Gas Mileage???

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I think 62cc is gonna be too small.Way too small
Here is the math; (4.07bore/2) x 3.1416pi x 3.31stroke x 16.387conversion =705.68cc swept
and 705.68/(11.2maximum Scr - 1) =69cc minimum total chamber volume.
now the minimum chamber volume includes the head,the deck,the gasket,eyebrows,etc.
so if the 340 has pop-up pistons, say .045, that is a deck height of -9.6cc;plus gasket of 8.9cc, plus eyebrows of say 5cc, that already totals 4.3cc. So 69 less 4.3 = 64.7 the minimum head cc to achieve 11.2 Scr. And to suck 11.2Scr down to 8.5/9.0 Dcr is gonna take a bigger cam than what you currently have in there.So really, 62cc is waaaay too small. But back up the bus aminute. I have assumed a deck-height of .045pop-up, which is the 340 blueprint spec.. You may have less. In fact, you could have anything in there,including in-the-hole pistons. And they may not have eyebrows.And the no eyebrows is incredibly important at this time. And the gasket could be half as thick. Or twice as thick. What I am saying is do not make a move until at least one head is off, and all the pertinent measurements have been made, and the final camshaft has been chosen.
If you like where the current cam is putting the power in the rpm band, you may wish to keep it. And if that is so, it behooves you to determine the ICA (intake closing angle). From the measurements you get and the ICA, you can back calculate the exact head volume to achieve run-ability on your 98 octane gas. It may not even be possible to hit all the targets (The targets being; Scr,Dcr, and 98gas.) with what you currently have, or propose.There is a strong possibility that the pistons will have to be changed or machined. So,
Off with a head! lol
 
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I will buy not even a screw....before I pulled the head /heads Promised !!
In the next 3 - 4 Weeks there are a lot of carshows coming up... so I will wait to pull the heads ...but in the middle of September I have the time to start ....with the "operation" I reduced the Timing just a little... and use the strongest springs MSD offers..to protect the engine against Pinging and rattling... and I only will drive up to
80 mph...

About the ALU heads... couldn´t the combustion cambers be opened a litte more to get more cc ?
Or...better..can you recommend a good pair of Aluminium heads ?

Greetings Juergen
 
Yes they could, but
A) you are getting ahead of yourself, and
B) that will likely destroy any favorable squish you may have
It is better to modify the piston crown, or replace the piston, to accomplish Scr reduction, AND create/maintain a favorable squish. Squish is worth compression. How much' IDK; but in your case, every little bit will be welcome.
And besides, you may have gasket thickness to play with, if you have pop-ups.

One thing I can tell you; My combo, on paper, should not go 93 in the 1/8th. I was hoping for 106 in the qtr. Is that all due to squish? Of course not. But every detail must have counted for something.
 
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so on the LONG RUN ...I probably need to think about a complete rebuid..? Because of the pistons... If I mess around with them..a complete rebuid is close... Hmmm....
The Pistons do not have a dome they are flat like a table... as far as I could see with my endoscope

Greetings Juergen
 
In this case pop-ups just means piston tops above the deck, which is normal for 340s. However with compression as high as yours, it is likely that the heads have been severely milled which might not allow pop-ups, or at least very little. I guess we'll find out soon enough, when the
head comes off!

BTW
It's not the road-speed or rpm that will be hard on that engine, but rather Loading. If it was mine, I would be blocking the secondaries closed, or defeating the linkage, whatever it takes, and then staying out of WOT below about 3000/3500 rpm.At least until you confident you are familiar with the sound and feel of detonation. Detonation can kill your engine real quick.Your 98 octane gas has saved your engine thus far.
Unfortunately, with 3.23s, 3000rpm is right around 30mph.So easy does it.
Happy motoring.
You know what tho, your 98 gas got me thinking. If your engine is only rattling below 3000 or so at full timing, there is a chance the Scr is low enough to not kill the bottom end.
If that were true, then she might only need an adjustment to the Dcr, to allow proper timing there. This might be able to be achieved with retiming the cam, or installing a bigger one, and/or thicker headgaskets, or some combination of those. So don't despair yet. We can figure that out later, as winter approaches.
If you wanted to, and the engine has a strong bottom end currently, I would be tempted to degree the cam and move the ICA up the road a bit, say 4 to 6 degrees. If you did do that, you would have to check the piston to valve clearance. I think 6 degrees might reduce the Dcr about 1/2 point. I'd have to do the math, but right now, I am off to work...............
Ok so,I reworked the previous numbers with a 270 cam that was previously done at ICA of 106. So I retarded it to 112 (so 6*), and the Dcr loss looks like .43 of a point. The new numbers might look like 11.3Scr/8.75Dcr/178psi. If it don't work with iron heads and 98, it will definitely work with aluminum and 98. I have run those numbers on 87E10 and aluminums, no problem.Others have run a tic over 9.0Dcr with aluminum and 93.
So there is hope for your combo.
I would reset the ICA and recheck the PV clearance. An afternoons work could tell you a lot. And it's not gonna make it any worse.
Remember I guessed at all the parameters. The only thing that remains plausable is retarding that cam. That will absolutely, drop the Dcr.
 
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Hello AJ/FORMS
If I would have known this before... I just changed my timing chain 2 month ago... also installed a chain tensioner... Btw.. what does ICA mean ? PV ( Piston to Valve clearance ? ) So my timing chain has 3 keyways.... before / neutral / after
in my case I have to put the key to AFTER right ?
Also called the shop that sells the aluminium heads....They said, they can make the Combustion camber bigger ( more cc ) so in case this opition is also still in the game
The owner of the shop is a well known Drag racer here in Germany...so he should know
what he is doing...

BTW... with my 3.23 my car makes around 65 mph @ 3000 rpm... that´s TRUCK territory here in Germany.... LOL
Greetings Juergen
 
ICA is intake closing angle. Compression does not begin until the intake closes. The later you close it the less distance remains in the effective stroke to build pressure, and the lower the pressure will be.
Forget the keyways,as a sole means of retarding the timing; you need tools.
You will need a TDC Finder, a degree wheel, a crank turner,a dial indicator, and a dummy lifter, and a wire coathanger. The intake may also have to come off, to get access to the lifter bores. You will also have to search the how-tos to learn how to do this.
If you used the keyways and did not verify by degreeing, then there is no way of knowing where your cam is in, now. It may in fact even be over-advanced as it sits, which might explain a lot.
 
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I just happened to degree the cam in the 360 I'm currently building.
Also installed a chain-tensioner on the shortly used timing-chain, which with pure luck brought the cam right into specs! The tensioner made a 2-degree difference in my case.

IMG_4635_zpsiqienhyj.jpg



BTW, the heads on this 360 have only 60cc chambers.
Pistons are KB107 w/ 5cc valve-reliefs.
 
I'm just above 11cr. Somewhere around 11.2-11.3 calculated.
60cc chambers. Piston quenchheight is 0.033-0.038"
The cam is small. It's CompCams 256H, or 20-221-3. DCR will be about 8.6 - 8.7:1.
1.6 rockers.

Engine will run on Propane only, which should be able to handle the DCR.
Also went to some lengths to prep/polish the chambers and remove sharp edges to prevent detonation.
This engine will be a daily driver, but with an emphasis on torque & economy.

Don't want to hijack Brasil's topic, but maybe some of this info can be of help.
 
It's cheap, about 1/2 to 1/3rd the price of gasoline and it's readily available overhere.
Also it doesn't have the negative issues of plug fouling or fuel dropping out of suspension on cold days/intake temps.
Oil stays clean much longer.
 
WOW! Heck of a thread going on here!
Getting dizzy from all the numbers LAMO!
 
Yup, I'm acquainted with propane and it's benefits. Was just curious. The half-price makes it attractive alright. I had considered it for myself in 99. but the Price difference was not as attractive then,and distribution here sucked, big time.Still does. And not knowing where to get it, 500 miles from home swung the needle back to gas for me.
 
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here in Germany 1 litre of Propane is around 40 Eurocent... Gasoline is 1,25- 1,45 Euro... so Propane is a good way to save a lot of money !

@ aj/forms ...@ Big Block Mopar.. I installed the tensioner... when I renewed the timing chain ... Hmm... but the issue with the VC was there before the change...
also.. But I will do a search about the correct cam degreeing

Greetings Juergen

Btw.... it is not my thread... y2swinger69 started the thread... about the gas milage - I was asthonished about the high numbers...some people get..so I asked why my milage is so low....
 
Getting "high" gas-mileage isn't that hard. Getting the engine to survive, and stay running, at ever leaner mixtures, is.
And "high" is relative.
In my experience, with a 360, the easiest way to mileage (after a decent tune), is rpm. And the 292/508 cam will not make "high" numbers no matter what you do.With a cam bigger than 223@050, I had a hard time of it, even with a double overdrive bringing my final-drive ratio down to 1.97.
The problem with the bigger cams as I see it,seems to be the overlap period,and the late closing intake.Between those two factors, the low-rpm efficiency, falls so rapidly that they actually lose gas mileage with a reduction in rpm. Gas mileage seems to be related to the engines peak vacuum. The bigger the cam, the higher the vacuum peak will be up the rpm scale, and therefore the higher the cruise rpm will need to be.
A factory teener cam makes a very early vacuum peak,and can be made to pull at 1300rpm@65 mph,and make really great fuel mileage there.
The fast rate 270*cam I had was pretty good at 1550=65.I was able to get her up to 32mpgUS pretty easily.
The 276 fast rate I currently have, likes to be at 1800 to 2000 or better. That's a pretty big jump in just one cam size.And it can't touch that 32mpg number.I no longer use that double O/D combo, and I like my 3.55s. So the current cruise rpm is tic over 2200 with the GV-od. And so gas mileage is no longer on the table. But she hasn't been a DD anymore either for many years.
The 292* was dismal. It was a long time ago. but I seem to remember the vacuum peak being in the 2200 to 2400 range.

