Dyno questions
- Thread starter bg64ss409
- Start date
Brett,
Sounds like you are doing the rebuild yourself and the dyno shop will just do the pull. If that's the situation then the dyno shop has no "skin in the game" and you will probably get an honest reading assuming the dyno is calibrated correctly.
I watched a small block Mopar engine being pulled on a dyno at a well know builder's shop. They did the engine build as well. After the appropriate warm up and checking the engine the first pull was done. The owner made a comment about expecting more power from the build based on discussions with the shop before the work was done. The operator said something like "the second pull is always better". Then I watched him turn the adjusted altitude knob to tell the dyno the air was less dense then it was on the first run. Wouldn't know it :eek: the numbers picked up and they never touched the engine.
Sounds like you are doing the rebuild yourself and the dyno shop will just do the pull. If that's the situation then the dyno shop has no "skin in the game" and you will probably get an honest reading assuming the dyno is calibrated correctly.
I watched a small block Mopar engine being pulled on a dyno at a well know builder's shop. They did the engine build as well. After the appropriate warm up and checking the engine the first pull was done. The owner made a comment about expecting more power from the build based on discussions with the shop before the work was done. The operator said something like "the second pull is always better". Then I watched him turn the adjusted altitude knob to tell the dyno the air was less dense then it was on the first run. Wouldn't know it :eek: the numbers picked up and they never touched the engine.
BubbletopMan
Well Known Member
Brett, as Dick referred to, a dynamometer can be made to read whatever the operator wants it to read. This is called "Correction Factor". All dyno operating systems use them, some can be manipulated directly, others indirectly. Correction Factors depend on several elements; weather conditions, air inlet temperature, water brake slippage, etc. Direct manipulation means that the operator can plug into the program whatever Correction Factor he chooses. Indirect manipulation means that the operator can only input information into the program and it calculates the Correction Factor, so the operator must manipulate one of the elements he inputs. Generally, the largest Correction Factor in the worst conditions I've seen is 1.03. I've seen operators input crazy barometric pressures, mess with altimeters, and put air inlet temp. sensors down by the headers! All so they can look good and get you out of their shop with a smile on your face! I had an engine builder very well known to this group build an engine for me. When we went to dyno it, I asked what the Correction Factor was for the pull, they looked at me like I couldn't possibly know what that was. They said it was 1.2! If your dyno has to have a 1.2 Correction Factor, get out of the dyno business! Jeremy
I have worked with Jim (Richmond Engines) on his dyno a lot in the last few years. Jims dyno is regularly checked and serviced and is as accurate as possible. It has to be with all the roundy round race engines he builds........ there is a bunch of them that race together and you can't fool those guys......... Any of the new crate engines that are purchased for roundy round cars have to be dyno'ed by Jim before they are allowed on the tracks up here....... so the racing association has checked him and his dyno pretty closely.
His first few pulls on a fresh engine are never to maximum power. He always works his way up over 3 or 4 pulls. I would guess he's breaking in the engine a little as he increases RPM & load. (I've never asked him why).......... By the 3rd or 4th pull the engine is starting to work and the oil temp is up..... that makes a huge difference if the oil is up to temp....... between pulls timing and air fuel is double checked and jets changed if needed......... the last thing you need is to take the customers advice that it's good to go and turn 6000 RPM under full load when the carb is to lean or the distributor is NFG.........
.............. he has told me that if you want more horse power you can drive about 100 miles to another dyno........ they'll give you what ever horse power makes you happy.
