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Discussion Starter · #1 ·
There has been a lot of chat about people wanting to change turbo to achieve larger power output, but there seems to be no mention of hybrids.

Turbo Technics in IMO are the best in the business and I am sure they could produce one hell of an Evo hybrid to what ever spec was needed.

Just a thought, and probably a lot cheaper than a new unit.


Discussion Starter · #2 ·
I hate those words - invented to make people think they were buying something special.

A hybrid is just built up from the turbo manufacturers parts bins - occasionaly with a bit of extra machining here and there to make them fit.

That is exactly what the engineers intend when they design all the bits to be mix and match in the first place.

Problem with evo 4,5,6,7 is the turbo spins anticlockwise (not clockwise as with all other turbos) so it's kinda tricky to find bigger compressor wheels than the 'big 16g'.

IMHO TT are .................

Not a problem for evo 1-3 , loads of hybrids are already available.

Discussion Starter · #4 ·
You really need a completely different blower;
if you want BIG power, you get BIG lag,
barsterd laws of physics............

Personally, the stock turbo IMHO can run near 400bhp with
bo11ox all lag......thats gotta be enough for most surely ? ROFL!


Discussion Starter · #5 ·
380bhp is good, but I'm more of a torque proponent myself :)

Is there a difference between tuning for bhp and tuning for torque? The figures I've seen tend to balance one against the other for a particular turbo, ie (made up figures 'cos I can't remember ;)) 380bhp-280lb/ft vs. 340bhp-310lb/ft from the oem td05. Rpm for max torque varied between the 2 as well.

Dumbass newbie question #2: charge airflow being the same, is a big turbo at lower boost better than a small turbo at higher boost ie. less stressful to the other engine parts?

There'll be a difference in lag (since a larger turbo has more inertial mass and will take longer to spool up), and possibly a charge air temp difference, but being unfamiliar with the physics I can't work out which would be safer/more efficient.

Any replies greatly appreciated :)


Discussion Starter · #6 ·
hi derek
big turbo same boost as the small turbo should be safer from the inlet charges point of view only.

the way i think about it an engine pushing 300 bhp is going to be safer than an engine pushing 350bhp. the more power the engine is producing the more wear and tear.


Discussion Starter · #7 ·
Ummm - sorry about the big reply - got a bit carried away......

There is a difference between tuning for torque and tuning for bhp.

Torque and power are essentially one in the same from an engineer’s point of view.
Torque is just power (energy produced per second) at a particular rotational speed.

Power |EQU| 2 x 3.14159 x Torque x rpm (P in kW and T in Nm)

So high torque at a particular rpm is also high power at that particular engine speed.
Quoting torque figures without an engine speed is pretty meaningless.
What you get accelerating you all depends on the gearing anyway.
Designing cars is a compromise between engine power/speed and gear selection.

Forget the turbo for the moment....
Tuning engines is all about air flow at various engine speeds. Air and fuel burn in an almost fixed ratio to give a fixed amount of energy. The more air you can burn ... the more energy you can have |EQU| more power.
A car engine is like an air pump – if you span it from the crank it would pump air in and out dependant on the speed you spin it and the displacement of the cylinders. The efficiency of this pump varies with speed – poor at very low speed – getting better and rising to a maximum at middle speeds and tailing off again at high speeds. To tune for torque you have to maximise the maximum efficiency of the pump at the middle speed range.
To tune for power you have to try and improve the upper speed range efficiency and increase the engine speed as much as possible – hence bike and F1 engine rev like crazy. Any given mechanical engine design has a given speed for which cylinder filling efficiency is at a maximum – this is where the maximum torque is produced.

Tuning for torque involves playing with cam timimg, port shape, inlet tract shape /length(long), inlet plenum volume, valve diameter(small), exhaust header length, exhaust diameter, ignition timing, etc. to maximise the filling of the cylinder at mid range speeds. Natural oscillations of the inflowing air can be harnessed by inlet tuning to pulse the air at exactly the right speed to help fill the cylinders to their maximum. Maximising exhaust scavenging by keeping exhaust air velocity high (correct diameter, free flow) and header length tuning will increase the overall flow efficiency and therefore torque.

Tuning for power involves similar processes but you are trying to squeeze as much air flow through the engine as possible at all costs – so lots of rpm, big valves, short inlet tracts, big plenum, big exhaust diameter.

The problem is that the requirements for maximum torque and maximum power are not the same. Long/Short inlet tracts, small/big valves, exhausts etc. Manufacturers balance the two against each other – especially when designing an engine for a group A rally car. The evo engine is designed for the group A restrictor – 300bhp worth of air flow. They then try and achieve this air flow from 0 to 8000rpm.

Time to add the turbo......
The basic theory of forced induction is that an engine breathing from an atmosphere with twice the density has twice the power of an engine breathing from the standard earth

Normal atmosphere at 1 bar |EQU|140hp.
Turbo at 1 bar |PLS| 1bar |EQU| 280hp
Turbo at 1 bar |PLS| 2 bar |EQU|420hp

Problem is that the turbo compressor is not 100% efficient and heats up the air. As the air heats up it expands so hot air at 1 bar boost doesn’t have the density and oxygen content of the same volume of air at atmospheric temperature. Intercooling reduces the temperature as close back to atmospheric conditions as possible and increases the air density.

Turbo design is as in all things a compromise. The engineer must juggle the air flow verses the efficiency of compression (and hence outlet air temperature) at various turbo shaft apeeds. Once you fix the maximum air flow an engine will see (max hp) you can begin to choose your turbo.

