AO

There are a few different versions. The latest (2yrs now) from DR is to use an auto tensioner off a Ford GT. Works very well. Sorry, I don't have a good pic of it at the moment.

auzivision

Following are a couple (not the best) photos of DRs new systems and a few other different examples:

victor25

Hey Tony
What are you thinking when you say that. I have tried to put some arc and shape in the top box to distibute the air more euqally, but I would like to hear your thoughts on what you think may happen. I still have the ability to add fins or director or sepatators to the top plate, so please speak your mind.
Vic

V2Rocket

the first and second pictures are the ones i remember seeing. are those pulleys available on their own or are those the ford gt ones

Tony

Basically what you describe. I think anything you can do to aid the air flow to make the turn will help. You dont want it coming out then BAM hitting a wall...changing direction then BAM hitting a wall and going into the intake runner. Space is the issue we are all up against and that makes it hard to do.

auzivision

Victor,

I wonder if horns (like in the stock system) would aid with the flow, but those are sucking rather than being blown. Maintaining laminar flow can be tricky and am not sure it’s as critical in a pressurized situation. Something along these lines might help:



V2Rocket,
The first two pictures are of Dave Roberts 928 Specialists setup. You might contact him to see if he’ll sell you one. Following is a little better picture that shows how it incorporates 4 idler pulley’s:

victor25

So basically the horns help bring in the air by getting rid of the sharp edges? If I remember correctly, with the current TS systems you guys have, its basically just a open square box down low with big round holes instead of up high like mine correct? teh holes are 2 1/4 inces and funnel down to the ports. I dont think there will be a problem there. I am little worried about the flow restriction before the supercharger.
Here is another picture. before the top is on

Louie928

Hi Andrew,
The top picture with the short direct drive belt is of the modified drive system originally from Andy's TS kit. I put it on a '91GT that John Ryall now owns. I changed the drive so the tight side of the belt was direct to the SC with no tighteners or rollers. Those are on the loose side of the belt. You'd be surprised at how much additional stress is put on the tight side of the belt when you accelerate the engine. Even though the static belt tension is quite tight, the loose side becomes visibly loose when you pop the throttle open a bit you can see the belt cinch down into the grooves of the SC pulley. That's how it should be and why the heaviest load (in this case the SC) should be the first device after the drive pulley. The drive system proved very reliable in the few thousand miles we drove it here and I believe performed well for John going across the country and after. Once the belt seated in, little roller tightening needs done. The rollers are from the local NAPA auto parts store and nothing special other than being ball bearing. I did have to turn the peaks off the SC pulley about 0.020" or the belt wouldn't seat into the grooves enough to provide positive drive under boost. In other words, the belt would slip and the pulley would get hot.

Louie928

The shape of the inlets from the plenum doesn't matter whether the air is forced in (boosted to above atmospheric pressure) or at one atmosphere as in a N/A engine. The shape of the inlet does matter if considering flow loss into the outlet tube(s). With a sharp edged hole, or one with a too small of radius the flow is concentrated in the center and the outer edge of the area is wasted. That phenomenon is called "vena contracta". For a sharp edge hole the effective flow area is about 0.62 of the physical area. The flow loss can be reduced by radiusing the hole edge. How big of radius? If the entrance radius is 1/4th of the hole diameter the loss becomes almost negligible. Often you don't have the luxury of space to have that large of radius so you do the best you can. Your plenum wall and intake tube wall is thin so you can't really get much of a radius by grinding into the edge. What you can do is to form donuts from metal tube, even copper tubing, with the ID of the donut being the same as the ID of your ports. Then weld or braze the donut hole over the port entrance. Smooth out the entrance as much as you can. Fill with brass. You could get the usual aftermarket bellmouth intakes and weld those in too, but that will cost a few bucks.

Your intake will work as it is except you'll use blower power (engine power) to force in the air through the inefficient intake. The effect will be to have fairly high boost in the plenum since the inlets are restricted and lower hp than expected. What you want is to have low boost and high hp resulting from an efficient system.

orangecrush

Using our collective knowledge and some off the shelf parts, isn't it possible to make our own new high quality twin screw supercharger with an air/water intercooler for less than $5000?

