Does anybody know much can be bored on the V12 5.3L fuel injected in a 77 XJS?

 

96mm total diameter IIRC. thats not on stock sleeves though. you would need rob beers big bore sleeves.

 

Stock sleeves can be bored to a max of 93.5mm with stock stroke giving capacity of just under 5.8L. This can be done without removing the engine from the car. Just remove the sleeves and have them bored.

96mm bore requires the block to bored to accept the larger liners.

 

Thanks for the replies. I just wanna know my limitations for making the 77 XJS v12 5.3L into a performance car.

 

What do you mean by performance? You can do a fair amount of mods to the car and engine that will improve its overall performance, but in the end it still won't be able to compete with many modern cars. You will however have a unique car with a distinctive V12 growl that is impossible to duplicate.

 

If I were to race(1 or 2 laps on track) it or drag race it on occasionally at shows etc. Do they make exhaust headers for the V12? How you I wouldnt be able to compete with modern cars?

 

yeah. i think rob beere makes them. or perhaps its AJ6 engineering. theyre over $1500 for a set. if i ever get mine running right, i plan on making my own.

 

Without major modification$, you can only expect to pull 400 horsepower out of these engines. If you wish to spend lots of money, completely rework the engine with new pistons, sleeves, crank, heads, cams and intakes, you can feasibly produce 700+ horsepower in a 2 ton car. Although impressive, you can get more horses out of a Toyota twin turbo in a car that weighs considerably less. It all comes down to horsepower to weight ratio.

I don't wish to discourage you from pursuing this, after all, I'm like many other members here who also strive to squeeze out as many ponies as possible. But you just have to be aware that there are many cars out there with huge advantages over the XJS.

 

the XJS is no supercar, but i dont want to discourage anyone from hotrodding an XJS. after all, plenty of people seem to think mustangs and chevells are race cars. if those ******** can do it, why cant we make something thats already a lot better.

 

Do they make a supercharger or turbo for these by any chance?

 

They don't make a kit if that's what you mean, but it can and has been done. Again, it requires major modifications to do. The compression has to be lowered either by changing pistons and switching to pre HE headsN or with the use of some sort of spacer plate between the block and heads.

 

nobody makes a forced induction system for Jag V12s(at a reasonable price).

but it is a good approach for power!

boring the cylinders on a 5.3L?? might give you 5.8L.. i would just buy a 6.0L V12 from junkyard, its allready stroked, and much less work,, then you could mod it according to your pocket book!

i modded my 78 V12 , starting with ;

complete engine rebild, for performance use.

new pistons 9-1 ratio,(Euro).

Crane race cams.

1/8" oversize valves,SS. hi tension springs, lite retainers.

ported and polished cylinder head ports.

inlet manifolds EXTRUDE HONED, aka, larger internal plenums size around 1/8"
runners blended and tapered.

throttle bodies 6MM larger, K&N filters

exhaust manifolds ported and thermal coated,in out.
2 1/2 down pipes,no cats, side pipe outlet 5",(loud).

complete EMS,, standalone ECU, fully adjustable fueling, distributor modded as required.
important; all LUCAS engine stuff out & gone. i use a cheap GM MAP sensor,$26. bucks AutoZone, it only has to tell ECU manifold pressure,electroniclly, no hoses to a remote mounted computor .

for spark a use a CRANE ignition box,with an Optical sensor and a Holley coil, works OK but little dated, by todays standards, CTS,etc.

absolutly have powerful electric fans,2, Jag V12s dont care for overheats, the dreaded dropped seat, could occur.

NOW i think on mine , a big help, is THERMAL coating the chambers, valves , and exhaust ports, reducing heat into the coolant system, and possible drop seats problems.

it seems as tho the later HE engines dropped seats easier, than the early PRE-HE flat chambered engines. that is still out on debate tho.

i did all these mods before this site exsisted, most before the internet had much info about Jags, so i just winged it on past experience.

been great for 16yrs. and if i where to do it today! (i got a ton of new ideas).

THX hope it gives you some ideas also.
Ron

 

remember that ron built his engine in the 90's when these cars were still in production. almost none of those manufacturers still make parts for these engine and even his standalone system is no longer V12 compatible.

AJ6 engineering is the best place to start with IMO.

 

so what did my V12 make for power, on a chassis DYNO, whp,

the best was 355whp at 6700rpm, some runs at 320-325whp.

many factors come into play, when on the machine, ambient temps, air flow under the hood,(bonnet), fuel octane, how many pulls before heat soak into the upper areas of the heads!

and of interest,, i have three performance cars, in my garage.

fastest is an 87 Mazda rotary big turbo, lite weight lotta HP.

next,, Buick GN 6.0L LS V8, 4L80E box, 3.73 gear also.

and last(but with a lot of CLASS) the XJS ROADSTER, and it is more than adequet for street use, and very dependable.

i got other cars but just ordinary stuff.

THX for interest.
ron

 

What you have with the Jag V12 is not an ultimate power house (unless you have deep pockets) but a torque monster, these engines at 326ci made more torque than a 454 BBC in their day.

If you plan your build around this you will have a pretty quick street car. IMHO a centrafugal SC is probably the most cost effecive power upgrade.

I know a guy who has a twin turbo XJS race car that was running a 6.8l TT V12 he had all sorts of overheating issues until it spun a bearing, he swapped it out for a 5.3l and his comments were that this was a much sweeter engine, it reved better, didn't overheat with the standard radiator and was still as quick around Mount Panarama even though it was 100rwhp down on the larger engine.

just my thoughts

 

4psi of boost will yeild an effective compression ratio of 14:1 (easily feasable on pump gas), and an effective displacement of 6.74 Liters (assuming a 100% VE.)

there are a few remote mount m90 variations that i was looking into, but CFS is easily the most feasable.

i disagree with warrens post about these engines being torque monsters. theyre not at all torque biased in respect to the amount of horsepower they make. but i would agree that the torque/horsepower figures nice and even, which is what you want.

 

Any reason no one's brought up nitrous? I keep coming back to that episode of Top Gear where a used XJ-S with a bolt-on nitrous kit wiped the floor against a Ferrari and a Porsche.

I always figured I'd do exhaust, 5-speed and nitrous and embarrass my father-in-law and his cammed C5 Vette.

 

they had to shoot that race 5 or 6 times before the XJS actually won. also, theres quite a bit of tuning involved for nitrous, and the factory ECU will be having none of that.

 

Nitrous has good and bad points.
It's not as difficult to install.
Provides instant horsepower.
Doesn't usually alter the everyday drive-ability of the car.

Expensive if used frequently.
Can be difficult to tune.
Has a nasty tendency to eat valves, pistons, etc...
Is only good for short bursts.

 

Nitros here in Australia is illegal to use in a road car in most states. It can be installed but can not be hooked up, the tank must be physically disconnected.

So SFSC is a good option. Lister used 2 Albrex in the 700hp Lister MK3, it can be done with 1 using a common manifold with equal volume runners to each throttle body.