If I could get Costco 91 for the same price as 87 here, that's all I'd run. (our Costco doesn't sell gas)
If you're worried about carbon build-up, look into RLI (Renewable Lubricants Inc) Bio-Plus
I run it at ~1oz per tank.
https://renewablelube.com/files/3614/4779/7630/2I-Bio-Plus_Injector_Cleaner_Gas_Conditioner.pdf
https://www.amazon.com/Renewable-Lubrica...A0J8HY0A4FQXAWS
It will last tens of thousands of miles, at the maintenance treat rate. It was recommended in conjunction with RLI oil on the older TFSI 2.0 Audi/VW engines that carbon'd up badly.
We still don't know if these new engines will have carbon issues, so I'm being proactive in running this stuff. I also will not feel the need to spend any cash on techron/regane with continual use of RLI, which runs me about $.25/tank. I'd like to get 150k miles out of my car, so I'm taking the extra step (also first new car).
I also run LC20 in the oil. Exceeding EPA hwy mileage, so something must be right.
Which octane for my situation? A carbon conundrum
- Thread starter TurboDieselPoint
- Start date
- Status
Originally Posted By: Cujet
For our discussion, a modern direct injected, turbocharged car will perform almost exactly as well at the top of Pikes Peak, as it does at sea level. The boost level is an absolute measurement, not a differential with the outside air pressure.
Yes, at extreme elevations, the turbocharger has to spin faster to achieve a given manifold pressure. However, from a drivers point of view, this is not particularly problematic, other than the driver may notice slightly increased turbo lag time.
Originally Posted By: TurboDieselPoint
Thanks for the responses and the warm welcome, everyone! I appreciate it!
I forgot to say earlier: I have read on VW Vortex that some members think the engine (1.8 TSI Gen 3) in my car will not advance timing to take advantage of premium. It simply retards timing if it needs to. I'm not sure if this is precisely true or if it changes things regarding my concern, but I thought I'd at least mention it.
Nevertheless, it sounds like I don't have to worry about additional in-cylinder carbon buildup from an incomplete burn of 91 octane gasoline instead of the unavailable-to-me 87 octane fuel.
When the car arrives, I'll experiment and try a few tanks of pure 88 and pure 91 octane to see which I like better. However, I know I will like the Costco station better and their 91 actually tends to be the same price or cheaper than 88 elsewhere.
TurboDieselPoint
Originally Posted By: y_p_w
Just to clarify, I get that maximum boost is regulated mostly through the waste gate and should hit an absolute max pressure that's regulated. At higher altitude this is probably going to require more work (or higher revs) to reach the pressure, but it should reach the specified pressure. However, the engine is not solely being fed by the boost pressure, so a lower atmospheric pressure should mean that there's still lower performance at higher altitude compared to being at sea level.
I've driven a turbo car at 8000 ft elevation, and there was a noticeable loss in power. Perhaps not as bad as when I drove a normally aspirated engine car though.
Last edited:
regular gas is fine for your engine unless you get it tuned for a higher octane gas.
if you are worried about carbon build-up on the valves just take it out for some spirited driving and keep the
RPMs high for 10 minutes or so to burn off the build on the valves
or you can use some intake cleaner spray while you are running the engine to remove
any build up you might have.
Originally Posted By: minis
regular gas is fine for your engine unless you get it tuned for a higher octane gas.
You can read a bunch of threads on this, but still not have a definitive answer
golfmk7
mwerks
Also the VW official numbers have an "*" which specifies 91 octane was used to achieve the posted numbers. Funny, as their numbers are under-reported, so they didn't need to put in premium to achieve their claims.
The timing did not increase any when i added 91 octane to my little 1.4L TSI according to the ROSS-tech software
and i think his should be the same but will not know 100% until he can connect his car
to some type of realtime monitoring software
Originally Posted By: surfstar
If I could get Costco 91 for the same price as 87 here, that's all I'd run. (our Costco doesn't sell gas)
If you're worried about carbon build-up, look into RLI (Renewable Lubricants Inc) Bio-Plus
I run it at ~1oz per tank.
https://renewablelube.com/files/3614/4779/7630/2I-Bio-Plus_Injector_Cleaner_Gas_Conditioner.pdf
https://www.amazon.com/Renewable-Lubrica...A0J8HY0A4FQXAWS
It will last tens of thousands of miles, at the maintenance treat rate. It was recommended in conjunction with RLI oil on the older TFSI 2.0 Audi/VW engines that carbon'd up badly.
We still don't know if these new engines will have carbon issues, so I'm being proactive in running this stuff. I also will not feel the need to spend any cash on techron/regane with continual use of RLI, which runs me about $.25/tank. I'd like to get 150k miles out of my car, so I'm taking the extra step (also first new car).
