Batass

I've been thinking about upgrading my S-trim to a larger one, using pulleys for max cfm to bring boost on quick, and a wastegate to limit max boost.

Read about it on a mustang magazine site. Seems sweet. Power curve like a turbo.

Only problem is, I dont know how the alky injection would react to it. Not sure if the alky would blow out relative to the air.

Sonix

iTrader: (1)

A wastegate? I'm gonna bite here, do you even know what a wastegate is? How would a wastegate DO anything with a supercharger?
Did you mean a blowoff valve? I mean, a wastegate "wastes" some of your exhaust gas in order to bring down the boost level before it gets dangerous. You can "waste" all the exhaust gas you want with a supercharger and it won't do anything at all. ???

project89

iTrader: (1)

im pretty sure he does mean wastegate,what hes talking about is using the wastegate on the charge pipe.in doing so he could change the pullys on the supercharger for super quick boost response ,and then say he only wants 12 psi use a watsegate with a 12 psi spring to bleed off the extra boost at higher rpms.

in theory this could work but id imagine it would throw the supercharger way outside its efficiency range

this could not be done with a blow off valve

Street Lethal

iTrader: (16)

383BackinBlack would be the guy to ask, but he hasn't posted in awhile....

Batass

Yep, thats what I mean. I have seen him in a while either(edit-hes been hanging out at turbomustangs.com, traitor!), but I don't remember seeing one on his car.

About the efficiency range, I don't know. I don't know at what rpm its most efficient at. Max rpm is 50,000. I know you can go higher than that, but efficiency takes a dive.
However, I would assume that its highest efficiency is at its highest recommended rpms.

Sonix, you must think I'm really stupid! lol.

tequilaboy

This topic was discussed recently over on CF.

A very simple alternative approach would be to use an inlet restriction to limit the boost. Something on the order of 2.5" to 3.0" in diameter should do the trick. There is a guy that had a bunch of large custom washers made up for this purpose.

As flow increases, the inlet restrictor comes into play reducing the inlet pressure (and the outlet pressure as well since it is dependent upon the inlet pressure). The supercharger output is just a pressure ratio.

Batass

I dont think I like that idea very much. Not very precise and forces the supercharger to work very hard. Thats gotta suck some power. I think a wastegate would be simpler. Simply weld it on!

I could also easily change the boost from race settings to street.

Whats CF? The chevrolet forum?

Sonix

iTrader: (1)

haha, well you certainly threw me off with that idea. A wastegate (at least by my definition), basically measures the pressure in one pipe (the intake charge pipe) and as it gets too high (depending on your springing) would "blow off" the excess charge in another pipe (the exhaust pipe).

What you're describing (blowing off excess pressure in one pipe based on the pressure in that pipe) is just a simple blowoff valve. *shrug*.

It won't work though. As mentioned if you're getting your boost down low, then once you rev it higher you'll be overspinning your blower. What you really want is some type of "clutch" on your supercharger pulley. So once it's spinning at xyz RPM it'll just start to slip so it doesn't over speed. I can't think of anything off the shelf that would work, but i'm envisioning something like a CVT eh? Changes the ratio as RPM changes.

project89

iTrader: (1)

if the blower is kept from over speed conditions it should work,but to see the ill effects of bledding off the air u would need some sort of map for the supercharger.u know how much air the motor moves at what psi,and u would knwo how much air its trying to move at a given rpm.

u could plot these across the map to see what it would do for compressor efficiancy by bleeding off the extra air

we could talk about why or why this wouldnt work all day,it may or may not work,theres only one good way to find out out and thats to do it,but to do it u better check on the blowers max rpm and over drive ratio,and do all the calculations.i know u can get a 2 bolt 35/38/40 mm wastegate on ebay for like 50$'s and + whatever the pullys cost ya,so i guess it wouldnt be that expensive of an experiment as long as u dont run the risk over over speeding the blower

tequilaboy

Here are a couple threads:
http://forums.corvetteforum.com/show....php?t=1982378

http://forums.corvetteforum.com/show....php?t=1995096

Batass

Good reads, but I dont see how any of those ideas are better than a wastegate?

Sonix, a way to disengage the blower would be a good answer. It would be cool if it was a 3-speed. A blow off valve uses manifold vacuum to open and release boost. Similiar but I'm talking about a spring controlled pop-off valve.

A wastegate would flow more air than that puny little pop-off valve, and I just don't like the idea of putting any restrictions anywhere. Sounds like more heat.

