Porsche Boxster gearbox conversion

[Mightymetro]

While I was digging up information for the rebuild on the car I’m still unsure where I will end up with the transmission.  I’m hoping the current UN1 box will hold up for 12 months until I can comfortably afford a good rebuild on it with the strengthened parts as with the unexpected bills on the engine rebuild its pushed me well over budget at the current time. Ssshhhhhhhhhh 

with the UN1 mentioned as a bit of a weakness (although there isn’t many cases of knackered transmissions) I did hear rumblings regarding the Porsche conversion.

i messaged Kennedy engineering who confirm they have a kit available to fit the boxster 987 S gearbox to the lotus v8 engine.  The kit comes with bell housing, flywheel to,suit the lotus starter, pilot bearing and bolts at around $1800  and a performance clutch kit is around $850 to suit

obviously the Boxster gearbox is not really made for huge amounts of torque and the kit does not include the custom items you would need to have such as driveshafts and gearbox mounts but I reckon they could be made for around $1000.  I think you would also need the gear tick and cables etc.

looking at it I think it would probably work out not far off the UN1 upgrade costs so is an option to consider in the future depending on feedback from the first couple of conversions.  
 

my main concern is that the few boxes listed on sites like eBay show a few gearboxes for spares........with blown 2nd gears!!!!  Sound familiar 😂

 

just thought I would let you all know 

 

[910Esprit]

I've no idea if all Boxter boxes are created equal. but both Boxters in my locale failed with terminal gearbox trouble!

[Barrykearley]

Think about it - and then dump the idea.

them pork gearboxes ain’t that great. The cost of buying a gearbox, sorting translaters, sorting driveshafts, adaptor plate and clutches will soon mount up.

Stick a shaft upgrade in your box and he quaiff lsd and all will be well. Your cars coming together lovely - keep her original but upgraded.

Look at the feedback on the first conversions sure - but be aware folks will think what they have done is great no matter what. One thing is for sure - loads of folks have installed lsd and shaft upgrades and we’ve not read about failures of those.

[red vtec]

I've been looking at tremec boxes, I heard jay Leno mention them, as he fits them to some of his cars. I've really only glanced at the site but wonder if that might be an option. 

[v8GTmac1]

On 01/05/2020 at 22:51, Mightymetro said:

 

i messaged Kennedy engineering who confirm they have a kit available to fit the boxster 987 S gearbox to the lotus v8 engine.  The kit comes with bell housing, flywheel to,suit the lotus starter, pilot bearing and bolts at around $1800  and a performance clutch kit is around $850 to suit

obviously the Boxster gearbox is not really made for huge amounts of torque and the kit does not include the custom items you would need to have such as driveshafts and gearbox mounts but I reckon they could be made for around $1000.  I think you would also need the gear tick and cables etc
 

my main concern is that the few boxes listed on sites like eBay show a few gearboxes for spares........with blown 2nd gears!!!!  Sound familiar 😂

 

just thought I would let you all know 

 

This brings a smile to my face. I don’t feel changing the trans takes away the originality unless you plan on selling it to a collector who’s idea of upkeeping is a battery tender.   If this conversion in fact makes it No stronger then the un1 then at least a replacement is always available from virtually anywhere.  Maybe I look at it differently then most on this forum. But when there is only a single v8 transmission for sale on eBay at all times, I tend to have a hard time enjoying the Lotus just going around town for a drive. I am not going to be the guy paying that eBay seller $6k for a used un1 that might last another year

This changes dramatically when the feeling is you can order a replacement using a local parts dismantler, eBay or phone apps while you sit on the side of the road waiting for a tow after having to frantically push or force your car out of harms way. 

If there is no stronger replacement ring and pinion then all I want is stock gearsets and an LSD till it grenades and then swap it out. If I have to worry about a seized trans with $6k of upgrades inside of it then I will be the slowest car on the road which negates putting in stronger gearsets. 

