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Daninplymouth

Fuel when lower compression

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Hi, just after opinions. I know as standard we should use 99ron fuel. Now if you forge the engine and drop the compression is it best to still run on this or would 97 be ok?

as I thought the higher rating was better due to the stock compression ratio, I just wondered what effect putting a slightly lower grade in would effect if lower compression but running more boost

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When one drops compression (usually because adding some forced induction of sorts), you still would be better off running better quality fuel due said FI, which with extra boosting blows in more air & fuel, "reverting compression change", to not knock much. Also boosting engine puts higher load/wear on it, more reasons to feed it quality fuel, to reduce knock.

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If you're boosting it, you'll still need want the higher ron fuel. It helps with detonation.

Your removing detonation risk by reducing compression ratio, but then you're increasing risk by boosting it.

If you can afford to boost, you can afford 99 ;)

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2 hours ago, Kaltorak said:

If you're boosting it, you'll still need want the higher ron fuel. It helps with detonation.

Your removing detonation risk by reducing compression ratio, but then you're increasing risk by boosting it.

If you can afford to boost, you can afford 99 ;)

Yeah I know that not the cost can get 97 less than a mile from my house whereas the 99 is a 15mile round trip.

I just weren’t sure if it would balance out on the poorer fuel with dropping the compression. Not forged yet, I was just thinking of the future and wasn’t sure what sort of impact it’d have

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The standard car is tuned for high octane fuel, and I saw a log here of knock events that showed that higher RON should result in fewer timing back-offs. In general, boost more than compensates for any drop in compression ratio. I would suggest that while going full 99 RON fuel and tuning to the max will give peak performance, a slightly less aggressive tune could allow you to run 97+ for greater versatility. You might lose out on say 10 Nm of torque, or a bit of peak output but being able to fill up more easily could improve your daily experience.

If you're building an engine, I'm sure you can dictate your objectives to a tuner. Some of the popular tuning packages set you up with a set of 4 maps anyway so you can have a bad fuel map for that trip to Anglesey. On several holidays I found myself forced to fuel up with 95 and I would have been mortified if I'd been running boost.

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18 hours ago, Daninplymouth said:

Yeah I know that not the cost can get 97 less than a mile from my house whereas the 99 is a 15mile round trip.

I just weren’t sure if it would balance out on the poorer fuel with dropping the compression. Not forged yet, I was just thinking of the future and wasn’t sure what sort of impact it’d have

Ahh gotcha. 1st speak to whoever is tuning it about your fuel situation.  Maybe they could do 2 maps, one that's more Conservative with ignition timing and maybe more Liberal with the waste gate, then you can pick the tune on the fuel you're running. 

The car will pull timing naturally if it detects knock /detonation, but it's better to prevent it before than after. 

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I have a "junk" tune for when I can't get good fuel. I've used it once in France on a long journey. 

Going out with the good fuel I got about 40mpg and the car felt great. On the way back I got 32 and it just didn't respond as well. Same roads, same speeds. But hey, it was safer right? 

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37 minutes ago, Kaltorak said:

I have a "junk" tune for when I can't get good fuel. I've used it once in France on a long journey. 

Going out with the good fuel I got about 40mpg and the car felt great. On the way back I got 32 and it just didn't respond as well. Same roads, same speeds. But hey, it was safer right? 

Wouldn’t be going junk fuel, as it’d still be super but BP ultimate is only 97ron. 
once upping the boost the car is capable of about 450bhp I was going to wind it back to 400bhp. Just wondered if I could hit 400 on 97ron, or would the different fuel make that much difference 

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Wouldn’t be going junk fuel, as it’d still be super but BP ultimate is only 97ron. 
once upping the boost the car is capable of about 450bhp I was going to wind it back to 400bhp. Just wondered if I could hit 400 on 97ron, or would the different fuel make that much difference 
Like others have said , you have 2 choices:

1. Ask you tuner to do 3 maps , 95 , 97 and 99 RON and use the right map based on fuel. A dyno run will show you the difference but I wouldn't expect a difference of more than 10 BHP from one tune to the other.

2. Carry an octane booster in the boot, Millers petrol power ecomax and use it to boost 97 to 99 Oct.

When going forged, the fuel will be my last worry. At such high power levels , you need to think of more supporting mods like , gearbox, Differential, fuel pump, injectors, clutch etc as stock components cannot go that far or will get worn very quickly.

Sent from my SM-G781B using Tapatalk

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