Anyone running open trumpets / velocity stacks?

AliK

Vehicle Dating Officer
Staff member
Club Member
While outside last night clapping for the NHS, I was speaking with my neighbour about my reversion issues.

He used to run a rally team so he does know a few things.

We got talking about carb trumpets and how restrictive the airbox is. I notice that my AFR drops by a whole number when I add the air filter.

He suggested running without the air-box or filters. Now this is something I am unlikely to ever do for more than a tuning run or webcam recording session as I will twitch with fear every time I see dust being kicked up on the road. But he reckoned that he never had issues running open trumpets and never had to tear his engines down because of foreign objects getting in.

One thing is for sure, you never want to run carbs without trumpets. I do like the sound of open trumpets and would as a minimum opt for ITG style trumpet socks for anything long term.

His logic was that unless you suck the big debris, it all gets in and out so fast it’s not going to get stuck in the cylinders. But maybe a race / rally engine does fewer miles between rebuilds than a road car to even notice the fine dust grinding the walls!?

So this got me thinking about how many people here run their triples, SUs or ITBs with open trumpets and if they have ever had issues. Anyone?

Interested to have a tech / logical discussion on this if possible and see where it goes.

I am on the verge of experimenting with trumpets to improve performance and reduce reversion, so it’s a topic of great interest but that isn’t the point of this thread. I guess I’m asking for long term experiences or views on open v filtered trumpets.
 

jonbills

Membership Secretary
Site Administrator
I think if you get a whole unit richer with the air filter you should get a new air filter.
 

AliK

Vehicle Dating Officer
Staff member
Club Member
I think if you get a whole unit richer with the air filter you should get a new air filter.

Well it’s a K&N that’s done 6K miles not sure the filter per say is at fault.

To Franky’s point, the tuners did try a with and without airbox and did the final power run without it but with the back plate and trumpets on. Maybe I’ll take the advice and paint it blue [emoji12]
 
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8658kv

Club Member
So this got me thinking about how many people here run their triples, SUs or ITBs with open trumpets and if they have ever had issues. Anyone?

.

Hi Ali

I run my triple weber's with open trumpets. Haven't had any problems, I do change the oil regularly .

If Le Mans had of taken place this year, would have put filters/ airbox on for the trip.

A belated thanks for sorting the dating letter.

Steve
 

AliK

Vehicle Dating Officer
Staff member
Club Member
Hi Ali

I run my triple weber's with open trumpets. Haven't had any problems, I do change the oil regularly .

If Le Mans had of taken place this year, would have put filters/ airbox on for the trip.

A belated thanks for sorting the dating letter.

Steve

Thanks chap and most welcome on the letter! [emoji106]
 

datsfun

Club Member
If you went to a vintage race meeting most of the cars don't have air filters but it's not a good idea. Neither is drinking beer.

Majority of the cars running DCOE carbs in Japan appear not to bother with filters either. Could it be they have less debris in the air? Are more risk averse ? Like their beer ALOT ??
 

atomman

Club Member
I drive my Z round with open trumpets , only reason I made the clear air box is to improve cold air feed ,

You could extend the heat shield out under the trumpets if you're worried about some thing finding its way into them from the road ?
 

toopy

Club Member
Ive been thinking about using foam covers on the trumpets, instead of the K&N's i currently have, seeing as the cold air box that Mike supplied is no longer available, and which i was planning on using.
 

datsfun

Club Member
Ive been thinking about using foam covers on the trumpets, instead of the K&N's i currently have, seeing as the cold air box that Mike supplied is no longer available, and which i was planning on using.

Caution with Foam...heard horror stories of parts of them being sucked in and in worse cases they are a catalyst for fires through carb spit backs etc.
 

AliK

Vehicle Dating Officer
Staff member
Club Member
Caution with Foam...heard horror stories of parts of them being sucked in and in worse cases they are a catalyst for fires through carb spit backs etc.

Yes I heard that too - mainly with DCOEs right?

I saw someone with triple mikunis showing the state of his half eaten filter as I am guess you get much bigger pulses up the inlet tract than you do with the more restrictive SUs.
 

datsfun

Club Member
Yes I heard that too - mainly with DCOEs right?

I saw someone with triple mikunis showing the state of his half eaten filter as I am guess you get much bigger pulses up the inlet tract than you do with the more restrictive SUs.

Yep, DCOE. I have first hand experience of a well known brand of Foam filter being a contributing factor to a 240z engine fire about 20yrs ago...the foam collects any spit backs or leaks from carbs and the rest as they say is...
 

Albrecht

Well-Known Forum User
So this got me thinking about how many people here run their triples, SUs or ITBs with open trumpets and if they have ever had issues. Anyone?

Open trumpets on several cars over many years here. Only had problems with foreign bodies getting into them when a bunch of 'bright sparks' (ie dim knuckledraggers...) decided to stuff crisp packets, old leaves and handfuls of turf into them at a Z Club-organised meeting.

So, leaving your bonnet open at a car show might actually be more risky than open trumpets per se.

I think the expression on the street* is 'Haters Gonna Hate'...

*one for the teenagers there.
 

johnymd

Club Member
I have run open trumpets on this car for some time now. This is the new setup I started test fitting today.
 

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AliK

Vehicle Dating Officer
Staff member
Club Member
Open trumpets on several cars over many years here. Only had problems with foreign bodies getting into them when a bunch of 'bright sparks' (ie dim knuckledraggers...) decided to stuff crisp packets, old leaves and handfuls of turf into them at a Z Club-organised meeting.

So, leaving your bonnet open at a car show might actually be more risky than open trumpets per se.

I think the expression on the street* is 'Haters Gonna Hate'...

*one for the teenagers there.

Gosh that is awful!!! It makes me wanna cry - what is wrong with these people!?

Good to know that normal driving didn’t cause issues though.

I have run open trumpets on this car for some time now. This is the new setup I started test fitting today.

As always: Wow Johny! That’s seriously nice - safe to assume Jenvey? And a BHJ damper too?
 

johnymd

Club Member
This time I’ve gone for an OEM product. Namely hayabua itb’s. The Jenvys are similar to the twm itb’s I was using. These can be a bit crude at metering air on very low throttle angles so I chose something better IMO.
 
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