This past week I finally convinced the wife it was time for her to drive the Lotus to and from our adventures. I have to say there was no other time in my life where I had to test my patience. I must have yelled at her “in my thoughts” 10 times but I kept telling myself.......when the time comes, then it’s time.  100f weather , AC and rad fans full blast, stalling at lights from apparent vapor lock in the fuel lines, then the trans decides it wants to stay in gear and not come back out. This wasnt the first time nor will it be the last. Don’t know if it was the clutch had overheated or the synchros, but had to shut her off and restart in neutral. 

I started telling her we need to get a trans cooler for the hotter months. Put those 2 front retired oil coolers to work again. Haha.

Anyways this is just my thoughts. I will plan on contacting Kennedy and sourcing a  Boxter S 6 speed. Not just a 5 spd from a base Boxter. Soo glad someone made the call.  

Edited May 5, 2020 by v8GTmac1

[CHANGES]

On 02/05/2020 at 06:51, Mightymetro said:

i messaged Kennedy engineering who confirm they have a kit available to fit the boxster 987 S gearbox to the lotus v8 engine.  The kit comes with bell housing, flywheel to,suit the lotus starter, pilot bearing and bolts at around $1800  and a performance clutch kit is around $850 to suit

I have recently had this discussion on another Forum with someone who was adamant that it could be fitted with nothing more than re drilling the original flywheel ..  When i pointed out all the other aspects and technical details to doing such a conversion he got very insistent and insulting... Funny how some don't want constructive advise and have all the answers..     At least on here we have people looking at the wider picture and exploring what is needed.. 

As someone who has traveled the road of transmition woe's due to performance upgrades , i have looked at most options to fit my needs..    Most of the time an alternative was binned due to drive shaft alignment,  if this is not right then you generate all sorts of issues, and moving engines backward or forward is just not practical.. Primary shaft length is always an issue when fitting an adaption plate, shoving and extension on it is a cobble and will fail  , so a custom flywheel with spigot bearing fitted within to match up the two halves is the common solution.  Next is clutch.. If you have upgraded your power enough to break the tranny , then your clutch will not be man enough for the job and will need sourcing at the same time. This will all need to fit on the Porsche primary shaft and within the Porsche bell housing as it is not detachable from the box like the UN1 is.  You will also need to adapt the clutch release mechanism to match the chosen clutch with the gear box and the Esprit clutch pedal ratio..  These are just a few points you need to be aware of even  before you start manufacturing rear mounts , gear levers , selector mechanisms and sourcing suitable cables, not to mention adapting drive shaft fitment. 

All of the above would be very interesting project to do and a great challenge..                                                                                  BUT, will it fix the initial problem ' power/torque limits' .... In most cases NO .. Some are a bit higher and better than the standard UN1 027 but not by much and the gear ratios / final drive don't all suit the Esprit set up..   The 987 6 speed box out of the 3.2 pre TDK is the best of the Boxster options , however this offers less than some of Audi  01E  box's..   What you also need to know is there are several variants of all of these , which all look the same from the outside.. internally very different..  When buying second hand you really need to be sure of what you are buying , because they wont have it back when you have fiddled with it..   

Another point to consider is , any second hand box you buy, should be rebuilt to insure it is not faulty, so cost that in . If you buy a new or specialist recon box , they ain't cheap..  The second hand box's on the net for under £1k  are usually tired or broken , so you are taking a chance and will need to factor in the rebuild cost and parts. 

Which brings us back to the UN1...   When you drive your Esprit sensibly , you should have no issues.  If you drive it hard but have considerations for its weaker points , you will minimise any issues..  But if you are regularly developing over 400 ft lb spike torque loads and want to use it ,  then do a UN1 upgrade ..   There are more options becoming available with on going developments and testing being done .  There are GTO , Elite Racing and Holloway already available ,  all well proven with ratio options etc..  These kits only cost the same as buying a decent standard 987 box but without fitment issues ..  There are even higher spec's you can go to using the UN1  as featured in the 412 thread in Esprit chat section .  These do come at a price, but when fully costed out will probably end up cheaper than a donor conversion with comparable torque capability, but without the fitment hassle... 

