Final Engine Compression Ratio?

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billsdartgt

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I now know about the 360 in the Blue Mutt since I have removed the heads. I confirmed the pistons are the older TRW 11.5-1 and I have some factory "J" heads with the 2.02 valves. I don't really have the means (or knowledge) to determine where the motor is for final compression. Any thoughts where it may be? I tried looking at some different calculators but can't seem to find all the specific info to input for the calculations. Below is what I have

360 block - bored .030 over for the 11.5-1 pistons
stock stroke
Stock J heads - no work on combustion chambers
will use felpro gasket - compressed thickness listed .049-.059 with 4.180 bore

haven't found the dome volume or piston deck volume - these seem to be what I am missing for the online calculators.

using the Lunati Voodoo cam 10200702, hoping I haven't moved into race gas with this thing
 
^ Thanks badsport - the setup to add a liquid is what I don't have and was hoping for some already available tech data to help with the calculation - will give it some thought on if I want to get that deep. That's a good thread
 
billsdartgt said:
the setup to add a liquid is what I don't have and was hoping for some already available tech data to help with the calculation
Click to expand...

Always best to measure, IMO. Summit has the kit fairly reasonable, that's where I got mine.
 
billsdartgt said:
good to know, freaks me out a little to put the liquid in the motor LOL
Click to expand...

Use grease around the ring area of the pistons and the water won't go anywhere.... Then turn it over and wipe it dry with a shop towel and blow it off with some compressed air... It won't hurt anything...
 
Might be able to use a calibrated syringe instead of a buret.
I was going to give that a try this winter...
 
Bad Sport said:
Always best to measure, IMO. Summit has the kit fairly reasonable, that's where I got mine.
Click to expand...

$30.00 for this ?
Summit Racing® Cylinder Head CC Kits SUM-980180

get a 5 inch by 5 inch piece of plexiglass from the local hardware store,
assuming that you already have a drill and a bit to make a hole in it
maybe $2.00

go to tractor supply and get two 60cc syringes for less than $5.00
the syringe will be much easier to work with when shooting the fluid in through the
plexiglass plate than an open graduated cylinder.

Producer's Pride Luer Slip Syringe, 60cc Capacity, Pack of 2 at Tractor Supply Co.

for the fluid I use plain tap water with a little food dye added, non toxic, cheap, ez clean up, just dry and oil the wetted surfaces when your are done.

when doing cylinder heads on the work bench I use a shoe-boot tray under the head to contain any spilled fluid. Again ez and cheap.

https://www.amazon.com/Stalwart-75-ST6014-Weather-Tray-Water-Resistant/dp/B01HJON6RI/ref=sr_1_5?gclid=Cj0KCQiAr8bwBRD4ARIsAHa4YyJbkGszj8DvuH5DQTbUgisseoOQq20uOfevCzTz0sKUsFIZQyK8vuQaAnTvEALw_wcB&hvadid=198230998239&hvdev=c&hvlocphy=9016154&hvnetw=g&hvpos=1t1&hvqmt=e&hvrand=12211687404052414370&hvtargid=aud-840076997981:kwd-340266498128&hydadcr=23163_9482757&keywords=shoe/boot+tray&qid=1578237081&sr=8-5
 
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You will likely be "about" 1 full compression point under the rated compression ratio for that piston, as TRW routinely used the smallest chamber for a given head to advertise compression ratio, so that would have been either the smaller 318 head or the smaller still 273. You'll need a camshaft with probably on the order of 70* IVCE (Intake Valve Closing Event) to keep from building too much cylinder pressure for pump gas. In other words, a "big cam", but it CAN be made to run on pump gas.
 
With the engine in the car you can't accurately cc the cylinder to measure the ratio. With engine build specs you can calculate the ratio but you'll need to know how far in or out of the bore the piston is, the chamber cc and head gasket thickness. Dynamic compression (according to your cam specs) tells the real story.
 
Bad Sport said:
Must have gone up, I paid 18 bucks for mine.
Click to expand...
click the link, actually $30.99 + shipping unless you buy another $70.00 worth of stuff, I am not saying that Summit is not a good place to shop, I have bought a lot from them, fast shipping, great service after the sale, just saying this is not one of Summit's better deals.
 
Got a PN on those pistons, OP? They are usually stamped on the head. Posting some pix may help.

If you have a good dial capiler, then if you pull one, measure carefully from the top of the pin hole to the flat area of the piston and let us know. That number + .492" is the compression height.
 
