I have owned a lot of cars and i have to honesty say that the xjr6 is the best that I have ever had. I have had the sc ported, have installed a true duel exhaust, cold air intake and the andy bracket. My car pulls hard. Now that all the low cost modifications have been done i am faced with wanting even more speed. Before I take the leap and spend the big bucks on developing the larger throttle body adapter and purchasing the throttle body I have to ask AM I THE ONLY ONE THAT WOULD LIKE TO HAVE THIS MOD? Would any other xjr6 owner be interested in in this, or am I the only one? Anyone interested in this please chime in.

 

surprised that I had no response on this post I have come to the realization that i am truly crazy for my jag. having said this I have made the decision to go ahead and make my throttle body adapter. Now to decide whether to purchase the 90mm throttle body first or to develop the sc adapter before the purchase. In any event, because of the cost, this project should be done before the end of the year. LETS GO CRAZY FAST!!!

 

Keep us all updated JJ

 

What about https://www.jaguarforums.com/forum/j...le-body-79174/?

 

The stock throttle body itself reduces in size in its center at the blade to about 72mm and in the front and back it is at 79mm, just had to know so I pulled it from the car and took measurements. Taking this into consideration it sure makes a lot of sense to just bore the throttle body. should be able to get it up to 81mm all the way through and at a save about a grand or more. great idea thank you! the only way to know the true potential of the xjr6 is to get rid of the all the twists, turns and bottlenecks in the intake system allowing it to breath easily and freely. Most guys remove the stock air box placing a cone filter in its place with noticeable improvement. I took it a step further and replaced the total intake system with 3 inch flex hose and made it into a true cold air intake buy getting the air from outside the engine compartment, getting rid of all the 45 degree turns, and have had really good results. Now the sc does not have sc drop off and the car pulls from start to finish, as long as it has air it will pull hard!!! Charles Warner from Magnumpowers has been using 85 mm throttle body on his 3.8 m90s for years and has had great results, he assures me that this is the way to go. After all, more air equals more fuel equal more hp. Take a look at his m90 case upgrade i placed a post with a pic under m90 case upgrade.

 

Using a basic rule of thumb you should have a 100mm throttle if you want to flow enough air to make about 400bhp without too much of a pressure drop.

You should aim to have the throttle bore coaxial with the SC inlet, unlite the std adaptor. If you fit an after market throttle you will need to make up an alternative arrangment for the the idle speed control valve. I would suggest taking the ISCV asewmbly from an old AJ6 engine. The valve itself is the same and you will then have a convenient valve body to carry it.

If you really wanted to go "crazy" with your XJR6, then you could fit an Eaton M112 supercharger from an XJR V8, as I did.

 

fitted the bored throttle body, now it is at 81mm. Now it idles high at about 1400 when it usually is at 800. The rpms also rev alot faster but the engine speed is less and does not match the rpms. time to check short and long fuel trims and have the pontentiometer oriented/reset with the cats. What do you think? please chime in and give me some peace of mind. and what do you think is better a throttle body with a taper or one that is bored straight thru with no taper? does the taper matter with the sc?

 

I've fitted an aftermarket 80mm bore silicone hose over the stub end of a std AJ16 throttle body as part of my Eaton M122 conversion, so I'm struggling to visualise how you can bore it out to 80mm. The casting wouldn't have any wall thickness left if bored out to 80mm.

If you bore out the throttle body at all you must have fitted a different throttle plate. Unless this is as a good a fit ast the original then it may well allow more leakage past the plate. The idle speed control valve will reduce the airflow through the bypass port to try to compensate. Howvever, if with the valve completely shut the leakage past the plate is sufficient to cause the engine to idle at an elevated speed, then there is nothing more that the engine management system (EMS) can do to reduce the idle speed.

