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320bhp N/A 5 cylinder engine

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Old Oct 4th, 2008, 19:33   #11
foggyjames
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I'm not sure that will apply universally. There is an optimum AFR for a given situation, and either side of that you'll not add power. I'm not sure of exactly what effect injector placement will have, but I wouldn't assume that "more is (automatically) more".

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Old Oct 4th, 2008, 22:20   #12
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An interesting project good luck mate

It’s got nothing to do with AFR’s James it’s about flow rates what you should be asking is why twin injectors would give more bhp than one correctly chosen injector.

F1 engines don’t use 2 injectors anymore despite the fact that they are not allowed but they do use up to 100 bar fuel systems, as fuel injector and pump technology has caught up so have the flow rates they can produce so it’s a fallacy that two injectors give more power, which is what it’s all about be it normally aspirated or forced induction.

For sure if you want drivability and economy go for two but don’t kid yourself it will give you more power unless you going to use a lower specific weight fuel than petrol
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Old Oct 4th, 2008, 23:21   #13
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I'm sorry...you've lost me. Surely flow rates are a secondary consideration...i.e. ideally you size an injector to give you the flow rate you need to achieve the optimal AFR for a given load and engine speed and no more, thus giving you the best resolution possible at the bottom of the map...right?

Do twin injectors give more power? In my experience, they're ususally used when a single injector is so large that its output at very low duty cycles is unstable, making for a lumpy idle, for example.

If twin injectors *do* give more power...all I can think is that it's related to distribution of fuel within the airstream. Standard injector placement is non-optimal, in my eyes, whereas the F1-style "in front of the ram pipe" is healthier.

cheers

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Old Oct 5th, 2008, 14:40   #14
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Not wanting to go off topic, i see the injector comment has gone over a few peoples heads

It has nothing to do with the amount of fuel delivered to the cylinder and has nothing to do with AFR

Is all to do with the fuel mixing with the air, the better it is mixed the better it will ignite

On a higher reving engine the air speed in the inlet tract will increase as revs rise, therefore if you use a second set of injectors further up it will give the fuel more time to atomise with the air giving a bigger bang in the cylinder.

This is why it is used extensively on touring, rally and rally cross cars I have come accross

The WRC Puma gained 12bhp from this set up
SB Developments has dyno proven it works too on there 2.0l 300bhp duratec

I have also used this on a 4cyl turbo engine in the past and seen noticable improveents in power and driveability

Do a google search for more info as its off topic
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Old Oct 5th, 2008, 18:17   #15
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So it is about fuel distribution within the airstream? That makes sense. Interesting that many race engines I've seen only have the 'outer' injector placement - presumably because they spend little of their operating life under low RPM & load conditions.

I'd be interested to see what you manage to measure on the Volvo 5-pot with this effect.

cheers

James
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Old Oct 5th, 2008, 18:31   #16
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Quote:
Originally Posted by foggyjames View Post
I'm sorry...you've lost me. Surely flow rates are a secondary consideration...i.e. ideally you size an injector to give you the flow rate you need to achieve the optimal AFR for a given load and engine speed and no more, thus giving you the best resolution possible at the bottom of the map...right?

Do twin injectors give more power? In my experience, they're ususally used when a single injector is so large that its output at very low duty cycles is unstable, making for a lumpy idle, for example.

If twin injectors *do* give more power...all I can think is that it's related to distribution of fuel within the airstream. Standard injector placement is non-optimal, in my eyes, whereas the F1-style "in front of the ram pipe" is healthier.

cheers

James
If your building an engine like this one James and you know what BHP figure you want to achieve you can calculate the size of injectors required. AFR’s can only be used when the engine is running so flow rates can’t be a secondary consideration.

Quote:
Originally Posted by austenw View Post
Not wanting to go off topic, i see the injector comment has gone over a few peoples heads

It has nothing to do with the amount of fuel delivered to the cylinder and has nothing to do with AFR

Is all to do with the fuel mixing with the air, the better it is mixed the better it will ignite

On a higher reving engine the air speed in the inlet tract will increase as revs rise, therefore if you use a second set of injectors further up it will give the fuel more time to atomise with the air giving a bigger bang in the cylinder.

This is why it is used extensively on touring, rally and rally cross cars I have come accross

The WRC Puma gained 12bhp from this set up
SB Developments has dyno proven it works too on there 2.0l 300bhp duratec

I have also used this on a 4cyl turbo engine in the past and seen noticable improveents in power and driveability

Do a google search for more info as its off topic
We are a bit off topic, however the examples you give are all low pressure systems so I assume you’re not aware that higher fuel pressure systems also = fuel evaporation hence an excellent air/fuel mix from one injector.
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Old Oct 5th, 2008, 18:47   #17
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This is all getting a bit pedantic...what I meant was that AFR is the priority/target...you size your injectors to get a certain AFR at full load and engine speed.

Perhaps I sold Austen short a little here, but I've heard it said far too often that "it's a race car, so it runs rich", etc...and his earlier post seemed to heading in that direction. Of course, more fuel does not automatically equal more power...there is an optimum AFR in a given situation, and richer/leaner will give you less. Apologies if I misinterpretted your point, Austen, but as a one-liner I think it was worth checking.

cheers

James
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Old Oct 5th, 2008, 19:31   #18
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Quote:
Originally Posted by foggyjames View Post
This is all getting a bit pedantic...what I meant was that AFR is the priority/target...you size your injectors to get a certain AFR at full load and engine speed.

Perhaps I sold Austen short a little here, but I've heard it said far too often that "it's a race car, so it runs rich", etc...and his earlier post seemed to heading in that direction. Of course, more fuel does not automatically equal more power...there is an optimum AFR in a given situation, and richer/leaner will give you less. Apologies if I misinterpretted your point, Austen, but as a one-liner I think it was worth checking.

cheers

James
James if you want to live in the 20th century and in ignorance of 21st century technology so be it, but please don’t insinuate my comments are pedantic because you don’t understand them or choose to ignore them because you are incorrect. The rest of your post is pedantic so I won't comment. This is my last off topic post so if you want to continue debating this subject start a new thread

Cheers
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Old Oct 5th, 2008, 19:32   #19
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If anyone has any hints and tips from 5 cylinder tuning i'd be interested on hearing your thoughts
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Old Oct 5th, 2008, 19:48   #20
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Here is a reply i got back from Polestar touring car team who run volvo's

Sound like a nice engine you are building, much like the old super touring Volvo engine built by TWR. I´m sure you will meet your target power with that specification. I can not help you with all your questions but I can give some hints to some of your questions. First of all, our rules prevent us from using some of the things you are using. For example, our valve lift is limited to 10.5 mm so we have to design our camshafts in a special matter to optimize performance. How does cat cam measure the duration?



We are also limited to use a single throttle body so individual throttles can not be used. You could probably use individual throttles with approx. 42-44 mm effective diameter. I expect you will be running the engine between 7500-9500 rpm and I would suggest you to run a inlet length between 260-270 mm.



The exhaust system I would suggest you to run a 5-1 with approx. 800-850 mm primaries. 50.8 mm diameter into the collector should be good. For improved range you could try to run a cone after the collector, starting at 60 mm and ending at 76 mm, 300mm long.
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