Old Car Guy Mindset

[b4z]

Don't mean for this post to be negative.
Several days ago I posted about how tire size effects gearing.
Since I posted that I have read several posts form people who are still
thinking a set of 4.11's in a 2003 Marauder are the same as 4.11's in 1960's musclecar. Nothing could be further from the truth.

The Marauder will not cruise down the highway at 3000-3500 rpms.
It will not get 15 mpg. It will not be noisy and tiring to drive. It will not wear the engine out more quickly.

The tires are so tall that the effective gear ratio is a good 10% less.
And the overdrive transmission will cut the cruising rpms by another 30%.

My '84 Z28 had 3.73s and 26" tall tires. That same gear in a Marauder acts like a 3.36.

Lets get out of the mindset of 30-40 years ago.

[Jim]

Hmm.

I'm not sure it's an 'old mindset' that makes me wonder what the RPMs will be @ highway speeds, more like a pondering...

No matter what the year, moving to a 4.11 gear is going to increase engine RPM at a given speed. The question here is, how high!

Undoubtably, a change here won't be like the last gear swap I did; from a 2.7xx to a 3.55 in a '71 Pontiac.

Of course, I still have to think that an increase in highway RPM would result in a reduction in fuel efficiency, or FoMoCo wouldn't have defaulted to the 3.55? They've got their eye firmly on the CAFE standards, I'm sure.

Either way, I'm changing mine out. I figure I can always change back if I hate it! Those giant (height) rear tires really do reduce the effective ratio.

-J

[Fourth Horseman]

Hmmm... I wish there was some way I could try out both 3.73 and 4.10 gears before deciding on which to purchase.

Dennis indicated that 3.73s really woke the car, up, though, which is really all I'm looking for. I don't intend to be racing the Marauder a lot, I'd just like to get off the line a bit quicker.

Should I just bite the bullet and get the 4.10s?

[b4z]

I am a Chevy guy, so I am not as familiar with Ford gearsets.
Don't they have a 3.89 or 3.90 available. A good compromise between the 3.70s and 4.10s.

[Logan]

After driving a 3.73 equipped marauder around for 3 hours this morning, I can safely say that 3.73's are not enough gear for this car.

I'll be equipping my marauder, which by the way, I picked up today, with 4.10's... No question.

With the 3.73's, in 3rd gear at 80mph, it was turning 3200rpm, it's power band is up above 4000rpm, so at 80mph, it's so low in it's power band, when you got to WOT, it actually downshifts to 2ND!!! AT 80MPH!!!!

Yeah, NO questions here... 4.10's all the way... My will be in later this week.

[MarauderMike]

I'd be curious to know what the rpm difference is at 70mph between the 3.55 and the 4.10. Mine is my daily driver so I don't want to totally kill my mpg. I downloaded a program the other day and here is what we get with the different gear combinations.

Gear Ratio 3.55 3.73 4.10

MPH @ 2000 rpm 66.4 63.2 57.5

I'm not a rocket scientist and I imagine if I'd sit down and work it out I could figure this out, but that seems like a significant difference from the 3.73 to the 4.10. Logan, give us a run down after you get the gear change done.

[SSMOKEM]

After I blew my 4L60E for the 2nd time, I installed the TH400, which has NO overdrive. With my 3.73s, I turn 3100rpm at 60mph on the highway. Needless to say, 60 is my cruising speed !! Of course, this is my toy, so it doesn't really matter :)

On the other side of the coin, it takes me a bit over 8 seconds to go from 60 to 120mph :D

If I had a Marauder, 4.10s would be my first mod, along with a 3000 stall converter..........

[b4z]

SSMOKEM,

The overdrive is .70 so it would be 3100 rpms X .70 = 2170 rpms.
Quite a difference. Maybe you should investigate a modified 4L80E.

I am not a math wiz, but we should be able to input the tire circumference by final drive and figure cruising rpms.

Or if we can get a marauder owner to give us the rpms at cruise, say 60 or 70 mph, then we can input the percentage change in gear ratio and figure cruising rpms.

[b4z]

I think I got it.

Using Marauder Mike's numbers this would be the difference in cruising rpms for each of the different gear ratios.

3.55 @ 66.4mph = 2000rpms

3.73 @ 66.4mph = 2101rpms

3.90 @ 66.4mph = 2197rpms

4.10 @ 66.4mph = 2309rpms

The 4.10 is a 15% increase.
If it were me I would go with the 3.90s. A 10% increase in rpms and torque multiplication.

If you were to cruise @ 80 mph with the 4.10s it would be 2,782 rpms.
That is getting up there. Things are starting to get noisy and gas mileage will go down.

If you substituted the 3.90s @ 80 mph it would be 2,647 rpms.

3.73s @8 0 mph would be 2,531 rpms.

3.55s @ 80 mph would be 2410 rpms.

[Fourth Horseman]

Interesting. I think I'll wait for Logan's report on the 4.10s before I do anything.

[MarauderMike]

Ok, I just ran my Marauder down I-275, at 70 mph she turns right at 2100. I locked out overdrive and she jumped up over 3100. I to am waiting to see how Logan does with his 4.10 gear set. Ok, so I'm semi patiently waiting :p

[Jim]

For my amusement, I whipped up this little tool (http://www.averagegeek.com/Evil_Jim/GearCalc.asp) to help me understand the impact of rear gear and/or tire changes.

There may be some error here, due to tire 'squish.' I'll add a correction factor when I get my Mo back!

-Jim

[Logan]

ooooo yeah. Thanks Jim. :)

Handy tool. Is it going to be a permanent link? Post it up in the Links section...


Look at that... 3854rpm at 80mph in 3rd gear with 4.10's... Much better.... as opposed to 3300rpm with 3.55's...

At 60mph, going WOT will kick you down to 2nd gear right into the power band at 4400rpm... Perfect for passing...

Yep. Just proves 4.10's will be the ****zy in this car.

[b4z]

Next modification should be a 3.06 first gear.

The most interesting thing about this gear comparison is how close the Marauder's first gear and rear gear is to the Impala's. If you factor in the Impala's lower first gear and it's much shorter tires, by 1.6".

Comparing Impala total gearing in 1st to Marauder's:
Impala 1st gear X rear gear X% of tire height = 3.51 effective gear
The Marauder's rear gear as we all know is 3.55.

So the Impala's deeper first gear and shorter tires more than compensate for it's 3.08 relatively tall rearend. Especially compared
to the Marauder. It's kind of the best of both worlds. Crusing economy and off the line punch. And since the engine has excellent low end torque the longer gear spread between 1st and 2nd does not to appear to hurt acceleration like it would in a DOHC higher revving engine.

So the Impala's pushrod engine and higher torque occuring lower in
the rev range is what gets it going better than the Marauder.

[MarauderMike]

Sure makes the 4.10 sound more inviting!!!

[Jim]

So, what's the redline on this car, as stock?

As well, what are the factory shift points? I'd like to integrate that info into my dazzlingly pointless tool.

Thanks,

-Jim

[MarauderMike]

From the Ford media site:
Shift Points
At Wide Open Throttle

1st to 2nd Gear
@ 6,000 rpm

2nd to 3rd Gear
@ 6,200 rpm

3rd to 4th Gear
speed limited @ 120 mph

I believe red line is 6200 rpm

Great calculating tool Jim!

[Fourth Horseman]

If memory serves it actually cuts off fuel at 6250 RPM.