Anyone running open trumpets / velocity stacks? | The Z Club of Great Britain
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Anyone running open trumpets / velocity stacks?

Discussion in 'Anything and everything' started by AliK, May 22, 2020 at 1:41 PM.

  1. AliK

    AliK
    Z Club Member
    Staff Member Moderator

    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.
     
  2. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator

    I think if you get a whole unit richer with the air filter you should get a new air filter.
     
    AliK likes this.
  3. franky

    franky Well-Known Forum User

    99% of the time engines seem to make more power with an airbox.

    could it be that you need a blue airbox? :D
     
    AliK likes this.
  4. AliK

    AliK
    Z Club Member
    Staff Member Moderator

    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
     
    Last edited: May 22, 2020 at 3:01 PM
  5. 8658kv

    8658kv
    Z 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
     
    AliK likes this.
  6. AliK

    AliK
    Z Club Member
    Staff Member Moderator

    Thanks chap and most welcome on the letter!
     
  7. Rob Gaskin

    Rob Gaskin Treasurer Staff Member Moderator

    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.
     
    AliK, Paul_S and datsfun like this.
  8. datsfun

    datsfun
    Z Club Member

    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 ??
     
    AliK likes this.
  9. Bazzateer

    Bazzateer
    Z Club Member

    That's not been my experience at all Rob. Some of my best ideas come to me after a beer or two.
     
  10. atomman

    atomman
    Z 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 ?
     
    AliK likes this.
  11. toopy

    toopy
    Z Club Member

    What about something like this as a compromise to stop any substantial debris getting in?

    s-l400.jpg
     
  12. toopy

    toopy
    Z 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.
     
  13. atomman

    atomman
    Z Club Member

  14. datsfun

    datsfun
    Z 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.
     
    AliK likes this.
  15. AliK

    AliK
    Z Club Member
    Staff Member Moderator

    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.
     
  16. datsfun

    datsfun
    Z Club Member

    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...
     
    AliK likes this.
  17. Albrecht

    Albrecht Well-Known Forum User

    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.
     
  18. johnymd

    johnymd
    Z 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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  19. AliK

    AliK
    Z Club Member
    Staff Member Moderator

    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.

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

    johnymd
    Z 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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