440 Engine tuning suggestions

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92b said:
I agree with some of what you say but not all. It seems like one of the reasons you use as an argument against MVA is that it messes up the curve elsewhere in the rpm range. The examples you use to support this are in my opinion tuning it backwards. You're adding the MVA first. Why not tune the curve the way you think is the best mechanical then add and tune the MVA last if the motor wants it.

My opinion is that MVA would be better named as "vacuum advance at idle". It's less confusing. Ported vacuum is the same thing as MVA minus the vacuum at idle. Why even have vacuum advance? Why not just have mechanical advance? (By the way I think mechanical or centrifugal advance should be renamed rpm based timing or rpm timing for short.) To start with you don't need mechanical or vac advance. You can lock your distributor down and set it to a best compromised number and call it good. In some applications this is useful. Because motors will run better with less or more timing at different rpms adding mechanical advance is helpful. Engines also want different timing under different loads. Using vacuum as an indicator of load on the engine allows us to change the timing curve based on load. And we have two options for vacuum, manifold or ported. Of course now we have electronic timing control. Some would argue that is the best.

If you add MVA (again if the motor wants it) last then the "right mechanical curve" will still be the "right mechanical curve above idle." So if a timing problem occurs after adding the MVA it is a problem with vacuum advance curve. Which can be tuned in most cases for starting point and total vac advance added with different, modified or adjustable vacuum advance mechanisms.

I don't completely agree that if you can benefit from MVA or vac advance at idle that your motor is built wrong. How you build your motor depends on a lot of things including your application. There is vast range of possibilities for different combinations and it is likely that some will benefit from MVA.

The problem you expose with the time delay of the drop out of the vac advance may or may not be a problem. I could be more of a problem with a sticky mechanism or stiff diaphram. But again in my opinion it's not certain to be a problem in every case so why not try it first. Also if it is a problem it is likely to also be a problem for ported vacuum.

Probably the biggest problem again IMHO is having the time, patience and understanding to develop the best timing curve for your application. It can be a real time suck and you will be tempted to say at some point "good enough " or "I give up" or "I need someone else to do this"all legitimate responses. But if your committed and can develop the proper mechanical curve you can probably handle the vac curve. This process may involve comprises.

All that said I have the timing locked on one of my street cars and on my racecar. It's Fast ignition, doesn't retard with rpm like others and has a built in start retard. Is it ideal for the street car? Maybe not but I'm satisfied. For now.
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I was going to respond to was paragraph but it’s way too hard to do from my phone. I can’t do it on my laptop because my mom had some chickencrap internet from Verizon that if it was Amish speed it would have been faster.

Verizon got fired from everything and it will be Wednesday before I get real internet here.

So I’ll do the best I can and hopefully not go so long. Way too many long posts for me lately.


Ok, I’m sure we agree we both have a pretty good handle on how much total timing say a sbm will need IF it’s not some weird deal like mine.

We also need to agree that engines want LESS timing at peak torque and MORE timing at peak power. That’s just how it is and I can prove that on the dyno and in the car but it’s way easier on the pump.

I can’t recall the peak torque and power rpm for a 1968-1971 340 but I think peak power was at 5500. Peak torque is usually 1500-2000 rpm less than peak power.

In cases like that you can run a very soft curve, make decent power, acceptable economy and drive nice.

A good tuner can change the curve from OE and pick up power everywhere. It gets tricky when we use long duration, high overlap cam timing, headers and other aftermarket stuff.

Compression and cam timing are directly related and that correlates directly to effective compression ratio.

I use and call it effective compression ratio and not dynamic because it’s not dynamic at all.

Effective compression ratio is the compression ratio calculated using the actual stroke length and effective compression ratio is calculated from the length of the stroke MINUS the length of stroke from BDC to IVC. That never changes and it has nothing to do with dynamics or anything else.

Effective compression ratio is what the engine “sees” while running.

Damn, right down the rabbit hole. Anyway, you can be 12:1 static compression ratio (SCR) and have an effective compression ratio (ECR) of 8:1 if you get the cam timing to do it.

It would be an understatement to say the ECR dictates the timing curve almost as much as combustion chamber shape (including the geometry of the piston top), rod to stroke ratio (yes, it affects ignition and cam timing) and spark plug location. Maybe more so than the last two.

I need to take a break. I’ll pick this up in a bit.
 
Newbomb Turk said:
Effective compression ratio is the compression ratio calculated using the actual stroke length and effective compression ratio is calculated from the length of the stroke MINUS the length of stroke from BDC to IVC. That never changes and it has nothing to do with dynamics or anything else.
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Not understanding what you mean here.
 
