Old old problem of mk1 air box / air filtration when installing 8v non crossflows

Discussion in 'Throttle bodies & non-OEM ECUs' started by Jon Olds, Jun 28, 2020.

  1. Jon Olds Forum Junkie

    Joined:
    Jan 28, 2004
    Likes Received:
    535
    Location:
    United Kingdom
    Been here many times, problems are multiple (well known, but humour me..);
    1.Carbs or ITB's above exhaust
    2. Bulkhead right where you want filters/airbox
    3. Clutch cable right between cylinders 1 and 2
    4. Brake master next to cylinder 1
    Nothing we didn't know there, then.
    My latest build (race) is being mocked up now, and i'll add a couple of pics to illustrate todays work;
    curved air intake 8v option 1.JPG curved air intake 8v option 1b.JPG
    I've fitted these 90 degree trumpets just as an experiment. Ideally some longer (45 degrees 150-180mm) would be much better.
    The bodies are the 30mm Jenvey ones. (45 bore)
    Current thinking is to build a big (really big) rectangular alloy airbox and feed ir via 5" pipe right to the front of the car (over gearbox side) then fit the biggest cone filter I can find.
    Pros: 1. ITB's as far away from the exhaust as feasible. 2. Trumpets are a nice shape and the correct diameter (45mm right through minimum) 3. Cold air 4. lots volume upstream of throttle plate. 5. top of the 90 degree horns is an easy good shape to mate to the airbox 'floor'.

    Haven't had the hardware to mock this, until now.

    Cons, as I see it : 1. Butterflies way too close to inlet valve(s) 2. 90 bend (not really worried about this, its just air) 3. very short run for each cylinder to plenum airbox (wild cams wont like this)

    So, discussion please.

    Questions: Apart from the jenvey 40 degree curved horns (possible, but a bit short) , does anybody else make them? Has anybody made some on a 3d printer (bought some straight ones this week, they seem ok, superlight , not a bad shape etc) Anybody run the short jenveys on a cammed engine? Anybody run ITB's into a home made plenum through a pipe to a cone?
    Jon
     
  2. Jon Olds Forum Junkie

    Joined:
    Jan 28, 2004
    Likes Received:
    535
    Location:
    United Kingdom
  3. drunkenalan Paid Member Paid Member

    Joined:
    Jun 11, 2004
    Likes Received:
    35
    Location:
    Leicester
    hi Jon, I remember having a chat with Jason about this or similar a while ago. Jason was considering a trial head where he bored through the injector ports for a better angle for the airflow the valve, obviously that then becomes a very bespoke head and manifold!!

    I have been looking into carbs and ITB myself recently too but for a mk2. I looked at IDF's for down draught, but the manifolds are generally compromised. the main issue being the port floor is almost horizontal.

    A custom manifold might be a better solution, pretty sure someone like DanST could make something up. alternatively, could you cut a V section out of the alloy manifold and re weld it back together, the re port it??

    one option I considered, was a manifold that leant the inlets over at 45 degrees towards the gearbox to gain some length.
     
  4. drunkenalan Paid Member Paid Member

    Joined:
    Jun 11, 2004
    Likes Received:
    35
    Location:
    Leicester
    Not sure it possible but saw this which got me thinking!
     

    Attached Files:

  5. Jon Olds Forum Junkie

    Joined:
    Jan 28, 2004
    Likes Received:
    535
    Location:
    United Kingdom
    These are the kind of things I was hoping my thread would raise. Try something different/left of centre etc
    Make it up as you go along, be creative, don't copy what everyone else does.
    Anyway, one of the main disadvantages of the dcoe is its mounting angle. I like that a throttle body can be fitted any angle, giving more creativity possibilities. My build is still in the fluid state now, keep it coming.. Expect some more mock up ideas, especially as I'm now a TIG owner operator, with my first scalp of ali welding under my belt...
    Jon
     
  6. mr hillclimber Club GTI Supporter and Sponsor

    Joined:
    Nov 24, 2005
    Likes Received:
    148
    Location:
    Southwest
    Hi Jon, what I've found:

    1: it's not the issue often touted. I've measured the intake temps when running both on a rolling road (warm) and on the move on the road (cold). When tuned on the rollers the mixture is wrong on the road (too rich), but closer to the mark from engine dyno to road (better temp control on the engine dyno). We for heat shields between the carbs and manifolds to further help reduce heat transfer. You still get some naturally creep up from the head on idle but it all settles out on the move.

    2: We don't run filters, not ideal but race engines arnt designed to 100k. I saw a 10hp loss on mine over 5 hard seasons and 50+ events with filterless 48's...I can't imagine it would have dropped much less with filters. Different ball game in rallycross or other loose surface events though compared to tarmac use. We ventilate the rain tray these days for improved airflow pick up through the std bonnet vents.

    3: We modify the clutch pedal to pull the cable down from inside the rain tray.

    4: Pedal boxes with either under dash cylinders or remote mounted in the std servo location remove that issue, though I've used a simple non servo Golf master direct on the bulkhead in the past that just clears.
     
  7. mr hillclimber Club GTI Supporter and Sponsor

    Joined:
    Nov 24, 2005
    Likes Received:
    148
    Location:
    Southwest
    Ive not run the very short bodies but have one engine on the medium Jenveys (90mm I think) with long trumpets, so overall length the same as normal. Default inlet manifold flows/performs fine when ported properly...if you've not broken into the bolt holes it's not big enough.

    Good thinking with the dowmdraught trumpets if you can get the overall length the same as a sidedraught set up (260mm)

    Alan, there's a dowmdraught manifold available from Rowlands manifolds in South Africa...could make a good road conversion.

    I have indeed experimented with a dowmdraught port through the std injector boss....no flow increase over the std inlet port location with the std 40mm inlet valve...looks cool though!
     
  8. mr hillclimber Club GTI Supporter and Sponsor

    Joined:
    Nov 24, 2005
    Likes Received:
    148
    Location:
    Southwest
    I like this set up Alan...would look good on my 197 Clio too!
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice