really confused with turbo charging..

[lsvag]

i was reading a book called 'Maximum Boost' by corky bell.. in it, it mentions how in theory, 1 bar of boost (14.7psi) the horsepower figures should double since theres 2 atm pressure.. fair.. one car that seems to defy this is the mazda rx7.. in stock form, it makes 220 rwhp (at 0.62 bar).. which is fair enough (136rwhp with no boost).. why is it that there are some rx7, with the same twin turbo's, apparently you can get 380 rwhp with 1 bar of boost :S.. thats like saying it made 200rwhp with no boost, and even then, there are points where the turbo isn't exactly fully effiecent so it should be nowhere near them numbers..

another car that confused me was the noble m600.. apparently in race mode, it makes 650 hp at, apparently, 1 bar.. the volvo engine, which its using makes 310 hp .. at 1 bar , it should be 310 x 2 which is 620???.. and that is before the hp loss from the 310 for decreasing compression and the effiency losses.. it doesn't make sense..

 

[HDi fun]

Are we talking 1 bar absolute or 1 bar relative to atmospheric pressure?

 

[bigbadjoe]

Right, I'm off to buy a 4 bar turbo

I think you have either miss read or been informed wrong. This is not the case at all. Far from it to be honest. I AM NO TURBO EXPERT but I know that what you said in your first post does not seem to be accurate.

My boost as standard is about 1.1/1.2 bar. If I changed my fuel pump, intake, exhaust and remapped, then my car would increase from 260bhp to about 320(ish) with a good mapper.

If I did none of the work and cranked the turbo upto 2bar pressure, it would put the bhp to about 300(ish) and then melt my pistons.

Turbo's are complicated. The most important thing is air flow. Im about to get my cams changed and my turbo will still only be at about 1.8bar. Not the full 2. There is no need to increase any more as I have not changed the turbo housing for the larger 10.5t housing off the Evo 9. That will be my next project.

 

[pgarner]

it would depend on the turbo in question.

A large turbo at 1 bar will shift more air than a tiny turbo at 1 bar

 

[Loz]

I was reading a book called 'Maximum Boost' by corky bell.. in it, it mentions how in theory, 1 bar of boost (14.7psi) the horsepower figures should double since theres 2 atm pressure.. fair.. one car that seems to defy this is the mazda rx7.. in stock form, it makes 220 rwhp (at 0.62 bar).. which is fair enough (136rwhp with no boost).. why is it that there are some rx7, with the same twin turbo's, apparently you can get 380 rwhp with 1 bar of boost :S.. thats like saying it made 200rwhp with no boost, and even then, there are points where the turbo isn't exactly fully effiecent so it should be nowhere near them numbers..

The stock engine is already running boost, so upping boost to one bar will = a pressure increase of original boost (say 0.5bar) -1 bar.

another car that confused me was the noble m600.. apparently in race mode, it makes 650 hp at, apparently, 1 bar.. the volvo engine, which its using makes 310 hp .. at 1 bar , it should be 310 x 2 which is 620???.. and that is before the hp loss from the 310 for decreasing compression and the effiency losses.. it doesn't make sense..

Why doesn't it make sense? I don't see the point your trying to make. The M600 is a twin turbo V8 making 650BHP, if your trying to account for the extra 30BHP then that could easily me made up from other engine changes, head work, lumpy cams, air intake & exhaust design & engine map will affect performance output.

The statement made by C Bell sounds to me like a generalisation, a rule of thumb if you will, It's not a hard fast fact. All he's saying is if you slap a 1 bar turbo on your car you will get roughly double the output, it might be a little less it might be a little more you won't know until you try.
Another factor to consider is that you need to take quoted horse power figures with a pinch of salt. Because the reading on the day demends on a large number of variable such as tyre pressure, air temp/pressure/speed & the operators interpration if the results.

 

[obi_waynne]

I'll try to put this in the simplest terms I can for you as it can get quite complicated the more you think about it.

If you had a large tank of air at 1 bar and a smaller tank of air at one bar you would clearly have different amounts of air in each tank although they are at the same pressure.

The Bar figure is merely the pressure, not the volume of air. So if you have a large capacity engine at 1 bar pressure will contain more air than a small capacity engine at the same boost level.

Air flow rates into the engine and volumetric efficiency also come into play here so often cars will not follow the double power rule of thumb.

Double the air does not automatically mean you get double the power, it just doesn't work like that in the real world.

 

[HDi fun]

More to the point if the small turbo is not capable of delivering enough air the the manfold absolute pressure will drop anyway.

The is exactly like the voltage/current thing with electrics.

 

[SLEEPER]

You simply cannott have a meaningful debate about supposed specific increases in performance without naming the turbo and the engine.

Then to get any accurate answers you need the compressor map and the engine spec

 

[bigbadjoe]

You simply cannott have a meaningful debate about supposed specific increases in performance without naming the turbo and the engine.

Then to get any accurate answers you need the compressor map and the engine spec

+ a whole lot more. They are not simple things.

It anoys me when people talk about turbos as a ''big blowey air thing'' and you espetially get it with Vaxhaul VXR drivers talking about pushing 30psi. Get a grip.

 

[SLEEPER]

For sure BBJ

TBH the number of "Im going to turbo my saxo/corsa/whatever" that appear on this site is so large that Ive got fed up with explaining "It just aint that simple"

so just the basics and I mean real basics.
(for people that cant work a seach function)

All turbos have an optimum operating envelope . Unless you can use this fully fitting a turbo is a complete waste of time.

All turbos have to reach this envelope before they produce any kind of power and to do that the engine has to spool up to whatever level the compressor map says.
It can only do this by being driven by the exhaust gases .

Keeping things simple - A bigger engine will spool any given turbo up quicker than a smaller one and a bigger turbo will spool up slower than a smaller one . Thats just basic physics (all things being equal of course)

The above is why only specific turbo questions can really be answered properly.