sryth

I'm swaying back and forth between SC and turbo.

I'd go with an SC, but I don't like the idea of hitting max boost at redline, only to shift to the next gear. I also don't like the fact that the SC is useless at lower RPMs.

I'd go with a turbo, but I'm afraid of unreliability as it's pretty new territory. I also don't like the heat and crowding that's created in the engine bay.

I could solve the SC problem (somewhat) by using a smaller pulley. That'll give me more boost, but I don't want to push it.

All this got me thinking: I could I get a real small pully to push the SC to ~14lbs. Bringing this rig to redline would be suicide on my stock engine with +120k on it. Would it be possible to mount an electronically controlled wastegate on the charged pipe? This would allow me to both get more boost earlier and control the boost level electronically.

This seems like it should work, but I'm curious as to why noone has tried it. (everyone probably knows something I don't, huh? )

ereet

Interesting idea. I don't know if it would work or not, but as for the 14lb boost idea, my car has 100k+ miles on it and I'll be switching to a 2.62" pulley assuming my injector plan works out. I'm currently running the 3.00" and the engine still works beautifully.

sryth

Ok...so you could use 30lbs boost with the wastegate

Stephen Max

iTrader: (59)

You don't need anything as complicated as a wastegate to limit boost at high rpm. You can get pop off valves that limit boost pressure to a predetermined setting. Or you can replace the spring in a bov with a softer one that will allow boost leak above a certain pressure. But it's inefficient to expend energy to create boost just to let it leak out.

Or you can set your belt tension so that it starts slipping when you hit 10 psi or so. I found out I was using this method last night. My boost pressure would get up to about 7 psi at about 5800 rpm, then drop down to 5-6 psi and stay there until redline. I was quite flummoxed until I remembered that my belt was still a little loose after removing the blower last week looking for the source of a coolant leak (turned out to be the water pump seal).

Edit: I need to add I was only joking about the loose belt method. A slipping belt won't last very long.

[maxi-overdose]

iTrader: (3)

I have a 2.87 pulley and it supposed to give me a 13psi boost. However, I dont want that much of boost, but I do want the quick response from a smaller pulley. So I make the BOV leak (my BOV is adjustable) and now, it only hits 10psi peak.

IceY2K1

iTrader: (3)

One problem with bleeding off compressor discharge air is that the MAF has already measured it and the ECU is dumping in EXCESS fuel, so you'll be pig rich. Of course, you can tune that out with a AFC, however when the bleed-off is not happening, you'll be lean.

My theoretical *IDEA* is to come up with a CVT pulley to drive the SC. Instead, of being limited by a FIXED pulley ratio(crank->SC), the CVT can start out super small(say for 30psi of boost) to spin the SC faster at lower RPM and then 'move' to a larger diameter that limits the boost to say 10psi. Crazy *idea*?

Stephen Max

iTrader: (59)

Us 4th gen guys don't have that problem with our heavy-duty blow through mafs.

Not a crazy idea at all. That's exactly what we need.

[maxi-overdose]

iTrader: (3)

hmmm....when the intake pressure builds up, the FMU will take over and increase the fuel pressure. I believe the stock ECU and MAF can only measure up to certain amount of air entering. If the bleed-off is not happening, you will still be ok because the FMU will add more fuel in the engine to support the extra air.

I am running rich because of the FMU that I am using. hope with my upcoming mod, I can lower the fuel pressure a little to lean it out. S-AFC is a good option...but it is kinda expensive.

IceY2K1

iTrader: (3)

True...I didn't think of that.

I agree, since the S-AFC is more for fine tuning out the dips/bumps NOT keeping things in the safe A/F range like the FMU or better the S-FMU. The S-AFC is probably only going to eek out maybe 20hp peak, but it also helps keep more area under the curve. Plus, it looks .

