340 compression ratio

[70dart65coronet]

I am trying to figure out my compression ratio on this dart i got a few years ago. i bought it from a guy that built it for racing. Can i figure this out without taking apart the engine?

So the things i need to know to find the compression ratio are:
Bore
Stroke
Clearance Volume
Swept Volume

Compression Ratio is swept volume plus clearance volume divided by clearance volume.

On a stock 340 the bore is 4.04 and the stroke is 3.31

So unless he bored the engine to a bigger size, the bore should be 4.04.

The stroke i tried to manually measure the piston #1 travel from TDC to BDC with a plastic pencil rod (through the spark plug hole) and i came up with about 3.5 (which is not very exact). so I'm not exactly sure what the stroke is.

I can find swept volume if i have the correct bore and stroke (i think you can also take 340 CI and divide it by 8 cylinders)

Clearance volume is the combustion area of the head? i was able to look up that head number and i found these numbers for combustion chamber volume 65.0 - 73.0. This gives me a range which is not exact…and is that CI? per cylinder? Where do i find the exact volume?


Here are my numbers and information that i have:

Car Vin: LH2360R202155

Block Casting #: 2780930-340-7

Right Head Casting #'s (i had to take the valve cover off to find them inside):
03671587 1 0823 123 360 AAWJ

Left:
3671587-12 0783 123 360 AAWJ

I found one place that said these heads would have 2.02 intake and 1.60 exhaust and another place that said 1.88 intake and 1.60 exhaust

Intake Manifold: 340 Victor

Carb: Holly 800 Double Pumper

Camshaft: (i don't know what these numbers mean, he had them written down in some of his notes)
High Flow IH
#420421
.470 Lift
298 Duration
229 @ .50
IO 44 IC77
EO 77 EC 41

Transmission left side:
3410452-2

I also need to find a dust cover for the transmission, to keep dirt out of the ring gear, starter area.

I ordered a new summit racing pro torque starter, because i wore out the factory starter by cranking so much trying to get it to start so i could tune the carb.

I also need to get a good carb kit and a good book for that holly 800. something that comes with all new gaskets, and jets and all that good stuff. i have so much black soot build up on this one because i was running too low of a octane on fuel.

Also, what do you recommend for racing engine oil for this motor. I think he said he was running Kendal 50 weight.

This is a lot of questions, but i really appreciate all the input. I need all the help i can get, i am learning….i would like to be a expert of this stuff, but am so limited on time because i work so much.

Thanks…

Steve rayer:

 

[OldmanRick]

Welcome Steve. I'll try to digest your post, but the easiest way to get some idea of compression would be a simple Compression test. The heads you have would be around 70/72cc in stock form and have 1.88 int valves, but they could have been milled and different valves installed? That's a pretty stout intake also. A vacuum reading at idle from a port at the base of the carb can also help reveal how mild/radical the cam is. I'll reread and see if there's any other info i can add.

Also, do you know what trans (904/727), torque converter (stall speed) and rear gear you have?

 

[72bluNblu]

Steve,

If the engine was built for racing, I don't think you can assume anything is stock. With that cam and intake, I'd guess that there was more work done inside. Which probably means the bore isn't stock. Pistons may not be stock. As far as the chamber volume, those heads are usually in the 65-72 cc range. That's per chamber. Most compression calculators do the math for you on the conversion to cubic inches. But, you won't be able to find out the EXACT chamber volume of your heads without removing them. From the factory they varied, which is why a range of 65-72cc's is given. Some are as small as 65cc's, some are as large as 72. And if the engine has been rebuilt, the heads may have been milled, which changes everything.

What are you trying to figure out?

I'd do a compression check to start off with. Dynamic compression doesn't translate directly over to static compression, but it'll give you an idea. Heck you can even just pull a few plugs and look at the tops of the pistons, should tell you if they're domed, dished, flat, etc. That should help get you in the ballpark. Ie, if they're flat top pistons with those heads, the compression is probably less than 10:1. If they're domed, it could be anywhere from 11:1 or up.

As far as the carb goes, black soot isn't from running too low of an octane. Its from running rich, which is an entirely different problem. And if its in the carb, its from backfiring, otherwise they're won't be any soot on the carb. Dirt maybe, but not soot from combustion.

Got any pictures?

