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Sander's 6.0 V12 745 project

Awesome project. Interesting to go to irs instead of a stronger live axle, given the various design issues with the irs unit. Did you consider a Toyota r220 diff as well?

Why would you want such a tall gear ratio? Wouldn't you want taller to allow for better performance?

Thanks! What design issues do you mean? The toe rods being made of spaghetti is easily changed and also the weak diff can be changed too. Finding springs that fit is easy too as it just uses standard 5" OD springs which you can get in any length and rate you could ever wish for. The difference between a car with a live axle and an irs are night and day in the corners (of which there are a lot on this side of the pond). Especially on not fantastic roads. Live axles are great on the drag strip but not much else. The nice thing about the BMW diff is that it can be found with the ratio I want, comes with a factory LSD, can handle all the power I can throw at it and the Volvo axles bolt on. I think the ones with a taller ratio than 3.something were never available in the U.S. Here the tallest one is 2.56:1.

The tall ratio is because the 5th gear ratio of the trans is 0.83:1 and I don't want to be doing 3000rpm on the highway. The engine's a torque monster too so it'll have more power than traction anyway. 2.65:1 is the stock ratio of the S600 too, it'll be one less headache to get this modification registered. No complaints by the authorities that the S600 exhaust norms aren't being met anymore due to changing the ratio.

This car should remain a fully usable road car, it's not going to be a toy for on the drag strip (which are almost non-existent here too).
 
Are you factoring tyre diameter into those ratio/speed calculations? If the authorities care about RPM to speed in each gear, then they'd care about that. On the other hand, they can't stop you driving along in any non-damaging gear, so it's weird to care about that.
 
Gotta think the big Benz ran a taller tire than the Volvo will - which would have the effect of shortening the 2.65's. Although, with a 25" tire, the .83 top gear and 2.65 rear - 70 mph is hair under 2100 rpm (assuming lock up converter). Just about exactly where I am with 3.55's, 25.3" tire and a .625 5th.
 
No complaints by the authorities that the S600 exhaust norms aren't being met anymore due to changing the ratio.

because the engine was not a stock volvo option, you are allowed to have like 3,5% co from the exhaust by the rdw people.
that is if you don't have to do the expensive tech inspection in lelystad. in that case its treated like a new 2017 (if you get it ready this year :-P ) car and it will require things like anti lock brakes and airbags and such.

does your volvo have U9 on the papers? if so, it might be different but i'm not sure.
 
because the engine was not a stock volvo option, you are allowed to have like 3,5% co from the exhaust by the rdw people.
that is if you don't have to do the expensive tech inspection in lelystad. in that case its treated like a new 2017 (if you get it ready this year :-P ) car and it will require things like anti lock brakes and airbags and such.

does your volvo have U9 on the papers? if so, it might be different but i'm not sure.

Gotta be nice building a hot rod over there - what with all the "help" you're getting!
 
Are you factoring tyre diameter into those ratio/speed calculations? If the authorities care about RPM to speed in each gear, then they'd care about that. On the other hand, they can't stop you driving along in any non-damaging gear, so it's weird to care about that.

It's true that wheel size also matters, the S600 runs 235/60/16 wheels stock, so that's slightly bigger than the 265/35/18 or something that I'd like to run in the back.

Gotta think the big Benz ran a taller tire than the Volvo will - which would have the effect of shortening the 2.65's. Although, with a 25" tire, the .83 top gear and 2.65 rear - 70 mph is hair under 2100 rpm (assuming lock up converter). Just about exactly where I am with 3.55's, 25.3" tire and a .625 5th.

Yes correct, the Benz uses bigger wheels but also not gigantic. If I run the 2.56 BMW diff with the tire size I'm planning, it should equate to practically the same RPM in all gears as the S600 with stock wheels. A certain variation is allowed in gearing and tire sizes compared to stock. I'm not sure how much though.

because the engine was not a stock volvo option, you are allowed to have like 3,5% co from the exhaust by the rdw people.
that is if you don't have to do the expensive tech inspection in lelystad. in that case its treated like a new 2017 (if you get it ready this year :-P ) car and it will require things like anti lock brakes and airbags and such.

does your volvo have U9 on the papers? if so, it might be different but i'm not sure.

but keep up the good work! would like to see this in person some day

Thanks! Once it's all running a road trip is certainly in the plans, so that can be arranged :). Apparently they changed the regulations a bit a few years ago regarding engine swaps etc and it's now much easier than before. The road handling test in Lelystad is also no more. If the car is from before 1998 all it has to apply to are the general APK requirements and some noise regulations. And if you're using stock stuff from another car with a type approval it's also easier. For cars from 1998 and onwards they are treated like a new approval and it has to fulfill all requirements of a new car.

Would love to a detailed write up about the IRS diff swap.

Sure, I'll make one. I was planning to do a write up about the bmw diff swap too.

Gotta be nice building a hot rod over there - what with all the "help" you're getting!

