I have found another XKR supercharged engine. It has 140,000 miles, so I know I would need to rebuild the supercharger. An XK8 has 10.75 to 1 compression, while an XKR has 9.1 to 1 compression ratio. That means I have realistically more static Hp, than an XKR without a supercharger.

It is my understanding that the XKR supercharger is an on demand unit, controlled by engine vacuum. It is set up to operate at twice the engine speed, and at 6000 rpm puts out a little over 5 psi of boost. It uses 60 hp to produce an extra 140 hp, so it comes down to producing 80 hp.

The catalytic converters are listed as the same, as well as the oxygen sensors. If I get the complete engine, I will also be getting the injector set, and I could use the transmission cooler in my radiator, as a cooler for the extra coolant going through the unit, since I installed a fan cooled oil cooler for my transmission.

The supercharger belt tensioner looks like it mounts close to the idler pulley, near the alternator. Are there holes already there, or would I be drilling into blank bosses? Since the supercharger puts out 5psi of boost only on demand, I could safely operate my stock transmission, since realistically I have more initial torque, than an XKR on initial acceleration, as long as I don't beat the car from a standing stop, which I can't do with wire wheels anyway.

I would need to use my old MAF sensor, from the XK8, because of wiring issues. I would not be able to use the complete 5psi, the supercharger puts out, so I would need a smaller crankshaft drive pulley to drop the boost to between 3 and 4 psi, to avoid detonation, or a larger blower pulley.

Does someone make a smaller crank pulley, or larger supercharger pulley? Would I need to install an adjustable boost controller to keep me within the 3 to 4 psi blower boost, or would the blower automatically compensate? If not, I would need to be running a minimum octane rating of 96. What sense does it make to push 5 to 6 psi through an engine, where the knock sensors could bring the timing down 15 degrees? This is a little more research, and theoretically can it be done this way? Just something to put out there.......Mike

 

Adding a blower to an engine that is already at 10;1 compression seems like a recipe for terminal engine knock. What's the point? Why not swap the entire engine and necessary allied components? Or even better, just sell the NA and buy a SC.

 

I can't say on your engine(s) but on the later cars it's all controlled by the PCM. If yours is the same you've more to change than bolting up the SC.

Also, the TB is different, so is the air path, and a lot more besides. E.g. the STR has 2 fuel pumps feeding forward unlike the NA V8.

Sorry if the above doesn't apply but in any case sell XK8 + buy XKR is likely cheaper and bound to work.

 

I'm sorry for bringing this up, every few months, but it is just the race car mechanic in me. Deep down, I know that 10.75 compression ratios don't belong on the street, if they are supercharged. Actually, I don't have a clue how Jaguar is even running that compression, on only 91 octane fuel, when Ford GT Mustangs have engine knock with a 9.5 compression ratio, running 89 octane fuel. I had a 1600cc Baja bug, with 8.5 compression, that I would fill with horse ****, and still pull the front wheels off the ground.

I was just putting down my thoughts, and answering questions out loud...I'm sure this will happen in another few months, but thanks for listening. My major problem is working off of a disability check, so when I can get a high mileage supercharged engine delivered to my house for $680, the old mind starts going through the math. That is the reason, I was looking for an XJS, and ran across a 99 XK8 convertible, covered in hay, lumber, and chicken poop.

I brought a battery, filled up the tires, and drove her home. After the initial $750 cost for a 41,000 mile flood car transmission, and pumping 80 liters of fluid through it with an electric pump, while it was running, everything else is cosmetic.

Now I have found a complete diesel S Type, with a manual transmission, that with a little effort I could probably drive home. I am just researching if the transmission would mate with my gas engine. Everything else should be fooling this damn ECM, that there isn't a transmission failure, and put me in restricted driving mode. If it survives a diesel torque curve, it should have no problems with gasoline engine torque. That's me....Always thinking....Just look at my car.....Be cool......Mike

 

The modern V8 mustangs are either 11:1 or 12:1 CR. In any case it is not static compression ratio (CR) that drives propensity to detonate, it is a combination of dynamic compression ratio (CR), mixture and spark advance. By running camshafts with high lift and/or high overlap you can increase the static CR without changing the dynamic CR. Additionally with variable cams you can control the valve overlap over a relatively wide range and therby run a large overlap off idle without sacrificing torque. Doing this allows modern cars to have static CRs which used to be for race only.

When you go FI the boost plays into this as well, all else being equal in terms of detonation you can have high CR and low boost or run a lower CR and higher boost, but the latter will usually produce more power. How much power you produce is directly related to your mass flow rate of air (aka mdot) and the efficiency of the engine. A supercharger or turbocharger is more efficient than your pistons at compressing air. This is even true for an innefficient roots style blower. Further increasing boost increases mdot as well (at least until you generate too much heat), while a bump in CR does not change mdot at all. As a result of these you will typically get more power by keeping CR low and boost high.

 

The diesel has endless major changes. Whole nuther topic.

 

Thank you....I was going by what I knew about a 2009 Mustang GT, because a friend's car has a Kennie Bell super charger on it, and if it isn't fed the best, it's knock sensors have the control unit retard the timing to the point, where you may as well be driving a 70s 6 cyl Ford Maverick.

We should live by each other, and talk about this for days. Given the proper motivation, I am sure I could be talked into blowing up my engine.