 

[MrDuster]

Steve,
My neighbor is an awesome engine builder. The other day I was in his shop and asked him what a tall thin glass beaker graduated in cc's was for. He said it was to check compression ratio's. it looked real fragile! I'm no expert for sure, but my understanding is you have to measure the volume of cc's in the cylinder with the head off, piston full down, and the cylinder level. Then measure cc's with the head on and piston full up through plug hole. That should give an exact ratio for particular engine. I can ask him exactly what he does if you're interested.

 

[Rocky_JS]

I think the 6 in the posted vin should be a G? which would make the car a 318 car. So the engine is not factory to the vehicle. On the front left under where the cyl head bolts on there should be a some letters and numbers, like XW340RXXXXXXXX what are those numbers?

The 587 head like Rick said above is a small valve 1.88 head by rule. Assuming the heads belong to the engine the 587 head it is likely a 73 340 engine. This was a low compression 340 in comparison to the earlier 340s 8.5 cr compared to 10.5. It also had a cast crankshaft so look at the balancer and see if it says for cast crank only on it's face, but generally speaking it is not flat from the ring see picture note outer offset ring with writing.

With that said if anything was changed it could be anywhere on the charts. The best thing to do is see using a bore scope and look inside a cyl and see if you can read anything off of a piston. many times the part number is stamped on the top LF2316 etc. and the bore size will be also. .030 .060 etc..

This information will likely go a long way towards getting you close to what you seek?
The only way to really tell is to pull the engine apart and mic and measure everything.

The camshaft is an Erson best I can determine and here is a link to some information on it.
http://www.forabodiesonly.com/mopar/showthread.php?t=29259

 

[70dart65coronet]

First of all, Thank you all for help and information!

Rick - I need to get a compression tester and a vacuum gauge, whats a good brand and where should i get them? Once i get them ill try that out. Thanks Rick!

BluNblu - Ill get some pictures on here soon, thats a nice car collection you got going, thanks for the info!

Mark - that would be great if you could get some more information on his process and where is a good place to get a cubic centimeters graduated cylinder. do i want cubic centimeters (cc) or cubic inches? Thanks for you help!

Rocky - I will double check that vin number. I looked really hard for any and all numbers and letters on the block, but i will double check under the front left under the cylinder head bolts. I will check the balancer to see if it says cast crank only, (what other types are there and what is the best?) Where is a good place to get a inspection camera and what is a good brand, ive been wanting to get one...then i can check the top of the pistons for numbers. i could also look at the shape of the piston like BluNblue was saying. (domed, flat, ect.) Thanks for looking up that camshaft info.

Thanks again for all your help! I have been working so much. i haven't had much time to work in my shop, i need to get in my shop and get going on this soon...maybe i can get some of theses tools ordered at least.

Thanks Again!

Steve

 

[sireland67]

Cast crank only mean it cam from the factory with lower compression.
But pistons can be changed, so look in the spark plug hole and see what you have for a piston.
The head cc will not vary much unless the heads have been radically milled.

 

[sireland67]

Also, be careful.
Cast crank 340 has a different balance than forged crank 340.

 

[Rocky_JS]

what is best - depends on what you want to do with it. and as said above piston can be changed and so can crankshafts. The thought is if someone changed to a steel crank or even a 0 balance crank then chances are other are also changed. if it still has the stock cast crank and balancer assy with the 587 heads then perhaps it was a more stock rebuild and a stroke of 3.31.

for what mark is speaking about requires removal of cyl head, if going through that take it to a machine shop and have them do it. it is cheaper.

 

[3406pk]

A decent borescope that will fit thru spark plug hole will cost a pretty penny. You will pay $300 or more, much more than a gasket set to pull heads.

 

[MrDuster]

Steve, My buddy who builds engines hasn't been home and I don't have a phone number…I stop in when I see his shop door open as he's close by. I haven't forgot about you and will get a picture and an answer for you as soon as I can. I might have it wrong about removing the head too. Maybe you measure with the head on and the piston full down and then again with the piston full up…I really don't know, but will find out what Al does!

 

[MrDuster]

Steve, Short answer to your first question is YES! However, Al gave the "32 molar suck" when I suggested it. Here's the long answer and a picture of Al's graduated cc beaker-sorry it's sideways! He uses transmission oil and measures the volume of the compression chamber with the head off. The beaker is called a "cylinder head cc kit" and is $200. It comes with a plexiglass plate to put across the chamber. Precision Measurement Supply in San Antonio, TX sells them. www.precisionmeasure.com 7050 Snowflake Drive, San Antonio, TX 78238. 210 684-6472.

