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Boy racer air induction kits


mad_pete
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All I swapped from carbs to EFI. This means my snorkel is now same side as EFI air intake. So as megasquirt means no air sensor my plan is to get an induction kit so the air filter can live under the heater box.

This is for a rover 4.2 V8

I'm just curious if anyone has done this.

Contenders are

K & N Apollo

http://www.knfilters.com/universal/apollo.htm

Green Cotton Twister XL

http://www.greenfilters.co.uk/Green_Filters_-_Twister_Filter_System-Twister_Filter_System_XL_Size/c683_688/index.html

BMC cda100-150

http://www.bmcairfilters.com/infoCDA.asp

At the moment I'm leaning to K & N but it might get a bit gaspy at high revs.

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I looked at this for mine a while ago but couldn't get any real sense out of the distributors regarding their suitability for bigger engines. They seem to insist on using HP as a measurement of airflow so it gets a bit confusing and, in the end, I came to the conclusion that a big V8 is going to need more volume of air than these can provide. I ended up sticking the air filter on top of the snorkel with a "safety wire" to catch it if it gets knocked off by branches. Over the top of the air filter I use a pre-filter/cover that keeps it fairly clean... http://outerwears.com/

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It might be worth noting that there was a thread on here a while ago (That I now can't find for the life of me :angry: ) that gave a few good examples of K&Ns etc letting far too much muck through, causing a lot of wear in the bores. I seem to remember that the conclusion was to fit a defender v8 airbox, and change the filter regularly.

For my money, any filter that has holes so big it needs oiling to work is a bodge at best... but hey, that's just my 2p :D

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you're not wrong there... A bit of a squeeze. Still, I think it'd be worth it to avoid spending nigh-on £200, or getting a K&No-good-at-all.

For the price of the green thingy, or indeed the carbon deposit, you could get someone on here to weld you up a custom airbox that takes standard filters, and still afford a massive pile of spare cotton filters.

I like the idea of the pre-filter though. Whacking one of those on the end of your snorkel sounds ideal, however you filter the air after.

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They seem to insist on using HP as a measurement of airflow so it gets a bit confusing and, in the end, I came to the conclusion that a big V8 is going to need more volume of air than these can provide.

I can remember the thread that Heath Robinson does too, and it was a regular that noted that an engine will use its own capacity in air every revolution (2.5 * 4000 per minute flat out for the 2.5NAD, 10,000 litres or 10 cubic metres a minute. for a 4.6V8 at nutter revs like 8000 that becomes 36,800 litres a minute!)

Trouble is, there is no direct conversion from cc to HP (think that the 2.5TD = 80HP @ 4000rpm on a good day (125 litres per unit horsepower), and F1 cars are 2.4 and generate 740HP @ 19,000rpm (61 litres per unit horsepower)!) What a weird way of measuring things!

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The reason it doesnt work is volumetric efficiency. The engine wont be able to ingest a cylinder full of air on each intake stroke. The cam profile and speed its rotating at mean the actual cylinder fill is much much lower. On a poor engine like a 2.5NA it will be really bad, which is why it only makes 80hp, a modern 2.5 will make somewhere around 200hp and on a good engine like your F1 engine, you can actually end up with a VE over 100%!

There is however a direct connection between the air ingested and power produced.

For a given quantity of air, you need to mix the correct amount of fuel and the resulting mix will make a certain amount of power. Regardless of the size of your engine. As a rough rule of thumb 80 grams of air per second will equal 100hp.

Therefore it doesnt really matter if its a 2.0 Turbo or a 5L V8, if its producing 300hp, its consuming around 240g/s, and therefore the flow through a filter will be the same.

I dont particularly like these aftermarket filters though. They really dont do that good a job of filtering the air.

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Just find something standard that will fit in there - I had a Xsara 1.9TD filter on my 3.9 setup and am running a Defender 200TDi airbox & filter on the 4.6, the old 110 V8 airboxes and filters are massive if you can fit one in. Stock RR V8 filters are quite small, even on the 4.2.

The full K&N Duramax report thing is here.

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Nice stupid question now. Do Air filters work both ways round ? So if I have a cylindrical paper filter can I feed air into the middle and have the draw to the engine on the outside ?

I'd want a metal mesh (as most filters have on one side at least) between element & engine, as if water gets in the paper can be sucked into the engine. This is the only positive argument for bling bling cotton/foam filters I've found yet.

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