Durable vs Reliable.

Chevy, Toyota, and Honda are considered reliable.  While they all break down occasionally   They are common enough that they can be fixed.  

Recently their durability has increased to the point where it approaches a JaguarV12?

Yes Really!! In my lifetime I’ve worked on probably 50 different Jaguar V12’s of those only Two had engine damage.  One from a loose oil filter the owner drove for several days without oil in it and eventually threw a rod out the side of the block.  The other from leaves and other trash blocking off the radiator because trash collected between the A/C and the radiator.  That engine dropped a valve seat because it finally overheated one too many times. 

I pull the heads off the early V12’s because they are prized for power output.  I’ve never seen a cylinder ridge. Including one with 244,000 miles on it!!  But if it did the sleeve slides out and a new one will slide in place. 

If you look at the engine it’s built better than any other engine I’ve ever worked on.  Bigger bearings. More material,  higher grade material.  Instead of a timing belt which wears out at 60,000 miles and needs replacement, it has an extremely durable timing chain  which as long as oil is full and changed regularly will last.  I’ve never seen one worn to the point of needing replacement.  

Transmission on most of them is the GMTurbo 400 or the overdrive version which is found behind big block V8’s  But the parts inside that transmission are the heavy duty ones found in tow trucks and ambulances because they can handle the prodigious amount of Torque a V12 has. 

The differential  is a Dana 44 found on 427 Cobra’s and modern Corvettes. 

OK the fuel injection on them is a very early one. While Detroit was still playing with carburetors Jaguar was pioneering fuel ⛽️ injection. Electronic ignition came in 1971. Improving with time until distributorless ignition was developed enough for the last series of V12’s 

clearly,    12 in a V is the way to be! 

Now when you open the hood you’d swear the pollution gods threw up in there.  That is a big reason why Jaguar has a bad reputation for reliability. Those rubber hoses develop leaks and few mechanics bother to do the research  to understand that the poor performance is caused by a leaking hose or something connected to one of those hoses.  Hoses and tubes oh my!! Hoses and tubes oh my! Sorry you guys who drive on the street. Just find the end of one hose. and trace it to the other end. Then replace that one. Go through and replace all the rubber tubes every 5 years. Replace the radiator and heater hoses while you’re at it along with the fuel lines. 

But Racers can get rid of almost all that mess and have a very neat and simple engine. They can even retrofit carbs if they don’t mind losing power and mileage.

 But the fuel injection itself is pretty simple. The parts for fuel injection are pretty much the same on any V8 6 or 4 cylinder Jaguar even makes it so you have only to count from one to six and remember side A or B 

I don't think those v12s are known for their power, moreso the inherit smoothness. I don't even think they displace over five liters.

In reply to JaxRhapsody :

The V12 has more torque than a Chevy Big block of the same year.  A V8 has only one power stroke every 90 degrees of crankshaft rotation while a V12 takes only 60 degrees per power stroke

Power, ? By that you mean horsepower ? The first ones had 500+ horsepower but they detuned them so It depends on the state of tune.  Mind you it was designed in the early days of dealing with pollution laws and thus California spec cars have the least. While European spec cars will have the most. Rather than bore your with endless numbers just use 300 horsepower. Mind you Chevy V8’s of that era typically had half of that number or less 

Stock the engine started out at 5.3 liters ( 326 cu. in. )  increased to 6.0 liters ( 366 ) and various options and specs brought it to 7 liters ( (427 ) 

it has been brought out to 10.6 liters  And over 8 liters for off shore racing applications.  

