Type 4 Camshaft selection

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

  1. I’ve heard AA barrels are not great. However their pistons are generally good and a set are usually within 1g of each other.
     
  2. GARRICK CLARK

    GARRICK CLARK Sponsor

    I've used AA kits for years. What I found was the ring gaps were too tight and needed correcting.
     
  3. I was apprehensive buying AA cylinders but I bought them from a supplier that inspected them before dispatch and I have to say they are bob on, exact same length on all four, same bore, parallel top to bottom and perfect cross hatch hone. The only thing wrong with them was that there was no cut-out to line up with the port in the crankcase – but there is now.

    I’m using KB hypereutectic pistons with Hastings rings.
     
  4. I have already left a question with VWH regarding the volume occupied by the recesses. I may ask a couple of quality questions with repect to repeatability during manufacturing and tolerance fits.

    Is there a spell check on here? my spelling is pants:thinking: and I rely on the sqiggly red line to make adjustments.:thumbsup:
     
  5. I doubt if they’ve been asked the question before and I doubt if they know the answer. Just looking at the pic it’s not going to be much but every little helps. You could also ask them if they have shallow dish pistons available – not deep dish 2.0l.

    Have you decided on a cam yet?
     
  6. When I know that that the chosen set up (P&C's) will give me the ideal CR with minimum hassel I'll be looking at 86 or 86a or Scat equivalent solids. Nice idle and low torque are the must haves here. Reading your comments 275+ duration will give me the smooth idle and a low rpm torque, I'll probably never touch 4.5k or even 4k so I'm not worried about top end too much. Being a bit of a detail guy I'm looking forward to setting this up as it should be with the ideal CR etc. so it runs at the right spec.

    Then all the work will be for nothing if I dont have the right exhaust system,headers etc.

    Who has the Webcam and Scat franchises in the UK?
     
  7. Jim at Stateside will probably have Web cams, although maybe not the one you want. I’ve bought Scat from VWH but the last one I ordered from the US, good price from Summit Racing Equipment. I can’t remember if Scat wouldn’t accept payment with an overseas credit card or wouldn’t ship overseas, they wouldn't sell direct to me anyway, no problem with Summit.
     
  8. I placed an order with Scat last week. Spoke to a guy called Ron very helpful. Prices are pretty good but don’t forget to add import tax.
     
    77 Westy likes this.
  9. I was told by Ron Greiner that Scat only accepted international orders if payed via Pay Pal or by a bank transfer. I don’t do PayPal.

    The C25 cam, lube-a-lobe lifters and a gear were cheaper from Summit than they would have been direct from Scat. Including delivery, $291.23 from Scat, $276.84 from Summit and yes, tax has to be added.

    And I’ve just noticed that I bought the cam more than two years ago and I still haven’t built the engine. New exhaust valves should be delivered tomorrow from Germany and the inlet valves from Switzerland probably Tuesday and that, at long last should be all the parts I need.
     
    Gooders likes this.

  10. Your question about Barrel & Pistons 96x71 2056cc For 2.0 litre Type 4 has been answered.

    Your Question: Hi, can you tell me the volume in cc occupied by the valve recesses.
    Can you comment on the quality of this item regarding tolerances and repeatabilty between like components, e.g.barrel to barrel and piston to piston etc

    Thank you

    Answer: The valve recesses are 7cc.
    With regards to quality they are made to a factory spec but if you are building a performance engine you should get engine components such as crank,rods,flywheel, clutch and pistons match balanced.


    So......... I'm assuming 7cc/recess X 2 =14cc per piston?? .........or is it 7cc/piston? Life is never simple :confused:
     
  11. I’m sure that is 7cc per piston. I’m surprised they knew.

    1800 heads are about 56cc, plus 7cc in the piston, deck 0.050, bore 95mm, stroke 71mm = 8.1:1 CR. With flat top pistons - 8.9:1 CR. For a car engine I’d go for the higher CR with a Web 86a (or maybe a Scat C35).
     

  12. Your question about Barrel & Pistons 96x71 2056cc For 2.0 litre Type 4 has been answered.

    Your Question: Hi, can you tell me the volume in cc occupied by the valve recesses.
    Can you comment on the quality of this item regarding tolerances and repeatabilty between like components, e.g.barrel to barrel and piston to piston etc

    Thank you

    Answer: The valve recesses are 7cc.
    With regards to quality they are made to a factory spec but if you are building a performance engine you should get engine components such as crank,rods,flywheel, clutch and pistons match balanced.


