Stroking/Boring a Jaguar V12

[AdeV]

Hi,

I've been hunting high & low for a good technical forum to post this question on, and here it was right under my nose all along....

I've got a Pre-HE 5.3 V12, which I'd like to put a 6.0 crank into, and 96mm pistons (up from 90mm). I'll be having the pistons made, so hopefully I can use the original rods & absorb the extra lift in the piston crown to gudgeon pin gap (if not, then I'll have to get custom rods). I also plan to run race cams & ITBs.

My first question is - the CR of the 5.3 is 9:1 if I recall correctly; that seems a touch low to me, would there be any benefit in moving to a higher CR?

Second question - the Pre-HE uses dished pistons with no appreciable "squish" regions, the piston reaches TDC around 5mm shy of the head. Jaguar apparently examined adding squish regions above/below the valves (leading to a sort of fat figure-8 shape cut into them for valve clearance/combustion chamber), but determined this gave lower power than the plain dish. So... should I, too, stick with plain dished pistons & around 5mm clearance (or whatever the cam calls for), or has piston technology moved on to the point where a shaped chamber would now be a good idea - a bathtub shaped cutout maybe? I don't want to mess too much with the heads, if I can help it, beyond a bit of porting/polishing.

Thanks in advance!

[AdeV]

BritishRacinGrin said:

What sort of ignition system do these engines run? will you be keeping it or going aftermarket? if you increase the CR you're probably going to need to increase the ignition advance.

I plan to use a Megasquirt in full sequential mode (ignition & fuel) - you're right to ask, the original Jag system would not be suitably tunable...

[AdeV]

Thanks for the further replies...

Gavin & E600 - I'll definitely bear this in mind, my project is a little unusual in that the only restriction on what I can do is "Head and block must be externally identifiable as OEM". I'm also doing it on a relative shoestring, which will rule out buying any serious performance mods (e.g. Rob Beere's £10k heads). On the other hand, I'm half decent at wielding a spanner - and a calculator and a milling machine - so I plan to do a lot myself.

Paul - obviously, I've been googling all around this subject (and plenty of others I haven't even touched on yet), plus I have various books, magazines and so on with additional information. My question is not HOW to increase CR, it's whether it's advisable/sensible or not. The engine has to run on road fuel (i.e. Shell V-Max), and I'm not planning to run forced induction (which would require a lower CR), so the question is, do I change the CR or not? Also - it's not the liners that need machining, it's the block IF you go above 96mm bore. 96mm liners are available OTC for a very reasonable £75/ea in ductile steel, or I could make my own in Ali and have them Nikasil coated for £105/ea.

I'm about to start measuring the piston-to-deck height, the approximate volume of the dish, that will give me the exact volume as it is now. I already know the stroke (70mm), and bore (90mm).


Another question - do I need to take into account the volume between the top ring land and the top of the piston as well, or is that regarded as being sufficiently small as to be irrelevant?

[AdeV]

chuntington101 said:

If the comp ration is only 9.0:1 the why not add a couple of turbos or a supercharger.

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...)

[AdeV]

Pumaracing said:

PeterBurgess said:

We run around 1mm crown to bore difference on many of our pistons,Peter

Then you are nuts. For a normal sized road car piston to expand by 1mm it would need to reach 600 degrees C at which point it is near as dammit molten and the piston has disintegrated anyway.

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 - but this is an aluminium piston running in a cast iron liner, so I imagine there is some differential expansion at working temperatures.

Measured (slightly estimated) CR, excluding the bit between the piston and the bore down to the top ring comes out at 9.2:1; some git broke my burette so I can't CC the piston dish accurately, estimating it using trig gives that figure.

All very exciting, however, reading various bits of "literature", would suggest the dynamic CR is of more interest than the static; and that a figure of around 7.5:1 would be a good compromise between power and detonation likelihood of detonation.

[AdeV]

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...

[AdeV]

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.

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...

[AdeV]

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.

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!

[AdeV]

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...)

[AdeV]

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.

Ah, patience testing, you're not wrong! I've been reading up on various materials, etc., CTE is not something that's frequently mentioned (annoyingly).

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?

[AdeV]

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...

And yes, some of the engines that have been through the championship are very expensive... some less so...

[AdeV]

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).

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.

[AdeV]

So, back to the original question then.....

Judging by my calculations, in order to retain a dynamic CR of 7.5:1 (approx.), if I've used the correct figure for the inlet valve closing (and I'm not sure I have, I need to check with the cam manufacturer that I'm not using the angle at 0.020" lift, or whatever), then I'll need to increase the static CR to approximately 10:1 (from 9:1), which - with the bigger bore - means having the piston rise approx 1mm higher at TDC which, given the longer stroke & same length rods, means having the piston-to-pin height approx 3.25mm shorter, which looking at the OEM pistons should be easily achievable with custom pistons, and I may even be able to find something off shelf.

[AdeV]

Pumaracing said:

A sensible DCR for engines on pump fuel is 8.5 not 7.5.

Or, indeed, anything in the range from 7.5 to around 9.0 depending on octane rating, with some engines capable of handling 11:1.

I think I'll stick to asking Google.

[AdeV]

Pat_T said:

Arriving late to this thread. It seems to be right old mixture of good information, miss-information and total rubbish!

...

We've always included the volume down to the first ring in our compression ratio calcs. Why wouldn't you?

