Carburettors - with or without filters? (Read 646 times)

[Al Ramone]

The biggest issue with sidedrafts and air filters is always the lack of space between the carb mouths and inner wing. More often then not there isn't adequate space for filter so they have something fitted that is far from ideal... The foam filters from ITG and Pipercross etc are sometimes the best solution as they don't have a lid.

Another very poor installation. doubtful there's even any trumpets at all here, let alone the massive restriction caused by having the filter lids to close to the carbs.

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[datsfun]

The only way to properly conclude the effects is to perform dyno runs with /without filters etc. I read a very interesting article and build thread where someone carried out these on a L6 stroker engine..they swapped trumpet sizes, ( length, conical shape , rolled edges etc)' filters ( K+N, sponge etc) on and off etc with the much respected Dave Walker at Emrald tuning. The end result was a closed air intake with a modern conical air filter which stabilised the air. BTW this is a dyno proven 300bhp L series running 12 sec qts so highly performance orientated.



www.mjpshop.co.uk/image/cache/data/products/IMG_0533_1%20(Large)-500x500.jpg

[Al Ramone]

Now that looks like a well designed intake system. Cold air supply to the filter and I'm guessing plenty of room in the air box.

[bananahamuck]

I think running with no filters looks and sounds waaaaay cooler.  
Heck if i had coupe as cool as yours i probably would drive it naked.

  BUT all the guys i know with Webers up here all run some sort of filters even though our driving on the "correct side"  of the vehicle prevents using anything remotely correct for making the most horsepower .  44s still sound pretty damn mean even with filters.

So would i/me drive without filters and just cones, maybe on a nice day to a show or something probably not every day though.  Replacing engines is expensive,, but i do like to do it,, kinda zen type affair. Except with antifreeze dripping on your face.

[s20]

Dec 28, 2014 10:54:49 GMT 1 Al Ramone said:

See most people look at that and think cool. I just see poor workmanship.

Can you build a time machine so that you can pop back to 1971 and tell Nissan's works race team at Oppama where they are going wrong?

The engine you are commenting on was built to take part in just ONE race. After that it was stripped, rebuilt, run in and dynoed ready for another meeting. The lives of such engines were measured in hours. Nissan knew all about proper filters, proper (cold air) ducting and everything else that is being discussed here, but simply chose to run with open trumpets on that particular car for those particular races.

What you are calling "bad workmanship" is nothing of the sort, and the judgment assumes that the people carrying out the prep of the car either didn't know any better or didn't do what they were supposed to. Wrong on both scores.

I don't know about anyone else, but I prefer MY old cars to reflect the period they were built in. I know that certain details and specs are outdated, old-fashioned or otherwise 'wrong' with the benefit of 40+ years of hindsight, but I choose to keep what I want. It's a good job that the people who own veteran and vintage cars do the same, or we'd see the likes of a 1914 GP Mercedes running a K&N cone filter in front of its radiator ("cos it's better, innit?). Where do you stop?

However, I have to be pragmatic. I can't - for example - get the tyres I'd like to run because they simply don't exist today in the sizes, construction and compounds that they used to, so I have to compromise. There are lots of other examples. On one of my cars I am being pushed into using a modern CDI igniter unit simply because supply of the originals is drying up and they don't last in service forever. I hate it, but I'll have to use it. I'm going to try to hide/disguise the modern unit because it looks like an aberration on an otherwise period-correct-themed car. Applying modern thinking and this "better" philosophy to its ultimate conclusion, I'd end up with a 1969/70 Japanese sporting car that was about as 'authentic' as my everyday driver Audi, with its aircon, heated seats, rain-sensing wipers and electric handbrake. It'd be like putting UPVC windows in a Georgian townhouse.

[Al Ramone]

I'd love to go back and ask them why they chose to run it like that. And I'd also love to hear more about it and what ever else Nissan was doing back then.

Obviously I've got the benefit of years of research, pretty much everything I know I have learnt from reading and speaking to people who have dedicated their lives to mechanical engineering (David Vizard is one of my biggest heros) So I certainly don't think I'm better then any of the old time racers and have much respect for them and love to read and learn from them.

