Kingtal0n

Its long, you might want to grab a bite to eat. and a drink. Dont want people keeling over on me from lack of food and all that good stuff. And don't flame me for this post its just for fun.
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Disclaimer: Everything here is an opinion. It could be wrong, and with that, good day.
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Its true, forced induction works. anyone with the brain sensitivity of a caterpillar knows that it really does work.
Most people say "hey im going to get a supercharger"
when asked why they say "because it will add boost and that will make my car go faster"
....
Lets delve into that for a moment.
We all know boost is the by-product of compressed air in the induction tract. what? you didnt? ok now you do.
Realistically, boost has little to do with the amount of "horsepower" we are adding. boost is just a measurement of the left-over air that the supercharger would LIKE to shove it, but cannot due to restriction/volume limitations. What the heck did I just say?
lets examplify this:
Stock 305 RS camaro:160 RWHP
Lets add a Holley 144 blower to it:
We see 7 PSI of boost, and now the RWHP is a whopping 220RWHP.
Lets swap out some stock crap ready?
Lets throw some nice AFR 190's on there.
New boost level: 6 PSI
New power level: 235 RWHP
So our boost DROPPED and our RWHP went UP. hmm..
but only a little? why?
<b>the most important component to a forced induction setup is the camshaft </b> the right cam can make or break a forced induction setup.
So lets swap out the crappy peanut l03 cam in our 305 toa nice comp blower cam.
New results: We see 4 PSI of boost and 280 RWHP.
As you can see the rigth cam opened up the brathing ability of the engine, it may be a 305 but its still a small block V8. Now we only have 4 PSI of boost however, so lets swap out the pulley on the blower for a little more umph.
Now we are seeing 8 PSI of boost and about 300 RWHP. A little scary on a stock bottom end, but not impossible with proper tuning.
<b>the biggest enemy of a forced induction motor is HEAT</b>
Heat is about the most undesirable byproduct of forced induction. Not only does it lower the density of air, it brings the engine closer to detonation and destruction.
Heat, however, is a necessary part of the combustion process. we cannot say "hey, heat, go somwhere else"
This means our coosling system needs to be exceptional, as well as our control of the ignition timing. Our little 305 with the blower would have blown up if we didnt add the boost-retard box to it. You, uh.. did add the box... didnt you?
So what did we learn just now with the 305? We learned more boost doesnt mean more power, and we learned a better breathing engine will produce more peak horsepower, and we also learned 305's arn't all that shabby. They just suck in stock trim because I think it was GM's idea of a joke; "hey bob, watch this. Ill take a perfectly good 350, and de-bore it to 305. Then ill put in a camshaft suitable for a lawn mower, heads with intake ports as big as my brain, and an intake capable of feeding a go-kart. oh yeah, ill also cut some huge dishs into the pistons just for fun. "
....
Lets look at boost a little closer. another factor that influences our engine is volumetric efficiency. Volumetric efficiency, or VE, is a percentage(%) that tells us exactly how FULL our cylinder is at the time of the intake valve closing. A VE% of 100% means that each cylinder in our engine is completelly filling itself up, to the very top, with a fuel/air mixture. that means a 350 engine would be actually compressing and using 175 Cubic inches of fuel/air every 1 revolution. a VE of 100% is very hard to obtain in a non-forced induction engine. most stock engines have average VE% of about 80-85%. Most high performance engines setup for street-strip see about 90-95% PEAK VE%. this means they only see that VE% at a certain RPM, the closer and further away from that RPM those engines get, the lower the VE%. this is one of the factors that influences PEAK horsepower, and PEAK torque in a powerband. more DURATION on a camshaft generally means a LATER peak of VE% in the rpm range, which means an engine is reaching PEAK VE at a high RPM, which translates to more horsepower, Later. the higher in the RPM range we see our PEAK VE%, the more power the engine makes up top, generally.
Heres where forced induction has its fun fun fun:
