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Thread: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

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    Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Hi there, I need the maximum ignition setting for a 1600 711M crossflow with a chambered head and flat top pistons running a 234 cam.Please let me know what more info is required for a figure if you need it.All information gratefully received. No mad planing of the head or decking has taken place. Ta
    Last edited by Frenchenstein; 23-04-2018 at 20:57. Reason: Incomplete
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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    35 deg !?

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    are the pistons flush with the top of the block or a long way down? flush probably only wants 28-30 long way down may need as much as 38 degrees

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Maximum setting for what? Power? No pinking?
    Depends on carb(s) used (venturi), compression ratio, fuel used.

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    The piston sits approximately 6mm down the bore at tdc, the compression ratio is 10.3:1, twin 40 Weber’s, 30mm chokes. Tune for power/torque. Standard valves. No one wants pinking.
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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    hmm that will want a LOT of advance probably something like 38 degrees

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Quote Originally Posted by Frenchenstein View Post
    The piston sits approximately 6mm down the bore at tdc, the compression ratio is 10.3:1,
    With pistons 6 mm down the bore and a chambered head I think a CR of 10.3:1 is not possible on a 1600.

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Hmmm...maybe I have misinformation. I’ll go over some old turbosport threads and see what is what!

    Thanks up until now.

    As Arnie said “I’ll be back”
    Are we there yet?

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    The chambered head needs to be just 12 cc to get 10.3:1

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    PS: and that 12cc includes the area "within" the headgasket which will be approx. 5cc.

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    I’ll check the swept and clearance volumes and do the calculation.
    Are we there yet?

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Quote Originally Posted by Miniliteman View Post
    With pistons 6 mm down the bore and a chambered head I think a CR of 10.3:1 is not possible on a 1600.
    I get 9.9:1 based on pistons 6mm down the bore and with 8cc chambers in the head (I've measured a few heads and that's what I get as an approximate figure) based on a 1600 with standard bore size, and with a head gasket 83.5mm diameter and 1mm thick when compressed.
    Last edited by HonkyWhiteTrash; 27-04-2018 at 19:08.

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    are they twin cam pistons? that will give a bit more compression as they are bigger than std x/flow and may have a raised bump on them

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    If the head has a chamber of just 8cc (thought they were more than that) the CR is 10.1:1 approx.

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Quote Originally Posted by HonkyWhiteTrash View Post
    I get 9.9:1 based on pistons 6mm down the bore and with 8cc chambers in the head (I've measured a few heads and that's what I get as an approximate figure) based on a 1600 with standard bore size, and with a head gasket 83.5mm diameter and 1mm thick when compressed.
    This is calculated with standard pre xflow flat top pistons, and also includes calculations for the volume from the top of the piston down to the top piston ring.

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Quote Originally Posted by HonkyWhiteTrash View Post
    This is calculated with standard pre xflow flat top pistons, and also includes calculations for the volume from the top of the piston down to the top piston ring.

    The combustion chamber, in the head, is just over 7cc, including the spark plug & ceramic electrode area (but not including the cylinder head gasket). With +0.030 oversize pistons how much from the top of the cylinder block will I need to have planed off to achieve 10.3:1 compression ratio?
    Are we there yet?

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    + 0.30 pre xflow or twin cam pistons?

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Pre crossflow 18400
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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Quote Originally Posted by Frenchenstein View Post
    The combustion chamber, in the head, is just over 7cc, including the spark plug & ceramic electrode area (but not including the cylinder head gasket). With +0.030 oversize pistons how much from the top of the cylinder block will I need to have planed off to achieve 10.3:1 compression ratio?
    By my calcs assuming you're using an 83.5mm gasket with crushed thickness of 1mm you wil need to have the pistons at TDC sat 0.231" down the bore.

    Alternatively you could leave the pistons where they are if your measurements are good and you could skim the head slightly to raise the compression which shouldn't be a problem in terms of valves being too close to the pistons. Approx 6.3cc's needed by my reckoning.

    Word of caution - do not rely on myself! or possibly even others to tell you exactly how much to take off - you'll need to do some accurate measuring as every engine is different based on numerous factors.
    Last edited by HonkyWhiteTrash; 01-05-2018 at 14:12.

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    However, 0.4 compression change - is it worth chasing?
    Last edited by HonkyWhiteTrash; 01-05-2018 at 14:15.

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Quote Originally Posted by HonkyWhiteTrash View Post
    However, 0.4 compression change - is it worth chasing?
    I understand your reason for the caution, you are speaking common sense.

    What I will do is get the head and the block planed for a true flat surface and a good seal (not to chase .4 of the final ratio) and leave it at that.

    Will a Kent224 cam give me more torque, or more torque at lower revs than a Kent234?

    Then to my original question:

    Maximum ign timing for this set-up?
    Are we there yet?

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    224 will give torque at lower rpm and be better suited to the compression. as for timing, you have been given a lot of educated guesses but a dyno or rolling road session is the only real way to know given there are so many variables
    Last edited by Graham; 01-05-2018 at 15:12.

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Quote Originally Posted by Frenchenstein View Post
    I understand your reason for the caution, you are speaking common sense.

    What I will do is get the head and the block planed for a true flat surface and a good seal (not to chase .4 of the final ratio) and leave it at that.

    Will a Kent224 cam give me more torque, or more torque at lower revs than a Kent234?

    Then to my original question:

    Maximum ign timing for this set-up?
    224 is a very good cam (understated by a lot of people really) - having the 224 rather than 234 will up your dynamic compression ratio so that will offset the fact you aren't going to do more to the static compression ratio by just cleaning the block and cylinder head faces up.

