Engine Oils, a question for the PetroChemists amongst us

[PeterCrespin]

I would have thought that there would have been a need for bigger jetting to cope with the increased cubic capacity, are the jets different then if the needles are the same?

They are constant vacuum carbs (or CD/constant depression) and therefore adjust air/fuel supply according to load. Within reason, they will deliver the correct fuelling on any suitable engine that can generate sufficient air flow over the bridge. At the absolute limit you might need to do some tweaking, or if you alter things from stock, but for all Jag's road cars the triple SUs were on the side of 3.8 or 4.2 engines - the 3.8 breathing faster at its higher rev limit and the 4.2 breathing deeper albeit at a lower red line. Hence things evening out overall and the same basic carb setup being used throughout.

Pete

[christopher storey]

Two points : the only correct setting for the needles is with the shoulder of the needle precisely flush with the bottom of the piston. There is no need to set it lower than that as one correspondent has done - moving the jet up or down has precisely the same effect

Secondly, re Peter's post, the first Jaguar road car to use 3 carburetters was the 3.4 litre XK150S, so all 3 sizes were accommodated by the same needle

[jag68]

Andrew

Chris answered the question on setting needle height. It's a very precise method.
You shouldn't be experiencing a torque dip at 3000 rpm with the stock intake, exhaust, and air cleaner. You will experience it if you go to larger exhaust manifolds. Headers are only useful for higher revs - that is they push peak torque and hp up the rpm range. The stock exhaust manifolds are very good at flowing, probably as good as most headers, and give a broad power response. When i switched from stock to headers I noticed the reduced torque at 2500 -3000 rpm, in other words it's significant enough to feel it in the seat of the pants. Similarly opening up the intake manifold or porting ups the power range to higher rpm. The stock air cleaner will cost up to 15 hp - Jaguar found this out, but thought the silencing was worth it, and I've confirmed the loss on an engine dyno. The good news is that the power losses are gradual - the full loss is at redline. At the usual rpm's we operate at it's not much of a loss.
I'd put a few more miles on the car before drawing conclusions about the power. I'd ensue the ignition timing was set properly, and that you do have full throttle when the pedal is fully to the floor.

[andrewh]

much to think about in these posts. Thanks.

Well it is not bore glazed I can assure you. Not wishing to blow my own trumpet the engine is beautiful, clean and powerful. It is not using oil puffing out any blue or black smoke. I am talking about black oil and a small dip at about 3000 plus when I have ventured past it. The more miles I put on the engine, the less that dip becomes. I expect it may be a still tight and or a bit rich so will go back to standard jets and work up a bit. The Graphogen is well known to turn oil black whatever the quantities Peter, I appreciate the calculations but am not sure whether they follow through or not.
The engine has been "excercised" in order to avoid glazing and certainly not left at low revs with no load on it. In fact last time I was out I did venture up to 3500 several times, but I keep looking at the running in sticker in my right eye, saying don't exceed 2500 rpm. Now the first oil change is carried out the fun can start.

I am tempted to see if there is anyone locally to me with a rolling road dyno. CKL are not far away but I will have to see whether they have one or not, they are pretty good with Jaguars of course!

[PeterCrespin]

Secondly, re Peter's post, the first Jaguar road car to use 3 carburetters was the 3.4 litre XK150S, so all 3 sizes were accommodated by the same needle

Well-spotted Christopher. I was thinking of the 3.8 XK150S. Didn't recall that triple SUs were an option on the 3.4 'S' as well. Did those use a straight port head too?

Andrew I don't doubt Graphogen darkens oil - it's carbon after all. It's just a matter of degree. Impossible to be definitive without analytical equipment or even seeing anything, same as people wanting odd noises sorted out without hearing. Glad to hear the engine is not being babied. I'd definitely have pulled to red line by now briefly in the lower gears but I'm not blessed with great patience :-). I remember the 'lightbulb moment' when I built my first race Triumph bike engine and figured out that running it in as per factory instructions for a thousand track miles would mean several busy seasons of travelling and entry fees just to get lapped at half throttle.

Err, no thanks! :-)

[malcolm]

Not wishing to de-rail the topic, but putting the E on a rolling road dyno was mentioned. Does this do any harm potentially? I ask because I had a motorbike dyno'd; they red line it for what seems an age, and it sounded dreadful - although awesome at the same time!

[Heuer]

I used Hitech Motorsport near Coventry. They hook the car up with telemetry and run it from tickover to the redline then back off. They have all the info they need to make adjustments. Process is repeated until they are happy, maybe 5 or 6 runs.

[malcolm]

Thanks David - is there a reputable dyno shop in Essex?

[andrewh]

I have found a chap who purports to work for a number of well known E Type firms , so will give him a try . I think I had better run it in a bit more first though. I am toying with dumping the standard inlet filter and fitting an ITG although its the thin end of the wedge for authenticity!

[mldwyer]

Hi,
Back when I was tuning a lot of various carburetor fed engines, I found that as the displacement increased, a smaller jet was required to maintain the mixture when there is no change in venturi diameter. The airflow through a venturi creates a negative pressure which draws the fuel through the jet. As the flow rate increases, more fuel is drawn through the jet. An increase in displacement pulling air through the same diameter venturi will cause an increase in the velocity of the air and pull more fuel in for a given throttle opening. So, I found larger displacements caused a rich running condition.

The Jag uses a variable venturi, so to speak, via the slide (piston) which is raised or falls based upon the airflow demand of the engine. So, the Jag's carburetors maintain a constant velocity based upon airflow and raise the needle to open up the jet to meet the demand. A 4.2 liter flows approx 140 CFM of air at 2500 rpm. A 3.8 liter flows 140 CFM of air at approximately 2800 RPM. Basically the carburetor is only reacting to airflow.

There is a lot more to carburetion, but I just wanted to share my thoughts as to why Jag was able to use the same setup across displacements. And remember, I could be completely wrong. I have been incorrect in the past, and probably will be wrong sometime in the future.

Just hanging it out there,

Mike

[max-it-out]

Only had my present " E " for a few months and it doesn`t seem to use much oil , but , I don`t have any in stock apart from the synthetic 5-40 that goes in the Merc turbo diesel ( that never needs topping up ) would that be ok for the " E " ? or Tesco do a range of good value oils .

Also , frequency of oil changes . I notice that there is no " sell by date " on a can of oil.From that in-depth research I have concluded that oil does not deteriorate over time , but does when in use , so...for a car that only does maybe 2 k miles per year , is it ok to change the oil every 3-4 yrs ?

[christopher storey]

IMHO Not really ok, no. The oil itself probably won't have deteriorated in lubricating quality , but its detergent properties / function will have been lost, and what you risk is that the engine may become gummy with that brown gum that can develop

[Series1 Stu]

Regular oil changes are probably the best way of preserving your engine and avoiding unwelcome damage and breakdowns. From a maintenance point of view, oil replacement is very cheap compared to other aspects of running a classic.

My advice is to avoid the excessively expensive oils, use a decent brand name and change it at least annually.

When it comes to grades of oil you'll get as many opinions as there are grades although I stick to the advice I was given by a respected marque expert and use a good 20/50 multigrade.

Regards

[Polse7317]

AFAIK in the MULHOUSE museum ( amazing BUGATTI collection ) they change oïl every year even with cars in stand -by.... they say the oïl loose its lubricant property .