Supercharging An Rb20det?

[mad082]

also note that i am not saying more can't be made by running a bigger turbo at the same pressure, i'm just saying that it isn't caused by air volume going past the afm. its caused by colder air charge and less exhaust restriction.

and i just did a test that proves my theory. i have a bike pump with a gauge that has a twin chamber system (both chambers are the same size). you can have it use either both chambers or just 1 by pushing a button in. the test i did was the pump a tyre from 10psi to 30psi and count how many strokes, and how long it took to do it on 1 chamber or 2. when you push hard on the pump the pressure spikes and it spikes more on 2 chambers because you are trying to force twice the air. so to make it a level playing field i set a max spike level of 40psi. this means that 1 stroke on the 2 chamber setting took twice as long.

now there has to be some tolerences in the equation for the following reasons. the gauge is anologue, so it means the reading isn't 100% spot on, and the time taken for the up stroke of the pump. now as for a turbo it doesn't have to stop and load up the air again. so the times were out a little bit (but very close), after taking into account the average time for an up stroke, but it was impossible to be exact as each 1 was slightly different.

so then i started pumping away. as far as number of strokes goes, take into account margin for error on the gauge they were the same. (on twin barrels was half a stroke less). corrected time wise was a little bit out. about 1 second, but take into account the up stroke time being twice as much on 1 barrel, arms getting a bit tired, and the fact that i was trying to pump and operate a stopwatch at the same time, you could say it was pretty even.

sure i could've done it quicker on the twin chamber, but not keeping under 40psi. if i went hard on both the twin would be done quicker, but the max pressure would be about 100psi on twin vs 70psi on single.

[StockyMcStock]

well i'm f**ked if i can explain it any more simply than i already have, so i'll just leave it there i reckon.

[Cubes]

lol yes, as do I.

Mad082, You think too much.

[Hakai]

yes true. but that is only comparable to saying a car with 3" intercooler piping will flow more than a car with 2" intercooler piping. if you get the 2 tyres and take a 1 cubic inch piece of air out of each tyre, the pressure of that cubic inch of area, and the volume of air, would be the same. the truck tyre just has more of those pieces.

This example you've used illustrates exactly what I was talking about.

Yes, each of the cubic inch of areas will have the same pressure and will contain the same volume of air, the key is exactly what you said, there is more of those pieces in the truck tyre. Knowing this, if you add up all the pieces together, you end up with both tyres having the same pressure level, but the truck tyre has more air in it. Same for my example. Sure if you remove one tiny piece of the whole you get each being equal, but when you add everything together to create the final product, they are not in fact equal. Basically, they have the same pounds per square inch of air each, there are just more square inches that require filling in the bigger tyre and hence the bigger tyre has a higher volume of air in total.

I will admit that I was unaware of the technical reason for the airflow increasing in an engine when a larger turbo was fitted, I assumed it was because the turbo itself was bigger. The truth as it seems, as Stocky pointed out, is that the flow increases due to a lessening of backpressure on the hotside of the engine. Thereby decreasing the resistance to airflow on the intake side. As the resistance to airflow is decreased, the amount of air required to generate the same pressure level increases. That's about it

If you wanted to look at it mathematically, then I'm sure there is a formula for working out pressure based on airflow and backpressure. But mathematically if you have a formula consisting of 3 values and you change one of those values, then it is not possible for one of them to remain the same, unless you also change a second value. In this case, you decrease backpressure, you want boost to stay the same, you must increase the airflow. I suck at explaining, but I hope this helps a bit more.

[Hakai]

also note that i am not saying more can't be made by running a bigger turbo at the same pressure, i'm just saying that it isn't caused by air volume going past the afm. its caused by colder air charge and less exhaust restriction.

and i just did a test that proves my theory. i have a bike pump with a gauge that has a twin chamber system (both chambers are the same size). you can have it use either both chambers or just 1 by pushing a button in. the test i did was the pump a tyre from 10psi to 30psi and count how many strokes, and how long it took to do it on 1 chamber or 2. when you push hard on the pump the pressure spikes and it spikes more on 2 chambers because you are trying to force twice the air. so to make it a level playing field i set a max spike level of 40psi. this means that 1 stroke on the 2 chamber setting took twice as long.

now there has to be some tolerences in the equation for the following reasons. the gauge is anologue, so it means the reading isn't 100% spot on, and the time taken for the up stroke of the pump. now as for a turbo it doesn't have to stop and load up the air again. so the times were out a little bit (but very close), after taking into account the average time for an up stroke, but it was impossible to be exact as each 1 was slightly different.

so then i started pumping away. as far as number of strokes goes, take into account margin for error on the gauge they were the same. (on twin barrels was half a stroke less). corrected time wise was a little bit out. about 1 second, but take into account the up stroke time being twice as much on 1 barrel, arms getting a bit tired, and the fact that i was trying to pump and operate a stopwatch at the same time, you could say it was pretty even.

sure i could've done it quicker on the twin chamber, but not keeping under 40psi. if i went hard on both the twin would be done quicker, but the max pressure would be about 100psi on twin vs 70psi on single.

This example can't really be related to a turbocharger. The reason for this is because with a turbo you have a compressor pumping air INTO an object that it is then also expelled from. While pumping air into a bike tyre, it isn't being expelled anywhere. As I said in my post above this one, quoting Stocky, the increase in airflow is due to a lessening of restriction on the exhaust side.

As SK has said plenty, and has been reiterated here quite a bit. Boost pressure is ONLY a measure of RESISTANCE to AIRFLOW. If resistance changes, then for boost pressure to remain the same, airflow MUST change with it. There is an increase of air going past the afm, there simply has to be.

If boost pressure is a measure of resistance to airflow, then boost pressure is, as I said in the post above, a calculation based on both airflow and resistance to airflow. For boost pressure to remain the same when you change the resistance to airflow (Which is what you are doing by decreasing resistance on the exhaust side of the engine), the airflow simply HAS to change. It's a basic mathematic principle. I'm not trying to say you're stupid, don't take me the wrong way, just trying to help you understand

I felt like an idiot when Stocky corrected me heh, but in the end I understand a bit better now

*EDIT*

I just thought of something else. Your example with the bike pumps. You say that when you pumped with 1 cylinder it peaked at about 70psi? And with 2 cylinders it peaked at about 100psi?

Those pressure readings are indicitive of the tyres resistance to the airflow that you were generating with the pump. Examine this for a minute. Using 1 cylinder the resistance to the airflow created is 70psi. You'd think that when you're using 2 cylinders, and effectively doubling your ability to generate airflow, that the resistance would increase to 140psi. However; It didn't. The reason I believe this to be, is that while it provided 70psi of resistance to the airflow from 1 cylinder, it could in fact, handle more airflow it just needed that airflow to be provided, which is why, when using 2 cylinders, providing double the airflow, instead of the pressure doubling, you only saw a 30psi increase. Pressure is resistance to airflow, what that tells us is that the majority of the extra airflow generated by the 2nd cylinder did in fact flow freely into the tyre. We can deduce this because that airflow was not resisted enough to turn into an increase on your pressure gauge Using 2 cylinders, you would have in fact pumped the tyre up much faster than using 1. Setting a pressure limit of 40psi (When 1 cylinder peaks at 70spi) is completely negating the advantage of using the second cylinder. See where I'm going with this?

Edited July 13, 2006 by Hakai

[StockyMcStock]

right that's it, if you insist on thinking any more, i will have to stab you through the internet.

[Hakai]

right that's it, if you insist on thinking any more, i will have to stab you through the internet.

I don't think!!!!

I promise!!

*Thinks*

*Runs*

Edited July 13, 2006 by Hakai

[Cubes]

right that's it, if you insist on thinking any more, i will have to stab you through the internet.

lmao.

[Hakai]

lmao.

Don't encourage him! He's a dangerous man.

[Rookie ROX]

and i call bullshit on a lot of this quote too. my reasons:

1: lysholm blowers are NOT very comparable to roots blowers, for reasons which the author later goes on to describe HIMSELF.

2. the lysholm is more efficient everywhere than any roots blower i've ever seen charts for, because it has an element of internal compression, which the author later goes on to describe.

3. "That means that a bypass valve can not fully shut it off". While this is technically true, looking at the 2300AX flow chart gives me a total power loss of less than 5kw when the blower is at 5000rpm and pressure change is 3psi. the chart goes off the bottom scale here but it would be safe to say that at idle, with an open bypass gate, your 700hp supercharger would be pulling less than 1kw from the engine.

4. "This also means that the supercharger is heating things up all the time which can result in a heat soaked intercooler, totally defeating the lower discharge temps." OOPS, that's bullshit too. outlet temps go up only when the blower is actually making pressure changes. if you have a bypass gate, it is completely unloaded at low throttle and idle, and outlet temps are always below 40 degrees. regardless of this, your gate will be recirculating the air PRE-intercooler so that "hot" air will never even make it through the intercooler core until you start boosting.

/end rant. buy a lysholm.

Glad to see the whole thing wasn't torn apart

As I said, I'm no expert and just knew of that section that may give you a better understanding behind roots style. The main point wasn't necessarily to sway towards getting a roots, but just to clear up misunderstandings and myths that people have towards them.

Listen to Stocky - he know's what he's on about!

ROCK ON

R~R