Al also loaned me his "Auto Math Handbook" by John Lawlor. On page 9 it has a cool picture of a Duster at the drag strip to kick off the chapter on Compression Ratio. To summarize: Compression ratio = (cylinder + chamber volume) divided by chamber volume. If you find your bore and stroke you can find the cylinder volume by the formula Cylinder Volume=pi/4 x bore(squared) x stroke. As combustion chamber volume is usually measured in cubic centimeters (cc's), you'll want to convert your inches by multiplying by 2.54 to convert to centimeters. Thus 4.04 becomes 10.2616 and 3.31 becomes 8.4074. Plugging the nuns into the formula gives .7853982 x 10.2616 (sqd) x 8.4074….which comes to 695.315 cc's. Now comes the hard part…measuring chamber volume or clearance compression volume…you need to measure it physically. Use light oil, cleaning solvent or even water. You can do this with the engine assembled, but the engine should be tilted so the spark plug hole in the cylinder to be measured is vertical. With the piston at TDC, the valves closed and the spark plug removed, pour liquid from the burette through the plug hole until it reaches the beginning of the plug threads. The amount poured from the burette will indicate the combustion chamber volume.
With the engine disassembled it is more difficult to measure combustion chamber volume. First, you have to cc the head. Then you have to calculate the added volume the head gasket provides. If the engine had flat-topped pistons that, at TDC, were perfectly even with the deck, or top of the block, that's all you'd need. However, that isn't true of many engines. At TDC, the piston may stop short of the deck height. In addition, if the piston top is dished, or concave, it will increase volume…if it's domed or convex, it will decrease the volume of the combustion chamber. In HPBrooks "How to Hot Rod Small-Block Mopar Engines", Larry Shepard of Chrysler's Mopar Performance offers a technique for ccing the block he calls the 1/2 inch downfall method. The head is removed and the engine is positioned so that the cylinder to be measured is vertical. Them the piston is lowered 1/2 inch or 1.27 centimeters from top dead center. The distance is arbitrary. The point is simply to be sure that the entire piston including the dome, is below the deck and fully within the block. Find the volume above the piston and by using the formula for cylinder volume, you can find what the volume would be if the piston were flat-topped. The difference between the figures tells you how much a dished piston increases the overall combustion chamber volume or how much a domed piston decreases it. {Above info was taken from John Lawlor's book}

Seems to me it might be best for you to pull your heads and see what you've got. Easy to measure bore and stroke then! Compute your volume's remembering to take into account the compressed head gasket volume and you'll know what you compression ratio is when it all goes back together. Best of Luck!! Mark

 

[70dart65coronet]

