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Discussion Starter · #1 ·
On my old 2.3 turbo, it used to run less well on Optimax (less smooth, less boost) but get better mpg by about 10%.

On my new 2.3 turbo, there is no noticeable difference in performance, or in fuel consumption when running Optimax vs. standard unleaded!

Both of these behaviours seem odd. Does anyone else see this (either one), or can anyone explain it?

Ta
 

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Try resetting ECu with the old Fuse 9 trick/ diconnect battery 20 mins. Then do a couple of adaptation runs as per Billj's website.

I can always tell the difference on mine, especially with low speed pickup.
Trouble is I have to go 3 miles out of my way to the nearest Shell station to get the good stuff!
 

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JohnCC, I can't tell any real performance difference in my 2.3 FPT Auto. I presume this is due to the restricted boost of the auto, i.e. anything over 95 RON is a waste of time, in most temperatures. My neighbour with a 225 bhp Audi Titty does not notice any difference either.

Strange old world eh?
 

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My 1996 aero ran like a dog on 95Ron - boost retarded all over the place. Much smoother and noticeably quicker on Optimax, post adaptation run. - Not the 'power' of the fuel but the fact it'll run full boost. Didn't analyse mpg much but I now get 30-35mpg (real)

Note: The aero is the only 9k model (I think) to recommend only 98Ron fuel - so it must need it due to the slightly increased boost. I think normal FPTs are less affected and LPTs unaffected(?)
As for the Audi's - the 1.8T 225 models recommend only 98Ron, but I believe that they deliver almost identical perfomance on 95Ron... can't say that for the last Toyota turbo I had...think they were brought up on that 100Ron stuff!
 

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my regular 2.3 FPT ('96 Auto) runs very much noticeably better on Optimax than on standard '95. You really notice it between about 20 and 50mph. If you floor it at 30, but not quite into kickdown, optimax still gives you a hell of a kick in the backside, 95 doesn't.

Also I get about 2-4mpg more out of optimax on average.

Funny old world eh?!
 

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My local Garage sells both unleaded and Super Unleaded (at a premium of course) with a 98 ron - is Optimax rated at more than 98 ron? i Know a colleague at works has a new Audi A3 with the new 1.6 FSI engine which is meant to run purely on Optimax to gain the higher MPG around town and give you the acceleration when required. He reports that the FSI engine is impressive for a 1.6 - didnt Saab investigate a similar engine a couple of years ago, if I remember they were investigating a small capacity high output engine of about 1.4 litres with the performance of a 2.0 Turbo or am i going mad!!
 

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there are many more reasons to using a good quailty fuel, other than more power, supermarkets for instance buy fuel on the spot market from many different oil companies, which in turn have many different qualities.
i always try to use optimax as it has been shown to be one of the best all round fuels available.
 

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Originally posted by Aero Nutter:
[qb]didnt Saab investigate a similar engine a couple of years ago, if I remember they were investigating a small capacity high output engine of about 1.4 litres with the performance of a 2.0 Turbo or am i going mad!! [/qb][/b]
I remember reading about a 1.6 variable compression engine that Saab were working on that was supposed to develop over 200 bhp. Saw a picture and it looked very complicated
 

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Saabs development engine had a crankcase which 'hinged' at on side to allow it to become longer/shorter . As I understand it this varied the swept volume/compression ratio of the engine & when combined with clever ECU /turbo management systems could produce high power output from a small engine.

Think one of the problems was produce a flexible seal between the moving crankcase parts that would have a reasonable lifespan

Not sure if I like the idea of having a crankcase in two bits with a bit of neoprene in the middle.
 

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Discussion Starter · #13 ·
Someone at work showed me about a year ago an article in Scientific American or similar, about a new design on variable compression engines.

It was a brilliantly simple mechanical design, which did away with the need for a hinged cylinder head.

I've found what I think is the design discussed here.

Click for bigger image
 
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