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 Post subject: Stalker BMW build
PostPosted: September 29, 2016, 10:17 pm 
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Starting a log here after some interest in the engine weight thread...

So, this one is going to take a while but I feel that if I don't start and keep up with some kind of documentation I'll end up regretting it.

After many years of designing my own 7 style car in solid works 'perfect' was clearly becoming the enemy of 'done' and I had a great solid model but years of fab work that wasn't all that interesting to me (I've built plenty of steel car/bike frames). I was an integral part of 4 FSAE cars at Michigan Tech so I had a good handle on what was ahead of me. Fast forward to last fall when I learned that Scott Minehart at Stalker cars was now building a kit for a miata donor rather than their typical 3800 V6 or LS V8 which both turned me off of their earlier cars. I am not using a miata powertrain either but the layout of this Miata frame worked better for me and saved weight over their LS V8 frames (which I am also not doing, more later).

Overall, it gets me 90% of the way to what I would have built myself but cuts a year or more off the build. I also really like the M-spec bodywork. I wasn't (and still am not) a fan of the M-spec in pictures but when my wife and I walked in the shop to talk to Scott about ordering a car we each independently looked at his car in the shop and said "huh, that looks way better than it does in pictures." During a test ride Scott pointed out that the new rear fender shape cuts down on the typical 7 buffeting and I realized we were driving in a rain storm and not even getting wet, sold!

Here's a pic of one of their first complete cars and then a shot of where mine sits now:

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Mine at home:

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I picked it up with a budget rental truck and drove it back from Florida to Michigan. I caught the reverse snow bird timing and got such a screaming deal on the flight and truck that I couldn't justify the $1400 to crate and ship it. Had a fun road trip and picked up some hard to find junkyard stuff on the way home.

Next post will be about the driveline and the first couple days of progress (which is what prompted starting this thread!)

This is cross posted at another forum too so if you see some joke that doesn't make sense I just forgot to edit it out :D

Alex


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 Post subject: Re: Stalker BMW build
PostPosted: September 29, 2016, 10:19 pm 
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Nice to see you've started a log, Alex. I'll be very interested in your build.

Cheers,

Lonnie

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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 Post subject: Re: Stalker BMW build
PostPosted: September 29, 2016, 10:29 pm 
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So, driveline choices. I've been all over the map.

Cliff notes if you don't enjoy hearing my justification for what is basically an emotional decision:

Car is going to be a BMW N52 running megasquirt with a Quaife 60G sequential box.

This car's primary mission in life is making me giggle on the way to work on nice summer mornings. Basically looking for a 4 wheel motorcycle (I have tried really hard to love riding motorcycles but just can't) That means the main metric for the driveline is a roll-on left turn getting just a *bit* sideways. Of course, it needs to do track days well but it's not a race car so there will be nothing to measure outright speed against, just has to be really fun.

I'll just get it out of the way and will accept no arguing about this part. It must have a sequential gearbox. That's about 50% of the reason for building it, I've driven a few sequential cars on the road and they make me laugh so much that it's a must do.

This is not cost-no-object but it's not a budget build either. Each piece needs to be 'right' from an engineering perspective but I can't go off the rails on money. Figure $10-12K for a complete driveline.

My day job as a development engineer at GM in the performance car group puts me in the full spectrum of pre-production Corvettes and Camaros on race tracks a few times a week so it also has to have some balls to keep me entertained :D I really don't mean to sound like a jerk :oops: , it's just the facts, I spend a lot of time in very fast cars at their absolute limit every single day so a Miata engine is not going to cut it even at this weight. It needs to keep up with, and hopefully beat, a C7 Z06 from a HP to weight category. That means my goal is an even 300hp. The weight goal is realistically sub 1400lbs but the stretch goal is 1250.

Also has to sound great, no normal 4cyl, sorry. Needs 5 or more cyl or a bike engine to get my motor running.

So, a few options here:

Hayabusa - the gearbox comes with the motor so that shaves huge cost and weight. However, 300hp out of a 'busa reliably is not cheap. Figure $10K driveline cost with turbo or supercharger, trick oil pan or dry sump, new gears to make the trans ratios nice in a car this heavy, etc.

All car engines - nearly $10K cost of entry for the sequential gearbox. No way around it, I've chased every lead I can find for 6 or more years, you just have to pay to play. That means I need to keep the engine pretty cheap to make this option comparable to the 'busa on cost alone. The resale on the box is crazy good if I totally F this up and decide to bail at some point, even after it's complete.