It’s extremely durable and in a racing application remarkably reliable.  The quality of the parts is what amazes me. All aluminum block, heads etc. when only a rare handful of Chevy V8’s were available with those. Forged high strength steel crank and Rods where most Chevy’s were cast iron 

in spite of short stroke ( 2&3/4 up to 3) it had { 3 inch mains} the rod bearings are significantly larger 2.30. Compared to either 2.1 inch or 2 inch.  In a small block Chevy 

For crying out loud, a 1976 XJS cost $19,200 new, a 1976 Chevy C30 heavy duty dually crewcab (basically the most expensive Chevy pickup you could get) cost only $5487 new and a Corvette cost $7600 new (source is www.nadaguides.com).  Of course the Jaguar is going to have the more advanced engine!  GM was able to produce the ENTIRE pickup, including the big block engine, for less than what Jaguar had just into the engine! And according to itstillruns.com/1976-chevrolet-k10-specifications-7565724.html a 1976 BBC 454 put out 355 lb-ft of torque, more than a 1976 Jaguar.  No BBCs were offered in a 1976 Vette so I included the truck for comparison.

And aluminum block and heads were advanced?  You do realize that Buick and Oldsmobile had an all aluminum V8 way back in 1961, right? 

How did the Jaguar V12 stack up against another 1976 V12, the 3.9 liter from the Lamborghini Countach?  Despite being more than 20% smaller than the Jaguar, the Italian engine pumped out more power (370hp) and almost as much torque (270 lb-ft) vs the 1976 XJS with 285hp and 294 lb-ft (source clarkesjaguar.co.uk/xjs-specs).

And while it's great that the engine has forged rods, enormous bearings, and a block so massive that it could be bored and stroked to almost twice it's original displacement, they were all a complete waste in the street cars because the engine never made enough power to even come close to stressing any of those parts.  Maybe Jaguar should have learned from the low tech big block Chevys and used cast rods, smaller bearings and a properly sized block to build an engine that would have made the same power, lasted just as long in 99% of cases and cost and weighed dramatically less.  They could have still cast special blocks for racing and still come out ahead.

With all this said, I'm very glad Jaguar did build such an over-the-top engine.  I'd love to build a car like Tom Walkinshaw's XJS race car (though toned down some and still street legal) and knowing that the engine will take whatever I can throw at it is great, but dear lord, can you tone down the repeated Jaguar V12 proselytizing?

And before you accuse Toyota of not being able to build a durable engine, read up on the massive power a 2jz Supra can make on the stock bottom end.

I think you need to define durability.  With many engines now supporting upwards of 1000whp with unopened engines, I would argue that they are quite durable.

Another for crying out loud, we all have a tendency to be diehard fans of what we like. Just like sports fanatics but with cars. Jaguar was/is known to be more of a luxury car than a performance car so smoothness (torque) is more of what the strong point is. Comparing to the Lambo V12 which is an all out performance car is apples and oranges. Although comparing the Jag V12 to Chevy V8 is like comparing oranges to tangerines. Different but similar. For that matter, Rolls-Royces have huge engines in them. Known for being real smooth but not necessarily quick. Yeah, gotta move a lot of weight but still a smaller engine could do it, just not as smoothly. The Jag V12 is no modern engine so can't compare equally. As technology improves over time, output and durability has increased. Just like you can't compare the modern engines or even the Jag V12 to say a Duesenberg V16. Again, apples and oranges. 

I found the Jag V12 info interesting. Didn't know any of that. Although I have heard the hoses are the biggest thing to go wrong with them and a nightmare to trace which one.  Having driven an XJS, I found that the V12 torque is addicting. Wouldn't mind having one. Of course, I've always liked the XJS.

I like reading about the Jag engine. I drove an XK120 with a fresh engine when I was 16 (1971). On the direction of the owner, pulled to the top of third gear, I think about 100 MPH. 

Only Jag I've ever been in. 

I have no experience with their V12 engines, but I have a seen a few Jag 6-cylinders from that era. They look and sound great with triple Webers (or even those stupid SUs the British car nerds love so much). 

I hear what you are saying, but most of the V12 cars I've seen for sale have less than 100,000 miles on them, are parked in the yard and don't run.  I cannot in good fiath give that high marks for reliability.  One of my fellow club members has had a few 6 and 8 cylinder Jags.  When he told his mechanic he was looking at a V-12, the mechanic told him  DO NOT bring it to him to work on.  He refused to touch it.  Whether it is because of mechanical issues or bad vacuum lines is almost irrelvant.       

