Stroking/Boring a Jaguar V12
Discussion
hidetheelephants said:
Do you have to stick with the Pre-HE unit? I'd have thought the Mays modifications would make a lot of difference.
For motor racing, the HE head is widely regarded as a step backwards - it shrouds the exhaust port badly, which reduces scavenging. The HE improves mid-range torque and power at the expense of top-end power; and, of course, it "hugely" increased efficiency - from near single digits to 16-17mpg...annodomini2 said:
Bl00dy hell! Any idea what superchargers they ran on that engine? AdeV said:
I measured the existing kit tonight, workshop temperature is around 5C, so that might affect things slightly. The piston crown is 0.75mm smaller than the bore
Assuming you're talking about 90mm pistons made of casting alloy, LM13 or similar with a coefficient of thermal expansion of circa 19 millionths per degree C that's a bit further down from bore size than I would expect.Can you confirm those measurements were taken with accurate instruments, micrometer or digital vernier calipers etc?
Hi AdeV
Your measurement seems realistic.
I measured with iso calibrated Mitutoyo micrometers(verynears whether digital or not, are just that, verynears) a range of piston crowns;
Omega MED 18 mm gudgeon pin 1380 pistons 0.8mm crown to bore difference.
JE pistons Race MGB 1840 pistons 1mm crown to bore difference.
Road spec MGB 1867 pistons 1.06 mm crown to bore difference.
JE pistons advise me they do calculate the volume down to the top ring for the CR and the vol will be up to 1cc depending on spec for the MGB pistons.
As I said in reply to your post, it is worth calculating vol as it does have an effect on CR.
Peter
Your measurement seems realistic.
I measured with iso calibrated Mitutoyo micrometers(verynears whether digital or not, are just that, verynears) a range of piston crowns;
Omega MED 18 mm gudgeon pin 1380 pistons 0.8mm crown to bore difference.
JE pistons Race MGB 1840 pistons 1mm crown to bore difference.
Road spec MGB 1867 pistons 1.06 mm crown to bore difference.
JE pistons advise me they do calculate the volume down to the top ring for the CR and the vol will be up to 1cc depending on spec for the MGB pistons.
As I said in reply to your post, it is worth calculating vol as it does have an effect on CR.
Peter
AdeV said:
That idea is being held in reserve in case I can't make enough power out of the NA version 
(I'm trying to avoid it because the championship rules mean I'd need to change from the "modified" to the "specials" class if I add forced induction - at which point I can go mad with the bodywork & suspension as well, which starts to get REALLY expensive and complicated...)
Not trying to change topic , what exactly(officially) are you allowed to do ? (I'm trying to avoid it because the championship rules mean I'd need to change from the "modified" to the "specials" class if I add forced induction - at which point I can go mad with the bodywork & suspension as well, which starts to get REALLY expensive and complicated...)
Pumaracing said:
Assuming you're talking about 90mm pistons made of casting alloy, LM13 or similar with a coefficient of thermal expansion of circa 19 millionths per degree C that's a bit further down from bore size than I would expect.
Can you confirm those measurements were taken with accurate instruments, micrometer or digital vernier calipers etc?
Yep, that's measured with a Moore & Wright micrometer which was dead-nuts on its calibration bar. I use a digivern for cheap & cheerful with a follow up with proper micrometers as required. Unfortunately I don't currently have any inside mics, so for bore sizes I have to use a telescopic bore gauge + micrometer. I do have a (Chinese) dial bore gauge, which I sort-of know how to use (I can set it up, but I'm not sure how I'm supposed to know what the initial diameter is). Handy enough for comparing multiple bores in relation to each other, and for checking roundness (e.g. one liner I checked, while it was still in the engine, was IIRC 0.004mm smaller in the front-to-back measurement as it was side-to-side. Or vice versa, I haven't got my notes handy.Can you confirm those measurements were taken with accurate instruments, micrometer or digital vernier calipers etc?
Regarding the championship: It's the BARC North West Sports/Saloons, the full tech regs are available on their website IIRC. However, the gist (for classes D,E & F) is: Head & block must be externally identifiable as OEM (but you can get away with putting ali heads on an iron block, so long as it/they look like the original(s)). Induction is free, except you cant fit turbo/supercharger unless OEM did - and if they used forced induction you can use either turbo and/or supercharger irrespective of OEM. Exhausts are free. Internals are free. Can be dry sumped. Ancilleries are free. It has to be mounted in the same place +/-50mm as OEM. It has to have been fitted to OEM (so you can't stick a Chevy engine in a Jag, but an XJS could have either variant of the original straight 6 or V12 engines). Gearbox is free. Can't fit a transaxle unless it was OEM. At least 250 original cars must have been built (so I can't use the Lister body kit to fit wide wheels).
Classes are split by engine size. D is anything over 2501cc, class E is IIRC 1201 to 2500 and F is anything 1200 or under.
The specials are even less restrictive - any power plant can be fitted (even hybrids are now catered for, albeit on a case-by-case basis), it can be moved in the car. e.g. my mate Pete has built a Honda CRX with a mid-mounted Jaguar supercharged Audi 4.2 V8 driving the rear wheels through a FWD Audi diesel gearbox...
PeterBurgess said:
Hi AdeV
Your measurement seems realistic.
I measured with iso calibrated Mitutoyo micrometers(verynears whether digital or not, are just that, verynears) a range of piston crowns;
Omega MED 18 mm gudgeon pin 1380 pistons 0.8mm crown to bore difference.
JE pistons Race MGB 1840 pistons 1mm crown to bore difference.
Road spec MGB 1867 pistons 1.06 mm crown to bore difference.
JE pistons advise me they do calculate the volume down to the top ring for the CR and the vol will be up to 1cc depending on spec for the MGB pistons.
As I said in reply to your post, it is worth calculating vol as it does have an effect on CR.
Peter
Thanks Peter. I've only measured 1 piston, and I am assuming the bore is the advertised 90mm as I can't measure that so accurately. I'll have another go tomorrow with the dial bore gauge.Your measurement seems realistic.
I measured with iso calibrated Mitutoyo micrometers(verynears whether digital or not, are just that, verynears) a range of piston crowns;
Omega MED 18 mm gudgeon pin 1380 pistons 0.8mm crown to bore difference.
JE pistons Race MGB 1840 pistons 1mm crown to bore difference.
Road spec MGB 1867 pistons 1.06 mm crown to bore difference.
JE pistons advise me they do calculate the volume down to the top ring for the CR and the vol will be up to 1cc depending on spec for the MGB pistons.
As I said in reply to your post, it is worth calculating vol as it does have an effect on CR.
Peter
I still need to CC the piston dish, I've estimated it so far, and got a CR of 9.22:1 (excluding crevice volume). As per pumaracing (Dave?), I'd expect the piston to expand into that bore, and I don't know what alloy it's made of. According to "the book", the pistons have steel expansion control inserts, but I'll be buggered if I can find them - unless they mean the very much steel gudgeon pin...
Interestingly, if my calculations are correct, in order to maintain dynamic CR of around 7.5:1 (which is where the standard sizes calculate to), I'll actually need my new piston to come further up the bore than the old one, by nearly 0.5mm!
Some more thoughts, if you've "been there, done that", I'd be very grateful if you'd chime in (but I do appreciate you may not want to).
So; it turns out that the CI liners I was planning to use will actually require me to machine the block - which has 98.03mm bores, for the 98.02mm liners to slip fit into. The liners I was going to use have a 101mm OD (approx). Arse. I was hoping to avoid messing with the block, partly because of the expense if I outsource it, and partly through fear of ruining it if I do the work myself on my machines.
However, I can have a set of steel liners made, which can have the required 1mm wall thickness to allow me to run a 96mm bore without machining the block. I'm waiting on a quote.... but steel expands even less than cast iron; so whilst it might be a nice slippy fit at 10 deg C when I put them in, what's going to happen when the whole thing's running at 80-120 C? Will the liners be flopping about fretting the head to pieces, or will the original 0.05" "pinch" be enough to keep them in place?
