Jaguar XK-6 DOHC port/cylinder head analysis

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Marquis Rex
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#1 Jaguar XK-6 DOHC port/cylinder head analysis

Post by Marquis Rex » Mon Sep 10, 2018 1:59 pm

Image


I’m an engine design and development engineer with over 23 years of experience who worked at Jaguar and the premier automotive group for 10 years, involved in the AJV8 and the Aston Martin V8 Vantage engine, amongst others. I’ve since been involved in heavy duty truck engines and the Indian V twin motor cycle engines, to name a few. I’ve always fancied turning my expertise to the classic Jaguar twin cam motor and indeed some of my old mentors told me a lot about that engine back in the day. I thought the community could benefit from some of my comments/experience

-I did some Flow bench work on the -XK head compared to other 2 valvers, some period some benchmarks from my massive archive
-Using CFM to characterize the flow of a bore is antiquated and of limited worth- it actually tells us very little
-“Alpha K” is normalized flow relative to a bore size.
-It allows comparison of various engines regardless of size
-It’s a measure of how well the bore is being ‘fed’
-For a two valve engine an upper value (at max valve lift of 10-12mm) of above 14% is good and towards 16% is outstanding
-From the above, normalized, the XK engine head flows similar to an original 70’s BMW 323i (with it’s outstanding shallow angle hemi M20 cylinder head)
-And better than a period Ford 1.6 cross flow (Kent engine)
-Porsche 993 cylinder head is one of the benchmarks for a two valve, only shadowed recently by the Gen 3 Chrysler twin spark Hemi
-426 Hemi is a period benchmark
-In its day, the 1980s BMW 325i cylinder head (shallow angle Hemi) was one of the best


Image

-Second plot shows data Normalised relative to inner valve seat diameter again allows valid comparisons with much smaller or much bigger capacity engines
-Valve lift has also been normalized in this plot to a ratio of valve lift to valve seat diameter- this allows us to see the C=1 line
-Cd=1 line shows idealized flow and theoretically you can’t exceed this for a 45 deg valve seat at low valve lifts. If you don’t meet it- it is often due to flow shrouding caused by chamber shrouding or bore shrouding (rarely the case with a 2 valve hemi engine)
-A high Flow coefficient value (Above 0.6 at 0.3 L/D) for a 2 valve shows a port that flows well
-A high flow coefficient and poor ‘Alpha K’ (flow relative to bore) indicates the intake valves are under sized for the bore size. I would say this is the case for the Jaguar XK engine for the bore size. This gets worse when you consider the huge stroke and the little valve having to feed about 700 ccs of cylinder
-The port flow efficiency of the Xk engine (from the 1960s) shows better than a late 1990s Chevy LS engine (much over hyped engine)
-One can clearly see here that the Gen 3 Hemi is one of the best flowing production heads for a 2 valve to date

If I were renovating/rebuilding an XK engine with my modern thinking of all I have learned I would look at the following- bigger valves- bigger than the series 3 1.875 inch, may be 2 to 2.1 inches (like the D types used), twin plugs, to allow shorter flame paths and reduce knock propensity, then raise the compression ratio, like Porsche did on the 911, to may be 10.5:1. Twin plugs allow shorter flame paths /better knock mitigation without compromising intake flow for motion to get the same effect. Even so, I’d guess that we couldn’t go as high as Porsche did (11.3:1) because of the inherent favourable thermal properties of a long stroke layout leading to earlier onset of knock. I’d probably go with little 10mm plugs for packaging. I’d like to get the peak ‘Alpha K’ to around 15-17% and the flow coefficient to 0.73. Even so , the high long stroke would be challenging in terms of friction and vibration. Oh well, I’m not about to do a tuned XK engine and ruin the originality of my E type, but I may do one day for fun for a dyno run!
"Live Fast, Live Well, Live Free!"
1970 Jaguar E type OTS

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#2 Re: Jaguar XK-6 DOHC port/cylinder head analysis

Post by Marquis Rex » Mon Sep 10, 2018 2:02 pm

I tried to post the images via my desk top and it wouldn't post the images regardless of size chosen. I ended up putting the whole lot on my iPhone and posting from there and now the images are super small.

