It's a standard British brake line fitting size, I think 3/8" x 24 tpi. It's a double bubble flare that seals the line to the body of the slave cylinder, quite different from typical US brake lines. The threads are different too, it's a finer thread that standard US brake fittings.

 

As I've bought brake parts only from dedicated suppliers, I've never thought about the thread standard, but I'd assumed that they were UNF. There must be British Girling/Dunlop brake suppliers in the US.

 

I need a thermostat for the 3.4. I've found 160-190 degree. What's best for summertime only driving?

 

To ensure that all coolant goes through the radiator when engine has warmed up.

 

I'm installing the 3.4 in a car I built and it will require a custom exhaust system. I like the way the XK series cars sound. Are they dual exhaust with 2 separate mufflers, or two into one? Is the stock exhaust pipe 1 3/4" diameter?

 

The car I built currently has Wilwood pedals and master cylinders. I'll be using a stock clutch slave cylinder. The clutch master cylinder should be the same bore diameter as the stock cylinder. What is the bore diameter of a stock clutch master cylinder?

 

so do these cars have one of those cooling systems with a bypass pipe, hose or combination (and will be referred to as the "bypass pipe"), such that the thermostat stops the flow, completely, to the radiator when the coolant is cold, and shunts it, via the bypass pipe, directly to the waterpump, to be pumped back through the head again, and then, as the coolant begins to warm, due to its unique construction, can slowly close that bypass pipe as it simultaneously opens the one to the radiator?

if so, i've read that just any old thermostat, even if it fits, will not do, or at least will leave the bypass open at all times. which was not the original intent of the bypass.

 

Dual Exhaust at 1 3/4" should be fine for XK 3.4, @CR 8:1. With OEM B head and OEM dual intake, you will be < 180 HP Gross.
Regards
David

 

There is a bypass pipe. According to what I've read the engine can over heat with a standard thermostat. I've seen where bypass blocks with no thermostat are used in racing.
What would happen if you block the bypass and use a standard thermostat, would it tend to overheat? It wont be driven in cold weather ever.

 

Would my engine gain much in gross HP using 2"?

 

When you first start, the intake to the water pump will not be getting flow, until the thermostat begins to open.... with no flow the thermostat will take a long time to open.
The suction may collapse the water pump intake hose.
My Opinion: For an occasional use vehicle, If you are in warm climate and you use 5-30 full synthetic oil, you would be ok to just leave thermostat out and block the by-pass. It will take longer to reach operating temperature.

The Best plan would be to put the sleeved thermostat in as Glyn recommends.
https://www.ebay.com/itm/25605623396...MakeTrack=true
Rgds
David

 

You would not increase HP with the 2" system, and may loose a small amount do to lower exhaust velocity. Look for aftermarket mufflers that are straight through to keep the exhaust velocity up.
My XKE 4.2 had a 1 7/8" OEM exhaust system. I did use 2" exhaust headers, as the calculated optimum of 1 3/4" were not available. I was about 40 HP lower than a 2" system called for.
There are more muffler options at 2" OD. You can use them with a pair of 1 3/4 to 2" reducers, if you can't get the right muffler size for 1 3/4".
Rgds
David

 

Since the discussion has started, these are my thoughts for the exhaust system. Keep the system standard from the engine to around the gearbox. This is where you want a good, negative reflection. At this point, you either increase the diameter of the pipe or have a crossover between the two. This should gain a few HP and some torque. In my opinion, the effect of many fancy manifolds and sports systems is mainly cosmetic (and cost. Perhaps, that's costmetic). Of course, make sure the joints/ports all match well and the castings don't have large imperfections (they are usually good).

 

I've ordered one of these. This is my first Jaguar engine, I've never seen a thermostat like this.

 

Is 2-3 PSI the correct fuel pressure for the SU HD6 carburetor's?

 

Highly doubtful. The later V12 Jaguars with 300hp used dual 1-3/4" exhaust.

 

Yes. SU's are sensitive to too much pressure.

 

There are 3 Stromberg 97 two barrels in the car now. The 97's can flood at 1 PSI, they also like boil over when parked.

 

What would be the best spark plug heat range for a 1954-1957 3.4 with 8:1 and a B type head? The engine had new Champion n12y plugs when I got it, but one plug had a broken insulator and another had minor damage to the electrode.

 

UN12Y were standard back in the day.