CT5BW Question about lugging engine

[Steve D14]

I have had my 2024 CT5 BW 6 speed since July 2024 and have put 4200 wonderful miles on it so far. I do have one question about 6th gear. The gap between 5th and 6th is much larger that between the other gears and when cruising at less the 70 MPH the revs are at or below 2000. If I downshift to 4th or 5th and hit it, it really takes off smoothly. If I stay in 6th and give it moderate throttle it picks up nicely, but if I apply more throttle it seems to bog a bit and I feel some roughness. Once I get above 2500-3000RPM that goes away. This is only noticeable in 6th gear when the RPM are below 2000-2500.

Has anyone else noticed this and is this considered lugging the engine? I ask also because I modified my previous 2012 CTS-V coupe and had it tuned on the dyno and when I left the tuner it did a similar thing in 6th gear but much worse. So I went back to the tuner he drove it around with a laptop connected and made some tweaks and that virtually eliminated it. Is this a characteristic of the tuning of the LT4s and could I do any harm to the engine by "lugging" it in 6th?

Thanks,

Steve D

 

[SS_Shooter]

6th gear is basically a fuel economy gear designed for MPG. It's fine lugging it in that gear, and once it comes on the power in 6th it does accelerate, but if you want good acceleration, best to go to 5th.

A lot of manuals have a big-ass 6th or 7th gear that is designed to maximize MPG so they can meet some kind of bureaucratic fuel economy standard nonsense. The CT5BW is really a 5-speed car with a slightly-overdriven 5th gear (that is still very drivable) and majorly-overdriven 6th gear (0.54 w/3.73 rear axle) that only really works if you are just cruising. (Side note: Early Caddy V's and Corvette manuals had a 1st-to-4th feature that pulled the manual into 4th gear AUTOMATICALLY if you shifted out of 1st gear under certain conditions. This created a dangerous situation where you couldn't really accelerate and was done for fuel economy reasons...)

Having a big overdrive gear was NOT the case with my 1999 E36 BMW M3. It didn't have a 6th gear, and its 5th gear was a performance gear, so you were pushing like 3,300 rpms at 80mph in 5th, Same was true with my 2007 Jeep Cherokee SRT8; that was 5-speed auto (all usable) that turned about 3,000 rpms at 80mph in 5th. I think the Blackwing RPM's at 80mph in 6th are something like 2,200 (low comparatively).

The Brits used to solve the 'good gearing vs. excessive rpms at high speeds' issue with the Laycock de Normanville (LdN) overdrive, which was an EXTERNAL overdrive gear mechanism with a switch - it bolted between the transmission and the driveshaft. Throw the lever, it engages the overdrive gear, and the rpms drop by like 28%.

This was done because cars like the MG-TD only had 54 horsepower, so they needed very aggressive gear ratios in their 4-speeds when on the track (or really anywhere given the limitations of 54 bhp). However, they needed to be able to go 60-70 mph on the highway. With this setup, they could engage the Laycock overdrive and drive home on the highway at much lower rpm (than without the Laycock), and hopefully avoid having their tiny 1250cc motor blow the hell up...

Also, here's something cool: The 1978 911 Turbo used a four-speed manual gearbox, designated Type 930/34 with these gear ratios:

• 1st Gear: 2.25
  
  
• 2nd Gear: 1.304
  
  
• 3rd Gear: .893
  
  
• 4th Gear: .625
• Final Drive: The final drive ratio was 4.220.

Funny story: I once had a loaner Jeep Compass with a 9-speed automatic.

• When I put it in 'manual' mode, it didn't have enough horsepower to accelerate AT ALL in 8th or 9th gear under wide open throttle.
• Even 7th gear was a stretch, but it would gradually accumulate speed in 7th.
• I don't really understand the nuances of automatics, but I know it would drop into those overdrive gears (8th or 9th) when I was cruising and totally off the throttle. Even around town. Weird, right? Maybe someone can explain how those 8th and 9th gears were making things better...