1 hour ago, v8GTmac1 said:

If there is no stronger replacement ring and pinion then all I want is stock gearsets and an LSD till it grenades and then swap it out. If I have to worry about a seized trans with $6k of upgrades inside of it then I will be the slowest car on the road which negates putting in stronger gearsets. 

  There are stronger ring and pinion options available .   You can strengthen and treat your original as the cheapest option, or have a special high torque set made as I have ..  Used along side one of the aforementioned gear kits , you should be able to hopefully meet all your torque requirements.. 

To summarise ,   A 3.2 ltr 987 Boxster  develops 236 ft lbs of torque through its gear box,  the 3.5 ltr V8 Esprit develops upward of 300 ft lbs through its gear box..   If you are having power issues with the Esprit box, Why are you looking at the Boxster box.    I believe a lot more research and proper testing will need to be done with the 987 box before it can be considered as a stronger alternative .. 

This is Just my personal input on the subject based on my own experiences and data available .. Hope it helps shed some light on what is available and involved..           

[Mightymetro]

22 minutes ago, CHANGES said:

I have recently had this discussion on another Forum with someone who was adamant that it could be fitted with nothing more than re drilling the original flywheel ..  When i pointed out all the other aspects and technical details to doing such a conversion he got very insistent and insulting... Funny how some don't want constructive advise and have all the answers..     At least on here we have people looking at the wider picture and exploring what is needed.. 

As someone who has traveled the road of transmition woe's due to performance upgrades , i have looked at most options to fit my needs..    Most of the time an alternative was binned due to drive shaft alignment,  if this is not right then you generate all sorts of issues, and moving engines backward or forward is just not practical.. Primary shaft length is always an issue when fitting an adaption plate, shoving and extension on it is a cobble and will fail  , so a custom flywheel with spigot bearing fitted within to match up the two halves is the common solution.  Next is clutch.. If you have upgraded your power enough to break the tranny , then your clutch will not be man enough for the job and will need sourcing at the same time. This will all need to fit on the Porsche primary shaft and within the Porsche bell housing as it is not detachable from the box like the UN1 is.  You will also need to adapt the clutch release mechanism to match the chosen clutch with the gear box and the Esprit clutch pedal ratio..  These are just a few points you need to be aware of even  before you start manufacturing rear mounts , gear levers , selector mechanisms and sourcing suitable cables, not to mention adapting drive shaft fitment. 

All of the above would be very interesting project to do and a great challenge..                                                                                  BUT, will it fix the initial problem ' power/torque limits' .... In most cases NO .. Some are a bit higher and better than the standard UN1 027 but not by much and the gear ratios / final drive don't all suit the Esprit set up..   The 987 6 speed box out of the 3.2 pre TDK is the best of the Boxster options , however this offers less than some of Audi  01E  box's..   What you also need to know is there are several variants of all of these , which all look the same from the outside.. internally very different..  When buying second hand you really need to be sure of what you are buying , because they wont have it back when you have fiddled with it..   

Another point to consider is , any second hand box you buy, should be rebuilt to insure it is not faulty, so cost that in . If you buy a new or specialist recon box , they ain't cheap..  The second hand box's on the net for under £1k  are usually tired or broken , so you are taking a chance and will need to factor in the rebuild cost and parts. 

Which brings us back to the UN1...   When you drive your Esprit sensibly , you should have no issues.  If you drive it hard but have considerations for its weaker points , you will minimise any issues..  But if you are regularly developing over 400 ft lb spike torque loads and want to use it ,  then do a UN1 upgrade ..   There are more options becoming available with on going developments and testing being done .  There are GTO , Elite Racing and Holloway already available ,  all well proven with ratio options etc..  These kits only cost the same as buying a decent standard 987 box but without fitment issues ..  There are even higher spec's you can go to using the UN1  as featured in the 412 thread in Esprit chat section .  These do come at a price, but when fully costed out will probably end up cheaper than a donor conversion with comparable torque capability, but without the fitment hassle... 

