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MAX BORE OUT TR6 BLOCK ?


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I havent started my restore / rebuild yet ( next spring - premises hold up - now simply planning ) BUT - before i start the engine does anyone know what is the maximum bore out that could be done on a TR6 block ?  it doesnt look like its possible to get much of any extra horses from it by boring out from my research - I dont know how much block there is to bore out without striking thru ?   Any info just on bore outs would be welcome..  Andrew

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Hello Andrew,

look at this. He wrote an article and helped me with my 2.7L engine.

As you can see, the majority of blocks can be bored upto 76.2 mm without any problems. After 77 it starts to be critical.

The matter is not the bore, it is the quality of the material. On my block an ultrasonic test was conducted to make sure the material is in perfect condition.

I ended up with 77 mm.

 

Possible Bore.JPG

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My engine was bored to 2.7L when it was rebuilt 25 years ago. I was told that capacity was as far as you could safely go. Mine was fitted with Mazda pistons but I'd have to rat through the paperwork in another place to find out which model Mazda they were intended for.

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The 6 cylinder block can safely be bored to 78mm giving 2725cc.
You need a special head gasket, currently only available at Racetorations I believe. If the engine is a CR series with a rebate in the block around the cylinders you will need to have it skimmed flat to get rid of that. 

78 mm forged pistons are available from a number of sources, Cambridge Motorsport Parts, TR Enterprises, Racetorations and probably others. They are expensive and really need other upgrades, steel Conrod, steel crank, etc to get the max benefit. 
Alternatively, max bore is plus 60 thou giving 2600cc, generally available pistons from usual suppliers, Moss, Rimmers, etc and standard head gasket, both flat CP or recessed CR. 
Hope that helps. 
Dave McD
 

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8 hours ago, ANDREW PERKINS said:

I havent started my restore / rebuild yet ( next spring - premises hold up - now simply planning ) BUT - before i start the engine does anyone know what is the maximum bore out that could be done on a TR6 block ?  it doesnt look like its possible to get much of any extra horses from it by boring out from my research - I dont know how much block there is to bore out without striking thru ?   Any info just on bore outs would be welcome..  Andrew

Why? Just because you can?

Jerry

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very interesting !

one day i will find out what is actually inside my engine....... history paperwork is a little confusing but i think it is +60th forged pistons.

I thought +60th was as far as one could go without changing the piston spacing ( due to the piston bores being paired ?)

I've been leaving the engine well alone since buying it in 2012 as it runs so well, but it does leak ever more oil !

steve

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1 hour ago, ntc said:

There is one supplier that has gone far more than that but don’t ask the price 

Equidistant block B)

Stuart.

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Elmeso Reban in Germany does the large bore gasket.

Also the cheap silver gasket from Rimmer does the job, but always the block must not have the recess. It can be milled off by taking about 0.7mm away if its a recess block.

I found the VW and MAZDA piston availiable and found a company who does the drilling. They meanwhile made about half a dozen 77mm bores and one 78mm.

So the VW piston in 76.5mm or 77mm is my choice not only for the 5HP it will give, but also the block becomes 4kg lighter.

Both pistons MAZDA and VW are very good quality and are pretty cheap.

Things should not be made more complicated than necessary......

 

By the way: Triumph sometimes did lining of the blocks and for that the drilling is done to about 77.75 and the liner is pressed in. So that is what the block can handle.

Edited by TriumphV8
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On 11/17/2020 at 4:29 PM, TRTOM2498PI said:

Come on Neil, spill the beans.  Is the engine still going in a car, with repeat reliability ?

 

Cheers.

Tom,

This is all hearsay but, I believe that a certain well known engine prep company built a limited number of engines with said equidistant block with larger bores (but not necessarily equidistant crankshafts to go with them) which increased the capacity.

I once competed at Snetterton over 10 years ago and there was a Vitesse in our race with an engine which, according to the event programme from memory. was somewhere between 2.9 and 3.0 litres. I remember it being very quick but not finishing the race for reasons unknown. You can only speculate about it's reliability. I can't shine any more light than that.

