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      01-07-2012, 06:13 PM   #1
DylanMckay
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variable length intake manifold?

I have had prior bmw's that have a variable length intake manfold to maximize power at lower, middle and higher rpms based on the length of intake tube the air goes through at different rpms. The lower rpms used a longer intake runner to build more velocity, middle rpms used a bit shorter and high rpms used a very short one ( I think it was this way). All controlled with DISA valves they were called.

Ferrari often uses similar things on many of their engines. Lots of other companies do the same. Dual intake path is more common but 3-intake paths is great.

I would think the s65 would have been a perfect engine to employ this in order to give it a little bit more down low and middle power while not having to compromise the great high end peak power. With one intake manifold as it is, has to be optomized for max power and therefore would require more compromise at peak power to tune it for any furtherh power down low or in the middle.

This would probably be way too complicated for a tuner to build and then tune to work with the million other engine pieces but too bad bmw did not go with this.

Also this engine would be absolutely perfect with valvetronic. Again with its ability to provide more low-middle end power without compromising top end power since it has ability to vary the lift of the valves as well as timing.

I would have really loved to see an updated s65 with valvetronic, variable intake runner, an electric water pump for less parastic losses and potentially direct inject.

This all would have been easily good for 40hp and would make a nice 450 with more efficiency and better mileage but still maintain the power curve we all love only it would be meatier down low and through the middle which is everyone's complaint
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      01-07-2012, 06:38 PM   #2
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Hmm did a bit of searching and seems like quite a few people have implemented these as an aftermarket product on other engines. Wonder if one of the more reputable tuners would be interested or willing to give this a shot. Would reasonably be good for 20hp I would think at least. Probably more with the right tuning. It could be relatively easy to swap by switching manifolds so easy to change back and forth.

Would be nice with 3 runners for 1k-3k-4-6.5 and 6.5-8.4.

I would volunteer to be the lab rat for this!

Another cool project that would be a first for this car would be a variable length exhaust project like some aston's use. Two sets of exhaust pipes of different geometry/diameter for lower-mid rpms and higher rpms. Would add a bit of weight but would be really sick benefits and also good for probably a really nice bump in mid-range since the current exhaust is maximized for top end power and is a larger diameter than what would be optimal for low to mid-range power.

I wish some tuners would step outside the box and produce some products like this thata would truly be unique. So many exhausts on the market all pretty much the same. Tunes all pretty much the same etc.

Many want to keep their engines NA and do not want to go supercharger so having some decent power gain mods without deleting cats or supercharging would be a big market IMO
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      01-08-2012, 12:41 AM   #3
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As far as valvetronic, I seem to remember reading that it would limit the RPM due to the mechanicals of the valvetronic system.
With 8 individual throttle bodies, are there even "intake runners" that can be tuned, or varied in length?
But I'm not sure... I'm probably in over my head here.

Last edited by MysticBlue; 01-08-2012 at 10:14 AM.
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      01-08-2012, 01:09 AM   #4
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Not sure how much more room a velocity stack setup would need to be installed inside the plenum and whether it would really make any benefit at all..... Its already pretty tight in there, here's a picture of the inside for those who haven't seen it, from when I had mine off....



267629_10150226305859184_574134183_6984825_8386223 _n by SchnellM3, on Flickr
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      01-08-2012, 01:43 AM   #5
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Valvetronic used to have inability to operate at super high rpms but it has signifigantly improved and is on the M5 with 7200 rpms. Not saying it would work at 8400 but I am sure they could make it work.

Maybe none of this is possible but sure would be nice to see the s65 evolve and get even better or it would have been SO exciting to see what bmw could have done with a new v8 for the m3 for the f30 with all the technology they have discovered since back in 04 when they designed the s65. I am talking if they stuck to naturally aspirated.

Could have been a beautiful 4.4L v8 with 8800 redline, direct injection, valetronic possibley for even better throttle response and broader torque curve. Could have easily made a nice 460hp and 340 foot pounds which IMO would be absolutely perfect. So sad to know there will never be any further M production high-revving engines. I just love the engineering precision and progression of each of the M engines thus far and its always been exciting to see the next M engine and how they squeezed more power out of it. Now it is not exciting because all they do is slap a turbo or 3 on their and power is unlimited. They are surely all nice engines but it was fun to see them really have to get creative to squeeze out more power each generation.

If we ever want a high revving NA V8 unfortunately the price of admission will be a ferrari. Can't think of anyone else even offering a high revving v8. Porsche is nice if you want a flat 6 which you cannot complain about the numbers they make but not quite like a screamin V8!
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      01-08-2012, 05:16 AM   #6
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The torque curve is almost flat from 3000 to 8000RPM which is a span of 5000RPM. Since all a variable length manifold does is broaden the torque curve I'd say there is no need for it here....... 5000 RPM is the full operating range of many engines on the market, Id say a 5000RPM plateau in the torque curve is plenty broad.

