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Good Day Gentlemen,

I'm new to the forum and Triumphs in general. Around 2010 when I was a kid, I first saw a GT6 by way of trying to buy an MG. Fell in love, and I've always wanted a GT6 since then. Finally got the opportunity to purchase one this year. In the preceding years I had a simple dream, and that was to build a PI GT6. What if Triumph made the best possible GT6, with a PI engine and overdrive and whatever other goodies I could think of.

I've been reading SteveA's old blog and trying to gather parts and information for the build.

So I've accumulated two sets of late PI gear and am having one MU recalibrated/refurbished, and I got hold of a cam and wideport TR6 head, which I think I'll need to shave to bring the CR up to something like on the UK spec GT6s.

I've never built an engine before in my life, and i'm not 100% sure what all I need to do to accomplish this idea, but I'm committed to making the dream a reality.
My first step will be to build up the head, so I've got to get all the right studs for manifolds and such, get the head height right for a GT6, and sort out the valves and springs and rocker gear.
I'm still looking for an engine block to build on, but it's not much of a priority right now simply because I'm loathe to lift a built up bottom end up and down the stairs of my apartment.

Here's some pictures of the car, and the new head with some of the components slapped on.

CsBl8qm.jpg

AM94s2Z.jpg

mgyPMs2.jpg

LHKeCl0.jpg

 

Needless to say, I'll be posting an awful lot of neophyte and naive questions in the coming months. So as my first question:
Did the PI cars have different valve springs than the non PI cars? 

Kind Regards,
AJ

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AJ,

My race Vitesse, SofS, (QV) presently has a 2L Pi engine.     And frankly it's a disappointment when previously it had the 2.5.     That engine blew up, after ten years of racing.

I hoped to find power at the top end, over 6K where a 2.5 dare not tread, but it wasn't there, so I'm building a new 2.5. 

I'll be glad to offer any advice you need - no doubt others with Pi will be do the same.

 

On valve springs, when I bought SofS - it had been in the back of a barn for twelve years, after an engine rebuild - the DPO had fitted ultra strong valve springs, I know not from where.    The result was that the cam ate the block!  Massive valve gap enlargement and so much bearing wear that it was impossible to recover that block.     Presently, I use Jaguar springs as recommended by Gareth Thomas, which are the same stiffness as the originals, but new.    I think you have double spings, essential if you want to rev your engine, and avoid valve bounce.

Yes, you will need to skim the TR6 head to bring up the CR with a 2L crank, unless you stick with the domed pistons that Triumph fitted to late GT6s, so that thye could fit unskimmed heads and get the higher CR.      Domes may not be ideal, but probably quite adequate for a road car.

You can use any block - they are all the same.   Make sure that it has a 2.5 crank, even if the block number is for a 2.5, as I've seen 2L cranks fitted.

Are you in the US/Canada?  Can't tell from the pics.

John 

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Hi AJ,

Welcome!  Looks like a solid car. Interesting that you call it a "Mk2" as I always thought it was known as the "Plus" in the US?

Just to be clear about your starting point, the Mk2 or plus should have the wide head anyway.  Perhaps you can clarify what you have fitted now as it's not uncommon to see the earlier Mk1 narrow head engines fitted.  There are also two versions of the narrow-head engine with the earlier one having a breather on the side of the block by the oil filter.  The early one also different size crank bearings and cannot be converted to 2.5L.

It is possible to put the wide head on the Mk1 block but means re-drilling the block deck for the large r7/16" UNF head studs.  As John says the TR6 head will need a skim (a BIG skim) to get the compression ratio up enough for use with a flat-top piston'ed 2L.  In the US you need to be particularly careful as in addition to some TR250 and TR6 heads being really thick to give a low CR even on a 2.5, some also have different inlet port spacings so the manifolds don't line up properly.  There is a stamped ID number on the front right corner of the head which is useful reference https://www.chriswitor.com/cw_technical/head_applications_chart.pdf

In the 2.5 vs 2.0 debate I've always stuck with the 2L, partly because they typically use less fuel, but mainly because the extra torque of the 2.5 really doesn't help the life of the marginally sized transmission components.  My modified 2L on electronic injection produces enough power for my Vitesse for road use.

The PI system has it's pluses and minuses.  Certainly you need to be prepared to learn how it works and how to fettle it yourself.  It's reasonably complex but not rocket science and is capable of good results.  I've not mastered myself but there are a few on here who have.