My target, again, based on LT4 powered Corvettes and Camaros is ~0.9G in 1st for that squirmy back end feel we all love and 0.6G in 2nd for that smooth left turn roll-on oversteer without being unmanageable.

Here's what brakes the 'busa option: It only exceeds 0.4G above 50mph in 1st gear. It easily makes the 0.9G target eventually but you're doing 60 by then. I just don't see this being a fun car to squirt away from a stoplight. Of course, you can clutch it and launch like a bat out of hell but that's not what I'm going to do leaving my neighborhood at 7:30 in the morning. I'm saying I want torques. I'm also really skeptical this can be a reliable package.

LS is out. Love the motor. Best power to package size and weight going. I just don't need that much power. If someone made a 3.5 liter LS7 that was half the weight and power I'd be all over it. A full size LS would ruin this car. Someday I will build a car for a really nasty LS, it's just not this car. Also, the engine plus the sequential is way over budget.

I've settled on a BMW N52. It's their ~2006-11 straight 6 naturally aspirated. Co-cast magnesium and aluminum block and reasonable strength parts make it sub 320 lb for a 3.0L six. That's a pretty awesome deal, basically nearly the weight of a typical aluminum 4cyl. They're also cheap since everyone wants the N54 with boost. I am very comfortable with megasquirt so I don't need to worry about BMW engine management. MS can run dual vanos, electric water pump, variable oil pump, etc. Locking open the valvetronic is pretty well documented already. I love the sound, probably more than any other option here.

I'm anti 4 cylinder turbo just because I already did a big turbo 4cyl for my Volvo. Doesn't seem like the motor I want in this car and there's nothing new to learn there that I'm not already learning in the Volvo.

I was actually in England when they 'Brexited' so I called up a Quaife dealer that Wednesday when the pound was at it's lowest and ordered the 60G gearbox with helical sequential gears and the BMW input shaft/bellhousing. Scrap yard N52's are between $1500-1750. Done and Done.

Alex


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 Post subject: Re: Stalker BMW build
PostPosted: September 29, 2016, 10:34 pm 
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OK, actual progress:

There are a few small things about the Stalker that make sense from a manufacturing/cost standpoint but I wanted to spend a little more time on. One is the diff mounting. The car uses a CTS style rear diff, the one I found after much searching is a 3.23 ratio with a limited slip.

The original Stalker mounts use a rubber bushing up front and then solid mount the rear ears of the diff case. I am sure this must work given how many cars are running hard with this setup, I just can't choke it down. Even the theoretical stresses and noises are too much for me to handle. Today's project was to add the factory rear bushings back into the diff mounting scheme. I can totally understand why Scott doesn't do this, it was a full day of fab work.

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Felt good to get the first thing checked off the list. I'm expecting 3-ish years of this now...

Alex


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 Post subject: Re: Stalker BMW build
PostPosted: September 29, 2016, 10:39 pm 
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Finished up the weekend's work this evening. I got the rear suspension mocked up to make sure everything was there and then prepped the rear knuckles.

Here's the finished product:

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The upper control arm mount is designed to use the stock Miata flexible RUCA bushing:

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The Stalker strategy is to replace the stock rubber bushing with Energy suspension poly bushings, again, probably totally fine but I have some time to burn. Also, I hate poly suspension bushings with a passion. If a joint needs deflection it should be solid, bonded rubber. If it needs precision it should be a spherical bearing. These squeaky nuggets of crap are just expensive turkey calls and have no place in a suspension :ack: OK, got that off my chest:

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I made press in/snap ring spherical bearing inserts to replace the poly. There are sphericals everywhere else so no NVH concerns and it's an important spot to add stiffness. To Stalker's credit their big engine cars come with custom knuckles so this adaptation of the Miata part is not their hot setup (although, I do kind of like OEM validated parts, the FMEA on a knuckle is pretty ugly).

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The lower mount needed a piece of tubing that Stalker provided to reduce it to the size of the spherical bearing bolt. I tacked it in place to make sure the bearings were spinning and not the tubing inside the cast knuckle. Was a fun excuse to break out the Nickle rod too.

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A friend picked up an Eastwood powder coating kit and I got the oven. I love these guns, I had one in college and they work great. I did the hubs in a textured powder and the knuckles in gloss. I really like the flat, textured black but I think with brightly colored, glossy control arms the knuckles would have looked odd or dirty in the textured finish. Nothing like cleaning up the garage from painting with a blow gun! Also nice to have painted parts ready for assembly in 40 min.

