Open trumpets

[stanley sweet]

What's the opinion among members of running a standard engined Fulvia with open trumpets? I don't mean fully open to suck flies in, but the type with a fine mesh over the end. I ask because I'm off to the historic races at Dijon in a few weeks and they had lots of items like that there last year. Not cheap though. The reason I was thinking about it is a) it takes a lot of weight off the carb mounting plate even though I have the support arm b)they look nicer than the big black box c) a friend once balanced my carbs and we took it out for a quick test on open carbs and it sounded fantastic. As you can imagine reason C is the main reason I'm asking.

[Richard Fridd]

one thing that has put me off open induction trumpets is a story barry waterhouse once told me about a customers car racing past a competitor stuck in a gravel trap, the concequence being much dust entering the following cars engine despite the fitment of an aftermarket foam type air filter hence  causing engine damage.the same could happen if oneself entered the trap obviously.best regards richard

[Dilambdaman]

Hi Stanley,

In the 70s I rallied an ex works, ex Jolly Club Fulvia 1.3HF and always ran on the gauze covered open trumpets without any problem.

I have the ex Barry Waterhouse Fulvia S1 1.6HF Fanalone rally car CUC 20H. When my son bought it around 10 years ago it came with the gauze covered open trumpets. My son rebuilt the engine at Barry's workshop under his supervision and retained the trumpets. Barry did suggest that a foam filter was fitted over them as a precaution and that is how we run it. Except that is for track days and occasional road use - as you rightly say, the sound is phenomenal and irresistible!

Robin Lacey

[stanley sweet]

Thanks for the replies. I haven't any plans to use it on track seriously (but I can't rule out an occasional track day) so in theory it should only encounter the usual air quality of a road. The use of socks generally and then the odd trip without them sounds a good compromise for road use. I am tempted but I imagine when I see the prices things might change. But the answers have given me something to go on so that's a big help.

[MikeB]

Having been a BMC engined Turner owner in the past, I had occasion to read Dave Vizard's excellent book on tuning that particular engine. He did quite a bit of studying into the use of trumpets and various types of air filters. His conclusions were that the wire gauze really mucked up the air flow. In the 50's 60's & early 70's modern foam filters weren't available, so taking off the sometimes rubbish paper filter and standard air box did help, and wire mesh was good at keeping stone particles out. But as has been pointed out it doesn't keep out dust/sand. So by using meshed open trumpets you might not significantly increase the air flow, and be leaving the engine open to damage.

I've seen it discussed on other forums and having talked to the folk in Norfolk, and I gather that really the standard Fulvia box isn't too far off the mark, maybe extending the intake tube to get a blast of cold air being one of the mods suggested.

Like everything, views vary, but I'm sure it sounds sportier on the open trumpets

[RhysHF]

I have an article from Practical Classics Feb 2005 called "Making Fulvias go faster", one of the cars in the article has a "unique cold air box, handmade by Richard Thorne Classic Cars" the air box contains a Piper Cross air filter which it suggest together provide a small increase in power. It does not say if it sounds any better though.

Rhys

[julian]

A few years ago I built a quite highly tuned Beta Spyder fitted with side-draft Webbers. I made up a pair of filters using universal Pipercross foam filters with base plates machined to size.

The results were good, giving a small increase in power and a good sound. Looking at the Fulvia set up it would be too difficult to replicate this.

Regards

Julian

[lancialulu]

I have run my 1600 HF with trumpets with pipercross socks on round goodwood this year and loved the noise (did 6 sessions) - it was also bearable/enjoyable cruising down at 70ish. Not having put on a rolling road but the engine has higher comp pistons, larger inlet valves and a near gp4 exhaust manifold anyway so quite spritely! I have returned to normal fulvia airbox and cant say I have noticed much if any performance drop - just loss of hooligan baiting induction!

[stanley sweet]

Lots of interesting views there. I must say I've often wondered about any kind of trumpets sucking hot air from the radiator as it is ideally cold air you want. It was good to hear that the 'Norfolk' experts think the standard set up is good anyway and I have to say that if Lancia did things there was usually a good reason. Having said that, not having heard that before I always thought the inside of a Fulvia box was the most convulated thing I'd ever seen as far as air flow was concerned. This isn't based on any technical expertise, just the what looks right is right priciple. Or in this case looked wrong. So I have to confess that I have run my Fulvia for the last 5 years or so with the standard air box, but with all the internal gubbins removed and a sock on the end of the intake so it still picks up cold air. Shame it still muffles that lovely noise though.........................
I have seen a Fulvia with the intake tube cut off and a modern cone filter fitted directly to the box where the tube was. Looked very neat but I still wonder about the intake of warm air.

[DavidLaver]

The other job the airbox and filters do is catch flame and contain fuel mist standoff so open trumpets are not without their dangers.   If you went the open trumper route a plumbed in fire system with a nozzle aimed at them would be some peace of mind, a hand held extinguisher inside the car would be the sensible minimum.   

Reading this back, if it was me, I'd go with the pipercross socks which will be more restrictive than a larger filter but "testing" shows still give the noise.

David

[MikeB]

One other point I've seen mentioned in some old articles, and a potentially expensive one, is that if you DO manage to get more air in with open trumpets, you need to make sure that at the top end, especially if you are going to run sustained high revs, that the fuel mixture is still correct.  It usually mentions reducing the size of the air corrector jet (and with the lack of Solex jets that means soldering the existing one closed and re-boring it). This can only be checked on a rolling road/dyno. If you are going to sprint or race the car this would be a very worthwhile check to make. Hillclimbing or road use probably won't see the high revs sustained for long enough to do any damage, errr ordinarily

David mentioned the stand-off pressure head that comes out of carb trumpets, again this can be crucial to getting optimum performance. The std airbox has the internal plate, that fits inside the filter, I'll bet you that it's probably just the right distance from the trumpet mouth to give the smoothest power curve, they weren't too daft those Lancia boys you know

[stanley sweet]

Having read through all the answers it seems that the nice noise isn't worth the risk of damage unless at least socks are fitted and then these won't perform the same functions as the original box. So I may even put it all back together with a standard air filter! Good forum this - would have taken years of bumping into people to gather this much info so quickly.