As to your valve spring question.  The valve springs used are not unique to the PI engine and would in fact be the same as those originally fitted to your GT6 from the factory.  You should also not that there are various different PI engines.  The original and highest bhp ones (150bhp) are fitted to the TR5 (Euro spec) and early "CP" TR6.  The next best are those fitted to the Mk1 and earlier Mk2 PI saloon cars at 132 bhp.  These have the same valve sizes,  double springs and cam profile as the GT6 Mk2 engine.  Finally there is the late "CR" TR6 and PI saloon version with 125 bhp which have smaller exhaust valves, single valve springs and shorter duration cam.  In fact, the original mk2 GT6/Vitesse engine is a good start point for a PI 2L as you will know if you've been reading SteveA's blog.....

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Hi AJ

Are you intending to rebuild the engine in yours or build another one outside of the car? Then do a transplant. The latter I assume?

My GT6 is registered as a 2.5 and the original block claimed it to be from a TR6 Pi but when I pulled it apart all the internals were 2 litre, which backs up what John just said about cranks in blocks.I had guessed that anyhow due to the sump. If you build it as a 2 litre you will be fine, but if you go 2.5 then you will have to mod the sump pan to fit as the crank will hit the sump pan. A club hammer is your friend. You cant fit a 2.5 sump. there is no room as it has to go over the steering rack. Looks like you want to stay 2 litre anyhow and just Pi it? When you look for a block make sure the thrusts have not fallen out and eaten the block/crank if you arent using your current engine.

 I have not played with Pi myself, but it makes sense to go with double springs on the valves. Somewhere here on this site N Coll did a homebrew head porting workshop, which I believe Nick has actually done, so if you fancy some head flowing work now is the time whilst it is all stripped down. That will then lead you to buy a decent(ish) term applied loosely exhaust manifold to make it breathe...... and on it goes! I suppose it boils down to if you fancy building one worked on engine, or just a good solid reliable one with Pi. I had mine built for me, regretted it then rebuilt it myself. Ditto gearbox. If you build it yourself you will know it is right, and there is so much knowledge on this site someone will always be able to help you. And if you are building the engine with the car still running its old one you can go to town on stuff, getting it machined how you want, balanced, block decked etc etc.

Again, there is a mountain of knowledge on here (not me, other people!)

As Nick has just said a nice 2.0 build with a decent cam will be plenty for road use, especially as being 5 inches from the floor makes 50mph feel like 90. 

Also with webers which is what I use you need a stepped down inlet manifold setup (and a weeks worth of modifying it) to fit under the bonnet of a GT6. I am not sure if Pi needs the same or if it fits, so it may be worth checking. I am sure it wont be insurmountable either way. Without looking at SteveA's blog I assume the answers will be there anyhow.

I suppose the last question has to be how in gods name your passenger/glamorous assistant can get her legs up that high in a GT6!? Its cosy in there at the best of times. I have to crawl out of mine!

 

 

 

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Gentlemen,Thanks for the response! I'm in the US.

The plan is indeed to build a separate 2L PI engine, and I'll swap the engines when I'm ready next year. I daily drive this car, so doing it this way is more convenient, and I can take the time to do it right. Then after some time living with the car and new engine, I'd rebuild the original engine for PI with the second set of gear, or at least do the work on the bits and carry over whatever improvements I learn from the first engine.

On the subject of the heads, at the time I couldn't confirm whether or not the heads on my car or the Mk2 GT6s in general were wide port heads, so I went with a known wide port head from a TR6 which had been magnafluxed and has no warping or cracks.  Thanks Nick for clarifying that the Mk2 cars do indeed have wide port heads.
I was looking into purchasing another GT6 Mk2 head with the circle B casting mark,  but the gentleman was unable to confirm the port spacing and has been quite busy to get back to me, I'd still like to get this head. 

The TR6 head is stamped 219019, casting number 313248, Chris Witor's page says it's 3.560" with 30.3mm exhaust valves. I measured from the between the gasket surfaces on the block and valve cover side, and it was a little less than 3.56". This head does have double valve springs, I will need to confirm the exhaust valve size.

My GT6 has a head stamped with 517528 and casting number 308351. Chris Witor's page says that is was found on MK2 GT6s, the head height is 3.3" with 32mm exhaust valves. The other head I wanted to purchase, (and still might), has the same stamp and casting numbers, but it's condition is unknown.

I had seen there was a 150bhp cam, which I was going to purchase, but I got a cam along with the TR6 head with the following specs:
o3zVwkS.jpg

Bumblebee - I believe everything fits under the hood without issue, I've seen two GT6's with the PI system, SteveA's and fellow by the name of Nolan iirc. The manifolds are well below the top of the valve cover, so I wouldn't suspect them to interfere. I've got no intentions to race, so I'm not going to be trying to extract every last hp/L as possible, I want reliable power.

