V1 5th gear slower than 4th on F23?!?

[SwerveMonkey]

hey guys.. It's been a hot minute since posting and I've been lurking in the forums for a few years now having gotten #197 to a good point.
I've been taking in the fruits of my labor and giving it a few trips around MD, but i keep finding that my 5th gear is very lacking.

I've tried looking up the gear ratios, understanding the overdrive feature for the Cobalt, and even sleuth-ed around to see if it something related to the PZEV version that my donor was. I've turned up nothing and need a sanity check of sorts to find out if there is something I am missing or overlooked.

If I am at the top of fourth gear and shift into fifth, the car begins to slow and RPMs never gain...
shifting into 5th gear keeps the car moving but there is NO accelerationat highway speeds.

Is 5th gear actually slower, to the point of deceleration, after shifting from 4th gear?

 

[Ross]

Lots of vehicles are faster in their top gear -1 shift. Top gear is often just to slow the engine down on the highway, get better gas mileage and make the engine quieter. Often the engine doesn't have the torque in top gear to push the car at 130+mph, and downshifting puts the engine at higher horsepower.

 

[devianteng]

If your F23 came from your 08 Cobalt LS was the original trans, it should be the 3.84 final drive model. That aside, 4th gear ratio should be the same across all F23's at 0.98; basically a 1:1. 5th on all F23's is effectively an overdrive, and for most all F23's it's a 0.69 (some did have a 0.81, but not many).

I'm no expert but to my knowledge the PZEV only effected the fueling system and tuning on the engine, but shouldn't have called for a different trans.

Based on all that, I wouldn't expect your 5th gear to keep pulling super easy, but you shouldn't really be loosing RPM if you're in power. I have no experience with the 2.2 engine, though.

 

[Rauq]

When I was making stock LSJ power, my car topped out in 4th and wouldn't accelerate in 5th, both on a 4.05 F35 (about 120mph) and a 3.84 F23 (about 125mph). I bet I could pick up at least a few MPH with a smaller windshield.

 

[Chubbs]

Is 5th gear actually slower, to the point of deceleration, after shifting from 4th gear?

I can't speak to the cobalt specifically, but it's pretty common. Often, a car can't make it to redline before running out of power in top gear.

I specifically remember in the 90's, the Mustang was faster in 4th gear than in 5th.

 

[Gtstorey]

And some transmissions are weaker in top gear, so shifting down can also protect the transmission if applying full power.

 

[Desert Sasqwatch]

Let's define 'power'. Torque is what creates acceleration, HP defines how quickly you get there. When a transmission is in gears at or above a 1:1 ratio (1st thru 4th gears), the gears in the transmission multiply the available engine torque. For example, the 1.5ish gear ratio in 3rd gear multiplies the engine torque - let's say 250 ftlbs - to 375 ftlbs at the output of the transmission. Thus the reason the car accelerates strongly in 3rd gear. 4th gear at about 1:1 is applying only the 250 ftlbs of torque and in 5th gear with a 0.67 ratio is only applying about 170 ftlbs of torque. Add the effects of aerodynamic loading into the equation and the actual acceleration capability falls off significantly when 5th gear is selected. This is the reason your Goblin is faster in 4th gear than 5th gear.

 

[Desert Sasqwatch]

Here is some additional information I pulled together a while ago about the different transmissions and final drive ratios that apply to the Goblin. Using the above conversation it is easy to multiply the published transmission gear ratios by the known max torque of each Ecotec engine to get the output of the transmission in each gear.

In the below is provided the gear ratios, shift mph when selecting the next gear at redline, and the rpm the shift drops down to when selecting the next gear. Please note all the data provided is based on the stock sized 25.0 inch tall tires and shifting at 6200 rpm stock redline. The last line of information is the cruising rpm for each transmission at 70 mph and is not a part of the acceleration/rpm calculations.

F23 - with 3.84 ring & pinion
1st (3.58) Shift to 2nd - 34 mph - rpm 3500
2nd (2.02) Shift to 3rd - 59 mph - rpm 4145
3rd (1.35) Shift to 4th - 89 mph - rpm 4500
4th (0.98) Shift to 5th - 123 mph - rpm 4365
5th (0.69) Cruise at 70 mph - 2500 rpm

F23 - with 4.17 ring & pinion
1st (3.58) Shift to 2nd - 31 mph - rpm 3500
2nd (2.02) Shift to 3rd - 55 mph - rpm 4145
3rd (1.35) Shift to 4th - 82 mph - rpm 4500
4th (0.98) Shift to 5th - 113 mph - rpm 4365
5th (0.69) Cruise at 70 mph - 2700 rpm

F35 - with 3.82 ring & pinion
1st (3.38) Shift to 2nd - 36 mph - rpm 3230
2nd (1.76) Shift to 3rd - 69 mph - rpm 4160
3rd (1.18) Shift to 4th - 102 mph - rpm 4675
4th (0.89) Shift to 5th - 136 mph - rpm 4875
5th (0.70) Cruise at 70 mph - 2500 rpm

F35 - with 4.05 ring & pinion
1st (3.38) Shift to 2nd - 34 mph - rpm 3230
2nd (1.76) Shift to 3rd - 65 mph - rpm 4160
3rd (1.18) Shift to 4th - 96 mph - rpm 4675
4th (0.89) Shift to 5th - 128 mph - rpm 4875
5th (0.70) Cruise at 70 mph - 2650 rpm

