will be redoing my heads and want to upgrade the springs. Any recomendations? The only specs I can find in the service manual are the free length of the inner and outer, but no diameters or loading info.

Thanks
Ken

 

Regrinds by ISKY and Crower will add power if combined with higher compression ratios. a gain of 100 horsepower is possible. Port work will add to those numbers.. The stock Valve springs: were reved by the factory to 7800 rpm before they bounced and since the power peak is at 5750 rpm not a restriction. If tired ISKY sells good valve springs cheaper than I've seen Jaguar valve springs priced at.. The pistons are typically 7.8-1 compression through 1980 (a handfull are 9.0-1 in the earliest XK-Es) Starting in 1981 compression jumped to 11.5-1 However those pistons cannot be used in the earlier flatheads.. (1971-1980)

there is always paeco
PAECO IMPORTS

 

Thanks for the info. I looked at the Isky springs and they are a good upgrade. Will also be using the oaky xm3 grinde with 10:1 Ross Pistons. I'm putting in the 96 mm liners as contemplating oversize valves but not sure what the improvement will be. Do you know what the max oversize valves are? Spoke with Paeco early on as well as Rob beere, AJ, and team cj to get some feel about how far I can push the envelope. Everyone but Paeco said that 10:1 was the limit on 93 octane fuel. Paeco said no issues with 11:1 but from all the input and everything I've read 10:1 is really it unless you want to run avgas. Any thought on the valve size? Thanks -ken

 

Also, has anyone had any recent experience with Paeco?

 

i use 3MM oversize valves in my 1978 5.3 engine, ported& smoothed!
i'm sure the inlet is close to the bore, but have no problems with contact(hindsight could have notched the top of bore).

springs are a new set of factory, with a 060. shim, revs past HP peak(7000) , cams are Crane #2 race profile, pistons 9.2-1 pre HE.
20yrs and counting! plus some mods that i'v forgot about.

also Jaguar valve train system(cam on bucket), needs very little spring pressure,dont waste power opening valves, (it aint no push rod motor).

 

Thanks for the info. I won't have any issues with the oversize valves at a 96mm bore. What are the specs on the Crane #2? Do you know what you picked up in HP? do you know what the max oversize valve is before the intake runs into the exhaust? Was planning on 45mm intake and 37mm exhaust. Thanks - Ken

 

unless paeco has changed some of there quality, i had some problems with spring retainers, actually had the valve stem keepers pull thru the hole(hole was to large).

so went with factory retainers and keepers, thers are good for at least 7500 rpm or more.
i,m more of a mid range torque guy, i rarely go past 6500 driving around the street!

a nice 800lbs.ft. at 3000 would more than make me happy! by the time the other guy got his 800hp up on the cams and closing fast, HA, we run out of road, coming into traffic.

 

of course an N/A Jag v12 will never make 800 anything!
on my Crane cams, been 21yrs,so forgot the specs,(they gave me a CD disc with all the info,but it lost in space), as close as i remember 280* at .004 clearence, i increased it to .010, much smoother idle and better mid-range torque(little bit noise tho,actually sounds cool to a motorhead).
lift was .400 now at .390, overlap around 40*,straight up on timing. visual compare to factory, a lot more over the nose dwell, had the covers off yr ago, easy to see the wide dwell period.

you wont have any probs. with valve to bore , but as i can remember my inlet is 45MM, and exhaust was 37MM i cut OD down about .020 thou., and gave me about .060 between valves!

have no idea how much power i gained, but much better than stock, i would prefer more mid range torque, but after 4500 it really comes to life, and pulls strong till i get antsy(gettin old i guess).
general consensus is,for the street,put all the stroke you can afford into it, and if money no object, go for a 7L build.

something of interest, TWR cams required oversize bore cam carriers, for larger base circle cams, good for 40/50hp(lotsa lift).

there is a book out "TWR and Jaguars XJS). Amazon, Barnes and Noble,etc.

 

now if i had the money, i do know i could put together an 800 torque V12 with 650 HP, using an AUDI V12 Diesel ,comes from the factory with twin turbos ,direct injection, dry sump, and 25lbs lighter than a Jag V12, couple it to a built 4L80E, and change rear gear to a 2.55-1, and i'd be happy.

thats a stock Audi engine, dont even have to take it apart, just custom piping,etc.

those numbers are with just a reprogram of the Audi computer, and two good intercoolers+ water/alky injection.
wishful dreamin

 

What a gorgeous engine bay!