Meh, most GMs and Fords will run bad longer than most cars will run. Reliable and durable, if occasionally boring. 

As much as I would love to tinker with a V12, it won't happen. Simple, cheap, HP, is only a LSx away. 

Schmidlap said:

For crying out loud, a 1976 XJS cost $19,200 new, a 1976 Chevy C30 heavy duty dually crewcab (basically the most expensive Chevy pickup you could get) cost only $5487 new and a Corvette cost $7600 new (source is www.nadaguides.com).  Of course the Jaguar is going to have the more advanced engine!  GM was able to produce the ENTIRE pickup, including the big block engine, for less than what Jaguar had just into the engine! And according to itstillruns.com/1976-chevrolet-k10-specifications-7565724.html a 1976 BBC 454 put out 355 lb-ft of torque, more than a 1976 Jaguar.  No BBCs were offered in a 1976 Vette so I included the truck for comparison.

And aluminum block and heads were advanced?  You do realize that Buick and Oldsmobile had an all aluminum V8 way back in 1961, right? 

How did the Jaguar V12 stack up against another 1976 V12, the 3.9 liter from the Lamborghini Countach?  Despite being more than 20% smaller than the Jaguar, the Italian engine pumped out more power (370hp) and almost as much torque (270 lb-ft) vs the 1976 XJS with 285hp and 294 lb-ft (source clarkesjaguar.co.uk/xjs-specs).

And while it's great that the engine has forged rods, enormous bearings, and a block so massive that it could be bored and stroked to almost twice it's original displacement, they were all a complete waste in the street cars because the engine never made enough power to even come close to stressing any of those parts.  Maybe Jaguar should have learned from the low tech big block Chevys and used cast rods, smaller bearings and a properly sized block to build an engine that would have made the same power, lasted just as long in 99% of cases and cost and weighed dramatically less.  They could have still cast special blocks for racing and still come out ahead.

With all this said, I'm very glad Jaguar did build such an over-the-top engine.  I'd love to build a car like Tom Walkinshaw's XJS race car (though toned down some and still street legal) and knowing that the engine will take whatever I can throw at it is great, but dear lord, can you tone down the repeated Jaguar V12 proselytizing?

And before you accuse Toyota of not being able to build a durable engine, read up on the massive power a 2jz Supra can make on the stock bottom end.

Not just Jaguar!! All those more expensive complex cars of that era. Mercedes Benz, BMW, Etc etc 

uber expensive to buy and often owners got shafted on maintenance. So of course when they started to get a little ragged, scruffy, the price dropped like a stone. Then some wanna be bought it and found out how much maintenance had been neglected or wanted to remove the scruffy  so prices tumbled down further.  

Finally some cheap-hose broke or a little part quit and it stopped running and now it’s at scrap metal prices.  But the bones are good/ heck great for racing. 

Oh with regard who was first, you miss the point.( but Jaguar had an aluminum head back in 1949)   All aluminum is a good thing for racing. Cast Iron is great for tractors and trucks but not so good for racing. 

Regarding  Ferrari Lamborghini etc. yep made more power, now go buy parts for them! Bet you can’t find complete engines for a few hundred dollars like you can the JaguarV12! 

ProDarwin said:

I think you need to define durability.  With many engines now supporting upwards of 1000whp with unopened engines, I would argue that they are quite durable.

1000 horsepower on the dyno? Great how is it over a 24 hour race?  Yes I’ll grant you the new LS engines are a major improvement over the old small block Chevy. 

But LS wasn’t available back in the early 70’s. Or 80’s heck, I had one in my 1997!  Didn’t the LS come out after they stopped production of the V12? And if you open a small block Chevy ( pre LS) up today and it’s either been rebuilt or needs rebuilding. Unlike most of the JaguarV12’s I’ve looked at. 

spitfirebill said:

I hear what you are saying, but most of the V12 cars I've seen for sale have less than 100,000 miles on them, are parked in the yard and don't run.  I cannot in good fiath give that high marks for reliability.  One of my fellow club members has had a few 6 and 8 cylinder Jags.  When he told his mechanic he was looking at a V-12, the mechanic told him  DO NOT bring it to him to work on.  He refused to touch it.  Whether it is because of mechanical issues or bad vacuum lines is almost irrelvant.       

