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 Post subject: Re: Stalker BMW build
PostPosted: September 30, 2016, 7:21 am 
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Omaha Vette Graveyard wrote:
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


That's a really good point about the staging of timing, fuel and airflow, hadn't considered that in the context of this setup. Even on my super simple megasquirt volvo I lowered my idle timing so that your first blip of the throttle comes with a huge jump in spark for faster off-idle response. If I had an electronic throttle and could slow the throttle down during that time I would which I think is your point, this would be an order of magnitude worse.

However, I'm not totally sure this is significantly worse than my current (and way more traditional) plan of individual throttle bodies very near the intake ports, though? Those have tuning compromises for the reasons you mention as well but lots of people make them run very well. (I haven't tried but the internet tells me I can :lol: ) I think the typical driving characteristic of ITB's is that you can't whack the throttle from low load (idle) or it will just cough out but once the engine is on boil the response is spectacular. Maybe this would be similar?

I'm going Megasquirt so no need for MAF (it's typically tuned as a speed/density or alpha/N system). The valvetronic method would have to be tuned as 100% alpha/N since there's really nowhere to even put a MAP sensor that MS typically uses with ITB's. This is another big concern, people are having a lot of success making ITB's really driveable with Megasquirt due to it's new blending feature between Alpha/N and Speed/Density, I would have to go old school with all Alpha/N.

Really interesting points, thanks for the discussion!

Alex


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 Post subject: Re: Stalker BMW build
PostPosted: September 30, 2016, 8:04 am 
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ajmacdon wrote:
Omaha Vette Graveyard wrote:
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


That's a really good point about the staging of timing, fuel and airflow, hadn't considered that in the context of this setup. Even on my super simple megasquirt volvo I lowered my idle timing so that your first blip of the throttle comes with a huge jump in spark for faster off-idle response. If I had an electronic throttle and could slow the throttle down during that time I would which I think is your point, this would be an order of magnitude worse.

However, I'm not totally sure this is significantly worse than my current (and way more traditional) plan of individual throttle bodies very near the intake ports, though? Those have tuning compromises for the reasons you mention as well but lots of people make them run very well. (I haven't tried but the internet tells me I can :lol: ) I think the typical driving characteristic of ITB's is that you can't whack the throttle from low load (idle) or it will just cough out but once the engine is on boil the response is spectacular. Maybe this would be similar?

I'm going Megasquirt so no need for MAF (it's typically tuned as a speed/density or alpha/N system). The valvetronic method would have to be tuned as 100% alpha/N since there's really nowhere to even put a MAP sensor that MS typically uses with ITB's. This is another big concern, people are having a lot of success making ITB's really driveable with Megasquirt due to it's new blending feature between Alpha/N and Speed/Density, I would have to go old school with all Alpha/N.

Really interesting points, thanks for the discussion!

Alex


20 min drive to work and i think you're right, too hard to tune. I suppose you could write some Alpha/N and MAF blending logic into the MS code that is similar to the existing Alpha\N and MAP blending but that's not what I want the focus of this project to be. Too much like work at that point!

Back to hunting for reasonably priced throttle bodies...

Thanks,
Alex


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 Post subject: Re: Stalker BMW build
PostPosted: September 30, 2016, 10:19 am 
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Thanks for the run-down Alex. It should be a super build. As to the expensive transmission, this emoji expresses it best . . . :drool:

As a sidebar conversation sometime, I'd love to hear your input on testing and development. We don't have anything like that as a specialty topic on this site yet. I was hoping to eventually start one. The only thing getting in my way is knowledge and a finished Locost. :lol:

But, eventually, I'll have the finished car. Then I want to get serious about researching, performing, and the writing up a basic testing and development program. I've not seen a book with that specific topic, although there are the Carroll Smith and Paul Van Valkenburgh books, which I have. They're getting pretty out of touch with modern technology, however. And, neither is really very explicit about identifying steps 1, 2, . . . N as essential and basic to a program.

So, in the mean time, I'll just enjoy your build log.

Cheers,

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 Post subject: Re: Stalker BMW build
PostPosted: October 1, 2016, 2:46 am 
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Have you thought about building a multi-level tune? Could MS support that? Even if you decide to use a traditional throttle body, the valvetronic offers a variable camshaft. In other words, you could have a camshaft that changes its lift and effective duration according to a dash mounted dial, a toggle switch, or throttle pedal input. That might be really cool, or it might be more trouble than it's worth. The variable cam stuff certainly offers some interesting opportunities.

One more thought:
What about running the motor as close to a stock configuration as possible until you're driving the car? The last thing you want is for engine tuning issues to keep you off the road. Once you're driving it, you'll probably have a better idea of what it needs and what you want.

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 Post subject: Re: Stalker BMW build
PostPosted: October 1, 2016, 7:51 am 
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Hi AJ-
Welcome to the builder's log section of the asylum... "Abandon all hope." :mrgreen:

Those Stalkers are cool cars. I've known the Mineharts for years, good folks. They occasionally come up to our Dixie Region autocross events and are always among the fastest. I really like introducing Krista (The Mama of the group) to new folks. "And here is somebody's grandma who is going to kick your butt today."

