Section : Exhaust

SPIT IV and 1500 Manifold Compatibility 

Posted By : Michael Charlesworth, 28-Jul-2004, 10:58pm

• SPIT IV and 1500 Manifold Compatibility 

  Posted By : Mark Stradling, 29-Jul-2004, 10:01am

  I've not tried it, but can't see any problems.
  
  The manifold face on the head is the same (most after market manifolds are for either car, and a 1500 inlet manifold will fit a Mk IV head).
  
  The standard (and performance) exhausts are the same between the two cars too, so provided you have the downpipe, it should fit.
  
  One thing I would say - I've yet to hear anyone with a good thing to say about the 1500 manifold/downpipe. Talk of the gasket requiring replacement every 6 months and the like. I'd guess it's not really THAT bad, but they don't seem to be the longest lasting part on a 1500...

  • SPIT IV and 1500 Manifold Compatibility 

    Posted By : Jonathan Pashley, 29-Jul-2004, 10:29am

    What benefits would I get swapping the Inlet manifold and HS4 carbs on to my late MkIV?
    
    Jon
    

    • SPIT IV and 1500 Manifold Compatibility 

      Posted By : Paul Bodiam, 29-Jul-2004, 11:17am

      probably very litle at normal engine revs, unless you have a hotter cam fitted.
      
      The HS4 carbs have 1.5 inch bore instead of 1.25 inch in the HS2. Therefore the engine can suck more air through the carbs, but this is a only likely to be a limiting factor when running at full-throttle and high revs.
      
      The HS2 carbs are jetted for the fuel/air demands of the 1300 engine.
      If you fit a pair of standard HS4 carbs to an unmodified 1300 engine, you will almost have to spend some time/effort to identify the most appropriate needle profile for the smaller engine.
      
      A much easier performance gain can be got by switching to a free-flowing exhaust system with a tubular manifold.
      
      cheers
      Paul

      • SPIT IV and 1500 Manifold Compatibility 

        Posted By : Jonathan Pashley, 29-Jul-2004, 12:14pm

        Thanks for that Paul
        I think I'll keep them until next years engine re-build
        any advice relating to what to upspec regarding this would be much appreciated
        
        Jon

        • SPIT IV and 1500 Manifold Compatibility 

          Posted By : Ben Ferguson, 29-Jul-2004, 12:51pm

          I put 1.5"s on my 13/60 (which Ive just found out has a mkIV head) and it made a huuuuge difference over the single tiny carb, which is basically the same size as 1 of your carbs, now that is restricitive! Mated with a 4-2-1 manifold and free flowing exhaust transforms the car; no loss in torque, but top end power is installed! To get the best out of these though, as mentioned before, you will need a hotter cam, which is what I'm doing at the moment. The standard mkIV and 13/60 cam produces max power supposedly at 5000rpm, but the powere curve has already gone quite flat by then. The cam I'm installing has a useful power band from 2200 to 6500, making full use of the revs! I was told when fitting my carbs to the standard engine however that I would need richer needles....I dont think I really did, it ran really rich at tickover... but anyway, rolling road is the best way to set carbs up I'd say.
          
          http://www.moss-europe.co.uk/MossUK/Pdfs/Spitfire/... ---go to page 16 and read from there, all you need to know!
          
          Ben

          • SPIT IV and 1500 Manifold Compatibility 

            Posted By : Philip Rosenberg, 29-Jul-2004, 04:31pm

            From what I've heard and read, upgrading to HS4s can help, but it's a case of how far do you want to go and what order you want to do things in.
            A tubular manifold, sports exhaust and freeflow air filters seems to be the first step, but to get the best out of them you'll probably need to change the carb needles and maybe the spring. I think after that step is when people start considering uprating the carbs, getting "hotter" cams and shelling out for freeflow heads.
            
            I'm no expert mind, and I've only got to that first stage so far.

            • SPIT IV and 1500 Manifold Compatibility 

              Posted By : Jonathan Pashley, 29-Jul-2004, 05:19pm

              Phil
              I just happen to have a pair if HS4s off my 'shed' and thought they might give my MkIV a bit of extra ooomph
              I think now that I ought to wait until it breathes out a bit better and the dreaded engine rebuild is done before fitting them to the beastie
              
              Thanks for the advice
              
              Jon

• SPIT IV and 1500 Manifold Compatibility 

  Posted By : Paul Bodiam, 29-Jul-2004, 11:05am

  The 1500 exhaust uses 2 downpipes. To accommodate this, a slight modification was made to the 1500 chassis, allowing greater clearance where the downpipes pass between the sump and the chassis. Your mark 4 chassis may not have this modification, and therefore you may well have clearance problems fitting the standard 1500 downpipes.
  
  oh, and as already said by others, the manifold-to-downpipe gaskets blows through depressingly regularly.
  
  cheers
  Paul