Dbilas vs Extruabody ITBs

[jlevie]

A question not asked elsewhere in this thread is why? ITB's will improve throttle response, affect the shape of the torque curve in not necessarily a good way, but not increase overall mass flow through the engine (the head is the limit in that respect). They look and sound cool, but there are other less expensive ways to make more power with an M20B25.

[nando]

actually they will increase power. on an engine where the head is well set up, the stock intake manifold doesn't have the volume to support the head. just look at digger's dyno charts in his stroker thread.

the previous setups on the market though, like dbilas, were poorly designed and had a small plenum so they didn't offer any real gains.

[jlevie]

Increasing peak power may sound good, but if the area under the torque curve is reduced, the net affect is negative. The twelve valve head of an M20B25 imposes a limit that nothing external can improve. And then there are resonance vs rpm considerations that affect the shape of the torque curve. There is a reason that the stock intake is built the way it is.

[nando]

look at his dyno charts. torque and HP increased basically everywhere, not just at peak HP. the stock intake doesn't have enough volume to support high HP.

My head is a peice of crap compared to digger's, and I know that my intake manifold/TB is costing me at least 15-20hp (I can't reach full atmospheric pressure at WOT above 5500rpm, it starts pulling vacuum because the intake simply doesn't have the flow/volume to keep up).

I think you know this as well, basically the reason bolt ons don't do anything by themselves is the whole motor is tuned from the factory as a system. you can't upgrade one part by itself and expect good results, you have to match every component and that includes the intake manifold.

[LJ851]

Increasing peak power may sound good, but if the area under the torque curve is reduced, the net affect is negative. The twelve valve head of an M20B25 imposes a limit that nothing external can improve. And then there are resonance vs rpm considerations that affect the shape of the torque curve. There is a reason that the stock intake is built the way it is.

Not sure what you would complain about with these results, Jim :

Here is an example of a back to back test we did fitting a set of our ITB's to a stock standard 325i engine, this is a high milage engine and the only modifications are a set of average headers and a single tail pipe

base power was 112Kw or 150Hp which is about right looking at other peoples results

We fitted a cheap ($800) stand alone ecu (called and EMU which by the way seems very good) and a set of our 40mm itb's, power went straight to 130Kw (174Hp) thats better than a lot of 2.7 strokers or engines with cams and other mods etc

To back up these results and make sure it wasnt some other irregularities we went to a different dyno and tested it again with the same result 129Kw

Note that it didnt loose any torque down low it gained everywhere from about 90Kph, which is probably where the operator hit full throttle. The mixtures are rock solid running purely as Alpha-n (TPS load control), more stable than the motronic was.

so there you have it.... a good ITB is worth good power on ANY engine if its done right and you wont loose any torque or drivability

[digger]

^+1 As everyone else already said, don't waste your time on the dbilas, and don't bother wasting your money on the extrudabody setup either.

RHD also has an ebay page (http://www.ebay.ca/usr/racinghardwar...p2047675.l2559) but you're better off ordering through their actual site.

The only thing I have an issue with on the RHD kit, is that I do not understand how the bitch tube hooks up. I don't see any provision for it at all.

bitch tube works same as the original

[digger]

A question not asked elsewhere in this thread is why? ITB's will improve throttle response, affect the shape of the torque curve in not necessarily a good way, but not increase overall mass flow through the engine (the head is the limit in that respect). They look and sound cool, but there are other less expensive ways to make more power with an M20B25.

I'll explain it as simple as i can.

Even though the inlet valve is the biggest restriction, with an unchanged head the act of removing an upstream restriction provides a benefit.

every time flow goes through a restriction there is some sort of a pressure drop. by the time the flow goes through the airbox & filter, AFM, bellows, TB, plenum there is a pressure drop.

flow works by pressure differential, so the pressure drop across the airbox filter, AFM, bellows, TB, plenum items serves to lower the pressure differential across the head because instead of having ambient pressure you now have less.

The effect is still there with a stock engine (it is with any engine) but the benefits are more pronounced the more mass flow you try and put through the engine so a modified engine will of course benefit more .

those who say there is no benefit without modifying the head as it is the biggest restriction quite frankly need to learn how engines really work....

Increasing peak power may sound good, but if the area under the torque curve is reduced, the net affect is negative. The twelve valve head of an M20B25 imposes a limit that nothing external can improve. And then there are resonance vs rpm considerations that affect the shape of the torque curve. There is a reason that the stock intake is built the way it is.

there is lots of evidence that a properly sized ITB setup doesn't lose bottom end or mid range and makes alot more topend.

the problem is most people don't preserve the right runner diameter and dont use the length that tunes with the rest of the engine and hence people like you still still have the wrong perception of what is possible.

the idea that the stock manifold is as optimized for maximum performance as you can get is laughable

[Ray Smoodiver]

Could we keep the idle speculation and misinformation out of these sorts of threads please?

If you don't have direct experience with any of the systems mentioned, you're simply posting either "what you read" or "what my friend said." And I will moderate the crap out of you.

Carry on.

[Liquidity]

$3,000 on ITB's and $1,000 on the engine.

[digger]

its not 3000 for itb and those who would benefit most have a bit more than 1000 into the engine

[nando]

Lol my dme was 1000 and that was before dyno time :p

[deutschman]

http://www.racehead.com.au/?wpsc-product=bmw-m20-itb-throttle-body-kit-40mm-plus-e30-linkage-kit

[digger]

http://www.racehead.com.au/?wpsc-pro...30-linkage-kit

add $120 for extensions and $240 trumpets and CNC manifold and you are looking at 1400-1500 aussie. this is good value compared to what is out there

[Ray Smoodiver]

add $120 for extensions and $240 trumpets and CNC manifold and you are looking at 1400-1500 aussie. this is good value compared to what is out there

Absolutely agree. It's whats going onto the Alpina after I finish the bodywork.

[Liquidity]

its not 3000 for itb and those who would benefit most have a bit more than 1000 into the engine

The dbilas ones he posted are 2,075 euros. That's over 2,800 dollars. Then they need to be shipped here and import duties paid. It might end up being more than $3,000.