So my conclusion was; rev it up slowly in neutral. The lowest rpm that the engine pulls the highest vacuum, is a good rpm to cruise at. This rpm is the lowest rpm at which the engine first becomes efficient, and there is no point in cruising much lower than this. So if your combo vacuum peaks at 1800 rpm, don't try to cruise it at 1350.Well you can, but don't be expecting great mileage.The headers will be sucking the fuel-charge right through the open valves during the overlap period.And the late closing intake valve may allow some of the charge to go back into the intake. So between those two that is no good for mileage.And then there is trying to build a timing curve to satisfy that mismatch.

If your stock-teener vacuum peaks at idle, anything is fair game, so then let performance be your deciding factor. 2.45s and an A500 while making fantastic mileage, will be a little soft trying to get away from the light(6.71 starter gear). And if your TC stalls at 1800, there is no point in trying to cruise it at 1450 (the cruise rpm with this combo).
But 3.23s with the A500, now that's something. The starter gear would be 8.85, and the cruiser would be 2.23. That would bring your Rs down to around 1800 with 27 inch tires. That would work with a 268 cam and an 1800TC. But it would work best with a 360 and lots of compression, to fill out the low-speed.But I sure wouldn't put a 110LDA cam in there :(
 
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FWIW, upto now I've never been able to get the mileage with my current 318/A518/8-3/4 setup, than I had with the 318/904/7-1/4" in my Dart.
But, the car is much more fun to drive now.
 
the A 518 has overdrive.... right ? or was it the A 500 ..
Overdrive is a good thing....to make more miles... per gallon

Greetings Juergen
 
They're both overdrive.
But the 518 is (internally) a heavy transmission which costs power to turn.

With my 904/7-1/4" combo I managed 17mpg @ highway.
With my 518/8-3/4" combo best I've managed is 15mpg @ highway.
And the 318 was better tuned with the 518 transmission than it was with the 904.

I'm dearly looking for a A500 transmission here, just to (try) and get some better mileage.
 
A lock up A-500 would suite for mileage but not so much for performance torque converters.
 
BigBlockMopar said:
FWIW, upto now I've never been able to get the mileage with my current 318/A518/8-3/4 setup, than I had with the 318/904/7-1/4" in my Dart.
But, the car is much more fun to drive now.
Click to expand...

What, if any was the change in final drives, between the two? and
What, if any, was/is the change in driving style?and
Were there any other changes made at the same time?
 
AJ/FormS said:
What, if any was the change in final drives, between the two? and
What, if any, was/is the change in driving style?and
Were there any other changes made at the same time?
Click to expand...


No difference at first, both rear ends had 3.23 gears. But later on with the A518, I used 3.9 gears and I'm currently running 3.55 gears.
One thing was, the 318 in the beginning was quite lean on highway speeds, and I couldn't drive over 65 or else the engine would get hot, also because of a leaky radiator.

After that, numerous of changes, but mostly tuning and timing curve changes aiming for better power and economy.
Also went from the stock 2bbl to an Edelbrock RPM intake and 4-bbl carb. (all still running on propane).
The engine still makes over 20" vacuum in Drive, idling at 600rpm. Oilpressure is 30 in Drive, 60 in neutral when warm.

Started using thinner oil, down to 5w20. Lighter 17" wheels.
 
With 3.55s your FD is now 2.45. If I assume 65mph, and an 80 inch rollout( 25.5 tires), then your rpm has dropped from about 2770 with the 3.23s, to about 2100, with the 2.45s. If I also assume that the stall is below 2100, then that should be close.
Now the question remains as to what the centrifugal timing mechanism is doing, at this new 2100, and if the sparkport is still pulling in the entire amount of vacuum advance. It is easily possible to lose 8 to say 18 degrees of timing.......Spark-ports are not all timed the same.The factory ports come in pretty early, others are up to the designer.
The weight penalty under steady-state cruising is not severe, being something like 3% and 4% of the total vehicle weight.
You didn't say what kind of four barrel; some are better than others.,
Ima guessing you changed tires with those wheels, so that may be a contributing factor.
Looks like you got a good handle on things.It will come around.
For reference, my 360 likes more than 45* at 2200,aluminum heads.
 
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I've used 3.23 gears with the A518 for a short while few years ago, but the engine would lug down on slight height increases on the highway. It just didn't have enough low end torque in that rpm-range to maintain speed.
Later on I renewed the timing chain, which brought back some low end torque, and played some more with timing curves and such.
These days I'm sure the 318 will be able to handle the 3.23 gears nicely on the higher speeds.

At around 65 I'm currently doing about 2200rpm.

These are my current ignition settings after a recent recurve-job;
12.5 initial
21.5 init + VA (@ 600rpm in Drive)
25 mechanical in distr.
37.5 Total
(Haven't checked Total + VA yet)
Full advance is all-in at around 1700-1800 rpm.
VA is installed on intake manifold.

The 318 feels good and 'strong' running, for its stock 8.6:1cr.

This weekend I exchanged the Impco 425 propane carb for another one, as it didn't want to lean out anymore.
Now, my idle AFR's are back to where I want them;
16.0-16.5 @ idle & cruise
12-13 WOT
14-15 Part throttle acceleration
(These are Propane stoich-values: 15.5 = 1 Lambda)
 
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