I will soon have to check the cams timing since I just bolted the head back on an mk2 3.8 engine yesterday.
As the driver of that car (my father) is driving it mostly low/mid revs I was wondering whether the cam shaft timing stated in the workshop manual could be optimized a bit for his usage? As I understand it the original angles are probably a compromise to cover the range from low to high(ish!) revs but it could be a bit of a waste to keep it that way for someone driving mostly on low end torque? (In my opinion it’s a pity to “never” rev it a little but anyway …!)
Is there some knowledge on the cam timings on here? (backed with serious data like torque curves ideally)
Thanks in advance!
(I guess I could find out myself to a certain degree with a few sessions on a rolling road but quite frankly I am just a newbie in this so …)
No a late full synchromesh gearbox with an overdrive (and a standard ratio LSD differential)
He has owned the car for 10/15 years so nobody is worried about it being good enough for his usage, but it’s just me, I am wondering whether it could be further optimized for him or if it’s not worth it?
Indeed this will be checked again (the car was driving perfectly fine before the head removal because of a coolant leak towards the exterior near the cylinder #1 at the rear)
But this will be checked properly again of course (we installed oxygen sensors ports a while ago so we could plug a wide range oxygen sensor when adjusting the carbs for instance)
As for the cam timing I should add that I also find it interesting to learn on that subject. So if it’s really not worth it we won’t lose our time to gain nothing at all, but if it’s still an interesting path to follow that could be cool to learn a few things while doing it.
But from what you say I understand it’s probably not worth it.
In reply to a message from Ponyman sent Thu 3 May 2012:
Retarded cam timing can most certainly cause overheating.
A 4 degree cam advance can improve your low end torque. This
would give your a little better performance for autocross,
but may result in a little loss in top end speed.
IIRC, set your engine to 8 degrees BTDC, and then zero up
the cams. It will only be a few clicks on each cam sprocket.
Since the cams turn at half the distance of the crank, when
you set the crank at 8 degrees, the cams will have been set
at 4 degrees.
Personally, I don’t know if it’s worth it for what you’re
going to get. I do more highway driving than I do autocross,
so I keep my cams at zero degrees.
ex jag, '66 E-type S1 4.2, '56 XK140dhc, '97 XJ-6
Denison, TX, United States
edit: do you happen to know whether the exhaust cam should be advanced too? I understand the intake should since it helps build pressure at low revs (I hope I don’t write nonsense!) but not too sure about the exhaust side? From the post you quoted I understand both should be advanced?
No, don’t touch the exhaust cam as you will lose work out of the exhaust pipe earlier, instead of using the heat of combustion to force the piston down a bit more. The inlet cam advance makes more sense on automatics, most of which live most of their life between 1,500-3,000 rpm. With a manual there is more scope to use the factory mid-range and beyond.
The 4 degree inlet advance would actually suit an overdrive gearbox very well, as you could delay dropping back out of overdrive on highway inclines, but most drivers use overdrive when they’ve finished playing tunes with the engine and just want a steady, quiet, cruise mode.
“Jaguar camshafts tend to get timed to the manufacturers recommended positions, and then left as they are. This is almost always very acceptable, as in most cases, setting the camshafts to the manufacturer settings, will be good enough to achieve excellent power.”
I’ve changed my cam timing, maybe there is some info in an old thread, it was so that it had lots of power at the top end but a lumpy idle, so I overshot in the other direction (less overlap being the idea) and I had a smooth idle, slightly more torque and a lot less top end. The Jaguar timing hits a sweet spot.
I had no issues and likely just did the intake cam. Try it, it’s fun! But it won’t create a miracle. I simply moved the cam by the width of the notch.
I am pretty sure my father is really not often past 3000 rpm as “it’s not a high revving engine” (to which I reply that 5000rpm is indeed very slow … )
Seriously I would say it’s the ranges he actually uses 99% of the time, so that looks good for him as well.
I understand this and I generally follow the official settings. But a fixed timing at the camshaft is a compromise since the variable ones were not invented yet (?)
As the manufacturer setting has to please everyone (low revs drivers and high revs ones too) I gather they have to choose a setting in the middle.
But as I said my father is using the low end of the range so I figured it could be a good idea to alter the intake cam timing since it’s so easy with this engine! (no need to change a pulley)
Precisely how much more low end torque do you think you’re going to get by a small adjustment? Sorry to disagree, but I think just leaving it the way the factory designed it is optimal for the indicated use.
Many moons ago I advanced the inlet cam timing 4º on my Series III XJ6. It did help the low/mid RPM power/response. Idle to 2500 RPM or so, as I recall. The improvement was palpable… but not life changing
But that’s a 4200 pound sedan with 170 horsepower, automatic trans, and a 2.88 final drive. Anything was an improvement.
In a lighter car with a better power/weight ratio and shorter gearing you might not notice any difference. You might “drive through” the small improvement, if you get what I mean.
5500 at least, if he enjoys it like that I wouldn’t bother experimenting with the cams… as Doug Dwyer says there is a slight improvement but it’s not much. Just as I said. Lot less top end, bit more at low revs.
Sure, but it’s a slow top end compared to a regular engine, that’s what I meant.
5500 at the top end being slow doesn’t mean you need to drive it even at lower revs “because it’s a low rev engine”. The usable range is 0-5500, not 0-3500 ^^ (you don’t need to narrow the range even more than it is already)