Can't offer much on the BMW tuning subject, but I do agree with "Graveyard" about keeping it as stock as possible to begin with. Makes for fewer things you have to do to get driving, and fewer things to potentially keep you from driving if they don't go right. You can always add bells and whistles later. You may find that a totally stock powerplant is quite sufficient for the much lighter car, at least until your learning curve catches up to the car's capabilities.

Either way, good luck with it, keep the pictures coming!
:cheers:
JDK

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 Post subject: Re: Stalker BMW build
PostPosted: October 1, 2016, 9:14 am 
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I 100% agree on making the engine as simple to run as possible at first. The megasquirt on my volvo was easier to get running than any carb I've ever worked with so I'm confident that with a normal throttle system MS is the way to go for me. The only problem is that that's not what it is in 'stock' config so some level of modification is needed to make it simpler!

The "odd" systems on this engine are Valvetronic (variable lift), VANOS (variable timing), electronic oil pump volume control, and a fully electric water pump.

Water pump is super easy with MS, just a PWM signal based on any two variables I choose or even just based on water temp. I think there are even knobs to do some simple circuit diagnostics? We'll see.

All three of the others could be locked in a safe but disabled state if needed. I don't think I need to start there, though.

VANOS is well understood in the MS world and a big tuning advantage so I'm going to leave that on.

The oil pump is easy in theory, I have the correct outputs in the hardware and software, and I understand the physics, I just can't look up someone who's already done it on the internet. It's got a bunch of mechanical backup devices to prevent low oil pressure so I think I can actually screw it up totally and still be fine.

I've decided the Valvetronic is getting locked full open based on the discussion in the past couple posts, that's too much science project and one too many things to worry about on the first startup.

Graveyard, I was talking with one of the engine cal guys at work yesterday and he and I arrived at your same conclusion. With ITB's I could probably still do something smart with the Valvetronic actuator to lower the deltaP across the throttle blades at low engine speed to help the typical ITB sensitivity at low load (coughing out with a throttle stab). That will be way into stage two :lol: Also, that actuator weighs about 4 pounds so I am going to leave it off but leave package space for it as a fun project later.

Alex


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 Post subject: Re: Stalker BMW build
PostPosted: October 1, 2016, 9:20 am 
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GonzoRacer wrote:
Hi AJ-
Welcome to the builder's log section of the asylum... "Abandon all hope." :mrgreen:

Those Stalkers are cool cars. I've known the Mineharts for years, good folks. They occasionally come up to our Dixie Region autocross events and are always among the fastest. I really like introducing Krista (The Mama of the group) to new folks. "And here is somebody's grandma who is going to kick your butt today."

Can't offer much on the BMW tuning subject, but I do agree with "Graveyard" about keeping it as stock as possible to begin with. Makes for fewer things you have to do to get driving, and fewer things to potentially keep you from driving if they don't go right. You can always add bells and whistles later. You may find that a totally stock powerplant is quite sufficient for the much lighter car, at least until your learning curve catches up to the car's capabilities.

Either way, good luck with it, keep the pictures coming!
:cheers:
JDK


Yeah, Scott is a great guy. The kit was on time and no budget surprises. I really hope to present any changes I make to their setup in the light of just fun engineering projects for me as the car is really impressive right from his shop and I wouldn't' hesitate to just build one per the original intent. I was planning on starting from scratch so most of the stuff I'm changing is just because the ideas were already rooted in my head pretty strongly.

Alex


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 Post subject: Re: Stalker BMW build
PostPosted: October 1, 2016, 9:40 am 
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Lonnie-S wrote:
...As a sidebar conversation sometime, I'd love to hear your input on testing and development. We don't have anything like that as a specialty topic on this site yet. I was hoping to eventually start one. The only thing getting in my way is knowledge and a finished Locost. :lol:

But, eventually, I'll have the finished car. Then I want to get serious about researching, performing, and the writing up a basic testing and development program. I've not seen a book with that specific topic, although there are the Carroll Smith and Paul Van Valkenburgh books, which I have. They're getting pretty out of touch with modern technology, however. And, neither is really very explicit about identifying steps 1, 2, . . . N as essential and basic to a program....


Yeah, I'm happy to give some feedback on how the kit car development process relates to the OEM process. Hopefully that will come out naturally as I get to that stage. It would be like writing a novel to start from scratch without some real world topics to jump off of! The hard part is our lack of a proving grounds. In reality, stepping up to even an autocross test and tune day skips 30 or 40% of the process that we do in the OEM world on specialized tracks just for early development (and more recently, stuff we do in simulation). I can't imagine jumping right into autocross work on a new platform, way too much going on dynamically to sort out what changes are needed quickly and efficiently.

That part will be a learning process for me as well. I imagine it will be like someone telling me to take the engine apart with only a crescent wrench and a screwdriver. It can be done but it will look a lot different than it would with a full tool box!

