Upgrade your 04/05 CV8 with the gear ratios from the 6.0VXR
Discussion
In 2004 the Monaro was launched in the UK to great a claim but more probing analysis critised the car for over long gearing. In May 2004 Auto Car said "Quick, but tall gearing hampers pace". In another review god himself (Jeremy Clarkson) said "Monaro was bogged down by an absurdly tall first gear".
GM Holden addressed this by fitting a different version of Tremec's T56 6 speed manual gearbox with shorter ratios. However for roll out in the UK the 05 5.7 CV8 failed its drive by noise emissions test and so as a quick fix continued with the previous box. The lower revs and presumably lower noise being apparently enough to get it through the test. Vauxhall messed up however and blindly copied the Australian brochure so erroneously quoting the new ratios for the 05 CV8. It appears I was the only owner out of 100 to spot this...
After failing to get Vauxhall to honour the brochure, I have fitted the correct gearbox myself. So probably I'm the only owner who's car is correct to published spec!
The gearboxes have the following p/ns and ratios:
MM6 was fitted to 04s and the 05 CV8. M12 is the one I have fitted and came on the 6.0VXRs. M10 is the very latest version on the VXR8 which appears the same apart from a marginally shorter again 1st gear - looks like they take notice of Clarkson! The VXR8 also gets a shorter final drive of 3.7 vs 3.46.
The MM6 ratios date back to the 1980s and are the same in the Lotus Carlton and various other lowish volume cars such as the Dodge Viper. The M12 set appears to be a relatively recent addition.
Shortening the gearing improves the performance on 3 accounts:
1 Actual acceleration, “shove in the back”, is proportionally faster, proportional to the actual numerical ratio.
2 Perceived acceleration is faster because the car will spend less time in each ratio and so gets up through the gears faster. For example 2nd is 16% shorter for the M12 box compared to the MM6. Actual acceleration is 16% faster. Maximum revs are reached at a 16% lower speed. These combine to mean the car spends 32% less time in the 2nd gear. So the subjective improvement is effectively double the actual ratio change.
3 In normal driving most time is spent in the bottom half of the engine’s rev range. For a given speed and gear, with shorter ratios the engine will be doing more revs and hence be higher up the torque curve, resulting in greater response. Particularly apparent in 6th on the motorway.
Shortening the gearing can of course be achieved with a higher ratio final drive. This was not however the way GM themselves chose. Also this doesn't help with the odd spread of ratios the MM6 has. 1st to 4th follow a progression getting closer but then there are wide gaps 4 - 6th. The M12 they are more evenly spread and more similar to competitive cars.
I obtained my M12 for much the same money as a differential change. Also I wanted to look at my clutch (story for another day). Changing the gearbox rather than the diff has the advantage of not affecting the speedo.
The performance is vastly better, the raw numbers don't really do it justice. If you have an 04 or 05 CV8 forget other mods get your gearing right. See Australian road test: http://www.webwombat.com.au/motoring/news_reports/...
The gearboxes are fully interchangeable. The only differences I spotted was a minor change to the casting inside the bell housing and the M12 has the ridiculous "skip shift" solenoid. This is a USA regulations economy bodge to avoid the "gas guzzling" tax. Have this to avoid the tax but 2/3rd are locked out when the car is warm! Fortunately it does nothing left disconnected.
If you are lucky enough to have a failure under warrantee just ask the dealer to order the M12 rather than another MM6. It is actually cheaper at £6.5K rather than £7K. More likely though you will have to go elsewhere. Clearly 6.5K is a non starter. I got mine from Regal Performance in the USA though it was their last one in stock at the time. £1500 plus £500 shipping and duty. Basicaly just scan eBay USA. Thanks to "motomk" for the link http://www.malwoodauto.com.au/. I've just got a quote of AUD4050 approx £1750 - Bargain. Unfortunately they couldn't do better than 1200 AUD air freight, no cheaper surface option. So with VAT and Duty on the total price it creeps up to approx £2700. I guess the value could be under declared but if it gets lost... Perhaps somebody out there can explain Vauxhall's X3 mark up. Needlessly to say they don't airfreight them individually. They are made in Mexico anyway. Get the actual ratios checked - 1st near enough 3:1. First box I got was marked TUET2066 but still had the old ratios. Ideally both Tremec and GM numbers should be quoted and on both the top label and side tag.
