Valve sizes for 1776

Discussion in 'Mech Tech' started by paradox, May 28, 2020.

  1. If he hasn't used them already these could work until you source another set.

    No cash would need spending on them as they are already cut for 90.5mm and have been ported & polished etc
     
    Lasty, Zed and snotty like this.
  2. The thing is snotty the valves in these heads are 2.5mm smaller on the intake and 2 mm smaller on the exhaust than stock valves so increasing the capacity by 191 cc more than stock but retaining the small valves will bring the torque curve down low but may end up strangling the mid to upper rev range too much.

    I do think stock size valves would be just right.

    It’s a shame these heads have small valves as the ports on these heads are wonderful compared to other heads I’ve seen.
     
  3. Zed

    Zed Gradually getting grumpier

    Para, are you sure the ex valve is 30mm and not 32mm?
     
    davidoft likes this.
  4. mikedjames

    mikedjames Supporter

    You would be surprised how far they go.. i think over 20000 miles for mine .. engine had cracked heads so I fitted Autolinea. Cracked those too but once cracked it stayed the same for 50000 miles until a stainless steel valve gave way , the valve seats and spark plugs were still in that head when the piston lay in fragments in the barrel..
     
    davidoft likes this.
  5. I don’t have the valve to measure and my callipers won’t reach inside the combustion chamber to measure properly
    But putting a piece of paper into the valve seat and using finger pressure to leave a mark and then measuring that I get 30mm

    Googling earlier today I found the following on the samba

    043-101-375A 35.5 in x 32 exhaust

    043-101-375 R or H 33 in x 30 exhaust

    9mm exhaust stems
    H heads have cht sensors R heads do not
     
  6. Zed

    Zed Gradually getting grumpier

    Have you checked Samba? Wreck provided a link to an article using these Beetle FI heads to build a mileage motor and they quote 32mm with 9mm stems.

    The consensus, if you haven't looked is positive - too big is bad, small no problemo. But that's just two guys so far.

    I'm running 2.4l on 1.7 valve seats, I like it. Don't bother messing with th exhaust seat, no point, you want a fairly large contact area for heat dissipation but the inlet seats could be "adjusted" like mine to run a slightly bigger valve and SS valves have a much better shape too.
     
  7. Zed

    Zed Gradually getting grumpier

    Sorry missed that the FI come in 2 sizes of exhaust but I wouldn't worry.
    Back to mine for your reassurance. My exhaust valves are 33.
    So I have 600cc with 33mm
    You have 444cc with 30mm
    I don't see a problem.
     
    Last edited: May 28, 2020
    paradox likes this.
  8. I notice alstrup has replied on the samba saying it will behave like a 1600 single port with more power.
     
    Zed likes this.
  9. Zed

    Zed Gradually getting grumpier

    Ha-ha, not knowing if that's good bad or just different (for a bus engine) I've asked him to expand on that.
     
    paradox likes this.
  10. Zed

    Zed Gradually getting grumpier

    Maybe the inlet is more of a problem that the exhaust, that 30 jumped out at me.
     
  11. I’d imagine he means low down torque
    I have read about them building stump puller engines from 2 litre plus on standard valves with single port manifolds
     
    Zed likes this.
  12. Sorry @paradox he has used the 1776 heads.

    He is looking to see if he has some 1600s.
     
    paradox likes this.
  13. Zed

    Zed Gradually getting grumpier

    I'm playing a bit thick, I would like his opinion on whether a boy racer like yourself would be happier with 36.5/32 heads. I really have no idea about single port top end behaviour.
     
  14. No worries cheers paul
     
    paulcalf likes this.
  15. I’m slightly more of a plodder nowadays but don’t want to be crawling up hills

    I think the power tails off further up with single port manifolds compared to twin port

    A bit like an 8 valve head compared to a 16 valve head

    I’m watching the thread hoping for some more involved replies.

    It could pull like a train from low down which would be great but not much use if it starts choking out at 3500 rpm
     
    Zed likes this.
  16. Zed

    Zed Gradually getting grumpier

    Exactly, clarification required.
     
  17. Zed

    Zed Gradually getting grumpier

    Right, Alstrup says...

    One of the reasons to why many people like the smaller valved engines is that they pull peak torque at a lower rpm so they´re nice around town. They - can support some hp but they require significantly more duration and lift than what a stock cam provides. If you chose to build it with the smaller valved heads and stock cam you should expect peak hp at around 3500. Peak torque will be around 2500 rpm but not a lot of it. Around 125 Nm.
    Many years ago I built a few of such engines and they were disappointingly slow. BUT! I also found out through a customers 1600 engine (He built it himself and I dialed it in) That with a W100 cam, 8,5 CR, a set of Kads and a decent header to it, such engine can actually bleed some very nice torque. I had some lower rpm stumble due to this header being a little on the large side for it (1½" BAS buggy header) so I did the classical mod with 1,25 rockers on intake alone to balance it, and it ended up pulling very nice power for what it was. 85 hp and 150 Nm torque.
    But as said, in stock form I would opt for a set of heads with larger valves.
     
  18. Morning Steve

    It’s as I suspected then that it’s going to get strangled out too early in the Rev range.

    Ive a pair of kadrons in the shed but I’ve no idea what jetting they have and I seem to recall the linkage was trashed
     
  19. I'd fit your Kadrons, para. A single Solex on that t-shaped manifold is going to strangle your engine anyway.
     
    paradox likes this.

  20. I know the engine will perform better with them.
    But it’s going to need some extra spending on a new linkage,air filters and jets etc
    Plus they would need modifying to add a vacuum feed for the dizzy as well as needing a fuel pressure regulator or electric pump and associated wiring.
    Plus I liked the simplicity of the single carb and the reliability of cold winter starts with the stock set up with its choke and pre heat.

    I’ve found aa do stock sized valve heads opened up to the barrel size you require and they will even adjust them to your required cc for an extra charge.

    The problem is all these heads seem to have stainless valves
    Now I know the shape of a stainless valve lends itself to better airflow
    But the valve stems are softer so you need to use lash caps or swivel foot adjusters and then start messing about with geometry and possibly cut to length push rods.

    So much for keeping things simple
     

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