Compression ratio

[My427stang]

I always add it in, it is there in all applications.

You could have also said that the CR was approx 11.7 and been a little closer to reality. As I said, it doesn't very much on a FE bore, from 4.08 - 4.26

Frank, you add another estimated variable and even estimate it for DCR?.   SCR to the second decimal point using an estimation is a little sloppy to base an argument on IMHO 

Here's a crazy fact, as you build many engines, the number doesn't matter...consistency in calculation and knowledge to apply what you see does, think on that

[blykins]

I always add it in, it is there in all applications.

You could have also said that the CR was approx 11.7 and been a little closer to reality. As I said, it doesn't very much on a FE bore, from 4.08 - 4.26

I said approximately 11.8.  11.7 is approximate to 11.8. 

Quit nit picking on something that’s inconsequential.

[Dyno]

I haven't used this link in a little while but it has some calculators for getting your numbers. Takes a little bit to get used to it.
Hope it helps.

https://www.gofastmath.com/Horsepower-Calculators/Horsepower-Calculator

[frnkeore]

So, you guys are trying to tell me accuracy isn't important, right?

I guess so, because you both have told me this multiple times! I'm not a engine assembler, I'm a machinist of 50 years and a mechanic before that. In MOST cases, there is a world of difference between the two, when it comes to accuracy. So, you can complain all you want about me being to accurate but, I will continue down this accuracy path. Who cares if there is very little or no difference between 7.8 and 7.82 DCR, the answer is I do. It's the way I was trained, to be as accurate as possible.

BTW Brent, you actually said 11.85 not, 11.8 and by your standards the 11.85, is closer to 11.9. Nit picking? I don't know but, I try to be as accurate as possible. If my calculation would have been 11.69, I would have said that.

BTW Ross, how much difference is there between the DCR for 87 oct and 92 oct at standard elev, intake temp and barometer pressure?

[My427stang]

So, you guys are trying to tell me accuracy isn't important, right?

I guess so, because you both have told me this multiple times! I'm not a engine assembler, I'm a machinist of 50 years and a mechanic before that. In MOST cases, there is a world of difference between the two, when it comes to accuracy. So, you can complain all you want about me being to accurate but, I will continue down this accuracy path. Who cares if there is very little or no difference between 7.8 and 7.82 DCR, the answer is I do. It's the way I was trained, to be as accurate as possible.

BTW Brent, you actually said 11.85 not, 11.8 and by your standards the 11.85, is closer to 11.9. Nit picking? I don't know but, I try to be as accurate as possible. If my calculation would have been 11.69, I would have said that.

BTW Ross, how much difference is there between the DCR for 87 oct and 92 oct at standard elev, intake temp and barometer pressure?

Use my words, not yours, I have never told you accuracy is unimportant.  I am saying you imply exactness when convenient to call out other people but are not really exact. It can be very misleading and frustrating

[blykins]

So, you guys are trying to tell me accuracy isn't important, right?

I guess so, because you both have told me this multiple times! I'm not a engine assembler, I'm a machinist of 50 years and a mechanic before that. In MOST cases, there is a world of difference between the two, when it comes to accuracy. So, you can complain all you want about me being to accurate but, I will continue down this accuracy path. Who cares if there is very little or no difference between 7.8 and 7.82 DCR, the answer is I do. It's the way I was trained, to be as accurate as possible.

BTW Brent, you actually said 11.85 not, 11.8 and by your standards the 11.85, is closer to 11.9. Nit picking? I don't know but, I try to be as accurate as possible. If my calculation would have been 11.69, I would have said that.

BTW Ross, how much difference is there between the DCR for 87 oct and 92 oct at standard elev, intake temp and barometer pressure?

1.  I’m saying that you’re nit picking because I said approximately, knowing that there were other variables.  You’d have to treat every single cylinder individually, Frank, to calculate the amount of accuracy that you’re discussing, that doesn’t have any bearing on anything.


2.  You don’t know the answer to the question you asked Ross, because you haven’t put an engine together in 20 years.

Lay off the nonsense.  Happy New Year.

[frnkeore]

Ross, all I said was that my calculation was 11.7 and that Brent had most likely left out the crevice volume in his 11.85. Both you and Brent, do that a lot but, it means something to me and it is the OP's favor, for his situation. We (Bent and I) used the same specs, because I re-calculated it with 0 crevice volume and I got his 11.85, doing that.

What is wrong with what I did?

Again:
 How much difference is there between the DCR for 87 oct and 92 oct at standard elev, intake temp and barometer pressure?

Happy New Year, Brent

[My427stang]

Frank, I am out the door shortly so can't keep up all this fun, to be honest I should keep my mouth shut. 

