LSs1Power

iTrader: (5)

I was always asking about putting a small pulley on a LS1 that gives 12psi and bleed some boost to make it 8psi. U have the option of using race gas and increase boost levels with a boost controller instead of swapping a pulley and also u will have the advantage of building boost early in the RPM and hold it to the redline in the case of pump gas. Anyways i found a guy who did it already and he was sharing how he did it.
Here is the thread :
http://forums.modular4v.com/viewtopic.php?p=640

greentahoe

iTrader: (2)

Wow!! Thats amazing Awesome post Thanks

NoGo

iTrader: (2)

You should not use this method to regulate boost on a supercharger.

It takes power to make power with a supercharger. The more you make, the more it takes.

If you want to regulate the boost of a supercharger without putting work into (ie loosing HP) flow that you aren't going to use, place a variable restriction at the inlet of the supercharger (like a throttle body ). This reduces the efficiency of the blower, but at least you aren't generating flow that you aren't going to use.

FYI: It takes nearly 200 HP to spin a procharger to make 22 psi on a stock LS1. Not to mention your intake temperatures are going to be that of a 22 psi discharge (ie MUCH HOTTER).

This is basically just an all-around bad idea to regulate the boost of a supercharger after the discharge point of the supercharger.

greentahoe

iTrader: (2)

It seems like the idea has merit. What would you suggest?? What other ways are there to get more boost at lower rpm while keeping the upper rpm boost levels sane??

LSs1Power

iTrader: (5)

I understand that SC's usually use power from the engine to move the blower. I disagree on ur statement the more u make the more it takes. The motor will use the same amount of power to move a blower at 3psi or 12psi. The internal gears aren’t going to change if u increase boost or decrease boost. That’s why I don’t see how the SC would use more power from the engine to produce more boost. I agree it will generate more heat due to higher boost, but i don’t think it will take more power from the engine to produce higher psi. IMO when the internal gears of the SC are moving they will gain momentum and it will be easier for the blower to produce higher psi than lower psi.

buschman

Twin screw. They have the best of both worlds. Instant boost and torque of the roots, and the high revving horsepower potential of the centri. In my opinion this is the best way to build boost fast. The heat and power loss of a relief valve make it not the best option for us blowers.

The only other off the wall thing I could think of is a clutch system on the pully itself. This would essentually only compress the amount you wished and save unwanted drag on the engine. We've all seen mad max I've heard that such a clutch doesn't really exsist. But they have it working for the A/C unit, so I don't see why some cleaver individual couldn't come up with something like this. It wouldn't be easy, but the coolness factor would be off the scales!

Mike

Blackbird

waste of money.

like nogo says put a tb in front of the blower

if your a wizard make one that is electronically controlled and use a programmable controller and then you could dial in whatever amount of boost you like at any given rpm

at low rpm the tb is open and as rpm rises the tb closes.

a real quick reacting version of an electric cutout and a controller and your in business.

hmmm the more I think about it, it's actually pretty doable.

LSs1Power

iTrader: (5)

Man i love the idea of an electric cutout. I might try it after i install the SC. I will just install it before the TB and control it. I will try it to see if i can get only 5psi out of my 8psi. If it did work without any problems then i can increase the boost and reduce it with the electric cutout. I think this could work and it would be very cheap too.

Blackbird

it has to go before the BLOWER.

your regulating boost by regulating the amount of air the blower can injest.

basically choking it off to see less boost.

Crunch

BTW, did you see that fake Mad Max car in PHR magazine this month?
Forget the clutch, the blower doesn't even work at all!

1dirtyZ

iTrader: (1)

actually, mercedes has a clutch on their roots or screw type blowers on the cl55. kicks in under WOT conditions if i remeber correctly.

NoGo

iTrader: (2)

Nope.

I'll do the math right here to show you how it works. The amount of power it takes to drive a blower is a function of flow and boost. I will do the calcs for a modified blower motor (VE near 100%)

Power Required = {(CFM * Boost) / 229} / AEff BeltEff

I will use 60% eff for the blower (industry standard) and 3% loss for the belts (industry standard).