 

[white98ls]

6th gear is basically a fuel economy gear designed for MPG. It's fine lugging it in that gear, and once it comes on the power in 6th it does accelerate, but if you want good acceleration, best to go to 5th.

A lot of manuals have a big-ass 6th or 7th gear that is designed to maximize MPG so they can meet some kind of bureaucratic fuel economy standard nonsense. The CT5BW is really a 5-speed car with a slightly-overdriven 5th gear (that is still very drivable) and majorly-overdriven 6th gear (0.54 w/3.73 rear axle) that only really works if you are just cruising. (Side note: Early Caddy V's and Corvette manuals had a 1st-to-4th feature that pulled the manual into 4th gear AUTOMATICALLY if you shifted out of 1st gear under certain conditions. This created a dangerous situation where you couldn't really accelerate and was done for fuel economy reasons...)

Having a big overdrive gear was NOT the case with my 1999 E36 BMW M3. It didn't have a 6th gear, and its 5th gear was a performance gear, so you were pushing like 3,300 rpms at 80mph in 5th, Same was true with my 2007 Jeep Cherokee SRT8; that was 5-speed auto (all usable) that turned about 3,000 rpms at 80mph in 5th. I think the Blackwing RPM's at 80mph in 6th are something like 2,200 (low comparatively).

The Brits used to solve the 'good gearing vs. excessive rpms at high speeds' issue with the Laycock de Normanville (LdN) overdrive, which was an EXTERNAL overdrive gear mechanism with a switch - it bolted between the transmission and the driveshaft. Throw the lever, it engages the overdrive gear, and the rpms drop by like 28%.

This was done because cars like the MG-TD only had 54 horsepower, so they needed very aggressive gear ratios in their 4-speeds when on the track (or really anywhere given the limitations of 54 bhp). However, they needed to be able to go 60-70 mph on the highway. With this setup, they could engage the Laycock overdrive and drive home on the highway at much lower rpm (than without the Laycock), and hopefully avoid having their tiny 1250cc motor blow the hell up...

Also, here's something cool: The 1978 911 Turbo used a four-speed manual gearbox, designated Type 930/34 with these gear ratios:

• 1st Gear: 2.25
  
  
• 2nd Gear: 1.304
  
  
• 3rd Gear: .893
  
  
• 4th Gear: .625
• Final Drive: The final drive ratio was 4.220.

Funny story: I once had a loaner Jeep Compass with a 9-speed automatic.

• When I put it in 'manual' mode, it didn't have enough horsepower to accelerate AT ALL in 8th or 9th gear under wide open throttle.
• Even 7th gear was a stretch, but it would gradually accumulate speed in 7th.
• I don't really understand the nuances of automatics, but I know it would drop into those overdrive gears (8th or 9th) when I was cruising and totally off the throttle. Even around town. Weird, right? Maybe someone can explain how those 8th and 9th gears were making things better...

One reason all those high-revving N/A performance engines of the '00s got canned is they really got poor gas mileage. My Honda S2000 revved at 3,800 in 6th at 70mph, and thanks to the low torque and need for super short gears, it was only rated 20/26mpg despite only 240hp and 2,800lbs. My E90M3 (8,400rpm 4.0L V8, 414hp) actually got slightly worse mpg than my 5BW! Could barely break 20mpg highway due to turning around 3k rpm at 70 in 6th. Fun engines, but terrible mileage.

 

[G.Newt]

6th is for highway cruising. Light throttle only until the revs come up. Yes, lugging is not great for the engine. That's what downshifting is for (and really part of the joy of owning a manual: rowing gears). There are a lot of articles around engine lugging, LSPI, etc. Basically high load with low engine speed is no bueno.

 

[Steve D14]

SS_Shooter

Thanks for your very detailed response. So, because of the high gear ratio in 6th it should be considered for cruising which was done to achieve higher highway mileage ratings and lower engine stress. For other than mild acceleration, one should downshift. I guess in 6th gear anything less than 2500 RPM night be lugging the engine.

My CTS-V coupe 6th gear ratio was not as high so that roughness was probably a tuning issue.