Alex


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 Post subject: Re: Stalker BMW build
PostPosted: October 1, 2016, 9:59 pm 
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I'm really surprised how light that N52 is. I didn't know they had shed so much weight. The S52 in my M3 is quite heavy, with a cast iron block. I think it rings in at 550ish in similar kit. I had long since decided a BMW powerplant was too awkward in shape and too heavy to power a locost, but this changes my mind. The I6 just sings so much nicer than a 4 or, dare I say it, a v8.

As to your valvetronic issue, I'd agree with the others: you're getting in the weeds on this. Mimic BMW, or do a simple, single throttle body. Get it on the road and drive it, then squeeze the performance iteratively, once modification at a time. I bet if you do, you'll end up with a fairly complex control method for the valvetronic in conjunction with your throttle body(s) by the end of it, and will have arrived there knowing it produced the desired results, rather than guessing if more performance was left on the table somewhere.


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 Post subject: Re: Stalker BMW build
PostPosted: October 2, 2016, 12:43 pm 
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Alex
Thanks for posting.
I am very interested in your project as I am slowly working on an XL.
Especially interested in any engineering changes you make to the kit ...such as the rearend bushings.
WELCOME!
Gale

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 Post subject: Re: Stalker BMW build
PostPosted: October 2, 2016, 2:03 pm 
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V8SEVEN wrote:
Alex
Thanks for posting.
I am very interested in your project as I am slowly working on an XL.
Especially interested in any engineering changes you make to the kit ...such as the rearend bushings.
WELCOME!
Gale


That's a gorgeous car! Love the top and the headlights. Also looks like you did something different with the front fenders? Really cool.

Alex


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 Post subject: Re: Stalker BMW build
PostPosted: October 2, 2016, 8:15 pm 
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Thanks Alex
It was fun to build and more fun to drive.
Gale

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 Post subject: Re: Stalker BMW build
PostPosted: October 10, 2016, 9:08 pm 
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I was hoping to get away with keeping the stock oil pan but wasn't sure it was likely given it's tough to find dimensions online. I've cut a welded aluminum pans in the past so wasn't worried about the process, just not looking forward to it.

However, now it's pretty clear that I need to cut 1.75" off the pan to fit everything under the hood. This is way more than I was hoping for. Hood scoop is not an option since the bulge would be in a very awkward location.

I made some sketches of the stock pan, then the stock pan cut down 1.75," and then the cut pan with a wing added to the driver's side. The sketches show a left and right 1G turn and the oil line to keep constant volume. I know this is WAY oversimplified with so many missing variables I can't even list them. However, it's an OK way to visualize the delta from pan to pan. Keep in mind the pan mating surface is tipped 30deg on BMW motors, the bottom of the pan is level.

Stock Pan turning left (pickup is the short line at the bottom):
Image

Stock Pan turning right (forgot the pickup on this one):
Image

Cut Pan turning left (with corresponding lower volume of oil):
Image

Cut Pan turning right:
Image

Winged cut pan turning left (wing volume included in oil volume but wing empty due to G force):
Image

Winged cut pan turning right (whole wing volume full. This could be improved with a trap door):
Image

I think the upshot of this is that I'm uncomfortable with any of these options. The depth of the pickup is just too low relative to stock. So, I'm starting to shop for used dry sump systems. We have a lot of experience at work trying to make marginal wet sumps work (better said, good wet sumps with crazy good tires) and it is one of the hardest things to do without learning by engine destruction.

Any thoughts are appreciated, I feel like I'm going overkill but I hate worrying about oil pressure. Also, there should be 5-10 hp available in drawing a high crankcase vacuum with a real dry sump.

Alex


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 Post subject: Re: Stalker BMW build
PostPosted: October 10, 2016, 10:13 pm 
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Dry sump would be great, and it would give you a nice horsepower boost. However, it's a lot of extra cost, complexity, weight and used space if you don't truly need it. Also, to get the most out of it you generally want different rings. Vacuum in the crankcase changes stuff. Could lead to an engine rebuild before you ever even get running.

Although an accusump is not a great substitute for dry sump, it can make an okay wet sump work like a a good one.

Or, you could always limit yourself to all-season tires. :D

Just some other ideas...

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 Post subject: Re: Stalker BMW build
PostPosted: October 10, 2016, 10:28 pm 
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Omaha Vette Graveyard wrote:
Dry sump would be great, and it would give you a nice horsepower boost. However, it's a lot of extra cost, complexity, weight and used space if you don't truly need it. Also, to get the most out of it you generally want different rings. Vacuum in the crankcase changes stuff. Could lead to an engine rebuild before you ever even get running.

Although an accusump is not a great substitute for dry sump, it can make an okay wet sump work like a a good one.

Or, you could always limit yourself to all-season tires. :D

Just some other ideas...


Hard to find much good info on rings. It seemed to me from what I've read that if you want to really take advantage of the HP from more vacuum you can do low tension rings but I didn't get the impression you needed them. I could be totally wrong, though. We had a dry sump on one of the FSAE cars that worked great with stock motorcycle rings but we only put a few thousand miles on those engines.

No accusump, they just give you a false sense of security until you hit a long enough corner and them BOOM.

I go back and forth on tires. I know myself and I think I need to be ready for Hoosiers one day.

Thanks,
Alex


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