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I plan to take the head off my TR2 and carry out some tuning work over the winter, it really needs a respray but that can wait. Turning to Kastners book he recommends a 0.090" head skin as a good way to release more power on a road engine (TR4) but then I turned to my well thumbed copy of Technicalities where Ian Cornish states a maximum of 0.050" for a TR3A head. I am carrying out this work on a low port head so how much should I take off? I have had a tuned low port engine years ago and it went well as did the Jabbeke TR2. Any help appreciated, I will be using the original H4 carbs on a Wilen manifold.

Cheers Richard

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I would agree Bob which is why I am on the Forum to see what the experts think. The British Leyland Competition Preparation Manual written by Bob Kastner for the TR4 recommends taking 150 thou off to give a 12.6 compression ratio for a racing engine and 90 thou to give a 10.2 compression ratio for a fast road engine. I would be scared to take that much off so perhaps 60 thou would be a good compromise.

Cheers Richard

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One thought is that measuring the low-port head precisely before you skim would reveal how much has already been taken off.  Most heads have already been skimmed by now.  One of my TR2 low port heads had about as much taken off as it could stand, and I had to use thicker head gasket to get to the stock compression, which was my goal.

Cheers

Dan

Edited by 2long
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Agree with Dan

Get it off.

Do not get all carried away reshaping the chambers unless you are prepared to make a gasket that fits the chambers once you have removed the overhang above the valve.  That overhang goes the moment you shave too much off the head face.   Leaving it thin (1mm or less) means it glows red hot and sets up pre ignition issues.     Gaskets are available with the modified shape from Racetorations or others  will sell you a sheet of copper that will need shaping and annealing.  That is only needed if you remove the overhang pocket over the valve.    Simply check the old gasket on the head before fitting, the gasket must not intrude into the combustion chamber.   Kastner covers all this.    Special shaped gaskets are not cheap compared to the standard item.


Information you must have to get the CR at the level you want.   The broad target is over 9 but under 10 to work with today’s fuel.    The last couple I have done I aimed for 9.5-1.  You will need that sort of ratio to get a sports cam to deliver improvements if you are changing the cam.    The Newman PH1 is a nice improvement without loss of flexibility.

So…..
Measure the chamber capacity and the head gasket thickness and bore size ( the one you intend to use and compare to the one you removed)  and the distance the piston is down the bore at tdc from the top of the liner (deck height) Also what bore size you have.    Crank throw is 92 mm unless it has really been got at.   The tech data in the service book tells you the fixed sizes like bore and crank throw in both imperial and metric.  
Armed with the info do a compression ratio check using one of the many online sites.   Here is one I use.

http://www.csgnetwork.com/compcalc.html

 

Edited by BlueTR3A-5EKT
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Another consideration is the gap (or lack of) between the bottom of the thermostat housing (on the head), & the water pump.
Later heads had a different shape here to allow for some machining.
On my TR3 high port head I had to grind the bottom of the head in this spot, & also the top of the weater pump to get a clearance.

Bob

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Thank you, wise words. I will measure the combustion chamber volume before I proceed any further. There is a section in Technicalities which looks very useful giving a comparison between combustion chamber volumes and compression ratios. Who stocks Newman cams?

Cheers Richard

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29 minutes ago, Dic Doretti said:

Thank you, wise words. I will measure the combustion chamber volume before I proceed any further. There is a section in Technicalities which looks very useful giving a comparison between combustion chamber volumes and compression ratios. Who stocks Newman cams?

Cheers Richard

You need a syringe, some paraffin, a sheet of perspex with a hole in it and a smear of grease to adhere the perspex to the head.  Simply see how much volume of liquid you can get in each chamber

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22 hours ago, Dic Doretti said:

I plan to take the head off my TR2 and carry out some tuning work over the winter, it really needs a respray but that can wait. Turning to Kastners book he recommends a 0.090" head skin as a good way to release more power on a road engine (TR4) but then I turned to my well thumbed copy of Technicalities where Ian Cornish states a maximum of 0.050" for a TR3A head. I am carrying out this work on a low port head so how much should I take off? I have had a tuned low port engine years ago and it went well as did the Jabbeke TR2. Any help appreciated, I will be using the original H4 carbs on a Wilen manifold.

Cheers Richard

Were the compression ratios on the USA spec cars lower which may have influenced Kastner's measurements. Not sure when Triumph started sending different spec engines to the States.

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Dic,

May I humbly recommend to you my article "How To Raise The Compression Ratio, Safely And Effectively" over on the Sideways board?

See: https://sideways-technologies.co.uk/forums/index.php?/topic/7551-how-to-raise-the-compression-ratio-safely-and-effectively/#comment-99739

Therein, I explain the volume measurement procedure (use a glass sheet - easier to use than Perspex!  A local glazier can make you one from offcuts and drill two holes in it for you) and the calculation to estimate the chamber volume, the CR that will result and how to calculate how much to skim the head to achieve a desired raised  CR.

JOhn

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Another consideration is that if you skim the head significantly it lowers the exhaust manifold and this can then catch the ribs on that side of the block.....result is a manifold air leak.

Iain

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25 minutes ago, iain said:

Another consideration is that if you skim the head significantly it lowers the exhaust manifold and this can then catch the ribs on that side of the block.....result is a manifold air leak.

Iain

Also, with an early head the underside of the water outlet casting where the thermo housing sits conflicts with the water pump housing.  This was resolved on 4A heads with a chamfered casting.

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16 hours ago, Lebro said:

Another consideration is the gap (or lack of) between the bottom of the thermostat housing (on the head), & the water pump.
Later heads had a different shape here to allow for some machining.
On my TR3 high port head I had to grind the bottom of the head in this spot, & also the top of the weater pump to get a clearance.

Bob

I think I mentioned this !:P

Bob

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Thank you everyone. I have ordered a burette and will check out the Sideways site. I will also be modifying a high port tubular manifold to fit the low port head, I did this many years ago on Robbie Coltrane's TR2 after a misunderstanding with Moss. Had a great run out in the TR2 today to take advantage of the sunshine so will not be stripping the engine anytime soon.

Cheers Richard

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