M O D I F I C A T I O N S :   ENGINE - Throttle Bodies

The air gets sucked or pushed into the airfilter and continues its flow into the throttle body and inlet manifold, where it get mixed with fuel. A throttle body can be opened in different degrees (depending on the pressure on the accelerator peddle). Some important things when talking about throttle bodies (TBs) and third party enhancements.

1) How the butterfly opens and closes... is it linear or progressive ? Is the butterfly restricting the air flow.
2) The diameter... the bigger, the more air can get into the engine (if the airfilter isn't avoiding that).
3) The build quality
4) Will there be just one TB, or is there a setup with four of them (complete madness and a great sound).

S i n g l e   T h r o t t l e   B o d y   o p t i o n s

The Mk1 standard TB is made from plastic and has a 48mm aperture
The Mk2 item is made from metal and I think it has the same diameter (BUT not sure)
The Trophy is equiped with a larger version, also made from metal. It can be ordered by a MG Rover dealer when you use the following partnumber: MHB000261. The opening measures 52mm.
The real die-hards can create their own one using an Opel/GM/Vauwhall TB from the C20NE engine. This TB carries the part number 90 352 920 B1 123 (and some variations) and gives you a full 57mm!!! Some additional parts are needed when you decide to install this one. I can strongly advice the following page of Dieter: http://www.mgf-net.de/throttle/index.htm.He was the first one (correct me if I am wrong) who made this popular Elise-mod work on the MGF, so all credits go again to Dieter.

picture of the setup on Dieters car, visit his page about this mod.

Mike Satur is offering a throttle body as well. It can be used to swap wih the plastic or metal 48mm, delivering power gains with its 52mm opening. Price: £ 112.00 (ex. VAT)

picture of the 52mm TB of Mike Satur

More info can be found on http://www.jenvey.com

UPDATE: Some people of the bulletin board have put their cars on the Rolling Road for some tests, and it looks like the Trophy Throttle Body (TTB) is adding a 5bhp to a properly breathing VVC and only 1bhp (or almost nothing) to the 1.8 MPi. Bit of a shock for all of us, 'cause we were thinking about (and experiencing) some improvements. Hmmm, could it be that the MEMS need some more powercycles and running miles before getting used to the new TB? Most of us are sure the TTB will add more value when more engine work is carried out, but it looks like the TTB isn't very usefull on a almost standard MPi.
There's still some hope that a VVC alloy inlet manifold could release the extra bhp's.
"The standard plastic item promotes low-end torque at the expense of high-end power. The alloy VVC plenum being the opposite. Given that all the power liberated by the 52mm throttle is top end, it may stand to reason that the standard plastic plenum represents a restriction to airflow, and thus negates the potential advantages of the 52mm TB?" (Rob Bell at the BBS)

PTP Ltd. VVC Style Inlet Manifold kit

Powertrain Projects Ltd. are selling the above mentioned part. As explained on their website: "Designed for the use with the PTP140 and 165 HTD engine upgrades, the VVC style manifolds are internally modified to increased plenum volume capacity, this in return maximises airflow for high speed performance. The kit can be fitted as a seperate item to the 1.4, 1.6 and 1.8i K Series engines." The kit comes complete including fuel pipe rail, blanking plate, gaskets, support strut and all relevant fixings ready for installation to the vehicle. (Price: £169.00 ex. VAT)

Q E D   M o t o r   S p o r t   M u l t i - T h r o t t l e   B o d i e s   d i r e c t   t o   h e a d   (D2H)

Compact fitment, 42mm bore
This configuration was the originally intention when the throttle bodies were designed and is the most compact and lightweight system available on the market today. As well as the inherent space saving of direct to head throttle bodies this configuration uses a more compact, 'Pico' design of injector, which allows the fuel rail to be positioned further back than would be possible with standard injectors. In this configuration the air trumpets are made from carbon fibre and with the shortest of these trumpets the fitted length from the face of the cylinder head to the ends of the trumpets is less than 7 inches.

Budget fitment, 45mm bore
It is also possible to use direct to head throttle bodies with the standard type of injectors. This obviously makes the system as a whole slightly cheaper. However because the standard injectors are longer than the Pico variety the fuel rail is now further forward and will foul on the air filter backplate.To get around this problem a spacer is fitted between the throttle bodies and the trumpets. To further reduce the cost of this system the spacers have a tapered bore which enables the fitment of a less expensive, 45mm, alloy trumpet. When fitted with the shortest alloy trumpets available the fitted length from the face of the cylinder head to the ends of the trumpets is about 7½ inches