You are right! I did say Chevy was more reliable and if it broke common enough so mechanics could fix it.  

If you have to have someone else work on your engine, you are right!! But what are you doing reading GrassRoots? 

This magazine is about racing on the cheap! That’s why you buy a Jaguar!  The bones are great for racing! Maybe the cruise control isn’t reliable  or the A/C breaks down a lot.  Heck the pollution control causes problems  that without proper training is hard to diagnose  so it doesn’t run or even start .  

Get rid of that cra  er stuff and what’s left makes a great race car!! Fast,powerful, good handling,  great brakes, and nice and durable without spending a lot of extra money to get that way!  

If you can get a go cart ready  to race  a V12 is the same thing except repeated 11 times. 

Look I understand when you open that hood and see it jammed with hoses and tubes and complex looking stuff.  You are scared.  

But race cars don’t have pollution controls. Or HVAC  

 That gives you a distributor right on top and 12 easy spark plugs. Plus 2 valve covers. And either carbs or fuel injection.  

Afraid of Stombergs? Swap em for SU’s. Still frightened? They do make a manifold that holds two Holley carbs. Or if you just won the lottery buy Weber’s 

Like fuel injection? Toss away the Lucas and use a Megasquirt then you can use Chevy injectors if you want.  It’s just gasoline give it enough and it’ll run fine. 

Toyman01 said:

Meh, most GMs and Fords will run bad longer than most cars will run. Reliable and durable, if occasionally boring. 

As much as I would love to tinker with a V12, it won't happen. Simple, cheap, HP, is only a LSx away. 

What would a Chevy LS 5.3 in Aluminum cost with all forged internals?  

I’ve paid as little as $50 but will pay up to $300 for a complete ready to run Jaguar V12 

Now  to be fair I used to be the go to guy for those. But my last Jaguar XJS complete rust free with a new Megasquirt and the running original Lucas  cost me $500.  To be fair the paint needs a buff and the leather seats needs treatment.  Tires are OK(but I’ll throw them away and use a set of Corvette wheels and tires since they fit.)  My buddy found that In Craigslist after I whined that prices were approaching $1000 

LanEvo said:

I have no experience with their V12 engines, but I have a seen a few Jag 6-cylinders from that era. They look and sound great with triple Webers (or even those stupid SUs the British car nerds love so much).

Sir William Lyons had an artistic eye and insisted  even his engines be beautiful. No less than Enzo Ferrari complimented Jaguars appearance. 

The V12 was SirLyons last engine under his leadership and when you see one naked on an engine stand you appreciate the real beauty that was his final glory. 

That was a bet the company moment and paying for that new engine forced him to sell his beloved Jaguar company to  BMC .  

How it became indenpendant again is an interesting story of its own. 

Schmidlap said:

For crying out loud, a 1976 XJS cost $19,200 new, a 1976 Chevy C30 heavy duty dually crewcab (basically the most expensive Chevy pickup you could get) cost only $5487 new and a Corvette cost $7600 new (source is www.nadaguides.com).  Of course the Jaguar is going to have the more advanced engine!  GM was able to produce the ENTIRE pickup, including the big block engine, for less than what Jaguar had just into the engine! And according to itstillruns.com/1976-chevrolet-k10-specifications-7565724.html a 1976 BBC 454 put out 355 lb-ft of torque, more than a 1976 Jaguar.  No BBCs were offered in a 1976 Vette so I included the truck for comparison.

And aluminum block and heads were advanced?  You do realize that Buick and Oldsmobile had an all aluminum V8 way back in 1961, right? 

