1 BAR of Boost is still 1 BAR of Boost.....right????

[reesestewww]

Ok so it seems, from what I’ve read, that the rule of thumb is not to exceed 1 Bar of boost on a turbo. 3.3L for example. So if a get 1 Bar of boost from a K26 turbo w/ a one bar spring , why does a K27 make it faster. I know it does, only because, that’s what I’ve been told. But why? What is that K27 doing to give you more HP, still not exceeding 1 Bar?

Hope that made sense???

[lendaddy]

Best I can imagine it would be a matter of efficiency. You would be shocked to find what HP a turbo "robs" to create the boost it makes. A more efficient turbo makes the same boost while robbing less from the front side.

[RallyJon]

CFM = horsepower, and a bigger compressor moves more air into your engine at the same boost. It will also be cooler air.

[lendaddy]

Oh yea,the deal about not exceeding 1 bar is due to the CIS fuel system and our distributor ignition system not the mechanical stress on the engine.

[reesestewww]

I’m considering adding one of the Andial fuel enrichment systems. It seems like a good idea to protect the engine.

[reesestewww]

I see, so its like an air compressor? For example two air compressors make 150 PSI, one can produce 8 CFM and the other can produce 3 CFM.

[sammyg2]

If the compressor is 70% efficient for a given air flow and boost, that means it creates 19.11 psig of back pressure to spin the compressor. That chokes the engine big time and also creates extra heat.
Take the same engine and install a compresor with an 85% efficiency rating and the exhaust back pressure drops to 16.09 psig.
The delta P across the boosted engine needs to be minimized to make optimum power.
I'm not sure of the compressor mapping of the K26 vs K27, I'm only throwing out those numbers for example but I'd bet they are reasonably close. The K27 may be even more efficient that 85%.
That and the fact that a more efficient turbo compressor will usually build discharge pressure quicker and at a lower spool up speed also make it seem faster.

Other things to make a turbo more efficient are properly ground cams with less than 270 degrees overlap and high lift, free flowing exhaust and intake, and insulated exhaust piping before the turbo to retain as much exhaust heat (energy) as possible so it can be absorbed by the turbine.
It is theoretically possible to have a turbo that is more than 100% efficient i.e. it can provide 14.7 psig boost with less that 14.7 psi exhaust back pressure due to the extra heat in the exhaust gasses. The energy of heat is mostly what spins the turbine, not just pressure.

[lendaddy]

Well, kinda. Think of it this way. Say you build an electric supercharger. It is powered off your alternator. the more efficient your compressor is the less amperage the motor will need to turn it at the required rpms, and the less horsepower you alternator will rob from your engine as it needs to produce less amperage at 14 volts. This is my theory, I believe I am correct but hey.

[ZCAT3]

Don't forget that the K-27 spools faster - meaning less lag and full boost earlier. That alone, even with the same peak HP, will make the car faster.

[ischmitz]

Pressure and flow is like voltage and ampere:

The higher the pressure (voltage) the higher the flow (ampere). The same pressure should by all means result in the same flow (at a given intake backpressure)

Efficienty is the key. The exhaust stream that is released unused into the atmosphere contains a lot of 'usable' power. The turbocharger makes use of that, but creates backpressure in the process and hence chockes the engine a little bit. Bigger turbo = more efficient thats the key.

is

[sammyg2]

One thing i forgot to add, a more efficient compressor will add less heat to the compressed air, so the air will be more dense. That'll make your intercooler more efficient. Higher density means more 02 molecules at the same pressure.

The energy that is absorbed by the turbo has to go somewhere. if it isn't absorbed by compression, it is absorbed by the air gaining BTUs.

[masraum]

I think a big part of it is what ischmitz said. You can put a huge turbo on a small engine, but then you have to wait much longer for it to spool, and by the time it has spooled you are getting ready to have to shift. I think displacement and rpm have a lot to do with what turbo works best for your engine.

Just a generallization. Say a 3.3L works best with a 6500 rpm redline and a K27, but if you build it so the redline is going to be 9000 at that point I think a K26 or K25 might be better so it is large enough to supply enough flow for that engine speed.

I'm no expert, but that is my understanding of the non technical portion.