Turbo efficency mumbo jumbo.

[ELiTeHaYDeN]

ok quick question.... or not.

Take a 1.8L 3T-GTE, with standard ct20 turbo(35mm inducer), no-intercooled, putting out the stock 160hp @ 8psi.

Take my 3T-GTE with rb20det turbo(50mm inducer), rx7 intercooler, 3" zorst + dumppipe, lumpy cams, at 3psi till around 4k then 5psi till 6k (unknown power output)

Power feels the same and acceration tests seem the same however its alot happier breaking out round corners and in the wet etc, probebly due to boost being availible at as low as 1500rpm

The question I have is, how does turbo sizing effect efficency in regards to a smaller turbo at higher boost agaist a larger turbo at lower boost, from what I have read, a turbo that is larger will not actaully be any better unless the smaller turbo is out of its efficency zone correctish?

Only reason im not running more boost is because i dont want it to run out of fuel, 5psi with the larger turbo im thinking would be equiv to the ct20 at 8psi?

[jondee86]

Hmmmm.... pressure (boost) is what causes air to flow against a resistance. Therefore, at a certain engine rpm (say 4000) 8 psi from a little turbo will make exactly the same power as 8 psi from a big turbo, and will require exactly the same amount of fuel.

The size of the turbo will affect lag, how soon it starts to boost, how much boost it makes, and how much air it will flow. In general terms, a small turbo will come on boost sooner and have less lag. But it may run out of puff at high rpm's because it is unable to flow enough air. This is a good thing as far as car manufacturers are concerned !!!

The compressor wheel in a turbo is a centrifugal fan, and it has a point of maximum efficiency where it will flow more air for less input power (from the turbine). Above and below that rpm, the efficiency will be less, but hardly an issue. What is more important is matching the flow characteristics of the turbo to the airflow demands of the engine.

This may or may not be of help

jondee86

[MrOizo]

also....

the RB20's turbo's are on ceramic (well light weight) and the CT20's are of steel... this might be why it can pull out of corners as it takes less (compared to a steel) to spool.

[dohca]

you will be fine with up to like 9, 10 psi i belive you may need to turn off your fuel cut out tho.

they have enough reserves for about 200 at the engine the ecu will do up to around 300ish

crank that boost y0!

[mister2]

ok... lots of misunderstandings around turbos

the size of compressor doesnt *really* affect spool rate - its more the exhaust side which determines the boost characteristics of an engine. a large exhaust turbine will spool later but also make more power due to reduced exhaust backpressure compared with a small turbine.

so running a larger turbo (say at 5psi) could concieveably make more power than a much smaller one running 8psi for this reason, but also the efficiency of the compressor comes into this too.

its pretty hard to compare different turbos... so many variables change.

cheers

nick

[jondee86]

I chanced across this web page :

http://www.stealth316.com/2-turboguide.htm

Its talking about turbo upgrades for 3 litre V6's, but there is a heap of good stuff there that you might find helpful.

jondee86