  There are stronger ring and pinion options available .   You can strengthen and treat your original as the cheapest option, or have a special high torque set made as I have ..  Used along side one of the aforementioned gear kits , you should be able to hopefully meet all your torque requirements.. 

To summarise ,   A 3.2 ltr 987 Boxster  develops 236 ft lbs of torque through its gear box,  the 3.5 ltr V8 Esprit develops upward of 300 ft lbs through its gear box..   If you are having power issues with the Esprit box, Why are you looking at the Boxster box.    I believe a lot more research and proper testing will need to be done with the 987 box before it can be considered as a stronger alternative .. 

This is Just my personal input on the subject based on my own experiences and data available .. Hope it helps shed some light on what is available and involved..           

Fabulous response , thank you

i saw the thread regarding the ‘simple’ conversion 😂😂😂😂😂

i just thought it would be good to put some solid Information out there on what is available and how the conversion is done etc with prices as there are so many whispers and rumours

to be fair I haven’t encountered any problems with sourcing parts for the UN1, I’ve even just ordered brand new cases from SJ as mine have a few dodgy threads that have been helicoiled at some point

thanks again for the impartial view.  
 

my wife has a PDK boxster 981 and it is an absolute weapon.  Pretty boring as it is so capable and easy to drive and that is also a worry for me.  I don’t want the Lotus to feel digital and I want it to make me ‘drive’ it

My main issue with something like the kennady kit is I believe it should be sold as a full bolt on kit with everything included.  Otherwise is it just a cad/cam computer simulation and then made without the thought into the other bits.  Hope that makes sense

when the metro / mini owners used to put Honda Vtec engine in their cars you could go to Watson’s engineering and they could sell you everything you needed for the whole conversion.  Gives you much more confidence this way 

[cweeden]

Another interesting discussion point is raised by GMendoza (Pancho) on LotusTalk here https://www.lotustalk.com/forums/f164/v8s-feel-clunky-hard-drive-compared-i4-462312/ where he discusses his thoughts that the clutch is to blame and not a weak gearbox. He has also helped to design a lightened flywheel which might be interesting but if nothing else it looks great. 😀  https://www.lotustalk.com/threads/esprit-v8-new-clutch-lighter-flywheel.473226/

cheers

-Chris

[CHANGES]

1 hour ago, Mightymetro said:

My main issue with something like the kennady kit is I believe it should be sold as a full bolt on kit with everything included.  Otherwise is it just a cad/cam computer simulation and then made without the thought into the other bits.  Hope that makes sense

when the metro / mini owners used to put Honda Vtec engine in their cars you could go to Watson’s engineering and they could sell you everything you needed for the whole conversion.  Gives you much more confidence this way 

This is so true and also very important..  If only a few basic adaption parts are available , then the concept is incomplete and untested.. With anything development wise there is always issues, these only get ironed out when someone seriously tests them .. If kennady have not done full make up testing with data to back up , then all you are buying is a box of bit that you have got to try and make work.. 

32 minutes ago, cweeden said:

Another interesting discussion point is raised by GMendoza (Pancho) on LotusTalk here https://www.lotustalk.com/forums/f164/v8s-feel-clunky-hard-drive-compared-i4-462312/ where he discusses his thoughts that the clutch is to blame and not a weak gearbox. He has also helped to design a lightened flywheel which might be interesting but if nothing else it looks great. 😀  https://www.lotustalk.com/threads/esprit-v8-new-clutch-lighter-flywheel.473226/

 

 This is a very interesting option with great potential along with info from people who have fitted and tested ..   What would be interesting would be the details on clamp and release loading's, along with torque capabilities..    The std V8 plate from AP racing had a corrugation section within the friction plate to make it more compliant than a race clutch ,  but as was said can still be a bit sharp compared to other clutches..   When asking AP for the 550 ft lb version , i was presented with a version that did not have the corrugation section due to space constraints, which made it less compliant so more of a race clutch..   To offset this we introduced a staggered plate engagement to make it more compliant. This does work well but will wear one plate quicker than the other.    So I for one  would be very interested in an alternative that bolts straight in , as long as it can take the higher  torque levels.      As for the lightened fly wheel , I agree a lot can be facilitated from doing this . Personally i would not go for the letter box option,  I have seen far to many of them fail over the years , straight drilling's can achieve similar results with better reliability.. 

