Aimed at Ash mainly but he's not a paid member so ..

On the BTCC throttle bodies, have they only been ported pre-butterfly? Going off tobeski's thread here it seems like it's only the area around the IAT sensor that has been machined, hence losing the progressive first 1/3 of throttle control.

Considering getting the dremel out on a spare body. Spending that much time redesigning the inlet setup I figured it might be worth a few hours of grinding. Anything to reduce turbulence, right?

Also Mei, didn't you get one off someone a few years ago?

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Bye bye Sundance Kid

Agreed, its the diameters of the runners on the plenum and the valve throat area that are the biggest restrictions. Forget doing anything like that with a dremel though, you need a long series industrial die grinder or serious motor and a flexishaft whith a 2omm allicut burr on the end of it to be able to do the job in a sensible timeframe. Either that or slice the manifold in half which you have to do to get at it al properly anyway. But unless you have all the cams, valves, exhaust etc. uprated to match it won't help you anyway.

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R H Davey Welding Supplies. I sell new and used welding equipment in the Hampshire area. I take on welding jobs in the evenings, ally casting repairs are one of my specialities but I can weld pretty much anything. PM me with your requirements.

Some of my services: (See my for sale threads)
Engine mount/chassis repair
Solid Beam Mounts BACK IN PRODUCTION
Harness bars

You could say that

Its worth noting that any mods done to create more airflow will actually loose you power unless accompanied by a remap as the car will run leaner and make less power.

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R H Davey Welding Supplies. I sell new and used welding equipment in the Hampshire area. I take on welding jobs in the evenings, ally casting repairs are one of my specialities but I can weld pretty much anything. PM me with your requirements.

Some of my services: (See my for sale threads)
Engine mount/chassis repair
Solid Beam Mounts BACK IN PRODUCTION
Harness bars

Does your new air intake setup work well then? better than standard? I only ask because frankly it just looks laughable!

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''Oh, it does handle like a golf!'' Why drive a Golf....when you can drive a GTi-6?

When doing these sort of mods the biggest difference I think you feel is in the pick up on low revs. Will look at doing this on my 6 at some point but probably won't have the time or the tools to remove that much material. I did port a few 205 gti TB's with again the same differences in pick up.

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306 GTI-6
205 GTI-6 Project
205 1.6 GTI - RIP
205 1.9 TT - RIP
E39 535i - Daily driver
*Newest edition* E60 M5 5l v10 - The weekend car

Wait, having had a look at it today, I see why "throttle response is improved"... there's a stepped bit blocking half the butterfly up to 1/3 throttle, throttle response must only feel better as that progressive restriction is removed and more air gets in at part throttle. Doesn't make any difference at WOT from what I see.

Oh well.

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Bye bye Sundance Kid

dead thread i know but....

after studying various air flow dynamics and other related literature after seeing that mighty car mods potato exhaust....i thought id weigh in after porting my own throttle body today (2+ hours with a dremmel)
big learning step for me was car engine airflow is pulsed....not linear...so some different rules apply.

1. Peirre must of made mine at 11:58 on a friday.
there are numerous steps/and shelves inside due to poor manufacturing, casting and machining, probably causing all sorts of turbulence. also, where the outlet of the TB meets the inlet of the inlet manifold...lined up by a blind man it would seem. not even close to centralised.

2.not sure if my inlet manifold hole has been widened in the past (there are linear chatter machining marks around its perimeter?) its inlet diameter is about 2-3mm larger than the exit of the TB, so some TB porting may help.

3. the narrowest/most restricted part of the whole intake system is the 60mm butterfly valve....the intake runner surface area in the inlet manifold when added up converts to more of a 90mm equivalent single hole, so its not there.

4. turbulence can effectively shrink that holes diameter dependant on severity. so any reduction in steps/turbulence around that area is probably more beneficial than you would imagine.

5. the TB hole is actually somewhat ovalled if you look directly through it. on the inlet side its restricted by the two lobes either side or the air temperature sensor...and on the outlet side its where the charcoal evap port lines exit, the actual body wall narrows/slopes in, which is a bit weird i thought...

6. knocking down those two high surfaces that make it oval adds a fair amount of extra surface area to its through hole area, probably 1-2cm squared... these two areas also choke airflow on partial throttle. i only knocked down the highest parts of the lobes closest to air temp sensor as they were what was ovaling it on that side, completely removing them would of taken probably another hour of grinding that i couldn’t be bothered with.

7. air/fuel mix is metered by the map and 02 etc....so extra air would be noticed by the sensors and corrected for. at WOT the gti6 ignores it all and dumps fuel in, running rich as it is...so id imagine the minimal air volume gains caused by this wont effect performance negatively in any way.

8. the map sensor is right behind the TB. reduction in TB turbulence should reduce wave pulseyness that the map sees which is a good thing. probably minimal effect though.

9. you could probably get another (1-2 cm squared through surface area) of material off the butterfly valve shaft, knife edging the plate also.......but im not that good (a fanny) and i only ground down the two screws extra protrusion out the rear.

10. the TB intake side front lip, not sure it its left over casting marks or by design, makes for a very sharp 90 face/edge for incoming air to smash against...especially as most of us fit a 76mm tube over it. i focused a lot on removing this and widening and smoothing/de-stepping the internal surface as much as possible effectively bringing its outmost ID as close to 76mm as possible. i also had a go at the front of the IAT lobes graduating it a bit more.

butt dyno says....engine induction note has changed, sounds a bit more uniform, bit louder and its slightly lower in tone... low and mid throttle response/pickup seems to of improved a fair bit. top end was always good but i can also feel some difference there.

theoretically.... the 60mm butterfly valves surface area is about 28.27cm squared, and depending on how well you port the TB... a 1-4cm squared increase in flow area is 3-12%. so power gains could be somewhere in the sub 3-12% range.

conclusion, fun, easy, quick-ish project, seemed to help.

if trying it yourself...i used a dremmel, small diamond cut/grind wheel, an 80 grit flap wheel, finishing with 120 grit paper by hand. i aimed too and successfully avoided all surface areas where the butterfly valve sits/interfaces at rest, DO NOT!! touch these areas.
go slow....thoroughly clean it afterwards with proper cleaning fluids and a compressed air gun.

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the world is changed by people in sheds