My OCD means I have a few pet hates and one of them is filtration.... (other hates include them silly fake aeroquip hose clamps that are just a cheap poor quality clamp in an alloy cover... but anyway... )

[randywanger]

Jan 1, 2015 13:54:59 GMT 1 s20 said:

I don't know about anyone else, but I prefer MY old cars to reflect the period they were built in. I know that certain details and specs are outdated, old-fashioned or otherwise 'wrong' with the benefit of 40+ years of hindsight, but I choose to keep what I want. It's a good job that the people who own veteran and vintage cars do the same, or we'd see the likes of a 1914 GP Mercedes running a K&N cone filter in front of its radiator ("cos it's better, innit?). Where do you stop?

That was my thinking and a point I made in post #2, maybe not as well as you put it, it's how it was run when it was racing and it's how it'll be run now.

I too have a lovely new Audi with electric everything for comfort, this, eventually will be a pure toy and will probably get used about twice a year.

[Al Ramone]

I do find it hard to believe that Nissan would have been running their 70's race cars filter less.

Even back in the 60's ferrari were fitting crude filters to their F1 cars.

[dialup2001]

Although my 2.5 Litre Spitfire has no filters (why it sounds like this)

www.youtube.com/watch?v=-Kit1s8BhVY

David Vizard (who I think of as a god) did a test and said you would have to be mad!

K&N used David Vizard's research in their own development so there you go.

I am mad however and don't care (as they get such little use).

I will find Vizard's article

[dialup2001]

So Vizard says:

"It is easy to fall into the trap of thinking that because a car is being raced on a circuit, the air it will be breathing will be relatively clean. In fact, nothing could be further from the truth. Remember, this is the age of the sticky compund tyre, and it's the use of such tyres which cause a high grit pollution level in the air around a typical race circuit. Basically the process which develops polluted air takes the following course.

Firstly, the race tyres warm up and become sticky. As these tyres pass over the road surface, they pick up minute particles of grit from the road. This happens mostly when the car is in or just existing a corner. As the car builds up speed down the straight, so these particles are centrifuged off the tyres. Each particle of grit is usually covered in rubber. This grit is thrown up into the air and can then be ingested into an engine. As it goes through the engine, so the intense combustion temperatures cause the rubber to melt resulting in the production of an excellent substitute for grinding paste. Do I need to say more?

During a ten lap race at Silverstone, it would not be uncommon to get a teaspoonful of this rubber/grit compound to go through an engine. Ingesting this much grit can quite easily wipe out 3% - 5% of the engine's hp."

He goes on and on after this.

I will try to find the results of no air filter vs filter in cfm.

[datsfun]

Feb 3, 2015 11:51:58 GMT 1 dialup2001 said:

[/p]

David Vizard (who I think of as a god) did a test and said you would have to be mad!

I am mad however and don't care (as they get such little use).

[/quote]

Blasphemy ...you decide not to adhere to your God's preachings ?

[gainsb1]

Not really wishing to ignite the discussion again BUT I have just watched the Classic Car programme with Quentin Wilson (quite like him) and Jodie Kidd (Can't stand her) and they featured a classic race car event at the Monaco Grand Prix. The programme car was running with open bell-end/trumpet carbs. Just a small grid over the top of the engine to stop kids getting sucked in.
Now, these cars are surely worth loads more than they were originally so why are they still running them with no filters if it's going to damage them?

Leigh (Area rep)

[Al Ramone]

Because they don't care? they do very little mileage and are not worried about wearing the engines out or keeping maximum power.

[dialup2001]

I love debates. If air filters are more restrictive than than the power level kept by filtering, then why do F1 engines use them?

www.racecar-engineering.com/articles/f1/technology-explained-f1-airboxes-filters/

Trumpets I would say are for show, people who don't care (like me) and drag racing.

I have a yellow spitfire which I have put about 5000 miles on with trumpets and not noticed.

People who run old cars on unleaded (like my Blue Spitfire) suffer the sam gradual loss of power as my seats wear due to the lack of lead salts. I don't care.

[Al Ramone]

it's all about choice.

My engineering head means some things really annoy me.

I do like seeing stuff like this...



But there's a voice in my head screaming about the poor wheel bearings and other stressed suspension parts.