If any admin can help- cheers!
"Live Fast, Live Well, Live Free!"
1970 Jaguar E type OTS

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#3 Re: Jaguar XK-6 DOHC port/cylinder head analysis

Post by politeperson » Mon Sep 10, 2018 2:11 pm

Very interesting.

Just press control and "+" three or 4 times on your keyboard and it makes the images on screen better. control "-" s few times to reduce the size.

You think it is less likely to pre-detonate with a 10.5:1 compression ration. I thought the higher the CR the more likely it would be to pink?

I am just about to build another cylinder head with .39in lift cams.

You reckon go larger than 1.875 inch S3 XJ6 "big valves"?

Well I might just do that. Need to find out where to buy them from.

I must say though that the valve seats are pretty close together on an S3 XJ6 head. Here is a picture of one below.


Image

James
Last edited by politeperson on Mon Sep 10, 2018 2:18 pm, edited 1 time in total.
James

L.J.K. Setright was right.
"You just cant beat a good E-type"

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#4 Re: Jaguar XK-6 DOHC port/cylinder head analysis

Post by Marquis Rex » Mon Sep 10, 2018 2:15 pm

I wouldn't raise the CR of a stock cyl head. You need to go Twin Plugs to reap the benefits of a higher Compression Ratio.

A guy in Illinois did this recently.
The Chevy LS7 cyl heads have the valve seat inserts pretty much touching- you have to be sure there's no porosity. So as long as they're not touching, you'll be ok
"Live Fast, Live Well, Live Free!"
1970 Jaguar E type OTS

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#5 Re: Jaguar XK-6 DOHC port/cylinder head analysis

Post by politeperson » Mon Sep 10, 2018 2:20 pm

OK.

Ill have a go.

Need to think about twin plugs though. Dont want to drill through the water jacket!

They would certainly give me cred down the pub if nothing else.

Need to get a section of a head and figure it out.
James

L.J.K. Setright was right.
"You just cant beat a good E-type"

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#6 Re: Jaguar XK-6 DOHC port/cylinder head analysis

Post by Heuer » Mon Sep 10, 2018 3:06 pm

Marquis Rex wrote:
Mon Sep 10, 2018 2:02 pm
I tried to post the images via my desk top and it wouldn't post the images regardless of size chosen. I ended up putting the whole lot on my iPhone and posting from there and now the images are super small.

If any admin can help- cheers!
I have modified the links so clicking on the photos will enlarge them. I have yet to figure out why some photos enlarge when clicked whilst others just take you to the Postimage page. In the meantime the work around is this:

After uploading you will see a link that looks something like this:
{url=https://postimages.org/]{img]https://s15.postimg.cc/68c4wtesr/IMG_3549.jpg[/img}[/url}

You need to delete this part of the link:

{url=https://postimages.org/] and this at the end {/url]

This will leave you with this part of the link and it will work correctly:

{img]https://s15.postimg.cc/68c4wtesr/IMG_3549.jpg[/img}

Alternatively (and simpler) just change the .org to .cc

So {url=https://postimages.org/]{img]https://s15.postimg.cc/68c4wtesr/IMG_3549.jpg[/img}[/url}

Becomes: {url=https://postimages.cc/]{img]https://s15.postimg.cc/68c4wtesr/IMG_3549.jpg[/img}[/url}
David Jones
S1 OTS OSB; S1 FHC ODB

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#7 Re: Jaguar XK-6 DOHC port/cylinder head analysis

Post by tim wood » Mon Sep 10, 2018 4:46 pm

I read somewhere in the dim and distant past that at one time the plug holes were welded up and redrilled to use 10mm motorcycle plugs ?


I will see if I can dig it out.

