stevesxm

this web site is all about performance and for you guys that means motors for the most part. i have read a lot of the stuff here and the level of intellegent analysis is really good and my suspicion is that the general technical smarts is really good as well... but what i see is a heavy reliance on the dreaded "dyno numbers" for these motors and some of the same folklore and voodoo that has plagued the motor industry forever... so... lets talk about the easiest thing first... the dyno.

the dyno is nothing more than a water brake that measures the torque the motor puts out at any given instant. period... nothing more. any information it generates beyond that for you is a function of a mathematical algorythm that has a number of different varients and a fair number of user assignable variables. this algorythm is called a " correction factor" and is used so that the operator can correlate his data from one day to the next in some intellegent and repeatable fashion. as you well know, different conditions will make the same motor make different power at different times.... nice cool 50 degree air will make a LOT more power than humid 110 deg florida august air. so what do you do if you are dynoing motors in dec AND august ? the correction factor is supposed to take care of that... and most dynos do it automatically based on the parameters dialed in by the operator...

also... the running conditions of the motor are critical.... 20 degrees of oil temp one run to the next can make 3 and 4 % difference in the raw number.... so if you run your base line run at 180 oil and make a change and then run your next run at 210 oil and see a 3 % increase you might believe you actually MADE more hp.... instead of doing nothing at all or actually losing hp. running a dyno so that the results are true and meaningfull and not just sales litterature is a science..not an artform or magic.

there where litterally dozens of occassion where we would get motors in the door, fresh from builders with dyno sheets attached that were LITTERALLY corrected over 100 hp...and sure enough...when we ran them in the cars they were slugs and when we ran them on our dyno they where slugs.

you need to use your heads and the good brains that you have and stop thinking there is some magic to all of this motor business... there isn't.

if someone tells you the changed their fuel pressure and got 50 hp... they are wrong

if someone tells you can run an 11: 1 motor on 87 octane ... they are wrong

if someone tells you they are making 650 hp out of a single 4 barrel 454 on 87 octane without a turbo or scharger... they are wrong

when someone tries to sell you the magic bolt on widget that will get you 30 hp with no other changes... they are wrong

a good number for a normally aspirated reasonabbly hot 9:1 motor that has a good wide usable power band and will last a long time and that you can run on 87 fuel is a little more than 1 hp per cubic inch. can you get more ? sure... but the law of diminishing returns will bite you in the butt VERY quickly in terms of reliability.

and remember.... the dyno sheets are just pieces of paper from someones machine. if the operator took the air temp sensor and out of the intake when he made the run and layed it someplace hot, then that dyno sheet now says that that motor made a LOT more hp then it actually did....

and when the next guy that tells you he has a bolt on flame arrestor that will make 50 hp just look down... he is probably wearing shiny white shoes and plaid pants and his other job is selling aluminum siding...

jpclear

Thanks for this, Steve... Now I know that there is at least one more person out there that thinks kinda like I do. I always maintained that the dyno was a tool to make comparisons of different components and adjustments as used on a given modified engine, NOT to generate a piece of paper to be used for bragging rights at the bar or to inflate the value of a questionable piece of iron that you want to sell. --- Jer

cstraub

Bottom line Power Numbers sell enignes. . .hell they sell cars. What would be the fun in comparing the Z06's interior comfort to the M3's!!! Automotive advertising and marketing caters to our needs of power. Dyno figures in our industry are used the same way. . .to sell engines. A dyno I agree is nothing more then a tuning tool. It allows any engine builder the ability to check, change, and develop power to fit a customers needs. When knobs are turned, false data inputed, then it becomes a marketing tool.

FOUNTAINATLAST

Well you would sure hope that a shop that you've been using for years or any other dyno facility would be playing the game straight and not falsifying data to mislead the consumers. If a person is trained to work the dyno I would hope they take these conditions and add them in the final results... But in the end if there selling you the motor and or parts they can tell you anything you want to hear.

Great now we know Stez dogs are really only 400hp anchors!!!!!

cmcnitt

dyno's are cool

Quiet Storm

From what I understand torque is the better # to look at or can that be fuzzy too?

stevesxm

well...as you say, you would hope so. and im not certain or even suggesting that these guys are dishonest... although i am equally certain that some are... after all... where is their risk ? unless you are racing against like boats, all you guys know ( and myself included) is that the thing makes a lot of noise and is gonna go fast enough to make everybody scream and thats why you bought the boat anyway. if they tell you you have 650 hp and you really only have 575, you wouldn't know the difference anyway. ( thats the corporate "you" not anyone specific)

the bottom line is that building motors and making power is a serious science andthat includes a lot of hours working on combinations on the dyno... an investment a lot of guys don't want to make. they buy the parts off the shelf based on mfg propaganda, bolt them together and , if it starts say... well there you go... 650 hp because i added up all the numbers that the cam, cyl head, and carb guys said... not because anyone took the time to load it up with all the ancillaries and exhaust that your boat actually has and then spend the time to break it in and jet it properly...

and if you believe the dyno sheets you get.... well ... lets talk about swamp land. i'm sorry im such a cynic but 25 yrs in the racing industry does that to you.... ive seen more magic beans come and go then you can count and suddenly anyone that can read a summit catalog is an engine builder.

z.zuperboat

That is so true about builders and dynoes. Its been that way for a long time. All I want is what I paid for. If they tell me it makes 1000HP you know its not going to be cheap. Their are plenty of packages out their for the doit yourselfers. I wish you guys all the best of luck with them because in the long run my season is short enough to have to do it again and again. And yes you can have 2 identicle motors make different power, Its more than just part to making power. The wrong carb can cost you 50hp. Happy Holidays to All.

cmcnitt

As a dyno operator, I think anyone that buys a performance motor should take it to a local tuner to have it dyno'd / tuned for local conditions. A good tuner has no interest in jacking the numbers, he'll be more interested in giving you a good, safe tune. If you already paid 15k plus for a motor, it's worth the extra 500 or so to get the local tune. Plus, tuner's have to eat too!

cstraub

Case in point. About 4 years ago a customer of mine built a very competitive Nascar Limited Late model engine. These 2 barrel engines by rule are very restricted. Well his combo was a 10th off of the track record, qualified the car in the top 10 just about every night, and at the end of the year the driver and car were 2nd in points. . .just a few back of the Champion. The driver owned the car and my customer's customer owned the engine. Due to some obligations, the driver bought the engine from his partner for $5K. Now for any of you that know anything about this class, that is about 25 cents on the dollar compared to what a new one cost. We'll he took it to an engine builder and the builder put it on the dyno and said it was down about 80HP from his best engine and it needed a list of parts to make it right. $7500 later the engine went back on the dyno and walla, it was 70HP better. Needless to say the driver/owner was excited. . .this lasted till opening day of the new season. The new engine was 3 tenths slower then the old engine and would not pull his old gear off the corner.

So do you think we really had an extra 70HP?