Dome Size?

[BSPolice]

QUOTE..RKTEK "I have several engines that crank over at 140-150 PSI than will not live on anything less then 110 ocatane".... That statement in itself is enough for any engine builder and most members on this board with half a brain to know that you are clueless. I thought your designs added performance and reliability in almost equal proportions?...that statement says just the opposite. It's not that I wouldn't agree that combustion chamber designs that create more power on the same given comprression ratio are more prone to detonation, its just that a chamber needing 110 octane at 145 cranking psi is obviously designed very poorly or the engine itself is set up terribly wrong...either way, reliability obviousy wasn't part of the design.

[.]

all I know is that I boosted my compression to 170 psi and the bottom end screamed. You dont add psi for top end, you add it for getting you to the top end. It is a torque increaser.

 

I agree that there is more to it than that, and that if an engine has been taken apart before the cylinders could have been decked, and that squish angle and all the other aspects could create a better detonation to push down on the piston.

 

Thats what R&D is all about. You build a head, create a dome for it and dyno it, pull that dome off and put a different cut dome on....and dyno it. And you find the best dome for a stock engine setup....and run with that for your line. And if you create a better dome....you start running that one.

 

Now say dan at patriot racing builds me a stroker motor, He's gonna know what kind of cut dome is going to create the best downward force on the piston and cut me a dome to go along with it. Again R&D comes into it.

 

 

All in all, to put out an aftermarket head, you are putting out custom cut domes for a stock style setup. There has to be R&D work to be able to put one out in the first place. So maybe another company knows of a dome that could create better downward force on the piston, and has done more R&D work.

 

I for example, have owned my banshee from day 1, and if it goes to a machinist, I know every little thing done to them. When I talk to a builder when I get my engine worked on porting/stroking etc. I'm going to ask him about his domes and what he's tried, and what he feels works best and have him cut me a custom dome for that engines specifics.

 

RK Tek, say I have my stock engine, which I have an aftermarket head on it, and running 18cc domes at 175 psi. When I put my 21cc domes it drops it to like 135 or so. I notice a drop in torque. I can let off the throttle on flat ground and it will chug along until I hit the kill switch with the higher compression and it wont with the lower. Are you saying that you can build me a dome thats at like 135 psi or so that will create more power/torque than what my 175psi domes are creating?

 

Granted you may have more R&D design work on your domes than what are on the domes I have now, and might be able to create an ounce or two more downward thrust but 40psi difference worth? I'm not discrediting you, I just find it hard to believe from the power difference I notice.

 

Building domes for a worked engine is a different story. I dont know how much a longrod stroker engine varies from engine to engine, or from builder to builder but that all comes down to R&D as well. If they dont vary, then I assume that you've done extensive R&D on longrod strokers and know exactly what dome application needs to be cut for each application possible to create the most downward thrust on the piston? And if they do vary, I assume I'd have to send you my engine for you to build the way that you build engines and know from again, R&D, which way a dome needs to be cut to create the most power?

[RK Tek]

Are you saying that you can build me a dome thats at like 135 psi or so that will create more power/torque than what my 175psi domes are creating?

 

YES!.. I am not sureon the 135 thing but more like 140-150. LIke I said, I don't give a damn about the cranking compression... it means nothing to me but a health check of the engine.. you know a snapshot of the engine's "health".

 

What your PSI comes in at depends on many factors like Air density of the day. how fasy your kicking it, porting, elevation and a few others.

 

When you state you are going from 18cc to 20cc domes and loosing power.. I can believe that because you are switching to a 20cc dome of the same poor design rather than a 20cc dome that is tailer made for your engine. So, yes, switching from a wrong dome to another wrong.. you could gain or lose power.. but switching from a 18cc wrong domes to a 20cc correct dome could certainly add power and engine reliability.

 

Kelsey

[RK Tek]

.....

 

Granted you may have more R&D design work on your domes than what are on the domes I have now, and might be able to create an ounce or two more downward thrust but 40psi difference worth?

 

I missed this earlier so I thought you may want an answer.

 

Here is a HUGE misconception among people... The 150,160,190 PSI...etc. etc. cranking compression is NOT, I repeat NOT the internal pressure in your engine!! There is not an exact formula (that I know of) to determine the actual cylinder pressures during engine operation...BUT I can tell you that the internal cylinder pressures will be in the magnitude of 4-6 times (if not more) of the cylinder cranking compression.

So.. equating the cranking PSI with the "push" on the piston is not relevant because once combustion occurs... the cylinder pressures sky-rocket! So, the 40PSI difference in cranking compression is miniscule(sp) in terms of the pressures your engine is actually experiencing.

 

Ya see... cranking compresion means very little in terms of what is really going on inside your engine!

 

Your engine's function is to take heat and transform it into mechanical work. The amount of work that will be performed is largely based on the efficiency of this heat conversion.