As for my glamorous passenger, being young helps, beats me otherwise, one of those mysteries you just have to appreciate.

Questions:

Nick, if I understand you correctly, the MK2 GT6 head and cam, with pi gear could yield 132 hp?

Can the valves be enlarged to the 32mm ones? Does it make that much of a difference?

It is quite a shave to bring the head down to size, is there any danger of getting into the cooling passages?

I can get a quote for the head skim and compare it to the cost of the other Mk2 GT6 head I have been trying to get. Maybe it's more worthwhile to start with the GT6 head instead?

Thanks and Kind Regards,
AJ

 

 

PS

Thanks for the comments about the car, it does have its good points being mostly original, but it does have typical rot in the floors, and a few DPO presents like cut off front crossmembers, hence the custom lower valance the gentleman I bought it from fabricated. I hadn't noticed them until I went to fit an original lower valance! Wish I did, maybe I could have haggled the price down some more...

3LTsdaE.jpg

19grskF.png

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JohnD,

 

Is there a spec for the valve springs spring constants? Are the Jaguar springs preferable to the double spring set up, and if so, what springs exactly are they from/part numbers?

Thanks and Kind Regards

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8 hours ago, saleon said:

Nick, if I understand you correctly, the MK2 GT6 head and cam, with pi gear could yield 132 hp?

Yes..... but that is the factory figure for the 2.5.  You might get that from a 2.0L (Steve A got more IIRC), but not with standard head and exhaust manifold.

 

8 hours ago, saleon said:

Can the valves be enlarged to the 32mm ones? Does it make that much of a difference?

They can.  You should bear in mind that Triumph reduced the size due to persistent problems with cracks between the valves and also that for road use you'll want hardened seats fitted for unleaded fuel.  As to the difference, I've not compared directly, but my Vitesse head has the 30.3mm valve sizes and that engine (2.0L) made 120bhp with the std cam and makes a fair bit more now (unmeasured as yet) with a rather wilder cam, so it's not showing as a severe limitation.  Cost wise, if you are having unleaded seats fitted anyway valve size will make little difference to the cost, provided your machine shop is prepared to tackle the job with the valves so close.

8 hours ago, saleon said:

It is quite a shave to bring the head down to size, is there any danger of getting into the cooling passages?

3.56" makes it the thickest one ever produced.  To get it down to the nominal 3.30" for a 2L with flat top pistons needs about 6.6mm removing, which is an epic skim with significant risk of striking water and quite possibly breaking through under the spark plug recesses.  I would strongly advise avoiding that route!  The GT6 Mk2 head will be a much better start point proved there are no cracks between the valves.

5 hours ago, saleon said:

Is there a spec for the valve springs spring constants? Are the Jaguar springs preferable to the double spring set up, and if so, what springs exactly are they from/part numbers?

As Craig says but also.....

Valve spring choice is a bit of a function of the cam you plan to use but if sticking with the std 308778 then these would be my preference
https://www.chriswitor.com/proddetail.php?prod=CW2906

Double springs reduce the chance of a single spring failure dropping a valve.

8 hours ago, saleon said:

I believe everything fits under the hood without issue,

Hmm.... don't take this for granted.  Don't recognise the Nolan one offhand but Steve's car was a Mk3, which has a wider/larger bonnet bulge than the Mk1/2 plus his engine was moved back about 12", which rather changes the game.  I do know of a couple of PI GT6s (or Gitfires) where all seems to fit but they are both Mk3 bonnets.  I also know that two of our regulars on here looked long and hard at using the PI hardware for EFI conversions and gave it up as even after cutting and shutting the throttle bodies there was insufficient space.  Admittedly they were also having to find space for a fuel rail, which you won't have, but I suggest careful checking to avoid disappointment!

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Things can get comfy under the bonnet. My Mk3 here (before manifold mods) you can clearly see the step down in manifolds to get the carbs under the bonnet. I imagine although I  cant say for certain that the inlets will be sitting outside of the bonnet bulge, ie in the lower bonnet section, and things get very tight very quickly under there . My engine is mounted normally, so not pushed back and its all tight on room

 

IMG-20171014-WA0001.jpg

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1 hour ago, Nick Jones said:

Yes..... but that is the factory figure for the 2.5.  You might get that from a 2.0L (Steve A got more IIRC), but not with standard head and exhaust manifold.