A potential advantage of changing the box rather than the diff is that the box is much move valuable as a used spare. I've seen a scruffy looking used gone go for £900 on eBay and I got £1500 for my incorrectly labelled new one. The MM6 ratios are fine for very high power to weight cars such an AC Cobra replica or similar.
The actual swap is straightforward and the Monaro appears a relatively friendly DIY car. You need to remove the exhaust and prop shaft (torx at the diff flange). The centre console unclips with just one screw under the rubber mat at the front. Remove the gear lever. Ensure the gearbox output shaft is plugged to avoid oil loss. Remove the gearbox rear support and lower the box slightly. The engine can only be tilted slightly before the sump comes close to crushing a PAS pipe. The sump can be supported on a cross member with an appropriate sliver of wood. Disconnect the clutch pipe and electrical connections. I found it easier to remove the shifter (small torx on the plastic cover) and disconnect the gearbox from the bell housing rather than bell housing from the engine. The gearbox can then just be slid backwards without lots of wriggling. Removing the bell housing on its own is then easy. If the new box doesn't have a clutch slave cylinder then swap this over. Just two bolts. Re assembly just the reverse. Bleeding the clutch requires an oddly shaped 11mm socket and preferably two helpers. One on the reservoir because it doesn't hold much fluid and one on the pedal.
On the road there are subtle differences between the boxes. Both suffer a raspy buzz from the gearlever at high load and middling revs, though the new one is better at least to start with. Also it bulks less when selecting gears at rest. 2nd to 3rd sometimes I feel some resistance however and occasionally manovering I hear a slight "clank" depressing the clutch. Both fine under more hurried use. Needlessly to say having lovingly cradled the new box lying under my car I'm not going to try any silly harsh tricks like trying to beat the clock with it!
Perhaps one snag with the M12 ratios is the lower 5th now looks a bit short for maximum speed, where this should coincide with max power. With the CV8 this is 5600 rpm. So this was 165mph - spot on, but now only 145mph. So now its likely to over rev. Academic in the UK of course. 6.0VXR and VXR8 max power is 6K equating to 156mph and 146 respectively. So again both of these are going to over rev. Ironically then the MM6 is better for top speed.
I think it will be interesting to see if the change has had any effect on economy. In theory with the shorter 6th it should and my daily motorway commute should show this up. I keep records of all the fuel I put in so I should get an accurate figure long term. So far, and on the computer, it doesn't look to have made much difference.
GM Holden addressed this by fitting a different version of Tremec's T56 6 speed manual gearbox with shorter ratios. However for roll out in the UK the 05 5.7 CV8 failed its drive by noise emissions test and so as a quick fix continued with the previous box. The lower revs and presumably lower noise being apparently enough to get it through the test. Vauxhall messed up however and blindly copied the Australian brochure so erroneously quoting the new ratios for the 05 CV8. It appears I was the only owner out of 100 to spot this...
After failing to get Vauxhall to honour the brochure, I have fitted the correct gearbox myself. So probably I'm the only owner who's car is correct to published spec!
The gearboxes have the following p/ns and ratios:
| GM Vin | GM | Tremec | Ratios | |||||
|---|---|---|---|---|---|---|---|---|
| Designation | Part no | Part no | 1 | 2 | 3 | 4 | 5 | 6 |
| MM6 | 92067136 | TUET2100 | 2.66 | 1.78 | 1.30 | 1.0 | 0.74 | 0.50 |
| M12 | 92155485 | TUET2066 | 2.97 | 2.07 | 1.43 | 1.0 | 0.84 | 0.57 |
| M10 | ? | ? | 3.01 | 2.07 | 1.43 | 1.0 | 0.84 | 0.57 |
MM6 was fitted to 04s and the 05 CV8. M12 is the one I have fitted and came on the 6.0VXRs. M10 is the very latest version on the VXR8 which appears the same apart from a marginally shorter again 1st gear - looks like they take notice of Clarkson! The VXR8 also gets a shorter final drive of 3.7 vs 3.46.
