i've been told it might be the mileage. I had my '06 z06 dynoed at a big tuner shop here in DFW and it laid down 453 sae with about 1600 miles on it. I was very pleased and asked if they had dynoed others. They indicated many, and said mine was slightly better than average for that mileage. However, they had 3 other 427 z's come in with 10,000 plus miles that laid down 465-470 stock like clock work. They attributed alot of it to the mileage. who knows?

 

Makes sense, since I am in that range as well.

Of course, now I need another 100 to keep up with you 427 dudes.

 

I've always heard since about '97 that the LSx engines do get stronger with mileage and that every once in awhile GM throws in a ringer of sorts, like some of the LS1s were actually LS6s(castings) a year before they were supposed to be in the cars. Like you said, who knows....

 

put it on a MUSTANG dyno and you'll see around 330 RWHP and then want to committ suicide different dynos give different results.....like the other poster said take it to the track if it goes 117 mph you have that power if it goes 110-112 you have a normal regular vette....not bursting bubbles just the truth my friend.

 

Dynojets always read higher than Mustang dynos.

 

Oh I know. I was just wondering whether the dyno was accurate or not, because it seemed like a high number for a dynojet. I agree 100% it is about speed. The reason I am modding the C6 is because it does not as fast as my '02 Z06 was. I wanted some of that feel back. What I am doing now will get me there and then some.

 

of course they do. but you'll also find that dynojets outnumber mustang dynos 10/1 in the real world. So, that being the case, 248C dynojet numbers, as long as they're sae corrected, will probably be the easiest to compare apples to apples when you see people posting dyno sheets around the country

 

I think more like 325 to 335 stock or that is what I have been taught. This represents 20% loss at 325 and 17% at 335. This is what the mags have suggested. I could find the formulas if I needed to, I know I kept the technical article they included on dynos. It was very interestiing.

I had my 02 Firehawk dynoed against my 2000 Formula (which had less mods) on the Hot Rod Power Tour a couple of years ago and the numbers didn't make sense. The Firehawk had 345 hp and the Formula had 320, yet with the mods they both had, they should have had more of a difference. In reality the Formula was close to the Firehawk. But the owner of the dyno said he had seen LS1s very as much as 30 rwhp. Of course, you don't know if what the customer says is really the truth, and he said so.

The owner talked about all the variables, like parasitic drag, dyno designs, and of course, the real world. He made some good points talking about how some shops knowingly adjust their dynos to show high indicated output. This makes you want to go back. Especially to the shop that shows the most HP and torque. It makes sense. He also talked about all the technical issues, of the various dyno type designs. A lot of went over my head, but I understood the concepts. I think the main thing is to use the same dyno all the time, and then compare that against "your" times on a 1/4 mile strip. This is what really matters and provides you a real world indication of how well "you" and "your car" are really doing.

I would be very surprised to see you trap a stock Vette at the speeds mentioned, unless you are very good at doing the quarter mile. But then again, I am sure their are folks on here that can do this!

My best speed, after about 15 tries, is 110mph. And, that is with a Granetelli MAF, Random Tech cat back, and CAI. I didn't have my custom tune installed, which might be some of the problem, but even on my best day I doubt I will see 115 to 120 mph. But, I am 52 and getting slower with age. HA!

 

Dynos have nothing to do with real world. Ram Air Trans Ams are good examples of this. The forced and ambient temp air through open snorkels is good for 5-8 rwhp at speeds above 50 or so. Induced drag--wider tires, a spoiler that doesn't angle downforce properly, slipping clutch, rear axle ratio, tires, ten million other factors affect real world speed but don't show up on a dyno run. Dyno numbers are only a reference point. The Firehawk had more induced drag and more downforce than the Formula. The Formula was lighter. Firehawk had better rubber and theoretically less internal friction with synthetic fluids, and so on. The bottom line will always be who crossed the lights first. And watching a graph on a screen is hardly the same as running the car on a track!

 

100%

 

I agree about the dynos and cold air kits. My C5 dynoed the same number before and after the Vararam, but at the dragstrip my car picked up an extra 2mph in trap speeds under identical weather conditions. That's about 15hp right there.

 

C6 Vette -

Cars now are more efficient and have less parasitic losses due to the drivetrain.

I believe the standard is 15% loss to the wheels with a manual tranny and 20% for an automatic.

For example, my 370rwhp SAE (SAE is used by manufacturers) =

370 divided by 0.85 = 435 horsepower at the engine

I have seen other people use 13% and 18% also.

Many people have dyno'd stock and a range of 320-330 for automatics and 340-345 for manuals seems to support both conversions.

Howard

 

There is a great dyno article out there that points to drivetrain loss being primarily a fixed number rather than a percentage. This is because the main loss (and heat) occurs through friction of parts and oil, and that is tied to rotation speed. Yes, there is some loss through additional side loading when you add torque, but it is minimal with these drivetrains, apparently. So as long as your peak power occurs in the same RPM range and you dyno in the same gear, the loss is the same fixed HP number. A great example is the C5 coupe vs 01 Z vs the 02Z.

C5: 345 crank - 45 loss = 300RW (shown many times)
01Z: 385 crank - 50 loss = 335RW. Why the extra 5 loss? because the max HP occured at 6K, 10% higher than 5.5K for the LS1.
02Z: 405 crank - 50 loss = 355RW
C6: 400 crank - 50 loss = 350RW, except, the C6 wheel is 2.5% taller, so you get 342RW, or 58HP loss.

