Ram tubes for 105 Webers

[Roo504]

Hello,

This afternoon I removed the original air box and filter from my 105 (2 litre), and replaced it with 4 ram tubes (approx. 50mm) and foam sock filters.
Unfortunately the engine isn't running well anymore - it bogs down and seems to choke at anything past 3500 RPM. I assume this is because the engine is now getting more air than it was previously and this has altered the air/fuel ratio, causing it to become lean?

I'll be putting the old air filter system back on it tomorrow. Any thoughts are appreciated.
Andrew

[McAnnik]

  Try it Without the socks, you may not be getting enough air flow at all!! just my 2 cents worth.

[aggie57]

Hello,

This afternoon I removed the original air box and filter from my 105 (2 litre), and replaced it with 4 ram tubes (approx. 50mm) and foam sock filters.
Unfortunately the engine isn't running well anymore - it bogs down and seems to choke at anything past 3500 RPM. I assume this is because the engine is now getting more air than it was previously and this has altered the air/fuel ratio, causing it to become lean?

I'll be putting the old air filter system back on it tomorrow. Any thoughts are appreciated.
Andrew

Highly unlikely.  It should still operate without any air filter on the standard jetting.  As McAnnik says you're more likely restricting the air flow and choking the engine. 

[Roo504]

G'day,
Yeah it turns out you're right - the filters were restricting the airflow into the engine. I swapped the foam filters for pantyhose (very expensive filter...) and took it for a drive - the car ran fine. I think the Unifilters are quite restrictive, and there also isn't enough room in the GT Junior engine bay for the two closest to the firewall to fit without being compressed against the wheel arch.

Does anyone have any suggestions as to what filters I should use? There is 20mm of room at the end of the rear trumpet.
The trumpets currently on the car are 55mm long; however, I do have a set which are 10mm shorter, which would give me 30mm of room for filters. I suppose an alternative would be to use curved trumpets.

Thanks for your help,
Andrew

[aggie57]

Is it the noise they make that you're after?  Ram tubes in the hot engine bay make little sense otherwise.

[McAnnik]

Wise words Aggie!             For best results refit the original plenum chamber and long cylindrical filter housing with front spout fitted.It actually functions as a cold air box and is more effective than short trumpets will be on their own. If they could be fitted inside the plenum it would be a plus but hardly enough to get excited about! I dont think there is space enough to even fit your shorter trumpets in there,and some cutting about would be needed.As for a best filter, the original of course,and much quieter too! Cheers.....

[AikenDrum105]

I've been thinking about this Pipercross airbox (or something along those lines)  for my 105 TS conversion - you can fit the short trumpets in there,  the box fits in the engine bay - and you can use a cone-filter (with cold air played over it) or their integral mouth filter for the box neck with cold air piped directly.

http://www.pipercross.net/competition/products_600_airbox.asp

Hope that helps !

Cheers,

[Roo504]

I've put the original air filter system back on the webers. It's much quieter (which was the reason I put the ram tubes on initially), but at least it has a proper air cleaner on it now. That pipercross box looks interesting, you'll have to upload some pics if you end up using it. For now I think I'll leave the standard system on.

Cheers,
Andrew

[McAnnik]

 For a street /road car keeping standard is a good idea, the Alfa factory knew what was good for us which is why they gave the option of a GTA if you really wanted to go a bit quicker,all the hard work done already and only a few bucks more. BMC did the same thing with the [original] Mini, racing Cooper S or shopping trolley,your choice! [Why did I write that? I could barely afford the shopping trolley back then!]..........Cheers.....Ian

[Cool Jesus]

I'll check my dellorto/weber bible back at work, but I've got in the back of my mind that jetting needs to be adjusted?
The ram tubes will have definately change your air to fuel ratio as you said. I'd also be surprised if the socks are that restrictive, perhaps its more that the ratio is just on the cusp of being too rich or lean and the socks are tipping the ratio over for that undesired performance. Ram tubes will also change your power band from memory. If you like, I'll have a quick flick through the book, it has suggested setups aswell. What size engine and webers are we talking about?

[AikenDrum105]

Apart from the effect of smoothing the air path into the carburettors, the ram tube / velocity stack effect is really interesting.  There's a nifty calculator here http://www.bgsoflex.com/intakeln.html   

As I understand it it's the distance from the back of the valve to where the intake opens out suddenly to a much larger diameter (the plenum / front of the carbs / end of your trumpets)   So if the carbs are about 4 inches,  and the intake tract in the head + manifold is about 8 or so (wild guesses here)  you have about 13 inches of intake tract with nothing on the back of the carbs  - giving a little benefit at 6k or so, and some more at 9k, and a good belt at 11k rpm

adding another inch or two with short trumpets doesn't really change that much, but adding a lot more and getting your intake up to 18 inches or so might make it more interesting for a bit of punch lower in the rev range, and a good belt in the usable 5-6k area.

A look at the TwinSpark Motronic intake runners   (or the inside of the Spica Air box CoolJesus! )    shows some work in that direction !

I'm probably parading my ignorance a bit here - wiser cognoscienti will have more concrete info - but that's the general idea I guess.

I think the F1 racers of the 60's 70's often had different length stacks on various cylinders to try and give a bit of punch across the range, rather than a lot of punch in a tight rev range.

Cheers

[1750GTV]

Ages ago and on the advice of a local tuning guru, I drilled a few more holes in the standard airbox. The car is slightly noisier (rortier), still runs well and has the advantage of using the standard filter.

Chris

[Roo504]

G'day,

I cleaned my original air filter before putting it back in the car, and I found that the cylinder it sits inside had some pretty large holes in it - similar to yours but a fair bit rougher and less tidy!
The engine is a 2 litre with 10.4:1 pistons and ported head. Aside from that it's pretty standard.

I know a bloke that makes a very nice cast air filter mount that has very short trumpets cast into it, and uses a K&N filter. I'm thinking seriously about these because they'll give me both the sound I like, as well as proper filtration. I realise they will be sucking in warmer air than what the original filter cylinder would though.

Thanks for the feedback,
Andrew

[Cool Jesus]

I wouldn't fuss too much about warmer air Andrew, its all relative really. What are you doing with your engine - street, race, both. What's the climate like in its usual habitat? Plenty of modified engine bays run as is. Some go to the extreme of seperating the engine bay as per image. Alternatively others merely direct the cooler outside air towards the trumpets as per 2nd image. You seem to be aware of the relationship of air density relative to its temperature, more dense, more air, better bang. The air box and tubing obviously gives a barrier to engine bay temperatures, however I believe its main purpose is to give sum minimal ram forced air into the throttle bodies, this air that is being drawn from a high pressure area of the car moves easier into the now low pressure cylinder that is seeking it.

[aggie57]

In fact the answer for best performance is of course a combination of all these things, and more. The final choice will inevitably be a compromise leaning towards the individual's preferences.

Regardless Andrew you should get the jetting sorted on the final setup. But looking at your posts I think you know that already.