In otherwords... the more effectively your engine (through combustion) can convert the heat to work.. the more work you will perform and hence the more power you can realize. This is why having a combustion process that is efficient can make your engine realize its full potential. Having a combustion process that is inefficient WILL make less power!!!So, even if you have an engine that has 60PSI more cranking compression than another engine ... If the engine with the lesser cranking compression is more efficient and can create more energy and push on the piston.. it WILL make more power!

 

Heat losses due to imperfect or incomplete combustion have a serious effect on the power that can be developed in the cylinder. Because of the short interval of time necessary for the cycle in modern engines, complete combustion is not possible; but heat losses can be kept to a minimum if the engine is kept in proper adjustment

 

Another common misconception is that the radial tension of the piston rings is what keeps the ring sealed against the cylinder wall.. But that is a whole other subject.

 

Hope this answered your question.

 

Kelsey

[.]

while cranking compression might not be the same compression as what the compression might be when the cylinder fires, it is a good guideline to gauge what fuel you need to run. Thats how the whole test came about. It would be hard to get a compression reading with the cylinder actually firing, so they found out what it was when it wasnt firing and found the area where you need to run race fuel etc. The 40psi difference could be a big difference in cranking pressure to actual firing pressure. You say 4-6 times greater. I'll say 5. say my pressure was 100. X that by 5 and its 500. Say it was 120 x 5. Thats 600. a 1/6th more compression. I'm sure thats not exact. But its the same general idea.

I tend to think of a cylinder as a pipebomb. To say that it is turning heat energy to mechanical energy is a little wrong. In fact it is the force of the explosion that needs to be transformed into mechanical energy. Take Nitromethane for instance. Very volatile, if you hit it with a hammer it will explode. One of the benefits of it is that it runs very cool and wont fry an engine literally. But it produces an immense explosion (600hp worth per cylinder in a hemi engine) Now explosion is a type of heat expansion, but not in the way that it is what is creating the power. If that would be so, those drag engines would be a molten piece of Iron by the end of the run. Thats why some run alcohol and methanol as well. Better explosiveness, and that burns cooler than gas.

 

 

Now back to the pipebomb theory. When it explodes it is going to find the easiest way of travel. In an engine it is the same theory. Which is going to be the piston. The idea of creating a better dome and combustion chamber is to create a way to direct that explosion more downard on the piston. And that is the way to effectively produce power in an engine. (That was the whole idea on creating the "hemi" engine in mopar which our engines have the same idea)

 

The way to create the most power in an engine with the fuel used is to find the compression that the fuel likes to be compressed at for the best explosion, and the right mixture of air mixed in to the fuel. And then take that force and direct it down on the piston as best as possible with combustion chamber design.

 

And as far as rings sealing, their is also the flex of the ring up and down that creates seal. Almost like a windshield wiper, but on a whole different level. I'm sure theirs other factors as well, but thats the main gist.

[RK Tek]

....

 

Well.. it appears that we will have to agree to disagree on this one.

 

1st of all.. there is not an explosion in combustion.. there is combustion which is quite different than an explosion.

 

You did some math and increase psi in the engine with the "5x" method.. BUT.. what you did not seem to understand was that if you have a head that combusts 60% of the F/A mix and you have another head that combusts say 75% f the mix... what does that do to the resultant forces acting on the piston?? Ya see.. this is the whole point.. it is about efficiency ... in otherwords.. how well the head does at combusting what is given to it.. if you have a head that combusts a higher percentage.. you WILL have more power than one that combusts a lower %...Make sense?? So when you are talking psi vs psi the lower psi chamber may have a higher effciency and therefore create more push on the crank train.

 

F/A that is trapped in the head and not combusted does NOTHING to aid the push on the piston.. So. if the head is such.. the energy created is not as great as a head that does not have a lot of trapped F/A mix that is not combusted

 

Kelsey

[.]

thanks for having this discussion with me, and our disagreeing has put us on the same plane. I'm all into new ideas.

 

Now for another question. Say your head that produces 140 psi is producing more power than anothers head that is 170 psi, can you produce a head that will produce 170 psi that will be even more powerful?

 

I dont know if designs would have to be changed or you could use the same idea, just on a tighter scale. I would guess it would change because you are dealing with a higher compression of the mixture which would be harder to make efficient.

 

I'm all into learning new things, and i've gotten crap about my posts being so long sometimes, but i'm like a curious kid that asks why a lot and you cant shut up sometimes.

 

Your last post put all the rest of the posts into a good general understanding.

[Blue Duece]

can you produce a head that will produce 170 psi that will be even more powerful?

