International Lancia Forums

Hey all. Maybe someone out there can help me understand something before jumping too quickly like I did with those cheap 175/75 chinese tires a while back. ;o)

I have a line on a set of the velocity stacks for the C35 Solex carbs which I have on my 1975 1.3s. You know the ones with the chrome mesh filters? I'm thinking of replacing my stock airbox with these, mostly for cosmetic reasons in that I think they look very cool on the HF engines I've seen them on. If I get better breathing and a few more ponies, that'd be cool too. However...

Before buying them, is there anything else I need to consider? They are available in a set of 4 with the backing plate and mesh covers/filters. Does installing them in place of the stock airbox imply/require any other changes I may not be aware of?

For example, there is a hose that runs from the airbox to a round component at the back of the engine underneath the coil/distributor. What is this, and how might I handle air supply to it if I delete the airbox? Any other connections or tuning changes I'd need to address to install the velocity stacks?

Also, if you have any recommendation what I should pay for these, that'd be welcome info.
Thanks...Chas

Hope everyone had a safe and happy New Year's Eve!

Is it ever dusty or sandy where you drive your Fulvia? If so, replacing a proper air filter with coarse-grained mesh will cause your engine to rebore itself very quickly. It might run weaker too, so the carbs could need re-jetting. The airbox hose runs to a duct around the exhaust manifold so the engine can be fed warmer air in winter (there's an adjustable diverter plate on the airbox spout). It's not essential but I've been using mine in warm-air mode this winter and it does run better from a cold start.

I agree that the velocity stacks look good but I would never use them naked on a road car whose engine I'm not planning to rebuild on a regular basis.

Whatever, have good fun with your Fulvia in 2008. I've just been out for a high-revs blast along the backroads in mine and I'm still on a high.

John

I use them on 42's with indivdual "sock" filters to protect the engine (get from Demon Tweaks etc). Induction sound is fantastic but tollerable for motor way cruising.

You need to ensure there is a backing plate that matches the airbox support strap otherwise the carbs are not supported and weigh to much for the rubber inlet adaptor.

Also ther should be a belt guard to protect a flailing alterntor belt from taking off the first stack.

Happy new year!

Tim

Ah, yes I remember now my mechanic showing me the warm/cold weather setting on the airbox. Thanks for the reminder Tim. I won't be driving in sandy/gritty conditions, but I'm starting to think nevertheless that this I will defer indefinitely. I have plenty of other things to work on still and this goes to the bottom of the list. Only reason I asked at all is that one dropped "in my lap" for 90 euros if I wanted them.

Thanks...!

What you were describing sounds like the crankcase ventalation hose. It comes out of the oil separator canister which has the screw cap allowing oil to be added to the motor but which also contains a steel wool/mesh which allows bypass fumes from the crankcase to escape and be sucked into the intake side of the engine. Not sure if this was also present on the later series cars but if so you'd want to make accomodations for it.

Also are you sure the bolt diameter is for the Solex carbs. I see lots of ads for velocity stacks for Webers but I'm not sure if the Solex has the same dimensions.

Be careful of the stacks with the mesh over the end. Dave Vizard, a much revered engine tuner, did tests with these on a Mini and found that the wire mesh actually disrupted the airflow to the carbs and could be even worse than the std airbox. You car better off with fully open trumpets and foam sock filters.

That said the car will breath better and you may need to check that it isn't running too weak on the fuel mixture at high revs

Other things to take into consideration, are the noise. Yes it will sound a lot sportier inside the car than before, fine to impress your teenage sons but a bit wearing on a long journey !!

As Tim pointed out you will have no filtration of note. So dust and small stones can enter and wear away your engine.

Finally the standard air box puts a metal plate a few cm from the face of the std Solex trumpet. This is important for the "stand-off" pulses you get coming out of the carbs, and removing this can also effect performance.

There are trumpets inside the air filter box under the flame extinguisher. There is already very good advice from others above. A missing flame extinguisher is another disadvantage of dropping the air filter box. There is also a discussion about the fact that open trumpets do pick up air from the hottest place under the hood which is counter productive.

I have done some testing with variations of the airfilter box on the rolling road tester. Dropping the air filter increases torque at high rpm but looses torque at medium / low rpm. You don't really want that on a road car. Not even on a car for regularity rallies. Note that HP is the product of torque and rpm. This means with constant torque (which is not the case in reality) HP increases with rpm. The max HP is always at (in reality "near") the max rpm. It is only useful to maximize HP at the max rpm if you do indeed drive the car at full throttle at max rpm all the time. If you don't drive the car at max rpm and full throttle all the time you loose useful torque. If you are under max rpm or throttle at less than fully open, rpm and throttle are the limiting factors in pumping mixture through the works not the air filter.

Driving the car at max rpm with throttle fully open does affect the life time of the engine (and all other parts of the car) considerably.

I looked up the design engineers of the Fulvia. It turns out they studied automotive engineering at the university of Turin. Unfortunately they did not study romantic subjects like carpenting or sculpture.

Huib Geurink wrote:
>
> I looked up the design engineers of the Fulvia. It
> turns out they studied automotive engineering at the university
> of Turin. Unfortunately they did not study romantic subjects
> like carpenting or sculpture.

LOL...
I assume this is a reference to the rather "plain jane" look of the airbox under the hood.

In any case, I have enough advice and input here that I'm not going to install these. I do in fact
drive the car carefully, and do not often rev it too far into the upper reaches of the tach. So it
sounds like replacing the airbox will cost me on the performance curve for most of my driving.

Looking cool under the hood is not THAT important to me!
Thanks all!