Max Lobe Ramp For Solid Flat

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My own mode of thinking about it - I would think that the only relevant part of designing an engine package that the DCR would be valuable for is to help determine the gasoline fuel type needed. That's how I use it anyway because I build pump gas street engines. But again - that's nothing to do with power output. Just the fuel type. By simplifying it down to "more DCR will give you more power" is relying too much on that one variable in the power equasion.

"Are you trying to say an engine with 9.5:1 DCR will not make more power than an engine with 8.1:1 DCR? I am sorry. I don't buy that. I think the assertion is incorrect."

I'm saying if that is the only indicator of power potential you have then you cannot provide any power output conclusions because in and of itself it's not enough info. That would only be the situation where the intake valve is closed earlier in relation to the piston position on the compression stroke. Take a Stock Eliminator engine. The intake valve can only move so far - so it has to stay open longer and the cams they run are long duration usually with some good overlap. That will reduce the DCR and the cylinder pressure at 100rpms significantly. So what does that tell you about how that engine might make power anywhere in it's operating range? What can you use that info for?
I'd call it similar to saying it's a 340 in a Dart vs a 340 in a Valiant. The cars are both blue. What horsepower does each one make? Without a lot more pertinent info you cannot predict power.
 
I have to disagree. Saying it only determines the fuel type, there's you giveaway right there. A higher DCR requires a better fuel, which in turn will make more power. You cannot just arbitrarily waive the type of fuel out of the discussion. It has everything to do with it. An engine with a 7.5:1 DCR that runs on 87 octane will in fact make less power than an engine with 10:1 DCR. I am taking for granted the builder of each engine built it as to take full advantage of each engine's DCR. In that way, the higher DCR will win every time, IMO. Again, more cylinder pressure, more power.
 
moper said:
My own mode of thinking about it - I would think that the only relevant part of designing an engine package that the DCR would be valuable for is to help determine the gasoline fuel type needed. That's how I use it anyway because I build pump gas street engines. But again - that's nothing to do with power output. Just the fuel type. By simplifying it down to "more DCR will give you more power" is relying too much on that one variable in the power equasion.

"Are you trying to say an engine with 9.5:1 DCR will not make more power than an engine with 8.1:1 DCR? I am sorry. I don't buy that. I think the assertion is incorrect."

I'm saying if that is the only indicator of power potential you have then you cannot provide any power output conclusions because in and of itself it's not enough info. That would only be the situation where the intake valve is closed earlier in relation to the piston position on the compression stroke. Take a Stock Eliminator engine. The intake valve can only move so far - so it has to stay open longer and the cams they run are long duration usually with some good overlap. That will reduce the DCR and the cylinder pressure at 100rpms significantly. So what does that tell you about how that engine might make power anywhere in it's operating range? What can you use that info for?
I'd call it similar to saying it's a 340 in a Dart vs a 340 in a Valiant. The cars are both blue. What horsepower does each one make? Without a lot more pertinent info you cannot predict power.
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exactly, as far as i know those motors spin 9000rpm or higher... they do that TO BUILD CYLINDER PRESSURE... because as you stated the long duration and overlap. they have to spin them to build power.
 
Rusty - I guesss we will just disagree.

kid - It's not cylinder pressure from the piston that creates the power. It's the pressure spike following the burn, and when in terms of crankshaft degrees that pressure spike occurs. Higher cylinder pressures prior to ignition are part of what's called pumping losses and do not indicate a higher output potential. Remembering that horsepower is just torque over time - the SE model is not a higher pressure at peak rpm. It's strictly a lot of firing events per minute that gives them horsepower at higher rpm. Here's something to play with - A factory 340 has a torque output of 289 pound feet at max horsepower (275hp @ 5000rpm). A Super Stock that makes 465hp @ 8500rpm, makes the same torque - 288 pound feet. It's the torque over time that drives the HP numbers. Play with some horsepower to torque calculators and you'll note that. It's not higher cylinder pressure.
 
I am completely open to agreeing. But no one yet has explained in any depth how DCR does NOT effect power output. I have explained how I believe it does. I'm all about learnin. School me. I ain't seen no evidence goin your way yet.
 
hypothetical:
You have a 340 (engine A) that has 8.75:1 dynamic and should have 180psi of cylinder pressure turning with the starter. How much horsepower does it make and how do you figure it out?
You have a different 340 (engine B) that has a dynamic of 7.9:1 and should have 130psi tunring with the starter. How much horsepower does this one make and how do you figure it?
Which one is the bigger power producer? Why?
Maybe you can school me - I'm always open to other ideas.
 
See...this is where we're getting to what "I" am talking about. The 180 PSI engine will be the winner they way I am talking about. What I mean with both engines built to take full advantage of their given DCRs. You understand what I'm saying? Not just slung together, but purpose built. In other words, all of the parts to make max power at a given DCR. In that scenario, the higher DCR wins out every time. Does that make sense?
 
It does when you make certain assumptions, yes. But how do you know it will just using those two figures?

edit - I think we are in agreement - but you are making assumptions that things are doen right and I'm not making any assumptions.
 
ok lets re-phase that question... how does higher compression. i mean DCR not make more power?
 
moper said:
It does when you make certain assumptions, yes. But how do you know it will just using those two figures?
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Of course I don't. But that would mean someone doesn't know how to build an efficient engine, now wouldn't it? I'd like to think that most of us here know how to take advantage of DCR and use it to its fullest extent. But of course, just DCR alone doesn't mean anything. DCR and common sense is another thing entirely.
 
805moparkid said:
ok lets re-phase that question... how does higher compression. i mean DCR not make more power?
Click to expand...

Simple. If somebody doesn't take it into consideration when building an engine. Id you don't build the engine to try and take full advantage of DCR, it will not make the power it could. But like I said, most of us here would not use that approach, so in our case, the highest DCR would win out.
 
You guys are way above my pay grade. 805 I'm glad your car is coming along, I'm sure you will get the most out of this combo. All that reading gave me a headache, I thought I was back in college. lol
 
Turning into a good post.Any new info,on grind possibilities ?
 
Ed I really think you can do what you're wantin to on a .903 lifter. You just aint found the right company yet. You call Howards?
 
Performance trends has a program called "Engine Analyzer PRO" which has a theoretical minimum tappet diameter calculator that seems to be consistent (+ or - .001") with lobe grinds from several different cam manufacturers catalogues.

It takes into consideration the following.
Duration at any two of three lift specs (seat to seat, .050" or .200")
Max lift
Lash

I wish I knew the formula it uses to come up with these calculations.

Unfortunately the program itself is marketed at commercial businesses and is VERY expensive to buy legitimately.
 
moper said:
hypothetical:
You have a 340 (engine A) that has 8.75:1 dynamic and should have 180psi of cylinder pressure turning with the starter. How much horsepower does it make and how do you figure it out?
You have a different 340 (engine B) that has a dynamic of 7.9:1 and should have 130psi tunring with the starter. How much horsepower does this one make and how do you figure it?
Which one is the bigger power producer? Why?
Maybe you can school me - I'm always open to other ideas.
Click to expand...

If both of these motors are purpose build race motors running in the same class with the same rules. my money is on the 130PSI motor every time!

as an engine increases RPM it's volumetric efficiency goes up. this is because air is somewhat "stretchy".

At low speeds induction air is difficult to trap inside the cylinder. it's like trying to take a stubborn dog for a walk when it's leash is made of elastic.

you have to stretch the leash 5 feet to get the dog to move 6 inches.
(you are the piston, the dog is the air)


At high speeds, induction air is like a rabid dog towing smaller dogs on skateboards.

When the rabid dog hits a brick wall, the other dogs on skateboards have no choice but to do the same

(the brick wall is the piston at BDC, again the dogs are the air)

At cranking speeds, inertia tuning doesn't come into play whatsoever.

the 130 psi engine would probably rev harder and create more dogs on skateboards when the pedal hits the floor.

Sorry for the ridiculous analogy.
 
Frosty - I have Engine Pro and the book that is meant to acompany it and I've spoke to Don before. Engine pro is based off both math (and every formula is available from him) and thousands of real world results from various racing programs. It's pretty accurate because it's more than just the math. However - in terms of valve motion - the the program only plots those three points because for the most part the subtle differences in lobe shape do not present dramatic differences in the actual power produced. So to simplify the calcualtions and better represent the empirical data that Pro was based on they dumbed it down.