Since the S65 has 58 degrees of variable cam timing on the intake and 48 degrees on the exhaust able to be adjusted at a rate of 360 degrees per second, a variable length intake manifold is redundant in this application. The cam timing is continuously being adjusted to maximize the resonance tuning available hence the broad torque curve, basically the variable cam timing is doing the exact same thing as a variable length manifold except better. Engines with single or dual throttle bodies have to use intake manifolds and that is why they can benefit from variable intake manifolds. The S65's ITB's allow it to use a large volume plenum and nicely designed intake trumpets instead of a conventional manifold. I can explain the way resonance tuning works in a naturally aspirated engine if you like but I will assume you know. If you want an explanation PM me and I will give it to you.

Of the other suggestions you made to improve on the S65 the only one I agree on is direct injection. The cooling effect direct injection has on the intake charge would allow an even higher compression ratio which would mean even more power. An electric water pump would gain very little but add complication and reduce reliability. Valvetronic was not considered for the S65 because at the time when the engineering was completed the engineers felt that valvetronic was not suitable for 8000+RPM

The fact is that the S65 only displaces 4 litres. Only so much torque is available out of 4 litres. If a person wishes for more torque out of this engine and still keep it NA he either needs to pony up and buy a stroker or realize that 4 litres is 4 litres, no matter how you stack it.

P.S. There is a 4.4 litre version of the S65, it is in the M3 GTS and CRT and has 450 HP and 325 Lb/Ft.
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      01-08-2012, 11:43 AM   #7
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As far as valvetronic, I seem to remember reading that it would limit the RPM due to the mechanicals of the valvetronic system.
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      01-08-2012, 10:41 PM   #8
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Quote:
Originally Posted by BMRLVR View Post
The torque curve is almost flat from 3000 to 8000RPM which is a span of 5000RPM. Since all a variable length manifold does is broaden the torque curve I'd say there is no need for it here....... 5000 RPM is the full operating range of many engines on the market, Id say a 5000RPM plateau in the torque curve is plenty broad.

Since the S65 has 58 degrees of variable cam timing on the intake and 48 degrees on the exhaust able to be adjusted at a rate of 360 degrees per second, a variable length intake manifold is redundant in this application. The cam timing is continuously being adjusted to maximize the resonance tuning available hence the broad torque curve, basically the variable cam timing is doing the exact same thing as a variable length manifold except better. Engines with single or dual throttle bodies have to use intake manifolds and that is why they can benefit from variable intake manifolds. The S65's ITB's allow it to use a large volume plenum and nicely designed intake trumpets instead of a conventional manifold. I can explain the way resonance tuning works in a naturally aspirated engine if you like but I will assume you know. If you want an explanation PM me and I will give it to you.

Of the other suggestions you made to improve on the S65 the only one I agree on is direct injection. The cooling effect direct injection has on the intake charge would allow an even higher compression ratio which would mean even more power. An electric water pump would gain very little but add complication and reduce reliability. Valvetronic was not considered for the S65 because at the time when the engineering was completed the engineers felt that valvetronic was not suitable for 8000+RPM

The fact is that the S65 only displaces 4 litres. Only so much torque is available out of 4 litres. If a person wishes for more torque out of this engine and still keep it NA he either needs to pony up and buy a stroker or realize that 4 litres is 4 litres, no matter how you stack it.

P.S. There is a 4.4 litre version of the S65, it is in the M3 GTS and CRT and has 450 HP and 325 Lb/Ft.
Very knowledgable! Thank you that was interesting. I am not at all educated in car engineering but rather just really enjoy reading and learning what I can about the various engine technologies out there.

I did not really think about ITB and how that basically does make it impossible to have a variable length intake.

I would appreciate if you clarify resonance in the case of the s65 trumpet set up v. a traditional 1 throttle body with traditional or variable length intake plenums. I understand how resoance works with the standard intake plenums and the reasoning for changing lengths but with the intake of the s65 is resonance even used? It looks more just like there is a ton of air available and it is equally sucked into each ITB but there is not tubing length to really have resonance correct?

Well maybe I am in the minority but I still think it would have been nice to have the option of a 4.4 litre from the gts tweaked with direct inject and a higher redline with corresonding changes to cam timing/tune and a higher compression ratio. Given gts output is 450, these changes on top of that would have EASILY yielded 475hp and 340-350 pounds.

I understand the mileage would not be a big improvement but it would probably be slightly better with DI and as anyone knows who drives the m3, the mileage is not nearly as bad as its made out to be. Its probably better than the new m5 when driving equally.