We'll do the first calc for 8psi

HP Required = ((900 CFM * 8 psi) / 229) / (0.6 * 0.97)
HP Required = 54 HP

Horsepower required for 22 psi

HP Required = ((1500 CFM * 8 psi) / 229) / (0.6 * 0.97)
HP Required = 90 HP (nearly double the loss)

Now lets do how much HP you are going to gain at 8 psi with a 90 HP blower consumption.

Rather than churn through all the calculations for power we're just going to say that your fully modified *****-to-the-walls blower motor squeaks out 27 HP per psi (about as good as it gets for a blower) with a baseline (blower disconnected) of 360 RWHP

Your Normal Power at 8 psi = Car Power + Blower Power - HP Required
Your Normal Power at 8 psi = (27 HP/psi * 8 psi) + 360 HP - 54 HP
Your Normal Power at 8 psi = 522 HP

Your Power Regulating from 22 psi = Car Power + Blower Power - HP Required
Your Power Regulating from 22 psi = (27 HP/psi * 8 psi) + 360 HP - 112 HP
Your Power Regulating from 22 psi = 486 HP

This is just a direct power problem. This doesn't even include the reductions in timing that you are going to have to do becuase your blower discharge temperatures are going to be higher.

JMO.........with math.

I1ULUZ

iTrader: (1)

But won't the charge temps decrease as the "bleed" valve opens, decrease in pressure results in a decrease in temp? Also the blower might be spinning faster but the backpressure/boost is being regulated to X psi by the bleed valve right, so it won't heat the air as much as if it was pushing XX psi.

One issue I have with the setup is a failure of the "bleed" valve, it fails to open and now the engine is seeing XXpsi for a microsecond before it

NoGo

iTrader: (2)

The temperature of the air will decrease AFTER the bleed valve, but the bleed valve BLEEDS to atmosphere, so we are not interested in that air. The pressure and temperature within the supercharger system will still remain at the target pressure (in this case 8 psi) and thus elevated temperatures.

The reason that the supercharger discharge temperatures will be higher is not because the discharge pressure of the air is higher (which its not, because it is regulated) it's because of the thermal efficiency of the blower. The more work that you put into the blower the more heat that it is going to generate because 100% of the energy placed into the blower doesn't directly transfer to flow. Roughly 25% of this energy will directly be transfered to heat.

Example:

Unregulated 8 psi compressor discharge temperature

Discharge Temp = Boyles Law Temp Rise + (Work Into Compressor * Thermal Efficiency)

The contribution that boyles law makes to the equation is going to remain the same because the discharge pressure is the same. However, the 2nd contribution of thermal efficiency is going to increase because we are putting more work into the blower.
For the above scenario you can expect discharge temperatures to be ~20 deg higher (after the intercooler).

QuickSilver2002

I still the idea has value. I would never build a car around it, but it would be a cool toy to have on board.

The big advantage would be the ability to tune boost. Sure you would be wasting some power and adding a little unnecessary heat, but the ability to turn up boost with better gas or more alky spray... would be very useful.

If nothing else, it would be a fun toy. Let's face it, these cars are just big toys and we all have just a little ricer in us.

The cost is what would keep me from trying it. A decent boost controller can be found for about $250 (and you basically get a nice boost gauge with some type of playback). So that seems worth it, but the type of BOV needed (probably 2) go for over $300 each. Then you have to wonder if it would even work once you put it all together. I can’t imagine the resultant boost curve in the intake being all that smooth. It seems to be working for the guy in the link, but you surely can’t believe everything you read (especially on the internet).

grub-2001z28

That guy was a local and his car was absolutely sick. If I remember correctly, it dyno'd in the 670hp range on pump gas. The reason he had the setup like that was so he could get max boost much lower in the rpm range and hold it. It worked beautifully on his setup....until he got run off the road by a semi a few months back and totalled it

LSs1Power

iTrader: (5)

From where did u get the formulas?

Also I was saying 12lbs pulley and decreasing boost to 8lbs which sounds more reasonable for us with stock motors who wants to run race gas on the weekends and build up boost sooner in the RPM range.

