Type 4 Camshaft selection

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

  1. Good morning, yes I am. I'm looking at Scat c25 or C35 camshafts from VWH. Cant find any flat top pistons except from aircooled.net and they are out of stock and P&P is tough. VWH has the recessed piston tops but no flats. Stateside is expensive.

    Think I will change the springs regarldess, I'd like to avoid using shims and longer push rods if possible and avoid changing rocker arms.

    still thinking about CR recess vs flat top.
  2. When I bought a Scat C25 a couple of years ago it was cheaper to buy it from the US than from the UK, suppliers are still paying for shipping and import costs and then adding their mark-up. I’ve bought all the major components for my 2316cc from the US – crank, rods, pistons, barrels, cam, followers, and bearings. Nothing is made in the UK so you’re paying for transport whatever you do.

    For cams I’d say a C25 is more suitable for a bus and a C35 for a car, it’s difficult to know what you’d be comfortable with but my gut feeling is a C25 would be more you’re style.

    Sensible decision to change the springs, you’re making progress. Forget about changing rockers you won’t be doing that. You should check the geometry; although a C25 probably won’t need different length pushrods it may need rocker pillar shims. And you could use lash caps on the valves to tweak the geometry. Incidentally, shims are cheap, pushrods aren’t.

    With 1800 heads and shallow dish pistons the CR should work out okay, I’m using flat top pistons and I’ve had to open up the combustion chambers. Use one of the engine calculators to help make a decision for CR and combustion chamber volume, get the deck to 0.050” if you can.
    Gnasha and Gooders like this.
  3. Got to agree with you about parts supply from the US. Altough i am waiting for some followers & valve springs which are held at customs at the moment. The supplier said about a week for delivery. I had forgotten about the time held at customs. They have had them a week now, how long do they usually take?
  4. I’ve just bought a set of 41mm inlet valves from Intervalve Tecnologie in Switzerland, about 500km from me here in France. The valves are 9 Euro each direct from the manufacturer; I placed the order on the 8th March and payed 40 Euro for shipping, then another 28 Euro for customs handling and tax. I received the valves yesterday, 20th March after less than a day at customs but 12 days for GLS to deliver. Insert expletive to describe the service from GLS.
  5. I was looking st VWH c25/35 camshafts and asked the following:

    Hi, regarding the C25 or C35 I have the following questions in relationship to fitting to a to a 2056cc with twin 40 webers.

    Can you estimate the compression ratio needed for the above using regular 95 octane fuel.

    Would you recommend a change from standard valve springs if the rev limit was kept below 5000rpm?

    Would there be a need to alter the rocker geometry, shims, pushrod lengths rocker ratio etc?


    Answer: 7.5:1 compression ratio should be fine for 95 octane with 28 degrees maximum advance @ approx 3500rpm
    Standard type 4 springs will be fine
    Standard type 4 pushrods are fairly robust but you may want to source 1700 rockers as they take Type 1 swivel foot valve adjusters

    Is the CR low at 7.5?
  6. Just checked my swivel feet again recently..no adjustment required after the last year.. not too many miles ..only a few thousand..( clock stopped turning last summer so not too sure!)

    10mm swivel foot ones from the nice man in Germany

    http://tp-technologie.de/produkte ventileinstellsch.htm

    so you don't need to go 1700 rockers if you want swivel feet and are happy taking a grinder to yours for clearance.

    All articulate happily still after 3 or so years..

    Sent from my SM-G930F using Tapatalk
    Gnasha likes this.
  7. 7.5:1 CR is low, but the engine will run, it just won’t be as efficient as it could be. aircooled.net recommends 7.5-8:1 for a C25 and 8.25-8.5:1 for a C35. Why don’t you ask Scat what they think?

    I’ve said what I think about valve springs and cams with more lift than standard. If you ask enough people the same question you’ll eventually get the answer you want but if you ask Stateside or aircooled.net they’ll recommend HD springs.

    The engine will run without checking the rocker geometry and if you do you might not need to alter anything but if it’s wrong component wear will accelerate and engine life will decrease.