Tim
Series 1 FHC purchased 40 years ago. Courted my wife in it.
Series 1 2+2 when the kids were small now sold.
Series 1.5 OTS in opalescent maroon, Californian car. My retirement present.

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#8 Re: Jaguar XK-6 DOHC port/cylinder head analysis

Post by Gfhug » Mon Sep 10, 2018 7:24 pm

S2 FHC Light Blue

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#9 Re: Jaguar XK-6 DOHC port/cylinder head analysis

Post by Marquis Rex » Mon Sep 10, 2018 7:48 pm

Here's an article on a twin plug XK motor.
https://www.enginelabs.com/news/video-4 ... p-on-dyno/

I'm somewhat skeptical of the 400 Bhp claim. They seem to claim it as 'net'.

But first a little history lesson- the original E type was rated at 265 bhp 'Gross'-which means no carb heat cross over, no back pressure, no air cleaner, etc. This makes a huge difference. Its been stated that the 205 Bhp fuel injected series 3 XK engine of the 1980s is the most powerful XK production engine. I can believe it. Therefore I would guestimate that the E type 3.8 fully dressed with proper air cleaner and back pressure is probably around the 190 bhp mark while the later twin carb series 2 cars probably sitting at 170 bhp.

This is at the flywheel and not the rear wheels.
By comparison the 426 Hemi of the time was rated at 425 bhp (Gross) but actually attained 480 bhp gross on the dyno ( I have the original dyno report from Highland park in Michigan!) but once you factor in the direct drive fan and other anciliaries- its closer to 360 bhp. So we shouldn't feel too bad!

In the above article they seem to claim 400 bhp net or fully dressed. Gross I can believe.

They're really not that far to me so I should reach out to them.
"Live Fast, Live Well, Live Free!"
1970 Jaguar E type OTS

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#10 Re: Jaguar XK-6 DOHC port/cylinder head analysis

Post by politeperson » Mon Sep 10, 2018 8:15 pm

Yes, I would go along with that.

I use 2 proper rolling roads with properly calibrated machines and they have been doing it for years.

They always have to say the right things to XK owners to prevent disappointment, as they rarely see 180 bhp, let alone 200 bhp on healthy XK units. That is at the flywheel. The 265bhp figure has caused lots lively discussions over the years I think.

I suppose its all about torque anyway, and the car is quite light.

They do see modified XKs over 300hp. They are very expensively put together. You could buy an F-type with the change, so you have to wonder if its worth it. Racers mainly.

I would be very pleased at anything over 275bhp. I am making approximately 240 bhp at the moment and the car really flies.
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L.J.K. Setright was right.
"You just cant beat a good E-type"

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#11 Re: Jaguar XK-6 DOHC port/cylinder head analysis

Post by Durango2k » Mon Sep 10, 2018 8:40 pm

I would reaaaly love to hear something about the Maserati C114 engine. It gave around 178 hp in 2.7 ltre shape, 180 to 190 in 3 ltre, and 220 in Merak SS and with huge valves (which usually broke).

I can get measures - I never dyno‘ed my own car. Its base was a 3 ltre with broken pistons, so I had to modify a set of Citroen XM pistons, raising capacity from 2.965 to 3.048 cc, plus compression to something like 10.5:1. It runs nicely. But higher compression also means the bearing shells life in danger, so I do not go anywhere beyond 5.000 rpm nowadays. I once did 7.300 rpm, speedo showing 263 km/ (which may be 245 in fact), but the, centre rod bearing gave up and I had to re- overhaul it again.

You don‘t have Maserati figures in your archive?

I am really eager to find out how a series 1 in 2+2 shape compares to the Grand Citroen Maserati SM....it‘s just 4 years between them, 1966 to 1970. Oh and both appaered first time in Geneva...

