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juan ruiz's Avatar
 
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Kenik

I was referring to AIR, but thanks for the explanation "not enough volume or storage capacity to be meaningful" that pretty much summarize it

Thanks for taking the time to explain so much in one day!!
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10.76@139-1/4 mile
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Old 06-11-2010, 12:13 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #21 (permalink)
Max Sluiter
 
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The Valvetronic BMW system is the variable-lift. It uses an intermediate rocker shaft between the camshaft and the valve tappet. This intermediate shaft is positioned by another cam lobe and as its position changes, so does the pivot point for the rocker arm. This changes the rocker arm ratio and therefore valve lift. I did a case study on it in my intro to metalcasting class. They investment cast the intermediate arms.

Double-VANOS is the BMW variable valve timing system which phases the camshaft relative to crankshaft. Many issues with hydraulic seals as these BMW engines age.

What is wrong with casting? I have seen jet turbine blades which are investment cast. They have tiny micro features like little ribs and holes to allow cooling airflow around and through them, as these blades work at or above the melting temperature of the Nickel Titanium Chrome etc. Superalloys in the jet turbine combustion chambers.

I would like to see a machinist machine ribs and holes on the inside of a turbine blade which is about 5cm long, 2cm wide, and 5mm thick.
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Last edited by Flieger; 06-11-2010 at 12:40 PM..
Old 06-11-2010, 12:38 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #22 (permalink)
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Old Alco deisel locomotive engines had an air compressor that stored high pressure air and shot it into the turbo to help spool it up faster when getting going. They called it jet assist.

Those are really big V16 diesel engines that spin a big generator that makes electricity that powers big electric motors that turn the metal wheels of the locomotive.

Obviously that doesn't relate to a 930 but it's the first time I've heard anyone else mention stored up high air pressure jet assist to help spin up the exhaust turbine.
Old 06-11-2010, 12:41 PM
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Good Info!

I suffer from the "it has to be a better way syndrome" lol
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10.76@139-1/4 mile
0-1 mile 193MPH
Old 06-11-2010, 12:47 PM
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Crotchety Old Bastard
 
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OK if that graph is a 4cyl what does the boost curve look like for your car?
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Old 06-11-2010, 01:00 PM
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3 restos WIP = psycho
 
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Flieger, you misread me. I in now way meant to dimish the value of casting. I was simply saying that certain processes lend themselves better to some applications than other.

I know for certain that creating a wheel of equivalent weight and strength to a CNC built unit is possible. It is simply that given the extremely narrow cavities required to die cast identical parts to billet, it would require using technology at the extreme margins of casting process. You'd need to build a VERY expensive and complex die casting mold, most likely requiring the use of both vaccum assistance AND centrifugal assist to evenly populate the mold at the thicknesses required to match a machined part. The number of units required to amortize this tooling is only realistic for entities at the scale of your example: BMW, etc.

Next, casting is very hard to implement cost effectively for negative draft angles, requiring multi-part molds that at the scale of small parts like a compressor wheel is nearly impossible to achieve with acceptible fidelity. Die casting molds also have finite service life...they wear out, so you need to replenish molds regularly. The tighter the tolerances required, the more parts in the mold, the shorter the service life.

CNC processes are much easier to manage in small production runs, given the part. That said, CNC is not great for large runs as it is slow and doesn't scale well as to reach large capacity manufacturing runs, machine costs and space rapidly become unwieldy. The process used fits the scale of the market and application which is why BMW casts and Blouch CNCs.

These processes do have material benefits the other doesn't, though. Bleeding edge casting technology can align grain structure of metals along chosen planes of a part through mold design in ways billet can't. Billet gives you whatever you get from the stock you use.

In the end combining the process benefits of forging, casting and machining can give the best of all worlds, as long as economically feasible. Machining a forged or cast part can make a part that is superior to a single process part, no doubt.
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Old 06-11-2010, 01:15 PM
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Juan I am curious to see how the new turbo works on my car. I have everything repaired CORRECTLY now. I am sure the turbo will rock. I have a bigger version of the billet series. My compressor has the 3 inch outlet. I would think the turbo with the two step on your car will launch plenty hard to break things lol
Old 06-11-2010, 01:33 PM
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Quote:
Originally Posted by juan ruiz View Post

...the graph is for a 4 Cly engine...
That makes more sense.


This new turbo looks like it has a turbine smaller than a Gt-35 (65 v 68 mm),

and a compressor bigger than a GT-4088 (67 v 63.5mm).


Wish we could get your old turbo's hot side exducer size.


Thanks for sharing.
Old 06-11-2010, 02:11 PM
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Quote:
Originally Posted by juan ruiz View Post

...the boost coming in at 2600rpm! from my 4200 rpm...
This much change seems to evidence a much smaller turbine section than before.

It is not very conceivable that a lighter rotating mass or larger & improved compressor would be able to do that.

My fear is a smaller hot side will keep the compressor from realizing some of its potential.

If you do have a larger compressor and a smaller turbine, the wast gate circut can have to work harder and that can lead to boost creap in some cases. Just somthing to watch for.

I am far from an expert on turbo's. Just very interested.

Thx again.
Old 06-11-2010, 02:40 PM
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I will have to dyno this thing to be able to provide accurate data, right now I'm just going with the seat dyno which means very little at least to me but Man how nice this thing rides now
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10.76@139-1/4 mile
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Old 06-11-2010, 03:07 PM
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Does the new turbo feel like you picked up alot more torque? That is what I am hearing along with much quicker spool. I have the billet 72mm unit

Last edited by strokher racing; 06-11-2010 at 04:32 PM..
Old 06-11-2010, 04:21 PM
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I believe that by definition, quicker spool always means more torque, at least early in the powerband. The mark of a superior turbo is one that spools quicker, yet gives up no top end power to the turbo in comparison.
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Old 06-11-2010, 05:36 PM
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How about earlyer torque v more torque.

Earler-Torque when it spools earlyer and more power is made earlyer (lower boost threshold).

More-Torque when efficencies have insreased because of a more efficent compressor or turbine.
Old 06-12-2010, 08:06 AM
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