Air filters

[Farmer42]

I'm looking for some advice on air filters for my HS6 SU carbs. Since I swapped from the Datsun Hitachi carbs, the OEM airbox & filter wouldn't fit to the HS6 so I am using 70mm Air Ram trumpets. These are great for performance and the fuel economy isn't too bad but I am a bit concerned that without a filter, it could suck in unwanted debris & damage the engine.

I have tried a couple of 1.5 inch depth round pancake filters but the performance dropped significantly and it misfired badly on revs over 2k. It appeared to be flooding the carbs with fuel due to not sucking in enough air no matter how much I fiddled with the tune up and mixture.

I was thinking of some deeper filters like the K&N filters in the link below but they are a bit pricey and I don't want to be wasting money by spending £150-200 and then have the same problems as mentioned previously.

https://www.ebay.co.uk/itm/56-1430-...rentrq:956e7d911690ac1c5d91e084ffff5e4d|iid:1

What are people running with on SUs? Does anyone know if there are filter socks that fit over the trumpets?

 

[Rob Gaskin]

I had a standard filter on my old track 240 with HS8s. Can you modify your's?

Later I used foam socks - the car ran well but they can dry out and crumble after a few years.

 

[Farmer42]

I had a standard filter on my old track 240 with HS8s. Can you modify your's?

Later I used foam socks - the car ran well but they can dry out and crumble after a few years.

I thought about modifying it but the distance between the 2 inlet holes on the carbs was too big and the backplate didn't line up. I didn't want to butcher a perfectly good OEM airbox and I have now sold it to Chris Vega so I don't have it any longer.

I was looking at the foam socks at Merlin Motorsport and I might investigate those further when I am at Castle Combe on Saturday. If they last a few years that isn't too bad given that they are pretty inexpensive compared to the K&N filters so if they start breaking down, I would just buy new ones. I just wondered if they affected air intake too much. They don't look as good as a nice bit of chrome though.

 

[AliK]

Would this sort of thing be a good compromise?

 

[SeanDezart]

Hmm - like those !

 

[chrisvega]

I thought about modifying it but the distance between the 2 inlet holes on the carbs was too big and the backplate didn't line up. I didn't want to butcher a perfectly good OEM airbox and I have now sold it to Chris Vega so I don't have it any longer.

I was looking at the foam socks at Merlin Motorsport and I might investigate those further when I am at Castle Combe on Saturday. If they last a few years that isn't too bad given that they are pretty inexpensive compared to the K&N filters so if they start breaking down, I would just buy new ones. I just wondered if they affected air intake too much. They don't look as good as a nice bit of chrome though.

If you need it Paul I still have your airbox and happy to let you have it back ?

Alternatively, one of my Zs runs well on ITGs over TWM air horns
JC20's shown here:
https://www.merlinmotorsport.co.uk/...ow-airfilters/air-filters/itg-jc20-air-filter

 

[Farmer42]

Would this sort of thing be a good compromise?

I'm with Sean. I do like the look of those and they also keep the look of the trumpet instead of having a big piece of foam. They might just fit the diameter of the trumpets I have. Good spot Ali.

If you need it Paul I still have your airbox and happy to let you have it back ?

Alternatively, one of my Zs runs well on ITGs over TWM air horns
JC20's shown here:
https://www.merlinmotorsport.co.uk/...ow-airfilters/air-filters/itg-jc20-air-filter

Thanks for the offer of the airbox back Chris however, as I said the inlet holes are in the wrong place & I don't want to butcher them. I was considering the ITG socks though but more along the lines of these:

https://www.merlinmotorsport.co.uk/p/itg-trumpet-sock-small-jcs11-itg-sox-s
Will have a look at them when I am at CC this weekend.

 

[Alphabettispaghetti]

You can/should oil the foam and it’ll last forever

 

[Rob Gaskin]

You can/should oil the foam and it’ll last forever

yeh, I did oil it. How long is forever? Mine lasted about 8 years.

 

[AliK]

yeh, I did oil it. How long is forever? Mine lasted about 8 years.

For an air filter that feels like forever - Assuming you did some thousands of miles of course which I know you would have!

 

[chrisvega]

You can/should oil the foam and it’ll last forever

They only last forever if no mice around. Their favourite snack when no chocolate available. Ask me how I know.

Oil - absolutely for the foam filters too, just don’t do what I did, ordered the wrong replacements and oiled them whilst still in the box No returns once oiled, Stupid boy !

 

[Alphabettispaghetti]

yeh, I did oil it. How long is forever? Mine lasted about 8 years.

I've got some that are about 15-20 years old. I

 

[chrisvega]

How are those foam socks held in place over the air horn ?
The Weber versions pictured on zstore have cable ties and look a bit scruffy.

 

[toopy]

Ive had K&N's on my Hitachi's for about 15 years, bought some of the K&N filter cleaner last year, worked a treat, re-oiled, good as new

I also had K&N's on some HS8's when they were on the car for a few years, worked just fine.

 

[AliK]

I don't know how they hold on but I wager with a bit of creativity / ingenuity, we can make one of those end of trumpet filters.

Here's my Heath Robinson on train ride home thinking without machining anything ...

Something like this ...

https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.co.uk/ulk/itm/362278261931

A bit of this ...

https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.co.uk/ulk/itm/261836344201

And a bit of an old air filter or a bit of this ...

https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.co.uk/ulk/itm/381260016063

 

[Woody928]

How are those foam socks held in place over the air horn ?
The Weber versions pictured on zstore have cable ties and look a bit scruffy.

Cable ties generally, because well, racecar...

 

[Woody928]

Would this sort of thing be a good compromise?

Anyone ever used anything like this? I really like the idea as it would massivly tidy up my engine bay....

 

[AliK]

Apparently they are only for "show" purposes. I would imagine it's way better than running open trumpets and yet it probably won't take out the very fine particles a traditional filter would. What does it do for the performance robbing reflected waves in the engine bay that skiddel analysed / wrote about? Who knows, but they do look cool!

All this talk makes me think there is definitely a market for something elegant for open trumpets rather than tie wrap held ugly blobs of foam.

 

[Rob Gaskin]

...............All this talk makes me think there is definitely a market for something elegant for open trumpets rather than tie wrap held ugly blobs of foam.

Ali they aren't 'ugly blobs of foam'. Mine were PiperCross and had a red band on them.

https://www.ebay.co.uk/p/Pipercross...Pair-C1050/1823260473?iid=272888314136&chn=ps

They worked fine too, listen to my car at 0.11s (with standard front pulley by the way).

When I built my car I was not 'flush' with cash so any expense was carefully considered. Yes a cold air box and ducting would have been nice but on a limited budget these work fine.

 

[AliK]

Sounds glorious Rob!