 

They can.  You should bear in mind that Triumph reduced the size due to persistent problems with cracks between the valves and also that for road use you'll want hardened seats fitted for unleaded fuel.  As to the difference, I've not compared directly, but my Vitesse head has the 30.3mm valve sizes and that engine (2.0L) made 120bhp with the std cam and makes a fair bit more now (unmeasured as yet) with a rather wilder cam, so it's not showing as a severe limitation.  Cost wise, if you are having unleaded seats fitted anyway valve size will make little difference to the cost, provided your machine shop is prepared to tackle the job with the valves so close.

3.56" makes it the thickest one ever produced.  To get it down to the nominal 3.30" for a 2L with flat top pistons needs about 6.6mm removing, which is an epic skim with significant risk of striking water and quite possibly breaking through under the spark plug recesses.  I would strongly advise avoiding that route!  The GT6 Mk2 head will be a much better start point proved there are no cracks between the valves.

As Craig says but also.....

Valve spring choice is a bit of a function of the cam you plan to use but if sticking with the std 308778 then these would be my preference
https://www.chriswitor.com/proddetail.php?prod=CW2906

Double springs reduce the chance of a single spring failure dropping a valve.

Hmm.... don't take this for granted.  Don't recognise the Nolan one offhand but Steve's car was a Mk3, which has a wider/larger bonnet bulge than the Mk1/2 plus his engine was moved back about 12", which rather changes the game.  I do know of a couple of PI GT6s (or Gitfires) where all seems to fit but they are both Mk3 bonnets.  I also know that two of our regulars on here looked long and hard at using the PI hardware for EFI conversions and gave it up as even after cutting and shutting the throttle bodies there was insufficient space.  Admittedly they were also having to find space for a fuel rail, which you won't have, but I suggest careful checking to avoid disappointment!

 

Nuts. that's rough about the head. But, I could achieve the CR by having slightly oversized pistons and skimming off less going by this chart:

good-parts-table.png

I won't know what the condition of the bores will be until I get the block. I'd really hate to destroy this head. I'll try to get a hold of the MK2 head, however maybe I might have to consider a smaller shave and the use of domed pistons? If I do stick with the TR6 head, i think i"ll keep the stock smaller valve size then, if cracking is an issue.

Nolan's car can be found in a thread on triumphexp called "GT6 with a 2500 pi engine". His also a Mk3 though. I hadn't known the Mk3 bulge was bigger than the Mk2.
I've taken some rough measurements of the vertical and horizontal distance from the intake/exhaust port face of the head to the vaccum pipe nipple on the manifolds which seem to be the highest/furthest point. I'll compare these to what i've got under the bonnet to get a better idea of clearance. I don't see them as being higher than the stock twin carb setup, the air box, or even the heater valve and gulp valve, but then again the latter two might be well within the bulge.

I might have the opportunity this weekend to trial fit them onto a friend's Mk1 which is being dismantled. So perhaps that can give a certain answer.

Perhaps something else I could do to get a bit more clearance is to have the mating faces on the manifolds milled at an angle to get them more horizontal, but there really isn't a lot of meat there for that I think. Another option I'm not sure would work is to make some stepped manifolds like on Bumblebees webers. Could lower the injection manifolds enough if that'snecessary.

 

Kind Regards,
AJ

Thanks for the spring info GT6MK3 and Nick,

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PI will fit tho No I injector union is real close. Idle valve needs twisted too. But it will fit.

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Tip Trim off the corner of the bulkhead seam nearest the dizzy and weld the corner up. This is for clearance to time the metering unit in situ

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Not at home tonight, AJ, ill get back to.you on your query, whiich may have been answered above.  I very much agree with RR's note about trimming the corner of the bulkhead (on my Vitesse, but same difference) to clear the M/u, but I had to take off more than just the corner.     A patch about three inches across at the top was needed.

You should note the need to totally avoid fuel surge for Pi.     Carbs discard any entrained air in the float chamber.   Pi does not, and severe fuel.starvation on corner exit can spoil your day.

John

John

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17 hours ago, JohnD said:

 I very much agree with RR's note about trimming the corner of the bulkhead 

Not RR but Gt6s 

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On 10/10/2019 at 7:55 AM, Gt6s said:

Not RR but Gt6s 

Thanks for the tip. To be clear, are you referring to this area?

hBrVRaK.jpg

On 10/9/2019 at 10:36 AM, Gt6s said:

PI will fit tho No I injector union is real close. Idle valve needs twisted too. But it will fit.

What's the best way to remove the idle-air valve? Mine does not want to twist easily,  don't want to force it and damage the part.

