445 Stroker Build Help

[My427stang]

Ahhh, I remember the days of having hair.

No doubt!  and I will one day fit in the suit I bought in college (1990) so I am not throwing it away

[scott foxwell]

I can calculate SCR without even having the parts in hand. It doesn't change in a running engine.
DCR or dynamic compression ratio... IMO there is no such thing. The word dynamic, alone, says it all...changing. It's a changing number and it changes throughout the operation of the engine. It might be useful as a reference, but I've never used it. Couldn't care less about it. Get the valve events right for the combination and it is what it is.

Scott, nobody is saying DCR predicts a running engine except you, and DCR is calculated before you buy parts, just like SCR, and it doesn't change in a running engine. (other than potentially a little timing chain stretch) Hogwash. That's absurd. Change lash, it changes. Change rockers, it changes. Change valve spring pressure, it changes and if you think nothing more than a little chain stretch occurs in a running engine, well, I'll just reserve comment on that.

It is ONLY SCR adjusted for intake valve closure and piston dwell, that's it.  Not trying to make you use it, but you continue to get hung up on the word dynamic, it's a stupid word that doesn't apply, we should shoot the guy who used it and change the name.

I deleted my post because I really don't care one bit about DCR. Never used it, but since you went there, answer this:
How do you calculate it? (Rhetorical...don't have to answer) Even you talked above about all the variations in numbers:

Here's something that I would say is a problem with DCR though and what I would say people should "bitch" about...what is the one calculation we will all use for DCR so we can compare results?

You can not tell me that you can accurately calculate the exact crankshaft degree where the intake valve closes. Just way too many variables. A running engine, that all goes out the window. Even if you can get close or have a consensus, it's a useless number. It means nothing. It references nothing useful. That, of course, is just my opinion.

[KMcCullah]

I've always liked Werby's explanation of DCR. In a nutshell...how much air are you "trapping"?

http://www.network54.com/Forum/74182/thread/1481408780

[My427stang]

Scott I see that you deleted your post, sorry I quoted you and it stayed.  However, you posted, so take a breath and realize that there are many people out there that build engines, you included, and we all have ways we do things.   This is not a fight, I will be respectful and I hope we can learn from each other, or if I am actually a moron, I hope to learn from you.  Believe me nobody wants out of this discussion more than I do. 

1 - Good point on changing intake valve closing point with rocker or lash. I simplified and you jumped, good on you.  However, we aren't talking about accounting for lash, we are talking a hyd roller.  You bring up a good point though, if a solid lifter cam is rated at .020 tappet lift plus it has lash, if someone wants to compare it to a .006 rise hyd lobe, it takes a little measuring and adjustment.  In fact, it's important to know your advertised measurements regardless of design, because as I pointed out, my little bench build cam is rated at .004 which I had to measure to accurately compare to an equiv .006 lobe.  I will even add fuel to your side, because the calculators plan for a symmetrical lobe, so if you want to use an asymmetrical lobe, you need to think a little. It's all about the valve event, something you hold dear, and should. 

So how does someone account for rocker and lash changes?  Well, if I put even more stock in DCR than I recommend, I would degree the cam off the retainer to know real IVC, but that's getting a little anal for that reason, but I have seen some wildly crazy rocker ratios so it is worth doing for other reasons. Most rockers are pretty good on FE, but have one roll in with Comp or PRW and things can be very different

However, what do you do when you do a rocker or lash change anyway, ignoring DCR?  Are you going to regrind a cam for a rocker change or lash change?  It's simply a tuning tool, and it's easy to say, more lash DCR rises, less it drops, more rocker ratio same thing.  You are grasping at things that affect your cam recommendations just as much...change rockers, set up rocker sweep, pushrod length in a stud mounted rocker, all that DOES affect DCR, but it also affects how a cam Straub grinds for you will behave. So it's an argument that applies with or without DCR in the picture. No one calculation provides all the info

2 - I will also agree that you cannot calculate exactly the intake valve closing point on a running engine at all speeds  However, you claim "Get the valve events right"  Talking out both side of your mouth, because if we cannot accurately tell when a valve will close, how do you get valve events right?  IVC is a valve event and it's based off of crank location.....that's what DCR uses

3 - Finally how do I calculate?  I trust a calculator built by someone else with results that I use over and over again and built experience with.  However, it isn't rocket science, just some trigonometry, as a guy who understand engines and specifically valve events, open your mind a little.  It's simply the SCR calculation using the volume of the cylinder at IVC.  It's the SAME as SCR after you figure out IVC, although it is adjusted a bit for rod angularity, which I am not sure how they account for in the programs.

Here is Pat Kelley's math for reference, keep in mind, once you get the adjusted stroke, its just an SCR calc

Calculating DCR: Calculating the DCR requires some basic information and several calculations. First off, the remaining stroke after the intake closes must be determined. This takes three inputs: intake valve closing point, rod length, and the actual crank stroke, plus a little trig. Here are the formulas: (See the bottom of the page for a way around doing all this math.)

Variables used:

    RD = Rod horizontal Displacement in inches
    ICA = advertised Intake Closing timing (Angle) in degrees ABDC
    RR = Rod Distance in inches below crank CL
    RL = Rod Length
    PR1 = Piston Rise from RR in inches on crank CL.
    PR2 = Piston Rise from crank CL
    ST = STroke
    1/2ST = one half the STroke
    DST = Dynamic STroke length to use for DCR calcs

What's going on: First we need to find some of the above variables. We need to calculate RD and RR. Then, using these number, we find PR1 and PR2. Finally, we plug these number into a formula to find the Dynamic Stroke (DST).

