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Tuning & Upgrades Discuss performance enhancements for your Alfa Romeo

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Question fact or fiction

Been reading and with different results .

Is it true or false

That you need roughly 1cc of fuel for every Hp of power
Example 220 Hp requires injectors that give roughly 220cc of fuel


Thanks in advance
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220cc in what time? 1 sec, 20 secs or 30 mins??! ?
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Surely it'll depend on your stroke/bore sizes more than anything

220cc of fuel would require at least 3 litres of air to burn (fairly rich at 14:1 air:fuel if memory serves) ... and if that's per revolution of a 3.2 litre engine - a 50 litre tank won't be lasting very long at even 2000rpm ... (about 10 seconds to empty the tank?)

2000 rpm @ 220cc / rev = 440,000 cc / min. Tank is 50 litres or 50,000 cc so lasts a whole 44/5 or 8.8 seconds

My 1.8 TS 156 (about 140bhp) consumes about 7 litres per hundred km (in round numbers)
At 100km/h it's sitting just below 3000rpm
So - consumes 7 litres of fuel for every 3000 * 60 revolutions of the engine
7,000cc per 180,000 revolutions = 7cc per 180 revolutions = 0.04 cc per revolution (or 0.1cc per cylinder per revolution)

So, I'm guessing fiction by a few orders of magnitude
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Quote:
Originally Posted by proinsias View Post
Surely it'll depend on your stroke/bore sizes more than anything

220cc of fuel would require at least 3 litres of air to burn (fairly rich at 14:1 air:fuel if memory serves) ... and if that's per revolution of a 3.2 litre engine - a 50 litre tank won't be lasting very long at even 2000rpm ... (about 10 seconds to empty the tank?)

2000 rpm @ 220cc / rev = 440,000 cc / min. Tank is 50 litres or 50,000 cc so lasts a whole 44/5 or 8.8 seconds

My 1.8 TS 156 (about 140bhp) consumes about 7 litres per hundred km (in round numbers)
At 100km/h it's sitting just below 3000rpm
So - consumes 7 litres of fuel for every 3000 * 60 revolutions of the engine
7,000cc per 180,000 revolutions = 7cc per 180 revolutions = 0.04 cc per revolution (or 0.1cc per cylinder per revolution)

So, I'm guessing fiction by a few orders of magnitude

I get your point i wished i could find the bits i was reading . i have no idea on what time the cc's were dished out , But when i was looking about i did notice a pattern that cars seem to have injectors about the cc as its hp .
like the alfa 3.0 & 3.2 have injectors about 226cc and hp 220 and 250 but the 2.5 the injectors are about 192cc with 192 hp .

thats why i asked it made me think you cant blame me
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It's not related.
Because the cc figure is per one injector and you can have various amount of injectors in your engine.

For example the 2.5 busso has 192 hp and 190cc injectors, but the 2.0ts has 155hp and again 190cc injectors. But in the TS there are four of them, and in the V6.... six
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Quote:
Originally Posted by mirlock View Post
Been reading and with different results .

Is it true or false

That you need roughly 1cc of fuel for every Hp of power
Example 220 Hp requires injectors that give roughly 220cc of fuel


Thanks in advance
It's in the ball park for a 4 cilinder multipoint engine..
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Quote:
Originally Posted by proinsias View Post
Surely it'll depend on your stroke/bore sizes more than anything

220cc of fuel would require at least 3 litres of air to burn (fairly rich at 14:1 air:fuel if memory serves) ... and if that's per revolution of a 3.2 litre engine - a 50 litre tank won't be lasting very long at even 2000rpm ... (about 10 seconds to empty the tank?)

2000 rpm @ 220cc / rev = 440,000 cc / min. Tank is 50 litres or 50,000 cc so lasts a whole 44/5 or 8.8 seconds

My 1.8 TS 156 (about 140bhp) consumes about 7 litres per hundred km (in round numbers)
At 100km/h it's sitting just below 3000rpm
So - consumes 7 litres of fuel for every 3000 * 60 revolutions of the engine
7,000cc per 180,000 revolutions = 7cc per 180 revolutions = 0.04 cc per revolution (or 0.1cc per cylinder per revolution)

So, I'm guessing fiction by a few orders of magnitude
Injectors are rated in cc/min

your 1.8 consumes a LOT more at top speed where it's making it's 140 bhp...
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Quote:
Originally Posted by Cuore_Sportivo_155 View Post
Injectors are rated in cc/min

your 1.8 consumes a LOT more at top speed where it's making it's 140 bhp...
Each injector may be rated to push a max of Xcc per min - let's say 140cc/min to tie back to the cc/hp equation

So 140cc * 4 = 560cc fuel / min, or about 1 hour 40 mins flat-out to empty ... certainly more plausible on the numbers



Though, I doubt the injectors are pushed beyond 80% capacity at design / spec time

Edit: 560cc/min at the claimed top speed of 210km/h (let's assume that's at the 6500rpm horsepower peak)
= 33.6 litres per hour == 16 litres / 100 km (17.6 mpg)

Last edited by proinsias; 26-06-17 at 10:54.
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You can push them to 100% if you want, but this is indeed not usual.

My diesel does 12.5l/100 km at top speed but power will already be dropping from 170 bhp, and BSFC is better as it's a diesel, and fuel has higher energy content.

16l/100 km doesn't seem too far from reality.
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