92b said:
Not understanding what you mean here.
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I mean you can have a static compression ratio of…I’m just picking a number here 11:1 and by changing the IVC you can end up with an effective compression ratio from 8:1 to 11:1. Well maybe not to 11 because you’d be shutting the intake valve at BDC.

Following that line of thinking you can’t build compression until the intake valve is shut.

You can do the math using stroke length, IVC and I think r/s ratio but I don’t have the math right in front of so I’m not 100% sure on r/s ratio.

Let’s say (I’m going to make up numbers here for discussion) you have a stroke of 4 inches and the IVC is 65 degrees ABDC.

Doing the math you calculate how far the piston is up the cylinder by IVC and that is your effective stroke length.

Your effective stroke length will be the distance in inches (or mm if you like that better) from IVC to TDC.

Stroke length directly affects compression ratio. But, it doesn’t change your static compression ratio because we calculate that without regard to intake valve closing.

I’m going to run 12:1 or a skosh more SCR on pump gas with iron heads. It won’t rattle (the timing curve will be a bit of a challenge for sure) and I won’t have to retard total timing any more than if the SCR and the ECR are the same.

Wallace has a calculator for this. I can’t remember my IVC or I’d run the numbers and post them.

Let me see if I can find it.
 
Ok, I took a couple of screen shots showing the inputs on the Wallace racing calculator and another showing the results using numbers from my engine.

You can see that the piston is over 3/4 inch up the bore when IVC occurs.

That means my effective stroke length is 2.543 inches.

If we used the exact same numbers we used to calculate my SCR but we only changed the stroke length to 2.543 inches you would get my ECR and that’s what the engines “sees” when it comes to octane rating verses compression ratio (ECR).

IMG_1172.png
IMG_1173.png


In the first picture you see all the inputs.

In the second picture you see the results.

The second picture shows an ECR of 9.74 and an effective stroke length of 2.543 by doing the math.

That all means that under running conditions the engine “sees” a stroke length of 2.543 inches. And if we use all the same numbers we used to calculate the SCR except we change the stroke from 3.313 and enter 2.543 we get a compression ratio of 9.74, which is what the engine “sees”.

I don’t think too many people would say you can’t run pump gas on 9.74:1, assuming a proper spark plug heat range, correct coolant temperature and a timing curve that matches the torque and power curves.

Thats why IVC, effective stroke length and effective compression ratio are critical to calculate so you know what you have and then make an educated decision on the fuel octane rating you need for ECR.

There is nothing “dynamic” about ESL and ECR. They don’t change, just like SCR doesn’t change.

Each one is a distinct and different calculation and they don’t change with rpm, load or anything else.

That’s why I never say dynamic compression ratio because it’s totally different than ECR and it’s based off VE and a bunch of stuff that is over my head.

If you calculate you SCR and then do the math to get ESL and ECR you have won the war.
 
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Newbomb Turk said:
If I can’t get what I need then I’ll have to buy a crank trigger and a Programmable Digital 7 from MSD.

I really do NOT want to do that.

If by some miracle I get the curve acceptable then I need to start working on the VA
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This is kind of why a lot of people just end up locking the timing with H.P engines. Then have some kind of starting retard.

It’s not the ‘correct’ way to do it, but you can get 3/4 the way there without the endless hours of trying to mechanically curve a distributor. Plus not having to go digital and spending buckets of money.
 
Newbomb Turk said:
Ok, I took a couple of screen shots showing the inputs on the Wallace racing calculator and another showing the results using numbers from my engine.

You can see that the piston is over 3/4 inch up the bore when IVC occurs.

That means my effective stroke length is 2.543 inches.

If we used the exact same numbers we used to calculate my SCR but we only changed the stroke length to 2.543 inches you would get my ECR and that’s what the engines “sees” when it comes to octane rating verses compression ratio (ECR).

View attachment 1716375683View attachment 1716375684

In the first picture you see all the inputs.

In the second picture you see the results.

The second picture shows an ECR of 9.74 and an effective stroke length of 2.543 by doing the math.

That all means that under running conditions the engine “sees” a stroke length of 2.543 inches. And if we use all the same numbers we used to calculate the SCR except we change the stroke from 3.313 and enter 2.543 we get a compression ratio of 9.74, which is what the engine “sees”.

I don’t think too many people would say you can’t run pump gas on 9.74:1, assuming a proper spark plug heat range, correct coolant temperature and a timing curve that matches the torque and power curves.

