kwiksilverz

If you pulley the blower for more RPM and max boost, a side effect will be faster "spool" also due to the blower spinning faster sooner. This will provide more "under the curve" torque (similar to, but not as violent as a turbo). The problem is, people want the faster spool, but cannot have it if the higher peak boost comes with it. That is why people are using restrictors on the inlets- it limits the MAX airflow the blower can provide, allowing you to run the smaller pulley for faster spool, yet the same max air flow and boost you had with the larger pulley. I hope I explained it well- much better at thinking than explaining .
Joe

kwiksilverz

Yeah- what he said .
Joe

Pro Stock John

iTrader: (34)

...And so why not short shift?

LSs1Power

iTrader: (5)

You will limit your wide powerband if you short shift. Lets say your HP peak happens at 6000 RPM and you see 12psi.... Now if you shift now you will be back around 4800 RPM or so, but if you limit the boost at 12psi and shift at 6400RPM you will be back at a better area (5200RPM) in the powerband hence picking up more power with every shift. This explaination is with manual 6spd in mind.

Pro Stock John

iTrader: (34)

I see.

Fire67

iTrader: (3)

When explained this way I understand. Interesting idea for sure.
One think I would like to add, under no educated circumstances, just my own heads theory.
Would bleeding the extra boost with the wastegate produce less heat and less stress on the blower than trying to squeeze the air through a smaller hole?
Subscibing out of interest

engineermike

Whether you use a restrictor or a blow-off valve, this method of "flattening" the power range WILL:
- require more hp to drive the blower.
- heat up the air more than normal.
This much is fact.

Whether it is better to use a restrictor or blow-off valve depends on where the compressor ends up on its map. The restrictor would move it up vertically, while the BOV would move it out to the right. You would have to use the compressor efficiency to calculate (gasp! dare I attempt to calculate anything!) the hp to drive it and the discharge air temp to really determine which is better.

Mike

CHRISPY

I have thought about this and posted about it a couple times. I was actually thinking about doing this to be able to run a F1A on a stock motor. (Put a wastegate and MBC in and 9# spring) With the lowest boost pulleys I could fit I'd probably still make 9#'s at 4000rpm with a F1A and barely spin the blower.

If you wanted lower boost you could run a 5# spring and use a MBC (Hallman or similar) and control the boost easily from the cockpit or under the hood without swapping pulleys.

I think it'll work like a champ personally.

Cheers
Chris

engineermike

Except that it would take 100 hp to drive the F1A with it venting air to the atmosphere while you're only getting 50 hp worth of boost in the motor.

LSs1Power

iTrader: (5)

D-1SC, F1 and F1-A get close to losing 90-100HP at the 800HP mark. So IMO unless he pulle for 13-14psi he won't be losing that much. I came down to this conclusion based on the fuel needed to run an N/A, Turbo and S/C at the same level.

Since we are talking about calculations and formulas... Do you have a formula for calculating power loss from a supercharger.

andereck

You can't lose what you never had.

engineermike

The point still stands that, if you vent air off that you compressed, you are putting more hp into the supercharger than you are taking advantage of in the form of boost.

Hp to drive a supercharger = flow in lb/min x (discharge enthalpy B/lbm - suction enthalpy B/lbm) / 42.4

discharge enthalpy = enthalpy at T2. T2 = (T1 x (p2/p1)^(.286) - T1)/efficiency + T1

suction enthalpy = enthalpy at T1. T1 = ambient temp

Unfortunatly, you need a Thermo book to converter the temperatures into enthalpy. I'm sure this chart is somewhere on the internet, but I couldn't find it during a quick search.

Also, keep in mind that all units are in absolutes (deg R and psia).

Mike

LSs1Power

iTrader: (5)

What is p2 and p1? How can you calculate efficiency?

andereck

Inlet pressure absolute / Outlet pressure absolute

engineermike

Andereck is right. p1 is atmospheric pressure (~14.7 psia, less if your filter is restrictive) and p2 is outlet pressure (boost + 14.7). Efficiency comes off the compressor map, or can be calculated if you measure p1, p2, T1, and T2. Automotive centrifugal compressors peak at around .78 (78%), but typically run in the .65 - .75 range.

Mike

LSs1Power

iTrader: (5)

I found these links that talks about enthaply, but it seems everywhere i looks it talks about energy more than temps. http://www.grc.nasa.gov/WWW/K-12/airplane/enthalpy.html
http://www.webchem.net/notes/how_far...f_enthalpy.htm


Very nice conversion calculator
http://gordonengland.co.uk/conversion/

LSs1Power

iTrader: (5)

Ok i did put everything in Excel. The results don't seem right

100 F= 560R
Lb/min= CFM/CFB
CFB= 13.0 in dry air

With only 8psi and assuming 800 CFM I got 155HP to drive a blower which can't be right. Even when i used 90% efficiency i still got 133 HP to drive the blower.

At 15psi and 1400CFM with 200 F = 660 R i got 515HP to drive a D-1SC blower at maxinum speed. LOL

That means people who are making 750rwhp with a D-1SC generate over 1200HP of energy?!! That means they will need 100-110lbs injectors running at 70psi of fuel pressure at the least which is not the case in real life.

I would be glad to send the Excel file to anyone who can recheck everything so It can be used by other people as a refrence.

engineermike

I took a quick look at the spreadsheet and picked out a couple of errors. First, T1 should be ambient temp, or around 540 R. T2 seems too high also, as 863 R converts to 400 deg F. The flow of 107 lb/min equates to about 1160 hp. Is this right? Also, I didn't see any enthalpy numbers. I wish I could take a closer look or make my own spreadsheet, but I'm going out of town today and not coming back until Friday.

kp

iTrader: (34)

be a lot easier to put a restrictor on and see what happens

I was always under the impression that if you restrict the intake the IATs wont be as high since compressing the air makes the heat. If there is less air to compress there should be less heat. Except for the extra friction heat of turning the blower faster anyhow.

I would think using some type of valve on the inlet (like a giant cutout) would be a better way of acheiving some sort of traction control but a little more complex then just blowing it off.

Funny thing is the ATI inlet hat is a restrictor of sorts, with the hat/filter on at the track at 55 degrees ambient my boost is 16psi @ 6000rpm and 17psi @ 7000rpm. With the hat/filter off its 16psi @ 6000rpm and 18psi @ 7000rpm but the IATs are hotter and the car picks up nothing at the track. I have tried it several times, summer and winter, with the same results so I dunno. Generally I would be the first to agree with that any kind of restriction/blowoff would be silly unless you were just cutting boost for pump gas or traction control but in my case the results go against what 'should' be happening. It will be interesting to see what happens with inlet hat on and off with the F1A.

engineermike

kp, I always value your test data because a) your car is very consistent and b) you understand the concept of keeping everything else the same.

Increasing inlet pressure on a compressor will almost always result in a net increase in flow and discharge pressure. I've seen positive results in the past by reducing compressor inlet restriction. However, if the compressor is near "choke flow" or "stonewall", then increasing suction pressure in an attempt to produce more flow will result in a reduction in efficiency, increase in discharge temp, and increase in hp required to drive the compressor. To me, yours has tell-tale signs that you are at the flow limit of the D1. Do you have any idea what the mm size of the compressor eye is?

Mike