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oldtuckunder

Thinking of increasing CR, thoughts?

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The head for my MK1 2ltr engine had been ported within an inch of its life, and had the 36.5mm Inlet and 32mm Exhaust valves squeezed in. The project the head was made for was never finished, so when I got the head it still need some finishing. The work had been done on a low compression MK1 saloonhead so there was lots of meat to skim to what I wanted. Being conservative and thinking about decreasing octane fuels I actually plumped for a final 9.3:1 CR, the MK1 Vitesse and GT6 as originally produced were both 9.5:1 CR.

So as I don't have to rebuild the engine this winter :banana: all I was planning on doing after the Compression and Leak Down tests was just giving the head a clean, re lap the valves, and fit new stem seals, Oh and I'm fairly certain now swap to Megajolt ignition.

But I have been pondering on just upping the CR a bit to 10:1    Why?  I'm not sure, but its one of those nagging "What If" questions. I know the engine will happily take 9.5:1, and as I always use 97/98 octane fuel a 10:1 CR is fairly safe. Given my Chamber Volume this would require a .030 skim, I'm sure there is plenty of metal to do it, but will check with Chris Witor who seems to know more about MK1 heads than anybody else I know.

SO thoughts for and against

Alan 

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You run the 308778 cam IIRC?  Or the increased inlet lift Witor version?

I ran that cam in the PI with 10.25:1 IIRC.  That was EFI and distributorless by MS and I mostly ran it on 95 octane, though it was happier on the better stuff in hot weather.  I reckon that represented the limit.

2.5 lacks squish compared to the 2L Mk2 and I think the Mk1 has at least as much as the Mk2 2L, which will help.  The dead accurate/consistent Megajolt will also help.

With my cautious hat on...... why not go up half a point to 9.8:1.  You could then go further if so inclined.  Much harder to go the other way!

Nick

PS. FWIW, my Vitesse is running more like 10.5:1 at present, but with a longer duration cam so not much use as a comparison.  It would probably stand more but there's nothing left on the head (219016 2.5S originally) and I've already got 0.005" pop-up on the pistons!

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Practical as usual! 

On the subject of CAMS just about to post a bit or work I have been doing on Rover V8 Cams to try and sort Hype from Utter Baloney, might be interesting if we did the same for Triumph Cams?

Alan

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I build my engines to 10.5 - nominal, anyway, as of course in practice it won't be as high as that, even with your optimised breathing, OTU!

I think that this is the limit.     The last I built I started and ran on an old tankful of fuel - and it pinked.    Soon as I put in some fresh fuel, it didn't, and I've driven it on V-Power ever since, no probs.   May be possible to creep closer to 11, but not much to be gained and at some risk, I fear!

On the Trium[h cams database, your posts about V8 camd made me too think that might be useful.   I have data on a number of cams, but most are unobtainable now.

John

Edited by JohnD

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What you need/can get away with is heavily dependent on cam choice.  Alan currently uses the standard Mk2 Vitesse/GT6/PI cam - so not that wild and not needing massive static CR.  Goes very well on it too.

Nick

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35 minutes ago, Nick Jones said:

What you need/can get away with is heavily dependent on cam choice.  Alan currently uses the standard Mk2 Vitesse/GT6/PI cam - so not that wild and not needing massive static CR.  Goes very well on it too.

 

Not quite standard its the Witor CW3021 with increased inlet lift, and if I'm reading correctly from spec sheet a 1 degree difference in Inlet timing.  Anyway as I now have a cam spreadsheet thought I put the CW3021 in to see what came out.

Alan

cw3201cam.thumb.jpg.65f6fad0eed3c9d125b94498ef197930.jpg

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Ah, ok.  Works well.  If my TB experiment doesn't work out I may fall back to this instead - it's only meant to be a road car after all!

Nick

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On 02/01/2018 at 4:57 PM, JohnD said:

I build my engines to 10.5 - nominal, anyway, as of course in practice it won't be as high as that, even with your optimised breathing, OTU!

I think that this is the limit.     The last I built I started and ran on an old tankful of fuel - and it pinked.    Soon as I put in some fresh fuel, it didn't, and I've driven it on V-Power ever since, no probs.   May be possible to creep closer to 11, but not much to be gained and at some risk, I fear!

On the Trium[h cams database, your posts about V8 camd made me too think that might be useful.   I have data on a number of cams, but most are unobtainable now.

John

John, 

If the regs do not forbid it, then water injection will get 97RON up to effectively 107RON. At a guess that would get you to 12:1, knock-free ?

I based my estimates of water flow on WW2 aeroengine data, they're on the blog ( but the write-up is a bit disorganised)

Peter

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Wow! I'm tussling with Megajolt at present.    Water injection!  I must read you blog again - please remind me, and posisbly tell Sideways memebers it's address?

JOhn

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2 hours ago, JohnD said:

Wow! I'm tussling with Megajolt at present.    Water injection!  I must read you blog again - please remind me, and posisbly tell Sideways memebers it's address?

JOhn

Hi John,  I

They are here, the design evolving with each post. Its not yet built !

https://supertrarged.wordpress.com/2014/11/10/tr6se-28-water-injection/

https://supertrarged.wordpress.com/2014/11/22/tr6se-29-distribution-of-injected-water/

https://supertrarged.wordpress.com/2016/01/19/tr6se-35-water-injection-revisited/

(note p14, you get a ca 5% gain in torque with WI, not only the higher comp rat)

https://supertrarged.wordpress.com/2016/02/06/tr6se-36-water-injection-effects-on-combustion/

Its a matter of pride that it works 'out of the box' ........should know by summer...by the lack of clouds of blue exhaust smoke !

Peter

 

 

Edited by PeterC

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