In ur calculations u said
"HP Required = ((1500 CFM * 8 psi) / 229) / (0.6 * 0.97)
HP Required = 90 HP (nearly double the loss)"

Then u did this
"Your Power Regulating from 22 psi = Car Power + Blower Power - HP Required
Your Power Regulating from 22 psi = (27 HP/psi * 8 psi) + 360 HP - 112 HP
Your Power Regulating from 22 psi = 486 HP"

U used 112HP less instead of 90HP... Why?

Why did u use 900CFM for 8psi calculations?
"HP Required = ((900 CFM * 8 psi) / 229) / (0.6 * 0.97)
HP Required = 54 HP"

I thought the blower (D-1SC) will give u 1400CFM at 8psi or 12psi.

NoGo

iTrader: (2)

Common sense. It's just thermodynamics and fluid mechanics.

You'll still have the same results, just not as dramatic. I'm not saying the sky will fall if you set your car up this way, there is just a better way to do it, where you don't have to eat the power loss.......or at least not as much.

My bad. I originally did the calc taking into consideration intercooler losses. I then just decided to keep it simple so it was easier to follow. I forgot to change the 112 to 90. The result is correct though.

1400 CFM is the max rated flow of the D1 blower not the actual flow. To backcalculate from boost to supercharger flow follow below.

Boost = [(CFM Blower / CFM Engine) * 14.7 )] - 14.7

Using a little algebra......

CFM Blower = [(Boost + 14.7) / 14.7] * CFM Engine

To calculate Engine CFM:

Engine CFM = [(Displacement * RPM) / 2] * Volumetric Efficiency

I used a VE of 1 (not the norm, but just for simplicity) so engine flow is

Engine CFM = [(346 * 5800) / 2 ] * 1.........divide by 1728 for in^3 to ft^3
Engine CFM = 580 CFM

Blower CFM for 8 psi:

CFM Blower = [(Boost + 14.7) / 14.7] * CFM Engine
CFM Blower = [(8 + 14.7) / 14.7] * 580 CFM
CFM Blower = 895........I just rounded to 900

Blower CFM for 22 psi:

CFM Blower = [(22 +14.7) / 14.7] * 580
CFM Blower = 1448.......I just rounded to 1500


The above calculations don't take into consideration any intercooler losses or system losses. The typical system loss for an ATI system is 20%. So basically take your engine boost and divide it by .8 to determine what boost the blower is actually putting out.

frcefed98

iTrader: (16)

If you want to control your boost, use your right foot. With a centrifugal its that easy. The higher you spin the engine the higher your boost. If you are making 8psi at 6100rpm and want only five psi shift at 5800(or where ever you see 5psi)
Or get a turbo kit.

NoGo
Like he said it takes power to make power with a centrifugal blower. It is bascially a "parasite" on the engine. Yeah it makes good power but it soaks up some HP to spin it. The higher the PSI level the more power it takes to spin it(compressing air to 20psi is pretty hard to do)

Dirty has it right on the Merc S/C and its electric clutch. A rice company also make a roots blower with a elect clutch that engages when you want. The company is Blitz Power Innovation www.blitz-na.com They call it the blitz compressor.
J

QuickSilver2002

uhh, i don't think that is the idea. The point is to create a certain boost pressure at a lower RPM and hold it steady or control it via some input (like speed or RPM). There are a million factors that come into play here that could end up resulting in better overall performance and versatility.

I think you guys are being a little closed minded about this. Sure, it has some efficiency issues and some basic calculations can prove that, but I've seen calculations fail many times in the real world. The reason is related to missing dimensions to the calculation. It is very easy to look at one side and miss one of the 500 other factors that impact the overall system. Remember, the best performance does not always come from the highest peak power levels. Also, fluid dynamics are crazy and even the most experienced engineer focusing on the discipline will tell you that little things can throw you so far off that you end up being completely off in the practical example. I'm not saying that this type of setup could produce more power on the dyno...(pretty much anyone can figure that out) but I do think it is possible to end up with a better performing car that is more versatile with a better power curve (not for everyone, but this could be just the ticket for some people).

The only reason I think this has some potential is the fact that somebody has done it and has had good results. It may be a total waste of time and money, but I might give it a try just for fun. Again, this is all for fun (we are not saving lives or bettering the world here).