PHR tests correction factor, 'splain please. [Archive]

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Damn True

10-01-2006, 09:25 PM

Bow Tie 67

10-02-2006, 05:50 AM

The way I see it, is they are adjusted for a more or less a standard day at sea level. That way comparisons can be made.

Damn True

10-02-2006, 07:28 AM

Well a meteorlogical "standard day" is 68degf, 38%RH and 29.92 which is neither.

harshman

10-02-2006, 07:30 AM

i'm not sure but i think they got that setting from NHRA.

Steve1968LS2

10-02-2006, 02:24 PM

Disclaimer: I am a geek.

That said......

I have a couple of questions regarding the different correction factors in use.

SAE J-1349 assumes 77degf and 29.92"hg
SAE J-607 assumes 60degf and 29.22"hg

Why?

Given that the avg. temp is about 62degf and the avg bar-alt is 29.921"hg it seems that both correction factors are less than representative of what an engine might see.

Also, in the lead photo used in your dyno test article this month the operators screen is reading 29.08"hg wassupwithat?

Because different groups use different correction factors. Long ago magazines, dyno shops and the like started using J-607.. why? Maybe just to give larger more impressive numbers. I dunno. Either way we use J-607 so that people can relate it to other magazine stories and dyno runs. However, I wanted to make sure I point this out and why our numbers had a stockish LS2 putting out way more than GM advertised. GM uses conservative numbers so they don't get caught in a legal bind (as happened to Ford with the Cobra)

I have no idea why the BareP read 29.08" and since I'm not up to speed on this I don't even know what a correct reading would be. I do know that some of the sensors were not hooked up to that screen like oil temp, Voleff and some others. If you look close you will notice we accidentally left the fan off as well.. doh! lol

You can also see that the correction factor was 1.046 (less than 5%)

Damn True

10-02-2006, 03:09 PM

Just to be clear Steve, I am not calling you or Westech out here. Simply trying to understand why the "correction factor" dosen't seem to correct to anything close to a "standard day".

Steve1968LS2

10-02-2006, 03:15 PM

Just to be clear Steve, I am not calling you or Westech out here. Simply trying to understand why the "correction factor" dosen't seem to correct to anything close to a "standard day".

Oh, I know your not "calling me out" :)

That's why I put it in both engine stories.. to make it clear. There are certain correction factor formulas that you can choose from. In other words (as far as I know) you can't make up your own correction factor, at least easily.

I guess a standard day depends on where your are located. A standard day in SoCal is not a standard day in Orlando, Florida or Detroit, Michigan. The OEM's use the 70 degree one and most other places use the 60-degree one. Most likely the OEMs want to be conservative and the others want to be generous.. lol

However, the important part is that the correction factors are given and that the before and after tests both use the same factor.

We have a story coming out in the December issue about "dyno shenanigans" and the tricks some places use to inflate the gains made by stuff.

On a side note I am very proud of my opening shot at the dyno.. I'm a newbie at this and the shot came out better than I had hoped. I also thought it would be fun to see the actual dyno screen.

Blown353

10-02-2006, 03:33 PM

Speaking of Westech (the can of worms is now open), we recently dynoed an engine almost identical to what a magazine known as "SC" just built and tested. Same cam, same intakes (we actually tried the engine with a Super Victor, Vic. Jr and an RPM Air Gap), same carb and also a Holley HP750, 2 less cubes, same heads, 1/2 point less compression. Our engine did have coated SRP pistons though. We also tried 1.6 rockers on the intakes and exhaust.

Here's the kicker. Our "near clone" on my friend's SF-901 with the best rocker / intake / carb configuration made 83 hp less than the magazine engine. I don't think 2 more cubes and 1/2 point more of compression would get our engine up to the magazine numbers.

Several well known and reputable engine builders and even a very well known cam designer have all taken jabs at Westech in casual conversation. One of these engine builders was actually asked by a magazine he was doing an engine for to bump his numbers by 75hp because the project primary sponsor "wouldn't be happy." The engine was eventually dyno'd at another shop and it made the numbers the magazine & sponsor wanted.

Also, there are other ways to slew a dyno besides ambient condition correction factors. I've seen purposely shifted load cell calibrations on a known to be "friendly" dyno around these parts. I've also seen the load cell's mounting location altered to give the waterbrake more leverage on the load cell, this way the dyno zeros properly but the load cell returns an incorrect and too high reading. These are all obvious hardware "alterations" that I've seen firsthand, software "fudging" can be made almost invisible if one was motivated enough.

