Post by LRS getting 12.22 with minor mods.

http://www.allfordmustangs.com/forum...011-track.html

 

nice

 

Funny how the one guys said, "had to be 3.73's with those numbers" LOL
Actually he'd probably of gotten the same ET but a bit better trap speed with the 3.55's
as the 111.x trap speed meant a shift to 5th in the 3.73's which hurt his trap.
If the rev limiter was raised to 7300 rpms he might of gotten through in 4th with the 3.73's but crossing the line around 7200 rpms. In a 3.55 car he'd of been crossing in the 6800+ rpm range.
I'd put money on a 3.55 car accelerating faster at 6800+ rpms than a 3.73 car accelerating at 7200 rpms.

 

So far as most of the tuned 5.0 dyno graphs show, power was still increasing above 7000 RPM. Depending on proper flow modifications, that bet might be a bad idea.

 

At what "Minor Mod" point does it push the 3.55 cars into 5th gear?

 

Even if you did raise the rev limiter via tune to both cars, this ain't no M3 or M5 high revving motor that makes it's peak power 100 rpms before redline.
Tune for tune, you'd still make more power at 6800-6900 rpms than you will at 7200-7300 rpms.
Now if you change cams and other flow modifications as you mentioned, things might be different, but that's getting into a built motor scenario so those comparisons take on a different meaning than minor to moderate modded 5.0 that most will do if they plan on modding.

 

235/50R18 (761.9 rpm per Pirelli) + 3.55 = 115.1 mph @ 6850 rpm (Roughly 113 mph trap)

235/50R18 (761.9 rpm per Pirelli) + 3.55 = 120.2 mph @ 7150 rpm (Roughly 118 mph trap)

In really good air I expect to see stock 3.55 cars sometimes hit the limiter in 4th. However it will only be in the last few feet. Not unlike a stock 2005-2009 3.55 car in 3rd.

I believe a 500 rpm bump in limiter would give you more than enough room for CAI/Tune and Full Off-Road Exhaust Including Longtubes. Roughly 5-6 mph.

If you are going to run race type tires fine tune with tire diameter.

 

But I wont be shifting at the peak hp point at the strip. It will be several hundred over that. I if I remember correctly you should be about 8-10% over peak hp rpm at the finish line also. Its all about the power under the curve...not the peak. You want to minimize the rpm drops between shifts.
I would not be surprised to see 1st-2nd at 7400ish, 2nd-3rd and 3-4th at 7200. End of the track at 7500. I will know more in a few weeks when my car finally shows up.

Can I get a seasoned racer to explain this better? Bob? Anyone?

 

For drag racing, you absolutely want to shift several hundred rpm above peak HP. Exactly how much will vary, and depends upon the shape of the HP curve, tranny gearing, and driving style (ie...how long it takes you to begin shifting once you know it is time, and how long it takes to actually complete the shift). 600-800 rpm above peak is probably a good starting point, but that will vary based on the above, and also with each gear change, as the percentage drop from 1/2 is different than 2/3 which is different from 3/4 and so on.

The bottom line is you want to maximize average HP in each gear. With a 6600 rpm HP peak and a stock 6850 rpm rev limit, the 5.0 is pretty handicapped. In fact, if I could only do one thing with a tune - and one thing only - it would be to raise the limiter to 7500 rpm.

EDIT: Based on the stock dyno graphs that I've seen, the HP on internally-stock 5.0s do start to drop beyond ~6600 rpm (as they should), and actually, they do it fairly quickly. However, it is likely you're still making more power at ~7400 rpm than you would be at whatever rpm in end up in immediately following a gear change.

Maximize average HP in each gear......

 

Thanks Bob,
That's what I was trying to state earlier. As more people get experience behind the wheel we will end up getting the right recipe for good ET's. It's a little early to tell just yet.

 

CAI/Tune with 500 rpm Limiter Increase (7350 Soft / 7500 Hard). This is why you have to spin past the power peak for optimal acceleration. This is for the 4-5 split but doesnt take into consideration the extra power consumed by the 1.32 gear set in 4th.

7350 - 270 t / 378 hp
7250 - 280 t / 387 hp
7000 - 300 t / 400 hp
6500 - 325 t / 402 hp
6000 - 350 t / 400 hp
5500 - 375 t / 393 hp
5000 - 390 t / 371 hp

1.32 x 270 = 356 t (After Trans) at 7350 rpm.
1.00 x 370 = 370 t (After Trans) at 5600 rpm.
It appears that 7350 rpm is to high a shift point.