The steel liners will come chrome plated, so I presumably run regular CI rings on that. Not sure what the CI liners have, they are induction hardened IIRC, but since I've misremembered everything else about them from the motor racing show, I may have misremembered that too...
As I say, your thoughts welcomed (probably...)
So; it turns out that the CI liners I was planning to use will actually require me to machine the block - which has 98.03mm bores, for the 98.02mm liners to slip fit into. The liners I was going to use have a 101mm OD (approx). Arse. I was hoping to avoid messing with the block, partly because of the expense if I outsource it, and partly through fear of ruining it if I do the work myself on my machines.
However, I can have a set of steel liners made, which can have the required 1mm wall thickness to allow me to run a 96mm bore without machining the block. I'm waiting on a quote.... but steel expands even less than cast iron; so whilst it might be a nice slippy fit at 10 deg C when I put them in, what's going to happen when the whole thing's running at 80-120 C? Will the liners be flopping about fretting the head to pieces, or will the original 0.05" "pinch" be enough to keep them in place?
The steel liners will come chrome plated, so I presumably run regular CI rings on that. Not sure what the CI liners have, they are induction hardened IIRC, but since I've misremembered everything else about them from the motor racing show, I may have misremembered that too...
As I say, your thoughts welcomed (probably...)
link to youtube for setting up a Mitutoyo bore gauge, we only have the humble dial gauge versions in four sizes to accommodate little ends up to big v8s.
https://www.youtube.com/watch?v=5r-WY2IMQNk
The regs could make for pretty expensive engines!
Peter
https://www.youtube.com/watch?v=5r-WY2IMQNk
The regs could make for pretty expensive engines!
Peter
AdeV said:
but steel expands even less than cast iron;
Nope, usually the reverse although the CTE (coeff of thermal expansion) of both steel and iron depends heavily on the alloying elements. Most of the grades of basic gray and ductile automotive cast irons have a CTE of about 11 (millionths per degree C) as do most of the basic carbon steels. Heavily alloyed and stainless steels can be all over the shop. Put a good dollop of nickel, 20% or so, in to cast iron and the CTE goes way up to 18 or so. Put even more in and it comes back down again. All great fun sent to test ones patience.So without knowing the exact materials you're dealing with you can't make sensible judgements. However I would be very surprised if the cast iron that has likely been used for the block and the normal grades of steel I can envisage for liners had CTEs that differed by very much at all and if they do it's most likely the steel will be a tad higher.
The above notwithstanding I'm not really sure why you're doing this anyway. The extra capacity will not release much extra power which as always is primarily dependent on breathing ability so the place to spend your money on a 2V engine is on the heads and induction system.
It seems I'm compelled to write a bit about piston land diameters given what's been posted above. I do this from the perspective of someone who has actually designed and made pistons and by that I don't mean phoning up Accralite and seeing what they have in stock. At one point when I was considering actually going into piston manufacture as a business enterprise with a friend I designed and made, totally in-house, a couple of hundred 94mm pistons we intended to use in Rover V8 applications. I designed the piston on the computer, we made the casting mould from huge lumps of cast iron and steel, selected a foundry, specced the aluminium grade, machined the castings back in our workshop with my friend doing the outsides, lands, skirts and ring grooves on his cnc lathe and me doing the gudgeon pin bore drilling and reaming on my own mill. I then built an overbored highly tuned 2 litre Pinto engine for my Sierra and ran it around for a year on pistons I'd made from scratch myself. I doubt many people can say they ever did that.
The sole purpose of the reduction in ring land diameter is to allow for the thermal expansion of the crown. Piston crowns in spark ignition engines reach about 300C at WOT with a design maximum of 350C by which time the metal will have lost so much strength it'll start to fail anyway.
Bores tend to stabilise at somewhat above the coolant temperature and we can take 100C as a reasonable approximation which keeps us on the safe side of the calculations.
The CTE of LM13 casting alloy is 19 (millionths per degree C), 4032 forging alloy is similar, 2618 low silicon forging alloy about 22.3 and hypereutectic high silicon alloys about 18 or a tad less. The CTE of cast iron blocks or liners is about 11. Taking 20C as ambient we can now calculate the increase in size of the pistons and bore for say a 90mm diameter engine at these temps.