Anyway its just kind of sad to not see bmw push the limit of NA engines anymore. I enjoyed watching their engineering
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      01-09-2012, 05:19 AM   #9
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I am heading to bed now but I will post a reply explaining how resonance tuning works in a naturally aspirated engine sometime in the next few days. Please keep an eye on this thread for for the explanation.
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      01-09-2012, 12:16 PM   #10
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Quote:
Originally Posted by BMRLVR View Post
I am heading to bed now but I will post a reply explaining how resonance tuning works in a naturally aspirated engine sometime in the next few days. Please keep an eye on this thread for for the explanation.
I will clarify. Not resonance tuning in NA engines but rather NA engines such as the s65 with equal length trumpets in a common plenum. I did not think resonance plays much of a factor in this setup?
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      01-10-2012, 02:38 AM   #11
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As promised here is as an explanation of how resonance tuning is used in naturally aspirated engines to broaden a torque curve and increase power. Before I discuss resonance tuning though, I have to explain a few principles first.

The reason some engines produce lots of torque and not a lot of horsepower is due to the fact that they have a very narrow operating range and are unable to maintain torque at higher RPM. This is the reason why many engines have lower redlines. Variable valve timing, variable valve lift, and variable length intake manifolds were all developed to allow engines to have a wider operating range or in other words a broader torque curve. Horsepower is Torque x RPM / 5252, and you can't increase power without increasing torque. So realize that any modification the increases horsepower either increases torque or allows the engine to make torque higher in the RPM range.

1 Lb-Ft at 2000 RPM equals 0.38 HP, the same 1 Lb-Ft at 5252 RPM equals 1 HP, and everywhere after 5252 RPM horsepower is being multiplied by RPM. In the S65 at it's 8300 power peak every Lb-Ft equals 1.58 HP. I hope I am making my point on horsepower and it's relation to torque clear. (If you would like to find out how much torque any engine is making at a given HP output you can use the equation HP / 5252 x RPM = Torque).

Every naturally aspirated engine has a natural resonance where pressure/sound waves aid in filling the cylinders is greatest. The reason for this is as the intake charge is travelling down the intake manifold runner, the intake valve suddenly slams shut this column of air is stopped dead. This sudden stop of the column of air creates a pressure wave that travels back up the intake runner at the speed of sound and enters the plenum. Once the wave hits the walls of the plenum it reverses direction and flows back down the intake runner and all of the other intake runners in the engine still at the speed of sound. This pressure wave (also described as the Helmholtz resonance effect or acoustical intake tuning) is above atmospheric and creates a supercharging effect to the engine when it is timed properly with the opening of the intake valve.

In older engines the intake runner length and plenum volume was decided upon based on where the engineers wanted the peak volumetric efficiency (torque peak) to occur. The reason for having to carefully decide runner length was because valve timing was not variable and the rate of opening and closing depended upon RPM. The pressure waves, however occur at a static frequency dependant upon the speed of sound and the runner length/plenum volume.

The reasoning for developing variable valve timing and variable length intake manifolds were invented so that engines could better take advantage of this supercharging effect at more than one specific point in the rev range. With a variable length intake manifold there are two or sometimes three lengths of intake runners which allow the engine to have a much broader torque curve since this supercharging effect can now occur at more than one point in the rev range. The reason for this is as the runner length and or plenum volume is changed the frequency of the resonance also changes. This allows the pressure pulse to be occurring when the valve is open at two or three specific points in the RPM range. The variable length intake manifold is also used in conjunction with variable cam timing to actually be able to flatten the torque curve somewhat too (since the intake valve can either be opened later or earlier depending upon when the pulse/pressure wave is occurring.

The majority of vehicle engines are not nearly as advanced as the S65 from a computing standpoint. Since the DME on the S65 is able to do 200 million calculations a second, and the cam phasing can be carried out extremely quickly and over a wide range of advance and retard it is able to use the resonance tuning to its advantage strictly by using the cam timing. Basically at low RPM's the cam timing is retarded quite a bit but as revs increase the cams are advanced at a rate that allows the engine to take full advantage of the pressure waves. The fact that the torque curve is nearly flat means the DME and cam phasers are doing a very good job of adjusting the cams over the extremely wide operating range. By the way the plenum volume and trumpet diameter was just as important in the whole design phase of the engine as anything else. I am quite sure that many smart Germans did a lot of dyno testing, math, more dyno testing, and more math to come up with the optimum volume for the plenum and the optimum length, diameter, clocking and air horn radius of the trumpets. To answer your question above about the trumpets and the resonance effect, the trumpets act just like an intake runner in a conventional manifold.

The thing is, this engine may have been able to make more torque, more peak horse power or both, but the compromise that the engineers gave us was, good peak torque for the displacement (the S65 actually makes more torque per litre than a Z06 corvette, C63 AMG, or Lexus ISF to name a few), an extremely wide operating range (extremely broad torque curve) and a very high specific output (103.5 HP Per litre)




I hope that I didn't ramble on too much, but basically, next time you look at torque curves of naturally aspirated engines, the flatter the torque curve the better a job that that engine is doing to maximize volumetric efficiency to broaden the torque curve through resonance tuning.
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Last edited by BMRLVR; 01-10-2012 at 02:54 AM.
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