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GP2.5

2.5Pi Cylinderhead Modification

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Dear all,

 

Being in my middle ages, I just bought my second classic car, a lovely 2.5PI MkI. Low milage,rustfree, Royal blue time machine.

I have studied this forum for a while and concluded that it probably has the largest gathering of Triumph scholars on this planet.

 

Reason for choosing a 2.5PI goes back to 1973, I then had the luck to test drive a works 2.5PI at the Leyland general agency in Stockholm. Ever since I had a weak spot for the make and model.

With great interest I have read this forum and also what is written on the internet by Mr. Garreth Thomas. I agree with his dislike of some of the "go fast" tuning experts - their services and parts that often are of no or little value. Although it surprised me to read that Mr.Vizard had no knowledge about Triumph cylinder heads. Almost a ligh year ago -1974 I modifyed a TR4 cylinder head according to Mr. Vizards intentions.

On top of that I back cut the inlet valves, did a 3 angle seat job and fitted a Lucas sports coil. In that tune - and I swear by a one inch ring spanner - that TR4 had more grunt from idle to it,s red-line than before,engine was more powerful and consumed less petrol than before. It was a real joy to drive

This winter I am planing to do the same Vizard treat to the 2.5PI I would really have this forums opinion on that. Is Mr Vizard totally off? Are there any new "truths" applicable? I also intend to fit i TR6 exhaust manifold and a decent 2.25 exhaustsystem, and maybe soft beehive valve springs

 

Looking forward to your posts,.

 

PS: the new owner of the TR4 left it to a "tuning expert" that did some severe cave excavation to the inlet ports and ruined the charachter of this lovely engine.

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Welcome! I am still learning to like my PI (and I still don't think it likes me!). It's like a dog that was badly beaten by previous owners and needs alot of love! Sounds like you got a better one!

 

Anyway, I made some modifications to the cylinder head of this car earlier in the year and did a write-up to follow on from Neils that Nick already linked to above. The car has not yet been on a rolling road but it goes pretty well.

 

http://sideways-technologies.co.uk/forums/index.php/topic/6080-nicks-diy-head/

 

Cheers

 

Nick

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Almost a light year ago -1974 I modifyed a TR4 cylinder head according to Mr. Vizards intentions.

On top of that I back cut the inlet valves, did a 3 angle seat job and fitted a Lucas sports coil. In that tune - and I swear by a one inch ring spanner - that TR4 had more grunt from idle to it,s red-line than before,engine was more powerful and consumed less petrol than before. It was a real joy to drive

 

You can gain a lot on the TR4 engine because there are 2 well known weaknesses on that head.

 

1/ The Inlet ports are much too big.

Even my 3.6L Jaguar engine which has 235bhp & the same basic bore and stroke has smaller ports.

 

2/ The exhaust ports are very poor. The majority of people mess up the SSR on that exhaust port when they start touching it.

Even Croft, who thinks the sun shines out of his bum, fools cluelessly around with the exhaust ports.

Like some Peugeot engines, the exact shape is really hard to get right, and is somewhat counter intuitive.

Luckily ONE highly experienced head guy, showed me the right way to do them after struggling for months myself.

 

In the next 2 weeks I could give you the results of some heads I just did.

These were done entirely without using a flow bench, but on the basis of having used one a lot to achieve the ideal shapes in the past.

You have to have a good pictorial memory and be prepared to spend many many extra hours doing things which other people have not even thought of before.

The Spitfire heads are capable of flowing as much as a K series VVC head.

That is really astonishing when you see how dreadful the results are from ever single so called "specialist" over the decades.

 

In one (recent and now quite well known case) this gave an extra 35bhp on a 2.5 saloon compared with a previous head which had exactly the same CR.

Another 2/3 cars who are active forum members here, will tell you they had the same experiences.

The 6 cylinder heads are capable of behaving almost as well as a modern 4V head, giving similar power, torque & fuel economy.

 

In this case I would say the majority of what Vizard had written had either nor relevance at all, or was no earthly use at all in getting this result.

