Benefits Of Tb's

[Doof 11]

Just wondering what the benefits of throttle bodies and in fact carbs are. Obviously they get more power etc but what im wondering is why?

 

Lots of people run them with airboxes which make them essentially a normal manifold with a plenum chamber and runners right? Each runner (TB) has its own throttle plate which maybe helps keep air velocity up in the runner at lower speed?

 

Could a modified manifold with bellmouthed runners (I've not looked inside any inlet manifolds but i presume our pugs dont really have these) produce similar effects? If not, why not?

 

Cheers,

 

Lewis

[Normski 1]

Could a modified manifold with bellmouthed runners (I've not looked inside any inlet manifolds but i presume our pugs dont really have these) produce similar effects? If not, why not?

 

There's a good example of this on test in one of the Ford mags (I just had a quick scan in WH Smiths). They do a before and after dyno test of a Cosworth inlet manifold on a Duratec. The cossie manifold is a work of art and it gains a good bit of power.

[welshpug 1,627]

they are all designed to get more air in, and therefore fuel, giving a bigger bang = more power.

[Sandy 189]

The GTi6 manifold has trumpets inside. The basic principle of multiple throttles and tracts, is that cylinders breathe independantly of each other and don't "rob" each other of charge, especially at part throttle when manifold pressure is lowest. They also have the benefit of making inlet paths equal and easy to tune. A well designed plenum can sometimes equal the full throttle performance of TBs over a narrow rpm range, but will almost certainly be less responsive and suffer poor performance at other speeds. They never sound as good as TBs either and for my money, since most of the cars discussed on here are for pleasure, the noise of TB's is a worthy reason to use them, if you can afford to have them.

The problem is, many TB set ups are simply bolted on without proper consideration to the variables and their effects, so the net result can often appear inferior to a single throttle manifold that has had the benefit of development. Set up and mapping are also huge variables, the entire nature of the engine can hinge on this and the difference can be night and day.

[Doof 11]

Thanks for that Sandy. I had forgotten about charge robbing completely.

 

I'd be interested to see the results of a GTI-6 manifold with a throttle plate at both ends and two air filters. That would stop the number 1 cylinder recieving less charge but then maybe extra turbulence would be encountered. With no AFM to deal with it surely wouldn't be too hard to fabricate.

[Rippthrough 98]

Thanks for that Sandy. I had forgotten about charge robbing completely.

 

I'd be interested to see the results of a GTI-6 manifold with a throttle plate at both ends and two air filters. That would stop the number 1 cylinder recieving less charge but then maybe extra turbulence would be encountered. With no AFM to deal with it surely wouldn't be too hard to fabricate.

 

The way we did it once when the original plenum had to be used, was to bring in 5 small pipes at 90* to the runners, bellmouthed into the plenum, then joining 5/2/1 to a throttle plate at the other end, which worked immensly well in getting even airflow into each port. THe runners cam in at the same point as the the runners exited, so the bulk of the air flow would go around the plenum and into the runners, with a slightly stagnent centre that helped control pressure drop under sharp throttle application

Edited February 10, 2007 by Rippthrough

[Doof 11]

Rippthrough, so the 5 pipes going into the top or bottom of the plenum spread accross it?

 

Any power / flow comparison info?

[Sam 4]

Thanks for that Sandy. I had forgotten about charge robbing completely.

 

I'd be interested to see the results of a GTI-6 manifold with a throttle plate at both ends and two air filters. That would stop the number 1 cylinder recieving less charge but then maybe extra turbulence would be encountered. With no AFM to deal with it surely wouldn't be too hard to fabricate.

 

Thats very true. In a forced induction setup the GTI6 inlet is hardly ideal, the cylinder nearest the TB is likely to receive more boost than the cylinder furthest away, the design should be slightly sloped towards the end runner or perhaps have the throttle body half way down the plenum to equalize flow. This is the plan when getting the outer plenum made for my BTCC inlet,

[welshpug 1,627]

I'm not 100% on this but dont 8v turbo and T16 manifolds have the throttle body central between the 2 pairs of runners?

[Miles 331 1 Cars]

I know that the 8v XU10J2TE has a central T/B on a std engine, Not sure on the T16 one but I think it is

[cybernck 400 1 Cars]

correct, T16 has it like that too (but a bit longer manifold than the "T8").