Under "boost" the pressure in the induction tract (intake/heads/etc) becomes pressureized to FORCE air into the cylinder. but we all knew that. What Im pointing out is that since we now have PRESSURE holding the air IN, as well as PRESSURE in the cylinder itself, our VE% generally jumps up above 100% immidiatelly. Generally that is. Keep in mind a PISTON On its way up the BORE will still push Fuel/Air OUT even WITH pressure holding it in. This means that the LATER our intake valve closes (IVO, <b>IVC(intake valve close)</b>, EVO,EVC) the less air we trap in the cylinder at lower rpms.
But at higher rpms? The game chages.
Fast moving air becomes a lot like water. it begins to have substance, and obstacles that normally would not affect it, now become restrictions. Ever hold a straw in a cup of water and take your finger off, then slam your finger back on and trap a higher level of water in the straw than is in the cup? This is because the water thats rishing in carries momentum and shoots past highest level of water around it, as the momentum slows it will fall back down and even out. But your slammed your finger back over the straw, thus air cannot come in to replace the water, and the water is trapped in a low pressure area.
We see the SAME EXACT THING happening in our engine at higher RPMS. this is why more duration on a camshaft makes more horsepower at higher rpms, generally. a later Intake valve closing point (IVC) means the cylinder is moving UP while the intake valve hangs open longer. At high RPMS the air is like water in a straw, it rushes in to fill the cylinder, regardless of piston position. Even though the piston is still moving up, air continues rushing in due to momentum. As the momentum goes away, yes the piston will begin to push the air back out. this is where we need to slam our intake valve closed (slam our finger over the straw) to trap the absolute most fuel/air in the cylinder. of course, this is only going to happen when everything lines up perfectly, and only for a point in the rpm range. this generally becomes our PEAK point. With a supercharger, the effect is multiplyed. the reason is because instead of normal air, we have compressed air. and trapping MORE compressed air, faster, means a much bigger explosion and thus more power.
what happens if you just change the camshaft and leave the rest of the induction system stock? Well a camshaft only control valves. it does NOT control the engines ability to flow air in the from the outside world. Lets use the straw example again, that was fun. Well use analogies this time. Our STRAW SIZE is our HEAD/Intake port size. Our camshaft Duration is the amount of time our finger stays open. our valve is our finger. our camshaft LIFT is how far we remove our finger from the straw. our cup of water is our air/fuel from the outside world. we want it to go through our straw and into our engine. got all that?
our stock engine's straw size (head/intake port size) is similar to one of those coffe straws, you know the red ones that are so small you can barelly suck coffe through them? more suitable for stiring than anything else. if we take that straw and hold our finger open for more duration the effect will be extremelly BAD because not only is the straw so SMALL it cannot build sufficient momentum to force air into our cylinder, the excess DURATION will simply push all of the water(air/fuel) we just took in, right back out. Remember that in a cup of water there is no cylinder pushing the water back down, but in an ENGINE the cylinder WILL push air right back out the intake valve and into the intake manifold. this is called "REVERSION" and its the main reason a high-duration camshaft will sound "lopey". the more air thats pushed out of the cylinder, the "lopier" the idle, generally.
Theres a moral here:
You cant just change out a part and expect it to reach its maximum potential. Remember our AFR 190's on that 305? They only added what, 15 horsepower? Bull. and that cam swap, 45 horsepower? Bull. Whats the story there? The nice heads helped a little, but when matched to right right cam they reached a LOT more potential, thus the cam swap probably only added about 25 horses, the heads added that 15 + the other 30 making 45 total just from heads. Sowheres the moral? ok you asked for it:
<b>"everything must match. changing one thing may actually REDUCE performance until everything matches up. "</b>
so lets open up that straw for some real breathing ability. what now? oh yeah, more power.
....