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I need to get after the transmission dealer, it should be done any day now and I think I need the trans and an engine to go much further. I can jump into the roof hinge/latch design and fabrication before that stuff shows up, I guess.

Alex


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 Post subject: Re: Stalker BMW build
PostPosted: September 29, 2016, 10:43 pm 
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Getting to the point that I need to commit to a tire size and I'm still struggling. Stalker recommends a 245/40R17 and that's what's on all the cars they've shown. To me this seems too large for the size of the car visually but I go back and forth between the 10 year old car sketcher in me that likes the big wheels and the more mature side that likes a sort of 'meaty' tire and smaller overall OD you would get with a 15" wheel in a 45 or 50 aspect ratio.

Aside from appearance the weight, inertia and tire availability are huge factors. I did some math to help decide and I'm not sure it got me much closer:

Image

I think based on this I would toss out the 16's since it's really hard to find wheels and they don't offer many advantages.

From a visual standpoint I am worried about the 225/45R15's (which I love for weight, inertia and pretty good availability) looking small at 1.7" less than what Scott intended with the bodywork.

I like the 17's for that reason and since there are 64 tires available.

From a weight and inertia standpoint the small 225/45R15's are also less of an advantage than I expected. In first gear they look to the car like a 60lb weight reduction (~30lbs from mass and ~30lbs effective mass from inertia). Not sure that's worth the lower tire availability and possible fuglyness?

I like the 235/50/15's from a weight/inertia/OD/appearance compromise standpoint but I really don't want to bank on Toyo making 888's in this size for the rest of time.

Any input here? So far I am leaning towards taking the 30lb (60lb effective) penalty and running the intended 17" size rather than trying to make it look OK with the 15's.

Alex


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 Post subject: Re: Stalker BMW build
PostPosted: September 29, 2016, 10:44 pm 
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You'll have fun with the gearbox. Just going to say maybe what you like is the dog clutch gears not the sequential part? My Hewland is one of the most fun parts of driving my formula car. Shifting without the clutch, it happens as fast as you can blip the throttle. The sequential keeps you from short shifting though. I'm starting to think a Richmond which you can get any ratio for with dog clutch gears...

Nice motor, that's an impressive weight.
OH, and welcome!
:cheers:

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 Post subject: Re: Stalker BMW build
PostPosted: September 29, 2016, 10:45 pm 
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Engine is home! I got really lucky on ebay and found a local guy (6 miles away!) selling his 2009 N52 out of a pretty sweet 1 series that's getting an N55. He was willing to leave the accessories and harness on so I get all the connectors, etc. Most of the junk yards just cut the motors out with a torch and side cutters.

I like the idea that my engine swapped Volvo project (running a Nissan SR20DET) now hauls the engine for the new project.

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 Post subject: Re: Stalker BMW build
PostPosted: September 29, 2016, 10:45 pm 
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Pretty good evening's worth of work:

Got the engine torn down to just the parts I will use in the finished car and on the scale. I am still amazed with the BMW attention to detail. There are re-usable O-ring clamps on every water hose and 50% more clips, covers and strain relief for wiring than any other car I've worked on. I also took it all apart without breaking one single connector, never made that happen on anything else.
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It weighs 311 lbs in this state. I had predicted 305 to 320 based on internet folklore so I was quite happy with 311. Only items to add to make it a runner are the 12lb lightened flywheel, ITB's and header. Electric water pump, starter and alternator are on there.
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One more pic of the state it's in for the weigh in given I was so frustrated with trying to figure out who weighed what engine with what parts on all the various forums:
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It even kind of fits! This pic doesn't show the 3 or 4 places where it fouls the frame by more than an inch but those are just details...
Image

Alex


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 Post subject: Re: Stalker BMW build
PostPosted: September 29, 2016, 10:48 pm 
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So, Valvetronic...

The original plan was to put on ITB's or use the stock intake with a normal, cable operated, single throttle. For those that aren't familiar with it, these engines have valvetronic so the main throttling with the factory engine management is done by varying the valve lift rather than a traditional throttle blade.

They use a very strong stepper motor to turn an eccentric shaft that controls intake valve lift. The problem is that this setup should give awesome throttle response with the throttling occurring right at the valve itself but the stepper motor can only transit in 300ms which is not that fast. Most hot rodders lock the valvetronic full open and add a normal throttle but I'm not convinced they've thought very hard about it.