 

our member "357" has seen improvements by swapping the GTI-6 manifold for the T16 one (if i remember correctly!) .

[Rippthrough 98]

Rippthrough, so the 5 pipes going into the top or bottom of the plenum spread accross it?

 

Any power / flow comparison info?

 

 

Came up from underneath, only power figures is via arse dyno, but it was quite an improvement.

Swine to make though.

[sonofsam 5]

I know that the 8v XU10J2TE has a central T/B on a std engine,

 

But unfortunately as Henry Yorke proved, the manifold wont fit straight onto a XU9 head.

Edited February 11, 2007 by sonofsam

[Sam 4]

The T16 and "T8" don't have a plenum chamber though.

[Alastairh 47]

I'd be interested to see the results of a GTI-6 manifold with a throttle plate at both ends and two air filters. That would stop the number 1 cylinder recieving less charge but then maybe extra turbulence would be encountered. With no AFM to deal with it surely wouldn't be too hard to fabricate.

 

Anyone ever heard of someone trying this? Sounds intresting, and logically it should work.

[rjw205 8 3 Cars]

Would it not be possible to bastardish a cossie manifold onto a mi16 inlet manifold. It looks at though they might mate up if you hold the two of them side by side (bearing in mind that the cossie casting goes from being oval at the 'head' end, to being circular at the bell-mouth end). The lengths i cannot be sure of, but i don't know if the injector bosses would be in the right place (probably not).

 

You would have to cut both inlets, and then weld up but i reckon it will fit into the space provided. The cossie inlet, as someone mentioned is bell-mouthed on the inside part, and the inlet for the single throttle body is in the centre. Works on a 500bhp cossie, ought to work on a little pug.

 

Any comments appreciated, as this is partly how i propose to make my inlet for my turbo motor, and the side that the throttle body will be on will be condusive to good pipe runs if the turbo sits where the battery should go.

 

Rich

Edited February 12, 2007 by rjw205

[Sam 4]

Ideally you would want a spacer plate between the parts though, volume is quite small.

[pdd144c 0]

Thats very true. In a forced induction setup the GTI6 inlet is hardly ideal, the cylinder nearest the TB is likely to receive more boost than the cylinder furthest away, the design should be slightly sloped towards the end runner or perhaps have the throttle body half way down the plenum to equalize flow. This is the plan when getting the outer plenum made for my BTCC inlet,

 

One of the reasons I'm doing what I am with my inlet Sam.

[Miles 331 1 Cars]

The cossie manifold onto a mi16 inlet manifold has been done and it works

[Doof 11]

Any ideas on gains Miles?

[pdd144c 0]

Rich, we are currently doing something very similar for my car. Also allows a very good route for the charged pipes when using a RS500 intercooler. There were some pics kicking around of a blue 205 with a cossie inlet fitted, can't find them now...

[pdd144c 0]

[Sam 4]

I'm going to put the TB in a similar position. Paul, do you know what the size of a standard throttle body on a YB is?

[niklas 1]

The GTi6 manifold has trumpets inside. The basic principle of multiple throttles and tracts, is that cylinders breathe independantly of each other and don't "rob" each other of charge, especially at part throttle when manifold pressure is lowest. They also have the benefit of making inlet paths equal and easy to tune. A well designed plenum can sometimes equal the full throttle performance of TBs over a narrow rpm range, but will almost certainly be less responsive and suffer poor performance at other speeds. They never sound as good as TBs either and for my money, since most of the cars discussed on here are for pleasure, the noise of TB's is a worthy reason to use them, if you can afford to have them.

The problem is, many TB set ups are simply bolted on without proper consideration to the variables and their effects, so the net result can often appear inferior to a single throttle manifold that has had the benefit of development. Set up and mapping are also huge variables, the entire nature of the engine can hinge on this and the difference can be night and day.

 

In whole I agree, but worth mentioning is that a plenum intake do have an advantage over TBs with spindles. If it's of any significant importance is another matter though.

However it's very difficult to find the space to create a plenum big enough to compete with the TBs. I don't know on the top of my head how big the plenum must be in comparison to the displacement but it's quite big. The main importance is that the air inside the plenum will be considered "atmospheric" if the volume is big enough. Thus almost fully comparable to ITBs..

[pdd144c 0]

RS500 is 3 inch and normal one is 2.5 inch Sam.