.....that's the Spirit....

 

My redline is set at 6500. This latest dyno graph only reaches 6345 rpm but I don't see a fall off either.

Les

 

Unfortunately, the horsepower number doesn't exactly relate to performance at that RPM as the figure has only a computational relationship with the RPM itself. The torque is the real power figure here. As in your graph, 5640 is about the area where your power starts to fall off.

For example, assume you're actually racing in the same environment, but have actual load applied. Where the car is pushing through all resistance and torque falls off, the car is no longer accelerating at the same rate.

Essentially, as those have said earlier, the extra revs are a point of diminishing returns.

 

Well, I don't completely agree. It depends on where and what your measuring. (distance/speed to complete the task) My torque has hardly changed and with the headers actually dropped with my modifications but guess what, I'm going down the 1/4 mile faster. Torque is the amount of work that the engine can do. HP is the speed in which it can be accomplished, at least that's how I understand it. So as long as you have enough torque to overcome the force of wind, weight, friction, etc. then the additional horsepower is going to make you quicker finishing the work. I think 300 ft.lbs. of torque at 6500 is plenty for our cars until reaching 170 or so. Am I wrong or understanding the same thing in a different manner? Diminishing returns I agree with but a lot depends on how diminished and where the goal is set.

Les

 

I haven't done the calculations with my car but it would also depend on the comparison between the stock redline to after gear change rpm torque average compared to the higher redline rpm to new higher gear change rpm torque average. Being the same would mean the higher redline would be advantageous.

Les

 

That's really a tough question, lots of variables at play. You could argue that given the drop in twisting force at the axle, your tires weren't being overcome. Could also be the time of year or even other mods, such as raised shift points.

While I think overall, our views agree, it all boils down to what you put on the pavement. Area under the curve is great, so long as theres traction.

But back to your statement: Do you have a pre and post header dyno sheet? Same dyno, and similar ambient conditions? How about the headers, were they installed in conjunction with other mods? Etc.. Etc..

 

To answer an earlier question, it looked to me as if things are forged, inside it is like a fine Swiss watch.

 

I meant to address this point earlier, but this damn phone keyboard kept miffing up my words, got distracted.

Anyway, higher shift points in and of themselves aren't necessarily bad. If set properly, they'll set the stage for your next gear to fall well within your tq&hp range, meaning you go faster (less time spent revving through the entire range).

I pulled off a similar feat in my 300-SRT, 12.3 @ 110 with just a base tune, 3200 stall, intake and DRs, 12.52 on street tires. The shift points gave me an edge over similar setups on factory shifts.

Sorry if I'm carrying on here, but I just wanted to clarify the things I've stated earlier.

 

I did a pre instal dyno, open header dyno and one with the stock exhaust reconnected. There was a problem with the software settings with the post instal dyno's so I threw them out and did about 10 more pulls the next day. Similar temperature, same dyno that I always use. Confirmed the results at the 1/4 and 1/2 mile. (4 hp) Now with a retune and raised rev limiter (posted dyno sheet) it seems much healthier and I hope to confirm the power this weekend, if the rain stops falling.

I really don't know much about torque vs. horsepower. All I know is the racers build and tune for HP and the torque is what it is. It's a good bet tractor pullers built for torque and the HP is what it is. I agree it's foolish to rev to 7000 rpms without beefing up the valve train. I'm nervous at 6500 and leave the car shifting at the stock redline most of the time.

Les

 

how do you "leave" this aspect - is it easily tweakable?

 

I have an Evotech TCM. When the transmission selector is in S it's 100% stock. When W is selected it's manual. I'm not liking the manual mode. I end up bouncing off the rev limiter too often. It's real difficult to time the shifts. It makes it easy to get a beautiful dyno graph from low RPM though!

Les

 

Thought about this for a mminute....
Why isnt the Rev limiter a basic?

L8tr....a couple of things.
- Its relatively easy: $900 and you have a swap in out TCU with S/W-manual mode to boot.
- Its as plug and play as a pulley change, you can switch back to stock with your old TCU in 5mins.
- If you're starting from basics (stock) - you really dont have to watch your AFR's 'cause your not "stacking mods"
- Assumption - You might not run into some of the walls that have challenged others with this mod when stacked with other previous mods.
- You gain ~10% more air at the top end (negating any significant drop off in VE).

Downsides that make it "non basic"?