This ought to create some heated debate...

Being new to this forum, I have spent the better part of 3 months reading all the information that I could about improving the overall performance of the C6.

I have taken some of that advice and my car "feels" like it runs better. But...having an engineering background, I am aware of the subjective nature of "feelings" and how they can distort reality. (IE: An exhaust mod may make the car sound faster, more powerful etc., but have no objective effect on the cars HP or performance.

So, I would think that the only OBJECTIVE way of determining HP improvements would be on a DYNO, preferably the same dyno each and every time a mod is made in order to minimize variables.

I have read some threads where members have made the argument that DYNO numbers don't mean anything, it's how the car performs on the track that counts.

But... isn't track performance affected by so many potential variables (primarily human) that making claims of actual HP, torque or overall engine improvement almost meaningless?

 

I believe that Occums razor centers around the most simple explanation???

It ain't all about horsepower. Especially if you are talking about other forms of competitive driving besides straight line ie drag racing.

The Lotus Elise does not produce half the dyno number of a C6, but on a road course it will give a C6 all it can handle.

Dyno numbers are fine, but if given the choice, I'd rather have good track numbers as opposed to good dyno numbers.

 

Try putting some 390 gears in your car. No dyno effect but your SOTP and track times will be very happy!

 

imo, it really doesn't matter what method you use to measure your performance / gains as long as you use the same method process for each consecutive measurement.

 

When strictly discussing performance at the track, I heartily agree. However, most discussions center around how to effectively improve performance of the machine.

My assumption would be that an experienced driver will have faster times at the track driving a car with an engine that produces 400 HP than one that produces 250 HP.

Conversely, an experienced driver with a 250 HP vehicle might perform better than a novice driving a 400 HP vehicle.

For instance, you undoubtably have more competitive driving experience than I do. Consequently, if each of us drove my car at a track, you would likely produce a better time than I would.

So, track times are dependent on other variables beyond the car. Is that a fair assessment?

 

If some of the threads that I have read are correct, there can even be significant differences in HP measurement between different DYNO manufacturers. Consequently, one would really need to gauge each performance modification on the same machine to "keep it real."

 

When you say "track" do you mean drag strip??? Because if you do, then all bets are off. I have already pointed to the Lotus Elise.
http://forums.corvetteforum.com/show....php?t=1515476
The Lotus Elise does not have nearly the horsepower of a C6, but with a competent driver can more than hold it's own against a 400hp C6, also piloted by a competent driver, on a road course.

Like I said, it ain't all about horsepower.

As you can see from the above link, on a road course, that same competent driver could take a car with considerably less horsepower (and hence dyno numbers) run it, and then get behind the wheel of a car with considerably more power than the first car, and not do much if any better in the second car than he did in the first.

On a road course its not necessarily all about horsepower/dyno numbers. Now if you are accelerator pedal mashing an automatic down a drag strip, and going along for the ride, then perhaps it is.

Indeed it is but in any track comparison its best to assume equal drivers or at least competent drivers.

A poor driver can run poorer times in a 505 horsepower Z06 on a drag strip or a road course than will a skilled driver in a 405 hp C5 Z06 in either venue. Does that mean that the 405 hp C5 coupe is on par or "better than" the C6 Z06 performance wise?

The results would not be a reflection on the performance capabilities of the car, but rather the performance capabilites of the drivers.

 

The dyno just like any other tool you have is just that a tool. The only real objective measure though is the track.

 

Clearly the best thing to do is install the parts in Forza (xbox) and then do some laps and compare times.

 

I agree the dyno is great for measuring HP improvements. But for measuring performance that must be done at the track. Personally I could car less how much HP my car has. For me the dyno is for tuning.

Also if you know the weight of your car you can measure HP from your trap speed.

 

A dyno removes some variables such as driver experience,weather,track prep. It can also isolate some variables such as fuels,oils (not just engine),state of tune. This is where the dyno shines as being a "tool."

Dyno~tuning is the only way to fly!

