highest street compression?

[14.5 drift]

Sorry, but by comparison I consider alcohal to be an aggressive form of fuel, or are you on some craxy planet where every one runs alcohal on the streets?

 

[14.5 drift]

Oh yeah, and for ignition they probly just used a set of magnecore wires and called it a dey right?

 

[Mirage2LTurbo]

Oh yeah, and for ignition they probly just used a set of magnecore wires and called it a dey right?

WTF are you attempting to talk about now? Just stop.

 

[14.5 drift]

WTF are you attempting to talk about now? Just stop.

I guess I am just trying to piss people off, they should really not let people like me on the boards, oh wait thats right, I'm not. Your just trying to be a dick, maybe it is you that should stop. I'm not attempting any thing, you can't just say stop, who the #### are you? Are you a wiseman, moderator, no. I guess statements like "aggressive fuel and ignition components" is completely out of line right? All I was saying is it is quite more than a set of wires and a fuel pump upgrade. I don't know, your right though, this is stupid. You leave me alone and I will probly dissapear, you continue to screw with me, I will be back on the principle that i dont roll over for assholes

 

[autronicDSM]

Sorry, but by comparison I consider alcohal to be an aggressive form of fuel, or are you on some craxy planet where every one runs alcohal on the streets?

Do you know anything about alcohol fuels? They produce less power per same volume as gasoline, have a slower burning rate, and detonation is not a problem for the most part. Hardly anything aggressive about that.

 

[Mirage2LTurbo]

Do you know anything about alcohol fuels? They produce less power per same volume as gasoline, have a slower burning rate, and detonation is not a problem for the most part. Hardly anything aggressive about that.

Careful there hoppy, they may produce less power per same volume of gas, but you also run 6:1 a/f instead of 12:1 Alcohol = more power

 

[autronicDSM]

Thanks for enlighting me. Could you please tell me too that alcohol engines run pretty rich to cool exhaust valve so pre-ignition doesn't happen... mixture burns so slow it's still burns on the exhaust stroke. I didn't know that one either.

 

[LandoAWD]

Good crap, people. Keep this civil and ON TOPIC.

 

[1fast97gsx]

yea no joke ... has anyone succesfully ran a 9.5:1 compression motor at 23-25 psi on pump without the use of alchohol injection on a decent sized turbo? Lets take a 50 trim just since everyone is familiar with it in some way. Horsepowerwise at 9.5:1 at 24 psi and then an 8:1 motor at 24 psi how much more hp would the 9.5:1 motor make? This is assuming both cars are properly tuned. I'm just curious if it's only a 10 hp difference or more like 50 ...

The reason for starting this whole post kind of comes from the honda world. I hate hondas with a passion, but I've also seen them make 360+ whp at only 10 psi on a turbo that it would take us 25 psi to make the same power. I realize they can't run as much boost as us without sleeving, however why do they make just as much power at lower boost levels?

 

[Mirage2LTurbo]

Thanks for enlighting me. Could you please tell me too that alcohol engines run pretty rich to cool exhaust valve so pre-ignition doesn't happen... mixture burns so slow it's still burns on the exhaust stroke. I didn't know that one either.

That's why most full alcohol cars do not run intercoolers

 

[crankbender]

I am going to weigh in on this in a little bit...The post is going to be a little long in length to try and address some of what has been said here.

At this point please stop with the stupid this and stupid you comments...it doesn't help.

Please stop posting on things you don't know about. Out of the like 20 posts about the CR of top fuel cars maybe 1 or 2 had some real knowledge on the subject.

Stop being agressive.

If you just have to try and prove somebody wrong the topic of my upcomming post will be the capabilities of airflow with lower cr and how maximum power potential is based on airflow.

In other words typically lower compression will allow a higher max power...but is this what you really want?

 

[NDgsx]

depends on combustion chamber setup....a pent roof combustion chamber can allow boost but will be limited by compression. while a hemispherical combustion chamber can handle alot more compression.

