Airflow Question... - Honda Forum / Acura Forum

outlawtas · 03-27-2002, 05:17 PM

Using the LPM formula, you can determine airflow of a given engine, not under boost.

so,
Flow = Displacement x VE x (rpm/2)

I'm trying to find the flow rate of a b18b engine, when I came across a question...this is what happens when you fill out the formula...

Flow = 1.8 x .85 x (6000/2)
Flow = 1.8 x .85 x 3000
Flow = 4590 LPM

1 CFM = 28.317 LPM, ergo 4590 LPM = 162.09 CFM

Now, my question to you is, does airflow rate determine power? Because, if you would see that a B18b1, B18c1 and B18c5 all have the same airflow rate...so why does one have more power than the other? thanks...

slickhonda · 03-28-2002, 07:59 AM

what is VE?

outlawtas · 03-28-2002, 11:35 PM

volumetric efficiency....lol

slickhonda · 03-29-2002, 08:51 PM

oh, yeah...that was dumb of me....so obviously there is more to the power an engine can produce then just flow. Flow is big but there are other variables like efficiency of the engine which is linked to compression ratios and combustion chamber designs.

Honda_Guy · 03-30-2002, 02:38 AM

First, the B18C1 and B18C5 have higher compression, making them more thermally efficient. Second, the B18B, B18C1, and B18C5 do not each have the same volumetric efficiency, so you would have different numbers to calculate into your formula.

outlawtas · 03-31-2002, 01:08 AM

thanks...out of curiousty, how come Honda_Guy is driving a mustang LOL?

anyways..I understand now, it's so simple. They both flow the same amount of air, but some compress that air more, maybe are less restrictive in the exhaust ports and intake ports just simple stuff
thanks

neophyte · 03-31-2002, 02:09 PM

anyone know a page or anything that has the various VE's for different hondas, or nissans? While I was trying to match a turbo for a b16 with a compressor map I came across a guy who had plotted the different VE's at different rpms of his mitsu eclipse motor across a compressor map.

Honda_Guy · 04-01-2002, 11:34 PM

Quote:

Originally posted by outlawtas
thanks...out of curiousty, how come Honda_Guy is driving a mustang LOL?

Well, I've been a Ford guy all along. My first car was a '65 Mustang, then I decided to try out the imports for a while in the form of a 91 Civic hatchback. I wanted to go faster, but I would have to spend alot of money I didnt have to make it quick(did I menton it was an STD? 1.5L, 4 speed, dual point ignition, etc), plus the CA smog hassle. The 5.0 was just more economical for me. Sometimes its a little awkward being on SHO with a Mustang in my sig, but I'm into anything with an engine so its all good.

Quote:

anyways..I understand now, it's so simple. They both flow the same amount of air, but some compress that air more, maybe are less restrictive in the exhaust ports and intake ports just simple stuff
thanks

Right. Comparing the B18B1 and the B18C5, the C5 has mild portwork and matching cams, so it is more volmetrically efficient than the B1. It also has higher compression, making it more thermally efficient. That why the C5 has 195hp compared to the B1's 142(?), even though they are both 1.8L.

slickhonda · 04-02-2002, 08:33 AM

yup exactly...hand ported

Nikolai · 04-02-2002, 03:22 PM

The B18C1 and C5 motors are MUCH more volumetrically effecient, especially at higher RPM's, where peak power is important (thank you high profile VTEC cam).

Speaking of higher RPM's, your figures also were for a 6000 RPM redline, as opposed to 8,100 or 8,500. If you change that factor, then that's 30% more air alone, in the case of the B18C5.

Also, the effects of higher compression do not increase linearly, and though they are a factor, it's not as important when comparing B18b/b18c1/b18c5.

Nick

Dr Drew · 04-03-2002, 01:19 PM

Port crossdirectional width is narrower on the C5 giving a higher intake velocity flow enabling it to make higher rpm power. The intake manifold primaries are shorter and straighter for a higher rpm power band. Exhaust primaries are longer for higher rpm power.

C1's manifold has 60% more surface area than the C5. More surface area the more 'drag' and less velocity. C1 and C5 for instance produce about the same power at 6K rpm. The C5 glows in the 7.5-8.5k range. The B1's ports aren't designed from the factory to have enough flow velocity to support flow at that rpm. The diameter of the intake should have an area that is 25% larger than the TB port area to give proper flow velocity. Pop the hood on the Ls and an R and see which is larger (in comparison to the TB).