Thats why IVC, effective stroke length and effective compression ratio are critical to calculate so you know what you have and then make an educated decision on the fuel octane rating you need for ECR.

There is nothing “dynamic” about ESL and ECR. They don’t change, just like SCR doesn’t change.

Each one is a distinct and different calculation and they don’t change with rpm, load or anything else.

That’s why I never say dynamic compression ratio because it’s totally different than ECR and it’s based off VE and a bunch of stuff that is over my head.

If you calculate you SCR and then do the math to get ESL and ECR you have won the war.
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I'll read your reply tonight when I have time. Go back to post 27 and re-read where I quoted you. I think you accidentally got words crossed up. I think I have a pretty good understanding of effective compression ratio. What you wrote in the quote had me scratching my head.

Also don't take this wrong but I think we might be to the point of hijacking this thread. I share in the blame for this. Hope the OP is getting his engine run on problem figured out.
 
92b said:
I'll read your reply tonight when I have time. Go back to post 27 and re-read where I quoted you. I think you accidentally got words crossed up. I think I have a pretty good understanding of effective compression ratio. What you wrote in the quote had me scratching my head.

Also don't take this wrong but I think we might be to the point of hijacking this thread. I share in the blame for this. Hope the OP is getting his engine run on problem figured out.
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I’ll go back and read 27 again in a bit.
 
AJ/FormS said:
@69dodgedart360
Your inbox is full.
When you've had enough of these clowns, call me.
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Clowns? CLOWNS?

If you have information that is useful and correct put on your big boy pants and post it on the forum.

This is exactly what “peer review” should look like.

Don’t be afraid that you will get exposed as a fraud and a troll like someone else did.

That’s a very bad look.

Man up and post it.

CLOWNS??? Hmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
 
It was hard to climb over the others stuffed in this car at the circus to post. The most informative post from the FABO "war and peace" writer is one of the shortest. Irony is thick in that one. :rolleyes:

To answer the OP about some questions
Initial timing, Based on other stuff I've worked on, somewhere in the 16-20 range is a decent start point.
Feed the mechanical in up to about 4K and have it around 34 total, no vac adv with this verification.
Should idle at 800 or so and drop to 700 in gear.

If it drops more than that, put a light on it to verify it still has whatever the original idle timing was set. If it drop from 18 to 16 in gear, fix the distributor with a heavier advance spring. You can't have timing drop when in gear, creates a tail chasing issue, lower timing lower rpm, less torque converter acts tighter. Slippery slope.

Now, I hope I can get outside and my big red shoes don't get caught on the door sill/jams tripping me up. LOL Stay humble up north there.
 
MVA is just one method of giving an engine what it needs for best idle. Best idle is when the engine makes the most hp from the timing you have given it. If you change the idle timing, & rpm drops, it is making less hp [ at idle ]. Co-inciding with the highest idle rpm will be highest idle vacuum....vac [ at idle/cruise ] being an indicator of engine efficiency: efficiency from the correct timing & fuel delivery.
There are other methods other than MVA of increasing idle timing. In the 70s, I was running a solenoid on the side of the dist. I am not familiar with the programmable ign systems, but they are another choice. And a locked dist.
For Hot Rod Joe, MVA is probably the easiest, cheapest & most reliable. Set it & forget it....
It DOES take time but the final results are well worth it.
I did an MVA simulation 4 weeks ago on a Trans Am. Driver test drove the car & his exact words: it is a different car. His brakes were also better from the increased vacuum.
 
DCR of 7.8 that what I aimed at once i had dug myself out a "BAD purchase" hole

This dictated by my Static CR, bore, stroke, rod ratio, allowed me to choose a cam that fulfilled my need to run on pump gas,on the street, with a motor that had what is considered a not street friendly 12:1 Static CR.

I found it a useful tool when trying to fit together a block and heads that had been seriously cut.
with a set of new pistons that now sat 40 thou proud of the deck.... i just cut the edge off them, to make a dome, now they miss the head.. :)
you may ask why.....and the answer is that it was all i had at the time...
i had purchased someone else's problem, mismatched chevy pistons in a slight overbore block with half a mile cut off the deck to make em work .. supposed to be a running "good" engine...
it came out good in the end.

mechanical curve is just a shorter version of the standard curve with vacuum advance hooked up to manifold vacuum

it would have been very easy to build an unworkable motor, that pinged at the slightest sniff of mechanical or vacuum advance, or one that needed race fuel

getting a handle on DCR saved my build.

its a useful tool, amongst many other useful tools

Dave
 
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