How did the Jaguar V12 stack up against another 1976 V12, the 3.9 liter from the Lamborghini Countach?  Despite being more than 20% smaller than the Jaguar, the Italian engine pumped out more power (370hp) and almost as much torque (270 lb-ft) vs the 1976 XJS with 285hp and 294 lb-ft (source clarkesjaguar.co.uk/xjs-specs).

And while it's great that the engine has forged rods, enormous bearings, and a block so massive that it could be bored and stroked to almost twice it's original displacement, they were all a complete waste in the street cars because the engine never made enough power to even come close to stressing any of those parts.  Maybe Jaguar should have learned from the low tech big block Chevys and used cast rods, smaller bearings and a properly sized block to build an engine that would have made the same power, lasted just as long in 99% of cases and cost and weighed dramatically less.  They could have still cast special blocks for racing and still come out ahead.

With all this said, I'm very glad Jaguar did build such an over-the-top engine.  I'd love to build a car like Tom Walkinshaw's XJS race car (though toned down some and still street legal) and knowing that the engine will take whatever I can throw at it is great, but dear lord, can you tone down the repeated Jaguar V12 proselytizing?

And before you accuse Toyota of not being able to build a durable engine, read up on the massive power a 2jz Supra can make on the stock bottom end.

The torque spec you gave on the 454 is different from what I’m looking at, pretty easy though because there was the California spec’s and 49 state specs. Since more than 50% of Jaguars sold in 1976 were sold in California I used those specs and you probably used 49 state specs.  

We can argue details forever but tell me what can you buy a good running big block for nowdays?  Or even the whole truck you spoke of?  Assuming a rust free nice truck with less than 90,000 miles would it sell for more than the $500 I paid for my last acquisition?  

Even better, what would an all aluminum big block sell for?  Maybe a few dollars more than an all aluminum V12?  

As far as durability how did those big blocks do at LeMans?  

I’m not saying a big block was a bad thing. I’ve owned many a Chevy in my life and they offer good value. 

But I hope you see what a bargain Jaguars are and can be.  Yes for the street they are complex. But so were most cars of the era.  Especially luxury cars.   Open the hood of a Cadillac or Lincoln from the mid 70’s to the mid 90’s. Is it really much better?  And underneath all those hoses and wires  with American cars you had cast Iron,  I’m sorry but not much beauty there.  

frenchyd said:

ProDarwin said:

I think you need to define durability.  With many engines now supporting upwards of 1000whp with unopened engines, I would argue that they are quite durable.

1000 horsepower on the dyno? Great how is it over a 24 hour race?  

Its pretty obvious that people aren't taking production 200-300hp engines, boosting them to 1000+whp and running 24 hour races with them.  But they aren't doing that with Jaguar v12s either.

In reply to ProDarwin : I’ve spent my share of time on a dyno. In fact when I first started a dyno was a magical speed secret. Often we’d put camshaft after camshaft in an engine to see which made the most power and then go out and be soundly beaten  by some guys cheap regrind because it was better suited to the race track than a pure numbers producing camshaft.  

Eventually I learned to really understand what the dyno was actually telling me  and how to apply that to the racetrack. By the time computer dynos became available I used the computer to decide which parts to use and then the actual dyno to tune the engine.   

That gave me an advantage because I was able to tune the car based on the weather conditions not some one off shot. 

Of course then cars got their own computers and took that advantage away.  

With regard 1000 hp?  Lovely number but seldom realistic.  Unless you race 1/4 mile at a time and don’t mind sweeping up parts when things go wrong. 

750- 850 horsepower is likely the most Jaguar V12’s made during the LeMans 24 hour race. The later number was found in the Listers while the Jaguar  factory cars probably ran in the 700-750 range. 

My point was simply that if you can take a motor, unopened, and boost it to 1000whp and have it survive for a while (dyno, dragstrip, whatever), it qualifies as durable.

OK, your definition.  I wonder what a V12 with a real load of boost and decent cams would produce. 

