difflvl

This dyno graph shows them running the motor to 8000rpm with some power drop.

http://www.gmperformanceparts.com/En...2397&engCat=ls

Does this mean the motor is good up to 8k rpm?

tomato

They may have simply extended out the trend lines. Either way, I would NOT run mine past 6500. As with all LS7 (stock) charts I've seen, HP begins to fall off after 6,250 or so. Why would you want to run much past that anyway???

dgdoc

Because even though the HP is past it's peak, it is still higher than when entering the next gear. To illustrate this concept, take a look at the HP of an LS7 at 7000 RPM and compare this to 5000 RPM and see which one is higher.

In order to get the best possible times from any car at the drag strip, you have to pay attention to the "area under the curve" and try to maximize the HP applied throughout the run. In order to do this, you will have to go beyond the HP peak.

BTW - The Rev-limiter on the LS7 is set to 7100 RPM.

aharte

To go faster... Shifting when hp starts to drop is not optimal when racing.

tomato

Can't aruge with that, but...I spend my time on a road course and not a drag strip, so techniques are different.

Does anyone know the actual RPM drop between gear through 4th??? Also, why don;t any of the dyno charts I see posted here show the shift points and associated "blips" in the graph? Do the new reports "smooth" them out??? The old dyno I ran on many years ago showed this, and it was helpful to see the time intervals during shifts to give you an idea on your shift speed or your autos efficiency.

jvp

Dyno runs for manual transmissions are normally only run in 4th (1:1) gear. That's the most accurate RWHP number. The "blips" you've seen in the past are still there, if you look at a dyno for an automatic tranny car.

jas

dgdoc

You calculate the RPM drop based on the gear ratios of the transmission.

BLU-BY-U

you can do that, tomato, but I assure you, at least for a straight line, you will go slower than someone getting right to the edge of the limiter. maybe for a road course guy like yourself, no big deal. it pulls awesome even to 6500

Painrace

On a road course time under the curve is not as important. Road racing means you want to be in the optimal gear all the time. That is why the top race teams have so many transmissions and rear gear sets. When I was racing we had a transmission for every track with different ratios for each gear. You want to be in the best power range ALL the time. Naturally, this is impossible. Therefore, rev chips are used to assure the driver does not over rev the engine during normal racing actions. Each transmission had gear sets that worked best for each track and each corner. It was always a compromise but the guys with the track specific transmissions and read gears almost always won.

UTVOL06

I know Ranger aims to shift at 7k rpms on the drag strip..anything less is "not a perfect pass"

dgdoc

Optimally, you'd pick your shift point so that your HP at the point you shifted was about the same as what it would be when you entered the next gear.

On a (stock) C6Z, even making your shifts at redline will still produce more HP than when entering the next gear at approximately 5,000 RPM.

Take a look at the HP profile from a dyno of C6Z to get a better picture of how this works.

glass slipper

Not really, the techniques are the same. If you look at running from one corner to the next or going down the straight as drag races, the same techniques apply. If you shift at 6500 RPM and I'm in the car next to you going to 7000 rpm, you just left HP on the table and I just left you behind. Quickest lap times will result when shifting at red line with few exceptions.

tomato

If you can drive this car at its limit on a road course, then put me down for a lesson. I'm close, but not quite there yet.

kelp

The dyno graph you referenced is an ad. You will find it drops off faster over 6500 than that "graph" indicates.

Ranger

To add a point of clarification.

Let's assume a proficient driver makes two acceleration runs, 0-130, identically driven except for shift-points.
One run he shifts at 6500 and the other at 7000.

Now, the 6500 run will be slower by about 4-5 tenths of a second. That's about five car length, a considerable margin.

If you think about some of the videos you've seen where the difference between two racers is a couple car-lengths, giving up five car-lengths due to short shifting is pretty much driver error.

Your dyno operator can print the results (or give you a file) in the form of a spead sheet with rwhp and rwtq in plain values at 100 rpm intervals. If you study those tabular data, you'll find that the rwhp value between 6500 and 7000 is higher than it is between (post-shift) 4700-5200. That was the point dgdoc made in post #11.

Ranger

glass slipper

Ok, here's your first lesson...shift at 7000 RPM. However, this lesson will be wasted on you as you've already stated emphatically you won't do it.

You asked why go past 6500 RPM, I simply gave you an answer.
I'm wasn't telling you how to drive your car as that's a personal matter and I'm not the one paying for it.

Read the last paragraph of Ranger's post above, that is the best explanation here. And again, it's your car, enjoy it how you want to as that's all that really matters.

PS I haven't met a car yet I couldn't drive past its' limits. Not that I'm that good, I'm just that stupid!

tomato

I don;t disagree with Ranger's or yours logic. My "argument" is that it makes a much bigger difference in a straight line versus on a road course - unless you are running for time or against equal cars/drivers AND can really take this car to its limit while maintatining control. It's easy to take a car to its limit for a brief period, but to do it throughout an entire session is another story. Additionally, I was curious what the RPM drop was post-shift, and, thank you Ranger for pointing that out.

Just to clarify, I did not emphatically state that I would not do it. Actually, I shift closer to 7 on the street. Road course I aim for 6500-7000.

Again, thanks for the tips.

Painrace

Well, let me add another 2 cents. The guys that run flat out on a road course all the time will be the fastest. If you are a half a lap ahead sometines finishing is more important than being the fastest. However, since braking is involved shifting at 7,100 RPM and then immediately downshifting and braking may not always be the fastest. Speed coming out of a corner is all important in road racing. If you watch video from inside the car you will see guys seting up for corners to maximize out of corner speed not minimizing time to and into the corner. You can give up time into some corners so that your exit is better and be faster. The overall objective is to be the fastest into and out of each corner and the fastest down each straight away.

tomato

Good points. Smooth in, fast out is key. And, again, Ihave met VERY few derivers that can truly run the Z at edge, mastering shif tpoints and heel/toe braking...

I'll steal a quote from another member...Let's stop "bench" racing and get out to the track!