In terms of my hypothetical - in my opinion - assumptions have no place in the discussion. The "correct" answer (again - by my thoughts) is there is not enough information given. you cannot tell which makes more power, or where in the rpm range based soley on those figures. In and of themselves, they mean very little in terms of total output until you apply them to a specific engine and in that case they are more of an indicator than a result.
Thinking of it in terms of a person - if I say "my temperature is 102°" you can assume I'm sick and have a fever or ask about more details of the situation. Is it hot out? What have I've been doing? How long has this been going on? Or even ask if I'm estimating or using a thermometer. But just saying I'm 102° means nothing on its own. I could be just sitting in a warmer room, I could be feeling "hot" and estimating, I could be running a fever, I could be suffering heatstroke, or I could have just come in from running and haven't cooled down yet and nothing's wrong. Same deal with DCR and cylinder pressure.
I hear over and over that you can tell output by those two figures alone. I have not yet seen any facts nor any formulas that can back that assertion up. Assumptions and gut feelings - certainly - but that's where I think the differences lie. I have the same conceptual ideas but I'm taking them out of the discussion and thinking about "just the facts".
 
Agreed, obviously measuring cranking pressure is not a good way to estimate the power output of an engine.

I was just trying to point out that if you have two motors. the one which has LESS cylinder pressure at cranking speeds *may* actually have MORE pressure at high RPM due to inertia tuning.

To my knowledge. In race engines, this is the case more often than not.

It's exactly the same as why a "big" cam makes less horsepower at idle than a factory cam.
 
well i have today off and i am going to try and squeeze in Crower, Howards, Bullet(Tim)... see what else was back in this thread...

Thanks Guys
 
Frosty's argument makes the most sense yet about how the lower DCR engine can win out. I do agree that as an engine's RPM goes up efficiency, cyl pressure all go up, to a point. Then fall off. You know, the old bell shaped curve again? You can see it on any dyno graph. Are there any simulation programs that take DCR into consideration? I guess if they all take all of the valve events for the cam into consideration, they do. That might be a half assed way to tell. And I'm sure there are advantages to both kinds of builds.

So then how bout I throw this question into the mix? If DCR makes no difference in power output, why does most everyone strive for the highest number given the fuel they intend to run? I certainly don't think it's for bragging rights.
 
RustyRatRod said:
Ed I really think you can do what you're wantin to on a .903 lifter. You just aint found the right company yet. You call Howards?
Click to expand...

frosty_the_punk said:
Performance trends has a program called "Engine Analyzer PRO" which has a theoretical minimum tappet diameter calculator that seems to be consistent (+ or - .001") with lobe grinds from several different cam manufacturers catalogues.

It takes into consideration the following.
Duration at any two of three lift specs (seat to seat, .050" or .200")
Max lift
Lash

I wish I knew the formula it uses to come up with these calculations.

Unfortunately the program itself is marketed at commercial businesses and is VERY expensive to buy legitimately.
Click to expand...

frosty_the_punk said:
Agreed, obviously measuring cranking pressure is not a good way to estimate the power output of an engine.

I was just trying to point out that if you have two motors. the one which has LESS cylinder pressure at cranking speeds *may* actually have MORE pressure at high RPM due to inertia tuning.

To my knowledge. In race engines, this is the case more often than not.

It's exactly the same as why a "big" cam makes less horsepower at idle than a factory cam.
Click to expand...

but you base SCR is also higher...
 
Geezzz this went out of whack. LOL Compression is good. OK? Dynamic compression or what ever you want to call it as I don't pay any attention to it unless I'm building something that will be octane limited and want a little backup for what I already feel. I can take a good running engine with say 180 cranking,run it on the track or dyno,recam it,lose 20 pounds cranking and pic up a bunch of power,no big deal,could I make more power with more comp? Yep, but I'd be looking for better fuel. CRANKING,DYNAMIC WTF ever numbers mean very little,but don't go crazy if your octane limited,there are no magic gains by pushing those magic numbers. Cam timing as well as other factors contribute to HP output to a larger degree than what happens at 400rpm on the starter. NO I'm not saying that good cranking numbers don't help drivability and mileage for a good running street car but do not think that that numbers tells the entire story if performance is your goal. Sorry if I made things difficult to understand.
 
skrews said:
Call Tim at Bullet.
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Once you have all your details in hand this would be very good advice. Tim's a great guy and I can say after knowing him for 25 years he will give you great advice.
 
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