.......... he has to deal with that everyday !! Dave
Yep, thats what they do, dyno your head. That inlet air temp sensor placed down by the exhaust is a real winner. I just want mine on the dyno to tune it, timing,jets, etc.Started out with 340 hp engine and curious to see if I made it better or screwed it up. I've known my dyno guy 20 years, he laughs at some of the engine builders that claim 600+ hp with a stock 4412 2bbl 10:1 engines stock iron head 350ci. Then the car he sponsors making maybe 450horse goes out wins 5of the 6 races and the championship. He finally quit doing the local dirt trackers cuz they'd walk in and he'd tell them what power he could give them by the rules, and they'd say "well engine builder A or B could show more hp on the dyno". He refused to dyno their brains just to make them happy. Thats why he does my work. At the time I used Dyno 2000 software for checking parts combos for a build and it came within about 3% of a dyno run. I'm sure the newer softwares are probably dead on if you have the correct flow numbers of the heads. By the way they can tune your brain with the flow numbers also. You also have to know the measured CR. I had a 454 with 11:1 pistons to get 9.3:1 with the heads used. I have 10:1 pistons in my 409 truck block and I'm hoping to get 9-9.3:1 when measured. It will be interesting to see what my old software shows compared to the dyno. JMO
Ray
Ray
BubbletopMan
Well Known Member
In the NASCAR world, we call this "dyno races". You would hear of one team making astronomical numbers, but if you could take that very same engine and put it on a different team's dyno, you'd lose 20 hp. We had a lot of that at ECR when we first merged the RCR and DEI Engine Shops. We finally adopted the philosophy of "You don't see any dyno's or flow benches lining up on pit road to race, so don't race em!" Most engine shops are honest, but there's always some yahoo around that wants to play the dyno or flow bench game. But I will say if you want a driver to go bust off a lap, tell him you found some horsepower. Dyno-ing a driver's head is not always a bad thing! Jeremy
Skip FIx
Well Known Member
Before my old machinist retired his dyno would "run the numbers" at the track as far as mph and weight. You could take the same motor to the shop across the street and pick up at least 5%!
You really have to just look at the dyno as a rough ball park and use it for tuning in a more controlled environment than the track.
As the others said as oil temp and water temp go up things can change. Most guys will try and keep them the same especially when doing fine tuning.
You really have to just look at the dyno as a rough ball park and use it for tuning in a more controlled environment than the track.
As the others said as oil temp and water temp go up things can change. Most guys will try and keep them the same especially when doing fine tuning.
The only Dyno I trust is our driver
Like Dave said about Jim's shop we run a race car in the American Canadian Tour for Rules which means our sealed motor is dynoed at a calibrated and monitored shop and then sealed. All we know is that the numbers are inside a box that is legal. I have built open motors with 400 to 410 hp that beat alot of 430 and 440 hp.
Like Dave said about Jim's shop we run a race car in the American Canadian Tour for Rules which means our sealed motor is dynoed at a calibrated and monitored shop and then sealed. All we know is that the numbers are inside a box that is legal. I have built open motors with 400 to 410 hp that beat alot of 430 and 440 hp.
I don't know what was going on in the dyno room tonite but I'm head out there first thing in the morning to find out. I live 4 miles north (as the crow flies) and I've never heard his dyno here unless there was a south wind. No wind tonite and holy crap I thought someone was a block away with headers open. Very big headers.
Ray
Ray
Can't wait to see a the dyno picture with a boosted 509" BWR!
DaveMcLain
New Member
Dynos are very much like flow benches in that there are many folks who compare numbers from one to another without realizing that other than using them to get a general picture about the engine's performance or airflow they are largely meaningless.
The way they are used correctly is to run the engine, warm it up properly, do a few pulls, get a good solid baseline. Make changes, see if those changes make it better or worse performance wise etc. Compare baseline to the numbers when everything that you wanted to test has been tested. If you gain 10% you probably gained 10% irregardless of what the number was when you started.
Correction factors are often manipulated greatly in order to make people feel better about a particular engine. But remember that how much correction is being applied does NOT necessarily mean that the dyno operator is being shady in any way. Someone mentioned needing a 20% correction factor meant that someone should get out of the dyno business. I bet that much correction would never be needed near sea level but what if the dyno was in Denver? At our shop my correction factor is normally about 4% and generally my uncorrected barometer is about 29.00 inches. I've seen it somewhat better and a lot worse too.
Correction factors are intended to take out performance variations which are induced by atmospheric conditions alone, not tuning changes caused by those changes in conditions. From my experience I feel that they are probably accurate to about 1-2% from day to day which is probably fine for most testing. Getting a baseline before each day's testing is very important and often overlooked.
