High compression, equals?

tx2000gt · Feb 10, 2006

Well, what exactly is compression? I mean, I know you can't have a lot of it with forced induction applications, and to much of it on an N/A motor can be a bad or hassling thing.

bcd · Feb 10, 2006

its the amount of pressure inside the cylinder. if you get too much you have to run less timing and premium fuel.

tx2000gt · Feb 10, 2006

So, an N/A motor would benefit from it then?

speadfreak · Feb 10, 2006

more compression makes more power. More compression makes more heat. More heat means your engine will detonate or spark knock easier. I have seen guys build higher compression engines, then crank the timing back so far to run pump gas that it defeated the purpose of the higher compression in the first place. Both forced induction and higher compression create more pressure in the cylinder, making more power when tuned properly. Nitrous is sorta the same principle, it basically creates a greater pressure in the cylinder. Basically, the more dense that you can make the air and fuel volume in the cylinder, the bigger the explosion will be when it is ignited. The bigger the explosion means the piston is pushed down with more force=more power. I hope this might have helped and not confused more. Now with adding more cylinder pressure, the engine will be moving alot more air into the cylinder and pushing alot more exhaust gas out.......this is where free flowing exhaust and intake components come into play. I'm one of those people who knows how things work, but have a hard time putting into words

5spd GT · Feb 10, 2006

http://e30m3performance.com/myths/more_myths1/comp_ratio/comp_ratio.htm

speadfreak · Feb 10, 2006

5spd GT said:
http://e30m3performance.com/myths/more_myths1/comp_ratio/comp_ratio.htm

Thats exactly what I said, aint it.........

tx2000gt · Feb 10, 2006

Alright guys, I finally understand . What would be, in your opinions, a nice nitrous 331 stroker build compression ratio?

Modular2v · Feb 11, 2006

10:1 on the bottle fed 331....thats what im going with

tx2000gt · Feb 11, 2006

Alright, sounds cool .

90mustangGT · Feb 11, 2006

There is two types of compression

1. Static
2. Dynamic

Static compression is what your motor is rated, the difference between the total volume of the cylinder at bottom dead cylinder (piston all the way down) and the volume it is compressed to at top dead center. (piston all the way up)

Dynamic compression is much different. The compression ratio changes with rpm, different cams, heads, induction systems (blown or naturally). It has to do with the actual amount of air that is drawn into the cylinder and how much it is compressed. That is the important one.

If you want to know more, it's too complex for me to sit here all night and type, and I'm no expert, but do a search and I am sure you'll find it.

5spd GT · Feb 11, 2006

Dynamic compression begins once the intake valve is closed I believe....

Here is a pretty detailed article on dynamic compression:

http://cochise.uia.net/pkelley2/DynamicCR.html

90mustangGT · Feb 11, 2006

5spd GT said:
Dynamic compression begins once the intake valve is closed I believe....

Here is a pretty detailed article on dynamic compression:

http://cochise.uia.net/pkelley2/DynamicCR.html

Pretty complex. Say you have a blower at 7-8psi, you are effectivly adding half another atmospheres, so a 9.0:1 is now a 13.5:1 compression motor, but because of the restrictions in the intake, heads, and exaust, not all that air can be pushed in the motor, so determining how much actual air is getting into the cylidner is dynamic compression. (I think I'm right, correct me if I'm wrong).

Oops, I was wrong, looking at cylinder pressure, your right 5 speed, it's when the valve closes.

Dynamic Compression Ratio, on the other hand, uses the position of the piston at intake valve closing rather than BDC of the crank stroke to determine the sweep volume of the cylinder.

Rick 91GT · Feb 11, 2006

For a N2O PUMP GAS 331 I would run a static 10:1-10.9:1, although with the later one you may need race fuel at the track.

Looks like you guys have settled the dynamic issues...

tx2000gt · Feb 11, 2006

Yeah, this would be my daily driver....so 10.5:1 would be pushing it for the street on 93 octane?

Rick 91GT · Feb 11, 2006

What head are you running? What cc chamber is it?

IntenseBlue · Feb 11, 2006

10.5:1 compression.

tx2000gt · Feb 11, 2006

This would all be a future build, but I'm thinking port and polished Twisted Wedges or AFR 185's.

cjman15 · Feb 11, 2006

So is it possible to build a 347 stroker with a blower?

IntenseBlue · Feb 11, 2006

cjman15 · Feb 11, 2006

Would you just need to keep the compression under like 10:1?

I'd like to do a 347 stroker in the future and have a blower too.

High compression, equals?

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