Does this prove David Vizard's 128 lsa formula ?

[Newbomb Turk]

I guess what I meant was there a limit how low you'd run total timing to gain more CR,
Say your 10.5:1 engine runs at 35, but to go 11.5:1, you got to run 32, and 12.5:1, 28 etc..
Is there a point where you'd stop? I get it ain't simple as that and there's a bunch of variables.

Good question and I'm not sure I have an answer. If we are talking about pump gas stuff then about the highest I'll go for compression is 12 or 12.2:1. It may come it a skosh higher than that but on this particular build I'm kinda stuck there. Maybe on the W-2 engine I'll shoot for 12.5 or even 12.8:1. I don't have the gonads to try 13 unless I'm 100% sure I can make it work. 13:1 is a lot to ask of pump gas.

At any rate, I go as high as the fuel and combination will allow then back off the timing to keep it from detonating.

I think the big thing is not actually the total timing, but the shape of the timing curve that matters.

As compression ratio goes up (making the assumption that you cam timing is correct for your compression ratio) you need less initial timing. Then once you figure out where peak torque is, you have to get the curve to fit that.

As an example, you might need 20 initial at 1000 RPM but peak torque isn't until 5300 and at peak torque it wants 25. That means you have 4300 RPM to gain 5 degrees of timing. That's about 1 degree of timing per 860 RPM.

Then if you need say 34 total at 6800 you have 2500 RPM to find 9 degrees of timing. That's about 278 RPM per degree. Can you see the issue?

And most likely it won't want 34. It may only want 30 at 6800. What if it want's only 28? Or 27? That's what you do on the dyno.

So how low would I go? I don't know. If I could run 26 I would. The last I knew what Pro Stock was doing they we only at 26-28 total and that was at 10k.

As an aside, my mentor says the way he tunes nitrous is to set the timing at 4-5 degrees total and put the hose to it until it runs with the timing that far down. He told me he thinks people don't retard the timing far enough using NOS.

To that end (whether NA or power adder) we shouldn't be setting timing based on anything other than making sure the burn is 90-94% done by 12-18 degrees after TDC. The later you can light the plug and still get the burn done at the right time you will make more power.

Steve Morris posted a video yesterday about a PST engine he had on the pump. On his last pull he added 2 degrees of timing and he gained 20 horsepower IIRC.

The up is if you look at the curve you can see that 2 degrees more around peak torque hurt it. He didn't seem to care because it was probably low enough at the track it would never see that RPM under load but he is abusing it on the dyno if he's pulling it that low.

For a street/strip car or even a foot brake car you get too much timing around peak torque and you will kill power by what I consider a lot. Like 20-30 foot pounds.

You are playing the game of trying to get the most power over the widest RPM range. And that's not all that easy if you are a street/strip car and you don't want to retard timing at peak power to stop tip in detonation.

 

[Bodyperson]

You are playing the game of trying to get the most power over the widest RPM range. And that's not all that easy if you are a street/strip car and you don't want to retard timing at peak power to stop tip in detonation.

Hmm… this sounds familiar.

 

[RustyRatRod]

Ok George, this is YOUR baby so I'll ask you. How did THEY come up with 20%? Pull it out of their ***? Did they do a coast down test? Consult the magic 8 ball? Did they conjure the Witch of Endor?

Like I said, 20% sounds at least a bit low.

This is what happens when you worship numbers without asking a simple question.

It's the same premise as believing one man's formula is the end all be all for every single danged combination out there. Ain't happenin, I don't care how smart the guy is. I would "JUST BET" I can get closer using a good "educated guess", a degree wheel and a compression gauge.

 

[Ant]

Sorry if I sound like a noob, but I'm getting confused because everyone is talking about LSA and DV's 128 formula is for the LCA(lobe centerline angel). I thought, but do correct me, that LSA and LCA are two different things. I thought the LCA is the centerline angle of the lobe timing or something like that. IDK help?

 

[273]

DV makes it clear he's talking about the angle of the lobes ground in, he and some call it LCA most use LSA

 

[Ant]

DV makes it clear he's talking about the angle of the lobes ground in, he and some call it LCA most use LSA


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Ah, I see now. Thank you.

I did some math for a low compression 8.6: 1 or so 318 with stock 1.78in valves and would need an LSA of 105 degrees. I'm assuming this is for a ballpark max performance cam and not a normal street use engine that needs high vacuum, or at least for some cases.

 

[273]

Ah, I see now. Thank you.

I did some math for a low compression 8.6: 1 or so 318 with stock 1.78in valves and would need an LSA of 105 degrees. I'm assuming this is for a ballpark max performance cam and not a normal street use engine that needs high vacuum, or at least for some cases.

No that would be his recommended lsa, for street and or race.