 

Kind Regards,
AJ

 

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3 hours ago, saleon said:

Thanks for the tip. To be clear, are you referring to this area?

hBrVRaK.jpg

What's the best way to remove the idle-air valve? Mine does not want to twist easily,  don't want to force it and damage the part.

 

Kind Regards,
AJ

 

Ah!   Significant difference between GT6 & Vitesse!     Esp.when you havwe shifted the engone as far back as it may be while still on the original mounts.     You may not have a problem, unless you do the last.

JOhn

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6 hours ago, saleon said:

Thanks for the tip. To be clear, are you referring to this area?

hBrVRaK.jpg

What's the best way to remove the idle-air valve? Mine does not want to twist easily,  don't want to force it and damage the part.

 

Kind Regards,
AJ

 

Yup that is the spot. grind about an inch off each side of the seam corner and butt weld it up. This is enough. The idle valve should turn just a tight fit.         Laurence

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Gentlemen, 

Was busy the prior weekend swapping an OD transmissio into the car. Not quite complete, will have to finish it this weekend.

I got a measurement of the port spacing for the GT6 head I was interested in. Please see below:

J2NT5Ur.jpg

I had thought the correct port spacing was 0.95", according to this image from BPNW 

https://www.bpnorthwest.com/catalog/product/gallery/id/1908/image/6392/

But checking my TR6 head, it's 0.90", which matches the photograph

Is the BPNW figure incorrect, can anyone confirm that the port spacing on a wideport head is supposed to be 0.90" ?

I'll also be purchasing a block or complete bottom end from the same gentleman

On 10/8/2019 at 7:36 AM, Bumblebee said:

Hi AJ

When you look for a block make sure the thrusts have not fallen out and eaten the block/crank if you arent using your current engine.

 

 

 

 

Are there any references for what that damage looks like? I can ask for the gentleman to check the bare block, but for the bottom ends I think he'd have to get an endfloat measurement. Can the damage be seen with he oil pan removed?

 

Kind regards

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All GT6 heads (especially the thinner ones, which can only be for 2L) are "wide port", so will fit the PI TBs.

Acc. to this TR register thread
https://www.tr-register.co.uk/forums/index.php?/topic/20161-usa-cylinder-heads/

only one head number, 516323, was narrow port and this was used on US market TR250s and early "CC" prefix TR6s only.  Anything else should be wide port.  The difference is about 1/8" (3.2mm) apparently.

Thrust washer area damage really needs the flywheel and rear oil seal housing removed, and ideally the crank too.  The quick method is to check the crank endfloat.  If it's less than say 0.5mm (0.020") then the washers are still in and the block/main bearing cap at least should be ok.  If the end float is 2 or 3mm then the thrust washers are out...… Damage to block, rear main cap and crank are likely but could be repairable dependent on how long it's run like it.

Flywheel side of the rear main cap takes the first hit...…

tr6_endcap.jpg

also the thrust lip on the crank

thrust-washer-2.jpg

http://www.customthrustwashers.com/ is an interesting site.  NFI, just satisfied customer!

 

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One thing never mentioned when discussing GT6 with Lucas Pi., is the positioning of the fuel pump and all its paraphernalia. Most Pi TRs seem to have smelly boots/trunks, whilst not so bad in a convertible, in a GT6 the smell of fuel would be annoying to say the least. I presume that the fuel pump will be mounted where the spare wheel would sit?

For the ease and simple maintenance, a pair of HS6 SUs is not a bad option.....appreciate that I may sound conservative her. But my GT6 mk2 2000cc with a TR5 cam, modded head and smooth bottom end is a powerful enough and I get to enjoy 30mpg...how much is fuel in the USA?

Pi of course offers great initial acceleration and in a light car such as a GT6, will be fun...but don't dismiss carbs...what about bike carbs?

Apols for the conservatism!

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Then there is EFI for the best of both worlds and more :tongue: Again fuel pump but lower pressure requirement makes in-tank a real possibility.

You make a very valid point re the layout and smells though Mr B.  Trying to stop mine stinking of fuel quite so much.  Hoping it's a breather issue and not the b@5tard tank leaking.......  I'm also greatly appreciating the incredible low down flexibility of the standard engine (it's built as a Mk2 spec, but don't remember the Vitesse engine ever being quite so tractable) when just pottering about.  The current Vitesse engine blows it away from about 2,800 upwards but even so.....

Nick

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3 hours ago, TimBancroft said:

how much is fuel in the USA?

 

last week it was from about $3.70-$4.80 per US gallon (uk gallon is 20% bigger)

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