28* initial timing for a 318? How can that be?

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I think thats enough snips for discussion while still falling under 'fair use'.
Curious if there are any observations about piston dwell time and intake valve closing points. In your own words is fine. Just a couple of other factors that can come into play with spark lead.
 
Mattax said:
I think thats enough snips for discussion while still falling under 'fair use'.
Curious if there are any observations about piston dwell time and intake valve closing points. In your own words is fine. Just a couple of other factors that can come into play with spark lead.
Click to expand...

Yup. Dwell time affects timing in my experience.

Plug location, rod to stroke ratio and then chamber shape are the three big factors that affect ignition timing, along with compression ratio and fuel used.

The quicker the piston moves away from TDC…
 
Newbomb Turk said:
Yup. Dwell time affects timing in my experience.

Plug location, rod to stroke ratio and then chamber shape are the three big factors that affect ignition timing, along with compression ratio and fuel used.

The quicker the piston moves away from TDC…
Click to expand...
You ever do any testing using various quench distance on a given combo.
 
Mattax said:
Geoff. This isn't tribal. People who disagree with your assertions are not traitors - that implies a personal loyalty or membership in the tribe. It's engineering, mechanics, and science. It has nothing to do with loyalty.
Secondly, a real friend tells you like it is, unless for some reason its so painful as to be inapporpriate.


Insults like this certainly haven't helped you win friends.

Yes, but you've made some outrageous claims, which makes everything else you post suspect.
Even if you were well known here, I don't know that would make a difference.
For example, I really liked David Vizard's writing. Then I got burned by following some of his guidance. Fame doesn't equate to knowledge. Not many have heard of Tuner, who prefers not to be named on the 'net, or Bruce Robertson for that matter, or Klaus, the founder of Innovate Motorsport.

I think you are referring to the person who has posted several videos running an Allen for the collective benefit. That's a pretty generous thing to do. Anyone who had not observed this with their own testing can see the facts.
Of the other people mentioned, I actually know who they are, either directly or indirectly. A surprising number of FABO I've met in person. One even showed up at an autocross with his family a few years back.
Tuner as I mention in the other thread has worked on several road race cars of people I know. Dick Ott in particular was builder and driver I highly respect, as did everyone who knew him. The guy who first mentored me was very successful tech and builder when he was involved in stock eliminator. Ten years later Jerry Stein told me yup, that guy was good - a little nuts - but thats another story.
So why do we beleive some people and not others? Some is about credibility, and the other part is that a bunch of this isn't about belief. It's about understanding what factors play into flame development under various conditions and various ways to create spark lead time.
Click to expand...
Excellent post
 
Newbomb Turk said:
Yup. Dwell time affects timing in my experience.

Plug location, rod to stroke ratio and then chamber shape are the three big factors that affect ignition timing, along with compression ratio and fuel used.

The quicker the piston moves away from TDC…
Click to expand...
Shape of the top of the piston (dome, dish, etc) is a HUGE contributor also.
 
StreetSleeper,
Do you have Hammill's book on Weber carbs? It says this about idle timing on p. 94

img402.jpg
 
Mattax said:
I think thats enough snips for discussion while still falling under 'fair use'.
Curious if there are any observations about piston dwell time and intake valve closing points. In your own words is fine. Just a couple of other factors that can come into play with spark lead.
Click to expand...
I think one could theorize the crap out of how timing might be affected by different variables.

Not sure how I would design the testing to actually prove it. You would need to control all the other variables so you can see the results of how just that single variable does or does not affect the timing.

As a thought experiment, how would you set up the test to determine the effect that piston dwell time has on the engines timing requirements? What variables do you see as a challenge to control?
 
Timing is such an easy subject to learn. There should be ZERO argument about it since you can try it a multitude of ways and put it back the way it worked best when you get through testing. It's not like you're set in stone when you change it.
 
92b,
The long-er rod engine has the piston dwelling more at TDC. So it needs less timing, all else being equal.
 