Say you like comps xe256h cam on 110 for your engine, to DV that choice basically you'd keep the same basic overlap and cut the cam on 105 lsa with that overlap and that would give you your new duration, probably something like a 250 cam on 105 lsa if you could find such a thing.

Basically find a small RV cams cut on 107-110 lsa and you'll be close to DV recommendation.

 

[273]

Really DV formula only helps you pick the LSA of the cam, your supposed to calculate the required LSA pick what you figure is the needed overlap and calculate the duration from those two, not really much of an overall cam formula.

His overall point is people generally run too much duration on too wide of lsa, instead running tighter lsa with less duration, with the same overall overlap.

 

[273]

 

[Mattax]

How much timing would you be willing to lose ?
Eg.. total 32/30/28

To that end, I'm not sure why being able to reduce timing is a bad thing. You want peak cylinder pressure by 14-18 degrees ATDC. If you have to fire the plug at 40 degrees BTDC you have pretty close to 35ish degrees of crank rotation where chamber pressure is working against making power.

Exactly. "Willing to lose" suggests that more is better. It's not. Timing is about what the engine wants under that specific condition. The only time less advance is a "loss" is when an engine is was designed to run with a fuel that was more knock resistant than what is actually being used. We see the newer engines and even heads alone are more efficient and so less advance is needed under full throttle. That's not a loss.

 

[273]

Exactly. "Willing to lose" suggests that more is better. It's not. Timing is about what the engine wants under that specific condition. The only time less advance is a "loss" is when an engine is was designed to run with a fuel that was more knock resistant than what is actually being used. We see the newer engines and even heads alone are more efficient and so less advance is needed under full throttle. That's not a loss.

The question was based on that to run more cr than people are generally willing to run eg 12:1 instead of 10:1 that you would have to run less than ideal timing cause of pump gas. (Wasn’t my assertion)

Say for 12:1 ideal timing was 33 degrees how much less than ideal timing would you run (for pump gas) that it becomes we’re it wasn’t worth going to 12:1, eg. 32,31,30,29,28 etc..

If I remember right that was the basic question.

 

[Mattax]

The question was based on that to run more cr than people are generally willing to run eg 12:1 instead of 10:1 that you would have to run less than ideal timing cause of pump gas. (Wasn’t my assertion)

Say for 12:1 ideal timing was 33 degrees how much less than ideal timing would you run (for pump gas) that it becomes we’re it wasn’t worth going to 12:1, eg. 32,31,30,29,28 etc..

If I remember right that was the basic question.

Yea well that's a rabbit hole, and one argueabley worth putting effort into by a magazine or publisher interested in helping hotrodders. Certainly many of us have been on the edge of this or well into this situation (ie screw up) with both street and race setups. It's a rabbit hole because there's many approaches to the engine combination in trying to come up with the appropriate static and dynamic (another area of debate, but I think a useful tool) compression for the fuel. Yes Vizard did try to provide some guidance on this back in those books. Another work around/solution was water injection.

Also its not just the octane that effects performance. There can be two fuels of similar octane that perform differently. Not just at the track. In some of the RFG studies its been shown some engines actually run better (better mpg ) because of the oxegenates while others run worse. This stuff is above my head but I think the extreme example is if one wants to run NOx as a power booster the best results will be if the engine was designed where NOx can be favorably used.

 

[Newbomb Turk]

The question was based on that to run more cr than people are generally willing to run eg 12:1 instead of 10:1 that you would have to run less than ideal timing cause of pump gas. (Wasn’t my assertion)

Say for 12:1 ideal timing was 33 degrees how much less than ideal timing would you run (for pump gas) that it becomes we’re it wasn’t worth going to 12:1, eg. 32,31,30,29,28 etc..

If I remember right that was the basic question.

Think it through. Compression makes power and it makes power everywhere. Compression makes the chamber packed tighter. A tighter packed chamber requires less timing.

So why not up the compression and unfuck the tune up so you can do it?

On pump gas, a 9:1 engine may want 35 total. That same engine at 11:1 with the exact same parts will maybe only need 30 because the chamber is packed tighter.

Plus that extra compression allows you to use different cam timing. It just works.

Unless of course you are stuck in 1980 and can't get out of it. That means slow cam lobes, coolant temperatures over 180, an all in by 2500 timing curve or worse yet locking it out just makes it much harder to run higher than orthodox compression ratios on pump gas.

I had a 12.5:1 engine on the dyno a week ago. He was bound and determined to run Avgas but it looked to me like it lost power with it. I say with what he was doing I could have easily tuned it for pump gas (safe tune up) and it would have made more power.

And 110 would have made less power regardless of how much timing was jacked into it.

But most guys won't learn because it's too hard and it upsets their lifetime paradigm of what can't be done.

 

[Ant]

So... once I have the duration I'm assuming that number is the off the seat number?