Indeed it was Paul Lucas who originally told me that, and he was completely right.

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Dear all,

 

Many thanks for the posts and support, I will deep study this. I am quite happy that my "random instinct" back cutting of the inlet valves back in 1974 is proved to be a reel benifit to gas flow. A good book on this topic is Gas flow in the Internal combustion engine, by Annand an Roe first published in June 1974 GT FOULIS&CO LTD SPARKFORD. YEOVIL.SOMERSET - great readiing!

 

Cheers

 

GP

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GP2.5,

You should not be surprised if it was GT who wrote that Vizard knew nothing about Triumphs. As you can read above, GT has that view about a lot of people!

If you want to, you can read Vizard's advice in a downloadable copy of his "Tuning Standard Triumphs above 1300cc" at:

http://www.scribd.co...Triumphs-Vizard It was my bible when I first did heads, but in the latest, I have followed GT's advice about unshrouding the inlet valve. We shall see, as I lack a flow bench.

 

But rereading your OP, you probably have read it already!

John

Edited by JohnD

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You should not be surprised if it was GT who wrote that Vizard knew nothing about Triumphs.

 

ACTUALLY it was Paul that said that, as did Ken Riley.

So what does Vizard ACTUALLY suggest you do?

 

b...llx 1/

1/ P53 A glance at Fig.28 -the chamber shaperemainsun-changed.

Oh right!

The chamber needs to be modified, especially in depth and shape.

This is one of the rather more critical aspects of the GT6 head.

 

b..llx 2/

2/ p53 the ports require little more than just polishing.

Nothing could be further from the truth.

 

The offset of the port to the chamber is even more than that of the Spitfire, so how is polishing supposed to help when the port shape is the single largest defect on the head.

I think Neil pointed this out rather well. NO?

 

b..llx 3/

3/ p56 suggest filling the guide depression up with weld. Nothing could be further from the truth.

This area doesn't affect flow in any way whatsoever.

 

b...llx 4/

4/ rather more work is needed on the exhaust ports than the inlet ports, he then tells you to remove metal in exactly the WRONG place.

Oh, so I waste 100s of hours of my time working on the inlet ports?

 

The SSR is the critical bit, he tells you not to touch it!!

Says you should not enlarge the exhaust ports, whereas this is quite an important mod when you get the rest working properly.

All utter b...ll...x!

 

b...llox 5/

finally he suggest down-drafting the head would bring an advantage.

It's been tried and only resulted in a collossal loss of performance.

All b.llox.

 

So basically if you follow all Vizards head advice there is only one thing you can be totally sure of at 100%.

It's a complete load of bollox.

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Thanks GT,

 

I look forward to study your pictures, I do have a good "picture memory" and I feel so relaxed having a high speed air tool in my right hand. You mentioned that your latest mod was made without a flowbench, thats absolute OK for me. I have a biased feeling towards the people in the ventilation buissiness. Flowbenching in Sweden started in the early 70,s, the influence came from the states. A lot of cylinderheads was ruined, maximum flow at a steady state condition did not mimic the complex dynamics in a running engine. But of course a flowbench used by someone who knows how to make the best of it is something different. Can I really expect 35 HP +, that would result in about 165 HP? I was aiming for 145-150Hp with the standard cam fitted.

I noticed that you mentioned someting about the vacuum plumbing for the brake servo, does it have a bad influence regarding the function of the PI inlet manifold? Would it be a benefit to fit an alternator from a Diesel engine? They have a vacuum pump fitted in their rear end.

 

Once again thanks and looking forward.

 

To John D

 

No I have not read it, but I will. Only thing I read by Vizard is the old " The Theory and Practice of Cylinder Head Modification" First published 1971. Regarding the TR4 his recomendations are very limited, cleaning up the bowl and cutting/blending the ridge in the inlet port, same for the exhaust, and some unshrouding around the inlet valve. Worked fine,

 

Cheers

GP

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I look forward to study your pictures, I do have a good "picture memory" and I feel so relaxed having a high speed air tool in my right hand.