 

you wouldnt think so, if its custom tailored to your combustion chamber the math would deterimine your psi, if kelsey can say oh yeah heres 170 psi regardless..... he would be doing exactly what he's saying is wrong with generic domes......but i could be wrong

[Oilsmoke]

Personally I like to see a Kelsey dome over a stock style Semi Hemi.

Any body Got a Pic?

[boonman]

QUOTE..RKTEK "I have several engines that crank over at 140-150 PSI than will not live on anything less then 110 ocatane".... That statement in itself is enough for any engine builder and most members on this board with half a brain to know that you are clueless. I thought your designs added performance and reliability in almost equal proportions?...that statement says just the opposite. It's not that I wouldn't agree that combustion chamber designs that create more power on the same given comprression ratio are more prone to detonation, its just that a chamber needing 110 octane at 145 cranking psi is obviously designed very poorly or the engine itself is set up terribly wrong...either way, reliability obviousy wasn't part of the design.

 

 

What y'all failed to notice hear, is that just because an engine has 140-150 PSI, that doesn't determine what fuel you ned to run. BSpolice, or whoever you are, is the one that is clueless. DO you know the port configuration and exhaust height and/or duration of the motor(s) that RKT has built that are in question here? Nope. That statement isn't the opposite. Here's why.

 

Say you have your bone stock motor, stock porting, stock everything, and you throw some 17cc domes and a coolhead on it. Now, lets say this yields you 170 PSI on a guage. you may or may not need race fuel. By the past thinking, you would run it, because you are over the 165 barrier. Now, lets say you send your cylinders off to be drag ported. You get the cylinders back, and throw it together. Lets say you now have 135 PSI on the guage. You scream oh no, and throw some 16's in there. Lets say that that brought you up to 145-150. You think, well, i'm under 165, so, no race fuel for me. So, you fill up wth 93, 94, or 91, whatever is the highest available, and you head out to Olds hill. You line up, take off, and halfway up the hill you have catastrophic engine failure. What happened? I'll tell ya, because you obviously don't know. DETONATION. Right here in this prime example it shows that cold cranking compressions CANNOT alone determine the octane requirement or all out performance of an engine. you don't need a ton of compression on a properly designed top end. I prefer to use the term top end, because if you have a shitty port job, and a rippin' combustion chamber, what will you get? Or, if you have a sweet port job, and a shitty combustion chamber, what will you get. SHIT. Everyone overlooks the fact that compression alone isn't top be used as a deciding factor in fuel selection. Well, not everyone...... And just stating that because an engine has 140 PSI and requires race fuel that it has a poorly designed head, is just simple ignorance. You don't even know the porting specs on it. So, how can you comment on whether or not it sucks? Maybe you are the almighty being, and can magically see these things. Either way, keep posting, I find your ignorance amusing.....

[Blue Duece]

i just run 100% race fuel, solves that problem we somehow shifted to the race fuel over pump vs psi topic, i want to know how all things being the same except one motor has 40 more psi than the other how the lower psi motor yeilds more power? since i can feel the power in the seat of the pants, am i just high or what, being a moron on the subject can someone answer this, "is the power i feel, not really real"

[boonman]

That rhymed!!!! lmao!!!! but, as you state, all things being equal, meaning same porting, same everything, except compression, I don't know how it can be possible. I am not an expert on the situation, but I am not a moron on it either... I would think that 2 motors, same exact everything, if RKT cut the domes for both bikes, optimizing the combustion chamber on both motors, how the lower compression one could yield more power..... All i was sayin was that with porting, static compression numbers mean nothing anymore..

[.]

hey deuce, I think he's trying to state that because of how the dome is cut, it is combusting a certain percentage of the fuel. Say I'm running a regular old pro design dome, and I switch from 21 to 18cc and run higher compression, I'm going to feel that.

 

Now say that I switch from my 18cc pro design dome to a 20cc dome that rkt custom designed for my engine. It may have a lower compression, but it will combust a greater percentage of the fuel, giving more downard thrust on the piston creating more power.

 

Now I'm sure if I went from the 20cc dome he designed to the 18cc dome he designed.....I'd feel the same increase, just on a greater level than with the pro design.....thats what he's trying to say I think

[Oilsmoke]

I agree with .

[Blue Duece]

that makes sense, would there be some sort of cut off point where the dome yeilding the greater psi just wins out over the custom dome?...and couldnt there only be one correct custom dome size, like i stated before if its designed behind your chamber and ends up being 100 psi, then i toss a dome that gets me 140psi it would have less power? can you make a custom dome yeild any psi you like? if so wouldnt that be the same as a generic dome?.....and bottom line is most guys just wanna bolt that head on and feel more power, i could see a guy who normally runs 180 psi go to a custom with 120psi start getting smoked and feel a hugh power loss, and when his buddies raze him he simply states "Your bike may smoke mine now, but i have custom domes, and your just running those shitty generic jobbies, so neneer, neneer"