BLKCLOUD

Fabulous! MOST impressive shifting! And God bless you for running a good gear and not being afraid to wring the motor's neck in the lights. Not sure how safe 7600 rpm is, but the drag racer in me LOVES it when someone crosses the finish line ~1000 rpm above peak power.

Good job! Errr....GREAT job!

Driver72

Well confirmed tonight, 119 mph in 4th with 3.55's when the redline redlights light up on the dash. Held it there for 3-4 seconds and the speedo is just under 120 mph.
That means good for traps of roughly 116-117 mph.

I should of checked but if stock traps are roughly 112 mph, I'd guess that's about 6600 rpms when you cross the line. Isn't peak hp on the stock motor 6500 rpms? So with the 3.55's on stock power you are going through the 66' trap speed box right at peak hp range and crossing the line just after peak hp. That seems pretty ideal to me.
It would be interesting to test/check but I'd say a 3.55 car is accelerating harder at the engines peak hp of 6500 rpms than a 3.73 car is at 7000 rpms when it's got less power going to the wheels.

So then with intake, tune, exhaust, etc that's crossing the line around 6900-7000 rpms.
Hot ****

And with the tune's ability to raise the rev limiter to 7200 rpms the 3.55's should be good for about 123 or so mph (traps of 120 mph), you could have a 500 crank hp GT and be crossing the line at 7200 rpms in 4th with the 3.55's.
Me likey.

Long Stroke

Thank You for the Kind Words Bob, means a lot coming from you.

I've got a lot of Respect for a fellow gear banger!

Thanks again!

BLKCLOUD

For optimum ET (not necessarily optimum trap speeds) you should cross the finish line several hundred rpm above peak HP. 600-800 is a good rule of thumb to start with, but it really depends on the shape of the HP curve. Go watch a serious drag racer...pay attention to their shift light. You'll typically see it come on in high gear WAY before the car hits the final beams.

The 5.0 makes peak power at 6600 rpm. Yes, a car with 3.55s is probably accelerating slightly harder at 6600 rpm than a car with 3.73s at 7000 rpm (though I'd have to do the math to be sure). However, for ET, the last couple hundred feet just don't make much difference. A much bigger deal is the first 60 ft, 330 ft, and 1/8th mile.

That said...if trap speed is your thing, then ya, I'd probably want to go through the lights very close to peak power.

Scott....be real curious how that MT82 holds up to your abuse. I'm seriously considering either a 5.0 (GT or Boss) or perhaps a 08/09 Vette after the first of the year.

Long Stroke

Bob, you are right on the money.

Say the car drops 1500 rpms in between gears shifts. If you shift at 7000 and it drops to 5500, then take several HP points in between those RPMs and get your Average HP.

Then do the same for 7500 - 6000rpms. Do the math and see what your average is HP is.

For Best ET you want to keep the car in the RPM range that produces the best "average" HP.

Bob, go for the 5.0, you will not be dissapointed!

Driver72

Yeah I'm not so much about ET personally. Yes i do like a good ET, but to me traps are more important? Why well because more often than not if you cross a dude on a road course, a private road or "somewhere in Mexico" you are rolling already, so your time from point a to point b is not as important as your speed from point a to point b.

Further, even as you that's it best to cross the line 600-800 above peak hp.
That would be 7100-7300 rpms on the 5.0 (peak power is 6500 rpms)
And as I pointed out if you are going to mod the car up in power to say 500-520 hp, you very well could have traps in the 117-118 mph range (or crossing the line at 120-121 mph).
That would be done on a 3.55 car in 4th at around 7100-7200 rpms.
Right at the perfect 600-800 rpms over the peak power (which on the stock motor is 6500 rpms and probably still about the same on a modded car unless cams are added).
So correct me if I'm wrong, but would not that be perfect?

Also again, I'm a street tire guy too. But even with DR's if say on the 3.73's you can launch at 4500 rpms max before spinning, with the 3.55's you would probably be able to launch at 4800-4900 rpms before spinning. So you have a launch with higher rpms that's closer to the higher power. Further, if say on 3.73's you spin 4-5 feet going into 2nd with 3.73's but with the 3.55's you spin only 2-3 feet you are actually putting more power down with the 3.55's and therefore accelerating faster with less spinning.
This may not be an issue on a track that's really sticky or on slicks but those of us who like to run street tires, it makes a difference.

Lastly, there's another reason or two I got the 3.55's as well.
I know I've spoken to a few guys who on earlier Mustangs and stated the shorter gears didn't make them any faster on the street and you go through the gears too faster. And having slightly taller gears allows you to stay in the lower gear a bit longer and also therefore in the power zone a bit longer too.