I got alot on my mind and i got alot of thoughts here, so i appreciate all of your help where ever you may help, haha i am learning!Ok guys this is what I came up with so far. I decided to go ahead and pull the intake manifold and the heads just so I could see what I am working with.
-
Rocky - I took a picture of that casting number on the block, left side just under the cylinder head. 2780930-340-7
I also took a picture of the harmonic balance on the crank shaft, I had to take off the pulley But I don’t see any castings that say cast crank only.
The only numbers on the top of pistons are “30”. I took some pictures of them.
As far as I can tell using a basic caliper, it is 3.300” stroke, 4.070” bore.
Right now I have the right side head off only. So I went to top dead center on the balancer meter. And piston six was right at the top of the deck, then I went to bottom dead center and that same piston seemed to be at the bottom. These pistons look dished? What do you call this type of piston. Im guessing they are forged pistons, not cast.
-
I measured the valves they are 2.02 and 1.60. I noticed that it doesn’t have roller rockers, they are just flat, since I am in here shouldn’t I put on some roller rockers? Is it a direct replacement or what do you have to do? They are supposed to increase horsepower?
It seems like the head intake and the intake manifold have been what do you call it? Ported? They seem very smooth and seem to match up really good.
-
That is another question I have is there is a gap between the head and the intake manifold, I think it is a coolant cavity that isn’t utilized by the heads and the intake manifold, I took some pictures of it. There is coolant cavity and a intake exhaust port that is in the head but Is blocked off by the intake manifold. What are those for and why is one just open the atmosphere? It’s a victor 340 aluminum intake, part number EDE2915
-
Rick – The transmission I have has a stamp “A-904-LA” on the bell housing. Also the part number that is stamped into the side of the oil pan flange is PK_ _ _ 10834276 7864. So I think this is a A-904 torqueflite. I don’t know what torque converter I have in there, or the stall speed, how do I find out? I don’t know what ring gear I have either? I could count the teeth to find out? He also doesn’t have the factory shifter any more…it’s a cable T handle shifter system, after market. I remember last time I had it racing, I would shift 2 to 3 and it would take a second for it to engage. Im going to have to do some research on the transmission and see if there is some adjustments I can make on shifter linkage cable. He doesn’t have the dust cover either…where can I get one? I need to get a compression tester and a vacuum gauge, whats a good brand and where should i get them?
-
Mark – thanks for getting me that information. I am going to order that cc kit, and some of those books and try to figure it out. I really appreciate your help on that! I will keep you updated on how it goes.
-
The carb I have is actually a 4150 r4779-6 double pumper. I think that means it’s a 750 cfm I got a renew kit they are calling it a “Trick kit” but I want to basically go through the whole carb and clean it and put all new seals in it.
-
I got new spark plugs, what should my spark gap be? I marked my position of my distributor before I took it out…but what if you forgot to mark it, and then you rotated the engine. How do you know where to put? I have the firing order marked on the engine and each plug labeled and the cap labeled.
-
It looks like he was running a factory stock starter on this thing, might be why it broke? I got a protorque starter from summit racing for 150, part number sum-820337
I also need to decide on what motor oil to run on this thing. And the proper oil capacity and oil level. He put on a oil pan part number MOR20710 273-400 10” DP with a ext oil pump pickup part number MOR24700. What oil do you suggest and how much with this oil pan? That way I can make sure the oil level mark on the dipstick is correct.
-
It also has a hurst line lock for the front brakes, and it is leaking out of the bottom where the wires are, where can I find a replacement that will match up with my line configuration? I haven’t had much luck, I attached a picture.
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Another thing I had to do was take out the steering column to get the headers off and out of the way in order to pull the heads. I was thinking about finding a aftermarket steering column. This column has the original on the column gear shifter linkage and the steering shaft itself is big bulky and ugly, since he had to grind the crap out of it to clear the headers. Is there a basic racing steering column that would take up less room? I could also take the ignition switch, turn signals, hazard lights off and out of the steering column and put them on the dash so I have easier access to that stuff for troubleshooting. Im not too impressed with these hooker headers either, the mating/sealing surface is really rough, which im guessing is why they were leaking so bad, I got all new bolts and gaskets, I was going to try to use a belt sander to smooth out the header flanges to make them seal up better.
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I need to get some tools, where and what do you guys recommend for this stuff?;
Vacuum gauge, compression tester, inspection camera, measuring tools for mic ing motors like inside calipers, valve spring compressor, inch pounds torque wrench.
What is the best way to keep the cylinders/pistons clean when you’re cleaning the deck for the new head gaskets? I would hate for anything to get down around the piston rings. Also how does the piston get its oil for lubrication? Somehow it must get oil to keep the piston oiled from the rings down.
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I also really don’t like how he has the motor mounts on this thing, they don’t seem like they would be very strong, hes got like a 1 inch plate as a spacer in there and some bolts with washers that look like they will pull through. Is there a good brand of motor mounts that I could make work in this application, you would think there should be some factory motor mounts in there…but they look custom made.
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Radiator fan is just a little small fan, I was thinking about getting a dual electric fan for cooling. See picture. What do you guys think..this one doesn’t keep up.
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I feel like I am having the re invent the wheel here because I bought this thing when I was young and dumb, and I didn’t get any information from the guy so now im playing CSI on this thing figuring everything out.
i appreciate all your guys help!

 

[70dart65coronet]

some more pictures

 

[nothingbutdarts]

some more pictures

That is a cast crank engine by the balancer.
That cavity in the head above the heat crossover passage is always exposed, no need to worry about it. I can't tell you why it is there!

 

[OldmanRick]

Hi Steve. I'm pretty busy lately, but I have to give you the FABO award for the most info and pics we've seen in a while when asking questions :thumrigh:. It looks like a very nice car there, and there are a lot of questions. I do remember your earlier post, but now we have a lot more info. I'll try and take some time to look thru things and give some advice and probably ask a few questions.

Of the bat, I see a low compression 340 that was running rich and had a pretty bad header gasket leak....

You'll get tons of feedback i'm sure, just weed thru it as it comes in, and it will help you moving forward in the process.

 

[OldmanRick]

That is a cast crank engine by the balancer.

Sure looks like one. I haven't been around internal balanced cast engines, but with all those drill holes, i have to wonder if this isn't one? Hope some current guys can weigh in.

Steve, what are your plans for the car? Street/cruiser, hot street or track use. That may help with some of the responses.

