Compression ratio calculator?? And power figures?

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7duce swinger

7duce swinger

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Anyone know how to calculate compression ratio. I would also like an estimate of where my horsepower level would be at? Ive found many formulas, but not sure if im doing it right. Can anyone let me know where my cr is at? Ive got a 318 stock bottom end, with "596" 360 heads that are milled to 61 cc's, a comp cam's hydraulic flat tappet thumper cam 486/473 lift, tri-y headers, and a 4 barrel intake and right now a 750 demon :D just messin around right now with carbs, the 600 eddy seems soft, the holley 650 seems good, but the demon seems really great, just alot of tuning though. Just trying to figure out where im at right now. Has excellent throttle response, and doesnt bog, hesitate. The compression calculator ive used says 9.0:1,i dont know if thats correct. Im using the mopar brand head gaskets, and dont know how thick they are?? Thanks to all!
 
It's not all that hard; High school geometry, multiplication, and addition/subtraction/division.

I could talk you thru the process much easier that I can type out how it's done.

MP engine book covers it pretty well also.

If you want to send me your phone number I'll call you and talk you thru. Your choice.

Jim Burch
 
If you're running a stock 318 bottom end, the pistons are probably .060"-.080" in the hole...and with just about any 360 head, your compression is probably gonna be closer to 8:1...but, just like you mentioned you need to know your head gasket thickness and diameter, how far in the hole the pistons are, combustion chamber volume, valve relief volume (if there are any).

...when you find your numbers, heres one I've used just to spitball numbers...

http://www.torinocobra.com/Randys_tools.htm

Hope this helps...

Edit: missed the part where you said milled to 61cc...my bad. I ran the numbers just real quick with what you provided, assuming .060 in the hole and an .040" gasket with a 4.060" bore...and it came up 9:1 just like you thought...
 
I think the pistons are .060 in the hole or .050 i cant remember correctly. the heads are at 61 cc's, and the gaskets are the mopar brand, i dont know the thickness of them, i got them for a 318cid though. Anyone know the bore dia. Of those gaskets, ive read the gasket thickness is .028 many places. Theye were really thin, i thought there was only one in the package lol.
 
You can find a CR calculator on the net just plug in the values
For a ballpark number
 
Jburch, i really was never to good in geometry, math, multiplication, or division lol. I googled a couple formulas, and they all seem to come out right about the same. Oh any one have a guesstimate, on my horsepower, torque figures? Just a guesstimate at where im at, crank hp, or rear wheel horsepower, really doesnt matter, i know its not much, just looking for a close estimate?
 
I'll use my dyno program when I get home after work.
 
cudascott said:
You can find a CR calculator on the net just plug in the values
For a ballpark number[/QU . Yea ive found quite a bit of them, "kb- silvolite", i think was one, and "bowlings compression ratio calculator", anyone know if they're accurate? Thanks 273. Does having different ignition's help out in the horsepower department, or do they just help out with better starting, and what not?
Click to expand...
 
Need some measurements to be more accurate but I came up w 8.8:1 if pistons are .080 below the deck or 9.25:1 if they are .060 below the deck. That was figured with the stock 3.91 bore 3.31 stroke w a .028 head gasket good for 4.12 bore. #s will vary depending on actual measurements. I was doing alot of guessing
 
273 how accurate is your dyno program? those are crank hp figures right? Give or take anny loss in numbers, in the real world? I know its just a guesstimate, but it just has me wondering. Swinger 340, as far as i know, the bore is 3.91, 3.31 stroke, heads are milled to 61 cc, and the pistons are .050 - .060 in the hole. The only thing i couldnt be sure on is the thickness and bore diameter of the head gaskets. Ive tried to check everywhere but only found .028 on those mopar brand gaskets. Its hard for me to remember correctly, but i think the piston was most likely.060 in the hole.
 
When I first got it every engine build I seen in magazines I'd put the spec's in my program and usually it within 5%.
 
Hmm, so its pretty accurate then, thats pretty cool. Thanks 273, Youve been much help.. Thanks to the rest of you guys as well.
 
So today i took my dart out to the street to see what it could do. I didnt floor it, but gave it some pedal, it took off great, gave me a little push, but suddenly died after about forty feet. It chirped the tires after first and second, then nothin. I also had trouble starting it, afterwards. could it be, that it flooded itself after takeoff? Or fuel wasnt getting to the carb? It has excellent throttle response also. It just died and wouldnt start. Can anyone help me out on this one? Any pointers on where to look? . Thanks, Eli
 
7duce swinger said:
So today i took my dart out to the street to see what it could do. I didnt floor it, but gave it some pedal, it took off great, gave me a little push, but suddenly died after about forty feet. It chirped the tires after first and second, then nothin. I also had trouble starting it, afterwards. could it be, that it flooded itself after takeoff? Or fuel wasnt getting to the carb? It has excellent throttle response also. It just died and wouldnt start. Can anyone help me out on this one? Any pointers on where to look? . Thanks, Eli
Click to expand...
Well are you getting fuel to the carb ? Maybe it flooded . Are you getting spark ? loose wire , bad ballast resistor , need more info
273's calculator is pretty accurate , sounds like you have a good setup
 
Thanks jerry6, have you used his program?, or has he tried with your setup? The car surprised me, it took off like a scalded/rabbid dog lol. It chirped the tires through the gears,(which surprised me also) and left a long friggin trail of tire marks. The carb is getting gas. With the car off i looked, into the carb, and it gets great supply of fuel, wires are new, and none are loose. After it stalled i coasted to the side of the road, and nothin at all. While i mashed the pedal it went grreat, then stalled(while my foot was still planted) i didnt leave off the gas. Good it be a bad coil? I have the echlin chrome ignition setup, new rotor, cap, and wires, new plugs. It idles all day long and has great throttle response to it. It stalled ,then i tried to start it, but just cranked over. Any tips on what to look for?? Bad coil?? Ballast resisitor i think is new as well, but not entirely sure??
 
7duce swinger said:
Thanks jerry6, have you used his program?, or has he tried with your setup? The car surprised me, it took off like a scalded/rabbid dog lol. It chirped the tires through the gears,(which surprised me also) and left a long friggin trail of tire marks. The carb is getting gas. With the car off i looked, into the carb, and it gets great supply of fuel, wires are new, and none are loose. After it stalled i coasted to the side of the road, and nothin at all. While i mashed the pedal it went grreat, then stalled(while my foot was still planted) i didnt leave off the gas. Good it be a bad coil? I have the echlin chrome ignition setup, new rotor, cap, and wires, new plugs. It idles all day long and has great throttle response to it. It stalled ,then i tried to start it, but just cranked over. Any tips on what to look for?? Bad coil?? Ballast resisitor i think is new as well, but not entirely sure??
Click to expand...
273 put in my specs , or close to ., and it came within 5% of my actual numbers , so yes his simulator works well .
As to why the car stalled and now won't start , good question . That happened to me once , it was the ballast resistor , if it is the B R it will sound like it's going to run and die as soon as you let go the key when starting . Check if your getting spark to rule out bad coil , make sure ECU is grounded well ,make sure carb is getting fuel . And always keep a spare ballast resistor in the car , you never know when they will go . mine went on the highway , felt like I ran out of gas .
 
Well i can rule out bad coil, and it gets fuel to the carb. Also it fire's right up, i just fired it up right now, would it be good to still go and buy a new ballast resistor??
 
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