Bill Ball

"Off the shelf" is where your plan fails. DR has spent years perfecting his design and I'm sure he would have rather used somebody else's parts if there were any that would fit/work. Everything from pulleys, manifolds, and brackets to intake plumbing needs to be fabricated.

FredR

Whole heartedly agree with what Bill has written. If you look at what DR has produced or the TS conversion that Louie did, they are really impressive pieces of engineering that look as though Porsche might have engineered them. I dare say there are others that are also very good as well but frankly, most I have seen [a couple in the flesh and the rest on photos] look like the aftermath of a dog's dinner plate and for some folks, that is just not a problem as long as they work which in most cases [I suspect] is some way from being the case if the truth be known.

For sure I would be proud to own the efforts that DR or Louie retrofitted to my GTS. For street 928's and particularly auto's, I believe the TS is a good way to go due to the low down torque being able to compensate for the 4 paltry ratios we have.

However, one thing I am sure about is that most of those who have attempted this will tell you is that if they costed their time and effort to achieve whatever lurks under their bonnet at $30/hr, they will inevitably tell you it had cost them zillions of dollars of their time to achieve whatever they did.

On the other hand, if one can take a DR type kit and fit it in a weekend knowing that [within a narrow band scope] it will work first time, that is worth an awful lot to me. A saving on material cost of $2k may initially look quite substantial but in reality it is little to pay for the benefits of being able to take full advantage of all the time and effort put into developing the detail of such a kit.

I suspect Dave will struggle to recover the real costs it has taken him to produce the TS kit but I sure hope he does- and that those in the 928 community who want to go down the TS route will help support folks Like DR who stick their technical and financial necks out to enhance the 928 ownership experience.

That it has taken DR quite some time to bring his kit to market should be testament to just how difficult it is to do something like this. I think the dyno sheets and the photographs speak for themselves.

That you can probably buy a half decent S4 these days for the cost of a TS kit is not in dispute but my instincts tell me that the grin factor/sensation of driving one of these TS converted 928's is priceless and well worth more than any $2k one may perceive to have saved going the DIY route.

For pretty much the very same reasons I am a big fan of what Murf and Carl F have done with their centrifugal kits and what John Kuhn has with the twin turbo kit and they are all to be saluted and encouraged.

Just dealing with the heat over here on my little more than stock motor is a continuous struggle- not sure I could handle all the heat that goes with the additional power of these kits.

Sure fancy having a go though!

Best wishes

Fred R

auzivision

I admire all the people that taken the initiative to do or have done these on their own.

Is it possible to do for $5K? Most likely not. It won’t be easy… something is going to be compromised… money, time, and/or quality being the first three that come to mind.

Is there enough knowledge around here? Absolutely! However, most of those that can do it; already have done it, so no ‘group buy' opportunities. Those that haven’t need to learn if they want to do it on there own.

Off the shelf? No way! You’ll need to design and fabricate an intake with intercooler and fuel injectors, throttle & MAF relocation, and drive pulleys/brackets. Those are just the big items, there are plenty of others like vent/breathing, tuning, air duct plumbing.

If you are seriously thinking about going it on you own, I’d suggest you get yourself a copy of Corky Bell’s book, “Supercharged!, Design, Testing and Installation of Supercharged Systems” and read it first:

http://www.amazon.com/Supercharged-T.../dp/0837601681

It gives you a great idea of exactly what is involved. I’m guessing you might have a change of heart about going it alone.

Vlocity

Hey guys,

I could use a little help. I have over 60 track days on my setup and so far it has been bullet proof. However, since my last outing I am only seeing 5 pounds of boost where I always had 8.5 pounds before.

I've checked to make sure the throttle is opening all the way and I plan to pull and check the air filter. I also snugged the blower belt back up, but there is no sign of it slipping on my 8 rib pulley.

It is warm here 85 - 90 degrees and was 88% humidity this morning....but I don't think that has anything to do with it being off by 3 pounds of boost. I guess it could be the gauge but it does feel off on power just a bit.

Your thoughts are appreciated.

Ken

Rick Carter

Ken,
My crank pulley was slipping, still is and I'm working on a solution. It started with lower boost for a few months and now no boost.