High Compression Build vs. Low Compression Build? Trying to clear something up..

[oneofakinduserid]

I've been trying to read up on the different ways to build an engine, and why one would go with each particular tactic (if any of that makes sense lol)

so what I think I've learned (and this thread is really just to make sure I've got it right), is that if you're planning on putting a turbo on an engine, you would want to build it with lower compression, right? Is this because of the air that's being forced into the engine, you don't need that much pressure?

And if you're going all-motor, you'll strive for higher compression to make up for the lesser induction? Do I have this right or am I mixed up? There aren't a lot of articles that really explain the difference between the two.

I'm learning slowly, a year ago the only thing I knew about fuel injected engines was "suck squish bang blow" lol.. I try to read about it as much as I can before I bother you guys with questions. Thanks for any responses =)

 

[George777]

You are correct with the HC for N/A and LC for boost. As for the logic (airflow) behind that, I don't know how valid that is. I'm sure someone will let you know the exact reasons.

Research is your friend. Now if only half the people would do their own research before asking stuff, things would be better.

 

[YBLEGAL]

You should read our article on Static vs. Effective Compression. That will give you an idea.

Think of it this way. A turbo is literally a compressor. And 1 atmosphere is literal compressive pressure. Natural aspiration builds the motor for a constant 1 atmosphere of pressure, and effective compression does not change, and the way air fuel ratios and heat work, there's an upper limit on compression. Forced induction builds the motor for a variable input of pressure, thus making the effective compression that much greater than the static compression which is at 1 atmosphere. Increases in boost, which is literal compression (just like an air compressor) will cause higher effective compression levels in the cylinders.

Basicly, too much compression or too much heat kills motors. And many factors go into both, including valve overlap and oil viscosity.

 

[oneofakinduserid]

I'm going to search for that Static vs. Effective now, there's so much to figure out lol

 

[YBLEGAL]

<the truth>

Very nice explination! Sets straight a lot of what I've learned so far too. Lots of info organized in such little space!

 

[oneofakinduserid]

I second that.. +rep

 

[YBLEGAL]

It wont let me rep you blanco, sorry. I have to spread it around more I guess.. but theoretical +1!

 

[newb]

It wont let me rep you blanco, sorry. I have to spread it around more I guess.. but theoretical +1!

Damn, I cant rep you either Blanco. +1 more theoretical rep.

 

[sunfowerggs]

Many thanks to ur post. I love it.


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[newb]

Many thanks to your worthless bump of a year old thread.

 

[johnvtec]

yeah your right because if your running high comp then your restriciting the amount of air the forced induction can allowe because it will create to much pressure on the engine but if you run lower comp then you can increase the amounts of boost pressure thats what makes big power.

 

[RoughKnight]

^ we have another winner!!!
Ding ding ding!!!

 

[78civic]

But what engine type are you planning on 'building'? Honda?
Some engines don't like to be boosted, and some even have a hard time running High compression normally aspirated.

Whereas you can boost the heck out of others (just as long as you have it tuned to it's optimum) or run very high n/a and not many at all problems arise.

There are tons of articles on the web that you could be reading for years. Endynes' site had some good info, and reading/seeing what 'they do' when they build a motor really makes you think at a greater level.
Thinking on these things will bring you down to a more economical environment of a build.

Read of motors that are in the HP rang you might want to be and see what was done to their motors. pic a build and try to replicate within your budget. You may even try to get in touch with that builder to pick his/her brain. (watch out for the B/S too. in other words: read read read) Unless they 'race' they may talk your arm and leg off.

E

 

[reikoshea]

this thread is over a year old, but since the OP is still active on this forum im gonna leave this unlocked. Don't post to this unless the OP is willing to keep this topic going.

 

[78civic]

Sorry, That would be nice if at a certain date the title would change color..

E