brain teaser

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pulsarboby

Guest
heres one for the clever people:lol:
say you have a standard tubby running at 1.2bar boost, then you have say a 3071 running at 1.2 bar boost
well the 3071 will make more power than the standard tubby but why?
they are both running at the same volumetric pressure at the inlet of plenum so providing that pressure is held at that end why would one produce more power than the other

i know the answer but i wonder how many others will know???
other than ed, stumo and red herring who are barred from answering:-D
 
PobodY

PobodY

Moderators
Staff member
Is it because pressure is only part of the equation; they flow a larger volume (being physically larger), so the same boost value actually equates to more air in the cylinders?
 
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iomegalinux

Guest
PobodY said:
Is it because pressure is only part of the equation; they flow a larger volume (being physically larger), so the same boost value actually equates to more air in the cylinders?
Click to expand...
we have a winner !! :D
 
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skiddusmarkus

Active Member
1 bar boost from a gt40 would be flowing the same amount of air as 1 bar boost on a t2.Its like saying a ton of lead is heavier than a ton of feathers.The difference is that the air in the gt40 would be cooler and there would be a shit ton less back pressure killing performance so the gt40 would make probably 50%+ more power on the same engine
 
Braveheart

Braveheart

New Member
3071 making more power because this turbo improved the volumetric efficiency of our engine and an improvement in outlet temperatures at the compressor outlet due to Adiabatic Efficiency... cough cough... ;-)
 
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ashills

Active Member
also have the bigger compressor wheel making the boost at a higher rpm so raising the torque up the band to give a higher bhp

but after a few of the above posts i need to write it in a way no one will ever understand lol
 
Braveheart

Braveheart

New Member
lol.... yes, the OE turbo will be spinning at 134,000 rpm with a compressor efficiency of 70% where as the 3071 will be spinning at only 97,000 rpm with a compressor efficiency of 82%... haha and to get over the late boost just increase the max rpm limit to 8000 and change gear later.
 
Fast Guy

Fast Guy

Moderators
Staff member
The bigger turbo is increasing the volumetric efficiency of the engine due to lower charge temps (the compressor wheel is more efficient) and lower exhaust back pressure.
 
Trip

Trip

New Member
Temperature is not all though. If both were running in the same efficiency island at same pressure both will be running approx the same temperature range but the GT3071R with make more power.

its all in the MASS(volume). Think of it getting hit by a Smart car at 40Mph Vs getting hit by a 10ton lorry at the same speed (or even lower).
 
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pulsarboby

Guest
haha well done

craig asked me just this question today at work and i tried to explain to him that it was due to the cfm and compressed air charge temps which would cause the drop in power between a larger and smaller tubby running the same boost level, also that this would then slow the turbine thus offering a further drop in power.
but he could not seem to understand my logic or my explanation and i didnt know how else to explain it so i wanted to see how some of you would have explained it so i can show him tomorrow:thumbsup:
 
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skiddusmarkus

Active Member
To give an example of how restrictions affect power, I just had my Janspeed 3" downpipe/elbow fitted and the boost shot up from 0.9bar to 1.15bar and the car went into warpseed.I had the OE elbow and mongoose dp before.The mongoose wasn't the restriction but the throttled elbow which it seems was potentially causing around 4 psi of back pressure.It was also enough to blow my boost pipe off the inlet mani the 1st time I gave it some throttle since fitting.
 
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steve963

Active Member
i asked this question a while ago, still dont get it though, if you blow a balloon up to 1 bar, is the same size whatever you inflate it with?!?
 
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skiddusmarkus

Active Member
Yes but if you blew it up with hot air it would have expanded more and have less oxygen in it than if you'd blown it up with cold air.I think the main gains are from reduced back pressure though.Just look at the gains from switching from the OE pipe cleaner to a mongoose.I gained something like 10 bhp and 30lbft from that alone.Plus the gains increase the more boost you run.

Edited to add switching from the mongoose to a Janspeed elbow/downpipe I noticed a little more lag initially but once it started spoolling it picked up better.I put this down to a smaller bore OE elbow being better suited to initial demands of the engine but quickly becoming a restriction as the revs rise.
 
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Trip

Trip

New Member
steve963 said:
i asked this question a while ago, still dont get it though, if you blow a balloon up to 1 bar, is the same size whatever you inflate it with?!?
Click to expand...

Now grab anther balloon double the size and blow it up to 1bar. They are still the same pressure but the bigger ballon has more air inside it since it has a bigger volume. If both are filled with oxygen, and you put a flame to it, guess which will make a bigger bang ?
 
Trip

Trip

New Member
heat isn't the main factor.. although cooler air is more dense. a Bigger turbo can pump out more CFM of air then a smaller turbo
 
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