Stingray69

I'm guessing you DO know, but there is a point to be made here.
COOLER air is more dense, having more oxygen, than warmer air.

ON TOP of the 'cooler air is denser' thing, there is the meterological fact that warmer air will hold more moisture, (dewpoint) FURTHER reducing how much oxygen is contained in the air.

I can see having 23 more hp on a cool, dry day, as compared to a hot, humid day, easily. Cool days tend to be higher atmospheric pressure days, as well.

articfriends

Lets look at the scenario bobl gave a little bit different. Lets say you lived in a giant town on top of a 10,000 ft mountain that had a big lake. You have a boat that needs a actual 750 hp at the prop to go 80 mph,your not going to ever run the boat at sea level either,only going to run it at lake mountain top. You call up mountain top blower motor co incorporated in your home town and xyz motor company in La Ca. and tell them what you want. M.t.b.m.c builds you a 8.5-1 540 running 12 psi of boost that makes 750 un-corrected hp on their dyno on pump gas at 10,000 feet elevation,in the boat it runs 80 mph,they also give you a dyno sheet that shows at sea level it would have theoretically made 862 corrected hp but actually it would blow right up at sea level on 93 octane from detonation. Xyz co builds you a 8-1 502 running 8 psi of boost that made 750 hp at sea level with a 1% correction factor due to slight air differences that day.You put Xyz's motor in your boat,it's a pig and won't go but only 73 mph,your pizzed and pull it out and have it dynoed on mtbc's dyno,sure enough it makes 750 hp with a 15% correction factor but your still screwed because you have jetski's blowing by you because uncorrected you only actually have 638hp,not the 750 you wanted and NEEDED. My point is,when a motor is built to run its whole life at high altitude,it would need and be able to run more compression and boost (if sc'd) because of the local conditions being such a extreme. I'm seriously into snowmobiling when I'm not boating and there are companys out there that sell higher compression cylinder heads and cdi's with hotter timing curves that are altitude specific(ie-don't run these parts below 6000 ft alt,etc). Back to my theoretical question-which motor made 750 real hp,both,but as you can see if you need something to perform at its rating in REAL world conditions,if you end up with a 15% correction factor your probably going to be missing 15% of your hp,Smitty

articfriends

So,my point is if your motor was dynoed at 10,000 feet,yes,it is going to have a serious correction factor. In the past few years though there have been several posted dyno test on oso and speedwake with 10-17 % correction factors,the problem with this is these motors WERE not dynoed on top of a mountain. Not mentioning names-there was a motor dynoed in West Mi a few months ago-it made just shy of 700 hp uncorrected BUT just a few hp shy of 800 with a huge correction factor. When A few VERY technical guys on OSO searched the weather underground for actual conditions at the time and location of this dyno test it was found to be done at 600 feet elevation on a mid 60 degree day with average air. When the numbers were crunched in a dyno correction calculator the dorrection factor was barely 2%,not the 14%that was used. This resulted in dyno numbers that were inflated by over 80 hp. Another example,a 540 was dynoed in new jersey or pa (was surrounded by obscurity and secrecy),the so called builder claimed he had made 750 hp from a common combination of parts other builders have used for years that wouldn't even make 650 hp. When the data was calculated for his location it was found his correction factor should have been just over 1%,not the 14.7% he used. The motor running lean with no accesorys made just over 650 hp but after he inflated the numbers-presto-749 hp. The weather data for his location showed air temp at barely 60 degrees,his exscuse was the dyno pulled hot 130 degree air out of his attic,pure BS. Its doubtful a attic would even be 130 degrees on a 58-62 degree day and no self respecting shop would pull their fresh air supply from the hottest possible place they could find. Time and time again people are duped by big numbers that are the product of hyper inflated correction factors,the results on the water ALWAYS fall short of what was expected,then the litany of excuses start when the offending builder is called-your boat must have hook in it,your not propped right,you don't know how to drive,etc,etc. The only way a boat is going to run the speed that it should when its 75 or 100 hp short of what it needs due to a inflated correction factor is if someone starts selling speedometers that are corrected too!!! Smitty

nordic95

Smitty,

Here are my dyno sheets and the address of the dyno sesion was West Wyoming ,PA and the dates and time are givin on the sheet.These are from my first dyno sesion with my first builder.

