Turbo Boost Vs Supercharger Boost

[T.Trophy]

As some may know I recently had my car fitted with the Ktec low pressure turbo conversion.

When the fitting etc.. was being carried out I was told it would be running approx 220bhp at 7 psi (0.5bar) boost.

After the fitting I took the car to RStuning for some tweaking of the original map, as it was originally done on Seans 172. On Pauls rollers the best he could get was 205.9 bhp (the print off confirmed 0.5bar of boost)

Moving on, there are a couple of supercharger kits being developed in both high and low boost formats. Both the low boost conversions are claimed to be running at 0.5 bar yet putting out 250+bhp.

So the question is what is the difference between turbo boost and supercharger boost at 0.5 bar that should yield such significant power differences? Considering both conversions use standard internals, CR's etc..

Surely boost is boost?

From all the research I've done, a turbo should have the highest gains due to the fact that it runs from exhaust gasses.
Where as a supercharger has to sacrifice some of the bhp gained, due to the extra drag placed on the crankshaft to turn it.

I did a search on google about this and all I could find was various groups argueing which was best. I'm not interested in which people think is best, I didn't want to rip the air con out of my car so opted for a turbo, no other reason bar that.

Hopefully some of the experts can break it down into simple terms for me.

Cheers

Steve

 

[Gstar2006]

Hey,

I know it's not what you asked but how much all in was the low pressure turbo?

Have you got anything else on the car like a decat, matched inlets, uprated panel filter and cold air feed?

Does seem a little low like you say.

 

[LegoHead]

I guess turbo would create higher inlet temperatures compared to same boost from a charger.

 

[Tucker]

you have intercooler?

 

[T.Trophy]

Car is fitted with janspeed exhaust, decat and induction kit.

Higher intake temps, hmm maybe but seens as there all fitted with intercoolers I honestly can't see heat soak accounting for such a difference

 

[LegoHead]

A set intercooler will only give a set temperature drop at fixed flow rates so higher temperature at the inlet will still be high at the outlet compared to a a charger which probably has lower temperatures.

 

[Tucker]

compressed air gets hot.

you could probably gain 15 horsepower with a front mount

 

[Tucker]

oooo actually 7psi

 

[LegoHead]

compressed air gets hot.

you could probably gain 15 horsepower with a front mount

yes it certainly does get hot when compressed. But I am saying that as the turbo is also alot hotter than a charger the air will pick up more heat when it pass through.

 

[T.Trophy]

Maybe but, to the extaent of losing 50bhp?

 

[Tucker]

yes legohead has a point, a s/c isn't actually being heated is it.

how many lb/ft do you have?

 

[franx]

it's still more hot

No intercooler ?

 

[LegoHead]

Maybe but, to the extaent of losing 50bhp?

It may account for a small %. I am sure steve172 on here gets about 250bhp with only 7psi as he has headwork too. There are many areas where improvements could be made.

 

[T.Trophy]

yes legohead has a point, a s/c isn't actually being heated is it.

how many lb/ft do you have?

182lb/ft

 

[Chris n nic]

Isn't Pauls RR a Dynodynamics which tend to read really low anyway (or accurate whichever way you want to look at it)

Chris

 

[T.Trophy]

It may account for a small %. I am sure steve172 on here gets about 250bhp with only 7psi as he has headwork too. There are many areas where improvements could be made.

True mate but the question was what is the difference between 7psi of turbo boost versus 7psi of supercharged boost on standard engines to produce such huge differences.

 

[T.Trophy]

Isn't Pauls RR a Dynodynamics which tend to read really low anyway (or accurate whichever way you want to look at it)

Chris

Good point but thats where Paul RR'd his own conversion which showed 250+

 

[Tucker]

how many revs do you have?

 

[LegoHead]

True mate but the question was what is the difference between 7psi of turbo boost versus 7psi of supercharged boost on standard engines to produce such huge differences.

All other variables being equal I could only guess it would be due to inlet temperatures.

 

[Waitey]

yes it certainly does get hot when compressed. But I am saying that as the turbo is also alot hotter than a charger the air will pick up more heat when it pass through.

Its acutally the compression of the air that heats it. Very little comes from the turbo oddly enough.

Some superchargers get to over 180deg f inside!

 

[Waitey]

You may have a problem somewhere else. Dodgy HT lead. Duff injector etc etc

 

[Tucker]

but will 7psi from a turbo be hotter than 7psi from a s/c?

 

[ditz]

well to answer your question yes boost is boost.. but you have other things to consider physical load on engine, exhaust restriction, inlet temps (and therefor fuelling/ignition compensation) all sorts... although none of that would make up 50hp and id imagine paul would have told you if charge temps were stupidly high whilst mapping it

 

[deltav]

sc pulls power from the engine yes, but dont forget the turbo acts as a restriction in the exhaust.

this isnt my area at all but from what little i know boost is essentially a measurement of restriction. the turbo sat in the exhaust will cause a greater restriction that the sc as once the air leaves the cylinder with the sc its straight down the exhaust. so im pretty sure even though they both show the same boost you will find the sc is actually flowing a greater mass of air. but rich or andy would know a hell of allot more than me.

also dont forget that our sc is on standalone management so we have far greater control over fueling and ignition timing and can therefore map more acuratly.

 

[stan*]

Given the engine has the exact same spec, 10 psi (or whatever) is 10psi for all intents and purposes, this is a measurment of restriction to flow caused by the intake syatem as a whole.
However with a SC there is less restriction on the exhaust system, so lower pressure accross the exhaust valve as it opens...so spent gases evacuate easier.