As I said earlier, the 78mm bore, with the correct head gasket is reliable.

Dave McD

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  • 1 year later...
On 11/17/2020 at 3:07 PM, TriumphV8 said:

Elmeso Reban in Germany does the large bore gasket.

Also the cheap silver gasket from Rimmer does the job, but always the block must not have the recess. It can be milled off by taking about 0.7mm away if its a recess block.

I found the VW and MAZDA piston availiable and found a company who does the drilling. They meanwhile made about half a dozen 77mm bores and one 78mm.

So the VW piston in 76.5mm or 77mm is my choice not only for the 5HP it will give, but also the block becomes 4kg lighter.

Both pistons MAZDA and VW are very good quality and are pretty cheap.

Things should not be made more complicated than necessary......

 

By the way: Triumph sometimes did lining of the blocks and for that the drilling is done to about 77.75 and the liner is pressed in. So that is what the block can handle.

Hi Andreas,

How many miles have you done with the VW Polo (Nural) ? pistons ? Any reliability issues ?

What kind of revs & cam are you using with this set-up, & what compression ratio do you run ?

 

Thanks in advance.

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Hi Tom,

its several years ago that I did the engine build.

Maybe close to 10.000 miles I guess.

In the beginning I set the limiter to 7000 but reduced now to 6500.

Cam is 290 degrees CR around 10:1

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2 hours ago, TriumphV8 said:

Hi Tom,

its several years ago that I did the engine build.

Maybe close to 10.000 miles I guess.

In the beginning I set the limiter to 7000 but reduced now to 6500.

Cam is 290 degrees CR around 10:1

Hi Andreas,

Many thanks for feedback.

 

I am tempted to try these pistons with the appropriate headgasket (Belgium) ?

Reliability is everything though, so trying to understand who has this set-up, and how many revs/mileage they do.

 

CheeRS.

 

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  • 2 months later...

I tried the cheap silver gasket from Rimmer and as it did not fail it stayed some time.

Later I swapped to the custom gasket from Elmeso Reban in Germany.

Price was around 120 Euros, do not know what it takes to bring that to GB......

This gasket is still in the car.

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Just to be clear - and avoid the gnomic posts of some - what is an "equidistant block"?

The standard bores are in pairs with a smaller gap between each pair, so may they be "equidistanted" by centering the rebores away from the centre of each pair to obtain a greater diameter?      But how then can a standard "unequidistant" crank be used at all?    The con rods and big end bearings would be stressed at every TDC, as the piston rose, out of line with the big end journal!   Possible, I suppose, on a short-life race engine, but one that according to Dave, didn't last a race!

John

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49 minutes ago, john.r.davies said:

Just to be clear - and avoid the gnomic posts of some - what is an "equidistant block"?

The standard bores are in pairs with a smaller gap between each pair, so may they be "equidistanted" by centering the rebores away from the centre of each pair to obtain a greater diameter?      But how then can a standard "unequidistant" crank be used at all?    The con rods and big end bearings would be stressed at every TDC, as the piston rose, out of line with the big end journal!   Possible, I suppose, on a short-life race engine, but one that according to Dave, didn't last a race!

John

Its a different crank.

Stuart.

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20 hours ago, ntc said:

Yep it’s a work of art and yes saw it built and run on a engine dyno 

I couldnt believe it the first time I saw the block, it was a definite "How the f**k have they done that!" moment. Oh and if you have to ask how much you obviously cant afford it.;)

Stuart.

 

Edited by stuart
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No expert with the TR block/internals but I'd be tempted to keep the strength in the block casting and go for low comp Wiesco pistons, Carrillo rods, bigger exhaust valves, forged crank (if you can get one) and ATI fasteners and go down the EFI/FI root it's more that likely going to give you more horse power and torque in the end. 

Has anyone gone down this root?

Will these engines reliably tolerate 1-1.5 Bar boost and would the transmission survive.

Andy

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I run the supercharger setup and it has been running 0.25 Bar for about 5 years with no issue. I have run it at 0.5 bar and it also seems good, but pre-ignition is an issue at times (running 8.5:1 CR).

Tim

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