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Some of this week's Letters to AutoSpeed

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MPS Test?

I noticed that the Mazda 6 MPS is in showrooms now and was wondering if you planned to do a new car test on one? I'm planning on buying one and would greatly appreciate your opinion, as it is always unbiased and very thorough.


Looks like a very interesting car - we’ll see if we can arrange a test.

DFA on RX8 Turbo?

The Digital Fuel Adjuster (DFA) - will this work with the RX8 rotary engine? I have the GReddy turbo kit installed and am looking for an alternative to the eManage.


The DFA can be fitted to any car running a voltage outputting airflow meter. For your application it is worth noting that the DFA does not give separate control over ignition timing.

Prius Turbo Problem

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Your articles on Turbo'ing a Hybrid Prius are incredibly interesting. But it seems to me that you trying to fire 9mm bullet from 7.62mm barrel – the result could be devastating at any moment.

See, the Prius uses so-called power split continuously variable transmission. Power from the engine is split and directed by two ways - 80% to one element of a planetary gear set and the other 20% to the electric generator, which generates electricity which is consumed by the electric motor driving another element of same planetary gear. By varying the torque that the second electric motor applies to spider of planetary gear, you can vary infinitely gear ratio and even direction of the drive.

Now... The first electric motor simply could not produce enough electricity for the second motor to sustain proper gear ratio and transmit more engine torque to the wheels when you apply full throttle. Only at some marginal modes the system could tolerate this abuse and produce better result – in your case, it is better at keeping the battery fully charged. This transmission just could not transmit more power than it is designed for - at least without changing of electric motors for more powerful ones.

Andrey Levin

You’re right. If you haven’t already, have a read of The Story of Turbo'ing a Hybrid Prius, Part 5 under the heading ‘Performance”. As written, “the hybrid control system acts in such a way that the peak combined power of the electric motor and the petrol engine is not substantially increased. In other words, total peak power is not much changed over the best it could previously ever be.” However, real-world performance is improved across a range of driving because at full throttle, the power is always at its maximum possible output.

Water Spray Qs

I’m very impressed by your water injection kit (AutoSpeed Shop). Beats the crap out of the prices I’ve seen for some other systems and, as far as I can see, it is just as effective.

I have a question about it though. Were the tested flow rates (mentioned in Motor Speed Control Module - Part 3 - Water Injection) tested on a bench or against pressure as in a forced induction system? I will be installing the nozzle after the turbo so it will be fighting against 16+ psi. Should I pressurise the container to boost pressure so the electric motor doesn’t have to fight the boost or will the motor be fine by itself?

Morgan Cox

The testing was done on the bench and, yes, we would expect water flow to be reduced in a real-world application. Pressurising the water tank is a good idea (so long as the tank is strong enough to withstand this amount of internal pressure). But stick around for an even better water spray system using an ultra high pressure pump – you won’t believe what the pump is!

We Must have “Killed that Poor Car”...

Re Holden VZ SV6 Manual Test... My Holden VZ 6-speed gets 8.8 litres per hundred km - not 15. I have to drive it hard to get 12 – so you must have killed that poor car. After 3000km, the car got more power and by 10,000km... hold on! I have lined up with Fords - they are good, but far from the Holden this year. Yes, the redline is low – but if you need more get the SS.


Our 15 litres per 100 consumption was recorded with the air con pumping and in mainly urban conditions – as mentioned in the article. We didn’t kill the car but, yes, it was driven fairly hard – it is, after all, a performance model! We’ve also returned around 13 litres per 100km in the 175kW spec 6-speed One Tonner S in similar conditions. See Holden One Tonner S

Subie Turbo Clarifications #1

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Excellent article about the Second-hand Subie Turbos (Second-hand Subie Turbos) - I'd just like to add a couple of clarifications:

The following applies to the Generation 1 Legacy/Liberty - both Series 1 and Series 2 (facelift). The VF-8 was fitted to all Legacy RS sedans (manual only, no auto option). The smaller VF-10 was fitted to Legacy GT wagons (auto) and Legacy GT sedans (auto only, no manual option), but I'm unsure if it was teamed up with the (rare) manual Legacy GT wagon or if Subaru used the VF-8. The VF-12 was fitted to the Legacy RS-RA, and Liberty RS, but from what I understand it's almost identical in size to the VF-8, to the point where it's not even considered an upgrade going from VF-8 to VF-12 (unless you get a free one!)

If anyone wants to chat further about this, join the RS Liberty Club forums at Hope that's useful - keep up the great work!

Rob Haylock

Subie Turbo Clarifications #2

Just a few quick notes about the Second-hand Subie Turbos - (Second-hand Subie Turbos). The Forester GT (from 97-02) was fitted with a TF035 not a TD35HM. Also, you can get both inlet and exhaust gaskets for under $30 - see We are also starting to see the VF37, 38 and 39s here. And you can get a TD04L in good condition for $250 or less these days.

Brent Muldoon

Exhausting Info

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I have noticed it has been some time since you have done any flow tests on extractors, headers, catalytic converters - exhaust products made by performance specialists through to production line equipment.

I have a ‘96 V8 Ford Fairlane and they all tell me the factory exhaust is crap - that it has way too much restriction starting from the factory headers. Some people even say that the factory VR-VS V6 and V8 cats flow better than the high-flow cats you pay twice the money for. But I can not find any real evidence as such.

Len Hutchinson

Our trusted flowbench operator isn’t too keen on fitting second-hand exhaust components to his flow bench – carbon pieces can fall into the machine and cause damage. We suggest first finding out how restrictive the existing exhaust system is and then identifying the sections of greatest restriction. See Pressure Gauges and Making Power under the heading ‘Exhaust’ for details on this. We’ve put this approach into action in the article Lung Transplant. A Holden V6/V8 cat converter is a highly cost-effective unit but a true high-flow cat can flow better. In your case (with a V8) it would be easy to run one of these cats for each bank of cylinders – this will give very little restriction. But, then, you don’t know how bad the factory cats are – time to get measuring!

Unit Muddle

With all the various units for economy in the Prius Turbo Pt 5 article (The Story of Turbo'ing a Hybrid Prius, Part 5) one of them was bound to be wrong!

You say "5.5 litres/100 km [18.2 litres/100km, 51.4 miles per imperial gallon, 42.8 US miles per gallon] "

Should that be 18.2 km/L?

Awesome article by the way. Modding a hybrid car took some guts and the techniques displayed show that traditional modding will be alive and well even with one of the most complicated ECUs on the market today.

Richard Laxton

Well spotted – 18.2 litres per 100km wouldn’t be too good from a hybrid!

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