Bewy said:
92b,
The long-er rod engine has the piston dwelling more at TDC. So it needs less timing, all else being equal.
Click to expand...
How would you test that? How much longer would a rod have to be to see a difference? How much of a difference would it be? I think engine masters did a rod length test. I can't remember if they swept the timing on both rods to see if there was a difference in optimal timing. Anybody else remember or have a link?
 
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Newbomb Turk said:
I do, but I’m in the middle of getting screwed by a Chrysler block and I’m going to have to drive over three hours to get it fixed.

No one here has the tool to fix it and that blows.
Click to expand...
Cool, maybe you can post it up when you get back.
 
92b said:
How would you test that? How much longer would a rod have to be to see a difference? How much of a difference would it be? I think engine masters did a rod length test. I can't remember if they swept the timing on both rods to see if there was a difference in optimal timing. Anybody else remember or have a link?
Click to expand...

The only way I can think of is you’d need to start with an engine like a SBC so you can get parts easier.

Then you’d need to start with a short rod, like 5.65 or whatever the 400rod length was (I’m sure that’s close but it may not be exact) and then test it against a 5.7, 5.85, 6.00 and 6.25 rod.

But…as you know none of that is in isolation. Changing the r/s ratio changes how the engine pulls fuel and burns it so that’s probably not very accurate anyway.

What I do know is I built one 5.65 rod 400 for a circle track deal back in 1996.

That engine always took way more timing than I thought it should have.

The owner of it was scared to death of an engine that wanted at least 42 total so he took it to a dyno that was about 5 hours from us and flogged it for two days.

He came back and said it was a waste of two days because the timing was what it was.
 
92b said:
How would you test that? How much longer would a rod have to be to see a difference? How much of a difference would it be? I think engine masters did a rod length test. I can't remember if they swept the timing on both rods to see if there was a difference in optimal timing. Anybody else remember or have a link?
Click to expand...


They built two engines, identical except for rod length and compression distance. I am not sure however if they published the necessary timing requirements between the two, but I can guarantee you that Brule ran timing sweeps on both.
 
RustyRatRod said:
Timing is such an easy subject to learn. There should be ZERO argument about it since you can try it a multitude of ways and put it back the way it worked best when you get through testing. It's not like you're set in stone when you change it.
Click to expand...
Quantifying the results of changes that move the needle only 5,10,or 20 hp is the difficult part. In your driveway you can run the timing all over the place and take it for a drive but all you can say really is “it feels better, or it feels worse”. This type of testing (minutia) really has to be done on a dyno under very controlled circumstances with very controlled variables.
 
TT5.9mag said:


They built two engines, identical except for rod length and compression distance. I am not sure however if they published the necessary timing requirements between the two, but I can guarantee you that Brule ran timing sweeps on both.
Click to expand...


I forgot about this.

Didn’t they say in the video what timing they used?

Dammit, now I have to watch it lol.
TT5.9mag said:


They built two engines, identical except for rod length and compression distance. I am not sure however if they published the necessary timing requirements between the two, but I can guarantee you that Brule ran timing sweeps on both.
Click to expand...



Ok, I watched most of this. I remember why I didn’t like the test.

There is no way, no way you would build an engine with a .2 point difference in r/s ratio and use the same cam timing.

You just can’t do that.

I get what Freiburger was doing. He wanted to isolate r/s ratio and changing cam timing would have taken away that isolation.

But that’s the rub. None of this happens in isolation.

If I get a minute I’ll do the math up for both combinations and show the difference in cam timing for both rod lengths.

I just need to go back and look at where peak torque and power occurred and what the exact compression ratio was.

Then I’ll do some math and post the results.

Frieburger also said there was a two degree difference in ignition timing, but he said the long rod wanted 34-38 and there was no difference in between. And the short rod engine wanted no less than 40-42.

I’m don’t think they used a curve because they had a crank trigger. Obviously they could have used a programmable ignition but I didn’t see what they are using.