MOre later. time for food and stuff.

Just right click it and hit "show picture" and you can see it. i think.

Justin 87 GTA

iTrader: (3)

Very well written and inspiring. Makes perfect sense. Now how do I apply it. I'd appreciate you looking at my link below. Tell me what you think. check out my post on this board. It'll give you an idea where I'm at w/ my motor. Thanks -Justin
BTW, keep up the good work.
(it;s a shame you have to type all those disclaimers)

83 Crossfire TA

iTrader: (2)

So, what’s that from?

Well, I would argue that while not entirely technically correct (ex: most of the blowers we're talking about (centrifugal superchargers, turbos...) don't create any pressure on their own (unlike what you wrote), but actually accelerate the air for more air flow and the pressure is whatever pressure rise you need to force that volume of air through the existing engine. That part would be technically correct for some positive displacement blowers, and I realize that is the example that you used, but it is not the perspective most would read this from) if most people that got involved in this mess knew at least that much they could make much better decisions and we could all avoid the classic stupid questions (my favorite, how much HP will 10psi boost make?).

One point that I would definitely add is that HP production is entirely dependant on the mass of the air pumped minus any inefficiencies in the system. So basically, the same blower, spun at the same RPM on different engines will make very similar HP no matter what the engine (assuming that it is designed so that it could be tuned correctly with that volume of air). The only difference displacement and other changes make is where that HP peak is produced and therefore how much torque the engine make (same HP at a lower rpm= more torque).

Your example with the head swap probably wouldn’t be as dramatic in real life unless the stock heads were so restrictive that the volume of air pumped resulted in a boost pressure that was in excess of what could be properly tuned for on that engine (EX, you needed to excessively retard the timing or run it very rich to stop detonation). If you ran high enough octane fuel so that you could run the same tune with both heads you would have almost exactly the same hp (slightly more loss on the smaller heads due to adiabatic efficiency, more boost = more heat).

The changes relative to changing cams are too generalized to be accurate. In general changing to a larger cam moves the torque production up (more HP) and what more overlap does will depend on the blower and even the individual setup. On most superchargers, more overlap will vent some of the boost out through the exhaust accomplishing nothing but wasting available air/fuel (unless you build everything else to work correctly at an RPM enough higher that there isn’t time for this to happen). The same cam in a ‘normal’ turbo engine will result in a loss since the backpressure in the exhaust will actually force the exhaust into the intake during the overlap unless it’s built for much higher rpm’s then you’d imagine. For that matter, there is little reason to build most turbo engines for rpm… Anyway, a book would have to be written to properly address this.

Justin 87 GTA

iTrader: (3)

well, it's good food for thought and a good topic, and we'll all learn something.
Btw, i don't believe he was trying to be aaccurate w/ his numbers, he was just trying to illustrate a point. . but you're right, you'd need to write a book to properly adress this. That's probably why he put in that disclaimer.

83 Crossfire TA

iTrader: (2)

Oh, I don't want anyone to get the impression that I was picking on what he was trying to do. From a practical stand point it is close enough to make the correct decisions, it's just not 100% techincally correct (what is if you examine it closely enough?).

MdFormula350

alot to read

alot of good info and points made...

Kingtal0n

Yeah, well, Just trying to help
Crossfire, heres somthing I noted on my L03 305 engine:
<b>Your example with the head swap probably wouldn’t be as dramatic in real life unless the stock heads were so restrictive that the volume of air pumped resulted in a boost pressure that was in excess of what could be properly tuned for on that engine</b>

Your on the right track actually when I made that comparison I was referring to "fake boost levels" Where the stock cam duration was so short that it didnt allow for a VE% of over 100% except near idle... which would generate "false high boost" levels on that particular engine. so much air left over... trying to get in... cant because of the peanut cam. This WAS address in the book labelled "Street Supercharging" I beleive. This is what I was pointing out with the "dramatic" head/cam swap on the stock 305.

and...
<b> most of the blowers we're talking about don't create any pressure on their own</b>
I guess I've got my mind set on positive displacment blowers.

