Herman and Operation 30MPG

Post by **Rattnalle** » 13 Mar 2018, 12:08

The ecu is always adjusting for pre ignition regardless of fuel. But yes the more it adjusts the more performance you lose of course.

Post by **abscate** » 13 Mar 2018, 12:27

My 1999 manual says I should put in 91 octane (that is the US 91) with the minimum requirement of 87.

My 99 turbo has a compression ratio of 8.5:1

My 05 NA has a ratio of 10.5:1

Im a bit less picky about the 99 as I drive it off boost for 95% of the time. The 05 gets 91 or 93 depending on how rich I feel.

Post by **June** » 13 Mar 2018, 13:05

abscate wrote: 13 Mar 2018, 12:27 My 1999 manual says I should put in 91 octane (that is the US 91) with the minimum requirement of 87.

My 99 turbo has a compression ratio of 8.5:1

My 05 NA has a ratio of 10.5:1

Im a bit less picky about the 99 as I drive it off boost for 95% of the time. The 05 gets 91 or 93 depending on how rich I feel.

Correct me if I am wrong, but the 8.5:1 increases durring boost and is the reason turbo engines don't have 10.5:1 as a starting point? June

Post by **Rattnalle** » 13 Mar 2018, 14:05

June wrote: 13 Mar 2018, 13:05
abscate wrote: 13 Mar 2018, 12:27 My 1999 manual says I should put in 91 octane (that is the US 91) with the minimum requirement of 87.

My 99 turbo has a compression ratio of 8.5:1

My 05 NA has a ratio of 10.5:1

Im a bit less picky about the 99 as I drive it off boost for 95% of the time. The 05 gets 91 or 93 depending on how rich I feel.
Correct me if I am wrong, but the 8.5:1 increases durring boost and is the reason turbo engines don't have 10.5:1 as a starting point? June

Effectively compared to atmosphere pressure, yes. So a turbo will lose more performance relative to its max output when the boost kicks in if it detects pre ignition due to poor fuel.

Post by **abscate** » 13 Mar 2018, 14:20

The compression ratio, formally defined, of the engine is constant but there will be higher pressure in the cylinder in a turbo, so it is effectively a higher compression ratio. Im not sure how much extra charge a turbo pushes into a cylinder - sounds googleable though.

Post by **Rattnalle** » 13 Mar 2018, 14:26

abscate wrote: 13 Mar 2018, 14:20 The compression ratio, formally defined, of the engine is constant but there will be higher pressure in the cylinder in a turbo, so it is effectively a higher compression ratio. Im not sure how much extra charge a turbo pushes into a cylinder - sounds googleable though.

How much depends on the car and how high the boost pressure is. But yes it seems googlable, I just did and found a bunch of articles discussing static vs effective compression ratio though I didn't read them.

Post by **abscate** » 13 Mar 2018, 14:28

Rattnalle wrote: 13 Mar 2018, 14:26
abscate wrote: 13 Mar 2018, 14:20 The compression ratio, formally defined, of the engine is constant but there will be higher pressure in the cylinder in a turbo, so it is effectively a higher compression ratio. Im not sure how much extra charge a turbo pushes into a cylinder - sounds googleable though.
How much depends on the car and how high the boost pressure is. But yes it seems googlable, I just did and found a bunch of articles discussing static vs effective compression ratio though I didn't read them.

I was hoping to get someone else to jump into he sinkhole of people talking about this stuff without having a clue of knowledge

Post by **Rattnalle** » 13 Mar 2018, 14:30

abscate wrote: 13 Mar 2018, 14:28
Rattnalle wrote: 13 Mar 2018, 14:26
abscate wrote: 13 Mar 2018, 14:20 The compression ratio, formally defined, of the engine is constant but there will be higher pressure in the cylinder in a turbo, so it is effectively a higher compression ratio. Im not sure how much extra charge a turbo pushes into a cylinder - sounds googleable though.
How much depends on the car and how high the boost pressure is. But yes it seems googlable, I just did and found a bunch of articles discussing static vs effective compression ratio though I didn't read them.
I was hoping to get someone else to jump into he sinkhole of people talking about this stuff without having a clue of knowledge

It's what I do professionally

Post by **June** » 13 Mar 2018, 15:01

abscate wrote: 13 Mar 2018, 14:28
Rattnalle wrote: 13 Mar 2018, 14:26
abscate wrote: 13 Mar 2018, 14:20 The compression ratio, formally defined, of the engine is constant but there will be higher pressure in the cylinder in a turbo, so it is effectively a higher compression ratio. Im not sure how much extra charge a turbo pushes into a cylinder - sounds googleable though.
How much depends on the car and how high the boost pressure is. But yes it seems googlable, I just did and found a bunch of articles discussing static vs effective compression ratio though I didn't read them.
I was hoping to get someone else to jump into he sinkhole of people talking about this stuff without having a clue of knowledge

It's a lot more fun than discussing vacuum cleaner vs broom. Oh wait I ride the latter!

June

Post by **Rattnalle** » 13 Mar 2018, 15:08

June wrote: 13 Mar 2018, 15:01
abscate wrote: 13 Mar 2018, 14:28
Rattnalle wrote: 13 Mar 2018, 14:26
How much depends on the car and how high the boost pressure is. But yes it seems googlable, I just did and found a bunch of articles discussing static vs effective compression ratio though I didn't read them.
I was hoping to get someone else to jump into he sinkhole of people talking about this stuff without having a clue of knowledge

It's a lot more fun than discussing vacuum cleaner vs broom. Oh wait I ride the latter! June

A vacuum cleaner is a turbo charged broom