installed my bbsc........

[Yellow Rose]

Gene - not sure if you mean to over-under drive the blower mechanically or electronically, but here are a couple of things to think of. Disclaimer - the electrical option outlined below is purely hypothetical, I do not know if such parts realistically exist and are easily available.

Mechanical

As Lud correctly points out, belt slip tendency (and belt heat) increases as blower pulley diameter is made smaller. For now, let’s ignore that issue and let’s also assume that the engine is built to handle higher boost. Let’s say you have a 6 PSI pulley on the blower, with an 8 PSI pulley and a 10 PSI pulley in your toolbox. To change boost is simply a five to ten minute task of swapping pulleys. Note - the fuel map and timing map will need edits for the new boost levels. This would be the "simple" way of over-under driving the supercharger.

Electrical

Let’s say you want to limit boost to 6 PSI on an OEM engine, but want more power / torque at the low RPM.....how can this be done? Intuitively what I’m about to suggest is possible; however, I have not done any research if the critical component is available. If the engine management controller has an auxiliary output feature, at 6 PSI a 5 VDC or 4-20 mA signal is sent to an end device. This end device is the aforementioned critical component - a solenoid operated boost divert valve. The technology exists in Formula 1, but is there a financially feasible variant available domestically? If so, put a 12 PSI pulley on the supercharger, but you limit the boost to 6 PSI at redline while producing more power / torque at the low end. This would be the more "sophisticated" way of over-under driving a blower, but one that (ignoring the belt issue) theoretically allows x PSI from 2000 RPM right up to redline. IOW, instead of the "ramp up" torque plot that is typical if a centrifugal supercharger you get a picture perfect flat torque curve over the entire RPM band. Where do I sign up? Wow, 10-12 PSI at 2000 RPM!

And who said only turbos make low end torque?

 

[KGP]

Gene - not sure if you mean to over-under drive the blower mechanically or electronically, but here are a couple of things to think of. Disclaimer - the electrical option outlined below is purely hypothetical, I do not know if such parts realistically exist and are easily available.

I was posting in response to your statement of "electronic boost control." So yes, electronic. Thanks for the info.

And who said only turbos make low end torque?

Electronically - you did when you said "the electrical option outlined below is purely hypothetical."

 

[bfrank1972]

Interesting idea if the compressor on the supercharger is large enough, but probably a few flaws. The centrifugal compressors have an exponential boost to shaft speed ratio - the wheel has to be really spinning to produce any boost. So to get significant boost at low rpms, you'd have to put a small enough pulley on there to have it spinning pretty fast at 2000 rpm. At that kind of ratio, the compressor would overspeed at higher rpms (read kaboom). There might be a middle ground though, implement this idea - you won't get 12 psi at 2000 rpm but shift it so compressor speed is at maximum at redline would shift the begginning of the torque increase downward. Other problems could be heat at high boost pressure, depends on the size and configuration of the compressor. How about a rotrex? It's a centrifugal compressor with a variable pulley drive.

 

[KGP]

How about a rotrex? It's a centrifugal compressor with a variable pulley drive.

Have to change the name:

VPEP - Variable Pulley engine Explosion Prevention system .

 

[sjs]

People have been talking about this stuff for years on other cars, but as Lud mentioned you don't see them around for good reason. The simple approach of a smaller pulley and some type of boost relief at the top has been done but has practical and mechanical limits, and means more wasted energy when free-wheeling.

A variable pulley design is what you need. I've heard of people experimenting with them for SCs but haven't paid much attention. If controlled by the ECU it should be possible to make a fairly effective system with boost where and when you need it, but still within certain limits.

I think the SC itself needs a variable drive built into it and controlled by the ECU. That way your pulley could be a reasonable size and the SC gears up/down to achieve the necessary boost. Perhaps a miniaturized version of the CVT used in various recreational craft.

 

[slashmatt]

Re: Where Is It ???

If we can get a turbo kit with 400Hp for roughly the same as a high-boost BBSC (i have no idea what either cost).. then we should see what is the best route to go.

Then where is it? Cybernation's kit is not available to the public yet

I was just down at Cybernation about a month ago. They'll install the kit (parts + install) for $6k. It surely is available.

 

[KGP]

Quite a signature you (make that your mom and dad) have there. Might read this.

 

[Lud]

Just sharing for general interest -- Paxton had a few mechanical variable rate setups about 50 years ago. http://www.paxtonauto.com/about/

 

[Turbo NSX]

Gene - not sure if you mean to over-under drive the blower mechanically or electronically, but here are a couple of things to think of. Disclaimer - the electrical option outlined below is purely hypothetical, I do not know if such parts realistically exist and are easily available.

Mechanical

As Lud correctly points out, belt slip tendency (and belt heat) increases as blower pulley diameter is made smaller. For now, let’s ignore that issue and let’s also assume that the engine is built to handle higher boost. Let’s say you have a 6 PSI pulley on the blower, with an 8 PSI pulley and a 10 PSI pulley in your toolbox. To change boost is simply a five to ten minute task of swapping pulleys. Note - the fuel map and timing map will need edits for the new boost levels. This would be the "simple" way of over-under driving the supercharger.

