Whipple twin-screw.... ???

[NoSoup4U]

This is a twin-screw, positive displacement blower. 330+ rwhp in a car that weighs less than 3000 lbs = WOW!

http://www.nsxprime.com/FAQ/Performance/comptech_sc.htm

I was thinking, why do people avoid twin-screw pd blowers (besides Steve)??

Why are centrifugal blowers predominantly used? The PD blower seems to give the BEST of both worlds ... you get the low-end turbo kick; but the building of power of a supercharger ...

[///3oris]

Originally posted by NoSoup4U
This is a twin-screw, positive displacement blower. 330+ rwhp in a car that weighs less than 3000 lbs = WOW!

http://www.nsxprime.com/FAQ/Performance/comptech_sc.htm

I was thinking, why do people avoid twin-screw pd blowers (besides Steve)??

Why are centrifugal blowers predominantly used? The PD blower seems to give the BEST of both worlds ... you get the low-end turbo kick; but the building of power of a supercharger ...

I don't think it's true. All those jackson racing SC's are all PD Screws... a lot of the domestic market uses PD blowers too..

One thing I can think of why NOT to use them is heat (Steve is putting an aftercooler in his kit, though), space constraints (size), efficiency (I believe it tops out at about 62% or something).

Can't really think of too much.... but I'm sure there's more...

Boris

[Shawn Fogg]

"Why are centrifugal blowers predominantly used?"

They are only predominantly used by the aftermarket. And that is simply because the packaging on them is much easier from an aftermarket stand point. For a PD blower you basically need to fabricate a new intake manifold along with all the extra brackets, mounts and everything else. Few in the aftermarket do it.

Most/all of the car manufacturers that use superchargers use positive displacement units.

Shawn

[Shawn Fogg]

"All those jackson racing SC's are all PD Screws..."

Unless Jackson has recently changed they all used Roots type Eaton blowers, not twin screws.

Shawn

[stimpee]

I can personally and vividly attest to Shawn's view of "why not" for everyone else.

The reason is not heat, at least I don't think so, since the twin-screw will peak at 65-66% (versus 72-74% for centrifugals), but the twin-screw will operate in a narrower efficiency "range" (the percent efficiency varies very little) so it is actually very efficient across the entire rev band. In my case between about 61-65% across the entire rev band. That is not too shabby IMHO, so the heat difference will not be very significant.

However PACKAGING IS A NIGHTMARE!!! It has been my life (at least my sideline life) for over 1.5 years now. It is STILL causing me issues.

If a company like RMS, or AA were going to put in the engineering effort to do this, they would go OUT OF BUSINESS (maybe that's extreme, but I'm making a point here) with the return on investment they could expect to get from the limited BMW market (which is why you see them on some vehicles, but not others)

Do you have any idea how much a thousand or so hours of engineering time costs? For a company trying to make money, why would you bother?

I am dug in so far in this, I can't even see the light at the top of the hole I have dug myself into. However, I am close to getting it running, so at least I can start heading back out of the hole. But then I have to invest in production tooling. Anyone have any idea how much casting patterns, etc cost for an inline 6cyl manifold? LOTS!!!

The only thing I can say, is that I started this as a "labor of love", which is probably the only way to justify it. However now, I need to find a way to make it work, sell some, and make some money just to pay back my investment in components, machining, equipment, etc. I doubt I will ever "get my money back" on the time investment, and I certainly won't if I include the time spent learning and doing research in the process of development.

If you want it, you will get it. There WILL be a high quality twin-screw kit available in the not too distant future. Either that, or I will dead, or insane...



Steve

[Boz.es.du]

Steve,

How much are you going to sell your kit for and when do you plan to put it out? I think I may be interested....either AA or you.

Let me know. Thanks.

[stimpee]

I have given up speculating when I will be done, as I will just put my foot in my mouth. I hope to have the prototype running "soon". I have the parts in hand (finally) and am wrapping up minor issues for final installation.

When I will have "kits" ready depends on a lot of things including what type of vehicle, where in the "testing and validation" loop you feel comfortable getting in, etc. OBDI kits for 325's and M3 will be first, with OBDII kits to follow hopefully shortly thereafter. E46 kits will happen as well, but are a bit down the road at the moment.

For pricing, it will certainly be significantly more expensive than the AA kit. Cannot help that due to the complexity of the kit. However it will have "Stage II" type of performance, and as such, should be quite competitive with RMS's Stage II kits, and significantly cheaper than AA's turbos. You can probably figure out a reasonable range of pricing possibilities from that, but I need to finalize some more things before locking it down.

Also, I MAY offer a non-intercooled kit at a pricing level competitive with the existing Stage I kits, and AA's kit with similar performance levels as well. And it would be a pretty simple upgrade to the higher boost intercooled kit.

Still lots of work to do though.

My suggestion is if you want to buy a kit, check and see if I am ready, if I am, then make a "value" and "risk" decision based on the available info. If I am not ready yet, then make the same decision and decide either to wait for me, or buy AA's kit.

Don't honestly think you would really go wrong either way, just depends on what you want, and whether you need "instant" gratification or not!!!

:atom

Steve

[zenon]

HAHA, if you die trying I'll continue the cause in your honour steve....
(there's no american flag so pretend the "BS" isn't there)

:
or hey, just pretend it reads TS

[Number9]

Originally posted by ///3oris
I don't think it's true. All those jackson racing SC's are all PD Screws... a lot of the domestic market uses PD blowers too..

One thing I can think of why NOT to use them is heat (Steve is putting an aftercooler in his kit, though), space constraints (size), efficiency (I believe it tops out at about 62% or something).

Can't really think of too much.... but I'm sure there's more...

