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New booster option for e30 - Bosch iBooster

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    New booster option for e30 - Bosch iBooster

    I thought I'd post this here since it's the brakes section, but this is mostly of interest to anybody doing a swap who's been struggling with finding a booster that will fit against a 24v intake manifold. I'm working on a swap right now and had resolved myself to doing a manual pedal box to avoid this whole situation.

    I spent an afternoon with hoveringuy picking up an engine for his swap at a specialty wrecker near us, and I think he was getting a little tired of me ducking in and out under the hood of every EV and hybrid on the lot. A lot of these have an electronic brake booster to allow for the computer to decide how much brake is provided by the hydraulics, and how much is provided by the regenerative brake system (so under light braking, you might push the pedal with 30% effort, and it might feel like your brakes are being boosted, but it's actually the electric motor braking to recharge the batteries). When your brake force request exceeds what the regen system can provide, it starts to add hydraulic braking with the electronic booster.

    When I got back from the yard I was convinced this was worth looking into, but the size of the plugs to these boosters was pretty intimidating. I found a reference on a DeLorean forum from YEARS ago about these boosters working in a failsafe mode... which makes complete sense, because if you lose a data connection you'd like to have the booster go back to "dumb" mode. Searching specifically for that, I came across Lars, (a Volvo 122 Amazon enthusiast like my brother) in the Netherlands. Not only did he have documentation for the pinout for the unit he used, which was from a Tesla:

    An iBooster in your car is very attractive. This article explains wiring the iBooster GEN1 and GEN2 in detail. Our connector kit makes that even easier.

    He also documented how he got the booster installed in his Volvo, which included the bolt pattern at the firewall:

    Using and installing the iBooster made by Bosch from a used Tesla in your own car can increase breaking performance. There are various ways of mounting it.

    What a cool guy.

    It didn't take long for me to confirm that the 72mm was the same pattern as the e30 booster, and I had one on the way in the mail. Here's what it looks like when you pull it out of a Model S:

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    A huge bonus to this unit is that orientation of the "booster" segment isn't important, the firewall pattern is square, and the master cylinder interface is symmetrical:

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    (sorry about the mess of brake fluid)

    ​​​​​​​The brake rod is so close to fitting.. but I did need to ream it out. It turns out it's slightly too short, but that should be very easy to fix:

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    Here it is with the booster flipped "upside down" and an e30 pedal bracket bolted up:

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    And here's a closeup of the 5 min wiring, it really is just two twisted CAN lines that we don't need, a big ground, a big power, a small power (for the computer) and the red/white ignition power (disconnected here):

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    So.. the exiting part... does it work? boy does it work.

    video, sharing, camera phone, video phone, free, upload

    (if ANYONE can tell me how the youtube embed is supposed to work that would be lovely)


      Just about the only thread I post in is related to the engine swap we're working on, and I have a pile of toys lying around related to that, including:

      1. A bare n52 block
      2. A set of engine arms that adapt the block to the e30 subframe via e46 motor mounts and locate it [what i believe to be] correctly in the chassis
      3. A partially stripped n52 head
      4. A loose 328i intake manifold, with the same exterior dimensions as the 3-stage DISA manifold that I'm planning on using for the n52 swap (from a 330i/Z4 3.0si)

      From everything I've read, this intake manifold is a greater challenge to fit against a booster than the other M5x/S5x 24v engines. There's been a few n52 swaps (someone tag them here if I'm wrong but I think it's cwlo and wazzu70) but they've been using the N54 intake manifold (from the later turbo engine) which is much shorter. We haven't seen a dyno result from this manifold on this engine yet (I don't think) and I certainly haven't seen one apples to apples comparing it to the 3-stage, but it's a very close match for the intake ports, and probably does fine or better at high rpm at the cost of some low end torque and of course with the huge benefit of more space under the hood.

      Here's the Tesla model S Bosch iBooster rotated 180 degrees with all of the components listed above stacked up next to it:

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      The booster actually *tapers down* where we need it to. Here it is from the front with a ruler behind it:

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      Here's one where I'm wiggling my finger in the gap because I can't believe how well this fits:

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      Maybe it would have still fit rotated the other way, but it's handy to have the wiring on top, and the computer module tucks so neatly behind the shock tower here:

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      Last edited by hubcapboy; 09-30-2020, 07:34 PM.


        So what do we know about this booster and what do I think?

        Won't this mess other stuff up?
        The e30 booster (I think, this is the brakes section so correctly me if I'm wrong) is dual tandem 23mm cylinders. There's a (I think) 7 series booster that's dual 25mm that some people use as an upgrade to a firmer pedal. As long as we keep both cylinders the same size there's no change to brake balance. The Model S booster is dual 25mm, so not only will the balance be fine, it's actually exactly what some people find is a better ratio (with a slightly firmer pedal and less travel)

        Will it stop the car?
        Yea. I think so. We weigh just about half what a Model S does, so if anything my fear is that in the failsafe mode this will be overboosted, although that'll be offset by the 23>25mm bore, so maybe it'll be a wash on pedal effort, but with shorter stroke? That sounds ideal.

        But the outlets are on the wrong side!
        yea. That's a bummer, and it looks like they're right where the intake pipe is closest. We'll see how that works. There are unmachined bosses on the other side so there's a chance it could be cut to accept the (correct size) brake fittings. Since we need adapters to go from our brake fitting to this, having the ports on the opposite side isn't the worst thing because it leaves room to run those adapters into the factory lines.