So if you do mods to a C6 which add HP and those gains occur at the same RPM as before, the gain is directly additive to the wheels. However, if you throw a cam on there which adds 40HP, but that HP occurs at 6600rpm rather than 6000, then you lose another 10% of 58, so I would expect that car to dyno 376RWHP, 34 more than stock.


Anyway, enough theory. I expect to get dyno numbers back this afternoon from the mods & basic tune and will post them here.

 

To begin with, there is no "standard" drivetrain loss percentage. It varies for each drivetrain type and even from car to car. A front wheel drive platform (with helical gears for the final drive/differential) will have less loss than a rear wheel drive platform (with hypoid gears for the final drive/differential) simply because there's much more sliding action (and therefore friction) in hypoid gears than helical gears. You'll see some FWD drivetrains with less than 10% loss!

There are two components that make up the amount of loss in a drivetrain: 1) constant losses and 2) percent losses dependent on the amount of HP going through the drivetrain. The only way to determine the HP loss through a particular drivetrain with a particular engine is to dyno the engine on an engine dyno, then install it in a car and put it on a chassis dyno. Anything else is a SWAG...Scientific Wild Azz Guess.

The engines are rated under a new SAE test that requires strict adherence to test conditions and 2% variance between engines in production (1% in the tests) and is done independent of the manufacturer. That means an engine rated at 400 HP can be any where between 392-408 HP and still be in compliance. If you dyno an engine/car under different conditions from the test conditions, you will end up with more/less HP. Also, Dynojet dynos have an error of +/- 2%. So 363 HP on a Dynojet could be ~356 HP at the bottom range and even that number is skewed upwards if done under better than standard test conditions. But we'll take the 356 HP number and use what the typical % drivetrain loss I've seen over the years for the stock C5/6 platform which is about 12.5% (some were higher, some were lower). 356/.875= 406.9, which is certainly within the 2% allowed by the SAE test. So while his may be one at the upper end of the range, I wouldn't say he has a freak and certainly wouldn't say he has 427 HP at the crank...the only way to tell that is to put it on an engine dyno.

And I love it when the high HP super/turbocharge guys take their RWHP number and back calculate FWHP using 15% loss...they're the same guys that measure their dick with a metric ruler then give the results in inches.

 

Good post!
But you can't reduce the C6 RWHP because the wheel is 2.5% taller. HP is HP...the 1st Law of Thermodynamics says you can neither create nor destroy energy, you can only change its' form. The HP loss through the drivetrain is in the form of heat due to friction. HP is heat (1 HP=746 Watts, grab a 60 Watt light bulb for a demonstration of heat), but it can take many other forms with the obvious being to accelerate the car. It can also take the form of light and sound as well as many others. But a difference in wheel height can not cause a reduction in HP, what form did the "lost" 8 HP take? 350 HP at the wheel is 350 HP no matter what the diameter of the wheel is.

 

Yes in thinking through this, I see your point. My rationale was from the torque perspective: that the larger wheel reduces leverage so there is less force applied at the contact patch. Since torque is lower at any given point, HP would be reduced as well, since HP = Tq x RPM.

Does that make sense?

How's the Scarab running?

 

Ouch!

 

What were the TQ #'s on that same run? Was it unusally high too? Please post them along with the dyno charts I'd like to see em...

 

Is the C6 Z51 lighter than the 04 Z06? Just wondering.

 

You are correct that less force is applied at the contact patch with a taller tire, but that is a linear force expressed in LB "force" (as opposed to LB "mass"). This will affect initial acceleration (since F=ma) much the same way as changing the rear end ratio. The force at the axle is a rotational force (torque) expressed in LB-FT which will not change no matter what diameter wheel/tire is used thereby making HP a constant.

Look at it from the standpoint of the direction of power delivery. With power delivered from the ground, a taller tire will create more torque (longer lever arm) but the RPM will drop by the same percentage making HP constant (again). But in this case, power is coming from the engine so the torque delivered to the axle (via the transmission/rear end gears) will be the same regardless of the tire diameter. Also, the Dynojet measures HP first. It does this by looking at the time required to accelerate a drum of known weight from one RPM to another (it does this for very small changes in drum RPM), which is why it is referred to as an inertia type dyno. Once the HP is calculated, torque is calculated by looking at the "average" RPM of the engine the HP was developed at and running it through the HP formula. As you can see, it never "sees" the wheel RPM so the tire diameter has no affect on the HP measured.

Actually, I could make a case for a taller tire causing an inertia type dyno to give a higher HP reading than a shorter tire on the same car. It's just like making a dyno run in a lower gear (say 2nd gear), with more "force" available at the tire contact patch, the dyno drum is accelerated quicker. The percent increase in drum speed is about the same but it happens at a lower drum speed so the HP is about equal. But the dyno run is accomplished in a shorter amount of time (the engine goes from say 3000 RPM to 6500 RPM quicker), making the inertia of all the cars' rotating mass a bigger factor. I.E. more HP loss is experienced accelerating the cars' rotating mass on a shorter dyno run. Therefore, taller tires will actually give a higher HP reading by virtue of a longer dyno run.

The Scarab isn't running quite yet, I had a few medical setbacks at the beginning of the year and put the engine build ups on hold. The short blocks are together now and I'm starting to work on the heads. I had Comp Cams make some solid roller cams with some really interesting specs that pushed the limits of what they normally do (hint: they aren't off the shelf cams). I'm just trying an experiment to see if I can get 600 HP (per engine) NA without having to run dry exhaust like my other cams.