Why is the dropoff so great between HP/TQ at the crank and at the wheels? Advertised is 287hp and rwhp is 220-230. Same thing with torque. That is a huge dropoff in power.

The WS6 has 325 and rwhp is around 305-310. This is a lot more reasonable.

Why are we having such a large drop?

 

dynos stock are looking more like 230-240.... Every car has a loss from the flywheel(287) to the wheels(230-240?) through the tranny, drivetrain, etc... If I am right I believe that FWD vehicles lose about 15-20% RWD lose about 20% and AWD around 20-25% to the wheels. All cars advertise the HP at the fly.... for example the RSX type S advertises 200HP but when dynoed is really about 170 give or take a few HP. It's not just the VQ's its all engines.

 

Yeah, you could say that! Most all chevy's are. They are smart that way.

 

Actually, the reason the FBodies were under rated is because there's no point in paying 45k for a Vette when you can get the same power from a Camaro or TA for less than 30K?

You'd be surprised how many people didn't know the two cars had the exact same engine.

 

Yeah plus Ford had some problems with the Cobra that they claimed put out 305 HP but it didn't. Better to underrate than overrate. With the Z you are seeing a true rating and true loss of power as a result. 17% drivetrain loss is avg. for a RWD car so we are ok. We just need to figure out how to actually make some power...

 

I actually dynoed at 246. What I want to know is why numbers are all over the place. I figure any set of engines should dyno within +-3%, is that fair? But I've seen from 220 up to 246-8. That's more like a 6-7% difference.

 

Different dynos, different conditions, different testing situations. There are few controls between what people are dynoing across the country.

 

The dyno's used by speed shops are not particularly accurate. I never heard of any speed shop owner actually calibrating one of those things. Engine manufactures and laboratories like SouthWest Research that do EPA certification spend a lot of time and money making their million dollar dynos accurate and repeatable. When I did diesel engine developement 25 years ago we could get the same engine to measure within +/-1% in 2 different test cells but only after rigorous calibration.

Also, there is a pretty good spread in engine output with all the hundreds of tolerances on all the parts that make up an engine and drive train. Thats why show room stock racers blueprint their engines. If you get all the tolerances to add up on the plus side for power output you can have a "stock" engine that puts out significantly more power than one assembled from random parts. Additionally, there is definately some breakin going on. Most cars today perform better after 10 or 20 thousand miles than they do new. A lot of the dyno curves published were on engines right after they got through the 1200 mile breakin period.

 

I've seen the term bluprinted used in lots of auto mags and never seen a good explanation of the process. How is it done and how are tolerances checked.

Also, it would seem to me that there are about a gazzillion variables betweeen dyno runs that would explain differences of 5% or more - temperature and fuel being biggies.

 

to be honest... Ive been in a plant, and for the initial runs, they are really still figuring stuff out... as in the grinding wheels they use to grind the cam shaft and all sorts of other engine components can wear down too quickly and throw off the measurements eventually they get it all set of properly, but at the beginning the peices can come off differently. they keep them within the allowable tolerances, but that can lead to slightly different numbers.

of course conditions and equipment can vary as well.

 

are there any mods that can be done that minimize this loss?or is it that these mods are too expensive to be worth it?

 

Yes and Yes. Basically look at any component between the engine and the wheels to help improve efficiency. We already have a Carbonfiber driveshaft so the only things left are Fly wheel and differential and to a small extent fluids.

 

Isn't the Pontiac a live axel car? The Z is an independent suspension. The Z has 4 universals of loss in the rear end.

 

TRUE!

On the difference in the numbers:

The difference is caused by a number of things. When a car manufacturer dynos the car at the crank (pretty neat process) they're getting power RIGHT FROM the engine. The engine is doing no work (i.e. moving a car) other than turning a crank. Put on a transmission and now you're moving an entire drivetrain. Add accesory items (i.e power steering, air conditioning) that require belt driven power and you lose some more power from what the original crank number was. Long story short: The dyno we run on takes power readings from the wheels (loss of power because of accessories and drivetrain (transmission)) the car manufacturer's take their readings from the crank because it is a constant value that has a controlled reading. If they took readings from the wheels there's ALL kinda of things that could factor in and make the numbers change. Hope this helps some.

FWD cars lose less because their drivetrain isn't spread from a transmission to a differential. Tha tranny does the work.

RWD loses more because the power is sent through the tranny to a differential gear to move the power to the wheels.

AWD loses the most (but makes up for this as it can transfer more of the left over power to ALL 4 wheels and make for some GREAT launches.) because of it turning a differential and a crankcase.

 

Changing your fluids (oil,diff,trans) to some high-end stuff can help a bit with drivetrain loss. I noticed a slight increase in gas mileage when I changed from regular/dealer oil to Mobil 1.

 

I COMPLETELY overlooked this post. My thoughts:

Lightweight underdrive pullies (i.e. alt./power steering/etc.) ,lightweight crank pully, lighter flywheel, transmission regearing, differential 'tweaking'. Just to name a few. I KNOW alot of these parts aren't available YET, but I can almost gaurantee you they will be out soon.

 

Don't forget lighter rims! And not stepping up rim size will help too!

Ben

 

VERY true. an 18 is IDEAL for the Z's going bigger messes a bit with the performance. As was mentioned, if you can take 6 lbs. off each rim and 2-3 lbs. of each tire yer gonna get alot more on the road.

 

correct me if im wrong but i thought we had a carbon fiber reinforced drive shaft i went under my car and it looked like the carbon fiber was wraped around the drive shaft

 

Key word, reinforced, huh?