Other ADA Girdled Head

[Matt_E]

Quick quote from the wiki.

A high compression ratio is desirable because it allows an engine to extract more mechanical energy from a given mass of air-fuel mixture due to its higher thermal efficiency. High ratios place the available oxygen and fuel molecules into a reduced space along with the adiabatic heat of compression–causing better mixing and evaporation of the fuel droplets. Thus they allow increased power at the moment of ignition and the extraction of more useful work from that power by expanding the hot gas to a greater degree.

 

[Matt_E]

yes it will.

lol, ok. :wavey:

 

[D-Roc]

haha, nice edit. good choice.

 

[D-Roc]

wow nice quote about how increasing CR will make more power, we know that, so now how about making the ideal amount of fuel to be burned increased and then what happens. mo power!

 

[Matt_E]

wow nice quote about how increasing CR will make more power, we know that, so now how about making the ideal amount of fuel to be burned increased and then what happens. mo power!

The ideal amount is based on a ratio of air/fuel. (That ratio is 14.7?, but real world ratio is typically a bit fatter than that)
Changing compression does not change the amount of air going into the engine. Hence the ideal fuel amount doesn't change. If you were to increase fuel in that mix, the ratio would decrease.

The only time that you would add fuel to make more power is if your air flow changes (i.e., porting, carbs, pipe).

What edit are you talking about?

 

[D-Roc]

if you have a complete combustion of a lean mix you will have less power. if you have incomplete combustion of a rich mix you loose power. the key is complete combustion of the most amount of fuel possbile for your compression, timing, and spark. if you go from 150psi to 185+ that is a large compression bump, all we are saying is try and burn some more fuel, this will keep from detonating and burning pistons. the higher the compression the more fuel you will want to keep this from happening and if you where at a perfect/almost lean mix at 150psi and you bump it up to 185........be aware. thats all.

hey matt, wasn't all your motors blowing up and stuff?

 

[Tyler Zane]

combusting more fuel will increase hp. i adjust my screws every ride this time of year as the temps change, just to keep it crisp. trying to burn too much fuel is no good either and you will loose a bit of power but keep your pistons clean.

i have recently leaned out my high screws as well. jetworks said to do this because of the humidity change from winter to summer.

 

[Matt_E]

the key is complete combustion of the most amount of fuel possbile for your compression, timing, and spark.

The ideal amount of fuel to be burnt is not determined by compression or timing or spark, but by air volume.

if you go from 150psi to 185+ that is a large compression bump, all we are saying is try and burn some more fuel, this will keep from detonating and burning pistons.

If you were on the lean side before the bump, then that is a great thing to do - because the greater heat at the bumped compression may indeed burn pistons.
More power from more compression = more heat. You're then dumping more fuel on it to decrease power (and thus heat) to keep a meltdown from happening.
So it's a safety factor. Perfectly reasonable answer.

hey matt, wasn't all your motors blowing up and stuff?

My last motor failure was in September 2009 from a bad crank bearing on a questionably rebuilt crank. What are you getting at? :lmao:

i have recently leaned out my high screws as well. jetworks said to do this because of the humidity change from winter to summer.

Eh, humidity never changes in Eastern WA. It's 10-20% year around.

 

[Tyler Zane]

Eh, humidity never changes in Eastern WA. It's 10-20% year around.

thats why i quoted D-ROC. it was to help others understand why we lean it out.

 

[D-Roc]

air density changes with temps.
what ever the ideal amount is for your motor, the more fuel you can burn will make more power. i will agree that the bump in compression is the biggest factor for the hp gains with the ada head. adding more fuel to the mix to cool and not melt down is proper saftey but if the added compression is able to burn a richer fuel charge completely, then you will have more power than if you burn a leaner charge. they work hand in hand imo. you haven't blown a motor since you stopped building them yourself? lol thats all. and you don't turn screws so that is fine too.

 

[Matt_E]

Never blown one due to deto or lean seizure.
Let's seeeee......water ingestion, throttle plate screws, and another bad crank. :biggrin:

 

[D-Roc]

oh my bad, poor mechanical assembly/failure but proper tuning. sorry. haha. I think we are saying somewhat the same thing and i somewhat agree with what you say. i have been able to swap my carbs from my 735 to my 771 and not rejet, yet. there was a 25psi drop in compression. it runs good but i am still chasing perfect piston wash and front plug reading. i almost have it but it is still rich even in these cold air temps. usually i need to fatten the carbs in cold weather but right now i am still leaning them out. mu 735 with 195psi had better burning than this 771 @ 170psi with the same jetting. I have been adjusting my high screws every ride to get it running clean and crisp and the last ride i noticed my back is perfect and front is getting there. when you add the high compression head, you don't adj. the screws to have an over rich reading, you set them so you get the perfect "ideal" reading which most likely will be achieved by adding a bit more fuel. so being able to burn more fuel (a richer ideal charge) will make more Hp.

 

[Proformance1]

We are getting off topic on this thread. What r your thoughts on exh then? It doesn't change the amount of air entering the motor??

 

[D-Roc]

different pipes will allow the motor to run different amounts of fuel in the "ideal" ratio.

 

[Matt_E]

We are getting off topic on this thread. What r your thoughts on exh then? It doesn't change the amount of air entering the motor??

Yes, different pipes make for different air flow.

 

[easyrhino]

My guess: increasing compression will make the mix more volatile and rate of cumbustion will be quicker.

If you're tuned to the edge of distruction, go richer or use higher octane or retard timming. Going richer and retard timming will improve bottom end and hurt top end. Higher octane will improve power thru the whole rpm range.

 

[D-Roc]

i advance timing for bottom end retard at high rpm which keeps my motor alive but flattens the high rpm powerband.

 

[easyrhino]

i advance timing for bottom end retard at high rpm which keeps my motor alive but flattens the high rpm powerband.

Advancing the timming makes cylinder pressure, similare to raising combustion ratio. You'll raise cylinder pressure when rpms are not on the pipe and retarding timming when gets on the pipe.

 

[D-Roc]

sure do!

 

[B3IS]

Absolutely. I have done so a few times in the past.

Tell me why increasing compression (and not changing to oxygenated race fuel or something like that) would require rejetting. I am intrigued.

When you guys rejet, what change do you see after tuning it and all that? 2.5 pts? 5 pts?


Thermodynamically speaking, the added power comes from a more efficient burn at higher compression (compression is one of very few factors determining the output power of an internal combustion engine).
This is what increases hp, not adding fuel. The air flow through the engine has not changed, only the efficiency at which fuel is burned. It doesn't need more fuel, it makes better use of the fuel that's there (hence the added power).
/nerd hat off.

Now, for real world experience:

Do you turn the screws a certain amount based on the engine stumbling? Do you turn them some amount "just because", or based on previous experience? Do you use a tach?
I'm asking because I've never felt the need to turn the screws after changing compression. No hesitation, no stumbling. However, I've never used a tach.

Wait dont get him started oooh well ok get em Matt. When I dont take you as serious it makes this so much more fun. Thanks for the tech info.