jp4 head - worth it?

  1. Saxperience Post Whore Joined: Mar 2008 Pembrokeshire Posts: 5598
    #1
    Have a spare engine that im currently building up to put in my 106, have a good j4 head already built to use, however ive been offered a bare j4 head for very cheap....

    my question is, is it worth changing everything over to the jp4 head? which uses slightly bigger valves? im aware you have to use j4 cams, j4 springs, retainers etc

    is for a boosted build so will the extra valve size be worth it or just stick to the j4?
  2. Established Member Joined: Mar 2006 Farnham Surrey Posts: 1542 AX GT 16v turbo 6 speed with NOS 205 gti6 E 320
    #2
    bigger valves on a boosted engine is always a good thing so if its cheap and you have the conversion parts already you might as well
    the only thin to work out is the comp ratio
  3. Saxperience Post Whore Joined: Mar 2008 Pembrokeshire Posts: 5598
    #3
    it is very cheap and have all the parts needed, how do i work out the comp ratio from there?

    also need to select what head gasket to use as using low comps
  4. Established Member Joined: Oct 2008 Milton Keynes Posts: 1210 Yellow 106 Rallye
    #4
    When I was building my turbo lump Atspeed recommended sticking with a j4 head, can't remember exactly why but they might be worth asking as they run some big power boosted engines
  5. Saxperience Post Whore Joined: Mar 2008 Pembrokeshire Posts: 5598
    #5
    thats interesting, anyone know if you can use aftermarket j4 cam or standard for that matter in a jp4 head?
  6. Established Member Joined: Oct 2008 Milton Keynes Posts: 1210 Yellow 106 Rallye
    #6
    You CAN run j4 cams in a jp4 and people do but the loebs don't line up squarly with the lifters and sit off to one side.
    You shouldn't and all cam manufacturers say don't but people do run them and appear not to have problems.
  7. Saxperience Post Whore Joined: Mar 2008 Pembrokeshire Posts: 5598
    #7
    thinking ill just stick to j4 to be honest but ill buy this jp4 as its silly cheap