intake manifold question

civic97hx · Post by **civic97hx** » Sat Dec 01, 2007 5:46 pm

i have a 97 civic Hx d16y5, what intake manifold if any can i swap to get a little better flow ? i have installed a short ram intake and 68mm tb, 4-2-1 header and full 2.25 exhaust pipe. Im still learning on the whole honda thing, so any help would be very helpful! thanks all in advance

JustRob · Post by **JustRob** » Sat Dec 01, 2007 6:19 pm

Get a 96-98 Honda Civic EX (D16Y8) intake manifold. Thats 68mm is way to big for your car. Go with an 62mm TB. They come factory on some Hondas (IIRC, ITR's and H22's have them)

civic97hx · Post by **civic97hx** » Sat Dec 01, 2007 6:25 pm

are there any mods i would need to do to swap that mani over? the Tb i got as a free gift lol so why not use it right?

N2HIFI · Post by **N2HIFI** » Sat Dec 01, 2007 9:22 pm

civic97hx;81494 wrote:are there any mods i would need to do to swap that mani over? the Tb i got as a free gift lol so why not use it right?

or why not sell it and buy the right parts that WILL work for your car.

just cause you can put it on the car does not mean that it will make more HP .. i would put money on the fact that you have even less HP now then with the stock one. If the opening in the intake manifold is not the same size (yours is WAY smaller ) it will actually have a lip which will cause the air flow to not be smooth and thus hurting performance of the motor.

chris

ObsesionWitSped · Post by **ObsesionWitSped** » Sat Dec 01, 2007 10:41 pm

N2HIFI;81535 wrote:or why not sell it and buy the right parts that WILL work for your car.

just cause you can put it on the car does not mean that it will make more HP .. i would put money on the fact that you have even less HP now then with the stock one. If the opening in the intake manifold is not the same size (yours is WAY smaller ) it will actually have a lip which will cause the air flow to not be smooth and thus hurting performance of the motor.

chris

so...you're saying you need a COMPLETE smooth surface for the BEST airflow...?

Spork · Post by **Spork** » Sat Dec 01, 2007 11:23 pm

yes.yes.yes.yes.yes.yes.yes.yes.
this is a BASIC principle of the physics of airflow.

with a throttle body as huge as a 68mm on a stock d-series i promise you that you lost a lot of torque
to benefit from a large throttle body, you need to bore the manifold to match, or run a spacer that tapers the opening of the throttle body down to the opening of the manifold and allows all of the air to flow smoothly into the throttle body...not to mention that you need more displacement and top-end to support a bigger t/b. All b,d,f,and h series throttle bodies are interchangeable, why would they make them all different sizes if larger ones are better on all motors? It's easy, thats not true! different size engines flow different amounts of air. the size of the inlet and outlets is designed to maximize flow for horsepower and torque for each motor. This goes for intake manifold runners and intakes too, if one size was best for all, they would ONLY make 3in. intake pipes... they don't. why? smaller diameter longer piping means quicker flowing air: this means more torque. since d-series motors don't rev high enough or make enough power on the top end, you see performance LOSES by putting big exhaust systems on stock d-series motors.

everybody laughs at hondas for not making any power below 'vtec'... I wonder if people modifying them without knowing anything about physics and the mechanics of motors and airflow has anything to do with that... hmmm

Silver Knight · Post by **Silver Knight** » Sat Dec 01, 2007 11:24 pm

ObsesionWitSped;81553 wrote:so...you're saying you need a COMPLETE smooth surface for the BEST airflow...?

yes. :violent5:

JustRob · Post by **JustRob** » Sun Dec 02, 2007 12:14 am

civic97hx;81494 wrote:are there any mods i would need to do to swap that mani over? the Tb i got as a free gift lol so why not use it right?

The only thing that I see getting in the way is the fact that you have an OBD2a car that has an EGR valve. I believe that if you just leave the plug for the EGR disconnected, you'll throw an check engine light, and you won't ever be able to pass emissions without putting you old IM back on the car.

As for the 68mm throttle body, take it off, put your stock one back on and sell the 68. Its doing nothing but hurting your car, as Spork and N2HIFI both said.

So, IMO. Just leave the intake alone. Save up a little money for a full motor swap.

ObsesionWitSped · Post by **ObsesionWitSped** » Sun Dec 02, 2007 8:31 am

funny you guys would say that..i always thought best airflow would be with a SOMEWHAT rough surface...which is why golf balls have dimples and aren't smooth :dunno:

Spork · Post by **Spork** » Sun Dec 02, 2007 9:18 am

not for all purposes, thats a whole different concept. you are talking about air flowing around an object as opposed to air flowing through an object.

For the type of flow you are talking about, you have to factor in the turbulent wake created on the backside of an object, and the pressure drag created on the front (basically, the areas where, in order to go around the ball, the air is forced to split on the front and back) into the equation... this adds a whole different dimension to the airflow equation that you don't see when you flow air through an object (or a tube)... but yes, in that type of airflow you are correct... to a degree. golf balls are dimpled, tennis balls are 'fuzzy', and baseballs have stitches because they actually do improve the distances and velocities that they can travel. The 'viscous drag' created by these imperfections in the surfaces serve to lower the pressure drag on the ball (they lower the pressure drag more than they raise the viscous drag) and allow the balls to go farther and faster. now this concept does not apply to things like airplane wings that are designed to allow the air to smoothly separate and re-converge around it. if you tried adding dimples or 'fuzz' to an airplane wing, you would hurt its performance.

I can get a little more in depth with the difference between the two types of flow (in vs. around objects) if you want me too, and i can draw diagrams of smooth vs. rough surfaces for both types of flow if you want, but its late and I don't feel like spending the time creating the diagrams unless someone need me to do it in order to help them understand it better.

who woulda thought that this thread would have turned into a physics lesson... maybe I should have stuck with engineering after all. oh well. :biggrin: