Larger valves in an 810?
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Thread: Larger valves in an 810?

  1. #1
    1000+ Posts bowie's Avatar
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    Default Larger valves in an 810?

    Having a look at the cylinder head again on this 810 engine, I was sad to see there is probably only 4~mm (2mm~ each side) at most of clearance before you would have to reshape the combustion chamber, or at least cut a groove in it to clear the valve.

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    That is, knocking out the valve seats, guides and fitting slightly larger ones with a valve to suit. I figure I'll have this head rebuilt with fresh seats and guides, so.. why not bigger?

    Now looking over readily available parts, it seems the exhaust valve from a 15/16/17 would be pretty good. They measure 35.35mm compared to the 33.5mm on the 12 TS/TL, the stems are wider (8mm vs 7mm), and... actually I don't have a figure for overall length. But I assume I can have guides cut into the stem should it need to be shortened. Are the collet arrangements on the 15/16/17 valves similar to the 12? That is with a single guide cut for the exhaust valve? Would there be any problem in using that on the intake side?

    Anyway, what have you done before with your 12's, 10's and 8's in order to fit larger valves?

    And how much material would one dare remove from the sides of the combustion chamber (forget about it lowering the combustion at this point as we will take as much as we can of the face anyway) before you would worry about it fouling the block? I assume the combustion chamber is already slightly larger in diameter then the cylinder in the block?

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  2. #2
    1000+ Posts Frans's Avatar
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    Personal opinion. If you want bigger valves the engine must be highly modified. The way you want to do it is wrong for a start because the 8 mm stem of the valve is going to block more of you flow through the port. Rather have a look and get yourself a bigger valve (if you want to go that way) from a 16 V Japanese engine or bike with a 7mm stem and have it shortened and grooved and hardened on the tip again.
    I am not sure of the ratio but I think that they say the figures are 33%. If the valve lift is less than 33% of the diameter it is a waste but this is on a full race motor that is maxed out and you are looking for more flow.
    Frans

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    1000+ Posts bowie's Avatar
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    Ah good points Frans.

    I figured in effort to keep parts reasonable, it made sense to recycle as much as I could (guides, seats). But yes the extra space eaten by the increased width of the stem is kinda a step backwards.

    And lift vs diameter much more reading for me. I haven't got my head around max lift available on these things without cutting into pistons.

    When you say highly modified, I suppose I had the impression that bigger valves was a fairly straight forward thing done after / as well as working out cams and combustion ratio?


    More reading.

    P.S. Great tip re motorbike valves, they are much closer in overall length.
    Last edited by bowie; 20th May 2018 at 09:10 PM.

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    Find yourself an 8G head, a 365 gearbox, a set of 17TS/G rear discs, plus a few other odds and ends, and create a proper FIA homologated Group 2 Renault 12 :-)
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  5. #5
    1000+ Posts Frans's Avatar
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    Quote Originally Posted by bowie View Post
    Ah good points Frans.

    I haven't got my head around max lift available on these things without cutting into pistons.
    From my experience you can go very high on the cam without worrying about hitting the pistons. This is not saying you don't have to check it when you build it. I think you can go to about 7mm cam lift, that will give you 10.5mm valve lift which should still be safe. I reckon you get a cam to suit your needs and make a plan afterwards if required. All will depend if you are going down draught, side draught or twin side draught and what extractors etc. Important is that the whole breathing system, carbs, cam, valves, extractors should be a matched system.

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    [QUOTE=Frans;1570422]From my experience you can go very high on the cam without worrying about hitting the pistons. This is not saying you don't have to check it when you build it. I think you can go to about 7mm cam lift, that will give you 10.5mm valve lift which should still be safe. I reckon you get a cam to suit your needs and make a plan afterwards if required. All will depend if you are going down draught, side draught or twin side draught and what extractors etc. Important is that the whole breathing system, carbs, cam, valves, extractors should be a matched system.

    Regards, Frans.[/QUOTe

    absolutely agree Frans. from my own experience, the maximum camshaft lift on these motors should not exceed 275 thou if you want reliability and longevity with the stock 19 mm cam followers.

    however, and again having experienced the gains (especially the early kick in the back all the way to 8k ) of using a 300 thou camshaft lift,i am going through the expense of installing 21 mm r8g cam followers to negate the wear on the lifters and consequently the cam lobes .

    i currently run 275 thou lift , 300 deg advertised duration .reliable and very drivable but i have to note this is a very balanced and matched unit. also highly addictive.
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  7. #7
    1000+ Posts Frans's Avatar
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    Thank you for confirming that Potentz, and Bowie, I doubt you will go further in development as Potentz has. So it is safe for a very hot cam even with twin DCOE's and to top it all is the fact that Potentz has a vernier gear adjustment on his motor and the cam is retarded from factory settings (old keyway setting), or the crank is advanced, same thing, which means that he will be more prone to hit the piston especially on the exhaust stroke with the exhaust valve.

    ie. don't worry about pockets in the pistons.

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    1000+ Posts bowie's Avatar
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    10.5mm valve lift has it at 14.5% of bore (73mm) so that's probably as high as you'd want to go anyway (stock lift is 7.34mm). But good to know. That's kinda the ball pack I was looking towards (well set a maximum at 15% of bore and work down from there).

    Trying to get my ducks in a row, expecting to end up with a revy engine with fsk all anything happening until port velocity picks up. Ideally, Power from 5.5-7k would probably be suitable. I suppose spinning these things much fast starts to decrease the life expectancy quickly.

    Inlet manifold / fuel was going to depend on how much air I could get into it. With 35mm~ Inlet vales, 14.5% of bore in lift, and 270-300 duration It's starting to look worthwhile. I'll start with the larger 36/32 downdraft, use that TS inlet manifold I'm stretching out with 33mm~ runners (porting the head to match), get a 2~+ inch exhaust system (using the TS exhaust manifold which all you seem to rave on about), shave the head to get at least 11:1 compression and start from there?

    "shrugs"


    Thanks for the discussion Frans and Potentz, and no.. unlikely I'll end up with anything much more developed then the pair of you.

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    If you're prepared to spend time trawling through the Supertech catalogue you may well find a 7mm stem valve that suits your needs. If you know the retainer lock angle it makes it even easier. For example, Kawasaki Z900/1000 use 7mm x 7 deg locks, the same a Peugeot XU9J4.

    Do you know the overall length and lock angle?

    https://www.supertechperformance.com...-engine-valves


    The other important consideration is valve seat geometry. I take all my heads to Rams at Windsor because they have a CNC seat cutting machine. My favourite profile is saved in the machine, making consistent and accurate seat/throat cutting easy. The seat heights are also then consistent, usually within 0.001", making valve spring installed heights consistent.
    Last edited by PeterT; 21st May 2018 at 03:58 PM.

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  10. #10
    1000+ Posts bowie's Avatar
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    Lock angle no, Simon? I see a reference to a square lock? 90 degrees then?

    Overall length yes, 89.8mm

    Also this site is also great for quick sizes of things (for other bowies out there).

    https://www.precisionintl.com/Engine...1516&EID=12850
    Last edited by bowie; 21st May 2018 at 04:31 PM.

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  11. #11
    1000+ Posts PeterT's Avatar
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    keeper/collet angle?

    Length is very similar to Z900. Would it take a std 36mm inlet and 30mm exhaust?
    Last edited by PeterT; 21st May 2018 at 06:17 PM.

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  12. #12
    1000+ Posts bowie's Avatar
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    Ah I see, wait surely I'll have to re cut to length suppose it doesn't matter.

    But no, maybe.. I don't think there is enough room for a 36mm, ah it would be close. Best get my yard stick out and have another look. Have a look at the link below to give you context.

    https://www.aliexpress.com/item/Free...678149262.html

    Those inlet valves are cut for a 33.5mm

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    1000+ Posts bowie's Avatar
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    Oh no Ali-barber is the worst,

    You can still buy brand new C1J / C2J heads..

    https://www.aliexpress.com/item/7700...ceBeautifyAB=0

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    1000+ Posts bowie's Avatar
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    But to answer your question I don't feel there is enough room for a 36mm inlet, That would leave about 1mm worth of material between the inlet and exhaust valve. Surely that is just asking for it to crack?

    Pictures to give you an idea of a dirty one

    https://photos.app.goo.gl/DLVLgDJeDT5nLjZGA

    As you can see the guides are trash, I suppose it's all going to have to come out so as long as the overall lengths match up, I suppose it doesn't matter that much?

    And perhaps I'm trying to hard, a big cam with heaps of overlap that lifts 9- 10mm with those 33mm inlet valves is going to be pretty cool too.
    Last edited by bowie; 21st May 2018 at 08:13 PM.

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    1000+ Posts alan moore's Avatar
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    There will be a point where you enlarge your valves for no more flow gain because of valve shrouding. Why wouldn't you go for an R15/17 motor, which has a 30Hp advantage before modification, minimal change in overall weight, with more hot up gear and info available. There has to be one around with a set of mounts to go straight into your 12.

    As others have mentioned much greater percentage of power will be gained with an R12 with carbs, cam and compression, rather than valve size.
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    More than 30. In fact, with no mods a 807 engine will double the power he has now.

    He has been offered one such engine, didn't want it.

    I always wondered why Renault never put the 807 in R12 (apart from the piss weak US version). Didn't want to cannibalise R15/17 sales? It would have been a much better car than both the 17 and the 12.
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    1000+ Posts bowie's Avatar
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    Didn't want it, couldn't afford it. That much hasnt changed. I thought you sold yours on already?

    Interest in valves is because as you can see that head will need new everything, why not if I can.

    Cam compression and carbs are a given (eventually)

    And it's still fun learning all this crap with a pos 810.

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    COL
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    Quote Originally Posted by schlitzaugen View Post

    I always wondered why Renault never put the 807 in R12 (apart from the piss weak US version). Didn't want to cannibalise R15/17 sales? It would have been a much better car than both the 17 and the 12.
    I think you will find that it was to do with silly rules of the time in Australia such as there had to be at least so many cc's in engine capacity between models in the range. Thats why the early R12's had 1250 cc engines here, because the R16 had a 1470 cc engine, and the 1289 cc engine was not small enough.
    Regards Col

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    1000+ Posts REN TIN TIN's Avatar
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    Quote Originally Posted by bowie View Post
    Oh no Ali-barber is the worst,

    You can still buy brand new C1J / C2J heads..

    https://www.aliexpress.com/item/7700...ceBeautifyAB=0
    Just be aware that these C1j and C2J heads don't have the moulding for the alternator mount.
    If you did want to use one of these you'll have to find somewhere else to put the alternator.
    Moving the alternator might mean a different water pump.
    Better to stick with a head for an 810 motor.
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  20. #20
    1000+ Posts schlitzaugen's Avatar
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    Quote Originally Posted by COL View Post
    I think you will find that it was to do with silly rules of the time in Australia such as there had to be at least so many cc's in engine capacity between models in the range. Thats why the early R12's had 1250 cc engines here, because the R16 had a 1470 cc engine, and the 1289 cc engine was not small enough.

    The car was sold globally and to my knowledge the 807 engine option was not offered in any market save for the seppos where it was seriously detuned.
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    COL
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    Quote Originally Posted by schlitzaugen View Post
    The car was sold globally and to my knowledge the 807 engine option was not offered in any market save for the seppos where it was seriously detuned.
    It was sold in France as the R12 Gordini
    Regards Col

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    Quote Originally Posted by bowie View Post
    But to answer your question I don't feel there is enough room for a 36mm inlet, That would leave about 1mm worth of material between the inlet and exhaust valve. Surely that is just asking for it to crack?

    Pictures to give you an idea of a dirty one

    https://photos.app.goo.gl/DLVLgDJeDT5nLjZGA

    As you can see the guides are trash, I suppose it's all going to have to come out so as long as the overall lengths match up, I suppose it doesn't matter that much?

    And perhaps I'm trying to hard, a big cam with heaps of overlap that lifts 9- 10mm with those 33mm inlet valves is going to be pretty cool too.
    Getting back to this, if your head is the same as this, you're limited initially by the diameter of the hardened valve seats. Fitting larger diameter seats would add considerable expense to your project. If it were mine and I wasn't racing it, looking for the nth hp, I would just give it a quality three angle seat cut and clean up into the valve throats. The single cut seats shown in the pics severely limit flow potential. A three angle cut could improve inlet flow by up to 10% alone.

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  23. #23
    1000+ Posts bowie's Avatar
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    Thank you Peter.

    I had assumed those seats would be required to come out and replaced.

    I'm not really racing this thing, but it will hopefully spend more time on a circuit then in a parking lot. I had neglected the idea of a simple valve job. Yes good idea.

    And this gets back to being able to order standard valves and guides without carrying on to much with obscure off brand parts. A much better idea.

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  24. #24
    1000+ Posts REN TIN TIN's Avatar
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    The easiest and cheapest way to get more power in any car is get a larger motor.
    Size does matter.
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    1000+ Posts schlitzaugen's Avatar
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    Quote Originally Posted by COL View Post
    It was sold in France as the R12 Gordini
    The R12G was sold in many other markets but I was talking about the run of the mill R12 and 807 engine. Not everybody wanted a thirsty race track monster, which was a pig of a dog to drive in city traffic, but 100HP instead of 54 would have been quite useful and perhaps put a serious dent in BMW2002 and similar sales.
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