Gearbox and clutch options for 300bhp+

[Andy]

As the title says. I am after some advice on options for what people do when running this level of power in a maestro/montego turbo. Surprisingly I cant find anything using the search function with over 20+years of threads but I know it has been done several times before. I no its fairly quite on here now so if anyone sees this and knows someone that will be able to help I would be very grateful if you could ask them to get in touch.
What is the maximum acceptable level of power/torque/boost the standard items can handle before failure becomes a problem? As I will get it set up to this level first. The gearbox is a good unit with less miles on than the car and a good quality clutch. Probably hasn't done 4k since they were fitted.
Every year since I have owned 500 I have been getting a lot of work done on it, haven't updated any of it on here for a long time. Last year I got the fuel tank refurbished again!!! Got a custom 3" stainless steel exhaust made but retaining the original pea shooter in place for the standard look. Got some welding done under the rear seat. Think thats it for the welding now. Power flex bushes all round, made a massive difference and new rear wheel bearings x2 plus the annual service. The year before I fitted a larger intercooler bought from a forum user, x4 new struts, and more welding! new grooved disks and brembo pads which still ain't brilliant. Braking still needs to be looked at. Along with other bits and bobs I cant remember.
Anyhow I seen these for sale on eBay last year and had to buy them as I knew the chance probably wont occur again, very rare parts The eBay links have gone but I took pictures as a sort of personal receipt. Who knows if they will really make 300bhp, not fused it certainly will be more than standard. Also is there anything that I have missed that is needed? So the spec so far will be:

• Larger intercooler
• 3" custom stainless steal exhaust from the turbo
• Turbo Technics turbo and manifold boost adjustable up-to 21psi
• Motobuild gas flowed head with bigger valves and fast road cam (Currently been rebuild as it has been sitting for 20 years)
• Turbo carb and modified manifold (going in for a rebuild by specialist next week)

Looking forward to hearing some advice and comments about this years work. Here are some pictures of the items and some pictures and work done last year by the garage (who is also my neighbor)

Thanks Andrew

[Andy]

Video of exhaust, please let me know if its not working for you.

https://1drv.ms/v/s!AuwIZXA-aUjIgkri...CfG5P?e=QVpCT5

[Andy]

Anyone?

[maestro dave]

Anyone?

That does look a very tidy job

[Jeff Turbo]

Seen your video Andy. Was the rear tailpipe too long as you've cut some out of the rear bumper and why point it downward like a diesel? Nice job with the cat and no rear box, must sound good when you're there. New bushes etc all round should be better road holding. Unfortunately the forum isn't what it used to be as most have now moved to Facebook, must admit I prefer the forum

[Andy]

Seen your video Andy. Was the rear tailpipe too long as you've cut some out of the rear bumper and why point it downward like a diesel? Nice job with the cat and no rear box, must sound good when you're there. New bushes etc all round should be better road holding. Unfortunately the forum isn't what it used to be as most have now moved to Facebook, must admit I prefer the forum

Hi, Jeff, no the rear tailpipe isn’t to long, the exhaust is custom made from scratch, I have some more photos of it been made I can upload later. I did ask for him not to cut the bumper, but he said he had to, to let the exhaust gasses flow away from the car and not enter the cabin. As you can see the original 'peashooter' is welded onto the new exhaust and when the car is on the ground you cannot see the aftermarket exhaust as I want to keep the look of the outside of the car completely stock looking. Hence why the pipe is pointing down. Its invisible!!!

Yes I know I have avoided Facebook for what 16 years now ha. I might be forced to join up just because of all the forums I use to enjoy are now all dead. I have pm'd some people on here with performance turbos about the problems I am facing and Paul has got back to me with some excellent information I can work with. A later kv6 pg1 box, I link to a clutch rated at 350 ft lb and the use of a quaife differential. But any other information would still be great. I would still like to know what power the standard gearbox/clutch can take though. Thnaks Andrew

[charliecosworth]

use a gearbox from MG ZS180, this gearbox uses more thicker shafts inside.
Also you need to swap speedo drive and diff, Whilst gearbox is in bits fit steal caged bearings widely available on ebay


Clutch.... fit flywheel from rover 220 turbo, so you can fit the larger clutch plate 228mm make sure its a early 2 gap one so you Ecu will run with it, and fit good decent diesel clutch or sports one if your not bothered about heavy or juddering clutch

[Jeff Turbo]

use a gearbox from MG ZS180, this gearbox uses more thicker shafts inside.
Also you need to swap speedo drive and diff, Whilst gearbox is in bits fit steal caged bearings widely available on ebay


Clutch.... fit flywheel from rover 220 turbo, so you can fit the larger clutch plate 228mm make sure its a early 2 gap one so you Ecu will run with it, and fit good decent diesel clutch or sports one if your not bothered about heavy or juddering clutch

Nice to see you back

[Andy]

use a gearbox from MG ZS180, this gearbox uses more thicker shafts inside.
Also you need to swap speedo drive and diff, Whilst gearbox is in bits fit steal caged bearings widely available on ebay


Clutch.... fit flywheel from rover 220 turbo, so you can fit the larger clutch plate 228mm make sure its a early 2 gap one so you Ecu will run with it, and fit good decent diesel clutch or sports one if your not bothered about heavy or juddering clutch

Hi thanks for the reply much appreciated. I have been in contact with Paul who has very patiently been helping me out. That was what he originally suggested which I was going to go for until he realised, I was still ruining 15" alloys with a 195/50 profile, I want to keep these standard wheels 17’s are not an option for me. He said this would be under geared and to go for a diesel box. Which I don’t understand as I thought they would be lower geared but I don’t know anything about gearboxes. Which diesel boxes are stronger? In an ideal world I would like to use my original box with steal cage bearings and a Rover (PG1) Quaife ATB Helical LSD differential as I have heard good things about these and it should put the power down but I still believe the box won’t be strong enough. Anyone any experience of using a diesel box, what code box did you use and what rpm did it sit at 70/80 and top speed? Also recommended a taller diff ratio but out of what? Thanks Andrew

[charliecosworth]

don't use a diesel box your wasting your time, been there done it and removed it! just get yourself good zs180 box code C6BKUH take speedo drive and diff and swap them with original box and fit the uprated bearings whilst it apart, Quaife diff are ok and have one fitted in mine, but unless you going racing or driving car like its stolen every day its a over kill.

[Andy]

Ok thanks for the advice. That’s what I will go for. Not the end of the world if its needs to come back out to try other options but it’s a good start. If it’s to low ratio like Paul said it might be back to the drawing board. I certainly won’t be driving it like I have stolen it every day, but I might want to occasionally ha. That’s why I wanted the Quaife. to put the power down and reduce torque steer as they aren’t brilliant in those regards with standard power. Also, I only drive it April-September and never in the rain so I was going to put on a set of Toyo R888r's to help with grip as wet performance or wear doesn’t bother me. Unless anyone has any other tyre suggestions? The Toyo proxy tr1's have been on 7-8 year anyway so will be due for a change.
There is a bloke on eBay that seems to just specialise in PG1 gearboxes and it appears these have already had the steal cage bearings fitted:
Reconditioned PG1 gearbox. Standard C6U or S6U ratio. | eBay Is there anymore to change other than the ones he has done? So, I will go for:

• Ebay C6 box with steal cage bearings
• Quaife ATB differential
• Speedo drive from my pg1 turbo box (Do I need the Crown and pinion from my original box?)
• Maestro turbo diff seals.
• Gbe t16 clutch (do I need the matching flywheel?)

Thanks Andrew