The MM6 ratios date back to the 1980s and are the same in the Lotus Carlton and various other lowish volume cars such as the Dodge Viper. The M12 set appears to be a relatively recent addition.
Shortening the gearing improves the performance on 3 accounts:
1 Actual acceleration, “shove in the back”, is proportionally faster, proportional to the actual numerical ratio.
2 Perceived acceleration is faster because the car will spend less time in each ratio and so gets up through the gears faster. For example 2nd is 16% shorter for the M12 box compared to the MM6. Actual acceleration is 16% faster. Maximum revs are reached at a 16% lower speed. These combine to mean the car spends 32% less time in the 2nd gear. So the subjective improvement is effectively double the actual ratio change.
3 In normal driving most time is spent in the bottom half of the engine’s rev range. For a given speed and gear, with shorter ratios the engine will be doing more revs and hence be higher up the torque curve, resulting in greater response. Particularly apparent in 6th on the motorway.
Shortening the gearing can of course be achieved with a higher ratio final drive. This was not however the way GM themselves chose. Also this doesn't help with the odd spread of ratios the MM6 has. 1st to 4th follow a progression getting closer but then there are wide gaps 4 - 6th. The M12 they are more evenly spread and more similar to competitive cars.
I obtained my M12 for much the same money as a differential change. Also I wanted to look at my clutch (story for another day). Changing the gearbox rather than the diff has the advantage of not affecting the speedo.
The performance is vastly better, the raw numbers don't really do it justice. If you have an 04 or 05 CV8 forget other mods get your gearing right. See Australian road test: http://www.webwombat.com.au/motoring/news_reports/...
The gearboxes are fully interchangeable. The only differences I spotted was a minor change to the casting inside the bell housing and the M12 has the ridiculous "skip shift" solenoid. This is a USA regulations economy bodge to avoid the "gas guzzling" tax. Have this to avoid the tax but 2/3rd are locked out when the car is warm! Fortunately it does nothing left disconnected.
If you are lucky enough to have a failure under warrantee just ask the dealer to order the M12 rather than another MM6. It is actually cheaper at £6.5K rather than £7K. More likely though you will have to go elsewhere. Clearly 6.5K is a non starter. I got mine from Regal Performance in the USA though it was their last one in stock at the time. £1500 plus £500 shipping and duty. Basicaly just scan eBay USA. Thanks to "motomk" for the link http://www.malwoodauto.com.au/. I've just got a quote of AUD4050 approx £1750 - Bargain. Unfortunately they couldn't do better than 1200 AUD air freight, no cheaper surface option. So with VAT and Duty on the total price it creeps up to approx £2700. I guess the value could be under declared but if it gets lost... Perhaps somebody out there can explain Vauxhall's X3 mark up. Needlessly to say they don't airfreight them individually. They are made in Mexico anyway. Get the actual ratios checked - 1st near enough 3:1. First box I got was marked TUET2066 but still had the old ratios. Ideally both Tremec and GM numbers should be quoted and on both the top label and side tag.
A potential advantage of changing the box rather than the diff is that the box is much move valuable as a used spare. I've seen a scruffy looking used gone go for £900 on eBay and I got £1500 for my incorrectly labelled new one. The MM6 ratios are fine for very high power to weight cars such an AC Cobra replica or similar.
The actual swap is straightforward and the Monaro appears a relatively friendly DIY car. You need to remove the exhaust and prop shaft (torx at the diff flange). The centre console unclips with just one screw under the rubber mat at the front. Remove the gear lever. Ensure the gearbox output shaft is plugged to avoid oil loss. Remove the gearbox rear support and lower the box slightly. The engine can only be tilted slightly before the sump comes close to crushing a PAS pipe. The sump can be supported on a cross member with an appropriate sliver of wood. Disconnect the clutch pipe and electrical connections. I found it easier to remove the shifter (small torx on the plastic cover) and disconnect the gearbox from the bell housing rather than bell housing from the engine. The gearbox can then just be slid backwards without lots of wriggling. Removing the bell housing on its own is then easy. If the new box doesn't have a clutch slave cylinder then swap this over. Just two bolts. Re assembly just the reverse. Bleeding the clutch requires an oddly shaped 11mm socket and preferably two helpers. One on the reservoir because it doesn't hold much fluid and one on the pedal.
