lsinlv

FYI - if you are running low boost, even under 12psi non-intercooled is not an issue, as S/C'ing doesn't add substantial thermal load.....compared to turbo.

there are hundereds of 10.5:1 CR VR6's running s/c's at ~12psi with no IC, and no timing pull due to knock. also, consider that this kit will be based on a centerfugal s/c, you will only be at your highest boost for maybe 2 seconds or so....

If you decide to go more than 12psi, then I would say you NEED an IC....otherwise you will just increase the volume of the intake, slow the boost curve (gerater volume to fill/charge), have boost-drop, and cause more delay on recovery once the DV dumps boost/partial throttle.

K.I.S.S.

RajDatta

Nope, you need to make mods to make it fit.
Raj

FRporscheman

The problem with a 951 intercooler is that in a 968, that space is already occupied with other stuff. Personally I think the best choice is a front-mounted IC. A small IC with custom brackets could be positioned in the 951/968ts position, but the FMIC would likely cool better. Longer pipes usually means more lag but SCs don't lag much do they?

Carl, when I had a 928 I really wanted one of your kits. I bought some other parts from your site, and I was always impressed with the quality and awesomeness. I think quality is something that comes naturally to you and your enterprise. I also think that you have the expertise to make an efficient, potent kit with your eyes closed. So please, my only suggestion is that you don't focus on power and efficiency, focus on cost.

A question: Why are you choosing a centrifugal supercharger? I know next to nothing about blowers, but I know centrifugal will push air linearly proportional to rpm while a roots will somehow push more sooner. The 968 is a dog at low rpm and this is where it needs the steroids most, so I always envisioned a roots blower being a lot more beneficial. You're the expert though! I look forward to your progress and great work!

To those who say a SC kit is cheaper than turbo: This is only because a turbo conversion always includes an engine rebuild, while a SC is always a bolt-on affair. Really, one should be able to make a low-boost turbo (the boost regime of a SC... say 6psi) without touching the inside of the engine. This would make the cost the same or less than a SC. Money takes an already complicated choice and makes it even more so.

H2

I'm not interested in an engine rebuild...I want bolt on. I got all enthused about turbo on the 968 but gave it up when I saw the high costs. A SC sounds exciting to me...if it can be made simple to install...relatively low cost...few engine modifications...and without sacrificing reliability....I think that would be a winner. Tall order but I think that's what most people may want.

Harvey

FRporscheman

Harvey, I completely agree. A SC is easier to install, that's for certain. And a kit made by 928 motorsports will be well crafted and a perfect fit. Heck it might even look factory.

notthd

Weighing all the options I too think the SC would be a great choice. Keep the AC, instant boost, and a cool whine to boot. That was always my favorite thing on the VR6 GTI, sitting at a stop light and the ricer guy next to you thinking twice about taking on a VW "hey man, what you got in that thing?" - too funny. An added 50-75 HP would really change the personality of our cars, and possibly make the car as fast as it looks!

I bought more lotto tickets this week- if I win the jackpot everyone on this thread gets one for free on me- Cheers, Mike

Lemming

I'm down with that Can you clarify, is that one per person or one per running car with a 968 engine, if the latter, I'll need two!

PorscheDude1

In...
just case you hit lotto!

Carl Fausett

I will use a small, ceramic-coated impeller, self-contained centrifugal supercharger called a Raptor. We use it on the Ferrari kits with success where we have to rev to 7500 red-line, and also the Porsche 928 32v kits, where we make 504HP with it.

A roots would be a very poor choice for a number of reasons. The roots-type blower has the lowest adiabatic efficiency (the ability for a compressor to compress the air without heating the air is measured as adiabatic efficiency).

Our goal is total air mass, or air density. Pressurized hot air is not our goal.
Hot air is not as dense as cold air.

Better than a Roots would be a Whipple or a Twin Screw - also a internal compression supercharger, but with higher adiabatic efficiency.

The Roots blower has about a 50% adiabatic efficiency. The Whipple or Twin-screw blowers can reach almost 70% adiabatic efficiency. The Raptor I will be using has an 85% adiabatic efficiency - amazing - and allows me to eliminate the intercooler safely as a result.

This topic is particularly important on applications where we may never be able to easily fit an intercooler.

Other benefits - a Roots, twin screw or Whipple would require at least a partial engine disassembly to install, and require we manufacture a completely new intake manifold casting for it. (Read $$$$)

If I use a centrifugal blower, we can avoid the expense of a new manifold, and keep the install a LOT simpler.

Then there is fueling: where a positive discplacement blower (Roots, Twin-Screw, etc) brings in the boost just off-idle, you have to be able to bring in all the fuel just off-idle also. This requires many fuel system mods, re-burned or replaced chipsets, large injectors, etc. A lot of dinking around and $$.

This 968 kit's greatest challenge is cost. It is a discontinued automobile that went through a limited production run. If the kit ends up at $7 or $8K it wont sell. My challenge is to make a good kit, easily installed by the common owner, under $5k. Then I might sell enough to make this project pay for itself.

When I start one of these supercharger kit projects, one of the things we do is determine what the stock fuel system can do at max. Then we adjust boost to that or just below it to match. In this way, we can keep the stock MAF sensor, throttle body, and injectors. That will keep costs down and simplify installs.

Let me see what the stock systems will fuel without modification, and we will go from there.

Darth Coupe

It sounds like a great project. I am interested to see what it does and I may be trading parts off of my kit to use some of yours if you can keep A/C and make it run smoother than mine currently runs. Are you looking to have a piggy back, adjustable fuel pressure regulator, or new chips to run the fuel?

Will it be able to run E-85 and regular premium? It sounds like it will be pump gas as you are looking to keep the injectors the same size.

I am excited to see what you come up with.

lsinlv

FPR's are a stupid "trick" to get around a bad tune....there are better ways to deal with fueling in FI.

E85 should NOT be run in our cars, as all of the fuel system components are not made to handle anything greater than 10% by volume of ANY oxygenate; they WILL eat every rubber seal/plastic component in the system. Add to this, that E85 is substantailly lower in available potential energy as a fuel.....it may burn cleaner and cooler, but it doesn't produce the same power by volume as gasoline.

my $0.02

Darth Coupe

It will not eat the fuel system components at all. If they did, my car would have leaked out the gas tank and caught fire a long time ago. If you are running methonal then I would agree. E85 is nothing more than cheap race gas for me as long as you have injectors and more fuel added to use it.

Though I do not want to get on an E85 debate thread. I just want to see and hear what options are being planned and see what path the kit is going down.

Carl Fausett

The Stage 1 kit will not be designed for E85. The Stoicheomteric air/fuel ratio for ethanol is almost 9:1, where gasoline is 14.7:1. To run E85 - like Darth Coupe said, requires VERY high flow injectors and a complete reflash or reprogramming of the LMB.

Those items are outside the design goals for this kit: low cost, simple installation, use stock components.

Moook

I suspect you will have a LOT of 968 folk watching this thread with interest....
I SO hope you pull it off... In budget...

Carl Fausett

Thanks, Mook. I have one small new product project to finish and that is scheduled from tomorrow to the 19th, then the 968 comes into the shop.