The driven man....ha ha good luck!

Headers are super noisy and from a performance stand point wont offer anything other than noise unless you the massily open up the intake, upgrade the cam and spin it past 5500. The stock XJ exhaust, especially the manifolds are very well designed except for the 70's era catalytic converter. A modern honeycomb free flowing unit may help as long as the cat you already have hasnt gutted itself. When this happens the expelled mesh takes up resisnce in the mufflers. So get in there root around and see when you can find. This can usually be undone with removal and shaking.

Milling the head to up the compression sounds like a possibilty but wont help much on a small bore long stroke engine. I dont know the feasabvilty reguarding timing change length as I'm not expert on the XK engine.

I do know that someone makes a 9:1 compression piston that was a popular upgrade when rebuilding.

 

Noise? That's not noise!
Well I had heard that the stock manifold was good and a better plan would probably be to keep it and still eliminate or gut the catalytic. Isn't the cat built into the manifold, or more likely the downpipe? That was the reason I consider a header. Problems with Driven Man? Anyone know where I could get a Euro downpipe sans Catalytic?

 

Correct!

 

Wow, that just makes it even clearer.

No wonder I've always been impressed by the stock ROW 4.2 performance, especially being coupled (in my case) to a T700 4sp!

 

I find that Jagbits has the downpipe and the Y pipe without catalytic converters in stainless steel. That's the plan! Edge me that much closer to Euro spec.

 

I used a milled head; no problems


Depends which spec sheet you're looking at. I've seen various specs from Jaguar over the years, some saying the low-comp version was 7.8/1.

The ROW engines (there were several "ROW" configurations) also used a different AFMs, timing curves, and ECUs but I don't know if these were significantly different..... or if they represented subtle differences that really wouldn't influence maximum power output. It's been years since I researched any of this but I recall that in some cases the ROW parts were the same as USA.

AJ6 Engineering sells some 4.2 mods that have received good reviews over the years but are expensive....about $3000 for the full package, as I recall.

Any power increases you realize will be at least somewhat blunted by the 4100 pound curb weight, 3-speed trans, and 2.88 differential.....so keep your expectations realistic. It should be fairly easy (but not inexpensive) to wring another 40-50 HP out of the old 4.2 but if what you really want is another 75-100 HP....well, I'd be looking at alternatives.

Cheers
DD

 

Two thoughts/stories:


1. Heads of various critters have been shaved/milled for decades. Circa 1947, My T was morphing. We drove it to a local machine shop. At the curb we drained the coolant. merely water. Removed the flat head. Easy. The machinist laughed, but played along. Whacked it a couple of times. Tested for valve interference by laying it on sans gasket til we got a tap. Just right !!! Paid up. Put it back together. whoah, hand cranking took a bit more !!! But, a strong teen arm did
it. Much more lively....


2. But, when the valves are in the head, rocker arm or OHC, milling is more complex. Two different but related issues to resolve.


Truism, compression increase is felt in the pants seat.


Carl

 

And, my quite staid 4.0 OHV six in my Jeep does have a tubular 'header". Why? More likely as a weight saving device than an improvement in breathing.


As to a better down pie for the Jaguar 4.2. A competent muffler shop can make one up just fine.


Sans smog restrictions, the two outlet stock manifold just asks for a true dual system all he way back. Muffler resonator combinations a plenty.


Carl

 

Yeah, it's a heavy car. I imagine that makes a huge difference but I don't think weight reduction is the way to go. Where would one even start? And it would surely ruin the character of the car - in my opinion.
Like I said originally, I don't plan to go crazy here, short term anyway. Call it Stage 1/2. It's just that the technology has advanced so much in the past 2 decades that what was OK in 1985, may have a hard time keeping up with traffic of the current day. Even my Mom's '07 Honda Fit is quicker with it's little 1500 motor. And then, I like to do it just because I can and spinning wrenches is what I do for fun. So, milling the head - Doug how much was milled and how much do you suppose can be safely milled?

 

This is a little hard to explain.

Take a look at the pic of the bottom side of the cylinder head and notice the brighter colored area where the head actually mates to the block....


http://www.inetogether.org/jaguar/im...tom-070607.jpg

This area is about .125" thick. Almost all of that can be milled off, about 100-thou.

I learned this on ordering a remanufactured cylinder head from Coventry West (they do loads of Jaguar heads) and being alarmed that so much had been milled off. It was explained that 100-thou can be safely removed and wasn't unusual.

And, sure enough, I encountered no problems.

Maybe Dick Maury, who posts here and runs the CW rebuild Department, will see this and elaborate.

Cheers
DD

 

Thanks, that head is from your V12 I assume. Same for a 6 - half a 12? Curious also how much your compression ratio increased.

 

No, that's a 6 cylinder "XK" head


Me too!

Cheers
DD

 

Jaguar used the head from the V12 for the 2.9 AJ6 engine, My 2.9 had something like 210 psi.