The bore will expand by 90 x 11 x 80c / 1,000,000 = 0.079mm
A stock road engine cast piston at 350C will expand by 90 x 19 x 330c / 1,000,000 = 0.564mm
So we're looking at just under 0.5mm differential expansion. Add in a safety clearance of say 5 thou and you'd spec the ring land diameter at 89.4mm. 0.6mm down on bore size. That's actually the number I used on my 94mm pistons and they ran just fine despite thrashing it to try and break them. For high expansion 2618 pistons you'd add 0.1mm clearance to that and for low expansion hypereutectics maybe knock a tad off.
Now don't get me started on what aftermarket piston manufacturers do. I went into that in great detail a couple of years ago. Most of them don't know their arse from their elbow and their main concern is you don't seize or break anything. So they may well use even more clearance but it's not necessary and hurts power and emissions.
However regardless of what the exact clearance is at ambient temperature the whole point of this is it will have almost disappeared at running temperature. That's why you don't take ambient temperature ring land crevice volume into account in CR calculations because if the engine designer has got his sums right it should barely exist at full chat. If you're running pistons that have such a huge clearance there it doesn't get taken up at running temperature then find a better piston designer or try and learn a bit more yourself!
The sole purpose of the reduction in ring land diameter is to allow for the thermal expansion of the crown. Piston crowns in spark ignition engines reach about 300C at WOT with a design maximum of 350C by which time the metal will have lost so much strength it'll start to fail anyway.
Bores tend to stabilise at somewhat above the coolant temperature and we can take 100C as a reasonable approximation which keeps us on the safe side of the calculations.
The CTE of LM13 casting alloy is 19 (millionths per degree C), 4032 forging alloy is similar, 2618 low silicon forging alloy about 22.3 and hypereutectic high silicon alloys about 18 or a tad less. The CTE of cast iron blocks or liners is about 11. Taking 20C as ambient we can now calculate the increase in size of the pistons and bore for say a 90mm diameter engine at these temps.
The bore will expand by 90 x 11 x 80c / 1,000,000 = 0.079mm
A stock road engine cast piston at 350C will expand by 90 x 19 x 330c / 1,000,000 = 0.564mm
So we're looking at just under 0.5mm differential expansion. Add in a safety clearance of say 5 thou and you'd spec the ring land diameter at 89.4mm. 0.6mm down on bore size. That's actually the number I used on my 94mm pistons and they ran just fine despite thrashing it to try and break them. For high expansion 2618 pistons you'd add 0.1mm clearance to that and for low expansion hypereutectics maybe knock a tad off.
Now don't get me started on what aftermarket piston manufacturers do. I went into that in great detail a couple of years ago. Most of them don't know their arse from their elbow and their main concern is you don't seize or break anything. So they may well use even more clearance but it's not necessary and hurts power and emissions.
However regardless of what the exact clearance is at ambient temperature the whole point of this is it will have almost disappeared at running temperature. That's why you don't take ambient temperature ring land crevice volume into account in CR calculations because if the engine designer has got his sums right it should barely exist at full chat. If you're running pistons that have such a huge clearance there it doesn't get taken up at running temperature then find a better piston designer or try and learn a bit more yourself!
Pumaracing said:
AdeV said:
but steel expands even less than cast iron;
Nope, usually the reverse although the CTE (coeff of thermal expansion) of both steel and iron depends heavily on the alloying elements. Most of the grades of basic gray and ductile automotive cast irons have a CTE of about 11 (millionths per degree C) as do most of the basic carbon steels. Heavily alloyed and stainless steels can be all over the shop. Put a good dollop of nickel, 20% or so, in to cast iron and the CTE goes way up to 18 or so. Put even more in and it comes back down again. All great fun sent to test ones patience.So without knowing the exact materials you're dealing with you can't make sensible judgements. However I would be very surprised if the cast iron that has likely been used for the block and the normal grades of steel I can envisage for liners had CTEs that differed by very much at all and if they do it's most likely the steel will be a tad higher.