Adiabatic efficiency is about the same, in terms of actual mechanical mechanicsm, but you will obviously get more heat transfer to the intake charge with a turbocharger due to its inherent positioning, and means of energy recovery...i.e. hot exhaust gases.

I personally think a large portion of the claimed gain for a SC over a turbo set-up is in the camshafts. Std NA cams will be far better suited to a SC application, than a turbo charger application....this will help output alot no doubt.

 

[Waitey]

but will 7psi from a turbo be hotter than 7psi from a s/c?

It doesn't have to be. Could even be the other way round in some applications.

From my Experience with MX-5's. 8 psi got me 197bhp with a turbo.

Whereas 8psi with an SC only made 180.

sc pulls power from the engine yes, but dont forget the turbo acts as a restriction in the exhaust.

this isnt my area at all but from what little i know boost is essentially a measurement of restriction. the turbo sat in the exhaust will cause a greater restriction that the sc as once the air leaves the cylinder with the sc its straight down the exhaust. so im pretty sure even though they both show the same boost you will find the sc is actually flowing a greater mass of air. but rich or andy would know a hell of allot more than me.

also dont forget that our sc is on standalone management so we have far greater control over fueling and ignition timing and can therefore map more acuratly.

Pauls SC'd clio is on OEM management is it not?

 

[LegoHead]

SC uses just engine power and turbo scavenges power from the exhaust, turbo seems more efficient use of engine power?

just found this interesting read http://www.superchargersonline.com/content.asp?ID=19

 

[ashy_gtt]

some of the information (or should I say guess work) from some members on here is total sh!te. Sorry but people who don't really know what they are talking about post some total tripe on threads like this one!

If you were told that at 7psi your conversion would make approx 220hp, and at 5psi you are making 205h then I don't understand the issue?

Why not just increase the boost to 7 psi? I guess on the low pressure conversion you haven't lowered your compression? so at 0psi you would be making 170hp and at 5psi you are making 205hp, so thats approx 7hp per psi. so if you increase the boost to 7psi you should "in theory" make 219hp... So thats not too far away?

Putting your car on the rollers is never an exact science, there are so many variables that need to be entered, differences between rolling roads and calculations made to give you a flywheel figure that your result is only ever an indication.

If the car runs well with the conversion, feels fast on the road then thats all that matters, isn't it?

If people are claiming 250hp with a charger thats fine but you can manage 250hp from your setup aswell.

Interestingly I've lowered my CR to approx 9:1 and I still manage to make 238bhp and 230lb/ft at 7psi.

 

[Waitey]

some of the information (or should I say guess work) from some members on here is total sh!te. Sorry but people who don't really know what they are talking about post some total tripe on threads like this one!

If you were told that at 7psi your conversion would make approx 220hp, and at 5psi you are making 205h then I don't understand the issue?

Why not just increase the boost to 7 psi? I guess on the low pressure conversion you haven't lowered your compression? so at 0psi you would be making 170hp and at 5psi you are making 205hp, so thats approx 7hp per psi. so if you increase the boost to 7psi you should "in theory" make 219hp... So thats not too far away?

Putting your car on the rollers is never an exact science, there are so many variables that need to be entered, differences between rolling roads and calculations made to give you a flywheel figure that your result is only ever an indication.

If the car runs well with the conversion, feels fast on the road then thats all that matters, isn't it?

If people are claiming 250hp with a charger thats fine but you can manage 250hp from your setup aswell.

Interestingly I've lowered my CR to approx 9:1 and I still manage to make 238bhp and 230lb/ft at 7psi.

Reading fail Ash. It made 205bhp and 0.5BAR not 5 PSI.

 

[Tucker]

it's already running 7psi

 

[T.Trophy]

Ashy I've posted this on RTOC aswell.

Also the boost is currently at 7psi/0.5 bar

I was going to pm you about you CR as I knew you'd milled your pistons and had heard that the wossners were possibly a bit low

 

[LegoHead]

we were just discussing the turbo vs supercharger debate and although I may be talking shite I am using thermodynamics theory as background for my ideas.

Please dont let the thread turn into a slanging match we just wanna throw some ideas out and test the theories.

 

[Tucker]

i think the heat/efficiency point is very valid

 

[stan*]

I think its more down to cams....

 

[Tucker]

http://peregrineperformance.com/Camshafts.htm

says alot about small turbos/ valve overlap

 

[Icarus]

I think its more down to cams....

I agree.

Cheers
M

 

[deltav]

what cams are you running on your low boost turbo? our sc is on totally standard 100k engine

edit: sorry i see what your saying now. thought you may have had non standard cams in there.

 

[T.Trophy]

what cams are you running on your low boost turbo? our sc is on totally standard 100k engine

edit: sorry i see what your saying now. thought you may have had non standard cams in there.

Nope mate totally standard bar the exhaust system. but nothing internal.

I still find it hard to fathom how theres 50bhp difference for the smae boost pressures.

Even though a turbo may restrict the exhaust gas flow and the standard cams maybe more suited to SC surely not to that extent?

 

[stan*]

I still find it hard to fathom how theres 50bhp difference for the smae boost pressures.

Read my posts again

 

[T.Trophy]

Read my posts again

Re read your post again mate and so basically

The hot turbo is increasing the inlet temps
The cams are more suited to a SC?
Turbo back pressure is slowing exhaust gas exit

Now I'm not being funny but if you were to also add in the the power lost from the rotation of the supercharger pulley then you could be looking at possibly 70+BHP difference.

A genuine 30-40% power difference.

Now come on superchargers can't be that much more effiecient really can they? Otherwise turbos just would't exist.

This is the only conversion that I've came across that has superchargers being the biggest gainer.