    I suggested Deefer66 use swivel foot adjusters and it looks like he’s happy with them but there is no need to change the rockers if you decide to use them. And no need to use them at all if you don’t want to.
    Gnasha likes this.
  8. Just picked up the Scat lube a lobe lifters & HD valve springs from the local Parcelforce depot.
    With import duty & Parcelforce charge the total cost was still less than buying in the UK not by much tho.
    The HD springs fit over the bosses on the head without having to get them machined which is a result :)
    77 Westy likes this.
  9. Been CC ing heads today and they all measure up at 53cc, including the step. So if I calculate for a 0.5 deck 53cc heads 14cc pistons i am getting 8:0 CR. Happy days:thumbsup:

    98F4DED5-785A-4700-B306-E71BCBBAA9DA.png 3F209D17-BA87-478E-B51F-5E6A904BD5BC.jpeg
    77 Westy likes this.
  10. I’ve been doing the same. Combustion chambers opened up to 61cc, no step, flat top pistons and a 0.061” deck, CR = 9.0:1 I’m happy with that with a C25 cam, deck is a bit more than I wanted but I have limited sizes of cylinder shims.

    CR calculator.png
  11. I have gone with the C25 cam and i am going to fit the Scat single HD springs. Are these ok with the std rockers & pushrods?
    On the AMC heads the HD springs are a light push fit onto the bosses is this acceptable? I am not really wanting to have them machined.
  12. That’s the set-up I’ve been running for the last few years with standard rockers and pushrods, I used lash caps and the geometry isn’t perfect but it works and has lasted without causing any excessive wear to the valve guides. I didn’t even use solid rocker spacers but you should because the rockers could walk off the valve stem.
    Single HD springs are a light push fit onto the bosses on VW heads too, no problem. I fitted a set yesterday.
    Gooders likes this.
  13. Good news,thank you for your help.
    I had already converted the rockers to solid spacers and elephants feet :thumbsup: . I was using pedestal spacers to get the geometry something like, hopefully it should work out right when I get the heads fitted.
    Last edited: Mar 30, 2019
    Deefer66 and 77 Westy like this.
  14. AA Performance flat top P&C's ordered
    SCAT C35 ordered, Ive been told these are compatablle with VW type 4 lifters??
    Single HD springs, stilll required, any ideas?
  15. 94mm or 96mm P&C’s?

    Use Scat Lube-a-lobe lifters with a Scat C35 cam, https://www.scatvw.com/product/scat-performance-type-iv-lube-a-lobe-solid-lifters/ Don’t use generic VW type 4 lifters from some other supplier/manufacturer if you want the cam and/or lifters to last.

    You need HD springs with a C35, valve lift is more and valve acceleration and deceleration is far faster than a standard cam. This might convince you, have a look at valve springs in motion - 20 minutes in.
  16. 96mm :D .

    The video just confirmed my thoughts for the need for HD springs, especially the residency oscillation, awesome stuff. Mr Vizard is a knowledgable man.

    I’ve searched for T4 HD springs and can only find T1 (do this fit T4 heads?) except for European Motor works or Scat both offering 1.550" Install Height=135Lbs Seat Pressure. Are both of these straight plug and play i.e. don’t require any head machining of an 1800cc head?

    Can I re-use the original collets and spring retainers with HD springs?

    SCAT followers on order soon.

    77 Westy likes this.
  17. quality

    77 Westy likes this.
  18. I’ve just fitted Scat HD springs & retainers to my type 4 build. They are AMC heads & they fitted ok without machining the bosses :thumbsup:
    Got mine direct from Scat in the US. Take about 2-3 weeks to arrive & clear customs. A bit cheaper than in the UK but not alot in it when you add duty. They are readily available though.
    77 Westy likes this.
  19. I bought my HD springs from Jim at Stateside, they fit without machining the head and I used standard collets and retainers. You should fit solid rocker spacers with HD springs, although I’ve run the C25 with spring loaded rockers for a few years without any problem. But I’m fitting solid spacers to the engine I’m building at the moment.

    I’m not sure if Type 1 springs are the same size as Type 4 but I think they are smaller. If you’re buying lifters from Scat you might as well buy their HD springs.
    Gnasha likes this.
  20. https://www.scatvw.com/product/single-springs-with-chromoly-retainers/ these are high rev, does that equal HD? Theses do not require any mods and fit T1 and T4
    and these

    looking good :D starting to get a tadge excited here.

    Now swivel feet, I know these require some mods to the underside of the rocker arm where the adjusting screw comes out, is this a DIY job or machinist?

    Thanking everybody for their patience and sharing their vast knowledge with a newbie.

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