1.32 x 280 = 370 t (After Trans) at 7250 rpm.
1.00 x 375 = 375 t (After Trans) at 5500 rpm.
It Appears that 7250 rpm is still to high.

1.32 x 300 = 396 t (After Trans) at 7000 rpm.
1.00 x 385 = 385 t (After Trans) at 5300 rpm.
It appears that 7000 rpm is to low.

In real terms if you could pull the line by the limiter at 7350 rpm you would likely lose less time staying in gear than shifting. If not you would want to shift about 7200 rpm. Horsepower is essentially just shorthand that tells you how much total torque you can apply. IE Engine Torque x Gear.

 

With this transmission, the 3/4 and 4/5 gear changes would be the lower rpm shifts. 2/3 would be higher, and 1/2 would be the highest due to the larger spread between the gears.

If my math is correct (not always a good assumption), shifting from 1st to 2nd at 7350 drops you down to ~4900 rpm, which using the data Gene gave, means optimum shift point for the 1/2 is actually a bit higher than that. On the 2/3 gear change from a 7350 rpm shift point, the rpm drops to ~5000, so the same thing applies.

Conversely, for the 3/4 gear change, if I'm shifting at 7350, I get an rpm drop to ~5800 rpm when I hit 4th, so it is with this gear change that I would actually shift at the lowest rpm.

Interesting stuff with this MT82 when you sit down and do a bit of math...

 

I think there's a bit of confusion as to the points I was making.

With the 3.73's even a stock 5.0 in sea level or below DA's require a shift to 5th to complete, or you bounce off the rev limiter which does nothing but hurt times and traps.

With a 3.55 car that's not an issue stock or even lightly modded (intake, tune, and maybe even exhaust).

So say in two identical cars that have an intake, tune and exhaust, but one has 3.55's and the other 3.73's.

The 3.73 car will no doubt HAVE to shift to 5th to finish, even with a rev limiter raised to 7300 rpms.
The 3.55 car however, with the same mods and the rev limiter raised to 7300 rpms should easily still finish in 4th gear (and probably be right near redline when it crosses the line).

There is no doubt that a 3.55 car in 4th spinning at 7000 rpms will be making more power and speed than a 3.73 car in 5th spinning at 5000 rpms.

So in the last bit of the 1/4 mile run the 3.73 car needs to use the time consuming and power robbing shift to 5th to finish, whereas the 3.55 car will be finishing the last bit of the 1/4 mile in the top part of 4th.

True all else being equal the 3.73 car will accelerate a bit harder in each gear, but it should be minor amount and then you have extra wheel spin to deal with at the launch and especially when hitting 2nd gear. Sure the 3.55 car will still have to deal with the same, but it will just be to a slightly lesser degree. Less wheel spin at launch and less wheel spin hitting 2nd means more power to the ground, which = faster acceleration.

The gear ratio is not that much we are talking 3.73-3.55 = .18 so acceleration wise it's not like it's a major difference. To me the biggest difference between the two when comparing 1/4 times is the need for the 3.73's to have to shift to 5th. Though scant, there is that additional .1-.2 seconds where there is no power being put to the ground while the 3.55 car is still putting power to the ground and then the following .1-.2 seconds it's in 5th while the 3.55 car is still in the harder accelerating 4th gear.

I think ET's will be very similar for both, but the 3.55 car may have a trap speed of 1+ mph faster. Clearly testing will be necessary to verify facts however.

 

Bob. I take it you noticed the 28% split on 3/4 as compared to the 32% split on 4/5 to. Unusual to see a reverse split like that (OD Cruising Gear excepted). I get the feeling the Engineers specified the 1-4 gear ratios for optimal acceleration and just let 4/5 end up being whatever it was.

3.73 is a good gear on a stock car if the air is suboptimal. In great air I think the 3.55 will be the gear but thats yet to be proven, At the current time the fastest showroom stock car (I know of) is 12.5 @ 112 on 18" All-Seasons and 3.31 at Atco.

 

But keep in mind Gene, most of that is just because it's ATCO.
Which is one of the fastest (if not the fastest) track for times in the country.
Has any 3.55 or 3.73 cars run there yet because I'm pretty sure both 3.55's and 3.73 cars will be faster, but either way ATCO's times/traps are always a few tenths and a mph or so faster than most.

 

Concur Gene. And BTW....I'm a bit hard-headed sometimes (understatement), but you convinced on the stock 3.55 idea some time back.