earl

Assuming that the mixture is cooled to the same outlet temp, is 20 lbs boost delivered from a large turbo equal to 20 lbs of boost delivered from a small turbo?

D-SPEED

you pretty much answered your own question......20 PSI is = to 20 PSI

SuperSteve

20 psi is the same but it will make a different amount of power depending on the size of turbo. The bigger the turbo, the more psi, the more power. The smaller turbo will need more psi to equal the power of the larger turbo. But larger isn' alway better...

Tomakit

at any given psi, a larger turbo will flow more air.

Tom

JM Performance

yeah.....but that doesn't make sense to me. If there is 20psi in the intake manifold, whats the difference what size turbo brought it there?

D-SPEED

ya how can one 20 psi be different than another 20 psi ....that IS how hard the air is pushing.

Tomakit

https://honda-tech.com/zerothread?id=96443

Tom

D-SPEED

Tomakit

Tom

DIRep972

iTrader: (1)

great thread but I dont think my mind can comprehend all those charts just yet.

to make it simple 20psi is not just 20 psi... a bigger turbo will be more effecient at higher boost levels, creating cooler boost, and more power.. at the same time it will last longer cause it does not have to work as hard as the small turbo to make the same amount of boost..

back in the 70's they didnt have wastegates and if you wanted to run 8psi you ran a turbo that maxed out at 8psi.. This was not very effecient and when porche(i think porche invented the wastegate) invented the wastegate this was a turning point for turbo effeciency.. At that point they were even put into a different class of competition.. Porche 2.0 liter turbo cars now had to compete with 3.0liter NA cars and were still blowing them outta the water.. unneccessary trivia but still interesting.. point is bigger is better till lag becomes an issue.


[Modified by DIRep972, 6:55 AM 12/17/2001]

dustin

A smaller turbo will have to spin faster to create the same flow and pressure as a larger turbo. Thus the pressure will be the same, but the efficiency will not be the same. The smaller turbo will heat the air up MUCH more when compressing it, and significant power will be lost. Compressor maps allow us to graphically compare the efficiency of compressors

Dustin

D-SPEED

ok, but ignoring temperature, and how hard the turbo is working (as indicated by the original post).....how is one 20 psi different than a different 20 psi ? how can one flow more than the other if they are the same pressure ? that is what is being asked

TypeC

20 does equal 20psi. once you compute your BAF (boosted air flow) of your motor (max amonut your motor can flow while boosted at X psi), and you find a turbo that will consitantly supply that amount of CFM at your psi, then it only comes down to effeciency. A smaller turbo may not be able to keep 15psi at 460cfm for my car at redline, but a bigger one can (an spin at half the speed, decreasing power).

So, once you can keep up with your motor flow and keep a certain psi and temp (efficiency), the rest is lag/response/cost issues, IMO.

-C

dbman96

The point is, you CAN'T ignore temperature. Temperature is one of the most important issues in any operation where you're compressing air, and is directly related to the efficiency of the compressor. Temperature determines how dense your intake charge is and thus how much oxygen is contained in a given cylinder full of compressed air. You'd better believe that there is a big difference in how much power you get from 20 psi at 65 degrees F compared to 20 psi at 200 degrees F.

dustin

Intercooled temperature is /not/ going to be the same for a small turbo compared to a large turbo. That's the whole point: One turbo is going to heat the air up more when compressing it.

Also, I have explained it a hundred times but I think we need a review in the relationship between pressure and flow.

And understand this: There is a wastegate regulating PRESSURE, not flow. This means that some turbos just cannot flow enough air to maintain pressure with certain motors in high rpms. And those small turbos that /can/ maintain the pressure will have insanely high shaft speeds that will place them well out of their range of efficiency... and thus the heat issue.

Dustin

SiR Kid

Lets not forget that wat you put in , you must get out.

Larger turbo's also flow more exhaust out without compromising the total system's efficiency.

Small turbo's are like putting a 1.5" exhaust system on your car. They don't like to flow out what is being ingested, and clog up the system.

jinxproof99

agreed.

Adi Radoncic

C'mon guys just think of it logically which of these two turbos will flow more air?:

A Mitsubishi 14B at 20 psi
Or a T-60 at 20 psi.

T-60 of course, Thats why you upgrade your turbo in the first place.

Bigger Turbo = More power

Simple enough......

falcongsr

on the same motor, they will flow the same amount of air. the rate at which the air 'flows' is determined by how fast the engine can inhale it at a given pressure.

a properly sized turbo will 'flow' the right amount of air into the engine in its most efficient operating range.

how many more ways are there to explain it?

Tomakit

graphically? hehe

(just f'in with ya)

Tom

Davy Crockett

Outlet temp are the key word, both turbos will give the same power at 20psi IF the outlet temp of the charge are the same.
AND IF both turbos can deliver 20psi at the same engine rews.

If you use a enourmos turbo from a dumptruck or something
it would sure as hell could deliver 20psi at a normal car engine. but NOT below the engines redlimit

turbotypeR@SPEC

more volume of air at the same boost level will make more power.if you take a hose pipe that is,say 1/2" inside diameter and pump water through it at 10 psi of pressure and take another hose pipe that is 3" inside diameter with the same amount of pressure,which one would fill a swiming pool with water first?

falcongsr

the problem with this analogy is that the pool doesnt act like an engine. what if the pool could only be filled at a rate of 1 quart of water per second? then your 3 inch hose would be pumping lots of water to maintain 10psi AND be dumping most of it out of a wastegate to maintain 10psi and not spike.

so its irrelevant which pipe fills the pool first, cause your engine cant be filled with more air than its displacement+combustion chamber volume can hold (at 10psi, or whatever psi).



[Modified by falconGSR, 4:45 AM 12/18/2001]

earl

FalconGSR...Your brilliant logic seems to prove that 20 lbs does equal 20 lbs...
or can the big turbo's 20 lb filling capacity be better than the little turbo's filling capacity?

turbotypeR@SPEC

i was trying to put it into lamens terms where everyone would understand that a larger turbo will flow more air and usually make more power.