I've run across power guides on other forums, Dodge diesels for example. There are enough of them, and enough people modifying them, that they can list off the changes needed to reach certain power levels. Of course there are always minor disagreements on exact output and which method is better. I heard the same idea mentioned in another thread(v12 twin turbo project), and thought it was time to get it started.
So, in progression from least expensive and easiest to I have more money than Bill gates and make Ferrari's racing program look weak how does the list go?

My thoughts, based on a '78, and feel free to correct or fill in. Someone with real data or experience will jump in soon enough. (I'm assuming a V12, and A/C, heat, etc to be kept.)

1) Open air cleaner inlet through simple cutting.
Free, easy, 1-2 hp gain at high rpm? Similar to low restriction air filter.
2) CAI from headlight bucket or grill area.
Cost of your choice of duct, easy, 2-3 HP related to RPM.
3) Low restriction exhaust
Cost of muffler delete tubes, low restriction catalysts, welding required, 15-20HP gain.
4) Larger throttle bodies
cost of throttle bodies and revised or replacement ECU, bolt on to machining difficulty, 15 HP.

Now we start diverging, I think.

5-100) Nitrous, increase displacement, forced induction, 6.0 transplant?
Nitrous $600-1000, nearly bolt on, 25-150HP.
Increased displacement very expensive, machining and disassembly required, 15-150HP. Intake and exhaust restrictive again choking top end if not altered.
Forced induction... where would you put it?
6.0 transplant?????

 

Power #s are nice, and can be an important milestone. I think for me, perceived power is more important. #1 on my list will probably be getting rid of the 3 speed slush box. That thing just kills performance before you even get started.

Not to derail your thread...

 

getting power increases out of a Jag V12 is difficult ,at best!

and easiest Bang for the buck is NITROUS kit, used on Ebay as little as $100, bucks, simply put ,making power reqiures more fuel, and then adding nitrous Oxide gas.

it ups chamber pressure,when it burns, so more push on the piston, Wahlah, more power.

and YES, it will test the integrity of your engine, headgaskets 1st, and so on from there.

i do have a realistic plan for increasing power from V12 jag, but hardly worth talking about, because no matter how you go, it'll cost money.
and it starts with turbocharging!

just read other sites that relate to the subject, turbochargers, very much out there.

what took me 20yrs to learn, internet can do it in 20days!

 

Fair enough. If you can get to 60 or 100 quicker and cheaper with a transmission change than power adders i feel it's a viable option.

 

i agree, if performance is your 1st priority, a manual trans. makes good sense. i was responding to your OP. engine power!

so seein as we are talking total performance, OOPs(this should do it),

just get a GM, LS series, engine and trans.6speed manual package, you can get an easy 500HP, out of a junkyard ,cheap. an LS Camaro, or Pontiac.

your gonna have to make modifications to the car anyway, pedals, drivshaft single pc,ETC. mounts are a simple kit. electronics GM,aka cheap!!

and if you went wild on mods, 1000HP turbo, is actually doable, a little extreme tho!
anybody on this site ABLE to drive 1K on the street??

 

Not yet, but a performance driving class is definitely on the radar!

 

I was aiming for power while retaining a 12cyl, but I can't discount lumping as a viable alternative due to economy, cost, reliability and ease. I think it should be included as a performance option. What has your research shown relative to power levels, cost, changes required, and effect on balance and handling? Where does it fit in out list?

 

if i was gonna lump a 5.3, it would be for a 6.0
its just not an XJS without a V12.
i think the best way your gonna get power from your car is get a tune, AFR, then run as much timing as possible. 93 octane, gutted airboxes, cat delete, viola.

doesnt matter how much power you make, your never gonna feel the gains with the 2.88 on american roads. all the power is up top with that trans.

 

well the fact that an aluminum LS engine weighs 200-250lbs less than a V12, thats a lot of weight removed over the front wheels, plus averages of each 100lbs removed from a 3800lb car knocks a tenth of a second off the 0-60 times.

and handling and braking are improved!

and all in all, i still like my XJS roadster V12.

 

I have to agree with Ron. I bought the car because I wanted a V12. I could easily have lumped it, but I think that takes something away from the car.

 

AMEN. No offense to our 6 cylinder brethren

 

I'm not sure there's that much power to be found in simple exhaust changes if the system is in good order to begin with. And I don't believe that big throttle bodies won't help much unless the small ports and runners are addressed as part of the solution.

But if you have a pre-HE "flathead" engine, the biggest bump to power could come from an increase in compression. Your engine has a CR of less than 8:1 primarily for emissions purposes.

With a good piston that gives adequate quench, and some attention to ignition, it's possible to raise that to 10:1 on premium fuel.

The potential power gain is somewhere between 8-10% just on the CR alone. It would also be a more fuel efficient engine as well. Even on the primitive EFI it should go over 325 hp.

 

why boost compression when you could boost the engine? lol

 

M90 , good idea, hard to beat a PRESSURIZED INLET MANIFOLD,!

the old 7.8ratio would make a good candidate for pressure, (turbos)

 

That has occurred to me. A single centrifugal mounted in place of the air pump(MIA) might even be possible. Now if only someone would make a centrifugal with a variable ratio drive.