        How does the booster feel when you're pushing on the pedal?
        It feels perfect and silky smooth, and then kinda seems to get confused. I think this probably has to do with how it's detecting my pedal input, and there not really being any resisting force from the brake circuit. After a few strokes it kinda freaks out and turns boost off until the pedal goes back to the rest position. Maybe this is because it's trying to encourage you to pump the brakes in response to loss of line pressure? I'll go with that theory.

        I can believe how well that fits and that the reservoir is the right shape and the firewall pattern is correct.
        Right. Me either. But I have a theory here. Tesla was one of the first models to adopt these boosters, and they aren't going to do more work than they have to. I have a sneaking suspicion that since this configuration is the one that appears in all the Bosch documentation and early press releases that it was their "reference design" and it's just based on a very stuffy old German standard (thanks Bosch) that matches our very stuffy old German cars. This unit, and the 2nd gen iBooster which is shaped a little differently, are in all sorts of EV's and hybrids, but always with some odd reservoir shape to allow them to be mounted at an angle, filled from 2' away, etc. The model s had a conventional booster and a vacuum pump before these were added when autopilot was introduced (since it can apply the brakes without you stepping on the pedal whooooooaaaa).

        Why are you so excited about this when you say again and again that you don't mind converting to manual brakes in the swap thread so you can keep the fancy intake?
        Yea, that's awkward. I'm excited because this means I don't have to compromise.

        The rest of the info on the n52 swap that a few of us are working on is over here if you want to follow along:


          This is an amazing piece of work and MacGyverism at its best! This seems like the holly grail of e30 brakes. No hydro boost, or massive extension and relocation, nor manual brakes. Pretty much a drag-and-drop swap to an incredibly modern system.

          A few things I've learned from watching all of the various videos is that Bosch has pretty much cornered the market with the iBooster. There are some other flavors of booster in Japanese cars but the Bosch units are found far in wide in electric cars. This one is already their second generation unit.

          What's even mrore exciting, is that once the Can-bus is completely figured-out, the brakes could change behavior and have "Sport" or "comfort" modes, or the pedal pressure could be read as a signal. These things can be programmed to have different response curves and all kinds of cool stuff.

          Also not mentioned above, but these are failsafe. Loss of electrics is kinda like loss of vacuum on the older systems. Brakes still work, just need to push harder.


            ^ add to the safety pitch above that not only does this retain unpowered “brake-through” exactly like a vacuum booster, but it maintains 100% of your power braking during an engine stall or failure.

            This should allow full power ABS stops following an engine failure.


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              Attached Files


                This looks a lot like the Chevy Volt unit.
                Good work.


                  Dude. That is rad. Plus, it helps pad my stock portfolio. ;)

                  Electronics, I think can be sorted out. There's probably some sort of brake pressure feedback that it's missing.

                  what did that booster cost you? I don't know how common wrecked Teslas are - but they're surely getting more common. Is that booster only used on the Model S or is it used on some of their other more common cars?

                  Is there any reason you couldn't mount an E30 master cylinder to the electric booster? Or perhaps, one from a more modern BMW if needed?

                  To me, manual brakes to get another 50hp or something always seemed to be a bad tradeoff. Or you have something like the hydraulic assist which takes up a shitload of room, weighs a ton, and has a bunch of extra leak points, plus it adds to the parasitic losses.
                  Last edited by nando; 09-30-2020, 09:34 PM.
                  Build thread



                    They’re all over ebay... I paid about the same because I called a wrecker directly and had them snip all the cables. Finding the plugs if you’ve already found a booster is nearly impossible, but somehow Lars sells them on his website above. I’ve warned him about the incoming e30 demand ;)

                    This report has a pretty good list of the cars with these boosters, but in each other case the master cylinder and reservoir isn’t a usable configuration:

                    You could absolutely adapt any master cylinder into the front of the booster... but some of these units also have a different firewall pattern... so it’s starts to look more daunting. The model s fits without modification.

                    The real price comparison you have to do is against a new factory configuration bmw booster and master cylinder. Right now that’s around $900 for bmw genuine, or about half that for ATE. This comes it at or below the cheaper option... and the old parts are becoming more scarce... and wrecked Teslas are becoming more common.


                      Heres the list in case anyone wants to broaden the search. My gut tells me that production numbers of each of these models are probably lower than the Tesla Model S since 2016. I figured it was going to be one of the more common on the list (but maybe that’s just because I live in Seattle and we’re tripping over them)

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                        Originally posted by hubcapboy View Post
                        Click image for larger version

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ID:	9953480^and add to the improbability of this whole situation that if you can find a right hand drive booster, it’s mounted in this orientation from the factory and has the brake lines tapped on the other side:
                        Just put an order down on one out of Ireland, RHD model. Once it gets in I can shoot you any dimensions/pictures you'd be interested in.


                          How difficult would it be just to tap the correct port size on the blank side and plug the other one?


                            I’m definitely looking into tapping it on the other side. I don’t have any experience with this kind of machine work, but I expect it would require disassembling the cylinder, facing the casting, drilling and tapping the threads, and cutting the seat for the flare... and then probably re-boring the cylinder to clean up the mess?

                            Its harder than drilling and tapping for a bolt, certainly.
                            LukeJ might be the guy to answer that.


                              Anyone check other US electric parts car diagrams for a MC with opposite facing ports?
                              Last edited by moatilliatta; 10-01-2020, 11:25 AM.

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