High Compression GDI Engines With 87 Octane ?

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ChrisD46

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I believe my Hyundai GDI Sonata 2.4L non-turbo has a compression ratio of 13:1 ... Makes me wonder how on earth Hyundai engineers can make 87 octane work in such a high compression engine ?
Also , even though 87 octane or higher is recommended in the OM - how would you tell what the best octane is for this engine ?
 
Well and running compression can be less than static/ theoretical once you add valve overlap and EGR into the mix.
 
Also employ variation of traditional Otto cycle which can lower effective cylinder pressure. Plus Stratified charge capability to improve flame front. My Jetta 1.4turbo has over 1 atm boost and 87 octane. It does like a little above that for low speed drivability, but nowhere near 91 or 93.

I mix in about 2 gallons of premium with a 10 gallon tank to good effect. More than that, the engine runs worse.
 
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The auto makers gotta make it work on the cheapest gas you can buy at the pump. You can make some vehicles and tune them for high octane like a Corvette, WRX, GTI, Audi A4, Focus ST.. where the owners that buy them new wont cheap out using 87 octane. Good luck selling a non sporting version of a everyday vehicle to Joe public that calls for premium.

The auto makers hate 87 octane by the way.

Yes, most vehicles you can buy new today are designed to run perfectly safe and wont see much if any benefit if running higher octane gasoline.

However, the auto makers have engines in skunkworks that cant survive on 87 octane and they cant risk Cheap Joe filling his new 2025 Accord, Camry, Jetta, F150, Tacoma??? with 87 octane.

The future of the gasoline engine depends on higher octane gasoline.
Years ago the future of the diesel engine being around mandated ultra low sulfur diesel.

https://www.autonews.com/article/20...o-industry-lobbies-for-95-as-new-regular

https://autoweek.com/article/car-news/battle-octane-95-might-be-new-standard

https://www.thetruthaboutcars.com/2018/04/premium-new-regular/
 
ChrisD46
My theory is that the fuel octane has more to do with LSPI than any oil. Could the blowing of engines have to do with fuel choice? I think so. Knock sensors, computer controlled timing and lugging the engine all factor in. We ran 93 octane in our ‘13 KIA Optima and we run 93 octane in our ‘17 Escape and ‘19 Tiguan. The extra cost of fuel beats the cost of a new engine.
 
Ford's 3.5 direct injection twin turbo runs perfectly fine with 87 in over a million F150s towing thousands of pounds of trailers. It will adjust for higher octane, but it's not necessary. How many fleet trucks never see anything but 87? Most, I'm sure.
 
Originally Posted by skyactiv
Good luck selling a non sporting version of a everyday vehicle to Joe public that calls for premium.


Smart. The buck or two more per fill up never bothered me.
 
Think I read where most turbo GDI's when under boost have an effective compression ratio of 16:1 give or take a click or two, and most of them are allowed to run 87. Suppose it's all in the engine management setup.
 
a lot of bull as 93 oct in Pa is at least 60 cents more + worse in many states! DI allows lower octane to work with higher compression as it cools the burn by squirting fuel directly into the combustion chamber BUT port injection works better at times + it cleans the intake valve to cut carbon deposits that are costly to remove. the bottom line is actual cylinder pressure thats effected by many things. in the end big $$$$ rules as always!!
 
With a normal engine the fuel is sucked into the cylinder. If for some reason there is a hot spot or too much compression it will pre detonate. Your gdi engine only has air in the cylinder untill fuel is injected in.
 
My take: I run premium in all my Ecoboost engines just because of the hp per cubic inch ratio. Hey that's just me. And they do run better with higher octane fuels, but it is comforting to know that if 87 is all you can get, ‘ol Betsy will be fine. Was visiting my dad during one of Houston's hurricanes and all that was available was 87. Not a problem. But when I finally got some 91 back in it you could tell the difference.
 
I thought the reason was, the fuel can't pre-ignite if its not there. Doesn't GDI inject just before top dead center?
 
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Originally Posted by MParr
ChrisD46
My theory is that the fuel octane has more to do with LSPI than any oil. Could the blowing of engines have to do with fuel choice? I think so. Knock sensors, computer controlled timing and lugging the engine all factor in. We ran 93 octane in our ‘13 KIA Optima and we run 93 octane in our ‘17 Escape and ‘19 Tiguan. The extra cost of fuel beats the cost of a new engine.


I can't comment on the other two, but my parents had a 2.0L Escape. The mileage increase from the premium fuel made it slightly cheaper to run. As in cents per hundreds of miles cheaper, but it wasn't more expensive.
 
Originally Posted by ChrisD46
I believe my Hyundai GDI Sonata 2.4L non-turbo has a compression ratio of 13:1 ... Makes me wonder how on earth Hyundai engineers can make 87 octane work in such a high compression engine ?
Also , even though 87 octane or higher is recommended in the OM - how would you tell what the best octane is for this engine ?

Is your Sonata flex fuel?
You will get a big horse power boost from E30 or even E85. Considering that direct injection engines like the cooling effect of ethanol and the high oxygen content plus the major timing advance allowed by the very high octane in such a high compression engine, your fuel mileage loss from the lower btu content of ethanol may not be as bad.
 
Originally Posted by Miller88
Originally Posted by MParr
ChrisD46
My theory is that the fuel octane has more to do with LSPI than any oil. Could the blowing of engines have to do with fuel choice? I think so. Knock sensors, computer controlled timing and lugging the engine all factor in. We ran 93 octane in our ‘13 KIA Optima and we run 93 octane in our ‘17 Escape and ‘19 Tiguan. The extra cost of fuel beats the cost of a new engine.


I can't comment on the other two, but my parents had a 2.0L Escape. The mileage increase from the premium fuel made it slightly cheaper to run. As in cents per hundreds of miles cheaper, but it wasn't more expensive.

Premium 93 around here is $0.60 above 87. Even 89 is $0.40 above 87. 87 was $2.549 today.
 
Originally Posted by skyactiv
The auto makers gotta make it work on the cheapest gas you can buy at the pump. You can make some vehicles and tune them for high octane like a Corvette, WRX, GTI, Audi A4, Focus ST.. where the owners that buy them new wont cheap out using 87 octane. Good luck selling a non sporting version of a everyday vehicle to Joe public that calls for premium.

The auto makers hate 87 octane by the way.

Yes, most vehicles you can buy new today are designed to run perfectly safe and wont see much if any benefit if running higher octane gasoline.

However, the auto makers have engines in skunkworks that cant survive on 87 octane and they cant risk Cheap Joe filling his new 2025 Accord, Camry, Jetta, F150, Tacoma??? with 87 octane.

The future of the gasoline engine depends on higher octane gasoline.
Years ago the future of the diesel engine being around mandated ultra low sulfur diesel.

https://www.autonews.com/article/20...o-industry-lobbies-for-95-as-new-regular

https://autoweek.com/article/car-news/battle-octane-95-might-be-new-standard

https://www.thetruthaboutcars.com/2018/04/premium-new-regular/






Great post here ^^^^^^

Exactly right in my opinion...

My step father who worked at the local refinery told me about low sulfur diesel well over 10 years ago.... And in fact he told me about lower sulfur gasolines has well... Both of those being being done helped get gas and diesel prices even higher.
 
5 years 71000 miles never had a lick of trouble on my 13 GLS with regular. The only big thing was it's fuel mileage suddenly dropped right at the end . I suspected that you be the valves starting to crust up but ditched it before needing to find out. I doubt that hi test is going to matter either way with that. Catch can and a prayer book highly recommended for those engines.....every little bit helps
 
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