    Max ignition setting? No idea but you could do with something custom to supply your advance curve rather than faffing with distributors - a mapped ignition system would be ideal for your engine as you are going to need a lot of advance for the low down RPM which will give you the problem of having a lot of advance when trying to start the engine. A mapped ignition would allow you to have 0 degrees engine cranking advance (or whatever you choose) while allowing you to choose all the other requirements. I can't see you needing more than 34-36 degrees. However, the advantage of the mapped ignition will allow you to test what's best much more easily should the engine need or not need as much advance.

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Interesting stuff about the 224.

    What sort of max advance would be too much at a low rev value. I can make any distributored engine pink and complain just by advancing the distributor body, but when would max advance be too soon on this set-up? or is that too general a question. As you can see I am over my head with this stuff
    Are we there yet?

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Quote Originally Posted by Frenchenstein View Post
    Interesting stuff about the 224.

    What sort of max advance would be too much at a low rev value. I can make any distributored engine pink and complain just by advancing the distributor body, but when would max advance be too soon on this set-up? or is that too general a question. As you can see I am over my head with this stuff
    It's the advance at cranking that is the first problem - anything from 10degrees BTDC static timing will likely give you "kickback" with more advance being more problematic, less advance less so. If your distributor has 24 degrees of crankshaft advance (which equates to 12degrees on the distributor) and you set the static advance to 8degrees you will have 32 (24+8) degrees total advance. If you set it at 12 you will have 36 (24+12) degrees. Chances are though that you will only get the best setting at either cranking/idle or full revs as you will likely only be able to obtain one of the two unless you have a perfectly set distributor (not much chance of that!) as a distributor isn't flexible unless you mess with the springs to tune the curve (which is a separate skill all in its self).

    As to when would max advance be too soon? Impossible to say. It's not a normal engine so it's very much a trial and error engine IMHO.
    Last edited by HonkyWhiteTrash; 01-05-2018 at 21:37.

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Quote Originally Posted by HonkyWhiteTrash View Post
    It's the advance at cranking that is the first problem - anything from 10degrees BTDC static timing will likely give you "kickback" with more advance being more problematic, less advance less so. If your distributor has 24 degrees of crankshaft advance (which equates to 12degrees on the distributor) and you set the static advance to 8degrees you will have 32 (24+8) degrees total advance. If you set it at 12 you will have 36 (24+12) degrees. Chances are though that you will only get the best setting at either cranking/idle or full revs as you will likely only be able to obtain one of the two unless you have a perfectly set distributor (not much chance of that!) as a distributor isn't flexible unless you mess with the springs to tune the curve (which is a separate skill all in its self).

    As to when would max advance be too soon? Impossible to say. It's not a normal engine so it's very much a trial and error engine IMHO.
    I have a Lucas 25d distributor which I will give to The Distributor Doctor to lose the vac unit and prescribe a customised advance setting for it. I have done the ‘bob weights, springs and stops’ tricks before with Motorcraft distributors and though it’s a real faff, I have been happy with the results! Even on my present engine which is a 1600 ohv, stage three Burton head, Kent 234 cam & twin 40’s I haven't messed that one up so I am looking forward to not messing this one up lol.

    So....here goes nothing
    Are we there yet?

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Quote Originally Posted by Frenchenstein View Post
    I have a Lucas 25d distributor which I will give to The Distributor Doctor to lose the vac unit and prescribe a customised advance setting for it. I have done the ‘bob weights, springs and stops’ tricks before with Motorcraft distributors and though it’s a real faff, I have been happy with the results! Even on my present engine which is a 1600 ohv, stage three Burton head, Kent 234 cam & twin 40’s I haven't messed that one up so I am looking forward to not messing this one up lol.

    So....here goes nothing
    Nice one on the diff faff!

    You should be alright with the Distributor Doctor, he knows his stuff. He might have done a flat top and chambered head crossflow before, you never know, will be worth asking him if he has.

    Keep us posted!
    Last edited by HonkyWhiteTrash; 02-05-2018 at 07:44.

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Thanks for all the information chaps. Every day is a learning day.

    I’ll let you know how it goes.

    Again many thanks
    Are we there yet?

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Update:

    I have been in touch with The Distributor Doctor and they do have the info for the Lucas distributor.

    Happy days.
    Are we there yet?

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Quote Originally Posted by Frenchenstein View Post
    Update:

    I have been in touch with The Distributor Doctor and they do have the info for the Lucas distributor.

    Happy days.
    Nice 1, look forward to some updates.

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Update:

    I have my distributor back from The Distributor Doctor, it looks a lovely piece of kit, however I have had some serious surgery and have been convalescing, post the event, which uses up money at a rapid rate when you are self employed! so stuff is ‘on hold’ for a while. Bugger.
    Last edited by Frenchenstein; 18-11-2018 at 19:25. Reason: Punctuation
    Are we there yet?

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    hope you are OK now ! keep us updated, interesting stuff !!!!

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Small update: recovered from surgery. Working to get pennies to build engine and repaint car after my being laid up and then relocating workshop. Rich tapestry of life and all that.

    Again much thanks to all that helped me with info. I’ve read thru this thread again and can’t wait to get this engine built.
    Are we there yet?

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    Re: Max ign setting 1600 ohv 711M, chambered head, flat top pistons

    Just beginning the rebuild. Cylinder head at the machine shop now. When that comes back I’ll lap the valves in and put it back together. Then it’s the usual stuff with the block, crank, cam bearings, cam, duplex valve gear etc.etc. and so on lol.

    If I’m happy with the performance I may sell the beasty that’s fitted in the car now. We’ll see
    Are we there yet?

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