Hey, heres a good time to address the old Blower VS Centrifugal supercharging comparison. When you look at it from an induction point of view, A roots type blower is more like a vacuum pump, and a Centrifugal supercharger is more like a Leaf blower. Both mechanics are designed to move air, but each operates on a different theory. The Blower theory is basically a "grab-n-hold" idea, where the blower simply "grabs" any fuel/air that happened to find its way under the carbeurator and forces it all down into the intake manifold... Then holds it there so it cant get out. Obviouselly, a blower has to be able to "grab" more Fuel/Air than an engine would NORMALLY accept to produce "boost pressure" in the intake. This means that the Physical SIZE of the blower is directly related to the amount of AIR it can shove. Notice I didnt say the amount of BOOST, just the amount of air. Boost is just pressure right? In a blower's case its pressure waiting in the intake manifold... directly above the heads. In one "gulp" a blower can instantly provide "boost pressure" making a blower "Instantly Effective"... From an Idle you can stab the gas pedal and see "Instant Full Boost". This is simply because as soon as you stab the gas, the carbeurator allows its maximum CFM rating to the blower, so the blower can grab as much air as it can handle and shove it into the INTAKE. Not the engine....
The ENGINE components then decide exactly how much of that stored AIR/Fuel to take in. As soon as a valve opens, the pressure in the intake instantly forces it's way into the cylinder, and if the valve stays open long enough, it can completelly fill the cylinder up... VERY FAST. It does not take long. In fact, most Long-duration camshafts will actually HURT a blower's performance because even with PRESSURE, The piston will still force some of that dense air OUT of the cylinder provided the valve stays open long enough. This primarilly only happens at low RPMS.
Whats that mean for you? Well if you drive the car on the street, A blower is recommended with a shorter-than-normal duration camshaft for high RPM operation. Examplify:
355 chevy, 3.73 Gear, 2400 Stall on a 700R4. Performer RPM heads. forged internals yadaa yadaa...
Small 144 Blower. 8-9 PSI pulley.
First camshaft: Lunati Blower Cam: 303/313 duration, 234/244 @.050. .550 Lift- 112 LCA
We make about 500 Flywheel horsepower, but only see about 5 PSI of actuall Boost pressure. From 1000-2500 Rpms, our Maximum torque is around <b>280 Ft-Lbs.</b>
Then by 3500 RPms, it peaks around 450 Ft.Lbs.
Car runs a mid-12 with a 2.0 60' and some tire spin.
Now examination:
Why did we only see 5 PSI of boost when the pulley should have made about 8 PSI? Why wasnt our torque any higher? it should have been around 450 Ft-Lbs from 2000-4500 Rpms, not 280~.
Lets do a cam swap and see what happens:
New cam: Comp Cam blower cam. 272/282 duration, 219/224 @ .050. .512 Lift, 114 LCA.
We see the full 8 PSI of boost, We see the full 450~ Ft. Lbs of torque from 2400-4200 Rpms, and we make about 480 Flywhel horsepower @ 5400 RPMS.
We run a mid 12, with a 2.0 60', and the car drives nicer, gets better fuel economy, idles quieter, and spins the tires much easier. our MPH also went down a little, but our ET went down a little too.