You mentioned that your latest mod was made without a flowbench, thats absolute OK for me.

 

..the influence came from the states.

A lot of cylinder heads were ruined, maximum flow at a steady state condition did not mimic the complex dynamics in a running engine.

 

I noticed that you mentioned someting about the vacuum plumbing for the brake servo,

 

Pictures is not something I do.

You will find a lot of the clues on here with the stuff Neil posted in detail.

TBH, they are far more informative than anything from Vizard.

 

I have to be clear here, the mods I do ARE done without using a flow bench, because I did a sufficiently large amount, using one, to know what works and what doesn't.

We won't start on polemics any more. I was told, "go fix it yerself", so I did.

 

This Triumph 6 cyl head is not easy to make TOP simply because there is not enough metal in the right places.

Like the blocks I prefer to use an ultrasonic probe in the future.

 

FYI:-from experience,-

The exhaust port work done by K Riley & another "head friend" was absolutely SUPERB, and they never use a flow bench at all.

It's just what they "BELIEVED" was good, and what ACTUALLY was good were 2 totally different things.

One of them does all the works Triumph heads as well the Radical Hyabusa things.

Never uses a flow bench at all. No-one ever complained his stuff was short on power.

 

However, they thought their Triumph inlet ports were brilliant, but in fact they were quite mediocre.

What they did on the exhaust ports, they thought was just "ordinary" in fact it was brilliant.

 

The heads worked really well because the exhaust porting was so good.

They believed it was for some completely different reason and were "proud" of their inlet ports.

That's alright, let them carry on believing it!

 

After a while you can get a good enough hunch on many heads to be able to say...DO THAT, it will work.

The FB only serves to back up your hunch was right.

In a couple of weeks I will measure those 6 I just did in one go, but it won't do any more than just confirm stuff.

 

In some cases, on more difficult heads, you could be "up a gumtree" without it,- if say you were doing a Lotus TC race head, or a Peugeot 205.

In those cases, take out too much metal and you can more or less scrap it!

 

Another bloke I know in Tallinn does loads of Honda Vtec heads.

They look really great with big ports and all, nice polish the lot.

But all he is doing is supplying them to "road racers" to chase each other around Moscow MKAD at insane speeds.

He doesn't have any idea what they do, but swears it's 300bhp or something.

Does it matter? Does he care?

That's not motorsport at all, and no real measurements have taken place.

 

Are they any good? who knows?

That's the other end of the scale.

Money, b..llx, chipping the ECU, a quick run on one of those dyno thingys that proves nothing and away yer go.

 

At this end the "enthusiasts" rather than the 'boy racers".

TBQH,

I think those Triumph heads are pretty tricky to get right, and every workshop that sees the quantities of them I do, says "what are they" what are you doing those for???

I have clear evidence, I could get an extra 20bhp out of what was basically a GT6 2L engine just flowing the head using the STD cam.

I've seen as much as 30+bhp changing from one "flowed head" to another "flowed head".

That's a lot from just 12hrs of input.

 

In fact it's got to rate as the biggest bargain you could ever get from a small investment.

I didn't stop people leaving me with unpaid bills though did it? :yucky:

 

I have figures for the TR4 head, but no-one has ever asked me to do one, so no doubt you did the right things.

 

If I am proud of anything it would be the very large improvement I managed to find for the Spitfire heads, but there again, you can't skim 3mm off the surface of a GT6 head.

 

I wish you could, but that's why I'm currently fitting a GT6 2L head on a 2.5pi. :sick:

 

As for servos better ask a Pi/EFI saloon enthusiast like Andy or James.

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To JohnD/ GT

 

Indeed they are the same. As far as I remember I did not do much more to the exhaust ports than blending away the ridge and some cleaning up, the manifold match was about 2mm larger than the ports.

 

I forgot to mention that I fitted a single pipe 2" exhaust, much of the piping and silencer came from a Volvo "factory 135 HP" kit for the B18 Volvo engine.

 

Looking forward to GT,s presentation of his findings,

 

Cheers

 

GP

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