dynos the same?
 

In theory they should be, but they are kind of bathroom scales. Each one will be calibrated different than each other, and some are just higher quality than others. Also add the variable of the dyno operator and how he makes his correction factors. When I have a engine run on a dyno after a rebuild I do it for several reasons. First, for cam break in, oil pressure checks, and to see if everything is tight, i.e. no leaks. It is better to get all major issues taken care of before it gets in the boat. For a tuning aid to at least get it close for initial boat trials. And as a comparison to the last rebuild. You can get a good idea of the success of the rebuild, but the real test is when it is in the boat.

Re: Are all dynos the same?
 

Thanks for the replies. I had no idea there was that kind of disparity. I was speaking with someone about my numbers and he said that the dyno/and or operator may not be accurate. Now I know what he was talking about. Just how much can a dyno be off?

Re: Are all dynos the same?
 

A good dyno with the right sae correction factor for actual conditions (altitude,air density,air temperature etc) should be accurate within a few percent to another dyno that is also corrected PROPERLY and using the same exact brand and style of exhaust . Lately though all I hear about is OUTRAGEOUS dyno claims with BS numbers. Lets say you build a good 502 with excellent heads,cammed perfect and it dynos at 565 hp using marine water cooled exhaust and all your stock accessories and total timing that can actually be ran for a sustained period of time,jets in your carbs that will give you a MARINE safe air fuel ratio (lets say 12.5-1). Another guy pays a shop BIG BUCKS to build him a motor and he is expecting BIG numbers for the bucks he spent. Lets say they build him a motor IDENTICAL to yours down to the final details. Now they dyno it using dry,stepped tube dyno headers and no accessories,WOW, this other guys motor makes 60 more hp (625hp)than yours and its identical. Now lets take it a step further,they PROMISED him he'd make 675hp,so they bump the timing to 38 dgrees total (yours was at 34) and they dump a 50/50 mix of race gas in,they jet it down to the point the air/fuel ratio is no longer safe for a sustained run and they do a QUICK pull,holy smokes,now this thing is making 650Hp,still not the 675 they promised though. Motor builder who is also the dyno operator takes a turn on the OL' correction facto knob a extra 5%,another quick pull,bang we're making682.5hp. This guy has 117 more hp than your motor with IDENTICAL cam,heads,induction etc. They print him off a pretty piece of paper for bragging rights,settle up on the bill,jet it back safe,turn the timing safe and send him on his way. You think you got decent power until you run into this guy and you lay your dyno sheets next to each other and can't believe the kinda power his identical build is making! The only problem is lets say his old motor made 430hp before the big bucks were spent and his boat went 65mph and now it goes 72 mph (1 mph gain for every 20 ACTUAL hp gain),he was thinking he'd see 80 mph. Its because he actually only made 565 hp also,the rest was smoke and mirrors and bragging rights.
I here and see this ALL the time,Smitty

Re: Are all dynos the same?
 

Well said!!!

Happens in the snowmobiling industry ALL THE TIME!

Re: Are all dynos the same?
 

On a 500 inch boat engine with supposed 750Hp I have seen a correction factor of 120%. On 358 CID circle track engines I have seen a dyno'd 70HP increase equate to a .5 second slower lap time on a 3/8" mile track. I have seen a 330HP 4 cylinder sprint engine lap a 450HP 4 cylinder sprint engine. Depends on what you are doing with the dyno, R&D or M&S...

Re: Are all dynos the same?
 

Marketing and Sales... LOL

Re: Are all dynos the same?
 

Yeah, a friend of mine sent his naturally aspirated 540cid engines to some smooth talkin' guys we entrusted our engines to for a rebuild a few years ago. They gave him a shady looking dyno sheet that said his engines made somthing like 704hp. He put them in the boat and it didn't go any faster on the GPS than when they originally made 585hp with the same props. They didn't even act like they wanted to REV any more either. :rolleyes:

The same people who rebuilt his engines proceeded to tell me my 565cid naturally aspirated engines made 787hp on the dyno after they rebuilt them and they always had some excuse as to why they didn't provide the dyno sheet. No wonder, ONE (just one) of the reasons was because the "custom cams" I pulled out were only 220*/220* :rolleyes: Heck, we ended up finding so much stuff wrong including wrong sized head gaskets that we never did get them in the boat. Ended up having to strip them completely down and start all over again. Live and learn.

Unfortunately, my current engine builder says he has seen this kind of stuff happen all the time as well----especially when guys bring their engines they had built from other shops. Not only do some have inflated/exagerated HP numbers, they also seem to have lots of other problems like reliability issues as well.

Now, you guys be careful----there's some SHADY FELLERS out there lurkin' for ya'll :snide:

Re: Are all dynos the same?
 

I went off in left field about all the dyno numbers and "variables" surrounding them in my first post,to help get your question back on track I have heard that merc uses a MORE conservative correction factor (something about 77 degrees vs 65 degrees corrected temp) and their motors normally exceed their ratings when dynoed at a std correction factor by a few percent. There are others on this board who can explain it better than me as I don't have any personal experience dynoing a stock merc motor,hopefully they will chime in,Smitty

Re: Are all dynos the same?
 

I've been in the marine racing engine business for almost 20 years now and I haven't seen two the same yet. I've seen some crazy numbers on the forums from time to time I personally take two or three engines a year to a couple of different places to compare with my own numbers to make sure my calibrations and correction factors are were they need to be . Sincerely Laz

Re: Are all dynos the same?
 