However

1 - The difference in what you said with an estimated crevice volume was 1.4% from Brent'... on a cranking compression of 200 lbs that under 3 lbs difference,.   Overlap effects will have more of a difference than that.

2 - Your DCR question is another attempt at the illusion of precision to pull away from the fact that yours was an apporximation too.  I can play a little but will not share the details of my "engine assembly"   I adjust a build based on range of variables I expect the engine to operate in, from experience,  DCR itself is only one tool in the box, when combined with all other factors that influence octane tolerance, it's a fool's errand to try to assign a DCR delta for the illusion of precision.

So despite your stern request, I can't answer in a way you would be happy with and your question is certainly designed to try to pit me against some other answer you found on the internet

[blykins]

What is wrong with what I did?

You know what you did.  You took a shot across the bow just to be a dingleberry about things. 

I put "approximately" for a reason.  The reason is that there are things, such as crevice volume, how far each individual piston is down the hole, what each individual combustion chamber volume is, etc.  that play into the compression ratio.  He gave a chamber volume of 68-69cc.  That's .1 of a point of compression right there.  If #1 piston is at zero and #4 piston is .002" down, that's another factor. 

You can't be anal about compression ratio when none of us have every single piece of data needed to perform the calculation.  So calling me out on being a tenth of a point off was completely asinine. 

To be straight up about it, every compression ratio calculation should be an approximation because so much plays into it.  Don't get me started on aluminum blocks again. 

And don't act like you have any idea on what octane numbers work with what DCR values.  You don't have any data for your own except for the data that we put up on dyno results or camshaft calculations that you see accidentally given out on a forum post.   You basically just read what the engine builders put up and then mooch the data. 

[frnkeore]

1 - The difference in what you said with an estimated crevice volume was 1.4% from Brent'... on a cranking compression of 200 lbs that under 3 lbs difference,.   Overlap effects will have more of a difference than that.

The question was, "What was wrong with what I did?"

Ross, regarding DCR, if you'll remember, you and I had a conversation (PM's) about 87 Octane and DCR, a couple of years ago, or so. Have you had any more insight, since then?

[frnkeore]

You know what you did.  You took a shot across the bow just to be a dingleberry about things.

Brent, I can't help it if you don't use all the info to calculate compression ratio's but, it's just like head gaskets, not all engines go together with a 1020 gasket. Head gaskets can vary from 4.65 to 14.20. As a matter of fact, the Cometic .040 (I just looked it up), comes in 2 flavors, 9.30 & 9.97 and it's on me, that I didn't ask.

Each time you leave out info, decimal points or round things, it changes the answer, in some way.

For everyone's info, Ford, at least through the '60's and earlier, didn't use crevice volume either, to calculate the CR's of any engines and in the early FE's it was substantial. The top ring land was .400 thick on the high compression engines of at least '58 & '59 on the E361 & 352's.

[blykins]

You know what you did.  You took a shot across the bow just to be a dingleberry about things.

Each time you leave out info, decimal points or round things, it changes the answer, in some way.

Exactly.  That's why I put "approximately" in my response to him.  I didn't have all the data and you don't either.   You can't call me out on not including crevice volume when none of us have all the data and his compression ratio can vary by more than .1 from cylinder to cylinder. 

Quit being a poser, Frank.  You try to come across like you're an engine building expert but you haven't put anything together in decades. 

[GerryP]

You know, Frank, it would be nice if a thread went on its logical course without falling into purse swinging, which adds zero value to the thread.  Nobody wins in these.

[frnkeore]

Gerry, I'm sorry but, I don't own a purse.

Brent is just trying to justify his non inclusion of something that is always included in real CR calculations.

I didn't start this, I only offered a CR calculation WITH the crevice volume. Brent didn't have to say anything or he could have said "yes, I didn't include that" but, instead, he took it to this level (with Ross's help, as always). I have only been defending myself.

I'd be interested in everyone's opinion on whether or not, people on this forum think that crevice volume should or should not be included in CR calculations, as a regular component of it.

I'm sorry that Brent can't take constructive criticism or correction where it's warranted.

[JimNolan]

If I were you (not knowing a lot about engines) I'd hang onto every word people like Ross Bullock has to say. He gave me advice on building an engine years ago. I built a 410 engine that produced 385hp @ 4600rpm, uses 87 octane gas for my 57 Fairlane. It's the big Fairlane (@4300 lbs w/me) and I consistantly ran the quarter mile in 14.3 seconds on 215 X 15 street tires. I've put about 35,000 miles on it so far and it's never been apart. When I got thru drag racing I put the engine in my 63 Galaxie.