 

Dyno tuning is good, up to a point. Advantage is that it provides a direct before/after comparison under similar conditions, so you can immediately see the results of any mods, or tuning changes. Disadvantage is that the conditions inside a dyno shop are not the same as outside at the track. You can't simulate the airflow at 110+ MPH, so your A/F mix could be different. Also, the car gets hotter more quickly, and stays hot longer in a dyno shop. I have seen many cars on the dyno start to lose power after a few pulls because the cats got too hot, and the ECM detected the cat overtemp and started adding fuel to cool them off. That doesn't happen so much at the track.

Another issue with dyno results is that too many guys only look at the peak HP number, which is of limited value, and is only useful for bragging rights. You can have two cars that both make 400 HP, and yet at the track one will outright stomp on the other. The key number to look at is average TQ, or the "power under the curve". For example, compare a heads/cam car to a Maggie-equipped car. The Maggie will never produce big HP numbers, because the blower case is relatively small and will only pass a certain amount of air. But it produces monster TQ. It will eat up many cars that produce far more peak HP, with ease.

Dyno tuning is very useful, which is why every NASCAR tuner uses them, and many performance shops spend big buscks for them. But you can't simply take the peak HP number from a dyno pull, and use it to accurately predict track performance.

"SOTP" tuning is almost useless. Some guys could install a new cigarette lighter and report that the SOTP feel was improved. 'Nuff said.

 

What has been confusing to me are the posts that show an increase in engine performance (be it a tune, CAI, cam etc.) on the dyno, yet there is a decrease in performance at the track.

A recent thread where a tune was done to the car which showed improvement on the dyno, but the poster was un-happy because his times at the track (drag race) were worse than before the tune.

The poster was quick to blame the tune. Yet from my perpective, the engine tune was about the only "concrete" item in the mix. everything else involved in the race (down to lane choice and baromateric pressure) were variables which would be difficult to duplicate each time one races.

However, I am the first to admit that I may not understand everything involved. I am just trying to understand the best method to use in order to determine whether any improvement has been made to the engine, whenever I make a mod.

 

It can be very expensive to do one mod at a time just to track performance improvements. I have found it cheaper to gain knowledge right here on the forum on what works and does not. Then I do my mods all at once, one dyno tune and done.

 

I can tell you what I used to do.

Whenever I made a modification to the car or the tune, I would take it to the track (drag strip) and run it. I would take note of the weather conditions for the time I ran and plug them into http://www.modulardepot.com/density.php

I would use time slips which were similar in 60ft time. For example, if I ran the car last weekend, made say 4 passes, I would correct all the time slips using the site above. This weekend, I would make more runs, sometimes less than 4 sometimes more than 4 and correct those too.

I would then compare the ones from last week to this week which had the same or very close to the same 60ft times.

My car was an automatic so driving variation was minimal. I ran the same tire pressures in the fronts adjusting only the rears and rarely doing that. I would try to run with as close to the same amount of fuel as possible, I never ran on more than 1/2 tank and would usually run on 1/4 tank and wind up needing gas for the trip home.

Luckily a gas station was about 1/2 mile down the road from the track. So when I left, I'd hit the gas station, re air my tires and head home to crunch the numbers.

By now, you can figure that raw numbers ie what the car ran last week, vs this week, solely for comparison sake mean little to me. Which is why that 1/4 mile list is IMO, of limited value.

Comparing the corrected numbers of timeslips with similar 60ft times gave me the best evaluation of what my modifications had gained me.

 

That seems to be a reasonably scientific way of comparing "apples to apples" giving you pretty accurate info and removing or compensating for variables.

I like it.

 

I guess my intent is to find the best way to cut through the "hype" of what each mod will do vs the reality.

You know, if you add the HP "claims" of each potential mod to your base vehicle, you could conceivably have a 600 HP motor with just "bolt ons." (Maggies don't count)

 

True, if you hang out here for a while you get pretty good at weeding out the BS.