Years ago I had a 1974 MGB (78HP) with a Laycock de Normanville OD like the MG TD with the OD switch mounted on the right steering stalk which you pulled towards you to engage OD. Made the car great for the highway speeds of the day (55-65MPH) while accelerating reasonably well through the gears. You could quickly switch in and out of OD and the OD worked on 3rd gear as well. That OD had a separate sump that used engine oil and not gear oil. Even though acceleration was leisurely by today’s standards that car was a blast to drive hard and through into the corners.

Steve D

 

[Steve D14]

G. Newt

Perhaps with the tall gearing the RPMs come up slower when down around 2K RPM and makes the lugging more obvious?

Steve D

 

[5VBW Nick]

My 1993 Ford Probe GT did 3,000 rpm 60 mph in 5th (final) gear! Never needed to shift to pass someone, but absolutely needed a 6th gear. Was my first car nearly 30 years ago.

 

[rubberduck]

I like to keep the engine above 2500 no matter what gear I’m in. Just need to drive faster if you want to use 6th.

 

[G.Newt]

G. Newt

Perhaps with the tall gearing the RPMs come up slower when down around 2K RPM and makes the lugging more obvious?

Steve D

If you've got some time to kill, I'd read up on gear ratios. The shorter the gear ratio (both final: ((rear diff)) and specific gear), the more acceleration. Revs will always climb faster in lower gears given the same throttle input. Here's a screenshot of the ratios from Car and Driver. You'll see that 6th has a very tall 0.54 ratio. For us CT4 BW guys, we have slightly shorter 6th at 0.63. Here in Texas, we're all going 80-90 mph so I'm typically already at 2400+ rpm even in 6th. CT5 BW guys have the benefit of a shit ton more power and torque though lol.

And with your car being supercharged, your powerband is directly tied to rpm's vs turbos which once they reach sufficient spool from the exhaust, we have the torque we need, which typically comes much earlier in the rev range.

 

[BimmerFan]

Side note: Early Caddy V's and Corvette manuals had a 1st-to-4th feature that pulled the manual into 4th gear AUTOMATICALLY if you shifted out of 1st gear under certain conditions.

Chevy continued to do this nonsense into the C7 generation. Just FYI, since I'm wearing my pedantic hat this morning. LOL

My general rule is that the engine is lugging if it starts to knock or exhibit some roughness. I haven't felt that in the BW in 6th, as long as I'm at 60 or better and am gentle with the throttle. If I need to get on it hard, I'll downshift.

Even so, I've found the performance at low RPMs to be plenty adequate. OP, glad to read that you are still enjoying your new car!

 

[shbox]

If I'm in a manual trans vehicle, I'm never going to be lugging. That's just part of the deal for me and I don't care for the feeling at the lugging threshold.

 

[rubberduck]

If I'm in a manual trans vehicle, I'm never going to be lugging. That's just part of the deal for me and I don't care for the feeling at the lugging threshold.

Exactly!!! And absolutely no reason to do it.

 

[bloominguez]

CT5-V Thread 'ZL1 1LE transmission in 5BW? Or, how the 5BW is a 7-speed missing 6th gear.'

Feb 7, 2024

The wild drop in RPM between 5th and 6th gear is irritating. Redline in 5th gear is ~162mph; upshifting to 6th drops the RPM to around 4500 and completely kills acceleration. The drop in RPM from 5th to 6th is so huge, the transmission feels like a 7-speed, where 6th gear is missing. To be fair, I also don't like the stupid-tall 6th gear during normal street driving, either. There are numerous times where if I upshift to 6th gear, the engine almost feels like it's lugging, but if I downshift to 5th, the RPM feels too high.

From what I understand, the ZL1 1LE transmission's 6th gear...

• thefleshrocket
• Replies: 23
• Forum: Blackwing General Discussion

• 

 

[SS_Shooter]

The wild drop in RPM between 5th and 6th gear is irritating. Redline in 5th gear is ~162mph; upshifting to 6th drops the RPM to around 4500 and completely kills acceleration. The drop in RPM from 5th to 6th is so huge, the transmission feels like a 7-speed, where 6th gear is missing. To be fair, I also don't like the stupid-tall 6th gear during normal street driving, either. There are numerous times where if I upshift to 6th gear, the engine almost feels like it's lugging, but if I downshift to 5th, the RPM feels too high.