What if the spec of cams to choose from only have the advertised duration at .050 tappet lift?

 

[Newbomb Turk]

So... once I have the duration I'm assuming that number is the off the seat number?

What if the spec of cams to choose from only have the advertised duration at .050 tappet lift?

You really need the seat to seat timing numbers and at what checking height was used to get it.

The engine sees seat to seat timing. Not at .050 timing.

 

[Hysteric]

Exactly. "Willing to lose" suggests that more is better. It's not.

Exactly the better the burn the less time that is required to do it.

 

[Mattax]

My opinion @Ant is for what you want, go with one of the cam guys that you're comfortable with. You want to experiment and/or compare? then sure do a DV formula and pick one yourself. You want something that will do what you want withoutout much risk? then go with one of the guys in the business. Guys spend a lifetime in this and the smart ones are always learning and they have the experience to keep you from taking a risky path. Mike Jones, Racer Brown, and there's others. In some cases it might be the guy your engine builder or shop has worked with. As part of my decision making, if looking to take advantage of the engine design - and it sounds like you are - go with a guy who is familiar with what makes your engine different from a Chev 350, or Windsor, etc.

 

[Hysteric]

As an example Dan Smiths 410 stroker 360 with stock ported heads runs 9.6s at 3050 lbs. He does that with just 28 degrees of total timing. The exceptional performance and the fact he does it with only 28 degrees of total timing is the give away. The burn is very fast and efficient. Slow burns don't make power.

If you want to make more power and increase the HP to CI ratio fix the burn......But to do that you need to understand what the burn is and how its place and that takes smarts.

You wont learn that from reading magazines and watching Youtube dyno clips.

 

[273]

As an example Dan Smiths 410 stroker 360 with stock ported heads runs 9.6s at 3050 lbs. He does that with just 28 degrees of total timing. The exceptional performance and the fact he does it with only 28 degrees of total timing is the give away. The burn is very fast and efficient. Slow burns don't make power.

If you want to make more power and increase the HP to CI ratio fix the burn......But to do that you need to understand what the burn is and how its place and that takes smarts.

You wont learn that from reading magazines and watching Youtube dyno clips.

What's the best combo you have built ?

 

[Newbomb Turk]

As an example Dan Smiths 410 stroker 360 with stock ported heads runs 9.6s at 3050 lbs. He does that with just 28 degrees of total timing. The exceptional performance and the fact he does it with only 28 degrees of total timing is the give away. The burn is very fast and efficient. Slow burns don't make power.

If you want to make more power and increase the HP to CI ratio fix the burn......But to do that you need to understand what the burn is and how its place and that takes smarts.

You wont learn that from reading magazines and watching Youtube dyno clips.

Yup. The Chrysler open chamber has to eat a lot of **** from guys who don't have a clue just how good that chamber is.

I expect my engine to be in the 28-30 range and maybe, maybe 18 initial. It may take less initial

 

[273]

Yup. The Chrysler open chamber has to eat a lot of **** from guys who don't have a clue just how good that chamber is.

I expect my engine to be in the 28-30 range and maybe, maybe 18 initial. It may take less initial

Do you use pistons with quench pads ?

 

[Newbomb Turk]

Do you use pistons with quench pads ?

The piston absolutely positively has to come out of the deck. I will check it when I start putting my junk back together but IIRC they are .054 out of the block and IIRC that's about .040 deck clearance.

As a general rule I don't go any closer than .040 because after that, any gains and benefits are so small it would take a world class dyno to measure it.

That's kinda why 35 is the number IF the deck clearance is more than about .055 or so. Even at the same compression ratio a tighter deck clearance will reduce total timing.

 

[Hysteric]

What's the best combo you have built ?

I didn't build I just ruined it. It was the 360 with 302's. It was a real eye opener.

 

[273]

I didn't build I just ruined it. It was the 360 with 302's. It was a real eye opener.

Any details of the parts and work put into it and it's performance ?

 

[273]

So... once I have the duration I'm assuming that number is the off the seat number?

What if the spec of cams to choose from only have the advertised duration at .050 tappet lift?

Umm this might be wrong lol

Say you want an 50 degree overlap advertised and 4 degrees @ 0.050" with a 105 lsa, I'm sure you just add half of overlap to lsa and x 2 for duration.

50/2 = 25 + 105 x 2 = 260 advertised and 4/2 = 2 +105 x 2 = 214 @ 0.050"

Edit* just 2 x lsa + overlap = duration guess is easier eg.. 2 x 105 + 50 = 260, 2 x 105 + 4 =214.

And if you want a split cam both have to add up to total duration of both intake and exhaust of a single pattern eg.. 520 (2x260) eg.. so 256/264 on 105 lsa etc..

Pretty sure that's right, maybe someone will verify