j200pruf

iTrader: (4)

Hey all, I have been reading the thread by zbrown about his SC project.

I was thinking of mounting the SC like zbrown with the throttles down stream of the SC. And I would be using and intercooler, and probably and Eaton M90. Is there and major problem with running the SC this way instead of having the throttles before the SC.

And does anyone know what the similarites performance wise between a M90 and say a camden 7 inch system.

And lastly does anyone think that ~250 at the wheels would be unreachable with a SP 6 port 13B.

j200pruf

iTrader: (4)

No one has any feed back on this?

Would anyone from Atkins beable to give me some more specifications on there 7 inch superchargers? Like maybe flow rate charts or outlet temp charts?

Thanks
-Justin

madsci

Short answer: a positive displacement SC blowing through a throttle is a bad idea.

Here's the situation:

At idle, he has a bypass valve to blow off the excess air from the blower.
At full throttle, everything should be fine - throttle's wide open so it doesn't matterwhere it is.
This is where it gets a little sticky. Say you're cruising along, the SC is gulping air wide open, and largely dumping it through the bypass valve. At some point, you are going to overwhelm the bypass valve and start building a head pressure (not boost pressure yet). This is wasting a bunch of energy. Bigger bypass would help in this regard.
Now let's say you open the throttle a little more, to where vacuum goes low enough for the bypass valve to close. The SC, as usual, it moving full volume because it is unthrottled. The pressurized air is restricted going into the engine by the throttle (throttle body downstream of blower), causing a pressure rise at the SC outlet until the blow off pops open at maybe 10 psi. "Head pressure" will continue to increase beyond this point dependent upon the size of the blow off valve.
So now you've got a range of small vacuum to anything less than full boost where the SC is compressing lots of extra air, making lots of heat, and wasting a ton of energy. You will also have undesirable response around the bypass valve operating point.
How bad will it be? depends on how much supercharging you are doing. The less boost you run, the less air you are moving, and the better it will work. But the idea here is to make power, right? You want to move air. You're best bet, if you insist on SC vs turbocharging, is to move the throttle body upstream of the blower. There is a good reason why every single factory supercharged (roots/lysholm) car has a draw through setup, and every single roots supercharger kit does the same.
I understand that some people are willing to live with a major hack job - that's up to them. Most people on that thread don't even know that things are not working as they are supposed to in his setup (which likely doesn't make much power anyway).
Intercooling is a must for making decent power. I can't help you with suitability of any particular model SC, as the only one I've ever dealt with was for a Chevy (and was subsequently replaced with a turbo for a 40% dynoed HP increase at the same boost level).
If you are intending to run pump gas, you may be asking alot unless you go low compression. Also you will need some sort of supplemental fuel injection. The factory ignition maps actually do cover full power all the way down to 1000 RPM (S4 ECU - S5 should be similar), so that may count as a "boost retard".
Yes - I think 250 whp can be done with an SC, but it'll taking some doing.

Phiber Optik

iTrader: (2)

madsci: I am planning on supercharging my currently NA 13b with the eaton m90. I was planning to have the m90 upstream of the tb, but I have noticed the problems that you have pointed out with zbrowns setup.

What is your suggestion for the most ideal low budget m90 setup?

kcr8

have you thought of using a twin screw? (not sure if there are any made for fd's??) the roots style blowers generate a crapload of heat so you'll need something to vent it. i could be wrong...i don't know much.

Jeff20B

iTrader: (13)

I can tell you I'm impressed with the specs on the new Whipple Chargers.

kcr8

agrees.

Jeff20B

iTrader: (13)

I bet the Whipple Charger will become a viable solution on the rotary very soon, as compared to what's currently out there.

We already know about the Nelson/Paxton belt driven 'turbo', regular exhaust driven turbos, and the (Atkins) Camden Roots blower. Each have their own strengths and weaknesses.

All we need are some people willing to purchase and install Whipples on their rotaries and then tell us about it. I know a guy who's installing one on a 20B right now. I can't wait to see how well it works.

Hamza734

The kit is a BAAADD deal. $3800 for 250WHP!?

I was on their website this evening and had a look at some of the pictures...the TB adaptor looked ghetto as hell. Without rehasing the whole "turbo vs. supercharger" argument, think about this: Say your cruising on the highway at 4000RPM. On a turbo you'll be fine, the compressor will be a bit of a restriction but yoy won't be building "wasted" boost. Contrast that with a Supercharger...boost is dependent on RPM, not load. The throttle is only partly open, but your creating boost which is not needed. The boost puts extra stress on the supercharger and the motor.

As for the lag thing, I think it's a relatively minor issue. Hell, sometimes I even enjoy turbo lag ! Only reason OEM manufacturers prefer SC's is that its easier and cheaper to manufacture.

Hamza734

Oh, just saw the 7" Supercharger Alright, not so bad a deal for $2400. I'd still take a turbo any day. Jeff, what are the specs on the new Whipple-charger? Is it the type that has an electro-magnetic clutch that can disengage the rotors at light loads?

I agree that Whipple makes the best superchargers, but damn! Those suckers are pricy. A friend has a supercharged SL500. He claims 430RWHP and 460RWTQ...then again the cars in Fl so there's no way for me confirm.

Jeff20B

iTrader: (13)

Do a google search on whipple charger. I found their website and it looks like their prices are comparable to Atkins. Then again, I could have read their pricing structure wrong.

88IntegraLS

Use the stock TB from the supercoupe, fab up the mazda TPS to this TB, use the supercoupe intercooler and fab up all your pipes / connectors / brackets.

In other words, hook up the M90 the way the engineers did in the first place, not like a turbo or centrifugal compressor.

j200pruf

iTrader: (4)

The supercoupe didn't inject fuel into the SC like old school set-ups, correct? I was thinking that using the stock TB would work, you would just have to make somehting that would allow it to mount to the M90. That would be fairly impressive.