soon2bdropped

okay let me think here.. compression means squeezing something together into smaller particles.. okay i get that..


so say i have a piston that has a very high dome.. like 12.5:1 or something of that nature..

the reason why they call it high compression motor is it because..

1. since the piston dome is taller when u slap the head on.. the space in the combustion chamber decrease.. so when it comes time for compression stroke there is a very high chance of denotation due to the fact that the space where it compresses is very small and it higher compression.. because its capable of igniting itself..


is this correct.. or does anybody has a better way of putting it..


also how does high compression motor is faster than one thats low compression.. NA motors....

themikewoo

if you put the pistons with the high dome on your car it will raise the compression ratio because with the dome it will help compress the air. so instead of 9:1 it could be 9:25.

detonation is over heating of parts until the fail. so with the high dome i would not say it is more prone to detonate then the other piston. it might be more prone to bend valve because hondas are interference engines.

diesel engines have really high compressions like 20:1 + up. so you don't have to worry about the air fuel mixture igniting itself.

na high compression motors do run faster then na lower compression motors. but there are exceptions. you have to find a balance

soon2bdropped

bump.. anyone else want to comment.. but i'm in the right track right?

doood

iTrader: (1)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by themikewoo &raquo;</TD></TR><TR><TD CLASS="quote">
detonation is over heating of parts until the fail.

diesel engines have really high compressions like 20:1 + up. so you don't have to worry about the air fuel mixture igniting itself.
</TD></TR></TABLE>

you sure you wanna stick with these statements?

Drugs Are Bad

Higher compression allows your engine to produce more usable energy with the same amount of fuel. As compression increases, heat increases. Under compression, the air / fuel mixture could become hot enough (spontaniously) and ignite itself; just from being compressed (no spark introduced). This self-ignition causes a flame front. When the piston reaches the point of ignition, the spark plug is then fired, creating another flame front. When the two flame fronts collide, they do so with explosive force.

It's like riding a bike. You don't pound your feet on the pedals; you'd break the bike. You gently push down on the pedals for smooth torque. That's what we want for our motors.

Under normal conditions the air/fuel mixture does not EXPLODE, it burns quickly. As it burns it loses density, expands and moves quickly. This is the source of your power. In essense, you could say that your motor is powered by heat.

To make the most power, ideally, the mixture should be compressed to the point where it is nearly ready to ignite itself. At this point, the flame front created by the spark plug will move smoothly and quickly. Igniting anywhere before this point will create less power due to slower expansion and less heat creation.

Of course, hand-in-hand, the added heat of high compression can prevent you from utilizing it. It creates more heat, but the greater ambient heat can lead to detonation at the higher compression ratio. This is why you need fuels that resist detonating more. That is what higher octane fuels are for. High octane fuel will resist detonating (higher ignition temperature) moreso than lower octane fuel.

Water injection can further boost your octane allowing you to run insane compression ratios or to utilize lower octane fuels in high compression engines.

soon2bdropped

anymore comments... good ideas

King V

I think water injection is not a needed thing if you can figure out how to properly tune and set up an engine. It is good if you're facing certain restrictions, but i think water in the mix just takes up space, like gas with alcohol in it. If you need that much cooling of the combustion event, you need to back down on the static compression ratio or adjust your timing.

Drugs Are Bad

Well, yeah. Most of the time water injection is not necessary, and I think it's a horrible idea to throw a prefab kit on a motor and expect it to work wonders; but it can be an effective tool for fine tuning a street motor that would otherwise be unreliable without race gas (i.e. 12.5:1 compression and higher). It also helps to lower combustion temps in turbo engines without an intercooler. I'd like to see some EMS with tunable direct-port water injection mapping. Direct port would be the way to go.

soon2bdropped

1. so when somebody says 12.5:1 what does 12.5 mean and the 1.. i think 12 is the amount of air and 1 is fuel.. not to sure..

2.. why is everyone saying don't turbo a high compression motor.. for what reason? detonation too or what? if its cause of detonation just add higher octane and advance timing so it doesn't ignite 2 much during compression stroke..

3. also is the read why u using thicker headgasket it lower the compression is because the head sits a bit higher now so its more air.. so the compression is lowered am i right?

NJIN BUILDR

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by soon2bdropped &raquo;</TD></TR><TR><TD CLASS="quote">1. so when somebody says 12.5:1 what does 12.5 mean and the 1.. i think 12 is the amount of air and 1 is fuel.. not to sure..