Do you calculate it cold, or after you've taken into account the piston expansion at temperature? And what temperature do you use, since I assume it's something of a gradient from crown to skirt...

Pat_T said:

Also include the headgasket thickness and depending upon the construction of your headgasket realise that it's compressed thickness might be significantly different to what you measure statically with verniers. Best to do a back-to-back dry build with the block on a marble table and measure the camdeck height with and without head gasket.

Well, the OEM gasket is plain copper, albeit with thicker fire rings. Since this is Al-to-Al (rather than Al-to-Fe), I'm guessing it doesn't really need a complex MLS gasket. Do solid copper gaskets crush that much?

Pat_T said:

Be very careful benchmarking OEM vs aftermarket piston-to-bore clearances. It is probably not as straightforward as it seems. In my experience OEM piston design will have as much to do with maintaining good 'piston posture' and reducing NVH/piston slap during cold-startup as it will anything to do with maintaining a minimal clearance at high load/temperature.

Hence the long skirt? That could make sense. Still, the main reason for the careful measurements is to try to get an accurate CR. Based on what I now know from the Cam manufacturer, I'm likely to need an even higher static CR than I thought to maintain a sensible dynamic CR. It also looks like I'll be running steel liners rather than iron, in case that makes a difference.

[AdeV]

Pumaracing said:

What I want to know is where can I get me one of those marble tables? I'm guessing I can measure the compressed head gasket thickness to a squillionth of an inch like that. I can then factor that in to the guesswork every engine builder does to try and decide on a CR which has a huge latitude either way but at least I'll know the head gasket thickness exactly. Or I suppose I could just measure the thickness of an old one like everyone else does.

Jeez this thread gets sillier and sillier.

Now now... admittedly, I did wonder about the marble table (granite would do just as well. ).

[AdeV]

Pumaracing said:

AdeV said:

Now now... admittedly, I did wonder about the marble table (granite would do just as well. ).

Good god no! Granite is compressible. You could be a billionth of a micrometre out if you use granite. Steel is even worse. You could be a millionth of a micrometre out if you just use the bed of a handy milling machine. If you don't bother with any of that and just measure the thickness of an old compressed gasket you could be several thou out either way which would be one tenth of three fifths of f**k all which could be 0.1 of a CR point and then the engine will blow up. What to do eh?

Depleted uranium then! Or, better still, water - my physics teacher back in 19-mumbleteen told me that liquids are incompressible, so that must be the perfect working fluid!


OK, so, help me out here..... if my calculations are correct, in order to get a dynamic CR anywhere NEAR 8 (let alone 8.5), using a cam with the inlet valve closing 105 degrees ABDC, then I'm looking to have to build to a static CR of around 17.4:1. That seems bloody excessive to me, but is static CR actually relevant to anything? Would I be better looking at a milder cam, given those numbers?

[AdeV]

Umph, I just worked out how much all this is going to cost me.... and there's no guarantee it's going to work.

Back to plan "F" (use original engine, with slightly uprated cam, and work on the heads & inlet.

[AdeV]

Pumaracing said:

AdeV said:

OK, so, help me out here..... if my calculations are correct, in order to get a dynamic CR anywhere NEAR 8 (let alone 8.5), using a cam with the inlet valve closing 105 degrees ABDC....

You're avin' a larf right? Or someone is having one with you. IVC at 105 ABDC would indicate a cam duration of something mental like 360 degrees. That's extreme drag race territory, coughing and farting at anything under 6000 rpm and then a brief surge of all hell breaking loose. The only place you'd want something like that in your car is maybe in the boot for ballast if the weight distribution is wrong.

That's what Kent Cams have quoted for their full race cam...

[AdeV]

Pumaracing said:

AdeV said:

That's what Kent Cams have quoted for their full race cam...

Twaddle. You're making a right bleedin' meal of this. The specs for all their cams are on their website. The JAG8 race cam has 310 degrees duration and closes at 85 ABDC.

I have it in an e-mail just yesterday (erm, last week I mean), from the horse's mouth:

Kent Cams said:

On 11/02/2015 08:03, Info wrote:

Hi

Yes that was a regrind price, new billets are £1600.00

Inlet is fully closed 105° ABDC

Regards
Del

From: AdeV
Sent: 10 February 2015 20:46
To: Info
Subject: RE: KC - Web Enquiry - 13/01/2015

Hi,

Thanks for answering that for me - is that a re-grind of my original cams, or is that a brand new cam? If the price is for a regrind, can you tell me how much it would be for a new cam to be manufactured? I understand there is approx. 12 week lead time on such an order.

Also - for the JAG8 product, can you tell me how many degrees ABDC the inlet valve is fully closed please? Trying to determine my dynamic CR.

Cheers,
Ade.

Pumaracing said:

http://www.kentcams.com/product-details/223/Camsha...

It's also clearly a sh11t cam with the wrong lobe centreline angle and not much lift.

I'll let you tell them that.

Pumaracing said:

Stick a JAG7 into it which has a better lobe centreline angle and not much less duration or lift,

http://www.kentcams.com/product-details/222/Camsha...

set the CR to 11.4:1, DCR 8.0 and get on with the job. It's not rocket surgery.

Of course, there's always Piper cams....

Edited by AdeV on Tuesday 17th February 12:34