Real FI performance

[Lordalfa]

Following up on the NA performance. FI is a much easier base to increase performance. FI is split to Supercharging and Turbocharging.

 

Supercharging is using the engine crank power to drive a mechanical pressure pump to supply pressurized air to the engine. There are 2 main types of pumps, centrifugal and root. Root pumps are favored by Mercedes Benz. Gives an instant boost straight from idle. Supercharging suffers from drive train stress. The higher engine rev you go, almost 30% of the engine power is used to drive the supercharger.

 

Turbocharging is using the engine exhaust to drive a mechanical pressure pump to supply pressurized air to the engine. All turbochargers are centrifugal pumps. Turbocharger suffer from lag. Exhaust velocities must reach a speed to drive the pump. The bigger the turbo, the longer the lag.

 

Both pumps depends on compressor maps. A map that says the characteristics of the pump performance. The map looks like this.

 

Using your engine capacity, rev, temp, intercooler efficiency, ambient temp etc. You can plot every rev point on this map. These points should rest near the centre of the oval. You will plot the points of Flow on the X-Axis vs Boost on the Y-Axis.

 

The pressure ratio is easy to read. 1 is atmospheric, 2 is 1 BAR, 2.4 is 1.4 BAR.

 

Before you rush out there the buy the biggest MF***er turbo, you need to always calculate the proper turbo for your engine. It is very difficult to find an all rounder turbo. In my opinion, there is one. Garrett GT28RS.

 

To be cont'

[Maded]

Dude. great article...

 

Just one question. a supercharger takes up to 30% of the engine's power... but what the supercharger does is to somewhat increase the efficiency of the engine to produce an additional 50% output power resulting in a nett 20% gain (or so...)

 

So this is... something for nothing?

[Lordalfa]

It gets only worst if you go high up the rev. This means for high rev performance, a turbocharger is needed.

 

Superchargers, especially root pumps are very good for traffic to traffic torque. Instant response. Try a C200 and you will know why.

[Lordalfa]

Too tired to write more. Will continue. I touch more on turbochargers. How to calculate the Maps, boost pressure, intercooling, intercooler placement etc.

Edited March 10, 2005 by Lordalfa

[Decibel]

All this is off the top of your head?

[Jiayong]

Its been a long time since such good articles come along.

 

Do continue pls...very refreshing from the usual

 

"on the road incidents" that pple like to lamment about here.

[Lordalfa]

No. Learnings from mistakes, reading, talking people who turboed their cars.

[Lordalfa]

 

How turbochargers work?

 

This is a turbocharger.

 

The turbine is driven by exhaust gases which turn a compressor that sucks air and compresses it to be delivered to an engine.

 

Why is there turbo lag?

 

Some turbos even at idle, your turbine is being driven by exhaust gases. This means the compressor is spinning, but why isn't there boost?

 

1. The compressor wheel speed is still not fast enought for compression to take place.

 

2. You engine is demanding more air than what your compressor can deliver. This is the "vacuum" state that you see on your boost gauge. Even if you floor it to zero vacuum, you are not getting boost pressure because your compressor is not supplying boost yet, ie, compressor is not fast enough.

 

How do we get a turbo to fit my engine?

 

1. Well you get a pencil and paper, go back to school, learn thermodynamics and fluid mechanics to start with. On the final year take up airconditioning as your specialty.

 

2. Go to http://www.turbofast.com.au/turbomap.html

 

3. Key in the relevant data.

 

4. Flip the compressor maps to find a suitable turbo.

 

5. They have outdated turbos. If you want the latest GT28RS and see if it can fit, download the catalog from http://www.turbobygarrett.com/turbobygarre.../downloads.html Use the maps and plot your points.

 

6. The whole idea is to put most of your engine conditions as close to the inner oval. The ovals are efficiency of the compressor. Why efficiency? The more efficient the compressor is the less heat the compressor will generate. It is a myth, turbochargers are hot because of the exhaust. NOOOOOO! The compressed are is hot when the compressor is not operating at the efficient range. Compressing air and getting hot and not getting boost is adiabatic compression.

 

7. With point 6, that is why you need intercoolers to cool the charge after compression. As a comparison, without intercooler, you'll get about 100+*C of compressed charge. With an intercooler, it is about 70*C. Of course for intercoolers, bigger the better right? I'll touch on the next post. Intercooler placement. Top mount vs front mount vs water cooled.

[Ferrariz]

ya, very nice..

 

just when we were discussing about TC yesterday and this pops up..interesting :P

 

note : more interested in SC, if u can , please pop more SC details here.

[Throttleb]

He hasnt started yet.....

[Jiayong]

hee hee...think he was just warming up...doing some typing exercises...

[Eugh]

"6. The whole idea is to put most of your engine conditions as close to the inner oval. The ovals are efficiency of the compressor. Why efficiency? The more efficient the compressor is the less heat the compressor will generate. It is a myth, turbochargers are hot because of the exhaust. NOOOOOO! The compressed are is hot when the compressor is not operating at the efficient range. Compressing air and getting hot and not getting boost is adiabatic compression."

 

 

A bit confused by your point above - turbochargers are not hot because of the exhaust; they are hot because of the compressed air?

[Lordalfa]

Yes. 90% of the heat in turbos are from the compressor not the exhaust.

 

Your compressed charge exiting the compressor is about 130*C without passing the intercooler.

[En0203]

wow, another nice article after real NA performance!

 

MCF has been less informative until ur post surfaced. Thanks!

[Lifexpression]

turbocharged engines should be made standard in all cars.

[En0203]

turbocharged engines should be made standard in all cars

 

haha, not everybody needs it. even for NA car, some ppl don't rev beyond 4k rpm, and in the case of TC, turbo just won't spool up at low rpm. so IMO, supercharged should be made standard instead

 

then turbocharged for ppl who is power-hungry

[Genie47]

You will drive up fuel prices. Imagine whole of Singapore everyone uses only RON98. Remember, with FI, you need fuel with higher knock resistance. Gahment sure catch you by the balls and squeeze damn hard.

[Lifexpression]

well....turbocharged taxis in brunei....guess the what car is it?