The bureacracy jungle is great indeed. And the Netherlands is still one of the easy countries to get things done. The real fun starts when I will get it registered in Germany.
 
Minor update, I've been mostly been working on the brakes, making old rusty stuff look nice again on the rear suspension and collecting parts. I ordered a BMW diff now with the ratio I want (2.56:1, with the wheel size I plan on running it'll be pretty much stock rpm's in all gears like on the S600) and a factory LSD.

For the brakes I 3D printed some adapters to easily test fitment, but it's not really sturdy enough so I cut 1 out of steel. The final ones will mount on the inside instead of on the outside like on these pictures. They'll be laser cut out of S355 steel. The shape will be different too, this was just something I could cut relatively easy out of steel with an angle grinder.






Decided to paint the calipers gold(ish):



I forgot if I posted this already or not, but a bit of background info on the BMW diffs: there are 3 different types, the small casing diff with a 168mm ring gear, the medium case diff with a 188mm ring gear and a large case diff with a 210mm ring gear. The outside of the casing varies between models, but internally there are just these 3 types. You can identify them by the amount of bolts that hold the axle flanges in place on the casing. Small casing is 4 bolts, medium uses 6 and the large case diff has 8. The small casing diff is pretty weak so I won't be going into detail about those.

The medium and large case diffs are both very strong with the large casing one being the strongest (obviously). The medium case ones can be found in pretty much any (older) BMW and come in ratio's anywhere between 2.56:1 and 4.45:1 (at least here in Europe. I think the tallest one in the U.S. is 2.79:1 or 2.93:1) and can have a factory clutch type LSD. All diffs have a tag on it with the ratio and if it has an LSD there's an S in front of the ratio number. The medium case diffs have been proven to hold upwards of 700Nm of torque, depending on the ratio.

The large case diffs can hold even more than that (900+Nm, depending on the ratio) and can be found on (most) M cars and V8 or V12 powered cars (except the 3.0V8 which has a medium case diff). The available ratios for these are a bit limited, between 3.15 and 3.91. There is a large case diff with a 2.65:1 ratio, but that one is rare as balls as it only came on the 850CSI with a manual trans.

The axle flanges that work with the Volvo axles are the ones found on all large case diffs. It has a bolt circle of 94mm (iirc) and is exactly the same shape as the flange on the Volvo diff. The medium case diff can be found with 4 different axle flanges, 2 small ones with a bolt circle of 87mm and 2 big ones with a bolt circle of 94mm. The flanges found on the manual 535i are the same ones as the large case diff. All these medium case diff flanges are interchangable. There is a guy on ebay who sells any type you want for $45 a set. Anyway, to be continued when I receive the diff I ordered. I got the flanges I need already. Here's how they (large type for medium case diff) fit the Volvo axles:


 
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Just received the diff. Here you can see the difference between the small flange and the big one. It takes 30 seconds to swap them as they just pop out and the big one just pops in again. The BMW diff with the big flanges appears to be 3 or 4 mm narrower than the Volvo diff. I don't have a 1035/1045 diff to measure anymore though. It roughly measured 295mm wide from flange to flange. Don't know if I have to use some 2mm spacers on each side or if it will work as is with the CV joints.



Factory clutch type LSD:



The big flanges installed:




And put a Brembo sticker on the caliper. A layer of clear coat is still to come:

 
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Can't wait to see your mounting solution for the diff.

I'll modify the IRS subframe to use the BMW diff mounting points. The rear mounts on the 2 points on the diff cover and the front is supported on the lower right side. I plan on making that one adjustable to set the pinion angle. It's a bit of a hassle that I don't have the stock diff for measuring and fitment purposes, but it'll work.

Finished one of the calipers with clear coat and new pads etc. I should have the adapters finished in a week or 2 maybe. If they fit as expected I'll do a group buy for them if there is enough interest. I'll make a set that fits the 960II too if there is enough interest.



 
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I should have the adapters finished in a week or 2 maybe. If they fit as expected I'll do a group buy for them if there is enough interest. I'll make a set that fits the 960II too if there is enough interest.

I'm interested if you'll provide a Teilgutachten for the 740 chassis!!!! :cool:
 
I'm interested if you'll provide a Teilgutachten for the 740 chassis!!!! :cool:

A Teilegutachten is never going to happen unfortunately, but a materialgutachten shouldn't be a problem (I'm making them out of S355 steel) and then it should be doable to get it registered with an einzelabnahme as all the other brake components are from already approved production cars. No weird aftermarket racing stuff.
 
Cut up the subframe to make room for the BMW diff. I had to remove quite a bit at the back of the subframe. Then I welded in a support structure to hold the diff in the correct place at the flanges when I make the new mounts. The bottom part of the subframe still needs to be modified because also there the diff is a bit too big. I'll try to keep the fill and drain plugs accessable. I'm planning on making the front mount of the diff adjustable so the pinion angle can be set correctly once it's on the car. To be continued.





 
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