2.. why is everyone saying don't turbo a high compression motor.. for what reason? detonation too or what? if its cause of detonation just add higher octane and advance timing so it doesn't ignite 2 much during compression stroke..

3. also is the read why u using thicker headgasket it lower the compression is because the head sits a bit higher now so its more air.. so the compression is lowered am i right?</TD></TR></TABLE>

1. The engines volume is 12.5 times larger at BDC than it is at TDC.

2. Because most people are using pump gas and even race fuel has its limits.

3. The volume of the head gasket is included in the engine cylinder volume.

soon2bdropped

OKAY THAT CONFUSED ME.. so where does the 1 come into play in the ratio? so if its 12.5 larger at bdtc so how much is it at tdc? i'm lost and why is high compression motor a big no no for turbo?

lakahang

high compression on a turbo setup isn't neccessarily bad on a turbo setup, it's just that u cant put out as much boost as you would a lower compression motor

lakahang

o yea and as far as the compression ratio thing goes...

-at bottom dead center, it would be this big:

l l l l l l l
l l l l l l

-and then at top dead center it would be this big:

l

not exactly in those sizes but yea, thats a little ghetto diagram i that my brilliant self came up with.......

DC-2uned

^ More like l l l l l l l l l l l l to l but thats probably what you meant anyway. The reason people go with lower compression for turbo is pump gas, because boost adds compression so if you can take some of that compression out you will be less likely to detonate at the same psi. The overall compression with 12:1 and 10psi is way higher than 9:1 and 10psi. So with the same theoretic reliabilty/overall compression you would have a 9:1 running 15psi and the 12:1 only running about 7-8psi. The fact is the 7-8psi more you could run will make tons more power than the 3 points of compression ever will.

soon2bdropped

alight but if the piston dome is higher.. thats less space that can fill up the cylinder.. so the volume is little.. so where are u guys getting 12..5 or 10.8 compression and why is there always a 1 12.5:1 that never changes why? confused,,

King V

The space between the dome and combustion chamber is smaller when at TDC, raising your compression. But there is a difference between static and dynamic compression, because the ratio changes due to cylinder filling efficiency, cam timing, etc.

King V

Static=mechanically calculated CR
Dynamic= CR as engine is running. The CR will be "less" at idle/part throttle(less air moving through the engine,less air to fill the cylinder) and climbs as engine speed/airflow increases.

soon2bdropped

i get that part at tdc less space due to the fact piston dome is higher... so less space more air compresses.. high compression.. but if the piston is at bdc.. less air can be filled up whyh because the dome sit higher than a stock piston would so less air... can be filled.. so a piston thats stock compared to a piston thats 12.5:1 is funny cuz the dome is higher at bdc so less air. can be filled as opposed to a stock piston.. sits a bit lower.. more can be filled..

soon2bdropped

anybody knows.. the dome sits higher so i know when it gets to tdc its less space.. but when its at bdc... its less space cuz the dome sit higher than the stock one..

lakahang

i c where ur getting at.....just think about it like this.....

............Low compression..................High compression
.................................................. .................................
........____.............____.......l........____. ............._____
......./.......\........../........\.....l....../........\............/.........\
.....ll ll.......ll ll...l...ll _____ ll....... ll ll..
.....ll_____ ll.......ll ll...l..ll./_____\ll....... ll ll.
.....ll llllllllll ll.......ll ll...l..ll.lllllllllllllllll....... ll ______ ll
.......-------.........ll______.ll.. l ll ..-------.ll....... ll./______\ll
..........lll l...........ll.lllllllllllll ll...l..ll ......lll l. ll.......ll..lllllllllllllll ll
..........lll l...........ll -------- ll....l..ll ......lll l. ll.......ll...--------.ll
.........................ll ....lll l.. ll.. l...ll ........... ll.......ll......lll l... ll
.........................ll ....lll l.. ll...l..ll .......... ll.......ll......lll l....ll


thats not too accurate.....but all it shows is that with the domed piston.....the dome on the piston will fit more directly into the chamber of the heads where to as a low compression will have space because even when the piston reaches its top dead center.....the crater of the lower compression pistons will result in more space for the compressed air to hang out in......



Modified by lakahang at 7:38 PM 10/3/2007


Modified by lakahang at 7:40 PM 10/3/2007


Modified by lakahang at 7:50 PM 10/3/2007


Modified by lakahang at 7:50 PM 10/3/2007

lakahang

aww crap.....that totally messed up my little diagram