I never really trust one dyno's numbers to another, even if the operator and machine is honest there are still a lot of places for error & repeatability problems. However, testing a couple combos back to back on the same dyno is definately worth something IMO to verify changes to an engine combination.

Steve1968LS2

10-02-2006, 03:45 PM

Don't know about Westech shenanigans.. I was there and saw no overt signs of screwing with the numbers. This is my car/engine so I want accurate numbers.

The week before FAST was there dynoing an LS2 and thier base numbers were just about the same as mine (I had better headers).

However, talking about rumors and hearsay really doesn't do much good. I know quite a few people that have their race stuff done at Westech and they are quite happy and certainly don't want skewd numbers. I've heard others knock other local shops but it's all just anecdotal. Westech does a lot of buisness and I would expect there to be less than happy customers out there, that's typical of any shop like this.

And yes, dyno's (both chassis and engine) are only as honest as the people running them :) -- the gains are what's really important and not the actual peak numbers. My 2000 SS would make 340rwhp at one and 320rwhp at another. Hell, at one I made well over 350rwhp.

I also can't speak about SC since I have no idea. All I know is that we never pad our numbers. If they suck they suck. This is why I go out of my way to discuss the concept of correction factors and actually give what they were in the story. I guess we will know more when I strap to a few different chassis dynos.

My phones are down at home (the whole neighborhood) so I don't know if my DSL will be up. If I don't answer right away then just be patient till I get back here in the morn.

Damn True

10-02-2006, 03:50 PM

Honestly, the test 2 results would suit me just fine. Ya think there might be a way to bring those peak numbers down about 3-400 rpm without dropping the output?

Steve1968LS2

10-02-2006, 03:58 PM

Honestly, the test 2 results would suit me just fine. Ya think there might be a way to bring those peak numbers down about 3-400 rpm without dropping the output?

hmm.. so instead of peak being 6500 you would like it at 6100? Sure, it's all in how the cam is designed. The cam I am running is by no means on the radical side. The graff shows it made 560hp at 6000 RPM. That's only 13 less hp for a 500rpm drop. Personally I really don't feel the need to have more than 450 rwhp. Much more than that just smokes tires (which is fun too.. lol)

Blown353

10-02-2006, 03:59 PM

All I know is that we never pad our numbers. If they suck they suck.

Good to know.

One of these days, time and money permitting, my friend and I are going to build an engine, dyno it on his SF-901 or his brand new SF-902, then drive it down to Westech to be dyno'd. We've been wanting to do this for years but haven't had the time. We have renewed motivation now given the recent article in SC. I'm fairly confident in his numbers, on a engine making in the mid-700's for power his dyno tracks within about 10hp of the dynos at Richard Childress Racing-- he's bought a couple engines from them complete with dyno/build sheets, first thing he does when he gets them is to throw them on his dyno.

The Westech guys have to know about their reputation via the magazine articles... it definately preceeds them even amongst top-level shops. Several of the shops I know have to deal with the other end of this, when guys come in from the street saying "Magazine XXXX built this engine and it made XXX HP, I want one just like it." The shop owner then has to try and convince the guy that it isn't gonna happen (and usually they'll lose the business when the guy goes to another more gullible shop), or worse yet they build it anyways and then the customer complains it isn't making the HP they expected, via either an honest dyno or the trap speed at the 1/4.

In fact, that's what I'd like to see on all these magazine engines. Have a standardized "test car" for these engines-- consistent chassis setup, tires, tranny, rear end. Dyno them, then throw them in the test car, report the new curb weight, then report back with the ET and MPH. I know that's asking a lot and will probably never happen but I can dream.

Steve, I beg you to take your car to the dragstrip and let us know the trap speed. Only then you will know if you received a "fair deal" on your dyno session.

Damn True

10-02-2006, 04:15 PM

hmm.. so instead of peak being 6500 you would like it at 6100? Sure, it's all in how the cam is designed. The cam I am running is by no means on the radical side. The graff shows it made 560hp at 6000 RPM. That's only 13 less hp for a 500rpm drop. Personally I really don't feel the need to have more than 450 rwhp. Much more than that just smokes tires (which is fun too.. lol)

Exactly. I would prefer to give a little more safety margin to the valve train and bottom end by not spinning the thing quite so high.