We lost 20 horsepower though! what gives? more boost? how! tell me tell me!
Its simple. Larger cam = more lost boost pressure, more reversion, less low end torque. That 112 LCA was also killing our little blower as well.
yep, thats right, theres a moral here as well. Yes, everything has to match, but even more so, this:
<b>"you dont need a huge cam for forced induction to work well, and this goes triple on the street"</b> i think thats pretty summed up.
Now this was mainly directed at bowers, lets take a look at centrifugal style superchargers.
In our blower application the blower was forcing the air to "wait" in the intake manifold to be accepted when a valve opened. The questions "how well do my heads flow" and "how well is my intake matched to my powerband" almost become M00t since the blower sort of bypasses the whole "flow" idea and puts the air RIGHT AT THE VALVE so even crappy heads make little difference in "flow" at the time of boost.
Since a centifugal supercharger (C.S. from now on, Im too lazy to write that again) Since a C.S. accelerates the air by using centrifugal force to "sling" it out towards the throttlebody/intake/heads/valve etc... the words "FLOW" and "RESTRICTION" play a MUCH BIGGER ROLE now. Now the air has to actually manuveur around obstacles in the pathway, obstructions in the intake, and through intake ports and bends around valves then finnaly into the cylinders, we need to consider this heavilly when deciding on what heads/intake/throttlebody/intercooler/pipeing/routing etc... to use... and when correctly assembled, a C.S. (or turbo for those of you wondering) will almost always out-perform a blower <b>Efficiency wise. </b> notice i didnt say "horsepower" wise, since "horsepower" is not related to blower size or C.S. size, as much as you want to beleive that. (ok example a 355 chevy setup for race will make more horsepower than a 355 chevy setup for street with the same exact "boost" levels and same exact blower setups. Notice i said boost levels, not VE levels. the more "racy" the engine, the more fuel/air you need to feed it to see the same "boost" level on the same exact engine that ISNT as "racy")
so in short a C.S. is more sensitive to "how" you install it, rather than how much "boost" it puts out.
Take this into consideration. Two exact engines with exact C.S. with the same exact everything should produce the same exact "boost levels" right? But lets throw in a variable. Lets say engine #1 has 3" diameter tubes feeding the intake, and Engine #2 has 2.5" diamter tubes feeding the intake. Engine #2 will produce more boost, more heat, and probably less horsepower, but will also be able to "spool up" faster, see "boost" faster, and thus make more torque faster. Engine #2 is more suitable for street, while engine #3 will not perform as well on the street. (when considering a stop-light-race point of view) Where Engine #1 would probably be more efficient at higher RPMS make more peak HORSEPOWER and run a better MPH in the 1/4 Mile.
All of this, just from a pipe size change? Remember the differences between the two engines would not be HUGE, in fact you would probably hardly notice them if that was the only change, But when SETUP and COMBINED with parts CORRECTLY (remember moral #1?) The differences WOULD BE HUGE!!!
Engine #2 with some Smaller CC heads (190 instead of 210) and a smaller cam (270 instead of 300 duration) and a smaler intake (Stock TPI runners instead of a SuperRam) and a more streetable exhaust (1 5/8 headers, and a single 3" catback flowmaster) etc... Would be MUCH MORE RESPONSIVE and FUN FUN FUN to drive on the street than Engine #1 with all of the "instead of..." listed above.
remember, same exact C.S.

Well time for food and stuff, more later.
oh yeah disclaimer #1 also applies here as well
And heres the picture I tried to post earlier...

Kingtal0n

<b>(it;s a shame you have to type all those disclaimers)</b>

I would like to point out some people on this board think its fun to ruin my whole day by saying stuff like
"thats wrong, I disagree, Your giving false information, you should do more reasearch before saying stuff like that, " etc...

I point out before anyone reads my posts that Im only trying to help poeple understand a little better, and that Im not perfect Im only 19 years old and I DONT know everything. Alot of my talk is theory and common sense I either read or deduced from experiments I've conducted on my own spare time. I havn't the money or the equipment to properly test every minute detail, but after quite a bit of reading and playing around Some things are just common sense. I've never owned a Centrifugal supercharger, But I've installed a few for free just to learn how.
That whole 3" VS 2.5" pipe was an actuall test of mine, although I never had it dynoed the smaller pipe made a huge difference in throttle response and earlier boost levels. Bigger isnt always better.
most of my testing has been done on the street as well, so most of my recommendations tend to be more "Street friendly" Because I know even though you want to build a race car, your GOING to want to drive it around town and show it off. Might as well make it fun to drive no matter where you are, thats my opinion. Unless your racing for $$$ thats another story. screw the street, go for the biggest HP peak # and set your drivetrain up to sit there for the whole 1/4 mile. thats my theory.