From what I've seen, this results in the automatic CT5V's having a higher top speed than the manuals. The auto's have more gears up top and can go about 205 mph. The manuals, stuck in that overdrive 6th, can only hit about 191-192 mph...

That's an extreme situation though. For everyday driving on the highway, I'm happy with the Blackwing 6MT's gearing. I use 6th when cruising at 80+ mph.

The amount of time I spend at 185+mph is none. Maybe I'd change out the 6th gear if I was planning on running down the Mulsanne straight (pre-chicanes) on a regular basis.

As I recall, the Porsche GT4's had some super-long gears and people were actually changing them out pretty regularly... Maybe there's a GT4 guy on here than knows about that.

 

[SS_Shooter]

Camaro ZL1..........Camaro ZL1LE...............CT5VBW

First: 2.66..........................2.6.....................................2.29
Second: 1.78....................1.78..................................1.61
Third: 1.30.........................1.30................................... 1.21
Fourth: 1.00.......................1.00................................... 1.00
Fifth: 0.80..............................0.75................................0.82
Sixth: 0.63..............................0.5................................0.54
Final drive ratio: 3.73..........3.91...........................3.73

 

[RDATLTE]

Camaro ZL1..........CT5VBW

First: 2.66........... 2.29
Second: 1.78.......... 1.61
Third: 1.30.......... 1.21
Fourth: 1.00.......... 1.00
Fifth: 0.80.......... 0.82
Sixth: 0.63.......... 0.54
Final drive ratio: 3.73.......... 3.73

The ZL1 1LE ratio is different then the ZL1 ratio.

 

[SS_Shooter]

The ZL1 1LE ratio is different then the ZL1 ratio.

Thanks. I added that in as well:

Tremec TR6060 Transmission
.......Camaro ZL1........Camaro ZL1 1LE........CT5VBW

First: ......2.66............................2.6.....................................2.29
Second: 1.78...........................1.78...................................1.61
Third: .....1.30..........................1.30....................................1.21
Fourth: ...1.00........................1.00.....................................1.00
Fifth: ......0.80.........................0.75....................................0.82
Sixth: .....0.63...........................0.5.....................................0.54
Final....... 3.73..........................3.91....................................3.73

The CT5VBW would be a little hotter if it had that 3.91 final drive ratio that's in the ZL1 1LE! I wonder if that is swappable? That could solve some of the complaints about long gears....

 

[5VBW Nick]

Thanks. I added that in as well:

Tremec TR6060 Transmission
.......Camaro ZL1........Camaro ZL1 1LE........CT5VBW

First: ......2.66............................2.6.....................................2.29
Second: 1.78...........................1.78...................................1.61
Third: .....1.30..........................1.30....................................1.21
Fourth: ...1.00........................1.00.....................................1.00
Fifth: ......0.80.........................0.75....................................0.82
Sixth: .....0.63...........................0.5.....................................0.54
Final....... 3.73..........................3.91....................................3.73

The CT5VBW would be a little hotter if it had that 3.91 final drive ratio that's in the ZL1 1LE! I wonder if that is swappable? That could solve some of the complaints about long gears....

I remember looking into this when I got my GT350R. I think somebody had done it and had a good result. The problem with this car is that there's so much torque that you would probably just light the tires up even more.

 

[white98ls]

I remember looking into this when I got my GT350R. I think somebody had done it and had a good result. The problem with this car is that there's so much torque that you would probably just light the tires up even more.

That's the thing I don't get about the "long gearing" complaints. Traction is already an issue in 1st, so not much point in making it shorter. 1-5 are stacked pretty close... Redline in 1st is 58 and 5th is like 165? It's a long 1st and 6th, but everything else is close together. It's like an 8-speed but with no 1st or 7th!