5thgenCory

I know I'll get ragged for this thread, but I'm new to the Honda scene, so I'm still learning. When someone is talking about compression, what are they referring to? I know that my HB has 11:5 compression, but I have no idea what that means. Is that good or bad? Help?!

lazy bum shaughn

It's when you squeeze something together. In car terms, it's air and fuel squeezed together to make a big bang.

You sure your hatch has 11.whatever compression? What motor are you running.

Generally, you want high compression for an all motor setup, and low compression for a forced fed motor to reduce detonation(a bang in your motor, but a bad bang).

Starscream

Compression, refering to cars and engines is the third of the 4 cycles of a 4 stroke engine.

In this stage, the piston goes up, compressing the air/fuel mixture in the cilinder, then the spark plug ignites the mixture. And the 4th stage begins: exhaust.

The compression ratio (CR) of an engine refers to how much the mixture is compressed.

A high compression ratio, gives more power, and is the best for a All motor setup.

A lower compression ratio, although gives less power, is the only way to go for a FI (Forced induction) setup...remember that a turbo or a supercharger already compresses air into the engine...if you have a high compression ratio already, then your engine is gonna suffer really bad.

And i agree with lazy bum shaughn...11.something looks really high for a hatch...what's your engine and setup???

blah13

Actually compression is the 2nd stage, Intake, Compression, Combustion, Exhaust. But as far as the low CR = FI and high CR = NA isnt fully true, you do know a high CR running smaller boost can have as much power as a low CR high boost motor right? And the high CR has power throughout more of its powerband. I dont see the point in losing power only to have to make it up with more boost. As with any motor tuning is huge.

NSX Bob

A ratio of the displacement when piston is at BDC/TDC

5thgenCory

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Starscream &raquo;</TD></TR><TR><TD CLASS="quote">Compression, refering to cars and engines is the third of the 4 cycles of a 4 stroke engine.

In this stage, the piston goes up, compressing the air/fuel mixture in the cilinder, then the spark plug ignites the mixture. And the 4th stage begins: exhaust.

The compression ratio (CR) of an engine refers to how much the mixture is compressed.

A high compression ratio, gives more power, and is the best for a All motor setup.

A lower compression ratio, although gives less power, is the only way to go for a FI (Forced induction) setup...remember that a turbo or a supercharger already compresses air into the engine...if you have a high compression ratio already, then your engine is gonna suffer really bad.

And i agree with lazy bum shaughn...11.something looks really high for a hatch...what's your engine and setup???</TD></TR></TABLE>

The car was purchased on e-bay and I still have the link on my e-mail. If I knew how to get the link to the site on a post, I'd post it so you can read the specs on the car for yourself. How do I do it???

5thgenCory

Here is the link. My car is the little yellow HB and as you scroll down, you'll see a list of the specs for the car.

I hope the link works...

http://207.68.162.250/cgi-bin/...29577


Modified by 5thgenCory at 6:47 AM 4/16/2003

AllmotorJunkie

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Type R Bob &raquo;</TD></TR><TR><TD CLASS="quote">A ratio of the displacement when piston is at BDC/TDC</TD></TR></TABLE>

I believe its the ratio of the VOLUME at BDC/TDC....not displacement.




Modified by AllmotorJunkie at 6:57 AM 4/16/2003

blah13

Volume = Displacement, its basically the same thing.

JaTaN

that link didnt work (tells me to login to hotmail), but heres how u post it =P
http://cgi.ebay.com/ebaymotors...29577

Starscream

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blah13 &raquo;</TD></TR><TR><TD CLASS="quote">Actually compression is the 2nd stage, Intake, Compression, Combustion, Exhaust. But as far as the low CR = FI and high CR = NA isnt fully true, you do know a high CR running smaller boost can have as much power as a low CR high boost motor right? And the high CR has power throughout more of its powerband. I dont see the point in losing power only to have to make it up with more boost. As with any motor tuning is huge.</TD></TR></TABLE>

ooopss...my bad, i screwed up the times...what a n00b mistake

And yes, tuning is the key here...

5thgenCory

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JaTaN &raquo;</TD></TR><TR><TD CLASS="quote">that link didnt work (tells me to login to hotmail), but heres how u post it =P
http://cgi.ebay.com/ebaymotors...29577</TD></TR></TABLE>

That's the link! How'd ya do that? That's my car and it's specs though, so you all can see it/them.

