Imo000

Key to keep the old SN series SCs to last is belt tightness. A lot of people over tighten the belt and the bearings end up getting damaged. Over spinning is another problem that will destroy the SN. For some reason people tend to under rate these SCs. They are perfectly fine to get ~55% hp boost without any problems. I guess the other SCs can stand abuse a little better than the Paxton SNs.

Now back to the Rotrax, looks to be a nice supercharger. It’s physically smaller than the competition and can produce some nice numbers. However a 6.0L V8 at 20psi producing 928hp is not really that unusual. I would imagine that other forced induction systems with that much pressure would produce the same hp.

I haven’t been able to find a price for just the head unit? I can see that the 350Z kit is over $7000 but I would be more interested in the SC alone.

Jim Nowak

True, but many centrifugals can get over 100% increase in power. The SN were good at the time but there are much better and more dependable centrifugals on the market now. I increased the power in my supercharged 560 Mercedes with an ATI Procharger P1SC by close to 75% with no intercooler but I did use methanol & water injection to control detonation. I'd imagine the Rotrex would do even better at the same boost level due to its high efficiency.

I like the Rotrex due to the very high step ratios and the adiabatic efficiency. They could have produced much more power from the 6.0L engine with the Rotrex superchargers but the engine may not hold together very well. It's still impressive to get over 26 hp per psi of boost.

Herr-Kuhn

One cannot talk turbo lag with a Vortech strapped down to the crank. The arguement holds no validity whatsoever. A belt drive is still a belt drive, it can slip and is always pulling power off the crank. Gears are subject to wear and make noise. You have neither with the turbo, the elegance is in the simplicity of the design. A CS without a variable speed drive is still down on boost compared to what you can have with a turbo or positive. The recent surge in Centrifugal use is for one major reason...it is a quick way to make a buck, even Dinan has jumped in. There is so much bad information out there regarding forced induction that a person who doesn't know the methods could easily be misled. Perhaps even some politics. Statements like "Centrifugal Superchargers don't have lag like a turbo does" are simply not true. If the CS salesman told the buyer the truth about the boost curves and how there is gobs more area under the curve with the turbo it might just shed some light on the situation. Not one of the CS people will come out and state their boost levels at 3000, 3500, 4000, 4,500, 5,000, 5,500, etc. I'm asking....again. Do we have any takers? Tony, I know you have it all right after the 9 mile burnout started.

The lag isn't a problem with a big V8, really. I'd prefer a car that is very docile off idle then come on hard when you lean into it. Lag isn't a bad thing and remember your "lag to full boost" with the CS extends from when you drop your foot until the tach reaches the redline. No thanks, I'll take mine when I ask for it. I rarely would have a use for boost right off idle, though 9 mile burnouts would be interesting...

That is why the turbo is so nice...it simply idles off in the distance until you need it. Unlike a CS it isn't always trying to crank up boost as a function of RPM. Thus there is less throttling done, the whole system is just a far better solution. Yes it might cost more, but it delivers so much more...torque, elegance, longevity, etc. You want cheap, go buy a fast Nova or Chevelle. For 1/4 the cost of a 928 you have a faster car. Jim, Did you see Lenno's 66 twin turbo toronado? That V8 engine delivered over 1100 HP with twin Garretts. Nobody needs that much power on the street, but the point here is the turbo can deliver a higher average HP across the driving RPM band, making for a better solution in terms of performance and efficiency. It is proven time and time again, on the street, the track and with the big diesel rigs.

I'd guarantee I could mount a full twin system on a 4.5 liter for little more than an extra day or so compared to a CS. It isn't that complicated. It is complex to design and fab, but install isn't as bad as you all paint it to be. I had both IHIs out on the floor in about 4 hours after a 2 year tour of duty in the car. You just have to know where you are going and what you are doing to pull it off, that's all.

Oh, when will the debate ever end? I do like these discussions though. More fab work to do this weekend...been busy at my crib.

Imo000

Agreed!

I had my Novi GSS left over from a different car and that’s the reason I’m using it. I’m only running 6psi and no IC or water injection of any kind. At lest not yet. Over the winter I’ll machine a smaller pulley (8psi) and install an IC. This should give me a better than the existing ~55% increase in HP. I think that will be about the max I can pull safely out of this head unit.

There is always something better than what I have….that’s’ just the way life is. But for a total cost of $1000, I doubt anyone can beat the cost/benefit ratio of my build!