You would have had to remove the throttle plate and spindle in order to bore out the throttle body. I assume that you then modifed the spindle to accept the different plate. If the spindle was fitted back into the throttle body at a slightly different angle, then the throttle potentiaometer reading may be higher. This would cause the EMS not to enter closed loop idle speed control. You would need to get the closed throttle adaption reset with a suitable service diagnostic tool such as JDS, WDS, IDS or Autologic to overcome this problem.

 

Thank you for your response as I and others value your opinion, after all you are the xjr6 guru. The throttle body was bored by maxbore.com, and they were able to bore the throttle body a considerable amount, I measured 81 mm but i may be wrong, it is at least 80. In any event, the new center butterfly plate is considerably larger and they would have had to modify the spindle to accept it. I will reset the pontentiometer and hopefully that will be the end of it, i was impressed with the tb and it really looked like a good job. Maxbore had done other jaguar tb as i found them recommended on this thread.

 

I checked the pontentiometer and it is at 14.1 percent and the car is at closed loop. isnt normal at 10 perecent? I dont believe I have a air leak because i blocked off the air intake at the mass air flow sensor and the car shut off immediately and I just cant find an air leak anywhere. the pontentiometer and isc valve were working fine before the tb was bored. This leads me to believe that throttle body plate position and or leakage at the plate is the cause of the high idle. Strangely, idle drops from 1500 to 1000 when I put it in drive. I dont want to reset the potentiometer at the dealer if my tb was made to be garbage.

 

14% seems a high value for idle. This would typically be sufficiently high for the engine ECU to not recognise this as a closed throttle and therefore not enter closed loop idle speed control. This is the regime when the ECU uses the idle speed control valve to control engine speed.

Jerimiah,
You say "the car is in closed loop". I don't know of an easy way to determine if the idle speed control is in closed loop. Are you refering to the fuelling control as being in closed loop. That may well be the case, but that is completely different to the idle speed control being closed loop.

My suspicion is that the 14% throttle opening is preventing the software going into closed loop idle speed control. You will need to get the closed throttle adaption reset using a suitable service diagnostic tool such as JDS, WDS IDS or Autologic.

The new 81mm throttle plate may be slightly more elliptical that the std throttle plate, so that when the plate is closed the spindle is at a slightly different angle, thus giving the 14% reading. The leakage around the edges of the plate in the throttle bore is likely to be higher that the std plate simply because the circumference of the plate has increased. Coupling this with the fact that the engine ECU probably isn't even trying to control engine speed would result in the high idle speed that you see.

The idle speed drops when you change from neutral to drive because you are putting more load on the engine because the output shaft of the torque converter is stationary whenthe transmisison is in drive and the car is stationary.

 

according to the scan tool the short term fuel trim was out of control going from -3 up to -20, constantly changing and long term was stuck at 35. well off came the tb and i checked the potentiometer with my volt ohm meter and found it to be defective, wow! Luckily I had a spare and after everything was said and done the short term trims are steady between -3 and -5 and holding steady, long term is stuck at 30. now the throttle plate is at 12.9 %. Now I have an appt with the jag shop to reset the potentiometer and orient the cats. I also notice at times one of the o2 sensors reads "na" and give me no values, guess it will need to be changed before my appt. I was hoping that the new potentiometer would bring the idle down to normal but I guess that would be to easy. All of this because I had to have a larger throttle body! but take a look at the pics, one of stock tb, one of bored tb, and one with the old plate in the bored tb so you can see the big difference. And the inner diameter is at 80mm , the outer diameter of the tb is at 82mm. tell me what you think. OH yes i was talking about the fueling is at closed loop, sorry still learning.

 

The potentiometer was reset and it now idles at 800 dropping down when it is in drive. I was able to get the experience of a larger throttle body without making any major changes and at the fraction of the cost. All in all I have to say that it is easily worth the money spent, after all the bore was only $125.00 and I was able to learn more about my car. After porting the sc, boring the tb, and fabricating a true cold intake, I would say that if it is bottom end torque that you are looking for you should forget about porting the sc. A larger throttle body and a good intake and exhaust would make you very happy. Now I think in order to take advantage of the ported sc and in an attempt to get that bottom end torque I will try a larger lower pulley. Or maybe just put a stock sc back on and call it a day. thanx to the XJRengineer, his knowledge about the xjr6 and his willingness to share his knowledge is greatly appreciated.