StorminMatt

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blah13 &raquo;</TD></TR><TR><TD CLASS="quote">Volume = Displacement, its basically the same thing.</TD></TR></TABLE>

Not quite. Displacement is a special volume. Specifically, it is the volume at BDC minus the volume at TDC multiplied by the number of cylinders.

blah13

Key word being basically. So my 1.5L beater with 1495cc of displacement, volume doesnt equal displacement?

Audipwr1

a subscript is needed for volume to denote what particular volume you are referring to

displacement refers to total volume of all four cylinders

Compression ratio is determined through the volume of one cylinder (this includes the combustion chamber, and the dish or cone on the top of the piston, and obviously the cylinder volume) at BC/TC
modern nomenclature removes the Dead. Not sure why this is, but that is what I have been told and have read in such books as: Engine: An Introduction, by John Lumley

JimBlake

I always thought displacement is the volume swept by the piston. So it doesn't include the volume of the combustion chambers. So...

V(bc) = total volume enclosed, at BC, with valves closed.
V(tc) = total volume enclosed, at TC, with valves closed.
(also known as clearance volume)

Displacement = V(bc) - V(tc)

C.R. = V(bc) / V(tc)

976

Per point dropped in compression it's something like a 2-4% decrease in power. Could someone correct me... I know technically it IS NOT a measurable figure, but kind of close.

I'm getting a built b16, it has a low compression where it used to run on a turbo. 9:1. I'm going to be running all motor for a while, I know I'm not going to have much power, but what kind of loss can I expect, technically my engine should last longer than a higher compression right?

I'm still learning this stuff as well, I guess we all are - never stop learning, if someone could help me out or point me in the right direction that would be cool!

Audipwr1

it does include the combustion chamber

5thgenCory

Well, I've learned a little bit here, thanks guys. To those who seem stumped about the compression ratio on my HB (11:5), a guy I know put a b18 type r motor in his HB and I think it gets 9:1 compression or something close to that. So, that's crazier than mine.

Spoonin

Compression is when the piston travels to the top of the cylinder to "compress" the air/fuel molecules together to make them easier to combust. Which is why you need higher octane gas with higher compression cuz higher octane gas is more stable. If you want to make more power (using a turbo) lower the compression to allow more fuel with more air from a turbo. Diesel engines have no spark plugs to ignite the fuel instead they use high compression to cause the air/fuel molcules to compress so much that they ignite. Hope this makes it simple for you. This should also explain why I might ask if your friend's engine is turbo since he only has 9:1 compression.

5thgenCory

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Spoonin &raquo;</TD></TR><TR><TD CLASS="quote">Compression is when the piston travels to the top of the cylinder to "compress" the air/fuel molecules together to make them easier to combust. Which is why you need higher octane gas with higher compression cuz higher octane gas is more stable. If you want to make more power (using a turbo) lower the compression to allow more fuel with more air from a turbo. Diesel engines have no spark plugs to ignite the fuel instead they use high compression to cause the air/fuel molcules to compress so much that they ignite. Hope this makes it simple for you. This should also explain why I might ask if your friend's engine is turbo since he only has 9:1 compression.</TD></TR></TABLE>

Thanks! Of all the posts, yours seems to be the clearest. His HB has no turbo in it and like I said, the ratio numbers could be different from what I wrote in my last post. I'll have to ask him next time I talk to him and find out what the real numbers are.

5thgenCory

Well, his motor is actually 11:1 compression. I was way off on those numbers. Sorry! I guess his is a racing motor and not a stock one.

Spoonin

Usually the type r motor is 11:1 compression stock.

RangerDan

Thanks for playing nice with my pal Cory. He is just getting into the scene and he works at my shop but we never really have time to chat about engine specifics.



Sorry about the mis-communication as to what my comp. is. We were IM'img and got confused on my comp. ratios between my old engine and my new replacement.

5thgenCory

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RangerDan &raquo;</TD></TR><TR><TD CLASS="quote">Thanks for playing nice with my pal Cory. He is just getting into the scene and he works at my shop but we never really have time to chat about engine specifics.



Sorry about the mis-communication as to what my comp. is. We were IM'img and got confused on my comp. ratios between my old engine and my new replacement.</TD></TR></TABLE>

Thanks Dan!!!