On the road there are subtle differences between the boxes. Both suffer a raspy buzz from the gearlever at high load and middling revs, though the new one is better at least to start with. Also it bulks less when selecting gears at rest. 2nd to 3rd sometimes I feel some resistance however and occasionally manovering I hear a slight "clank" depressing the clutch. Both fine under more hurried use. Needlessly to say having lovingly cradled the new box lying under my car I'm not going to try any silly harsh tricks like trying to beat the clock with it!
Perhaps one snag with the M12 ratios is the lower 5th now looks a bit short for maximum speed, where this should coincide with max power. With the CV8 this is 5600 rpm. So this was 165mph - spot on, but now only 145mph. So now its likely to over rev. Academic in the UK of course. 6.0VXR and VXR8 max power is 6K equating to 156mph and 146 respectively. So again both of these are going to over rev. Ironically then the MM6 is better for top speed.
I think it will be interesting to see if the change has had any effect on economy. In theory with the shorter 6th it should and my daily motorway commute should show this up. I keep records of all the fuel I put in so I should get an accurate figure long term. So far, and on the computer, it doesn't look to have made much difference.
I think the vmax figures were based on peak power. theory says that if you change the gearing then the fastest a car could go is when vmax occurs at peak power.
the current gearing has vmax past peak power but the power levels beyond peak are still greater than all the opposing forces so the car still accelerates.
the current gearing has vmax past peak power but the power levels beyond peak are still greater than all the opposing forces so the car still accelerates.
ads_green said:
I think the vmax figures were based on peak power. theory says that if you change the gearing then the fastest a car could go is when vmax occurs at peak power.
the current gearing has vmax past peak power but the power levels beyond peak are still greater than all the opposing forces so the car still accelerates.
the current gearing has vmax past peak power but the power levels beyond peak are still greater than all the opposing forces so the car still accelerates.
The suggested max at 6k for a VXR8 is 156, it isnt!
It does appear I am a little out on the top speed calculations, perhaps as I have not considered the different wheel sizes. Just assumed 18 in as the CV8. This does mean however that I have flattered the VXR and VXR8 in my previous posts.
Autocar's road test of the VXR8 puts it at 25.4 mph/1000 rpm in 5th (19 in). So this puts theoretical top speed as 152mph. They only achieved marginally better than this at 155mph/6100 rpm. Are the cars officially limited to 155? 170mph would equate to 6700rpm, well past max power and against the rev limiter? Speedo may be a little optimistic of course. Legally I believe -0, +10% is allowed. So it must not under read. So allowing for tolerances it is always likely to be slightly optimistic.
Autocar's road test of the VXR8 puts it at 25.4 mph/1000 rpm in 5th (19 in). So this puts theoretical top speed as 152mph. They only achieved marginally better than this at 155mph/6100 rpm. Are the cars officially limited to 155? 170mph would equate to 6700rpm, well past max power and against the rev limiter? Speedo may be a little optimistic of course. Legally I believe -0, +10% is allowed. So it must not under read. So allowing for tolerances it is always likely to be slightly optimistic.
greens vauxhall said:
Raggyman said:
tiler said:
VXR8 @6800rpm = 182mph.
So tom tom gps says / And road angle
So tom tom gps says / And road angle
Umm, wonder what gear box I got in mine then. I had it up to 170mph and was only sitting on 4000rpm..
5th Gear not 6th Jace.
DOH!... Ah man, feel like such a English Soccer Manager now.. -> exit door left..
bennno said:
I dont think this image needs any further comment.
stigmundfreud said:
bennno said:
I dont think this image needs any further comment.
as a spectical wearing IT bod I find it offensive that geeks are portrayed to always be wearing glasses. I mean we have outcrys at the golly wag and calling fat people "fat lazy drains on the nhs" is frowned up, yet we still to this day persist in such discrimination as this.
Just be grateful you're not GOY as well.
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