Boris

Boris, Comptech is NOT Jackson Racing. They are the folks that built Montoya's winning Indy 500 engine and their engineering is first rate. Their twin screw SC does in fact yield about 320 RWHP in 3.0L NSXs and about 340 with the 3.2L NSXs (and another 20 more with the so-called high boost kit). Ask me how I know...

[Boz.es.du]

Steve,

I live in MD. I'm located in Linthicum actually, do you know where that is? Maybe you can use my car as the guinea and give me the kit for free?

I will keep in touch with you and I'll be checking the FI forum often from now on...it sounds like a great kit, we'll see when you have everything set and done.

Where are you in MD? I'd like to check out the kit sometime...

[stimpee]

I am as far northeast in MD as you can possibly get, about 1/4 mile from the DE border, and about 1.5 miles south of the PA border. I am less than 5 miles from I-95.

No FREE Soup for you though!!!

Guinea pigs will get "benefits", but I am not a charity!!!

Send me contact info and details on your car in PM or email.

Steve

[Boz.es.du]

Steve, I'll send you a PM.

[stimpee]

Just made a correction to my wording in my post about 3-4 above in which I talked about the efficiency. If anyone cares, please re-read and see if it makes sense.

Thanks for Number9 for pointing out my inability to speak clearly!!!

Doh!!

Steve

[Shawn Fogg]

Steve,

"Just made a correction to my wording in my post about 3-4 above in which I talked about the efficiency."

My personal take is thermal efficency is sort of a red herring unless you are talking about the same form of forced induction.

For example the centrifugal vs. a twin screw (or a Roots). Sure the centrifugal has better thermal efficency when it is making the same boost. But is it really important when most of the time the centrifugal *isn't* making the same boost. No boost... little heat.

Same sort of thing with a turbo. Their compressor efficency itself is higher but drive a turbo car on the street for 20-30 minutes (so the turbo itself gets good and hot) then compare how much heat a turbo adds to the intake charge compared against a PD blower.

Shawn

[Number9]

Originally posted by Shawn Fogg
For example the centrifugal vs. a twin screw (or a Roots). Sure the centrifugal has better thermal efficency when it is making the same boost. But is it really important when most of the time the centrifugal *isn't* making the same boost. No boost... little heat.

The interesting point here is that the twin screw is working in its efficient range over most of the rev range and is providing boost across that range. The centrifugal makes little heat but provides pretty much no meaningful boost in the 1st half of the rev range, so though it has better peak efficiency, it yields less area under the power curve over the entire rev range. So for a pure track car that stays entirely in the top 2k RPM, you can make a case for a centrifugal SC, but otherwise, twin-screw wins and simply makes your car feel like you've got more cubes...

[///3oris]

EEP!!! Shawn, ooops... my bad

Number9, I didn't say Comptech = Jackson Racing, he just asked why there aren't many on the market... and I mentioned Jacksron Racing (mucho crap for 4-bangers)... but as Shawn pointed out, I was wrong...

Anyway, Steve, when I was talking about HEAT, I wasn't talking about the actual efficiency of the SC. I was talking about the air going into the engine! I could care less how much heat is generated coming out of the SC (efficiency), I care about the charge going into the cylinder. It's a lot easier to cool off a charge that has a long path through an intercooler for example than if there's only an inch or so of cooling between the head and the blower. This is speculation though... I don't know how fast the temperature change occurs... maybe that 1-inch is enough? You tell me!

Boris

[stimpee]

Distance has nothing to do with it. You are right, the thing that matters is the charge air temp to some extent. However if you are heating the air a LOT, then cooling it back down, you are still wasting a lot of energy to drive the blower, since it takes HP to make that heat.

The amount of cooling is dependent on the efficiency of the intercooler, not the "distance" the air travels. Travelling thru more piping may increase the amount of heat removed, but it will also incur more pressure drop, particularly if the piping is small enough in diameter to in require high air velocity.

Shawn is right though, it is somewhat academic at this point. If the efficiency of the centrifugals falls off on the low flow end to less than that of the twin screw, it is probably somewhat irrelevant, as it is making no significant boost anyway. However it is still taking a disproportionate amount of power at that point to make that small amount of boost, further detracting from the usable power on the low/mid range.

Steve

[zenon]

basically what matters boris is surface area... conceptually you can cool with one long small tube, or a fat short one... the total surface area is what matters... Now would you rather have a long small pipe or a short fat one?

[///3oris]

Originally posted by zenon
basically what matters boris is surface area... conceptually you can cool with one long small tube, or a fat short one... the total surface area is what matters... Now would you rather have a long small pipe or a short fat one?

I'd rather have a long-fat one... but hey, gotta work with what you got

Besides, it's not the surface area/volume... it's the motion in the ocean, baby!!

Back to installing SC!! BBL

Boris

[paul e]

>>I'd rather have a long-fat one... but hey, gotta work with what you got

Besides, it's not the surface area/volume... it's the motion in the ocean, baby!! <<

Very good. LOL!!

[zenon]

MMMM ocean..... but oceans can get too big, you must agree with that

[RicN]

Steve,
I don't know if this has been asked or addressed before, but are you planning to CARB-certified your kit and have some kind of a network in different states to install and service your kits, similar to dinan?
Thank you.

[stimpee]

I am certainly planning to try to put a "dealer" network together at various strategic locations around the country for install and support. I don't have any delusions of putting together a network like DINAN has with existing BMW dealers at this point, but by working with quality independent shops, etc I hope to be able to build something decent.

As for CARB certification, it will be dependent on demand. I am quite confident that the kit will pass the tests if I so choose. However as you know, it costs beaucoup bux to do so, so I will have to evaluate the business case for it. I have a feeling that once I get the E46 and Z4 kits together, that it may look good...

Steve