Piston P/N is 4007042 - I have tore the engine down as far as I am going to, already further than planned

Cam is Lunati #10200702
220 int/226 exh @ .050
int open 2.0 BTDC/close 38.0 ABDC
Exh Open 49.0 BBDC/Close -3.0 ATDC
negative overlap

Assumed engine was probably lower compression when I chose the cam, it will go back together and run as is, still want as much info as I can get. if it turns out crappy Blueprint may get a call from me when I can bolster more money LOL

Of course I always have the 292 solid lifter cam to put back in, but not likely
 
toolmanmike said:
With the engine in the car you can't accurately cc the cylinder to measure the ratio. With engine build specs you can calculate the ratio but you'll need to know how far in or out of the bore the piston is, the chamber cc and head gasket thickness. Dynamic compression (according to your cam specs) tells the real story.
Click to expand...

with the head off, which is the condition as described by the OP, if the piston is below the deck at TDC, it would be possible to accurately cc the cylinder.
 
RustyRatRod said:
You will likely be "about" 1 full compression point under the rated compression ratio for that piston, as TRW routinely used the smallest chamber for a given head to advertise compression ratio, so that would have been either the smaller 318 head or the smaller still 273. You'll need a camshaft with probably on the order of 70* IVCE (Intake Valve Closing Event) to keep from building too much cylinder pressure for pump gas. In other words, a "big cam", but it CAN be made to run on pump gas.
Click to expand...



At least a point lower. The minimum out of deck for that piston is .017 and even then, that usually isn't enough. Sometimes you have to go .050 out to get what you want.

You can also knock some of the dome off to get the CR where you want it if getting the piston out of the hole gets the CR too high.
 
billsdartgt said:
Piston P/N is 4007042 - I have tore the engine down as far as I am going to, already further than planned

Cam is Lunati #10200702
220 int/226 exh @ .050
int open 2.0 BTDC/close 38.0 ABDC
Exh Open 49.0 BBDC/Close -3.0 ATDC
negative overlap

Assumed engine was probably lower compression when I chose the cam, it will go back together and run as is, still want as much info as I can get. if it turns out crappy Blueprint may get a call from me when I can bolster more money LOL

Of course I always have the 292 solid lifter cam to put back in, but not likely
Click to expand...


You'd better hope your CR isn't 11:1 with that cam. You'll have issues.
 
yellow rose said:
You'd better hope your CR isn't 11:1 with that cam. You'll have issues.
Click to expand...


figured I might, why I am searching for info, when I did some short running around a month or so ago it actually did pretty good, of course it was probably in the 40s at the time, initial timing around 10.
 
billsdartgt said:
Piston P/N is 4007042 - I have tore the engine down as far as I am going to, already further than planned
Click to expand...
Roger. Look at the pix in this thread in post #8; you will have to click on the link to see it. Looks like a pretty big dome, at least 10 cc or more net with the eyebrows. Crane Cam

I see in that thread that the author found stacked head gaskets in it at teardown, so that's a pretty good sign that you're gonna have too high SCR.

Do you have a dial indicator or a dial caliper, or feeler gauges and straight edge across the deck, to see how far up/down from the deck the flat area is with a piston at TDC? With that and good guess at the dome/eyebrows cc's, we can get pretty close to your SCR and then DCR. (BTW, the CH in post 21 of that same thread can't be right for a 360....it's for a 340.)
 
pict of the piston, I will see what I can come up with for numbers using my caliper, also get another pict of the piston at TDC

IMG_4283.JPG
 
a few measurements and a couple of picts, thanks for all the responses

piston TDC .159" to .228" - couldn't get aa repeatable measurement LOL
bowl depth on head at deepest point .681"

IMG_4289.jpg
IMG_4290.jpg
IMG_4291.jpg
IMG_4292.jpg
 
Can you estimate compression ratio on an engine with just a compression gage reading? I know nothing about my motor. It is a 70s 360 rebuilt some time before I bought the car. Has a Holley, LD 340 intake and what seems like a little lumpy cam that pulls about 14 inches of vacuum at idle. 3:23 posi rear end & 727. Reading on compression gage dry is about 130. Seems to be a little doggy off the line. Wondering if the cam is to big for the CR.
 
Bill, I'm lookin at all this and here's what I think. Naysayers be damned, here's what I would put in there.

COMP Cams Nostalgia Plus Cam and Lifter Kits CL20-672-4

That's Comp's updated version of the Mopar 508/292 cam. I think it will be a great match for that engine, BUT, you'll need to match the rest of the CAR. lol No way will you have problems with detonation on pump gas and that joker will run like a beast.
 
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