F40 - 3.76 ring & pinion
1st (3.92) Shift to 2nd - 31 mph - rpm 3230
2nd (2.04) Shift to 3rd - 60 mph - rpm 4000
3rd (1.32) Shift to 4th - 93 mph - rpm 4460
4th (0.95) Shift to 5th - 129 mph - rpm 4960
5th (0.76) Shift to 6th - 161 mph - rpm 5060
6th (0.62) Cruise at 70 mph - 2200 rpm

 

[ah.b.normal]

Let's define 'power'. Torque is what creates acceleration, HP defines how quickly you get there. When a transmission is in gears at or above a 1:1 ratio (1st thru 4th gears), the gears in the transmission multiply the available engine torque. For example, the 1.5ish gear ratio in 3rd gear multiplies the engine torque - let's say 250 ftlbs - to 375 ftlbs at the output of the transmission. Thus the reason the car accelerates strongly in 3rd gear. 4th gear at about 1:1 is applying only the 250 ftlbs of torque and in 5th gear with a 0.67 ratio is only applying about 170 ftlbs of torque. Add the effects of aerodynamic loading into the equation and the actual acceleration capability falls off significantly when 5th gear is selected. This is the reason your Goblin is faster in 4th gear than 5th gear.

My 2017 Jeep has 5th and 6th O/D gears.(the Peugeot box?) 6th is so tall that I must be going faster than 70 or significantly down hill to accelerate at all, and I must downshift if speed happens to fall below ~60 on any up incline. The Aero-defiant design of a Jeep is certainly no help here! I believe at 60 in 6th the engine is turning below 1800RPM. The torque curve on this motor "shows up" about 200 RPM higher and grows significantly through 3500-4000RPM, but seems to level off there. It doesn't gain much above 4000RPM, but, makes a little more noise. Every motor is different! (I miss the old I6's! Gobs of low end torque and they just hum along at 4000RPM. The bent6 is a very different animal.)

 

[ah.b.normal]

Here is some additional information I pulled together a while ago about the different transmissions and final drive ratios that apply to the Goblin. Using the above conversation it is easy to multiply the published transmission gear ratios by the known max torque of each Ecotec engine to get the output of the transmission in each gear.

In the below is provided the gear ratios, shift mph when selecting the next gear at redline, and the rpm the shift drops down to when selecting the next gear. Please note all the data provided is based on the stock sized 25.0 inch tall tires and shifting at 6200 rpm stock redline. The last line of information is the cruising rpm for each transmission at 70 mph and is not a part of the acceleration/rpm calculations.

F23 - with 3.84 ring & pinion
1st (3.58) Shift to 2nd - 34 mph - rpm 3500
2nd (2.02) Shift to 3rd - 59 mph - rpm 4145
3rd (1.35) Shift to 4th - 89 mph - rpm 4500
4th (0.98) Shift to 5th - 123 mph - rpm 4365
5th (0.69) Cruise at 70 mph - 2500 rpm

F23 - with 4.17 ring & pinion
1st (3.58) Shift to 2nd - 31 mph - rpm 3500
2nd (2.02) Shift to 3rd - 55 mph - rpm 4145
3rd (1.35) Shift to 4th - 82 mph - rpm 4500
4th (0.98) Shift to 5th - 113 mph - rpm 4365
5th (0.69) Cruise at 70 mph - 2700 rpm

F35 - with 3.82 ring & pinion
1st (3.38) Shift to 2nd - 36 mph - rpm 3230
2nd (1.76) Shift to 3rd - 69 mph - rpm 4160
3rd (1.18) Shift to 4th - 102 mph - rpm 4675
4th (0.89) Shift to 5th - 136 mph - rpm 4875
5th (0.70) Cruise at 70 mph - 2500 rpm

F35 - with 4.05 ring & pinion
1st (3.38) Shift to 2nd - 34 mph - rpm 3230
2nd (1.76) Shift to 3rd - 65 mph - rpm 4160
3rd (1.18) Shift to 4th - 96 mph - rpm 4675
4th (0.89) Shift to 5th - 128 mph - rpm 4875
5th (0.70) Cruise at 70 mph - 2650 rpm

F40 - 3.76 ring & pinion
1st (3.92) Shift to 2nd - 31 mph - rpm 3230
2nd (2.04) Shift to 3rd - 60 mph - rpm 4000
3rd (1.32) Shift to 4th - 93 mph - rpm 4460
4th (0.95) Shift to 5th - 129 mph - rpm 4960
5th (0.76) Shift to 6th - 161 mph - rpm 5060
6th (0.62) Cruise at 70 mph - 2200 rpm

With my limited experience with I4's, I don't recall any that could muster much HP below 2500RPM. But get to 4K and it's "Katy Bar the Door!"

 

[SwerveMonkey]

As always so much to learn from you all!! Thanks, it really put things in perspective.
I'm probably over thinking it and worried that something isn't as it should be.
The way it sounds, this may be par for the course with the goblin F23 transmission and a lot of other 5 speeds as well.
I guess i am just not used to fifth gear ratio being the way this one is.