very interesting stuff here,i agree a 2 stage blower system would kick some seriuos butt,engineer it Mr engineer!!!

 

Honda NR arent those the oval piston motors???

 

Ahem ... I lieu of your English teacher ...

MAKING
SENSE
BARELY
BEFORE

HEH HEH HEH .....

 

No!

 

Good post!

Glad to read some interesting technical thoughts, as opposed to the dirty laundry in other threads that has been stinking up the place lately

 

original SVT_KY quote:

Ahem! Shouldn't that be-

In lieu...?

POT- KETTLE- BLACK?

heheheheh!

Sorry couldn't resist!

 

Very informative post! I agree with about 99.9% of what you wrote. Torque is produced by cylinder pressure. The more cylinder pressure, the more power up to the point of detonation. Only flaw that I see is that in order to fill the cylinders you have to get the burnt stuff out. I agree that most modern exhaust does a pretty fair job, but if it doesn't clear the cylinder out as fast as the incoming charge you have a large restriction. The blower will build boost but it is hitting a wall. You can't put anymore in if you can't get it out. Have you ever plugged a toilet? On a supercharged 5.0 Mustang the exhaust port flow is very important. If the flow numbers suck on the exhaust side of the head, power is down too. I realize that cam timing, lobe centers, and ignition timing have a lot to do with power as well. I guess what I am saying is that the exhaust must remove what the intake puts in. Maybe a Lightning has a good enough exhaust, that this is not a problem. That would explain the small gains picked up in changing the exhaust system. An engine is just a large self powered pump. It makes power by gulping air and fuel. Just like a person, it can't breathe if it can't exhale. Take the biggest, baddest Lightning on this board, stick a potato in the exhaust pipes and it won't win many races,if it runs at all. Just my feeble thoughts on the subject, thanks for taking the time to read them. Skip

 

Skip,

I think you are missing the point with stock exhaust systems. In your example you stated that if the stock sysem can't exhale, well in our case it can. Granted most of us can't even get more than 10% - 15% more hp than stock, but this is probablly within the stock exhaust design.

Yes the stock exhaust systems are probably good for 120% of what a stock engine can handle, but with after market systems, at least on motorcycles, the ideal is to create enought exhaust pressure or negitive pressure to suck the piston upwards when the exhaust valve is opened. This causes in effect the other piston pulling it's intake chagre down faster than a NA engine can, effectively creating a mini SC effect, this can't be done with a limited input from our SC. Usually this only produces a maxium of about a 5% gain in hp if the current system is very poor in an NA application. Also in this case (NA) "the total system" is more effective, but in our case we have a intake valve in front of the intake valve called a equal displacement supercharger. This limits the effectiveness of a header system on a ~stock set-up.

So the total sysem limitation is not the exhaust but the supercharger design. Stick a different supercharger on and all bets are off because you've changed the sysem design. Sure at the new SC bolt-on any and everything could lead to a significant increase in hp. It would be very interesting to see a stock dyno run with long tube headers then a normal full meal deal set-up.

At least this is the way I understood the above post. Someone anyone correct me if I'm wrong.

 

I have a little of an engineering background ( I can design a clutch, which actually written down is about a 2 page eqation) but my formal training is as an accountant (would you believe?)
So I have to agree, from my point of view what he says makes a whole lot of sense.

G

 

i feel so smart now

 

'99 White Lite,

Cool post! Thanks for sharing, that's what it takes to make this community work.





Actually, no. If you were to convert a Cobra to 2V heads, you'd see a power loss.

You're mostly right. But you're talking about airflow through the supercharger, while the real issue is horsepower. That's generated by the OTHER air pump under your hood: the engine. Mass flow through the engine is what it boils down to, and you can't ignore the fact that heads with crappy intake ports are a big restriction to airflow through the important air pump: the engine. If the supercharger's airflow were the only thing that mattered, and if your 2V 5.4L vs. 4V 4.6L were a valid comparison, I could put an M112 on a Briggs & Stratton lawnmower and make 380-390 hp.



No, these mods show good power increases ONLY when the stock components are restrictive. A Lightning's factory air filter is restrictive, so replacing it helps a bunch. A Lightning's factory throttle body is not, so replacing it doesn't net much.



No, it's because factory exhausts are, in most cases, not that bad any more. A $450 throttle body nets a few horsepower to the wheels. An $850 set of longtube headers - a "downstream" mod - nets over twice that amount.

It all comes down to gazinta/gazouta. You have to pump air THROUGH the engine, and that means in as well as out. It's not just all about the supercharger.

Re: The '03 Cobra:


Let's make a second bet!



The M166 isn't coming out. There are other upgrade superchargers that ARE coming out, though. But I won't go into it because it would turn into a flamewar.


Right, although you DID say that and now you're sayin the opposite! see:

A $200 filter makes so much power because the stock filter's so restrictive. An $800 pulley and chip combo make so much power because the pulley greatly increases the amount of air going into the engine, and the chip greatly revises the very mild stock calibration. A $1000 exhaust which includes shorty headers is barely better than stock because the stock exhaust is so good. NOT because exhaust mods don't work. If you disagree, try telling the boards that everyone's longtube headers don't work!

This is another totally invalid comparison. First off, the supercharger is an M112!! Why don't the cars make 380-390 hp as you claim they will?? Quote, regarding why a 5.4L and 4.6L with M112's both make about the same power: "The reason is no matter what you do downstream of the blower, the airflow is the same."
Second, the SVO heads have been proven to work great IF you do a chip to revise the calibration. Why? Because the '96-'98 heads have totally different chambers than the SVO heads, and require a hell of a lot different spark curves.