If the variable overlap cams helps with detonation, why have I been told, that the supercharged version of the 4.0 doesn't use them. Is that because the static CR is only 9.1. I have also read, that the root's style blower on the SCRs doesn't actually put out a lot of boost, unless it is running at over 12,000 rpms,(or 6000 rpm engine speed) as in only 9psi, yet they still do not have detonation issues.

Are you saying that a 10.75 to 1 compression ratio, with variable cams may not have issues with an extra 9psi of boost added?.....We are getting into dangerous Mike thinking territory here, as in you may be talking me into it. We need to discuss this a little more in depth.

Thank you for your input. You sound like an engineer, and I am but a lowly wrench, who has only been watching and listening to conversations.....This has been cool.......Take care.....Mike

 

The diesel also runs a minimum of 22 to 1 compression, and doesn't need to rev much higher than 4500 rpm, because of it being a torque monster. Could you imagine sitting at a light, listening to an XK8 with a diesel in it? That would be worthy of some type of award.....Good or Bad......Thanks...Mike

 

What do you want to do? Race, street race, just have it? Track days?
There is power through fuel. Race gas is available with octanes up to 116. Or you can use one of the two alcohol’s Ethanol at 114 or Methanol at 116. Or for rare use you can jury rig a boost detector to trigger a water methanol mist at a certain boost pressure. ( Don’l be fooled, you’ve been buying the water methanol mixture all your life. Except you call it windshield washer fluid)
Water really cools down the charge and helps make power without destructive detonation) when you add the effect of methanol to it there is potentially some serious power gains

 

this is a 4 year old post and OP has not logged on for 19 months

 

Given,

but just for general informational sake, the vintage Paxton supercharger that C. Shelby put on some of the ‘66 GT-350’s would put out a legitimate 6.0 lbs. boost @ 5,000+ rpm. The 289 ci k code engines used on the GT-350’s had 10.5 CR. I’ve owed a few
‘66 GT-350’s and the ones that didn’t already have the vintage Paxton on them, soon did. All together I’ve put those supercharger on 5 or 6 cars all of which had the same 289 ci k code engines, the same engine that was on the HiPo Mustangs 1965-‘67.

point is, 10.0 CR is completely doable with 5 or 6 lbs. boost.

PS: can anyone verify the boost numbers given by the OP ??? 5 lbs seems VERY low for a modern supercharger.

Z

 

Sklimii,

This is the thing I don't like about what you Guys call the NEW LOOK...I can think of 4 or 5 times that I got all up on a subject, only to find that it was 5 or 6 years old.....I realize that we are thinking about the same car as the guys were 4 or 5 years ago, but it just seems strange answering questions and then finding out the question was asked in 2008 or 2010! Surely there is a way, other than the way we are told about it today.....Seems like a some like a waste of time...………………..

Billy Clyde

 

Here is for instance an example for an Aston Martin AMV8 supercharger kit on the stock NA 4.3 engine.
GMR Design, Taking the V8 Vantage to the next level

They do run at low boost (6.5 PSI) , that has an additional advantage in the you don't need to cool it as the intercoolers create some restriction. They do add some water cooling as insurance though.

 

6.5 lbs. does sound more accurate than the 5 number i saw. I read the the Ford Lightning SVT Pickup used the same supercharger, but spins it somewhat faster.

Z

 

The engine capacity is larger, so its natural it would have to spin faster for a similar boost.

Many factors determine what you can run, like for the AM sample I gave certain choices where made. Just having to add intercoolers would make it a more expensive/complexer setup and they probably had other design criteria not to go higher in boost. Remember that engine is also revving way higher then our cars.

You can go pretty high in boost on NA engines, just look what's possible on the 5.0 coyote engine (12:1 compression):
Mustang 5.0 2011-Up | Kenne Bell

 

I hear you Billy - new look wasn't anything the Moderators had control over so we get just a frustrated as you. I guess the easiest way to prevent it, is for folks to look at the dates on posts to see how old something is before adding but easier said than done.

Anyway - enjoy driving and have a Merry Christmas!

 

+1

I always check the date a thread was posted shown in the top left corner before replying:





The reason we are all seeing ancient threads and posts appearing to be recent is the recent Infinite Scroll feature which links seemlessly through "relevant" topics. This spawn of the devil can be disabled in User CP:






Go to User CP - Your Control Panel - Settings & Options - Edit Options. Go down to the Infinite Scroll option box and check Disable Infinite Scroll. Finally go all the way down to the bottom of the screen and click on the Save Changes button. You will no longer see ancient threads in your browse.

Graham

 

It's a fun topic to discuss; whether or not to supercharge a naturally asperated engine... Or more germane to today's engines, to add a turbocharger

However, instead of anecdotal stories about other cars and their successful (or unsuccessful) attempts and doing this; I think the more important discussion would center around engine management tools and how one would control detonation, fuel maps, air intake temps, etc.

If I were to undertake a project like this, I'd want to have a standalone system, like a Haltech, to at least set the basic initial engine parameters using wide band O2 sensors to insure a safe AF ratio... plus some kind of knock sensor to control pre-detonation before piston damage, etc.

 

2003 Jaguar XKR Convertible. I got the low coolant level light. I lose a bit from time to time. No problem, I popped open the cap and added coolent. It wasn't too bad. I look again, and the warning light is still on. Further investigation revealed the wire to the sensor gone! Apparently some rodent took it. I see some chances to get another, but I could do it myself if I had access to the plug, (what is it called?) And most importantly, where do thr wires go? I have seen an electrical diagram that tells me nothing. Where do the sensor wires go? Physically. In the car?

 

Open a new thread. This one has nothing to do with your problem.