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lower octane fuel??

97AutoXVette

Passed Driver's Ed
Currently running APR Stage 2+ setup with the following switchable tune settings (stock, 91 oct., 93 oct., and 100 octane) on my Mk6 Golf R.

I am curious if it would be safe to run with all of the stage 2 hardware in the "stock" tune setting, and run a lower octane fuel? Say 89, or even 87 octane? For some longer commutes/trips, I was thinking that I could get away with lower octane on the S2+ hardware setup on the stock tune and the car not have any knock/timing issues.

Open to thoughts and suggestions. Thanks!
 

joeyfrost

Ready to race!
Believe you can without an issue


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97AutoXVette

Passed Driver's Ed
Agreed.. if I can run the 91 octane file and still make approx. 350hp/350tq, I feel like the stock tune setting on 87 octane will still allow plenty of head-room before any engine knock given the improved exhaust/intake flow, etc.
 

GIACUser

Master Wallet Mechanic
Currently running APR Stage 2+ setup with the following switchable tune settings (stock, 91 oct., 93 oct., and 100 octane) on my Mk6 Golf R.

I am curious if it would be safe to run with all of the stage 2 hardware in the "stock" tune setting, and run a lower octane fuel? Say 89, or even 87 octane? For some longer commutes/trips, I was thinking that I could get away with lower octane on the S2+ hardware setup on the stock tune and the car not have any knock/timing issues.

Open to thoughts and suggestions. Thanks!

The ECU will handle the knock issues as they occur and they will. Severity and frequency will partially up to how hard you push the car combined with terrain (inclines), weather (hot) etc. The ECU can pull 12 degrees of timing which is a lot so you should be able to do what you want safely.
 

ben_m

Ready to race!
Currently running APR Stage 2+ setup with the following switchable tune settings (stock, 91 oct., 93 oct., and 100 octane) on my Mk6 Golf R.

I am curious if it would be safe to run with all of the stage 2 hardware in the "stock" tune setting, and run a lower octane fuel? Say 89, or even 87 octane? For some longer commutes/trips, I was thinking that I could get away with lower octane on the S2+ hardware setup on the stock tune and the car not have any knock/timing issues.

Open to thoughts and suggestions. Thanks!

You're looking to save like $3-4/fill up?? Doesn't seem worth the risk. Want to play, gotta pay.
 

torga

Autocross Champion
You're looking to save like $3-4/fill up?? Doesn't seem worth the risk. Want to play, gotta pay.
It's more like $7-9 per fill up (at least where I live), which comes out to $200-$500 of yearly savings, depending on driving style and mileage.
So I guess I can see why OP wants to save money. But at the same time, this is a Stage 2 Golf R, not a Corolla. Drive it like it's meant to be driven.
 

ben_m

Ready to race!
It's more like $7-9 per fill up (at least where I live), which comes out to $200-$500 of yearly savings, depending on driving style and mileage.
So I guess I can see why OP wants to save money. But at the same time, this is a Stage 2 Golf R, not a Corolla. Drive it like it's meant to be driven.

EXACTLY. Even if you don't want to drive aggressively all the time, no reason you have to neuter yourself all the time unless you want to wait for empty and then re-fill. Also, if he's looking to save $500 a 40K car isn't really the right choice....
 

torga

Autocross Champion
EXACTLY. Even if you don't want to drive aggressively all the time, no reason you have to neuter yourself all the time unless you want to wait for empty and then re-fill. Also, if he's looking to save $500 a 40K car isn't really the right choice....
Yup, if I had a 330whp/350wtq AWD beast, saving money at the pump would be the last thing on my mind.
 

TimS

Go Kart Newbie
Even the stock Golf R tune requires 91 octane. Don't run 87.

Also, the stage 2 hardware will cause issues with the stock tune.
 

97AutoXVette

Passed Driver's Ed
Even the stock Golf R tune requires 91 octane. Don't run 87.

Also, the stage 2 hardware will cause issues with the stock tune.

Any idea why stage 2 hardware can cause issues with a stock tune?? I’ve heard of the possibility of “overboost”??
 

brobst

Go Kart Champion
Any idea why stage 2 hardware can cause issues with a stock tune?? I’ve heard of the possibility of “overboost”??
It won't. The dp will flow more but the stock car will compensate. The stock tune isn't asking for more so the car will probably just run more efficiently to get requested power.
Experience, I ran dp on stock tune for a yr, no issues to performance.

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97AutoXVette

Passed Driver's Ed
It won't. The dp will flow more but the stock car will compensate. The stock tune isn't asking for more so the car will probably just run more efficiently to get requested power.
Experience, I ran dp on stock tune for a yr, no issues to performance.

I also have run my Stage 2+ car in the stock tune mode and saw no adverse effects at all.

Just for some additional thoughts/info:

On other platforms, there has been plenty of experimentation with improving flow in the engine, which ultimately reduces knock/detonation, and allows room for more timing advance, boost, etc.. I used to do a lot of this experimentation and tuning on supercharged platforms. The same is true (though not always) that if you improve the flow characteristics and don't try and increase boost or timing, you can essentially run less octane and not cause detrimental effects (depending on how close the original octane rating is/was to causing detonation and timing reduction in the first place).

That being said, I am well aware that our vehicles (in my case the Mk6 Golf R) require a minimum of 91 octane fuel, in stock trim.. Holding that constant, if I add a free flow exhaust, intake, etc. and don't change anything else, there should be more headroom from detonation for the same octane fuel. I would then assume that dropping down an octane point (or 2? 3? etc.) would still allow the engine in stock form to perform well at stock timing table settings and boost levels without causing any issues. That in fact is what I am curious about, and wondering if someone has tried this, recording any engine timing, etc.

I certainly am not doing this to try and save a ton of $$ over the long run (as I would rarely ever operate it with lower octane fuel, since I consistently run 93 octane). However, am very interested to know if I decide to fill the car up with say 89 octane for a long trip across the midwest, how would it do?? :)
 

TimS

Go Kart Newbie
Any idea why stage 2 hardware can cause issues with a stock tune?? I’ve heard of the possibility of “overboost”??

Overboost is rare, but you'll get funky O2 readings that can trip the check engine light and affect fuel economy.

On other platforms, there has been plenty of experimentation with improving flow in the engine, which ultimately reduces knock/detonation, and allows room for more timing advance, boost, etc.. I used to do a lot of this experimentation and tuning on supercharged platforms. The same is true (though not always) that if you improve the flow characteristics and don't try and increase boost or timing, you can essentially run less octane and not cause detrimental effects (depending on how close the original octane rating is/was to causing detonation and timing reduction in the first place).

Octane requirement is dictated mainly by cylinder pressures and timing curve; changing the intake and exhaust doesn't change either of those things (the valves are closed and the cylinder is sealed during the compression stroke), so required octane doesn't change. Even if lower temps mean it doesn't pull timing as much, the difference is nowhere near allowing 89 when 91 is required.

If you want to run lower octane, you'll need a thicker head gasket to reduce compression and have the timing recalibrated, but your fuel economy will still be in the toilet thanks to inefficient combustion.
 
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97AutoXVette

Passed Driver's Ed
Octane requirement is dictated mainly by cylinder pressures and timing curve; changing the intake and exhaust doesn't change either of those things (the valves are closed and the cylinder is sealed during the compression stroke), so required octane doesn't change. Even if lower temps mean it doesn't pull timing as much, the difference is nowhere near allowing 89 when 91 is required.

Great info. really appreciate it!
 
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