I was amazed to see that the eccentric is quite easy to turn, maybe 10 ft-lbs or less. Earlier I had kicked around the idea of just hooking a throttle pedal up to the eccentric shaft but was pretty sure it would be way too much force given you are basically opening about 1.3 pair of valve springs as you turn the eccentric. In reality it's pretty easy to turn for some reason.

Now that I see it's not too much force, any idea why this is a bad idea? I know the stock engine used a main throttle for idle (it just goes WOT as soon as the engine comes off of idle) so that's my biggest concern. I can't find any documentation on why they used a regular throttle for idle, emissions, IAC control, simple FMEA etc.

I love the idea of straight runners right from the head to the trumpets with no throttles at all, just worried it's going to be way too much of a science experiment.

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Alex


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 Post subject: Re: Stalker BMW build
PostPosted: September 29, 2016, 10:48 pm 
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OK, caught up with the other forum so post will slow WAY down now :lol:

Alex


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 Post subject: Re: Stalker BMW build
PostPosted: September 29, 2016, 10:59 pm 
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Quote:
Also, I hate poly suspension bushings with a passion. If a joint needs deflection it should be solid, bonded rubber. If it needs precision it should be a spherical bearing.


Quote:
(although, I do kind of like OEM validated parts, the FMEA on a knuckle is pretty ugly).


You're making very sane and sensible choices and comments.

I was going to vote for the 50 series tire because I think it might be just a bit easier to drive. With only one available that's not so good though. It's too bad that fashion is meaning it's hard to get the right parts for our oddball cars. So I don't have much advice here, just that you're going to enjoy it anyway you go here.

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 Post subject: Re: Stalker BMW build
PostPosted: September 29, 2016, 11:14 pm 
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horizenjob wrote:
Quote:
Also, I hate poly suspension bushings with a passion. If a joint needs deflection it should be solid, bonded rubber. If it needs precision it should be a spherical bearing.


Quote:
(although, I do kind of like OEM validated parts, the FMEA on a knuckle is pretty ugly).


You're making very sane and sensible choices and comments.

I was going to vote for the 50 series tire because I think it might be just a bit easier to drive. With only one available that's not so good though. It's too bad that fashion is meaning it's hard to get the right parts for our oddball cars. So I don't have much advice here, just that you're going to enjoy it anyway you go here.


I know, I really don't understand why 17's were the target for this car but it's one of those compromises you make when you get a kit. Ideally I'd be choosing between 13's, 14's and 15's. I am comforted by the relatively minor change in inertia, I expected worse. I'm not going to do the math on 14's, it will just make me mad.

Oh, and thanks for the welcome earlier!


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 Post subject: Re: Stalker BMW build
PostPosted: September 29, 2016, 11:17 pm 
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I don't know about the BMW system. Throttles are terrible things, you never find them on steam engines or diesel engines only on gas engines ( not on turbines either ).

I'll bet they hoped to be able to idle it on the valve control and just couldn't. Basically throttles ruin your part throttle economy so they would like to avoid that. The issue is the motor has to work against the intake manifold vacuum, the manifold vacuum subtracts from the pressure you need to run the motor. Steam engines are all about valve gears to control their power, there are several hundred patented ways to do this. It was awesome to study the big locomotive in the Smithsonian and see the engineer's hand control which went to a 12" steam master cylinder and servo'ed it to control the main valve gear, solves their reverse problem too.

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 Post subject: Re: Stalker BMW build
PostPosted: September 30, 2016, 1:21 am 
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Cool build, AJ.

I think trying to hook up the throttle pedal to the eccentric shaft would result in weird feedback through the the pedal, and I suspect changing the position of the eccentric as quickly as you could with the pedal, and with no ECU intervention, would create tuning problems. Even small changes in valve lift can create very different requirements in fueling/timing, and I'm not sure an ECU could get things to work very well if you took away all of its control of the actual valve lift. I suspect that in many circumstances the BMW ECU grants the driver's requests (via throttle pedal) by changing fuel and/or timing before moving the eccentric. Messing with this very much smells to me like a tuning nightmare, though I suppose there might be people who could make it work.

As for the straight runners/trumpets/no throttle deal, I think you'll still need a MAF sensor, so you'd have to sort that out.

Don't know if that helps, but it's my two cents.

-Graveyard

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