OEM D-Series Intake Manifolds

[Dodo Bizar]

Inlet tube, ehm, not sure... I probably switched from the classic open air filter to the Simota aeroform with somewhat shorter tube.

And I thought a bit more about this. The refraction coeffecients will be low with the round plenums. Or differently, the wave is not reflected at the same point in time every were, the first wave will be sharp in shape but with each bounce it will be smeared out a bit, apart from the fact that refraction will be less than 50% probably. Have to look these up in my studybooks.

I think I made some nice calculations but with our normal design I think there is too much interaction and a whole bunch of other interactions going on. In the case of pure ITB's you can rely more on theoretical refractions etc. since you don't have the plenum to worry about. So lets say I thrust the engineering expertise companies like Skunk and Edelbrock have...

So don't take it to heavy. and even with refraction of 50% we are talking about 50% of 50% of 50% of 50% of 50% of 50% = 1.5625% of the initial pressure pulse of the closing valve (which I have no idea which order it is, 1 bar, 2 bar, higher, lower?) to give an idea... thats why you should aim for the 4th or 2nd reflection. Much stronger but also much trickier since you might end up getting the 3rd...

This is what normal motorbikes and NASCAR cars use... and I expect the very high power F1 engines use these techniques to the fullest potential.

[Law_]

very interesting ! this can be very important. thank you for you calculations. plenum reflections wow more words to say at dinner heheh

[ilya]

2 saxophonias:
Tnx about it!
i see some difference in image. but i waiting my order and think what i must do after receive. i think is not big problem (auto\manual). i hope...

i use EPC 14 for show difference between Civic 1.5 1998 1.5I AUTO \ MANUAL gear box. and this strange... not distinction. all part number in IM part are identical to both.

[saxophonias]

So maybe the differences is only between d16 auto and manual transmission!
Keep us informed!

[hondaNickx]

Afaik the best manifold out there is the Edelbrock unit.Skunk is good too but it has unequal runner lengths.I had a ported Blox manifold and it was tested on a flow bench with a stock Tb .The results were 260Cfm on all runners except on runner 1 it had 256Cfm.

I would say cut open the skunk 2 manifold and port it properly.

Btw something i never did understand Joris why did you ever used that 70mm Tb on a D14 ?It's seriouslyyy overkill on a d16 let alone on a D14.
Have you ever tested the stock Tb ?I would asume you gained hp with the stock tb.You never need a bigger TB on a D14 except if you're running Big Turbo or extreme N/a setup.My ported blox flowed 260Cfm with a stock Tb ,260cfm that's more then enough flow for a 200 hp engine.

[Dodo Bizar]

I never understood why smaller TB gains power, explain please. I heard this numerous times and the only thing I could explain it by the fact that the engine didn't get a re-tune. Whats the physics behind it? I went for 70 since the plenum is the same size.... making the plenum virtually extent towards my air filter you might say.

I do agree it was the worst spend money since it performed exactly the same except for some tiny hps I gained totally in the top... or even over the top already, still I did improve in power... not decrease... okay, never tried the combo of stock TB with Skunk2 mani, could do that theoretically, but getting the 70mm TB close of the manifold was very tricky and needed a lot of liquid gasket to fill up left over holes towrds EACV.... so not something I like to touch for nothing.

[hondaNickx]

Too big of Tb loses all the velocity , you'll gain at high rpm little hp.
You should always keep a small Tb with a big plenum or a Big Tb with a small plenum.Specially on a D14 you need lot's of Velocity.You want your Tb to be as small as possible without choking it at High rpm .

Port matching the manifold with the Tb is the worst you could do
The problem now is when air enters your manifold it supposed to build up pressure in the plenum ,with a manifold that is matched with the Tb some of the air goes back into the intake pipe.With a Stock Tb and at least a 4mm harsh step into manifold it can build up pressure and when the intake valves open you'll get a better filling of the cylinder.You can even read a little boost from your map sensor i believe 0.25psi or something.

The air coming in the manifold are pulses that go up and down in the runners of your manifold.In a N/a motor you need to get those pulses right in front the intake valve just as it starts to open .If your manifold can build up a little pressure you'll get a better and quicker filling kinda like a turbo .With a stock 55mm Tb and a intake manifold opening of 70mm you'll have a step of 7.5mm so the air stays inside the manifold.I'm not sure you even could place a stock Tb again onto that 70mm hole without drawing air from the wrong places.

[Dodo Bizar]

Putting the stock back on is not a problem if I remember correctly. It is getting the 70mm back on that worries me.

Hmmmm... well, having a back pulse is the only thing that can convince me so okay. But 0.25 PSi is just under 2%... something I hardly will be able to measure on a dyno since it only means 3 bhp... or is the gain at the inlet valves maybe a factor bigger?

Pitty I doubt the current performance... I really need a double dyno session to fiddle this one out.

But one very big remark.... TB size is NOT the actual issue. It is having reflective surface which is the issue. Since I ported it my reflective bump will be between 0 to 1 mm, so hardly non-existent. Getting the stock TB on gives me that reflective surface back. So okay point taken and I will try somehow in the future to see for myself.

[hondaNickx]

If you have the possibility test it on the Dyno Stock Vs. 70mm Tb .
I'm pretty sure stock will do better ,but i can't proof it to you either cause i haven't got results on paper.One thing i always think of is this crazy B20 build N/a engine from Endyn that has around 300chp and uses a ported skunk manifold with a 64mm TB.That intake manifold outflows ITB's.A 2.0L high reving engine with 300Chp and it uses a 64mm TB...That alone proofs a lot to me.IMO 70mm Tb are just a sales thing nobody needs them ,and everybody wants them cause bigger supposed to be better.If you got a drag race car that makes 400-500 hp then yes you need it...

[saxophonias]

Very detailed analysis
I had the impression that bigger T/B in a case like this will give better response to half pedal acceleration. In other words you will go the same fast but with less open t/b. Any experience on that?