mdvaldosta

With your setup theirs no need to raise the limiter, your best off shifting at around 5500 rpm for best acceleration as is. If you get a supercharger or aftermarket cams then consider raising the limit. Max rpm on a NA 4.6 would be about 6500-7000 or so before you get valve float or other undesireables. With your current stock engine you'll make alot more power at 4000 rpms than you would at 6500 anyways.

budgy

Yeah I dont see a point in raising your rev limit more than a few hundred higher than stock, unless you get some heavy duty valve springs and a cam that can generate more torque at the higher RPM's it seems almost pointless. But what you are explaining as far as the car "bogging down" sounds like you bounced off the revlimit, basically all fuel is cut off from your engine, so it feels a bit like running into a wall.

JHonor

I'm not too sure about the 05's cylinder heads, but the springs they used in the 2 valve motors will cause you to float not to far after that red line, and you might want to be careful going over 6k, considering you have the cast crank and a set of connecting rods that are not really performance oriented at all; they're made to be cheap for production and fuel efficient. Mess with the rev limiter at your own risk, but 4.6s are expensive to work on.

BRENSPEED

Here is just some interesting information for you to discuss since you are on the subject of redline. I pulled some dyno sheets and on an 05 GT 5 speed with only an air intake running stock headers. It was pulled to 6,000 RPM's on the dyno. It was making the most power when it was shut down on the dyno. At 6,000 rpms it was pulling more power than any other time and about 10 MORE hp than at 5,000 rpms.

I am going to put one back on Thursday so I will run it up to maybe 6,400 and see what happens to the curve.

budgy

No doubt the car has the potential to make good power at higher RPM's, its just a question of whether or not your valve springs are going to be able to keep up with the workload. It would be interesting to see what kind of power the engine can make simply with valve springs and a re-flash redlining @ 7000.

BRENSPEED

OK Today I pulled the 05 on the dyno to 6,500. Peak power was at about 6050 and peak torque at around 4,500 rpm. At 6,500 rpms the engine sounded just fine and made about 8 HP less than at 6k. Ideally you would want your rpm's to fall back down into your area of peak torque when you shift. So is it worth spinning it that high? I guess only if that is what you need to do to drop back down into your best torque area when you shift.

On the street I took it to 6,800 which is where I have the limiter at just to see what would happen. It pulled just fine but would most likely be over kill. I will have to test that much rpm at the track Friday. I have been shifting it at around 6000 so far.

In short I think this thread was about valve float. I made 13 pulls today to 6,500 rpm on the dyno with no float.

budgy

So...no one makes a good street cam and higher operation valve springs?

Crazyhorse393

One of the biggest reasons for raising the limit is throttle response. Though there have been some here posting better power numbers over 6000, generally if you gain HP you will lose torque in the lower rpm band. Many times the trade off doesn't equate to better times in the quarter. Sometimes it does. that will be something you will want to consider. If you will be running it down the quarter all the time, the HP may be the best way to go. Around town, stop light to stoplight you might want to keep some usable power in the lower band meaning you may want to keep the torque. I have a 65 stang that I am building a 500+ horse 500+ lbs. of torque motor for. I could have easily built the engine in the 650 to 700 horse range but would have lost almost the same amount of torque in the lower band. Because this is going to be a car I drive primarily on the street my usable power was better suited down low. If I was going to primarily drag race it down the quarter, I would have gone with the higher HP numbers as that is where the car would be operating mostly.

Anyway

Throttle response on the new mustang sucks. Because it is the "throttle by wire" type it can't be thrown open as quickly as a linkage type throttle setup. By raising the rev limit it actually speeds up the throttle response on the car giving you a positive throttle feel that you are likely more used to. It slams open quicker.

The problem about raising rev limits is many times its not a threat to the engine as it may exceed the limits of the driveline or other parts. For example: I owned a 97 Cobra that had (I think) a 6800 limit. The engine was capable of turning revs well into the 8000 to 9000 range. However the T45 tranny that was in the car would struggle if abused at that RPM. In other words, some broke, and some didn't. But the bottom line is Ford didn't want to warrantee the car at higher RPMs so the engine was configured to produce it's best power at about 6000 or so.

So in my opinion, if I were going to change the rev limit, it would be for the throttle response. You will feel more on the "seat of the pants meter" from the improve throttle. The additional power is just an added benefit. I would not raise the limit higher than 6500. There is no power gain at that 6500 RPM, the only benefit is the faster throttle. The HP gains you will see will be lower in the band. You will still want to shift at the same point as before. Give ar take a couple a hundred Rs.

Good luck. Here is a little reading that might help your decision.

http://www.alternativeauto.com/prods...tang_tune.html

It looks as though the flash tune wil help the power band on the low and high end. Looks like a good part. But you would be paying for 93 octane from now on. That could add up to mega bucks over the lifetime of the car.

That's my .02.

don_w

Excelent post, crazyhorse.

The only part I might quibble with is: "...you would be paying for 93 octane from now on. That could add up to mega bucks over the lifetime of the car." Let's say 93 is 16 cents/gal more (that may be high), and you average 16 mpg (conservatively on the low side), then it costs you no more than 1 cent per mile extra. After 100,000 miles, it would cost $1,000 extra... spread out over probably 5 or 6 years. To me, that is well worth the performance gains. Minor point, but worth mentioning.

NCMustangMan

You might need to spend that extra grand on a new set of tires Don.