Your correct on the RWD but only at 1:1 In overdrive like 0.69:1 the final is not the same as the diff.

Seeing the final drive ratios in overdrive it looks as though the differential gearing is 4.83 for the auto and 6.04 for the manual at 1:1. in other words 4.83 revolutions of the engine for 1 revolution of the front axle for the automatic.

My race car had a 4.56 gear set in the rear man 6.04 makes that manual hhr rev pretty high.

Somethin dont seem right. 4.17:1 for the manual for the final drive cant be right. Driving down the freeway you would need to be running at over 4000 rpm

 

Thank you. That is my point.

 

Gearing was never my speciality. But I can tell you the manual does not run at 4G's at highway speeds.

I do know that since no drive shaft like a RWD, the calculations are different than figuring a RWD.

I did find this "explanation" online....

 

The auto and manual = apples and oranges
The only thing thats counts is to me is what you are putting down to the road

The SS auto has less hp and 225 lbs of torque@1,650 rpm
manual is 260 hp@5,300 rpm and 260 lbs of torque@2,000 rpm

You can do the math anyway you want but if you buy the auto it can`t compare too the power and preformance of the manual.

The SS is not about mpg it`s about fun and fun = torque,hp,and rpm`s

 

Manuals are good for the twisty roads. For drag racing its all about the automatic!!!!

Now for the HHR SS they have detuned the motor for the auto but I bet ya that if someone was to retune that auto SS back up to what the Manual is your going to have a hard time beating a auto in a drag race. Although; that high ratio diffetrential in the manual will give you the hole shot. The first 60 ft. the manual will kill ya.

Now let someone retune the torque converter to launch at say 3000rpm and change the torque multification factor to a higher number you can say bye bye to that manual car. Would also help if one could find a smaller diameter converter.

My race car had a 2 speed powerglide coupled to the motor with a 6000 9" rpm stall converter with a 4.56 rearend. I had a 5500 rpm stall 8" converter also that I ran with shorter tires for 1/8 mile tracks.

There are alot more factors to gear ratios and final drives than just the gears in the tranny. One must look at the ratio of the differential plus tire height. Tire height plays a big role in rpm vs mph.

What we need here is rpm:axle ratio.

Is the output shaft of the transmission 1:1 to the front axle in both cars?

 

Don't know why there appear to be some discrepancies on the different spec sheets, but for discussion sake, I'll pick top gear and final drive for the auto as 0.68 and 3.91, then assume 0.69 and 4.17 for the 5 spd. to calculate speed at a given rpm, a simplified formula is; MPH=(tire dia x RPM)/(336 x final drive ratio) so for 2500 rpm, the 5spd would be (25.9 x 2500)/(336 x 4.17 x 0.69) = 67 MPH Calculating the same way for the auto would be (25.9 x 2500)/(336 x 3.91 x 0.68) = 72 MPH

 

My guess is GM was concerned about clutch life in the std. transmission models. The taller final drive prevents lugging of the engine on startup and on gear changes. Plus, turbos also don't respond well at low RPM's, so in order to pull the HHR weight, something would have to give....and that would be the clutch. Think old time VW's. Low gear was good for about 10 feet, before it hit max RPM. Auto should not have the problem because GM can engineer in the correct RPM range via the computer.

Pat

 

Hey C2 dont know where you got your numbers for the auto but they are wrong. Here are the numbers right from GM.

2008 Hydra-Matic 4T45 Transaxle( MN5 ) 101106
Type: four speed front-wheel-drive, electronically controlled, automatic overdrive transaxle with electronically controlled torque converter clutch
Engine range: 2.2L - 3.5L
Maximum engine torque: 221 lb-ft (300 Nm)
Maximum gearbox torque: 325 lb-ft (440 Nm)
Gear ratios:
First: 2.96
Second: 1.62
Third: 1.00
Fourth: 0.68
Reverse: 2.14
Final Drive Ratio: 3.05 3.29 dependent on sprocket


So now lets recalculate for the auto at 2500 rpm with the correct numbers.

(25.9 x 2500)/(336 x 3.29 x 0.68) = 86.13 MPH Auto
(25.9 x 2500)/(336 x 4.17 x 0.69) = 66.97 MPH Manual

for the auto with the 3.05 at 2500 you would be doing 92.91 mph

Now you can see that there is a huge difference between the manual and the auto.

For the auto to do 64.46 mph it would need an engine rpm pf 1900.

 

Keep on calculating because the SS Manual is rated at 21 mpg city 29 hwy and the Auto is 19 mpg city 28 mpg hwy so that is proof that you are still wrong.Like I said before the Auto and Manual trans= apples to oranges.

 

WHY DONT YOU STAY ON TOPIC? ARE WE HERE TALKING ABOUT GEARS OR MPG?

Yes I am yelling!

But since you brought it up about mpg I guess that whole 1 mpg difference really makes me want to go and buy a manual. Lets see here in the bay area it costs me 12 cents per mile highway in an auto vs 11 cents per mile highway manual using your 28mpg vs 29mpg

The topic is on "Why so high final drive ratio". Do you see anywhere that it says compare manual to auto for fun factor or mpg?

When your used to 1000+ hp and doing 6 foot wheel stands driving a 260hp manual doesnt get me too excited. But hey whatever floats yer boat im all for it. Im done with the manual stuff living in the bay area with all the stop and go traffic having to shift all the time gets tiring.

Lets see how much fun factor you have in LA traffic say 5pm with that manual.