PMed

 

Driven Man is now part of American Powertrain. At the time I talked to American Powertrain last year, one guy was assigned to the Tremec kits for Jags. I have purchased from American Powertrain in the past. They were always helpful to me.

 

Good to know! But I just looked them up and they do not list a kit for a Jag V12. Should I ask them if they have such a kit that they do not advertise?

 

Certainly worth the call to
Driven.
There is thejagguru on e-bay the makes three pedal set ups. You can put your year and model in for fit.

 

Roger Bywater is right. The stock cast iron manifolds are very good indeed. If you build a proper set of equal length headers you will fill the engine compartment with tubing, and prevent air from flowing past the engine and getting out.
That means overheating. The radiator works by air flowing through the radiator, picking off heat and on out below the engine. If that exit is blocked off by tubing that will reach up to 1200 degree f You’ll have heating problems.
Second additional power, you will gain at most 4% more. The stock manifolds are very good indeed, plus they only weigh 4 pounds each. ( total 16 pounds).
If you want improvements polish the raw cast iron up and have them thermal coated. Silver is traditional but they also have black and red. That not only gains you a slight power increase but retains the heat to exit out the tail pipe rather than in the engine compartment.

 

It’s all common sense. V12 in not V8 so the exhaust is not Siamese. Look at the firing order of the V12, you will see that every 180deg one cylinder exhausts into 1 cast iron manifold, and so on. They alternate between the 4 manifolds (180/1 180/2 180/3 180/4) and no exhaust stroke overlaps in those 4 cast iron manifolds. So not Siamese. Now on a V8 , or the Jaguar straight 6 (exhausting into 2 cast iron manifolds) you have overlapping, meaning for a short time 2 cylinders exhaust into the same plenum.. (one pushes exhaust gases into the other cylinder trying to exhaust). Then you sort that out with length of tubing on headers (noting the speed of exhaust gases, and distance traveled) So on a V 12 all you need is 4 independent manifolds. That’s it ! They are plenty big. Headers on a V12 shouldn’t exist. There is NO need for them. (Unless you try to route exhaust gases around an obstacle). All you need to avoid is a Siamese situation.
Now if you want to make it good you make it a quad exhaust pipe set up. So each manifold exhausts into one tube ALL the way to the outside, but you can also do the math and figure out (distance traveled/ exhaust gases speed) then you can merge the 4 manifolds into 2 pipes think a zipper , and that’s what Jaguar did. When they meet they zip together without Overlap. So when you put your hand on the exhaust it should feel like a steady stream of wind. Not puff puff puff puff.

 

Kind'a right. Where Jag lost the plot is in the secondary tubes. The 3 - > 2 - > 1 on each bank or side is a great setup for a V12. The 2 section is way to short on the Jag V12's. Most are just a few inches long and usually dump into a catalytic converter. That was clearly a compromise to the realities of packaging a production car with emmisssion controls.vvFor best performance the secondary tubes should l be about 24 inchs long and have a smaller 1-3/4 tubes that merge into a single 2-1/4 tube per bank to maintain velocity and scavenging at the moderate engine speed a road car sees. This setup would have been good for 400 HP and would have delivered more torque in the mid range where it was needed most on a raod car. Jag made a lot of compromises for cost and production. I wish they or TWR would have made and all out no compromises V12 road car. Even at a loss it would have been a great ambassador for the brand. Jag never went all the way, with the XJS and even the TWR car left a lot on the table with their automatics and stock curb weight.

Imagine a TWR 6.0 with the 5 speed and a few aluminum bits to get the curb weight down 400 Lbs. An aluminum hood, alu A/C compressor and alu radiator would have take 100 lbs off the nose alone. All those bits were readily availabe in the late 80's. Another 100Lbs for the 5 speed. The next 200 Lbs is a bit harder to find but it should be practical for a OEM to have done it.

 

naaaa that’s easy tell the driver to loose 200lbs, be like a jockey.