Stephen Max

iTrader: (59)

I'm not sure I agree with a SC being useless at low rpm. It is pumping air at low rpm, probably even more than a turbo. Just not enough to make positive manifold pressure - but the engine is getting more air than a NA engine.

If a SC is useless, then a properly sized turbo is useless at low rpm, too. It's true that you can choose a turbo for a specific engine to provide an extremely low boost threshold, but if you have picked a turbo for low end power then you're sacrificing peak power and power at high rpm.

That being said, gotta admit that the SC can't compete for total area under the curve against a well chosen and well tuned turbo.

Craig Mack

How would we go about making one? How long would it take to produce? What about price? Could it be built customly? I assume it would sit in place of the regular pulleys we have now?

Stephen Max

iTrader: (59)

I don't think there's enough room for a CVT type device to replace the present blower pulley. A CVT involves something like the cluster of gears on the rear wheel of a racing bicycle, but instead of discrete gears you have a cone. That's a pretty simplistic description, but you get the idea that quite a bit more space is involved than a fairly thin pulley. Maybe if you designed one to replace the crank pulley.

At any rate, CVTs are complex and not inexpensive devices, and a SC kit using a CVT would have to be engineered from a fresh start, not retrofit onto an existing kit.

Craig Mack

Well, looks like that's that then.

[maxi-overdose]

iTrader: (3)

yup...it is a cool looking device

FMU/adjustable FMU can only get me a close AFR. but to get a clean flat one...I will still need the S-AFC to get to there.

are you thinking about getting boost, alex? you've been visiting here a lot~

IceY2K1

iTrader: (3)

VERY very ROUGH sketch, which has a few holes in it, but just to give an idea of WHAT I'm talking about.

Stephen Max

iTrader: (59)

There ya go. When do we start making chips?

IceY2K1

iTrader: (3)

Are you poking fun at my sketch?

sryth

Yeah, you can use the BOV, but isn't an electronically controlled wastegate a better option? The spring in the BOV isn't exactly open/shut. When the pressure gets close to the "certain pressure", the BOV will start to open a little. It'd start bleeding prematurely. Maybe that's no big deal, I don't know.

Just how inefficient is it? Yeah, the fan's spinning faster, but it's not getting quite the resistance it would get if it were pressurizing.

I wouldn't call it a crazy idea. I was thinking something along those lines a while back, but it just seemed too impractical. I was thinking of either:

a) Making an expanding/contracting pulley with another pulley that slides to control tension

b) Putting a clutch on the pulley that I could control the slip with (probably too much wear)

I also thought about sliding a belt down a tapered pulley, but the belt would wear out too fast (IMO)

Hell, even a discrete state transmission would be a hell of an improvement.

Does that mean the wastegate idea is feasable? Using a wastegate over a BOV would also give you the ability to add a boost controller.

sryth

We could just get a variable pulley Doesn't look like it'd be too hard to incorporate any of the following:

http://www.andersoncvt.com/applications.html
http://www.berges.it/mech/pulleys.html
http://www.variablespeedpulley.com/ (Look at the fixed center drive pulleys)
http://www.hi-lo.com/

[maxi-overdose]

iTrader: (3)

that's no big deal. my car is a good example of using BOV to bleed off excessive boost. It never went above 10psi and it is a lot quick to go from vacuum to boost with that small pulley.

IceY2K1

iTrader: (3)

VERY interesting!

Now we need to figure out HOW TO MOUNT something like that. I peaked at the front of the engine this morning, but couldn't get a good look at what room there is to work with.

Craig Mack

I wonder what the costs would be just for the unit itself, nevermind the parts that need be custom fabbed for installation.

IceY2K1

iTrader: (3)

Keep the dream alive Craig!

I'm still thinking...just too busy to dig anymore.

sryth

As long as we could find one that can handle the speed/tension/size requirements, we should be able to get one in without too much trouble, IMO. If I actually had a supercharger, I'd prioritize the search for one of these pulleys. (Anyone got an extra SC I can have for motivation? )