Carsten
Jag E '66 S1 2+2, Citroen DS 23 Pallas iE, Citroen SM 3.0, Concept Centaur MK1, Citroen 11 BL '54, Sinclair C5, Velosolex

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#12 Re: Jaguar XK-6 DOHC port/cylinder head analysis

Post by Marquis Rex » Mon Sep 10, 2018 9:24 pm

Durango2k wrote:
Mon Sep 10, 2018 8:40 pm
I would reaaaly love to hear something about the Maserati C114 engine. It gave around 178 hp in 2.7 ltre shape, 180 to 190 in 3 ltre, and 220 in Merak SS and with huge valves (which usually broke).

I can get measures - I never dyno‘ed my own car. Its base was a 3 ltre with broken pistons, so I had to modify a set of Citroen XM pistons, raising capacity from 2.965 to 3.048 cc, plus compression to something like 10.5:1. It runs nicely. But higher compression also means the bearing shells life in danger, so I do not go anywhere beyond 5.000 rpm nowadays. I once did 7.300 rpm, speedo showing 263 km/ (which may be 245 in fact), but the, centre rod bearing gave up and I had to re- overhaul it again.

You don‘t have Maserati figures in your archive?

I am really eager to find out how a series 1 in 2+2 shape compares to the Grand Citroen Maserati SM....it‘s just 4 years between them, 1966 to 1970. Oh and both appaered first time in Geneva...

Carsten
I have very little on that. The only thing I know about those engines is that they are a 90 deg bank angle and uneven firing so produce interesting harmonics (sound interesting).

Was that engine or a variant of it- Turbocharged?

If so- and the bearings are the same size- the bearings would probably take revving fine.

Obviously you want to make sure you have good oil pressure (so your bearing clearances are good). When you rev an engine it's less to do with load but more to do with making sure your oil film thickness is maintained- so oil pump condition is important also. I'll see what.if I can dig something up.
"Live Fast, Live Well, Live Free!"
1970 Jaguar E type OTS

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#13 Re: Jaguar XK-6 DOHC port/cylinder head analysis

Post by 288gto » Mon Sep 10, 2018 9:30 pm

Below was Uryk at Evolution E Types pet project
I don’t know if anything came of it.

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Image

Simon
Simon
1969 S2 OTS

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#14 Re: Jaguar XK-6 DOHC port/cylinder head analysis

Post by Marquis Rex » Mon Sep 10, 2018 9:44 pm

288gto wrote:
Mon Sep 10, 2018 9:30 pm
Below was Uryk at Evolution E Types pet project
I don’t know if anything came of it.

Image

Image

Simon
WOW! That looks super impressive! I wonder if anything ever became of it. If it was possible to implement variable valve timing on the XK engine that would be huge! I would rate that over a 4 valve head!
"Live Fast, Live Well, Live Free!"
1970 Jaguar E type OTS

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#15 Re: Jaguar XK-6 DOHC port/cylinder head analysis

Post by Tom W » Tue Sep 11, 2018 7:22 pm

This is fascinating.

I always wonder what the improvements would be, if any, to have the combustion chambers aligned with the bores on the 4.2. What are the detrimental affects off the offset bores? Presumably the squish, mixture swirl and combustion characteristics are different from cylinder to cylinder.
Tom
1970 S2 FHC

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#16 Re: Jaguar XK-6 DOHC port/cylinder head analysis

Post by Marquis Rex » Tue Sep 11, 2018 8:13 pm

Tom W wrote:
Tue Sep 11, 2018 7:22 pm
This is fascinating.

I always wonder what the improvements would be, if any, to have the combustion chambers aligned with the bores on the 4.2. What are the detrimental affects off the offset bores? Presumably the squish, mixture swirl and combustion characteristics are different from cylinder to cylinder.
In my experience- Squish, combined with the right squish clearance or squish height makes some difference with a longer stroke length. The Jaguar AJ16 was effected much more by squish than the V12 or the AJV8 (both with shorter strokes) as its related to piston speed when it gets close to the cylinder head.

On the other hand the open hemi style chamber - with the slight flat edge - on the XK head is quite a small squish area- so probably not that much.
"Live Fast, Live Well, Live Free!"
1970 Jaguar E type OTS

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