I agree. They switched the minimum rating to 87 on the 4 cylinder TSFI’s a few years ago. For the GLI/GTI, I’ve heard they put a note in the manual with an asterisk that says “advertised power number achieved on 93 Octane”. The Golf R I believe still says 91 minimum (thank god).
Mazda had to do some clever engineering to get those engines rated to run on 87 at all lol. They some trick with the exhaust gases to lower the temperature inside the combustion chamber and prevent detonation. The SkyActiv engines might be the highest compression engines currently produced that can run on 87. I bet there’s a website somewhere that tracks that.
Yeah I consider TDI’s to be enthusiast type cars in the North American market. Most people have no idea what they are. Mine was the Q7 with the 3.0. It was push button and you would depress the brake and press start and the glow plug light on the dash would illuminate from 0.5 to 2 seconds depending on temperature and then it would turn over.
I can see how you would think that, but not really. It’s more about the manufacturer goal. High performance engines are almost always going to be tuned for the highest octane available. This is so they can have the most aggressive timings. Forced induction engines most often require high octane fuel or will make significantly more power on higher octane fuel (assuming they have the appropriate tune).
Best example is the VW 2.0T EA888 engine. It is rated for 87 on VW cars but 91 on Audis and Porsches. Same engine, different tunes to meet the expectations of different customers.
Octane rating refers to the fuel’s resistance to detonation. There is no difference in power per unit volume in 85 vs 93 octane fuel. The salesman believes in a common misconception that higher octane means higher power, but this is not how fuel works. His “summer” comment likely was in reference to the fact that warmer air produces less power than colder air. Living in Phoenix where daytime temps over concrete in the mid 120’s is common, this can be a noticeable difference. He was saying to run higher octane to make up for the power loss.
What makes this comment hilariously wrong is that you would actually want to run higher octane in colder temperatures, not warmer. Hot air has the effect of increasing the density altitude, that is, it makes the air less dense. The less dense the air is, the less air is available for the engine which means it won’t be able to increase the fuel-to-air ratio high enough to knock anyway. This is why you can run lower octane fuel at very high altitudes, its common to see 83 octane pumps in the Rockies.
There are some engines which will make noticeably more power on higher octane but can run on lower octane. These are typically high performance turbo charged engines and the ECU’s are basically programmed to push timing and AFR as far as they can until the car begins to knock.
The Atlas VR6 is already running at an 11:1 compression ratio and is rated for 87 per VW. People have actually pulled the timing logs on the VR6 to check if the engine is able to identify 93 octane fuel and the answer is yes, it can, but the difference is maybe 5 horsepower in the best conditions, which is about what you’d expect given the engine’s characteristics.
Salesmen not knowing anything is not unique to EVs. I’ve purchased 5 Audis and 2 VWs from dealerships and with the exception of one guy (who was a specialist shop/dealer combo primarily dealing in VAG diesels) every time has had me giving the sales person a lecture on their own product.
Guy who I bought the VR6 Atlas from told me “I’d put premium fuel in it, especially in the summer”. Which is wrong on so many levels I didn’t even bother to correct him.
Once I was on a road trip and my A4 started knocking and the nearest Audi dealership was 200miles away, but the city I was in had a VW dealer. I had to argue with the front desk for like 15 minutes that the A4 had the same engine as half the cars on their lot before a mechanic came out and was like “yeah I can look at it” and ending up changing a leaking fuel injector seal because, shocking turn of events, they had the part number in stock.
We buy cars from them because the dealership lobby forces us to. I’d love to order direct from Audi’s website, but alas, I have to go talk to Chad for 3 hours instead.