 

[jrlegacy23]

This is your heat crossover. What it is designed to do is heat up the intake manifold near the carburetor to atomize the fuel better. A lot of people block this off because it will give you a bit more power with a cooler intake manifold.

EDIT: And that top part is not part of the coolant passages.

 

[OldmanRick]

Rick – The transmission I have has a stamp “A-904-LA” on the bell housing. Also the part number that is stamped into the side of the oil pan flange is PK_ _ _ 10834276 7864. So I think this is a A-904 torqueflite.

It is a 904. Are the three dashes in that number just unreadable? Or are there any others on that pad? I believe what i'm seeing is.......

PK..............Kokomo, Ind. plant
_ _ _1083....7 digit part number
4276...........date code........Apr.12, 1973
7864...........sequence number

I don’t know what

torque converter I have in there, or the stall speed, how do I find out?

If your not pulling the engine or trans out now, I wouldn't worry about it at this point. Once your back up and running well, you can determine the stall/flash rpm by power braking and just nailing the throttle from idle. Once you get a close number there, you can decide if a change is warranted.

I don’t know what ring gear I have either? I could count the teeth to find out?

Yes you could, but if it's not apart, with it in neutral, just spin a tire one turn and count the driveshaft revolutions. If the other tire turns in the opposite direction, it means you have a open carrier (non-suregrip) and you have to hold one still during the test.

He also doesn’t have the factory shifter any more…it’s a cable T handle shifter system, after market. I remember last time I had it racing, I would shift 2 to 3 and it would take a second for it to engage. Im going to have to do some research on the transmission and see if there is some adjustments I can make on shifter linkage cable. He doesn’t have the dust cover either…where can I get one?

Nothing wrong with a cable shifter as long as it and the cable are in good shape and adjusted properly. As far as the shift flare/delay, i'll let one of the trans experts handle that....lol. Post in the wanted forum and you can probably pick up a shield from another member.

I need to get a compression tester and a vacuum gauge, whats a good brand and where should i get them?

Mine are close to 40yrs old and were parts store buys. I'm sure some of the chain stores have them or you could look at Summit. You don't need anything fancy, just get gauge faces the look good and easily readable. I'd think $15/20 could get a nice vac gauge and $30/40 would get you a decent compression tester.


More to come as I have time.......Rick

 

[sireland67]

Looks like from the pictures you have a .030 340, with about 8.5 compression with the heads you have.
The good thing is you have adjustable rockers from a 273.
Did you do a compression test before teardown?
A cheap gauge from any parts store is under 25 bucks and would have told you a rough idea of the overall condition of the engine.

 

[OldmanRick]

I also need to decide on what motor oil to run on this thing. And the proper oil capacity and oil level. He put on a oil pan part number MOR20710 273-400 10” DP with a ext oil pump pickup part number MOR24700. What oil do you suggest and how much with this oil pan? That way I can make sure the oil level mark on the dipstick is correct.

That's a 8qt pan, not counting the filter. To mark the dipstick for full capacity, i'd put about 8 1/2qts. in, run it to fill the filter and check the stick. Scribe a new line if need be.

Do you remember what the oil pressure was Cold, Hot idle and Hot with some rpm's? Might give a window into what pump and bearing clearance your dealing with.

I'll let others recommend oil type. Last oil I used in a performance engine, many moons ago, was regular ole' Castrol GTX. To many new oils out there now for me to make a choice for you.

 

[OldmanRick]

It also has a hurst line lock for the front brakes, and it is leaking out of the bottom where the wires are, where can I find a replacement that will match up with my line configuration? I haven’t had much luck, I attached a picture.

Kinda shakin my head on this one.
View attachment 1%20(16).jpg

As a rule, i don't like to give advice on brake issues, but you have to clean that up. I've used a few Hurst roll controls years ago and never had any issues. I also never mounted one in the wheelwell. I don't think the're rebuildable so your options would be to do away with it, or buy a current model of some type and replumb the front lines. You can get a tubing bender cheap enough and use some generic parts store already flared tubing. There is also the option of buying stock repro stuff if available and splicing the new line-loc unit in between somewhere. Like I said, this is something I don't like to do over the net, (brakes are serious stuff). I would recommend replacing the front hoses and hardline them back into the stock brackets.

 

[jrlegacy23]

...well, I don't see any zip ties.

 

[OldmanRick]

...well, I don't see any zip ties.

The eternal optimist.....lol.

 

[OldmanRick]

Another question? I see you have a block off plate and a regulator, so elec. only........What fuel pressure did you have back when it was running?