Type 4 Camshaft selection

Discussion in 'Mech Tech' started by Gnasha, Feb 25, 2019.

  1. Hi, I’m building a 2.0 type 4 conversion to DTM cooling to put into a 73 Karmann Ghia.

    I’m waiting for the machined parts to arrive and my thoughts are now with camshaft selection for the following spec:

    The majority of the engine will be standard, mainly used for road use and some motorway cruising. Reliability economy, and a little excitement thrown in would be the main requirements.

    Twin 40 IDF Webers.
    Larger 1800 valve heads (3 angle).
    Electronic Distributor.
    Running on 95 Octane fuel
    UK Based.
    How much would the choice of compression ratio affect my camshaft selection?

    Any advice would be much appreciated for a first time aircooled builder.
     
  2. Do it the other way, choose the cam then adjust the CR to suit the cam. Incidentally, you can have economy or a little excitement but not both. ;)
     
    Last edited: Feb 25, 2019

  3. Thanks for the response. Where would I get the technical assitance necessary? Ive always wanted my cake and eat it lol :D
     
  4. Search the various forums and you’ll get many opinions and more technical assistance than you could possibly need.

    Here is mine.:)

    With a relatively light Karmann Ghia you could use a cam that shifts the torque higher in the rev range and therefore make more bhp. I use Scat cams (because they’re good value for money) but Web is better and their 86A grind works well with power from around 1500 revs to 6000, this cam is used in bus engines but IMO it has too much duration with the torque too high in the rev range for a heavy bus. CR needs to be close to 9.0:1 with a tight deck height and depending on your piston choice getting the CR low enough could be a problem.

    I’m building a 2316cc Type 4 with flat top pistons, 1800 heads, Scat C25 cam and 0.062” deck (too big) and I’m having to increase the combustion chamber volume from 56cc to 61cc to get the CR down to 9.0:1.

    What size vents do you have in the Weber 40IDF? And what pistons and barrels are you using?

    A 123 distributor would give you a few advance curves to play with (or programmable).

    It should work with 95 octane but don’t use too much advance.

    UK Based - somebody has to be last to turn off the lights.:thumbsup:
     
  5. @Gnasha I see you are searching the forums.:) Good advice so far.:thumbsup:
     
  6. You sir are clever :thumbsup:
     
    Bulletooth and 3901mick like this.
  7. Steady, you’ll make me blush. I’m not clever and I certainly don’t know everything but I hope I’ve learnt something over the last 50 years or so building and modifying engines and if I can help someone else, I’m happy to do so. But if it doesn’t work, I’m not accepting any responsibility.:)
     
    Jack Tatty, Gooders and Bulletooth like this.
  8. Yeah.........that's what i thought ;)
     
    77 Westy likes this.
  9. What CR would you recommend for my 2.0 type 4 build. I went for a C25 cam and am hoping for reliability & economy more than all out performance.
     
  10. 8.5:1 with a tight deck height but if you’re using dished pistons you might not get the CR high enough. Depends on which heads you have, 2.0l heads have smaller combustion chambers than 1800.
     
  11. I think I would copy the Porsche 914 2.0 specs
     
  12. AE2AE96B-D3C9-4563-88DE-BA5871269C34.png
    Dished pistons with AMC heads. These are listed as 1800-2.0 heads with 39.3 x 33 valves so not sure whether they have the smaller combustion chambers.
    Same heads as MarkC68 used on his build. He measured 56cc in the combustion chamber so I presume i will need a tight deck height.
     
    Last edited: Feb 25, 2019
    MorkC68 likes this.
  13. Small valves and I think small combustion chambers. Measure the volumes but you’ll probably be in the ball park with CR.
     
  14. What are the Porsche 914 2.0 cam specs?
     
    theBusmonkey likes this.
  15. 77Westy thank you so much for the detailed response, much appreciated.:hattip:

    I have searched the main 4 forums Latebay (No1):thumbsup: Volkszone, Shoptalk and Samba. The information available is amazing, and if I'm honest I found it overwhelming, so many permutations few of which suited my requirements. theres some died in the wool smart VW people out there. Thats life.

    It will only ever see the road and motorways/freeways so I think max 5k rpm with the cam arriving on song about 2k rpm? I'd still like it to "behave" during slow town work. What CR would suit these requirements. I'm prepared to buy the cam and adjust the CR to suit, shims under the barrrel etc.

    I forgot to mention I'll be sticking with the hydraulic lifters, which will no doubt limit my choice of cam.

    What size vents do you have in the Weber 40IDF?
    Vents 28 Idle jet 50 Airs 140 Pump jets 50 Mains 115

    And what pistons and barrels are you using?
    P&C's are stock Type 4 2.0

    A 123 distributor would give you a few advance curves to play with (or programmable).
    I currently have an 009 thats been overhauled by the look of the internals (not sure if this is the original spec) Programable sounds good any info,are all 123's programmable?

    Thanks again
     
    mcswiggs likes this.
  16. :worship:
     

  17. never thought of this good idea ill take a look around, anybody used them ??
     
  18. dished pistons, 1800cc heads, if i cant adjust the CR to suit the cam with this set up I may have to resort to selecting the cam to suit the CR?
     
  19. 914 2.0 cam profiles
    In opens: 26 deg BTDC
    In closes: 62 deg ABDC

    Ex opens: 62 deg BBDC
    Ex closed: 26 deg ATDC

    Duration 268 degrees @ .318" of lift (would this be with standard rocker ratios?)


    Anybody familar with this Webcam 163/86B+5.
     
  20. Hydraulic lifters restrict your cam choice a lot, the Web 86A I suggested is a solid cam and so is the Web 86 from Sideshow and the (nice) split duration 163/86b that Alstrup recommended. Forget the 163/86B is any case; you can’t get the CR high enough with dished pistons and 1800 heads for the cam to work – unless you flycut the heads to reduce the combustion chamber volume and that's not a good idea because it weakens the head. And it would push the torque pretty high up the revs which might not be what you want.

    Okay, back to the drawing board and looking at hydraulic cams. A Web 91 would work well with carbs and you should be able to get close to the optimum CR with the parts you have. Measure the piston dish and combustion chamber volume so you know what deck you need – don’t use head gaskets.

    That Porsche cam spec might be suited to the factory FI, and is it hydraulic? The lift is probably at the valve with standard 1.3:1 rockers. It might suit your needs but there are better cams for carbs and I’d choose the Web 91 over the Porsche grind.

    Incidentally, I don’t recommend hydraulic cams and I don’t think you’ll find many that do; the lifters are hard on the cam and cause premature wear. If you’re going to buy a new cam why don’t you upgrade to solid lifters? And nobody can tell you what CR would suit your requirements without knowing what cam you have, you’re trying to put the cart before the horse.

    28mm vents are too small and so are 115 mains for the engine spec IMO. I use 30 vents and 125 mains in my 2.0l bus engine.

    A 009 distributor isn’t standard; VW didn’t fit a single advance distributor to any engine - for good reason. Not all 123 distributors are programmable; some/most have a choice of pre-selected curves.

    I probably can’t add much more, that bloke on VZi is right when he says ‘A car engine in a bus is hopeless and the other way round is milder than necessary.’ And he’s probably reading this.:D
     
    Last edited: Mar 1, 2019

Share This Page