Where is this statement coming from, real world experience or some theory? Real world results have proven that a hemispherical combustion chamber is a poor design, the large volume in on the head requires an big dome to get a high compression ratio. This makes the flame front move across a very long thin area, which lends itself to detonation. There is absolutely no squish in a true hemi combustion chamber, this makes for lots of endgas. While a canted head won't always produce the same flow numbers through the port they offer a better combustion chamber as they can have a very small head volume (I've seen some down in the 30cc range), allowing the use of flat top pistons to achieve high compression, which in turn makes for good squish. This is what is termed a "fast burn" chamber. A pentroof chamber is a great compromise between the two, you get the best port/valve layout in terms of flow, and actual quench pads on the head. This is a whole other discussion though, so I'll leave it at that.

Here is my view on compression ratio. Your first decision on what compression ratio to run is what fuel will you be using primarly. While you can run 9:1 and higher on pumpgas it does NOT mean that you will achieve the highest power level your setup could POTENTIALLY make on pump gas. Why? Very simple, timing advance. Ideally we want to get all of combustion event done between 5 degrees btdc and 10 degrees atdc. Remember there is a delay between the plug getting fired and the actual combustion event. If you do not run enough advance the combustion event is happening further down on the power stroke and you are loosing power. If the plug is fired too early you will actually loose more power than it being fired to late though as this will pressurize the cylinder while the piston is moving upward, just like preignition.
So in the end for each setup there is an ideal middle ground for compression ratio, it should low enough to allow you the correct timing advance, while not being so high that it causes detonation at that timing advance.
In an ideal world I would start out tuning on a low compression motor, find the timing that produced the greatest power, then increase compression until I saw detonation, then back off the comrpession one point.

In a nutshell race gas with high lead content burns slower, increasing resistance to detonation. You will be able to run high compression on racegas while keeping timing where it produces MBT, than the compression you will be able to run on pumpgas.
Pick your goal, pumpgas power or racegas power.

This is very simplified, I know there are small points I didn't cover, I just don't have 3 hours to devote to this.

 

[crankbender]

This is very simplified, I know there are small points I didn't cover, I just don't have 3 hours to devote to this.

oh so true.

I gotta run for a bit.

Just remember most of the race race drag cars (lots of race in there means you don't own one) run very low compression. The turbo celica that was breaking all the records back in 01/02 and was classed out specially modifiec the pins to get down to 7.8:1 where they wanted to be.

Lower compression will almost always yield higher power numbers if you can make the boost to back it up. The problem is at 8:1 and lower you start getting into boost above 30-40 psi. Now the trouble is can you make that kind of pressure in a reasonable ammount of time?

In general run the highest compression you can for your chosen gas and boost. If you want to go big...keep it low.

Now if you are going to run alcohol things change considerably because the fuel is detonation resistant and the intake temps are so low.

I have been told that getting into the physics and theory as to why this happens can just confuse the situation so i will leave it out for now. If anybody specifically wants me to explain why you can get more air and fuel through the cylinder with a lower compression please let me know and give me some time.

 

[hose101772]

has anyone succesfully ran a 9.5:1 compression motor at 23-25 psi on pump

Yea sorta-ran for a year(12k) anyway.This was with a 16g@20lbs on a 2.0 that had 210 lbs of compression cold.
9/1 j &e's with a severly milled head-into the seats a touch.It was awesome in the cool weather and always tempermental about fuel.

Finally after a year of battling a cold knock I loosened the knock sensor abit.Egts dropped-timing held to 18 would pick up a few counts-bought gas at a country store,I knew better but had to.It blew part of the fire ring out the back of the head within 2 miles.

 

[psychlow]

It is a very simple formula!

(Boost pressure + Heat + Compression + Timing) - Octane = Detonation/preignition!

To a certain extent, you COMPROMISE between these four left factors. By lowering one, you can increase the other. By upping octane, you can raise all or raise one (to an extent).

Now, as stated previously, a motor running less compression and more boost will make more power, everything else being equal and still being within the turbo's efficiency range. Why?

Well, think of it this way. You can smoothly compress the air more with a turbocharger blade and pressurize the air that way THEN run it through an intercooler to lower the temperature, OR you can compress the air more while inside the engine (when the air is already mixed with fuel) by slamming 25 PSI into 225 PSI with a 1000+*F piston in 1/25th of a second (at 6KRPM). Which do you think will be better at preventing preignition?

24lbs on 9:1 on engine A and 24lbs on 8:1 on engine B is a moot comparison. The idea is to run just as much timing on engine B as engine A, AND up the boost 6lbs before detonation or preignition occurs.