I find it very interesting that with the first build he achieved 634 HP,on my second build the second builder only achieved 565 HP and we had done a few things to achieve more power,like port and polish heads and flowe benched them,port match intake to heads,clean up and polish intake,etc.etc.

First build I could only get 75 MPH out of my 32 Fountain Fever,stock was 74 MPH with stock 502 415 HP.Now I am seeing 86 but I am still dialing in,hope to see around 88.With the new motors I actually ran 82 with full tank of gas,120 gals,and six full size people on board at the Lake George poker run.

All I know is that the new combo acts like a brand new boat,unbelievable the seat of the pants feel between the two set ups.

Thanks Nordic95

articfriends

looking thru your numbers I see your uncorrected hp was 588 vs 634 with a 7.3% correction factor BUT I am sure you had MANY other issues/problems holding you back with the shopping list of blatant assembly mistakes and mis-matched combination of parts that were used on your motor. Hopefully you will be able to enjoy your boat and it runs good next season after getting RIPPED off by a unreputable/unreliable engine builder. It really sukks paying twice for something but at least its finally behind you,Smitty

KAAMA

I hear you Nordic and I also agree with Articfriends! A 1-mph gain with an alleged 634hp engine. I'd be P'd Off too! "Gee, Mr. Engine Builder what a deal...I just happen to have all these THOU$ANDS of dollars in my pocket that I just picked off a money tree I have growing in my back yard....so, I'll take two of those engines like Nordic95 has!!!"

Buyer Beware...

Reminds me of my friend who took FOUR 540cid engines (my two and his two) down to some smooth talkin' cons down in N.C. a few years ago. After paying about twice the amount than what he was quoted, the cons showed him a bogus dyno sheet showing that the engines supposedly made something like 704hp (each). When he first bought the boat the same 540's made something like 585hp. Once he got them back from the cons and into his boat, it's funny how the boat ended up doing the same speed on the GPS (70mph @4900rpm) with the supposed 704hp engines as they did before when they were 585hp engines @4900rpm---NO CHANGE. We're talking about a 240hp difference in HP---and the boat didn't go any faster than 70mph before and after! ...and they still didn't even act like they wanted to rev any higher RPM's with the supposed 704hp con job engines either!

Mine came back from the same shop even worse---if you even want to call it a "shop"...actually ended up picking them up from the guy's house. No reciepts, no dyno sheets, no labor sheets of machine work that was supposedly done, head gaskets too small, water leaking into cylinders, stock GM cams that were way too small for my engines, all kinds of mis-matched components goes on and on, and stuff I paid for and didn't get. For the most part we caught them red handed because we never put the engines in the boat and decided to completely disassemble them as they came from the cons first---and found we had to start all over! They also told me my engines made 787hp @5700-5800rpm---I guess I should still believe it even when they didn't produce the dyno sheets---just because he said he was some big engine assembly guru at Hendrick's Motorsports! Just another lie!

Over the years here on OSO I have seen (myself included)several unsuspecting guys get lured in and then ripped off by these professional acting, smooth talking cons. When someone is out to do you wrong, they only look for more craftier ways to con you and the more they rip people off the better they become at it---and then if you question them they usually have a way or turning it around and on you---they have a way of twisting things around and are good at fogging the air---that's what cons do! Sometimes it can be very difficult to decipher who is telling you the truth and who's lying to you at times, and unfortunately the more you get burned the faster you learn!

Dave Wesseldyk knows of guys over the years who have dropped off their engines for a rebuild at some engine builder they have entrusted their money and stuff with, and in the mean time the engine builder had been calling the customer for money to order parts and to supposedly keep caught up on the bill only to find when they go to pick up their engines have closed up shop, and declared bankruptcy. No shop, no engine builder, and the customer's engines did a disappearing act, and the THOUSANDS in $$$ he sent for parts GONE!