The way they are used correctly is to run the engine, warm it up properly, do a few pulls, get a good solid baseline. Make changes, see if those changes make it better or worse performance wise etc. Compare baseline to the numbers when everything that you wanted to test has been tested. If you gain 10% you probably gained 10% irregardless of what the number was when you started.
Correction factors are often manipulated greatly in order to make people feel better about a particular engine. But remember that how much correction is being applied does NOT necessarily mean that the dyno operator is being shady in any way. Someone mentioned needing a 20% correction factor meant that someone should get out of the dyno business. I bet that much correction would never be needed near sea level but what if the dyno was in Denver? At our shop my correction factor is normally about 4% and generally my uncorrected barometer is about 29.00 inches. I've seen it somewhat better and a lot worse too.
Correction factors are intended to take out performance variations which are induced by atmospheric conditions alone, not tuning changes caused by those changes in conditions. From my experience I feel that they are probably accurate to about 1-2% from day to day which is probably fine for most testing. Getting a baseline before each day's testing is very important and often overlooked.
Dave, Sorta interesting about stuff that can be found by using that " Google" feature on these new fangled computer things. Your talent, knowledge and skill are very impressive. Just for curiosity sake, are you building any 348-409 engines?? If so, many of us would be interested in your input. Thanks 
M
monk
Guest
Dave
Jim Evans out your way built and dynoed my 409
Did pretty much what you described.......he made 5 pulls
adjusting as he went to get where he wanted to be
Jim Evans out your way built and dynoed my 409
Did pretty much what you described.......he made 5 pulls
adjusting as he went to get where he wanted to be
Skip FIx
Well Known Member
I'm planning on trying two sets of carbs , some different carb spacers as well as timing, rockers , and lash settings, when mine gets that far. If someone has some 2" Stahl's to lend me to compare the Jardine big Tri Ys we'll do that to.
My last two Pontiacs we probably had 20-25 pulls on each but we did intake swaps and multiple carb swaps.
My last two Pontiacs we probably had 20-25 pulls on each but we did intake swaps and multiple carb swaps.
DaveMcLain
New Member
We do all sorts of engine building in our shop but my 409 building experience is pretty limited.
Dyno testing is a LOT of hard work but it can be fun too. When I first got the dyno I sort of assumed that it would be an answer machine for a lot of the questions I had about engines. I think that it's really more of a question machine because I've had some stuff that I just knew would work, and vice versa. We've found power in some surprising areas of the engine too and more than I would have believed and this had me asking myself and others, "why?" "how?" etc.
Areas where I would always try to spend some time if possible would be carburetor spacers, jetting and timing. Sometimes you'll find that you have the right jetting, the engine doesn't need a spacer and you're running about the right amount of timing on your baseline pull. But it's certainly worth testing these things.
I've seen exhaust testing give killer results for the money invested. 25 horsepower with about $3 worth of pipe. I've seen it be just the opposite where no matter what header you tried it made no difference. Not long ago I had a big Chevy on the dyno where going from what would seem to be the right size headers to the wrong ones pick up an honest 30 horsepower, back to back. Later I tried the same experiment on another big Chevy and the difference between these two headers was ZERO! Why?
Dyno testing is a LOT of hard work but it can be fun too. When I first got the dyno I sort of assumed that it would be an answer machine for a lot of the questions I had about engines. I think that it's really more of a question machine because I've had some stuff that I just knew would work, and vice versa. We've found power in some surprising areas of the engine too and more than I would have believed and this had me asking myself and others, "why?" "how?" etc.
Areas where I would always try to spend some time if possible would be carburetor spacers, jetting and timing. Sometimes you'll find that you have the right jetting, the engine doesn't need a spacer and you're running about the right amount of timing on your baseline pull. But it's certainly worth testing these things.
I've seen exhaust testing give killer results for the money invested. 25 horsepower with about $3 worth of pipe. I've seen it be just the opposite where no matter what header you tried it made no difference. Not long ago I had a big Chevy on the dyno where going from what would seem to be the right size headers to the wrong ones pick up an honest 30 horsepower, back to back. Later I tried the same experiment on another big Chevy and the difference between these two headers was ZERO! Why?
