compression ratio

[studelover]

I have started getting my parts from Mr. Harris, next week I will be ordering my pistons. The pistons that are in my engine are dished.My question is how much compression does a stock 289 stude motor have? If I got flat top pistons and bored the cly to 60 over how much compression would it have? Mr. Harris suggested the semi dish piston. It is important to have a compression ratio that can run on mid grade gas. can anybody help?

Studebakers forever!

[JDP]

About 7.5 to 8 to 1 with the dished piston, a bit over 10.5 to one with flat top and a bore. (super premium gas)

JDP/Maryland


63 GT R2
63 Avanti R1
63 Daytona convert-63
63 Lark 2 door
62 Lark 2 door
60 Lark HT-60Hawk
59 3E truck
58 Starlight
52 & 53 Starliner
51 Commander

[Dick Steinkamp]

A stock 63-64 289 had 8.25-8.5 CR with the dished pistons. An R1 with flat top pistons had 10.25 CR. I'm not sure if the heads provided some of the increase in CR, however.

The .060 overbore is probably good for at least .3 points of CR.

If you can find all the numbers, go here and calculate...

http://www.csgnetwork.com/compcalc.html

Anything over 9.5 to 1 or so is probably pushing it for a street driven car with no computer controls.

If you want to be able to run MID GRADE and not high test, my GUESS would be you are right on the edge with the .060 overbore if you run pistons with the stock dish. This should put you around 9 to 1 with the thin head gaskets.

[1956 Hawk]

A few questions first. What are the casting numbers on the heads, what else are you doing to the engine, and how are you planning to drive the car.
As far as compression ratios go Studebaker built 289s with compression ratios from 7.0-1 up to 10.25-1. This depends on the size of the combustion chamber, and if the piston is dished or not. My car has 9.5-1 compression by using 7.5-1 compression heads with flat top pistons.
As far as using mid grade gas. It depends on a lot more than just compression ratio. The intake valve closing point and the quench height are two other important things to consider. If you are using an R series cam and the thin metal head gasket the car should run on cheap gas with 9.5-1 compression.
Anyway the semi dish piston should work just fine with cheap gas regardless of what heads you have. With flat top pistons you need to be a little more careful.

David

[studelover]

Good info, I was told by Mr. Harris that the flat top piston my not be what I want to use. I did order the r2+ cam and bearings and aluminum cam gear. today, the motor has been in the hot tank now for 2 days. There was alot of rust in the clys and they want to make sure it is all removed. They are hoping that we don't have to go 060 I was hoping 030 because of heat and overheating. When the motor comes out of the tank they will clean the bore and measure then we can proceed further, I don't know what heads I have I don't think they are anything special as my car 61 hawk came with an automatic trans, we will be doing some head work and going with slightly larger intake valves and using the stock exhast valves. these semi dish pistons maybe what I want 9.1 compression is fine with me.

Studebakers forever!

[53k]

quote:Originally posted by studelover

I have started getting my parts from Mr. Harris, next week I will be ordering my pistons. The pistons that are in my engine are dished.My question is how much compression does a stock 289 stude motor have? If I got flat top pistons and bored the cly to 60 over how much compression would it have? Mr. Harris suggested the semi dish piston. It is important to have a compression ratio that can run on mid grade gas. can anybody help?
Studebakers forever!

When I had to bore my ex-'64 Avanti R-2 .060 over, Ted Harbit also recommended using the "cupped" pistons rather than flat-tops or fully dished. Ted said the flat tops would have pushed the compression too high. The cupped pistons worked just fine. On our 6,000-mile Route 66 Trip I bought only the base (86 or 87 octane) gasoline with no pinging.
So, I should think your regular 289 should do fine with the cupped pistons and mid-grade gasoline.
As an aside, you may be surprised how little has to come of the cylinder walls even if it was pretty rusty. I bought a wrecked '64 Avanti R-1 for parts years ago. It had been sitting outdoors with no hood and no air cleaner. I ran in to the previous owner of the car and he told me it had only 1500 miles on a factory short block so I was determined to salvage it. When I pulled the heads, all cylinders had water standing in them and the walls were rusty. I was doing the work in a Navy base auto hobby shop. The old gent running the place took a look and told me to just clean it up with steel wool and kerosene. I did just that and the engine ran many thousands of miles with no problems. I eventually traded it to JP for a standard 289 (too hard to find high enough octane fuel). He planned to put the engine in a '64 Daytona convertible which he sold to Skip Lackie who years later sold it back to JP who then sold it to Nate, bought it back and sold it to Jim Turner (if my memory serves me).
And, just a couple years ago I responded to a plea for a overhead valve short block by offering one I got from JP in the 70s. It had been sitting in my barn for many years and had unfortunately gotten rusty too. I tried the steel wool and kersoene trick and it worked. The buyer had no problems using the engine in his car.