To say that people see no power gains from SVO heads because the blower is responsible for total airflow, is like saying "I once saw a red Yugo with a supercharger, therefore all red cars are slow."!

Dual stage compression is a LESS efficient package, but it is done for a totally different reason. Turning two air pumps (superchargers in this case), even at somewhat reduced speeds, is still two air pumps. Friction is a b!tch. You can get "better" airflow (lower discharge temps), but at the boost levels applicable to a Lightning, the total amount of horsepower required to drive two superchargers is more than a single one. Check the Eaton site and get some information from any centrifugal supercharger maker, add the two horsepower requirement numbers together, and you can see for yourself.

Don't take this as a flame. It takes *****, as well as generosity, to want to post on here to teach other people. It takes even more guts to not get bent out of shape when someone says you're wrong.

 

I did say that I was barely passing. English never was, is not, and more than likely never will be my strong subject. But throw math or science in front of me and it's gets interesting. But really, was it nessecary to call out my lack of spelling?


But with moveing on to the thread...
That is exactly why, this community was created. So people with one topic in common can come to gether and share their knowledge.

 

Is it possible for someone to post some factual info ,without those who can't copprehend it, making a circus of the info?
I for one really appreciate it when someone takes the time to ,relay GOOD FACTUAL info on the board ,instead of the[ kiddy corner jive ] that is posted half the time.
Thank you '99 White Lite for some Interesting L info...

 

Already deep into the making

--Joe

 

The OTHER airpump can only move as much air as it is fed by the blower. With a positive displacement blower, it is easy to calculate how much air is being fed to the engine. The B&S could theroetically (a lot of assumptions here) make the same power. In real life, it could never strucurally take the punishment, especially considering its small displacement.

I've only been on the board for three weeks, so I know intake system mods netted HP, but didn't know to what extent each worked. If the factory TB isn't restrictive, then its easy to see why it doesn't change the HP very much.

To be totally correct, if you look at cylinder pressure and measure IMEP (indicated power) over the full 720 crank angle degrees you get the NMEP (net indicated power including pumping losses). I you shove the potato in the exaust, the pumping losses do go up and the NMEP will go down. If you look at the cylinder pressure data and integrate under the curve, you will see that the pumping (exhaust) part of the curve is very small in relation to the expansion part of the curve. On a naturally aspirated engine, pumping loss is very important. Not only do you have the power loss due to pumping loss, but you have more resisdual mass (internal EGR) left in the cylinder. Since you are relying on atmospheric pressure to fill the cylinder, the cylinder can onlu fill to atmostpheric pressure. So every amount of air left in the cylinder takes away from what can get in.

When you put tuned longtubes on, you can evacuate the cylinder at TDC of the exhaust stroke to less that atmospheric pressure. This reduces pumping losses yes, but it also means that you get a larger mass of incoming fresh air (remember you have a pressure source, not a volume source) and a cooler initial temperature to boot.

On the L, an exhaust will reduce the pumping loss, but the same mass of fresh air is being fed by the supercharger. The only thing you are changing is the ratio of fresh air to residual mass. But since the fresh air is the same, the fuel is the same, and the power will be similar. Changing the pumping loss will net a small gain, but nowhere near what is does naturally aspirated.

380 on the L may not equal 380 on a completely different engine with the same blower, but it will be +/- a small percentage. Remember, on a different engine, the controller may be calibrated very different resulting in power changes.

I think I've gone over this already. But to recap, its not that they don't work, its just that they don't work nearly as well as they would on a naturally aspirated application, and not nearly enough to justify the $1000 IMO. My money is better spent elsewhere to get HP gains that are more significant.

There are two big differences between the mustang GT and the L and Cobra:

1) The inlet to the mustang is very restrictive. Since airflow IS a function of inlet density, the lower pressure of the blower inlet hurts airflow. Look at the plumbing differences. You can spin the blower twice as fast, but the airflow won't double since the inlet density will go down almost as fast.

2) The mustang lacks an intercooler. The volume displaced is going to be the same for the two cars at equal inlet pressures (which I already claim not to be the case), but then the hot outlet from the mustang isn't cooled. Now the calibration of the ECU has to change to stem off knock. Since it is a factory calibration, you can bet your a** its very conservative.

Having not gone through the calulations myself, I can't tell you the exact answer, but I can tell you what I expect to see. Maybe I will calculate it out later to see what it tells me.

On the L you are airflow limited due to the M112's speed. So you have two options. Spin the M112 faster and get more boost, or raise the density of the M112 inlet. I will agree that for small changes (like +2 or +4) spinning the M112 faster is the better choice. But what about when someone wants to go +8 or higher. Then you are so far off of the efficiency plateau for the M112 you are never going to make any power, not to metion overspeeding the blower.

So then you can go to dual stage compression. I will argue (for now, if my calcs prove me wrong I will back down) that the two blowers are a more efficient package than and M112 spinning very fast. From eaton's specs, the efficency of the M112 starts falling off at about 8000 rpm. I think that spinning below that with an upstrem centrifigal blower will make a more efficient package.

skip:
What kind of supercharger?? If your talking about centrifigal, I will agree with you 100%. This discussion only relates to positive displacement supercharging.

I like to discuss these things. Even if I am wrong at some point, at least I learned something. I won't even let my panties ride up!!