Dumb Question About Psi

[Mals BA XR6T]

This is going to sound really dumb.

Given that the car is a 4 ltr (as a NA) and you compress air into the piston chamber at 6 PSI, what would the otherwise volume of the engine be??? Is 6 PSI twice the amount of air volume, 3 times, 4 times???? :o

I hope I make sense here :o

[Simon]

Hey Mal

Normal air pressure (1 bar) is 14.7 psi. I assume, rather simplistically of course , that adding 6psi is upping the volume of the air in the cylinders by approximately 40%.

Someone tell me if I'm off the track here as that's just off the top of my head :o

[richdave]

Normal air pressure (1 bar) is 14.7 psi. I assume, rather simplistically of course , that adding 6psi is upping the volume of the air in the cylinders by approximately 40%.

Someone tell me if I'm off the track here as that's just off the top of my head  :o  

That seems to make sense...240kw is about 40% up on 180kw. 40% more fuel/air mixture would, I assume, make 40% more power :o

Coincidence or science??

[Turbo6man]

Simon> spot on mate.

[Mals BA XR6T]

So assuming all this, and as I said, I'm sure this sounds really dumb... but you could say that working this all backwards the 4ltr would be something like 5.6 ltrs.

Why I'm asking all this is because my Dad is from the "old" school of motors and he has his V8 and keeps telling me the XR6T is only a 4 ltr, and doesn't understand how Turbo's work...

At least I can now use this as an example when I try to explain it again :banghead:

Thanks Guys

[Mondie]

Yep, that's right Mal.

The engine has the same quantity of air in each cylinder as the 5.6lt engine due to the force feed from the turbo (when at full boost), effectively increasing the capacity of the 4lt engine. When the extra power is not needed and you are driving sedatley and so the turbo is providing little boost, the engine is effectively close to its naturally aspirated 4lt capacity, so saving fuel. that's the great thing about turbos, close to N/A economy when not using the turbo, and big engine performance when you are. The best of both worlds.

A turbo increses the volumetric efficiency of the engine beyond 1.... example. If a perfect naturally aspirated 4 lt engine went through one cycle of combustion in all 6 cylinders in a perfect world it would have sucked in 4lt of air. However in the real world this never happens due to friction on the intake side, heat causing the inducted air to warm up and so expand etc etc, so the volumetric efficiency is less than 1 as a result. But bang a turbo on and suddenly at full boost the 4lt engine is drawing close to 5.6lt of air (excluding the friction loses) just like your dads car and the volumetric efficency then becomes greater than 1.

l havent explained that very well, but l hope it makes some sense

[AMoffat]

I thought you explained it pretty well actually!

So Mondie, do you miss the low down grunt of the V8?

[Mondie]

I thought you explained it pretty well actually!

So Mondie, do you miss the low down grunt of the V8?

No, not at all.

l absolutley love the turbo rush, nothing beats plodding along at 20km an hour in 1st with one of your mates in the passenger seat and then just planting it, the car instantley launches. It seems to hit 70km in about the time it takes to reach for the gear shift. l love it

They dont bother asking how it goes after that, they just sit there in impressed awe.

l used to have a 72 XU-1, one of the late model ones with the uprated 202 for Bathurst and l loved it, my favourite car over all others l have owned. l hoped to recapture some of that 6 magic with the XR6T and l have, with a bit of luxury and comfort thrown in.

There is nothing l miss about a V8 really.

[AMoffat]

Thanks mate.

Just the answer I was hoping for. Most of the time, I'll be using it for over-taking from 80 klms up. I didn't think I'd need the V8 for that.

As you can tell - I have ordered the turbo without driving it!

[Turbo6man]

There is nothing l miss about a V8 really.

Except the fuel bill heheheheh.