The efficiency of the blower would no doubt drop, as it would spin enough to produce say 1100 cfm, but the engine is only getting 900. Peak power would surely drop with a pop-off valve governing 14psi, vs pulleying the blower for a max 14psi. However, I would be making a lot more midrange tq. Another 3-4 psi would be a good kick in the *** at 3500rpm.

project89

iTrader: (1)

id say go for it a 35/38 mm wastegate would be more then sufficant to bleed off boost,if it dont work u could just replace the pipe with the wastegate flange or just make a block off plate,and swap ur pulleys back.if u can find me a map for ur supercharger i could plot the maps out for u so u could see what u would be looking at before hand

Batass

http://vortechsuperchargers.com/maps/s-trim_map.gif

This is for my S-trim. I don't think it would make a big difference on one this small.
The next question would be, what size sc would I have to upgrade to, to make this worthwhile. Probably a Ysi.

project89

iTrader: (1)

what boost level would u set the wastegate to?

Batass

14 I would say. Probably about the most I want to run with 9.3:1.

project89

iTrader: (1)

opps i also need the drive ratio u would be using

Batass

For the s-trim, 7.8 crank, 3.3 pulley 6500 rpm

Here's a y-trim map that I would try this with. Say 7.8 crank, 2.95 pulley. http://vortechsuperchargers.com/maps/ys-trim_map.gif

Havent tried yet with the new motor, but I think I'm going to max out around 11-12psi with the s-trim.

Thanks man.

???

iTrader: (5)

here's my random .02

first i think everyone is over thinking stuff.


as far as putting something in front of the inlet to limit boost. since it is decreasing the amount of air going in, remember the blower isn't pulling. just just pushing enough to cause a vac and the outside air psi is pushing it in, to fill the void. your not putting more drag on the blower, your putting less because its compressing less air. its the volume of air that make is harder to turn your blower. i'd guess you'd still be throwing in a little more waste from the spinning belts and friction losses.



for the waste gate, kinda the same thing, once the waste gate opens, the amount of work done should be less, because its not having to build the extra say 5psi. as long as your not over spinning what its rated for. to test it, go take your intake pipe off and let the blower vent all its output. it will take wayyyy less power to spin like this, than when its hooked up to the intake making its 20lbs of boost.(i know my car idle's up from having less load when my intake piping would blow off) so any air you let out, lowing the over all psi. should be easier on the blower. plus as i understand it, most of your intake heat comes from the air being compressed. if your compressing it less, you get less. throw in a big enough blower to be happy making 25+ then limiting to 14 by releasing the extra. you may have even cooler intake temps than a smaller one thats right at its limit making 14.



either way would work, but i have a feeling that restricting the inlet air volume would be a better way to do it. but as someone else above said. you would pretty much have to try it out. to see who's right.

Batass

Restricting would cause more heat and more drag. It would also take a lot of trial and error to get the pressure right. Since 14psi is 14psi, the wastegate could be preset.

Sounds pretty simple to me, and like I said, it was done on a mustang. He gained about a hundred ft lbs at 3500rpms.

tequilaboy

Restricting the inlet reduces both the flow rate and the inlet pressure.The result is less work for the compressor. Think of the restrictor as a throttle.

The compressor will be compressing less air to a lower pressure than when unrestricted. This should be the most efficient approach, resulting in a cooler charge and reduced power consumption.

The only downside that I can see is that it will require some trial and error to achieve the desired result.

Good luck with your project.

???

iTrader: (5)

oddly enough I just pulled a turbo off from a K car a few weeks ago and the TB was in front of the turbo (hanging in the air on some brackets)and it had no blow off valve. I thought at the time that its was the dumbest thing I had ever seen. but having just got done driving the car before pulling the turbo, I knew that it would make 9lbs and letting off the gas it had no compressor surg at all. after doing a little research, it clicked. with the TB on the inlet side. when it closed. the turbin wheel was still spinning but under vac, quite a lot of vac too as you just slammed the tb closed. and a wheel free spinning in a vac with no air to compress, it has nothing to slow it down and no boost to be made. also no lag between gears. back to this topic, I have no dought that either way would make more power at lower rpms, just for the fact that you have more boost. I just wouldn't throw the smaller inlet idea out the door so quickly. it would be cool to see someone with the time and money to do a dyno compairo

Batass

GM used to do it that way back in the early 80's and maybe sooner. Why did they stop?

With a turbo, it makes a little more sense, since the turbo will slow its spinning due to the restriction. A supercharger will continue to spin, increasing the load. A wastegate would be less of a load on the supercharger.

A restriction may also cause pressure to drop at low compressor speeds. Which would partially negate the whole reason for using a large pulley.

tequilaboy

Here's an interesting link on the subject:

http://www.turbotechnics.com/docs/supercharger/expo.htm

???

iTrader: (5)

cool stuff.