I know the bottom end will take it. Just open one up and look (darn I wish I could figure out how to post pictures to save you the effort ) 

but if you’ve ever seen the bottom end of a top fuel dragster’s engine just imagine 4 more cylinders and you’ve got a pretty good idea.  

frenchyd wrote:

. Cast Iron is great for tractors and trucks but not so good for racing. 

It's also good for strength.  BMW have used cast iron blocks on their performance M series when the regular lower output engines had alloy.  CI gives much less flex.

I have nothing against the Jag V12 - I've driven them in stock form (XJS, sluggish with zero indication of what sort of engine it has - in bad need of a louder exhaust) to de-smogged lightly hotted up (with carbs, God knows why the guy tossed the injection) which was decently peppy.  Have to say I still preferred my 3.9 Lamborghini V12, but to each his own.

In reply to wspohn :

 Top fuel engines that make nearly 10,000 horsepower are made with aluminum. Indy car engines are made with aluminum. formula 1 engines are made with aluminum.  Ferrari and Aston Martin and yes your Lamborghini are made with aluminum.  

Speaking of Lamborghini, it’s nice to compare a big 4200 pound sedan with a light little sports car, I’m flattered. But the point I was making is about costs.  There I think a Jaguar at $500-1000 is a whole lot less money than you’d need for any  Lamborghini . 

Totally stock XJS  are slow on acceleration. That’s because of the 2:88 final drive, a three speed automatic and 4200 pounds.  Even still they can do near 150 mph.  

Cleaned up for racing they come alive. 3:54 rear end 5 speed manual transmission and less than 3000 pounds, in fact 2700 pounds is possible.  

They will still do 150+mph even with a stock engine because they have a low CD, lower than the XKE they replaced.   It doesn’t cost much to get them over 500 horsepower, and 850 was normal for Lister to race at LeMans  more than 2 decades ago. 

In reply to frenchyd :

Thanks for taking the time to write that up. I really like your writing style. I have no opinion one way or another about the stuff that others are debating.  I do know that the V12s are cool power plants and I am also a fan of all things jaguar so if nothing else it was a great read. 

ProDarwin said:

My point was simply that if you can take a motor, unopened, and boost it to 1000whp and have it survive for a while (dyno, dragstrip, whatever), it qualifies as durable.

In England there is a class just for Jaguar XJS  that is well subscribed.  There they take engines right out of the junkyard and race them often for several seasons.  

Yes it’s under cammed and in an extremely mild state of tune. ( it was developed for LeMans and made over 500 horsepower back in the mid 1960’s ) so stock at 300 it’s like asking a track star to walk around the block. 

But that’s a very good thing. It keeps costs affordable. 

dean1484 said:

In reply to frenchyd :

Thanks for taking the time to write that up. I really like your writing style. I have no opinion one way or another about the stuff that others are debating.  I do know that the V12s are cool power plants and I am also a fan of all things jaguar so if nothing else it was a great read. 

This is GRM. It’s not about the most power or fastest. It’s about people having fun racing cars on a small budget.  

Jaguar’s scare people they open that hood and all they see is wires and hoses tubes and gadgets. Few  people really understand them and because of that the prices on great cars is cheap dirt cheap. 

But by the time you remove the pollution stuff and HVAC stuff suddenly a simple engine appears. It can be carbs or fuel injected. 

Compared to a Miata a decent JaguarXJS is about 1/3 the initial cost yet handles on par. And is fast 

It has good brakes that can be easily updated with Wilwood to last a whole season of racing.  300 horsepower to less than 3000 pounds stripped  to race weight means speed is easy.  

Most people will swap in a 5 speed manual gearbox but you can convert the. Automatic to manual with kits sold by several venders for less than$200.  

Stock the V12 makes around 300 horsepower and the fuel ⛽️ injection isn’t that complex when it’s  race ready. But the system isn’t easy to alter, what is needed  is a mega squirt so you can change and adjust stuff.  

Once you change to that the 1981 & newer one can take a cam change easily and suddenly you are near 400 horsepower. Headers at most will improve power by 5% and the cast Iron manifolds only weigh 4 pounds each.  Not worth the money or time.