Electrical

Let’s say you want to limit boost to 6 PSI on an OEM engine, but want more power / torque at the low RPM.....how can this be done? Intuitively what I’m about to suggest is possible; however, I have not done any research if the critical component is available. If the engine management controller has an auxiliary output feature, at 6 PSI a 5 VDC or 4-20 mA signal is sent to an end device. This end device is the aforementioned critical component - a solenoid operated boost divert valve. The technology exists in Formula 1, but is there a financially feasible variant available domestically? If so, put a 12 PSI pulley on the supercharger, but you limit the boost to 6 PSI at redline while producing more power / torque at the low end. This would be the more "sophisticated" way of over-under driving a blower, but one that (ignoring the belt issue) theoretically allows x PSI from 2000 RPM right up to redline. IOW, instead of the "ramp up" torque plot that is typical if a centrifugal supercharger you get a picture perfect flat torque curve over the entire RPM band. Where do I sign up? Wow, 10-12 PSI at 2000 RPM!

And who said only turbos make low end torque?

Andy I will make a suggestion to you....I am sure that the Mustang crowd has already tried this since the paxton is really popular on them. You could check their forums and see if anyone has tried it.

And again my point. Buy the right product for the performance you expect. If you want torque, Go turbo. IMO You are flirting with disaster trying to operate a blower other then the way it was intended to be used.

 

[Black&Tan97Tnewportbeach]

Yeah, like you probably could turn an electric carving knife into a chainsaw, but they still make chainsaws, so why bother

 

[tunapie]

One other consideration is that any blower has a max RPM limit. With the high redline this car has you might be there going for the low end. Dan

 

[Yellow Rose]

Andy I will make a suggestion to you....I am sure that the Mustang crowd has already tried this since the paxton is really popular on them. You could check their forums and see if anyone has tried it.

PRIME is the only forum I visit, and I don't need to be getting myself into trouble on their playground. Whomever the NSXer was that started a smackdown on the BMW forum was not very smart at that time.

You are flirting with disaster trying to operate a blower other then the way it was intended to be used.

Point-counterpoint. I am not saying to operate the Paxton outside of its mechanical limits. I have never said that. Ever. The Paxton has an internal speed increaser gearset that will spin the impeller in the neighborhood of something like 45,000-ish RPM.

What I am saying are three very simple concepts.

1 - install the smallest pulley such that, at 8000 RPM for the NSX engine, the max impeller speed of the Paxton is not exceeded.

2 - be sure to mod the engine to withstand the resulting boost.

3 - set the aux output of the engine management controller to x PSI so that this results on a flat torque curve from 2500 RPM right up to redline.

With those three steps, nothing is being operated outside of the manufacturer's limits. The critical component as I have predicated my "conceptual" kit upon, is if a 5 VDC / 4-20 mA solenoid operated boost divert valve is realistically available.

We all know that a turbo will make more torque than a centrifugal super, especially at low RPM, as you have beaten into my brain needlessly. That is why I have always said to compare the two is silly because of the two different operating platforms - crankshaft belt vs exhaust gas. Simply put, the turbo rules at low end because the hot exhaust gases are expanding through the hot side of the turbine, spinning it faster than its super brother in the next lane. My proposal spins the super "faster than normal" at a low RPM, but still within its design limits.

Closing note about chainsaw vs electric carving knife. I take this to mean that if you want low end torque buy a Viper or go turbo. I don't like Vipers and I don't like turbos. I have my reasons you have yours, so in my simpleton mind, the three steps outlined above plus a Paxton equal low end torque. Hmmm, looks like I need to get to work to squelch the naysayers.

 

[bfrank1972]

Repost for whoever didn't read the last line of my other post

Rotrex superchargers (european company) have a whole line of different sized variable pulley superchargers. Active Autowerke, a highly regarded BMW FI tuner, recently added a Rotrex supercharger to their line with good torque & hp results, check out these sites:

http://www.rotrex.eu.com
http://www.activeautowerke.com/supercharged/E36-M3supercharger.asp

Sounds like a good product to develop for the NSX.

Brad

 

[tunapie]

Andy, I heard MB is building a turbo kit.




















God, I could not resist that one. I see you are going to be the last one going down with the HMS Paxton!! Really, just kidding. I have a lot of respect for the MB kit and all the work that goes into a FI project of that scale and hope we can fly around the track together sometime soon and just enjoy our creations. Oh, there is a idea, drop the dyno thing and have a NSX FI track session. Im there, Dan

 

[Yellow Rose]

Andy, I heard MB is building a turbo kit. God, I could not resist that one.

Not sure if you are in joke mode or serious mode. I think in a catatonic daze, I may have heard that as well.

I see you are going to be the last one going down with the HMS Paxton!!

Better than going down on the SS Comptech, where I paid for my own life ring.

Oh, there is a idea, drop the dyno thing and have a NSX FI track session.

NSXPO.

 

[tunapie]

Just pulling your leg. Two questions though, what is the HP required to spin the Paxton 1000/2000 with the small pulley and the engine @ 8,000 with 6lb boost. Also, were you at NSXPO? Dan

 

[Yellow Rose]

Just pulling your leg.

I know.

Two questions though, what is the HP required to spin the Paxton 1000/2000 with the small pulley and the engine @ 8,000 with 6lb boost.

I do not know exactly, but in another thread, sjs and I were thinking something like 4-5 HP.

Also, were you at NSXPO?

Which one? 98, 00, 01, 02 - yes

 

[sjs]

...
I do not know exactly, but in another thread, sjs and I were thinking something like 4-5 HP

Actually, I was thinking that to be quite low based on the parasitic losses of a simple emissions air pump. So 4-5 (or less) may be true while cruising, but I suspect it to be higher under boost. Then again, I have no solid evidence either way.