IMO with a curve the long rod engine would have made more torque at and around peak and more power at and around peak.

That goes for both engines. But they would want different curves.
 
That's a good analysis and I think sums up the challenges of what they were trying to do given their situation.
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@92b Totally agree one could go through many permutations but fortunately we don't have to. We can generally find a baseline developed for something the same, or at least similar.

As far as 'thought experiment' that's where I've observed people get into trouble. Just 'cause we think something is going to behave a certain way, doesn't mean it will.
However, there are several pretty well developed computer engine simulation programs. I have Dynomation 5, which is now a bit old, but still a decent one although it has limitations. Anyway at one time I tried to change the rod crank to see if it had any effect on the 'best' timing and it didn't. However IIRC I was using the Fill Empty model. Perhaps if I used the wave modeling, that would have taken into account the piston dwell time. So maybe Dynomation 5, and more likely its replacement can model that. The limitation may have been the user (me).
 
I ran my math for this engine. The numbers are startling in several ways.

I used the exact same specs for both combinations where it mattered. Peak torque at 5700 and power at 7300. And an effective compression ratio of 11.5 with a SCR of 12.4

The numbers they gave on the show for the cam the picked is 284/296 on a 112. We have no idea where it’s timed at because Dave didn’t say.

My numbers for the long rod engine:
271/282 107/105

I quickly picked some bullet lobes. This is probably what I would have used. If I looked harder at Comp and Howard’s I may pick different lobes but this is close enough.

Long rod engine:

R303/4665 303-271-193-.4665 (.782)
R314/4620 314-282-200-.4620 (.785)

IVO 46.5 BTDC
IVC 76.5 ABDC
EVO 86.0 BBDC
EVC 48.0 ATDC
94.5 overlap

Short rod engine:

R303/4665 303-271-193-.4665 (.782)
R320/4414 320-285-205-.4445 (.756)

IVO 43.5 BTDC
IVC 79.5 BBDC
EVO 92.0 BBDC
EVC 48.0 ATDC
91.5 overlap

The long rod opens the intake valve 3 degrees later than the short rod.

The long rod closes the intake valve 3 degrees sooner than the short rod.

The long rod opens the exhaust valve later than the short rod.

The long rod and the short rod engine close the exhaust valve at the time.

The long rod engine has 3 more degrees of overlap.

It would be interesting (and costly) to repeat the test and change cams for r/s ratio.

I’m not sure why the torque peak was at as low rpm as it was with 13 more degrees of intake duration on the cam they used in the test.
 
Mattax said:
That's a good analysis and I think sums up the challenges of what they were trying to do given their situation.
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@92b Totally agree one could go through many permutations but fortunately we don't have to. We can generally find a baseline developed for something the same, or at least similar.

As far as 'thought experiment' that's where I've observed people get into trouble. Just 'cause we think something is going to behave a certain way, doesn't mean it will.
However, there are several pretty well developed computer engine simulation programs. I have Dynomation 5, which is now a bit old, but still a decent one although it has limitations. Anyway at one time I tried to change the rod crank to see if it had any effect on the 'best' timing and it didn't. However IIRC I was using the Fill Empty model. Perhaps if I used the wave modeling, that would have taken into account the piston dwell time. So maybe Dynomation 5, and more likely its replacement can model that. The limitation may have been the user (me).
Click to expand...
Agree. I was thinking the thought experiment would be more for the design of the test and not so much predicting the results.
That being said I re-watched the engine masters test ( thanks @TT5.9mag for the link) and their question was more about the power difference. But they did sweep each rod combination for timing. There was a lot of behind the scenes work that was done to do this test. Probably no test is ever perfect but in my opinion it was well thought out and custom tailored for the format of the show.
I like to look at a test like that from the perspective of if I had to do the test what would be all the steps I would have to take to complete the test. I wonder how many man hours, including the building of the two short blocks when into that 25 minute show?
 
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