Hi Everyone,
Taking my vette for its first dyno tomorrow and was wondering what kind of numbers do you think I will see. It's a '04 C5, 350hp stock, and then I have added a Magna cat-back exhaust system and a Callaway Honker C.A.I. system.

Just wondering. It feels really quick, but have no idea how what it feels like translates into hp here in the real world.

Thanks in advance.
Take care. Stay safe.
RJ

 

Well, it's going to depend on the type of dyno, if its run tight (say NaSCAR certified calibration) or loose (some shops like to make them a bit optimistic to please customers), but if its a well set up Dynojet then I would expect about 315-320. The honker won't help much on the dyno (its ram effect only works when the car is really moving, ), and the cat back ought to be worth about 7-12 over the stock 308ish range for an M6 or about 290-295ish for an auto.

 

Thanks so much.
I wanted to have realistic expectations going in. I mistakenly thought if it was 350 stock the number would go up from there.I'm not into racing, just love feeling the power.

Will be sure to post the result for anyone interested.

 

350 is the factory rated horsepower (often called flywheel HP). To measure that you have to remove the engine from a car and mount it on an engine dynonometer, which is expensive.

The rear wheel dyno test measures what comes out to the rear tires after passing through the clutch, dirveshaft and its joints, transmission, differential, and the rear axle shafts, and includes the loses in the tires, too (think tires don't absorb a bit of power? Feel them after you've driven hard sometime, they are hot -- where does that energy to heat them up come from? Ultimately, from you engine).

Generally, GM M6 cars loose about 12% and automatic trans cars about 14-15% of their power: my Z06 (405 HP rated fromt he factory) made 357 RWHP in a test of a certified dyno when tuned up and broken in 5000 miles. A stock C6 with the manual 6-speed makes in the range of 350 RWHP, the ZO6, about 445 or so. 350 HP C5s made about 305-310 RWHP with the M6 and around 10 Hp less with the auto.

 

That is all so interesting! Thank you very much for taking the time to explain the difference betweenrwhp and fwhp. I've learned fromthis board that the fwhpis always higher than the rw,and now know why. Ithought the tires got hot due tofriction with the road (and that's probably part of it) but never thought aboutthe power loss aspect of it. Very interesting.

Thanks again for your time and this info.

 

Yeah, the tires get hot due to friction with the road, but think for a moment like a physicist: where does the energy come from to overcome all that friction? The car's engine provides the power for all of it. When a car moves, or is turning the rollers on a dyno, the tires flex, bending and twisting their cords and synthetic compounds as they roll, and that takes quite a bit of power to overcome (if you ever have push a car by hand on a flat road even a few hundred yards you will know what I mean). The engine provides the energy to overcome that friction and all that energy of friction ultimately translates into heat: the flexing and bending of the tire tread is converted into the heat, most of which, as you drive, is lost to air flowing over the tire and cooling it a bit.
Similarly, all the other loses between the 350 HP at the flywheel and the 310 at the rear wheels convert to heat, too. I don't advise ever feeling a transmission after you have driven hard for a long time (you can mildlyburn your fingertips), but the reason that the transmission and the differential get hot, and that some cars have transmission oil coolers and almost all transmissions and differentials have cooling fins, is because the friction in the gears and bearings, which the engine overcomes just like the tires, converts to heat.
Ultimately, all the energy lost between the flywheel and the road is converted to heat somehow, and then lost to the air flowing over or under the car, etc.It represents alot of energy: at full throttle that is about 40 HP (350-310) which translates to just under 30 kilowatts of energy -- so the heat loses ona a C5 topped out at 175 mph are the equivalent of twenty 1500 watt portable electric heaters! the car doesn't melt because air at 175 mph does a lot of cooling. More normally, running down the street at 40 mph the car is putting about 15 HP to the ground and losses (say 12%) are about 1.8 Hp or the equivalent of 1340 watts - less than one portable electric heater, but still enough to make tires, transmission, etc., noticeable warm after a few minutes.

 

Thank you so much for thisdetailed information and more importantly your valuable time. The more I am learning aboutcars the more fun they are to drive - and I didn't think that was possible.

Unfortunately, over the years, I have pretty much done everything you've suggested I don't try:
-did try to push a car once - afew moons ago, my VW Bug, and without much success,
- and did slightly burn my hand on the inside of an engine.
Live and learn.

I'm looking forward to getting dynoed.A friend (true car enthusiast) referredthese guys to me and I am hoping they are fair and honest. Will be sure to post my results.

Again, many thanks.

 

question ? lee willis . what would you do with a 04 auto with a 3:15 rear. to get more hp to the tires. air intake and exhaust. what after market would you change to?

 

Start with the usual. Cold air intake (it doesn't matter that much which brand ), say $500. Long tube headers if they are legal where you live ($750), short tube if not ($600)and a cat back exhaust ($500-$100 depending). Get 1 3/4 inch diameter header tubes -- do not use 1 7/8 inch on a near-stock engine.

Then, find a good shop with a dyno and ECM (engine control module) re-programming capability and have the car tuned to run best with the new parts ($500). You should pick up about 25-35 RWHP for all of the preceding.

Beyond that, for further mods, you need to have a long-term plan: cold air, headers and a cat backfit within any plan for more power from mild to wild, but beyond thatparts you buy could later be unnecessary if you don't plan ahead.
1) Inexpensive. You can add high-ratio lifters (and I'd replace the valve springs and retainers, too, if the engine has many miles on it) and pick up another 10 RWHP for about $500. This is partly a dead end, though: you can't go to an aftermarket cam or heads and cam kit without going back to standard ratio rockers.
A FAST intake manifold(smallerof the two sizes will work best of stock displacement) and a ported throttle body will add maybe another 5-7 RWHP. Say $750 more.
2) An aftermarket cam, along with the manifold and throttle body, might add 25 more RWHP. With labor this will cost a bit more than (1) above but you'll get maybe 25 more RWHP rather than about 15 more.
Anything beyond this gets into serious money. You can do a heads and cam kit: maybe $2500-$5000 depending for 45-50 more HP, or a supercharger, $5500-$10000and get 100-150 more. Or a stroker engine ($4500-$35000 depending and get from 35 RWHP to 200 more. Or all of the above for even more $$, for even more HP.

 

Rita, just to give you a good example - my 01 produces 320 RWHP and approx. 343 lbs-ft of torque using SAE-correction. Using STD correction, those numbers become 328 RWHP and 352 RWTQ. (My torque output is actually higher than most stock 02-04 Z06's torque output - I guess I'm lucky!)

My stock numbers were about 308 RWHP SAE and 313 RWHP STD. I can't recall the stock torque. However, I do know that a simple intake and cat-back swap ganed me about 12 RWHP. From what I've seen, the cat-back alone adds only 1-2 RWHP. Dyno tests are normally performed with the hood opened, so having a true Cold Air Intake vs a warm air intake will not make much of a difference (for this type of test). However, either type will boost RWHP by about 10.

Your CAI intake will guarantee you that your added HP will not wither during slow-moving or stop & go driving conditions. This is good!

By the way, which dyno shop are you using? I've used the Dyno Shop in Santee.

Dave