The evo turbo is sized for Group A rally requirements – and is designed to be as efficient as possible across it’s whole operating range. The trick to Group A rally cars is to maximise the air mass flow across the full engine rev range. The turbo can easily achieve this by boosting very high throughout the low,mid range and then reducing at high rpms. In a perfect world it would be possible to flow 300bhp worth of air from 0 to 8000rpm with a correspondingly crazy torque curve. In reality the turbo cannot create enough boost till the engine has a couple of thousand rpm – even with anti-lag. This is the ultimate in tuning for torque – as air flow is limited by the restrictor you try and create your 300hp as low down the rev range as possible and hold it all the way to the rev limiter. The turbo is the tool to enable this.

The Big/Small turbo question – at a given boost pressure and air flow a turbo compressor has a given efficiency. As a rule the smaller the turbo the more efficient and the lower the charge air temperature exiting the turbo. This is not always the case as turbo design has improved vastly with computer simulation techniques over recent years. The only real way to tell is to look at the compressor map and see what th efficiency is at your particular operating conditions. Some big turbos are very efficient - some are terrible - you need the compressor map to be sure.

On two engine running at the same boost and rpm , one with big turbo, one with small, aside from lag differences and compressor efficiency – everything else will be the same. It is the boost and rpm which set the stresses on the engine. The only reason for running a big turbo is that you want greater maximum air flow – ie. more power than the small turbo can produce.

Discussion Starter · #10 ·
lightspeed, that was the most interesting thing i have ever read on here, thank you...

would you be able to answer me: i am running 351bhp and 315 of torque, i am fitting at boost controller to sort out my torque curve (see, would i be better to increase the boost pressure in the areas where the torque dips (between 3000-4500 revs) to bring the power in smoothly and then drop it off again for safety, or i am reading your reply wrong??


Discussion Starter · #11 ·
You got it.

But gently does it.

If you up the boost too much without ignition timing control you run the risk of detonation.
Programmable ecu or Apex'i SITC required.

Discussion Starter · #12 ·
i have a sports ecu and a blitz sbc-id (tuesday), would this allow higher boost low down (like the extreme) safely, or would a fully mappable ecu be the only one up to the job.

when you say gently does it, what sort of parameters would you suggest??

thanks again

Discussion Starter · #13 ·
Sports ecu should do - but no-one in the English speaking world really seems to know exactly what is different in the mapping.

I don't know what boost level you are running at this engine speed. 315ft-lbs torque must be around 1.6 bar.
That's 425Nm - WRC cars are only around 500Nm.

For reliability I wouldn't run a road car over 1.6 bar. Possibly less - 1.4.
Too many evos sh*tting themselves.

Do you run a boost gauge? Does it fluctuate in this rev range or hold steady.
A drop of 0.1bar would cause this drop - alternatively - slipping on the RR rollers.
If it's a noticeable wobble in power delivery then tune it out with the boost controller - otherwise don't worry.
I think you're at the limits already for road car reliability.

Discussion Starter · #14 ·
i have a guage, and the boost is set to 1.3-1.4 with a restrictor (at the moment), it spikes to 1.5 (or more seeing as the HKS guage stops at 1.5).

i will see if it wobbles tonight.

thanks for you help


Discussion Starter · #15 ·
another question (sorry):

i have done the arp bolts, but would you recommend a uprated fuel pump at this level of performance, i know i keep asking this question all over the place, but the reply's are always different, what is your opinion

thanks again


Discussion Starter · #16 ·

Get your tuner to put a tester kit on the fuel pump to see how much it flows. To run 1,5 or 1,6 bars you should be flowing 4,5 bars at idle and 6 to 6,2 bars fuel pressure at max boost. If your OEM pump cant do it, rewire it. If that still doesnt flow enough, buy a pump.
I just bought a pump and regulator to be safe...

If you can, get a AVC-R instead of Blitz. Same functions but better screen. You cant see the Blitz display as well as the AVC-R. It dims nighttime too. Other than that. same thing. You can set boost, duty (selenoid opening time), overboost etc. Gear dependant.

Discussion Starter · #17 ·
Standard pump on a 6 is 150lph - but do the re-wire as this is at full voltage. (BTW lph|EQU|litres per hour)
Even 400hp is little over 130 lph so the stock pump is within range ( a bit marginal at this level).

Evo 4 was only 120lph - so needs upgrading above 320hp.
Evo 2-3 were only 100lph so need almost immediate upgrade with any tuning.
Evo 1 is only 80 lph - pass me the spanners!

Discussion Starter · #18 ·
Impressive degree of patience 2 type that lot out m8 :)

Just a couple of points 2 fill the thread out ,

Stress and reliability , when engines r modified 2 develop more power , heat and larger mechanical forces r 2 byproducts. Without attention , as power increases these 2 factors will reduce reliability over time and up 2 a certain point the reduction in reliability will not b noticed b4 1/ the owner sells the car , or 2/ something fails.
So minimise temperature increases and contain mechanical forces. That means bigger water and oil radiators , and tougher bolts and internals.

I reckon that up2 about 400 bhp and lbsft , an Evo engine will last an acceptable time without 2 much work , certainly pistons and rods etc seem 2 b up2 it , and except 4 track days the water and oil rads r ok 2.
Beyond this more attention is required 2 prevent premature failure.

The above assumes the engine is set up correctly as far as fueling , timing , boost control etc r concerned.
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