hi at all x150 members.

i have a question for you:

what is the internal diameter of the butterfly valve of 4.2 engine of x150?

and part code please...

Thank You!

 

Stock throttle 76mm
Maxbore throttle 81mm

Unsure the potential gain to be had on forced induction

If upgrading make sure parameters are adjusted in tune otherwise issues with idle and cold start can occur

 

i have a XKR 4.2 year 2005 ( x100 ) and i want send my TB to MaxBore. i love his works

 

George's work is high quality nothing but praise for his craftsmanship.

Before you go throttle upgrade I'd recommend 200cell cats, x pipe & tune to suit (proven upgrades)

Once I get back to the track I'll post up my new et with the larger throttle see how beneficial it is.

 

see here my exhaust ( 100 cells cats ).

https://www.facebook.com/media/set/?...1&l=77d8f5ea41

for see more about all my upgrades, read here from pag.72 ( my name also in cover-page ) : https://www.yumpu.com/en/document/vi...issue-187-2017

or simply search on google: LUCA MANNI JAGUAR

 

A note on MaxBore: He removes the original throttle plate. There is an access port on the throttle body to allow the throttle plate shaft removal. In my case, there was a faulty reseal of this access port (visually looked o.k.). This caused a slight vacuum leak and code. Took a smoke test to discover the leak. "Fixed" it with a JB Weld plug.
Not necessary to do a "remap" with this mod. The car's ECU can compensate for this change in closed loop. But, do recommend a "reboot" of ECU.

 

Generally, increasing throttle body plate size is more beneficial to a "suck through" supercharger system, like Jaguar, than a "blow through" system in a typical turbo system. Graham Bell in his book "Forced Induction Performance Tuning" at page 225 estimates the maximum hp through a suck through 85mm throttle plate at about 600 hp (rear wheel or dyno?) and 750 hp via a blow through system. BTW, this is a great book, but now out of print.
There has been some criticism of enlarged throttle bodies causing jerky responses at small settings, but this applies to wire-controlled (obsolete) throttle bodies. Modern throttle bodies like Jaguar are electronically controlled from ECU and nicely adjust to increased airflow.
Hope someone does an A/B dyno test for this Forum.
The aftermarket has produced many large bore throttle bodies for GM LS series motors, but to my knowledge nothing for Jaguar.

 

The problem with huge plate style TB's is once you get over a certain small degree of opening they flow like sewer pipes. That was what was wrong with the old cable systems and still an issue with fly by wire motor driven ones. Hard to modulate at low throttle inputs. I also assume that if our cars 'learn' to open the throttle only as much as needed to hit the other expected calculations that they'll really never go wide open throttle with a huge plate. Dyno's are good but it would be nice to see opening data from one to another.

Per the work I saw SOTP gains on my old speed density 5.0's from just chucking the TB in a lathe and opening up the inlet side as much as possible. Once the plate opens to where the original bore was increased there was a felt difference for part throttle performance. Of course being SD which just looks at the throttle position, manifold vacuum and engine RPM and 'assumes' the fuel dose it was most likely because the engine went slightly lean at that blade angle. No WOT gains but it felt peppier on the street at part throttle.

 

Compared to a NA engine where the pulses play an important role, a steady flow and low vacuum are more important for a SC engine. The small increase by boring out the tb will not trigger the ECU for errors on a Eaton setup, nor cause drivability issues.

 

Had some direct experience with a larger throttle body on my '05 Cadillac CTS-V. Stock, I think, was 78mm. Installed a 90mm TPIS throttle body, which involved removing/replacing-gluing a new mounting base onto the composite intake manifold. Nice increase in hp. Original rwhp was about 335hp. With just headers and throttle body it was 384 rwhp. No driveability issues whatsoever - just like stock with lots more response. Drove the car as modified another 90K miles. At that time 90mm seemed to be the acceptable limit, at least that was what FAST was offering. Now you see 102mm throttle bodies.