    So......... I'm assuming 7cc/recess X 2 =14cc per piston?? .........or is it 7cc/piston? Life is never simple :confused:
    Reply from VWH "That looks to be in total."

    63cc, 96Bore, 71 stroke, 0.05 deck = 8.1:1CR .......I dont know if AA make a flat top for a cheap as chips outlay:)

    Would the lower CR give me a lower head temperature?

    I'm going to take a look at the specs for 86 86a Scat C35 tomorrow and do some serious reading. I dont want to alter rocker ratio, or have to change springs. I think the 1800cc already had thicker springs?? I'll be back :D

    Thanks again.
     
  13. Regarding valve springs its not the thickness of the coils its the gap when compressed. Too tight & they become coil bound which is likely to break something. Some have said you can get away with std springs with a Scat C25 some say you need heavy duty. As Mr Westy has mentioned in a former thread you need to measure the coil gap at full lift when assembling to make sure you have enough clearance. I have ordered a set of HD springs from Scat in case I need them, otherwise they will be up for sale.
     
    Last edited: Mar 11, 2019
  14. Reducing the CR could give you a lower head temperature, but it reduces engine efficiency and therefore power. Might be useful for a bus but in a Karmann Ghia you don’t have to worry about head temps simply because the engine isn’t working very hard.

    You might get away with standard springs with an 86, 86a or C25 but a C35 has more valve lift and you’d definitely need HD springs – why don’t you want to change the springs? Because of the high lift a C35 would be fairly hard on the valve train which seems at odds with your reliability requirement. And a C35 needs more CR to work.

    Rocker ratio is 1.3:1 and you’re not going to change that by changing the cam.

    Happy to be proved wrong but as far as I know all bus Type 4 engines used the same valve springs regardless of engine capacity.
     
  15. Just found the gumph on the webcam we bought..stock grind... turns out that's the stock 914 that they put up as the stock bus one... works fine for us so far..[​IMG]

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  16. If you look at those two examples^ you can see why a standard cam tends to make the engine run hot at low revs. Compare the exhaust valve lift and duration to the 73 grind – the standard cam doesn’t allow enough space (lift) or time (duration) for the exhaust to escape.

    Did Porsche really use that cam for the 914? If they were selecting a cam for the engine today I doubt if they would pick that one, although because it runs hot at idle measured emissions would be reduced.

    The 73 is a mild upgrade and would work with a low CR, good for a bus engine with maximum torque at low revs, not so good for a car engine (low bhp).
     
  17. That'll explain the getting warm if you're in a big motorway que then.. .. ah well avoid ques....

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  18. Morning, I've been thinking reading and some more thinking:thinking:

    Firstly: VWH states recessed pistons are for the clearance of a high lift cam, are the 86 and 86a spec'd as high lift? If flat tops are used surely the deck height must increase to maintain valve clearance with the piston crown? and in so doing increase the CR . what am I missing here?

    The 1800 heads are complete and ready to go, I'm reluctant to disassemble as I did want to maintain stock as much as possible for reliability. However, I do want a decent cam so if I have to alter the springs I will but I want to keep the current rocker ratio.

    Whats the maximum lift the stock rocker geometry will accept?
     
  19. The 86 and 86a cams have a higher lift than standard but the valves shouldn’t clash with flat top pistons. However you should check valve/piston clearance as you build the engine.

    If you use standard valve springs you must check that they aren’t coil bound at full lift. If you attempt to start the engine and the springs are coil bound the pushrods will bend or the rockers will break.

    With anything other than a standard cam I strongly recommend that you fit HD springs, even if they are not coil bound. When you increase the valve lift the valve has further to travel and acceleration increases and you do not want the cam follower to lose contact with the cam as the valve closes due to the inertia in the valve.

    Fitting a cam with a higher lift does not change the rockers ratio. All standard type 4 rockers have a 1.3:1 ratio. Alternative rocker ratios are available but I don’t think you should go there.

    If you use anything other than a standard cam you’ll need to check the rocker geometry; you may or may not need pedestal shims and/or different length push rods.
     
  20. @Gnasha are you still pondering?
     

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