This hobby/sport and the mark-up on marine stuff is expensive enough the way it is...so, to those who are reading this, pardon us if we're a little gun shy after some of us have been RIPPED OFF and are not so trusting enough to throw ourselves down before every Tom, Dick, and Harry wanna be engine builder who comes on here talkin' the talk and waving a BIG HP and DYNO flag!

jdnca1

We do the tried and true here and primarily use the dyno for a tuning tool. Whatever power numbers get churned up in the process....well, I look at it as a measure of how well the combo works together...but the true test is how the boat performs...end of story. I recommend people talk to others who actually have an engine they are thinking about (or close to it) and see how it ran in their boats. I've talked with builders about how they are making 100 more hp than I could with similar heads, similar compression, and 1 carb instead of 2 on an "all out" high HP NA applicaticion...their answers didn't add up..."well we have a custom ground propriatary cam".....Oh really, well I have a custom ground cam from Gordon at Comp and had another from Steve Tanzi @ Erson and I'm sure both of them (and all the racers they support) would pay you a hefty consulting fee for your "secrets" on theat extra 100hp....hello, hello, hello... I never found out the secert, but I suspect significant correction factor or flat out BS was the culprit.

There are plenty of good honest people in the industry, on the boards, and (at least around here) in the immediate area who can help tackle any particular build...The art, is sifting through the BS and keeping your focus.

rmbuilder

Rob,
This is a great example of how correction factors, used properly, can be invaluable, and used improperly, can be deceiving. When you dyno an engine for R&D/testing purposes, the single most important factors are accuracy and repeatability.
For example: (using round figures for the sake of clarity)

Our test, (Day 1), is made at:

77 Deg F / 29.235” Baro / 0% Humidity, and our shop is at sea level.
Our pull registers 750 Peak HP.

Our testing, (day 2), is made at:

47 Deg F / 29.235” Baro / 0% Humidity, and our shop is at sea level.
Our pull registers 776.25 Peak HP.

This is where the proper use of correction factors is important. We did not make an additional 26.25 HP overnight due to the dyno fairy. Atmospheric conditions account for the power increase. Obviously, to correctly assess any tuning changes, and their effect on power, we need to keep an accurate baseline in order to compensate for the atmospheric changes that occurred. Day (2) would necessitate the use of a correction of (.966) to return to the baseline of our previous days testing.

If (in day number 2) we had subtracted 2 degrees timing and added 4 jet sizes prior to the pull, and the peak number had read 720 HP without a correction factor, we would erroneously conclude that we would have picked up 20 HP due to the tuning changes. In fact, we would have lost 6.25 HP as a result of the timing and jet change. Hence, the legimate necessity of correction factors.




[/QUOTE]Bob is this SAE what most Dyno shops use?????????

SAE J1349
SAE J1349 standard of 77?F (25?C) / 0% humidity / barometric pressure of 29.234 in-Hg (99 KPa). [/QUOTE]
No.
The J1349 is the current SAE standard used by the OEM’s (GM/FORD/Mercury Marine/ etc) and R&D firms to conduct their testing. It is the most current standard used today. The older J607 (60 Deg F / 0% Humidity / 29.92 Baro ) is actually considered obsolete by the SAE. It is, however, far and away the most commonly used C/F in the high performance industry today. Why? It will correct approximately 5% higher than the J1349. That is the reason why the Merc 525 EFI rates @ close to 550, and the Z06 Corvette (SAE 505 HP) around 530 HP, with the J607 factors. Being that peak HP numbers largely drives the high performance industry, most engine builders and performance parts manufacturers, are forced to use the J607 factor to avoid the appearance of giving up 5% to the competition.

Bottom line, no matter what C/F you use; slight changes in the input of data can greatly alter the perceived performance potential of your investment. If an engine builder or dyno shop cannot or will not provide ALL pertinent data and VERIFY that is 100% accurate , your choice of engine builder/assembler is greatly simplified. I agree, the ultimate dyno is the water. Unfortunately most of the pre-purchase advertising claims happen on dry land.

Bob

articfriends

AMEN to that,Smitty

rmbuilder

Rob,
J1349 Correction is:
1.038 or 3.8%

Bob