Pic of custom light weight drilled chrome molly version for the 4 pot engine using the  V8  clutch . 

       

[jonwat]

There was a guy who used to race a V8 Esprit with a 911 transmission which he'd flipped upside down, can't remember any more details than that though. 

[mike_sekinger]

17 minutes ago, jonwat said:

There was a guy who used to race a V8 Esprit with a 911 transmission which he'd flipped upside down, can't remember any more details than that though. 

Yes, that would be John Hazzard.  I bought it all from John, but did not want a flipped G50 in the Esprit in the end.

Here's some images:

[jonwat]

1 hour ago, mike_sekinger said:

Yes, that would be John Hazzard.  I bought it all from John, but did not want a flipped G50 in the Esprit in the end.

That's the guy, watched him race at Silverstone, if I remember correctly he retired early from every race when something broke. 🤢

[mike_sekinger]

2 minutes ago, jonwat said:

That's the guy, watched him race at Silverstone, if I remember correctly he retired early from every race when something broke. 🤢

Yes, it was all a bit "rough and ready".

[red vtec]

how about this for a lightened gearbox? found on a Porsche RS

[cweeden]

Wow, there are more holes than gearbox. 🤣

[v8GTmac1]

On 04/05/2020 at 23:21, CHANGES said:

On 04/05/2020 at 23:21, CHANGES said:

I have recently had this discussion on another Forum with someone who was adamant that it could be fitted with nothing more than re drilling the original flywheel ..  When i pointed out all the other aspects and technical details to doing such a conversion he got very insistent and insulting... Funny how some don't want constructive advise and have all the answers..     At least on here we have people looking at the wider picture and exploring what is needed.. 

As someone who has traveled the road of transmition woe's due to performance upgrades , i have looked at most options to fit my needs..    Most of the time an alternative was binned due to drive shaft alignment,  if this is not right then you generate all sorts of issues, and moving engines backward or forward is just not practical.. Primary shaft length is always an issue when fitting an adaption plate, shoving and extension on it is a cobble and will fail  , so a custom flywheel with spigot bearing fitted within to match up the two halves is the common solution.  Next is clutch.. If you have upgraded your power enough to break the tranny , then your clutch will not be man enough for the job and will need sourcing at the same time. This will all need to fit on the Porsche primary shaft and within the Porsche bell housing as it is not detachable from the box like the UN1 is.  You will also need to adapt the clutch release mechanism to match the chosen clutch with the gear box and the Esprit clutch pedal ratio..  These are just a few points you need to be aware of even  before you start manufacturing rear mounts , gear levers , selector mechanisms and sourcing suitable cables, not to mention adapting drive shaft fitment. 

All of the above would be very interesting project to do and a great challenge..                                                                                  BUT, will it fix the initial problem ' power/torque limits' .... In most cases NO .. Some are a bit higher and better than the standard UN1 027 but not by much and the gear ratios / final drive don't all suit the Esprit set up..   The 987 6 speed box out of the 3.2 pre TDK is the best of the Boxster options , however this offers less than some of Audi  01E  box's..   What you also need to know is there are several variants of all of these , which all look the same from the outside.. internally very different..  When buying second hand you really need to be sure of what you are buying , because they wont have it back when you have fiddled with it..   