Herr-Kuhn

The point you guys are missing here is powerband width. The turbo delivers it, centrifugals can't match it. My little K-24 equipped 3-spd 928 was a full 0.3 seconds quicker across a 1/4 mile compared to a 5-spd 4.5 liter running the same boost on the same engine. Those two engines made about the same "HP", but the turbo car, even when crippled with an automatic proved quicker. The key is power production across much of the RPM range, not just at 5,500 up.

Kaz

These debates need to stop Herr, or you need to start ignoring them. I think it's a ploy by the Supercharger guys to keep you out of the garage and on the web.

Imo000

Naaaaah, the point you are missing is how much all this costs. B/C is what most people are after.

bcdavis

Yeah, but he's rarely debating cost. Just which system is better...

Tim Murphy

Here is the data logging chart from my stage one as well as the dyno sheet. EDIT: I thought this represented more of an rpm range. I'll get a screen shot of that one and post it.

You can see that the boost is very linear with RPM and that is why the centrifugal works so well on a stock engine and stock engine management. If you bring on the boost any quicker you will run the risk of detonation because of the stock ignition advance. This is not guess work, it has been proven to be fact. Even with the centrifugal, if I turn up the boost too high I have to take out timing below 4k rpm to avoid detonating (or roll into the throttle works too).

I'm not saying there is ANYTHING wrong with turbos. I like turbos.

Imo000

Rarely????? More like never. For some reason cost is not a factor to him. Just look at how big of a financial flop the Goldmember project was.

Herr-Kuhn

Hey, give me another 3-4 weeks and I'll show you what came out of the GM development. A lot was learned on project Goldmember. It was my decision to sell the car at a loss so I could move onto somethng more, shall we say, interesting. Much R&D was gained in the process as were some nice jigs for reproduction purposes. I'm just literally in the middle of installing the K26 units into the Callaway. The car should be running just before Christmas. Better match on the hot sides, bigger compressors, more robust hardware and the ability to crank down the screw! My old IHIs were for the most part not a real great match for the 4.5. The hot sides were too large and the cold sides on the small side. Cost is always a factor, but as you know my setup was never about being cheapest. The project was far from a flop, technically or financially. Somebody got a good deal on the car and I got my R&D. What do you think, you make a huge profit on the first one? Show me any product development that ever did that (besides the pet rock). The car drew lots of attention this year at SITM. There always seemed to be a crowd over the Goldmember. It would have brought a little more cash with a 5-speed for sure.

Tim, I disagree on the issue with detonation. The point here is if the system has the ability to pull ignition (which it probably should) you won't have a problem. I agree, the CS is easier on the motor across the mid range, but it also makes less power there compared to the turbo. If it is tuned in properly then you don't have issues. Even on the 4.5 I pull timing out with manifold pressure, you have to do that or you are asking for it...specifically with the 928's weak pistons. I would never expect a setup optimized for NA to work the same for boost. I take it the above curve is without charge cooler? Are you clamping MAF voltage or pulling any timing at all?

bcdavis

I have a suggestion.

Just a suggestion mind you...

Seeing that 928Turbosports is already planning on putting out a kit for stock
928s, why don't you focus on making your version of the ultimate turbo 928 s4?
Don't be held to stock configuration. Run stronger pistons, different cams, etc...
That way you can have something to compete with the Devek white car, etc...
The MURPH guys are experimenting with low compression engines,
special head gaskets, etc. All the the quest to contain more boost.
So why not go that route? Instead of starting with a stock s4 engine,
why don't you build one built for your application?

Tony

Tim, was that with the stock injectors ?

He is right with that H-K . All the tip in problems you hear with the TS are timing related IMHO. You can throw all the fuel at it you want to prevent it but pulling timing is the best way.
See Prof Otts comments on the 928 detonating on the dyno he witnessed....the installers tuning solution was to add more fuel. While it is a bandaid and perhaps works to some degree its not the best way to do it..
My guess is that the 928 on the Dyno was a GT,perhaps a red one? i havent had any issues with my S4 yet, although i try to drive it smartly. I keep the revs up and the laboring "load" off the motor. When i want to down shift i do it manually with the lever, instead of opening the throttle and waiting for the tranny to down shift for me. Much quicker response and just more fun manually shifting the auto...unless i have a coffee in my hand .

Tim Murphy

That's TOP SECRECT

Okay... that was with the stock injectors but as you can see I was pushing them to the limit. The dyno was actually done with a slightly smaller pulley therefore less boost (about 1 psi).

Tony

this is the whole thing that puzzles me...PM if you like, but my injectors go full 100% on a 402rwhp run and they are 24lb. You can see that when they do the AFR starts to lean out as the rpm increases over the last 1700 rpm of the run. It actually parallels the RPM line .