Inches Mercury -> PSI

[StuiE]

On Derrick Walker's website, it claims that the Toyota RV8F in the ChampCar is running 34 inches mercury of boost, what would this figure in PSI? The converting program that I use doesn't have either measurements, and I was wondering how much boost this thing is making compared to some road cars. ( I don't understand inches mercury!)


http://www.walkerracing.com/pages/tech.html


Cheers

[Adam43]

1 inch Hg weight density =
0.491154077497229 pounds per square inch

Therefore:

34 inch Hg weight density = 16.7 psi

Does this help, soes it give a sensible value?

[Dave Brand]

Originally posted by AdamAshmore
1 inch Hg weight density =
0.491154077497229 pounds per square inch

.....approximately!

[Adam43]

give or take...

[StuiE]

Originally posted by AdamAshmore
1 inch Hg weight density =
0.491154077497229 pounds per square inch

Therefore:

34 inch Hg weight density = 16.7 psi

Does this help, soes it give a sensible value?

Thanks Adam

16.7 psi seems to make sense, as boost was turned down this year, and with how the engine is designed I would say that would be about right, although I was expecting something around about 40psi! (dreaming sorta...)

Thanks again.

[RWC]

They measure the boost 'from' atmospheric don't they?
So 16.7psi boost = about 31psi total ??
Inotherwords the boost they are using approximately doubles output..?

[Arneal]

No, it is the other way around. The 16.7 PSI is absolute pressure, not boost pressure. In other words, you have to subtract out the atmosphere in order to get the boost.

Jeez! That last paragraph is jiberish. Lets just do the math.

16.7 psi - 14.7 psi = 2 psi or
34 inches Hg - 29.92 inches Hg = 4.08 inches Hg

Where, 14.7 psi and 29.92 inches Hg are normal atmospheric pressure.

This tiny amount of boost is the reason that CART will need to dump its current engine soon. When the 2.65 liter V8s were introduced many years ago they ran with a huge amount of boost. In the interest of safety CART decreased the power of the cars every year by reducing the allowable boost. Obviously with only 2 psi of boost they have gotten to the end of its life cycle.

[275 GTB-4]

Originally posted by Dave Brand
.....approximately!

Thankfully its not using a head of water as we are up around thirty feet so far!!!

[StuiE]

Originally posted by Arneal
No, it is the other way around. The 16.7 PSI is absolute pressure, not boost pressure. In other words, you have to subtract out the atmosphere in order to get the boost.

Jeez! That last paragraph is jiberish. Lets just do the math.

16.7 psi - 14.7 psi = 2 psi or
34 inches Hg - 29.92 inches Hg = 4.08 inches Hg

Since when?

Over here the boost pressure given is how much above atmospheric, eg 10psi is 10psi abouve atmostpheric = 14.7 + 10 = 24.7psi, theres just no point in measuring it like that.

[Arneal]

Originally posted by gtr69
Over here the boost pressure given is how much above atmospheric

It is done the same way here! My old Eclipse turbo had a max boost of 11.1 psi, which was 11.1 psi above atmospheric.

Why CART uses absolute pressure I don't know. I also don't know why they use inches of mercury instead of psi. I think it creates a lot of confusion.

[Robin Plummer]

Yeah and what does that convert to in "BAR" turbo pressure?

[malcolmstrachan]

1 bar is equivalent to atmospheric pressure, so about 14.7 psi.

Also, although champ cars may only run 16 psi of boost, consider that they may be running very high compression ratios. I don't know the proper math, but as an estimate, if champ cars run 16 psi of boost, with a 12:1 compression ratio, it would be like having an engine with a 8:1 compression ratio have like 40 psi (just a guess... my rudimentry math method came out with 24 psi... not what I believe is close to correct...).

I know that F1 cars in the height of the turbo era were running about 80 psi boost during qualifying... Those were the one-lap wonders of engines... I can't even imagine 80 psi of boost...

I think that current champ cars use revs and compression more for power than they do turbo boost. I think with the spec engine they have now, they should reduce compression a bit, reduce revs, beef up the engine a bit, and run more boost on the road courses (obviously less on the ovals). Have it so the bhp on a road course is around 900, but the bhp on an oval would be like 700. With turbos it is very easy to do...

[alfasud]

Yes, but...... in most cases when people talk about "20psi boost" they tend to mean atmospheric pressure PLUS 20psi e.g. 14.7+20=34.7psi total, but when people talk about "turbo boost limited to 2.5 BAR", they normally mean 2.5 x atmospheric pressure e.g. 2.5x14.7=36.75psi total.

i.e. 1 BAR generally means 0psi boost (14.7psi absolute at sea level).

The following pages help explain the relationship between inches of mercury, psi and BAR, etc:
http://www.intendedacceleration.com/html/tip_1.html
http://www.sjmautotechnik.com/10vgauge.html

[zefarelly]

so IF your hill climbing, or doing Pikes Peak your boost pressure will change as you go ;-)

[Robin Plummer]

I find it amazing that WITHOUT air valves only using steel that they have been clawing back the power by reving to nearly 16,000rpm!

If the formula remained the same but had to use petrol instead if methonal would the power remain the same?