Calcs:

    RD = 1/2ST * (sine ICA)
    RR = 1/2ST * (cosine ICA)
    PR1 = sq root of ((RL*RL) - (RD*RD))
    PR2 = PR1 - RR
    DST = ST - ((PR2 + 1/2ST) - RL)

This result is what I call the Dynamic Stroke (DST), the distance remaining to TDC after the intake valve closes. This is the critical dimension needed to determine the Dynamic Compression Ratio. After calculating the DST, this dimension is used in place of the crankshaft stroke length for calculating the DCR. Most any CR calculator will work. Just enter the DST as the stroke and the result is the Dynamic CR. Of course, the more accurate the entries are the more accurate the results will be.

[scott foxwell]

LOL...ME take a breath? That's rich.
I don't care how many 1000 word posts you write.
You seem to want to dominate the discussion so I'll just let it go. I said what I had to say. Sorry you don't agree but you're not going to shove your "opinion" down my throat.

[blykins]

Aren't forums fun?   

[fryedaddy]

Aren't forums fun?

its better than days of our lives as the world turns or another world

[andyf]

Not sure why a 445 build thread turned into a DCR discussion but I'll jump in and say that I find DCR to be generally a bad thing. That is, people who don't understand much grab onto the DCR as a comfort blanket that tells them they can run cheap gas in their high compression engine. I see this all day long on various forums where some guy with a 12:1 engine with a big cam says he can run cheap gas since his DCR is 8:1.

For some reason people don't understand that the DCR calculation only works at low speed. As soon as the engine comes up on the cam and VE gets close to 100% you've got a 12:1 engine on your hands and there she blows. I can't think of a single good reason to pay attention to DCR unless perhaps you are designing a tug boat engine that only runs at 1500 rpm. If you're working on a performance engine then you need to pay attention to what the wave theory fairy is going to bring in the intake valve. The wave theory fairy doesn't care about DCR, when the intake and exhaust hit their sweet spot the cylinder is filling up regardless of what the DCR is. That is why Pro Stock cars with low DCR's make 1500 hp.

[Thumperbird]

Can someone please describe what the "scavanging affect is and how a cam plays into it?
It is my simple understanding this is related to overlap among other things.
Is DCR, for what it is worth which is obviously very debateable, really a numeric indicator of some sort of scavanging effectiveness?

Thanks.

[blykins]

Scavenging is when the exhaust port helps the intake port.  Scavenging is important and is really important when you have a big, slow, lazy intake port.  However, it only works when both valves are open at the same time, which is directly related to overlap, but not related to DCR.  We keep an eye on overlap when we have lazy ports, or when vacuum is a key factor.  There are ways to manipulate it in each direction.

[My427stang]

Not sure why a 445 build thread turned into a DCR discussion but I'll jump in and say that I find DCR to be generally a bad thing. That is, people who don't understand much grab onto the DCR as a comfort blanket that tells them they can run cheap gas in their high compression engine. I see this all day long on various forums where some guy with a 12:1 engine with a big cam says he can run cheap gas since his DCR is 8:1.

For some reason people don't understand that the DCR calculation only works at low speed. As soon as the engine comes up on the cam and VE gets close to 100% you've got a 12:1 engine on your hands and there she blows. I can't think of a single good reason to pay attention to DCR unless perhaps you are designing a tug boat engine that only runs at 1500 rpm. If you're working on a performance engine then you need to pay attention to what the wave theory fairy is going to bring in the intake valve. The wave theory fairy doesn't care about DCR, when the intake and exhaust hit their sweet spot the cylinder is filling up regardless of what the DCR is. That is why Pro Stock cars with low DCR's make 1500 hp.

Andy I agree with you, especially the first paragraph, but we part a bit on the RPM discussion.  I can't respond without writing a book LOL but if it helps, I see why people don't like it. 

As you pointed out, it's not a tool to pick parts.  Nor is it a tool to make maximum horsepower, but I use it as a tool to verify, tweak, and back up build planning, and that planning has to be logical.  Like anything...garbage in=garbage out.  In fact, I would say I use DCR primarily on street engines to see if I have room to gain a little vacuum and part throttle torque from cam timing more than anything with a secondary "no-go" use as Barry said.

If someone uses it to pick parts, especially picking a cam to kill compression, it's the wrong use of a tool.  I don't believe in that use of DCR at all and honestly, the guy who will do that probably has big problems, with or without DCR.

FWIW, I also look at water hammer and wave theory, old school 5th cycle stuff, effects of overlap and primary pipe sizing, and you are 100% correct that there are forces inside that increase cylinder pressure that are way more important than DCR for creating the curve, never mind the N20 planned here.

If anyone wants to discuss how I use it, I am happy to share by PM or another post, but I am going to wave off to save you all  from my broken record

[turbohunter]

Ross some of us enjoy reading and mulling over your "1000 word posts".
What I have a hard time with is why others are so easily offended when someone has a different take on the subject.

[fe-starliner]

  "X 2"..... N/M

[Drew Pojedinec]

Ross some of us enjoy reading and mulling over your "1000 word posts".
What I have a hard time with is why others are so easily offended when someone has a different take on the subject.

Marc, I'm offended by you being offended regarding other people getting easily offended.
I thought I knew you better than this.....
 

[turbohunter]

LOL
Hard time, not offended