I also run LC20 in the oil. Exceeding EPA hwy mileage, so something must be right.
Quote:
where I live all regular grade gas sold at the pumps is 86 octane, not 87, due to the altitude (3300 feet above sea level).
Quote:
burning 91 all the time is that I've heard it might cause carbon buildup
Originally Posted By: Ken2
Quote:
where I live all regular grade gas sold at the pumps is 86 octane, not 87, due to the altitude (3300 feet above sea level).
Quote:
burning 91 all the time is that I've heard it might cause carbon buildup
Firstly, I want to add, I totally respect the details provided by knowledgable & experienced members in this post.
My daughter has a 2014 Jetta 1.8T, so I've read quite a bit on this engine before, and after she, I mean, I purchased it for her.
If you look at the times this car puts down,and rwhp measurements, it looks like it is putting out closer to 190 hp in stock form.
Every turbo I have read about increases power if premium fuel is used-----except this 1.8-----.
Someone here posted correctly, in this engine ECU can only pull timing from base map--not increase timing over base.
It has been such a great little engine/car, my son is thinking of getting one next month.
Steve
I can't wait till she gets tired of the car---I'll get my hands on it and add a Stage II 93 octane tune & other mods to gain an easy dyno-proven 100 hp over stock----> talk about a sleeper........
It's hard to believe that one octane point (87 to 86) is going to cause serious issues. OK there's a strict order for 87 minimum. Remember that a margin of error is always built into consumer products. Yes the engine will pull a bit of timing, as designed, but the OP doesn't care about maximum power anyway. I always run the recommended fuel grade in all my vehicles and they still ping a bit here and there, once in a while. Occasional brief pinging is normal with modern ignition systems, also modern engines run at higher temperatures for efficiency. Sustained pinging, that is a problem.
Would a major manufacturer like VW release an engine to the public, knowing that 86 octane fuel is widely available to the intended user, and think that no owner ever will inadvertently buy it? Are they going to mass produce an engine for the public that is tuned to the very edge of explosion? Who knows, with all the recent nonsense from VW leadership, maybe they would.
I would at least try 1/2 tank of regular 86, drive it moderately and see how it does. If the drive is not to your liking, then use higher octane. If you are driving aggressively, you should buy premium 91+ anyway.
It is nice when there is a mid grade between 87 and 91. Some places do not have that, but many do. I would tend to go with a 89 octane in a turbocharged setup that said 87 was fine. Jumping to 91 is a hefty cost over the 10 cent jump from 87 to 89 in my area.
Originally Posted By: TurboDieselPoint
First off, hello Bob is the oil guy forum! I'm very excited to be a new member of this knowledgeable community! I've browsed here from time to time, reading topics topics discussing motor oil or small lawn equipment engines. Now I am here to seek your advice.
I am about to get my hands on a brand new 2017 VW Passat with the 1.8 TSI which has a turbocharged, direct-injection 4-cylinder (compression ratio 9.6:1). Having been in the diesel game for years without a gasoline car, I want to make sure I'm not going to screw up and use the wrong grade of gasoline in my new car.
VW states the car should be used with regular gas having a minimum octane of 87. No matter what, never ever go lower than 87, they say! Additionally, VW gives no recommendation or implies no gain for using higher than 87 except for in one discreet location: their website's spec sheet for the engine states that the maximum 170 horsepower output was "achieved using premium fuel," whatever that means. Can the 170 HP be achieved with regular,too...who knows? I don't really care either.
What does bother me is that where I live all regular grade gas sold at the pumps is 86 octane, not 87, due to the altitude (3300 feet above sea level). Where I want to fill (Costco--clean pumps, cheap, fresh fuel, and Top Tier!) the only grades offered are 86 octane and 91 octane.
Since I wouldn't want to violate the octane requirements for my new turbo VW, I see three different options:
1. Fill with 91 octane
2. Fill 20% 91 octane followed by 80% 86 octane with each fill-up
3. Abandon Costco and buy mid-grade 88 octane elsewhere
I would prefer option #1 since I trust Costco and mixing grades of gas sounds like a pain. Plus, I'm not sure I could achieve a homogeneous mixture of 86 and 91 in the tank every time anyways. This (maybe?) could cause troubles for the car if it briefly ingests small, unmixed portions of 86 when it wasn't expecting it. I know the knock sensor would react and pull timing...but that is a reaction to knock or detonation, not absolute prevention of it!
The only concern I have with burning 91 all the time is that I've heard it might cause carbon buildup inside engines not intended for premium, which is something I do NOT want to have happen. If I burned 91 for the life of this car, would the engine likely develop abnormal in-cylinder carbon deposits?
Thanks,
TurboDieselPoint
- Status