However, it sounds like I should be OK with steel so long as the alloy isn't a particularly outrageous one. I also don't know what materials I'm dealing with (exactly) yet, it'll be down to what the liner manufacturer uses.
Pumaracing said:
The above notwithstanding I'm not really sure why you're doing this anyway. The extra capacity will not release much extra power which as always is primarily dependent on breathing ability so the place to spend your money on a 2V engine is on the heads and induction system.
The induction system has been completely replaced, I'm using 12 BMW ITBs + injectors. As for head mods, I understand the concepts of porting & polishing, and I do plan to make some modifications to the head to try to improve matters; but I have a limited number of heads, so I need to be sure that what I'm going to do will help.... Of course, I COULD just shell out £10K and buy a set of exchange heads from Roger Beer - but I don't have £10K to spend, and I'd rather learn how to do it myself so that if I do stuff a head for any reason, I don't have to spend £thousands repairing/replacing it...This is very much a learning experience for me...
As for why do the bottom end? Well, I doubt I'll get much more than 100bhp/litre out of the old 2-valver (I may not even get that), so why limit my top end power to 530 when I could have 680...
BTW, interesting stuff about the pistons, how did the Pinto do? Did you get the power you were expecting?
PeterBurgess said:
link to youtube for setting up a Mitutoyo bore gauge, we only have the humble dial gauge versions in four sizes to accommodate little ends up to big v8s.
https://www.youtube.com/watch?v=5r-WY2IMQNk
The regs could make for pretty expensive engines!
Peter
I also have only the dial gauge version... also, mine came with absolutely no documentation whatsoever... I'll check back with the seller as it may be there should be some kind of chart with it...https://www.youtube.com/watch?v=5r-WY2IMQNk
The regs could make for pretty expensive engines!
Peter
And yes, some of the engines that have been through the championship are very expensive... some less so...
AdeV said:
As for why do the bottom end? Well, I doubt I'll get much more than 100bhp/litre out of the old 2-valver (I may not even get that), so why limit my top end power to 530 when I could have 680...
Once again, with feeling. The capacity of an engine under a given head and induction system does not greatly affect the power potential. My own rule of thumb is you'll maybe get 1/3 of the percentage capacity increase as a power increase. So 5.3 litres to 6.8 litres. 28% capacity increase, perhaps 9% power increase.You really ought to read up more on basic engine theory, most of which is covered on my website.
https://web.archive.org/web/20110902010921/http://...
Pumaracing said:
Once again, with feeling. The capacity of an engine under a given head and induction system does not greatly affect the power potential. My own rule of thumb is you'll maybe get 1/3 of the percentage capacity increase as a power increase. So 5.3 litres to 6.8 litres. 28% capacity increase, perhaps 9% power increase.
You really ought to read up more on basic engine theory, most of which is covered on my website.
https://web.archive.org/web/20110902010921/http://...
So according to your own website, torque is largely a function of capacity; so - since increasing the bottom end size is relatively inexpensive (ah, unless I have to have bespoke rods, pistons AND liners, that might get a bit pricey), why not do it anyway? I can work on the heads too, and the induction system I've already changed completely (again, for relatively little expense).You really ought to read up more on basic engine theory, most of which is covered on my website.
https://web.archive.org/web/20110902010921/http://...
Flow benches - well, not hard to construct one of those, I have the Vizard book which explains the use of one pretty well.
Yes, of course, I could be on a hiding to nothing with all this work, but I'll have a lot of fun along the way (if the stuff I'm cleaning the block with doesn't kill me first). TBH, if I listened to everybody about wasting my money, I'd be some miserable hermit living in a cardboard box with a bank account literally bursting at the seams.
Yes peak torque tends to increase fairly closely with extra capacity but does little to make the car go faster! Torque goes up but the revs at which everything happens comes down so gearing needs to increase in proportion and torque at the wheels stays the same in each gear.
The only thing that accelerates a vehicle is power at any given instant.
The only thing that accelerates a vehicle is power at any given instant.
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