I noticed there has been some talk on fitting Wider Throttle Body Openings, to improve Performance.

And while I know you do not buy an XJS for Economy, where according to the read out on the in Car display, I seem to be getting an Average of around 14.9 with my driving style.

How much difference do these make, in Terms of Performance as well as Petrol/Gas Consumption.

Bearing in mind that in the UK we pay a lot more than you guys across the Pond.

 

bear in mind, the ' larger ' bit only comes in at WOT ( wide open throttle ) up until then its modulated by your right foot and the revs are what the revs are as is the speed


so large TB's are only really useful on the racetrack , as how often do you get them right open ( legally ) on the road


just something to think about

performance increases can be achieved in other ways, as in an adjustable gearbox modulator, better exhausts, aerodynamics ( ground effects ) etc

and even with all the things i have done to my own V12, i still get 25 mpg, or better on a long run , ( 26.3 on a trip to north wales last summer )

BB

 

Hi BB

Thanks,

That is something that I never thought of, so maybe not worth while in my neck of the woods with lots of Suburban driving to get out of Town.

Any Chance of a Sound Video, to compare your exhaust note with mine?

 

i will see what i can do ,

but past attempts don't seem to do the ' rumble ' justice

BB

 

Now I want to hear it more than ever!

I'll also do you one of mine but my smart phone one came out upside down, no matter how many times I tried to re shoot it. (I must be doing it wrong!)

I'll do one with my DSLR and also have it 'Miked Up'

 

Larger only comes in at WOT??????? If you buy the larger TBs they are bigger all the time, except closed. The volume of air introduced will be bigger across the entire range NOT just WOT. That defies the laws of physics.

 

i hope this works

i will see if i can record one from the engine bay while blipping the throttle rather than idle like above

BB


ps, turn up the volume, lol

 

if the revs are set at 750 , even with larger TB's, then the same volume of air is still entering, and the TB's are never closed, they are set to 2thou , which is too wide on larger TB's and makes the idle revs too high , so they need setting back to get your 750 revs idle ( and once hot the AAV has no effect on idle revs in reality )

if the revs are 2k when driving, then even with larger TB's the volume of air is still the same, even if the opening has a different diameter ( right foot modulation )

at WOT the larger TB comes into effect to allow more volume to enter , thus more air=more fuel=more power

admittedly , the induction sound is changed due to the larger TB characteristics , but the opening can not be larger in total for the equivalent revs

thats physics m8

BB

 

Fun!


Add more air, the engine management adds more fuel.


Intake "whoosh" is almost as pleasing as exhaust noise. Fun.


Oh, oh, management system not capable of adding the fuel.
Mix goes lean. Issues!!!!


Carl

 

very true ,

especially on a relatively unsophisticated management system on an XJS

the system can cope with smaller amounts of improvement within its perimeters ( such as exhausts and free flowing air filter ) but add too much like the larger TB's then you need the enhanced ECU offered by AJ6 engineering,

your better off ensure the car is highly well maintained and driven properly to get the best performance , dont throw money at enhancement unless the basics are correct, even down to correct tyre pressures, it all starts somewhere

BB

 

This would be true if the stock TB is limiting the air flow by being undersized. Is this the case?

 

yes, its widely accepted that the standard TB is limiting , but not by too much ,

there is also a modification that can be carried out to the intake manifold, its cut open and induction tubes are added to the casting separating and improving air flow to the cylinders,

again , all this costs lots of money for gains that can only really be seen on the race track

BB

 

Thanks for the info!

 

OMG! BB, its doing it for me, I really thought I'd hate it but I don't, so Cheers for Posting that.

I'll will try and do one of the Purrrrh mobile, so everyone is able to make a comparison.

 

That sounds like Rocket Science, so I'll leave it to you Experts to come to your own Conclusions.

 

From all I know, the throttle bodies on our cars are plenty big enough as is. I did a quick search, and came across information leading me to find that our 5.3 liter engines, if running at 100% VE (and we know that CAN'T happen on ANY engine), were turned 7000 rpm, it would need a throttle body 2.261 per inch dia per side. The throttle bodies stock are 2.5" as is. Say what you want, but seems a bit a stretch to think that a larger throttle body will do anything at all for a stock engine.

 

The stock TB's flow about 500cfm each 1100cfm total good for around 700hp so once you reach this then larger the TB would be required.

They would benefit more from bell mouth inputs to smooth flow