MilesOrbell

The new twinscrew supercharger kit from 928 Specialists has really caught my attention, (apart from K&N type airfilters). I really like the idea of boost from low revs with this type of blower. (Opposed to rising boost with centrifugal types).

Nice fitment that leaves front of engine clear for cambelt maintenance etc, it looks like the perfect solution. Keeping it simple is good stuff.

I have never driven these different types of blower, any of you have experience with centrifugal blowers vs twinscrew types ?

One concern is, supposed higher parasitic drag from the twinscrew when cruising, but I am assured by 928 Specialists that this is not an issue as it is bypassed in the cruise, but I believe even in a bypass condition a twinscrew type is still compressing the bypassed air, therefore more power lost to drive it ?

In normal day to day driving, one is probably only really using boost very rarely, therefore it would be nice to have a blower which draws minimum power under low boost conditions.

Thanks for any comments.

89 S4 Euro Auto.

bigs

Oh jeez. Not this battle again!!! *Heads for the bomb shelter*

You might want to check your friendly "search" function first.

Or else fix yourself a big vat of popcorn.

MilesOrbell

Sorry about this, remember when you were a new & enthusiastic owner !

Have searched, but looking for new comment.

Cameron

Can't advise on one vs the other. I have the Andy Keel setup using an Eaton M112 (might I call it the base kit that has been refined into the masterpiece 928 Specialists kit) and can say that I am a very satisfied customer. The install was involved, but fun.

One successful damn hot Florida summer track day under her belt since the install. Plus about 4k road miles. Scientifically speaking, the car goes like hell!

IcemanG17

Several of the Twinscrew owners report better fuel mileage after the install "when" they are not driving hard....benefit of the bypass and a simpler intake manifold (think short and straight)

Imo000

Tom. M

If you want opinions..well...heres mine..just remember ...it's an opinion...

If you have an 87 and up S4 with AT and 2.2 rear I think the twin screw setup will work wonders...give you that ooommmphffff at the bottom end and pull like a train. I suppose the same goes for the other AT ratio too.ie. 2.54 for 89.

Now if you have a five speed or GT, my personal opinion is that you will want to rev the car more and thus a vortech setup (which I believe gives more on the top end) is a good choice. There are GT's out there with twin screws that put out some awesome numbers, but again I think the vortech in this app is better suited.

As far as the fuel economy goes...just make sure you measure the actual mileage and don't rely on the dash indications. The dash gets it's input from the injector duration and thus if you are running other than 19lb injectors...it'll show better milage since the 30 lb or 24lb ones won't stay open as long as the 19 lb to deliver the same amount of fuel... Sure looks good on the dash though..haha..

Either way....it's great to be pondering these options....isn't it?...

Later,
Tom
89GT

BC

Great Advice Tom.

drnick

yeah, it would be nice to see back to back comparisons between two GT cars with the different superchargers. if i had an auto id definitely opt for the twinscrew no question but the 5spd is different, it likes to rev and i like the feel as the flappy opens at about 4k in NA form and id be afraid to loose that. id just like to hear the subjective driving differences between the two compressors on the same 5spd model.

lorenolson888

I think that the bypass which is basically a little throttle like valve is open during wide open throttle. So boost is only applied when that valve closes.

when open the bypass serves to relieve much of the backpresssure on the charger by dumping the excess pressure in the manifold (to atmosphere or pre SC intake). So there is not a lot of energy required to turn the SC at that point.

Question, is the MAP at or slighty above atmoshere with the bypass open?
NA cars are slightly lower than atmosphere.

Not sure about how much parasitism the two have but the roots and screws do seem to be more massive which means that that the moment of rotational inertia may be greater (based on diamater and mass)

The cenfrifugal blower may be lighter but also may has a larger diameter than the 2 screws or lobes.

Both should be about the same as far as friction I imagine... belts right... but some centrigfugal blowers are geared.

Also the longer distances that the centrifugally charged air travels may make for some losses due to plumbing. The swincrews may have an advantage here.

The screws supposedly have much higher tolerances than the roots and centrifugals

centrifugals may have an adantage in ease of install and may be a little less invasive. But if your intake is shot that is not an particularly simple or cheap job anyway. I have also heard that the centriguals may be a bit harder to get to work right and boost tends to vary a lot with spindle speed. I have beard and it makes sense that screws tend to be the best at giving constant boost across all RPMs

This is just my spouting about what I have learned during my research into getting a SC... it may be too general... but I hope this helps. anyone have any comments?

happy thanksgiving.

LO

MilesOrbell

Thanks Tom, I am thinking along your lines, & will probably go for the TS option, mainly wanted actual info from people who have got these units with respect to gas mileage in cruising conditions, our fuel here is over $1 per litre.

There are a few references quoting better fuel mileage, I cannot understand that when some HP is being used to drive the TS, probably as you say, referencing an incorrect instrument display.

It is an 89 S4 Auto Euro spec, and I really like what I see with the DR kit, one problem may be oiling of the MAF hot wire with those oiled type airfilters, & poor filtration compared to other types filters.

As you say, spoilt for choice.

drnick

loads of people use k&n filters without issue. john speake in the uk is one of them although im not sure if that s a ploy to garner a little extra business!

John Speake

I have lots of spare MAFs, Nick !

Seriously, I doubt I would feel happy reusing my K&N when the time comes to clean and re-oil it, so I will fit the OEM version at that time...

Regards

Bill Ball

I have 10K miles on my Andy Keel Jag/Eaton under all kinds of driving conditions. If it has high parasitic drag, it sure isn't apparent to me. When cruising or just putting around town there is ZERO indication that the car has been altered from stock. My gas mileage, not using the now misleading dash computer (as Tom explained), is about 10% better than before the SC, but to avoid a battle over how that is possible, let's just say gas mileage did not go down. And this includes the fact that I'm quite a bit more into the pedal than I used to be - It's fun to leave a huge trail of tire smoke up the freeway on-ramp!

There's no real need to have an emotional debate of centrifugal verus roots or whatever. They deliver power differently, and there are times when one is better to have than the other, on both sides. There are MANY very, very happy Murph kit people. Had I put one of them in, I'm sure I'd be very happy. I helped my buddy George Suennen put a Murph kit on his 90 S4 and he's ecstatic, especially at 180+ MPH (and heading for 200+ in the near future).

IcemanG17

Its safe to say that George has the fastest S/C (of any type) 928 out there right now.... I don't think anyone else with a T/S has gone that fast? But 440whp will be quite fast!