Kingtal0n

Wee and now a word from our... er... from me.

today i found an interesting fact about blowers.
I saw a boat today with 2 big blocks on it :hail:
then i noticed they both had 8-71 blowers on them :hail:

I found out that, during cruise, and unlike cars, boat motors are always under some strain (load) and thus blowers (like those 8-71's) would be under constant boost due to throttle position to maintain cruising speeds....

I asked a few questions... got a closer look..
see normally an blower under constant boost like that would overheat quickly... without EXTREME cooling measures...

and guess what? both 8-71s had an intercooler beneath them, above the intake manifold, called "The Chiller" And it directly pumped SEA WATER into and back out into the ocean to intercool the boost as it enters the engine.

combined, i was told, both big blocks (wouldnt tell me how big) made roughly 2200 horsepower. thats 1100 each :hail:

mxcrazed

bump! bump! bump!


everyone should read this it is good information!

flaming-ford

iTrader: (7)

very very nice, generalized and mostly common sense but, it sums it up and gives great examples, i'm 19 also and this is was a great reading for me.

I know plenty about engines and flow in theory but, differences between superchargers and how boosted engines aren't affected by the same restrictions as a naturally aspirated was quite helpful to me!

shinobi-x

You did a very good job of summerizing supercharger basics. Believe it or not you've stated better information and its more accurate than what Weiand says in there blower intall manuals. I've had a 142/144 and a 177 now and the instructions are the same for all. The best thing I've found from the manual is the chart in the back showing you the highest boost you can run theoretically with "your" compression on pump gas. Its a good chart to go off of but you article write up was good.

The camshaft statements hold true to about 90% of cars. the other 10% of those aren't door slammers or street cars. The methods of feeding blower motors changes heavily from style of racing. But,again,your write up is accurate for what all of us do on this forum and most all other street cars on the road and track.

My cam in my 355 is a summit grind 224/234 @.050 .465in/.488ex lift with my 1.5's. I make a solid 10psi at 6k rpms with my 177. I wish I knew what it does in the 1/4 ever since I ditched the 144.

Damon

That was a fun read and a decent write-up. I could nit-pick a few things, but I'm not going to.

I'll just remind everyone reading that a roots blower like the 142/144 you used in your example is a positive displacement pump. It moves a given amount of air with every revolution. As such, what it cares about most is pulley ratio. How much restriction everything is below it (right out to the tip of the tailpipe) determines the boost you see on the gague, but the power level for any given pulley ratio will be similar, even with engines of different displacements!

NOT comparable to a centrifugal compressor like a centrifugal blower or turbo.

Kingtal0n

Holy @#*&# guys I Wrote that #@(*&# when I was 15 years old, that was 2002. Im not sure what it says but Im sure I could change a few things myself! I havnt seen that picture in 6 years! LOL!

ANyone seen crossfire?

83 Crossfire TA

iTrader: (2)

Who me? I crawled out of the woodwork again a few days ago...

I don't know about the rest of you but _I DID_ know everything when I was 15. I don't know what happened since then, either I'm forgetting more and more stuff daily or there's a lot more to "everything" then there was when I was 15... Funny how that works.

Kingtal0n

Whats up man, hows life. good to see your still kicking and paying bills haha. B4Ctom's still alive too, but you all probably know that already.

Batass

I must say thats a pretty bright writeup for a 19 yr old. I wish I knew half that much then and I was an engineering student!

I wish I could find more info like that. I have a lot of cam duration questions about my C.S.!

vwdave

Holy crap, jordan's alive! I lost your number....

Justin 87 GTA

iTrader: (3)

wow. i can't believe how long ago this was. i am 29 now...have a broke *** car in my nice house. built a new motor, just can't get it to run. actually, i drove it around a little a year or 2 ago, had it running crappy, but running. car's in good shape though...same shape it was in 2002 when i broke it. wish i could find a place on long island that knew what they were doing with these cars, cause i sure forgot a lot and i don't care to know it, just want it to run..

8T9 BANDIT

i have the perfect place for you.. oh and click the link in the bottom of my sig.

Justin 87 GTA

iTrader: (3)

your sig is missing.. thnx