Another point to consider is , any second hand box you buy, should be rebuilt to insure it is not faulty, so cost that in . If you buy a new or specialist recon box , they ain't cheap..  The second hand box's on the net for under £1k  are usually tired or broken , so you are taking a chance and will need to factor in the rebuild cost and parts. 

Which brings us back to the UN1...   When you drive your Esprit sensibly , you should have no issues.  If you drive it hard but have considerations for its weaker points , you will minimise any issues..  But if you are regularly developing over 400 ft lb spike torque loads and want to use it ,  then do a UN1 upgrade ..   There are more options becoming available with on going developments and testing being done .  There are GTO , Elite Racing and Holloway already available ,  all well proven with ratio options etc..  These kits only cost the same as buying a decent standard 987 box but without fitment issues ..  There are even higher spec's you can go to using the UN1  as featured in the 412 thread in Esprit chat section .  These do come at a price, but when fully costed out will probably end up cheaper than a donor conversion with comparable torque capability, but without the fitment hassle... 

  There are stronger ring and pinion options available .   You can strengthen and treat your original as the cheapest option, or have a special high torque set made as I have ..  Used along side one of the aforementioned gear kits , you should be able to hopefully meet all your torque requirements.. 

To summarise ,   A 3.2 ltr 987 Boxster  develops 236 ft lbs of torque through its gear box,  the 3.5 ltr V8 Esprit develops upward of 300 ft lbs through its gear box..   If you are having power issues with the Esprit box, Why are you looking at the Boxster box.    I believe a lot more research and proper testing will need to be done with the 987 box before it can be considered as a stronger alternative .. 

This is Just my personal input on the subject based on my own experiences and data available .. Hope it helps shed some light on what is available and involved..           

 

 

To summarise ,   A 3.2 ltr 987 Boxster  develops 236 ft lbs of torque through its gear box,  the 3.5 ltr V8 Esprit develops upward of 300 ft lbs through its gear box..   If you are having power issues with the Esprit box, Why are you looking at the Boxster box.             

thank you for the good points although I dont agree with your view on some of it.

 the Un1 didnt come out of a 350hp car originally am I right?

The un1 and the Audi boxes both come with hollow input shafts that translate power back to the driven shaft?

The Boxter trans appears to NOt be hollow? 

Boxter 2nd gear issues? Rather that then snapping the input shaft while in 5th when passing a car and you engine suddenly bucks/misfires. 

If you have made a custom stronger material CWP, how much did the R&D set you back? What will it take to get a set made or get a CAD file? 

Because GTO already exists and Quaife is still on option, a stronger CWP is the only thing I believe that is driving my worries with the un1, oh and lets not forget the Roll Pins which I still havent gotten out. 

 

Edited May 7, 2020 by v8GTmac1

[tread72]

Very cool video of a six speed Esprit v8 by the forggotten Exotiv - Lotus Esprit

https://www.youtube.com/watch?v=2RWndflhzlA

 

 

[dclare]

I have to say I keep thinking about doing this coversion for no other reason than I think the standard gearbox and clutch really detract from the driving pleasure of the Esprit. The rest of the car is really tactile and has lovely control weights but the clutch and gearchange are just not a pleasure to use (in my opinion of course!) and results in a series of lunges rather than a flow when you're pressing on.

There are now many higher powered versions of the Boxster/Cayman and even the 718S 4 cylinder versions put out over 300 ft lbf as standard so will support a higher load quite easilly. The problem seems to be a very high 2nd gear ratio, but different gearsets are available if the Lotus v8 torque doesnt mask the gap.

The issues of driveshafts needing fabricting, mounts need fabricating and gear change/linkage are not really big issues. Any number of companies will make up a hybrid driveshaft if to take the old donor shafts to them and specifiy the overall length of the new shaft (Ive used DaveMac Propshafts in the past).  The gearchange and (I think) cables will transplant directly from the donor Boxster/Cayman so that just leaves the simple fabrication of new mounts and cross-member. Not difficult jobs if you are into any kind of fabrication, or know someone who is.

Still just musing, but I do dislike the standard gearbox.....