I believe test 2 was just the OE cam, FAST intake, throttle body, AFR heads and headers right?

Would a little more lift/duration against the OE cam via higher rocker ratio drive the peak up or down?

Steve1968LS2

10-03-2006, 07:00 AM

Exactly. I would prefer to give a little more safety margin to the valve train and bottom end by not spinning the thing quite so high.

I believe test 2 was just the OE cam, FAST intake, throttle body, AFR heads and headers right?

Would a little more lift/duration against the OE cam via higher rocker ratio drive the peak up or down?

My lift was under .600 and that's pretty safe, especially since I upgraded the springs. The OEM cam is SOOO small.. I would at least upgrade to a 224 cam.. still pretty small but larger than the one from the factory.

The super bitchen headers I have were worth 10hp over the hookers. Keep that in mind as well. And yes, test 2 was all the goodies minus the cam.

Steve1968LS2

10-03-2006, 07:10 AM

Good to know.

One of these days, time and money permitting, my friend and I are going to build an engine, dyno it on his SF-901 or his brand new SF-902, then drive it down to Westech to be dyno'd. We've been wanting to do this for years but haven't had the time. We have renewed motivation now given the recent article in SC. I'm fairly confident in his numbers, on a engine making in the mid-700's for power his dyno tracks within about 10hp of the dynos at Richard Childress Racing-- he's bought a couple engines from them complete with dyno/build sheets, first thing he does when he gets them is to throw them on his dyno.

The Westech guys have to know about their reputation via the magazine articles... it definately preceeds them even amongst top-level shops. Several of the shops I know have to deal with the other end of this, when guys come in from the street saying "Magazine XXXX built this engine and it made XXX HP, I want one just like it." The shop owner then has to try and convince the guy that it isn't gonna happen (and usually they'll lose the business when the guy goes to another more gullible shop), or worse yet they build it anyways and then the customer complains it isn't making the HP they expected, via either an honest dyno or the trap speed at the 1/4.

In fact, that's what I'd like to see on all these magazine engines. Have a standardized "test car" for these engines-- consistent chassis setup, tires, tranny, rear end. Dyno them, then throw them in the test car, report the new curb weight, then report back with the ET and MPH. I know that's asking a lot and will probably never happen but I can dream.

Steve, I beg you to take your car to the dragstrip and let us know the trap speed. Only then you will know if you received a "fair deal" on your dyno session.

My car will hit the dragstrip.. and the skidpad.. and the cones.. and... lol -- I will also have total weight, front axle and rear axle weights.

Yea, your magazine idea would be cool but not very likely. Most engines have "project cars" they are destined for and nobody has time to install the engine multiple times. g/28 is sorta our "test mule" and we just did a carb/intake swap for an upcomming issue. What would be nice is if we had our own engine dyno cell. That's not likely to happen since it takes quite a bit of $$$ and infrastructure to run one.

We are also in the process of installing a Mustang Dyno at our PHR tech center. I plan on doing chassis dyno pulls there as well as another shop that is gonna tune the car.

Every shop has junk said about them. Westech has been around a long time so it's bound to happen. Had another shop build an engine and engine dyno it. It came out as 405hp or something like that. Took the car to Westech for a chassis dyno and it came in at 280rwhp.. that's not an appropriate drivetrain loss. So who's dyno was off? If it was Westech then it was reading low. We ran the car on our old Dynojet and got about the same chassis number. The only way would be to take the same engine to several diff shops then install the engine, chassis dyno, weigh and run it at the track. Lot of work.

Dyno's are tools best used to guage gains or losses due to part installs or for fine tuning an engine. All the rest is just banter for bench racing and braging rights.

Scott Parkhurst

10-03-2006, 10:40 AM

FWIW - Westech has one of the largest engine rooms anywhere, and they move a ton of air through it. Most other dyno cells I've been in are truly cells - tiny rooms with inadequate air movement and the potential for both heat and exhaust recirc to negatively affect the outcomes. This is virtually impossible at Westech, by design.

The cool thing about Westech is that since so many of the engine tests for the mags are done there, those numbers are all comparable to each other.

~SP~

Steve1968LS2

10-03-2006, 10:49 AM