 

I have already had my ECU remapped will it need to be done again if i go the larger throttle body modification

 

As long as your fuel trims are ok your good to go, no need to make any other changes. how are your fuel trims now and what uprgrades did you do in order to need your ecu remapped.

 

I originally started trying to replace the ECU as my car ran excessively rich to the point I was only getting 250 k,s to a tank of fuel when I took it to a local dyno shop they couldn't get it to lean out so recommended I replace the coils injectors and so forth $2500 later it was going worse at this point I nearly lost the faith
They then said it was not possible to remap the ECU so I would have to use a piggy back ECU to control the fuel at this point I had joined another forum XJR6.com and Andy stodart gave me some pointers to look for so after doing some research found a guy on the north side of Brisbane 180 k,s from my home who had the factory diagnostic gear he found out it was a one way valve under the back seat allowing fuel from the charcoal canister to be sucked up into the manifold behind the electronics once he repaired the car correctly the car went alright but if that was 320 hp under the bonnet I must have had some fast cars before
that's what lead me to try to try replace the Ecu completely
But not wanting to be a guinea pig (been there before) I installed one of Andy timing brackets a better inter-cooler pump again the car went alright but getting beaten at the lights by rice rockets was embarrassing and after my cast headers cracked for the 4th time
I decided to get a full stainless exhaust system built using some of Andy,s designs and some of my own the car has a set of headers minus the front cats so full tuned length then it goes into a 3 inch single system to a resonator then where the original underfloor cats where it splits into a twin 2,1/2 inch system with 2 metal substrate cats another set of resonators then over the hump to another set of mufflers all in 304 stainless steel it should last forever now
At this point I drove the car for another year but found the car was really set up for highway cruising and decided to change the diff gears fitting a set of naturally aspirated 3.54 gears now the car is really fast I have seen more high speeds now than ever before if there where no highways I would use 3,7 gears but with the 3,54 gears it sits 400 Rpm up the range
I might not have such a high top speed now but it pulls away from 09 WRX subbies now as before they where already gone by the time I built up speed
After reading your post on throttle bodies I was intrigued I had also wanted to send a spare throttle body of to max-bore to play with but again did not want to be a guinea pig and was not sure if it was even possible your post has affirmed it is
That will be my next step to do to the engine it should then have the 320hp that it started with back again
the car mixture is perfect with the remap 12 across the board I have dyno sheets and so forth just cant post pics yet as I am a newbie to this forum so have to wait my turn

 

The only thing that I would do would be to get rid of that single straight pipe in your exhaust and make it a true dual exhaust, the engine will breath easier and you will have a noticeable power increase. your engine can only take in as much air as it can get rid of, and more air is more gas is more power. My local muffler guy did mine for very cheap, $150.00. Then if you have the need for more speed the bored tb is the way to go. The only reason I would consider a larger lower supercharger pulley is because my sc is ported, havent decided, maybe put the stock sc back on and call it a day. Or I can just get the pulley for xmas.

 

im interested !!!

i also want an any bracket, but cant get intouch with xjrengineer. anyone got any ideas?

how have you adapted your cold air intake ? pics?

my xjr6 motor is in my 1996 xjs

 

Thanks for asking such an interesting question Jerimiah. It definitely started a very informative conversation.

Question: Is there any risk, say of structural integrity of the TB itself, by boring out the TB this amount? It is noticeably thinner in your photos, so wondered if metal fatigue, etc and cracking could be a concern?


.

 

If you want more acceleration change the diff to a 3.77 LSD. It is a great improvement & bolts straight in.