But as you both stated, with increased power you often want the slightly taller gears. I've been considering putting the supercharger on in the future and in that case, there is no doubt the 3.55's are the best ratio for that power level.
The reason Ford puts the 3.55's on the GT500. And they've stated the only reason they put the 3.73's on the SVT PP is simply because the rear 20" tires are actually a bit taller than the 19's so they did it so it actually makes it the same gearing as the 3.55's on non SVT PP 19 inch wheel.

In any case, I'm actually running about 3.60 gears as I have 285/35/19's on that are a bit shorter than the stock 255/40/19.

I'll do some tests soon and let you all know. I could be totally wrong or completely right. It also may end up being a complete wash and they be equal.
Cheers guys, sorry to derail the thread.

Driver72

Scott, from what I checked the other day the rpms dropped just 1000 rpms between 2nd and third gears on a 3.55 car. Shift at 7200 rpms would put it at 6200 rpms from 2nd to 3rd. Thats pretty darn good for a car whose peak hp is at 6500 rpms.
Not sure what the drop is from 3rd to 4th and then from 4th to 5th is

I'd have to do the math.

I'm also going to (as I usually always do) dyno my car baseline and then after each mod to see actually where the best power curve is stock and after each mod.


What's also interesting about all this gearing talk is there is at least one guy with a stock 3.31 car that ran around a 12.7 at 112 mph. Every bit as fast as any of the 3.73 geared cars.

Long Stroke

Might of been me. But I only went a 12.93 Bone stock with 3.31's. But then tune and CAI I went a 12.45 @ 115. Then slapped on the Nittos and went a 12.23, still with the 3.31's. All on the EXACT same night too. The 3.73's with no other mods got me to the 12.13 (terrible weather, 98% humidity), then we bumped the rev limiter and in better weather went the 11.96.

Good Tech in this thread guys.....

cgjarvis

From what I have always read, a steeper gear will give you better control over wheel spin
than a taller gear. (IE..Once a 3.31 spins, it is harder to recover than a 3.73..... Correct?)

Sure, on the street it's easier to spin a steeper gear, but easier to modulate than a taller gear once traction is broken. Where is the physics major when you need him/her....

Long Stroke, I wonder how your car would do with a taller slick? 28x10 or something?

BLKCLOUD

To their own, but I'm not a street racer and sure don't care about doing 120+ on the highway. If I did, I would gear the car for top speed. What gear would that be? Nobody here knows.

What tire size? What does the HP curve look like? Have you calculated average power in each gear and run an acceleration program to get an idea of exactly what gear would be best, then chose the closest available gear ratio?

We can go round and round in these circles. You like 3.55s - great! You don't need my justification nor anybody elses to prove to yourself (and perhaps others) that you made the best choice for you.

Personally, if I were never going to raise the rev limiter in my car, and always run on hard-compound street radials, I'd get 3.55s too. Other than that? Forget it.

Ok. I'm glad you got the gear that you like. We're all happy!

Uncle. I'm glad you like your gear choice, and it probably wouldn't serve any usefull purpose replying to the rest of your post.

Enjoy your car.

BLKCLOUD

You might want to do the math. Shifting at 7200 rpm from 2nd gear (2.43) into 3rd gear (1.69) will give you an rpm drop of approximately 2200 rpm (7200 - ~5000). Further, rear end gear has ZERO effect on how much rpm the engine will drop between gears. That is 100% determined by transmission gearing.

Not surprising. In fact, there are many of us that think the quickest bone stock 5.0 will have 3.55 gears.

Driver72

Thanks Bob, you are correct, to each their own, and that's why we have options, so everybody can get what suits them best.

Cheers.

BLKCLOUD

Indeed!

Long Stroke

Now I want to throw mufflers and a bottle on it!!

Ltngdrvr

Leave the bottle off, anyone can go fast with a power adder.

Long Stroke

Huh? Why did you bolt up a supercharger? Anyone can go faster with any type of modifications....

I just grew up with a 5.0 and I needed a Healthy shot to get the stock long block into the 11's back in the day. Since the 2011 is so impressive from the factory I'm curious what a nice 125-150 shot would do...

Ltngdrvr

I did it mostly because nobody believed that I could do a all custom built blower install all by myself on the V6 and make it work.

I took it off a while back so I could go back to using horse-**** gas.

Nitrous is for those who just want the cheap out.

Put a power adder on it, just make it a supercharger...

Ssgthooligan

****, guess I need a tune. With 295/50 drag radials on my 13 Gt/ track pack I ran 12.72 @111 mph. My only mods are lower control arm relocation brackets and Airaid CAi.

FromZto5

Holy thread revival batman

Ssgthooligan

Can't say that I didn't do my research lol.