The engines I am speaking of are the new 540's 680 hp @ 5,600 and 675 ft lbs of torque @ 4,900. I am now having the Dart Pro One aluminum heads CNC'd. The shop doing my porting on my 310's thinks he can get another 40 hp. But we both wondered about the initial dyno figures.

Re: Are all dynos the same?
 

Do you have bsfc numbers from the dyno? RM builder was explaining to me how the numbers correlate to correction factors and realistic hp numbers,if you post them I'm sure he will pipe in. Were your motors dynoed with dry dyno headers or marine exhaust and were the accesories installed or left off? Those are good numbers,even if they are high from using dry headers etc,your still should be making 640 or so in "marine trim". What kind of tq were you making around 3800-4200,sorta surprised to see only 700 rpm's between tq peak and hp peak and tq peak farely high up the rpm band,you must have a pretty big cam. In your other post you were asking about having your heads ported /cnc'd,personally I'd be worried about shifting the tq and hp peaks up higher yet to the point where your boat will be hard to prop and cruise with but I'm no expert,all my fast marine stuff has been supercharged,there are others that may pipe in with more hands on experience with N/A marine motors, Smitty

Re: Are all dynos the same?
 

Smitty, I believe it is fine of what you said. It's good to focus on the topic, but it's also good to be aware some of those "variables" of what can happen to a consumer who doesn't always know any better and give them a bit of a "heads up".

Re: Are all dynos the same?
 

Rebel Heart,

Your engines sound very close to the 540's I once had. A few years ago I was running a pair of 540's that made something like 682hp @5700rpm on Tom Earhart's dyno with some fully ported 310cc Dart Pro-1 heads by JimV. I was using a Crower hydraulic roller cam 236*/244*@ .050" (300*/307* advertised duration) on 114* lobes, 950cfm Holley carb, Dart intake, 8.7 comp ratio, 32* of timing.

Peak torque came out at 4800rpm. It sounds like you have very close to the same cam in yours as I did. However, my heads were already fully ported by JimV. We didn't dyno the engines above 5700rpm though...so, if there were any better HP numbers I obviously cannot report any after that and I wasn't really interested as 5700rpm was as high of RPM that I wanted to turn the engines with my 32" labbed props.

By the way, the type of exhaust that we were using at the time on the dyno were dry tubular dyno type headers that I believe had 1-7/8" primaries. I use Stellings full length dry tubular headers in the boat.

Re: Are all dynos the same?
 

Thanks for your replies. I had spoken to Jim V. at the Shootout last year and was impressed with his knowledge. I just spoke with him again last weekend about what he would be able to do with my application. Again, I thought he had some great ideas. Is there anyone else that I should be talking to about porting the heads or is he the best?

Re: Are all dynos the same?
 

Another thing to consider is what are your correction standars sae or stp. At my work we can gain 30 hp or more just by using stp versus sae

Re: Are all dynos the same?
 

HVH is one if not the best in the cylinder head porting business. There number is 865 573 9151. Ask for Joe Petelle and tell him Chris Straub had you call.

Other good guys are
Larry Meaux in LA
Ron's Porting in St. Louis
Carl Foltz in MI
Wilson's in FL

just to name a few other good guys.

Re: Are all dynos the same?
 

When comparing dyno's there are multiple factors to consider. First most shops correct to Standard, not SAE. SAE corrections will show lower HP figures. The way the testing is done will also change the numbers. A dyno is a great tool for comparisons if used properly. The majority of dynos in the country are used as very expensive test stands. The engine didn't leak water, and it had oil pressure send it on its way. There are some very good shops out there with Great equipment, and procedures but you will pay for that. Testing procedures can vary the repeatability of the numbers you're looking at.

You can spend 20 Grand, get a used dyno and with your buddy the plumber and an electrician your a dyno operator. OR, you can spend hundreds of thousands of dollars to build the "proper" cell for repeatable testing. I try to always keep an engine within the same environment that it will run in. If in the boat it's going to run at 120 degrees water temp that's what you run it at. All pulls should be started within a degree of each other on water, and oil temp. This is not something most shops can do due to time constraints, nor is it something most people would be willing to pay for.

When it comes to dyno testing there are a few bottom lines. First, a good dyno test should save you time, and money setting the engine up in your application (boat, car, etc.). Second, they are a good tool to compare on that specific dyno. Not all dynos are set up the same so not all comparisons are fair. LASTLY, we don't race dynos. You've if you had 500HP, and your boat runs 80, what good is a dyno sheet that says you have 600HP if you run 75! Unless you're working on R&D how the engine performs in it's intended application is the only thing that matters.

Re: Are all dynos the same?
 

Lots of good advice here. If you really want to compare numbers between dynos, you have to be sure that the engines were accessorized the same. Most dynos use a load cell to measure the torque and you want to see proof of recent calibration. After that you get observed HP from the test, the actual HP under the temp, pressure and %RH in the cell.

For your corrrected HP numbers to be valid the values used for these weather conditions must be accurate. Check the dyno sensor for air temp against a thermometer that you know to be accurate. Use barometric pressure and %RH from an instrument you know to be accurate. Now you have corrected HP figures that you can trust.

The easiest way to increase the corrected HP is to stick the dyno air sensor in a location where it is measuring higher air temp than is actually going into the engine. That would be called cheating.

We actually have to make sure that we don't accidentally do the opposite; measure a room air temp that is actually lower than what is entering the blower. Centrifugal blowers are mounted down near the valve cover and it is quite possible to suck hot air into the blower from the vicinity of the headers.

Tom