[img=right]http://www.frontiernet.net/~thejohnsons/Forum%20signature%20pix/R-4.JPG[/img=right][img=right]http://www.frontiernet.net/~thejohnsons/Forum%20signature%20pix/64L.JPG[/img=right][img=right]http://www.frontiernet.net/~thejohnsons/Forum%20signature%20pix/64P.jpg[/img=right][img=right]http://www.frontiernet.net/~thejohnsons/Forum%20signature%20pix/53K.jpg[/img=right]Paul Johnson
'53 Commander Starliner (since 1966)
'64 Daytona Wagonaire (original owner)
'64 Daytona Convertible (2006)
Museum R-4 engine

[John Kirchhoff]

Personally, when if comes to compression ratio, I'd rather err on the low side than the high side. Too high and you're going to be gassing up with the highest priced fuel out there and lightfooting the gas pedal. So much for being able to tromp it and enjoy the hp gains from higher cr. You'll then try to reduce the pinging by retarding the ignition timing but all that'll do is make you think you have a 6 cylinder under the hood. Ignore the pinging and you're liable to end up with holes burned through the pistons which will really ruin your day. Having the cr a little low will reduce low and mid range hp potential a bit, but it's doubtful very many of us could actually feel the difference of those few extra horsepower without seeing a dyno test. Besides, a loud muffler and cam would probably give you the impression of increased horsepower more than would a few extra actual ponies under the hood. With cr on the low side you can pour the coal to it in the hottest weather and not have to worry about detonation or overheating. Besides, it would be cheaper and easier to increase the cr at a later date by using a thin head gasket or milling the heads a bit than it would be to pull out the old pistons and install low cr pistons. But that's just my opinion.....

[Dick Steinkamp]

Found this on the net...


For a typical carburetted engine,
without engine management

Compression Ratio/Octane Number Requirement
5:1 /72
6:1/81
7:1/87
8:1/92
9:1/96
10:1/100
11:1/104
12:1/108

http://www.faqs.org/faqs/autos/gasoline-faq/part3/section-1.html

[StudeRich]

Wow Dick, those numbers must have been created by the Co. that makes Engine Management Computers!

It is common knowledge, and people have stated here that ordinary 87 octane works great with up to 9-1 compression, but they say you need 96? Not even available! Is $6-8.00 a gal. race gas that high even?

StudeRich
Studebakers Northwest
Ferndale, WA

[PlainBrownR2]

I know my R2 Lark handles 87 without a problem, but the heads are a question mark as somebody scratched off my raised numbers and stamped them. Me myself I would try to err on a lower compression ratio, as it would be a little easier on the wallet each fillup. Call it mindless rambling, but I miss my father's L87/L88 (the Vettes that could only handle the high test petrol) days where Sunoco 110 was somewhat cheaper and plentiful, but I think those days are long gone . So I have to opt to make the Lark run on the lower CR to get the cheapest gas.
The Gas City here has 100 octane at the pump, as well as a couple of the Marathons (I think thats due to the race attitude of the city though). Unless your into racing though, running to those pumps these days may get mighty expensive pretty quick if your filling once or twice a week. Course if your really ambitious, you can fill up at the track with Sunoco as mentioned, or get AVGas at the airport. I know those two are north of the 100 octane barrier, but they're expensive as well.


1964 Studebaker Commander R2 clone
1950 Studebaker 2R5 with 170 turbocharged
[img=left]http://i158.photobucket.com/albums/t102/PlainBrownR2/DSC00003.jpg?t=1171152673[/img=left]
[img=right]http://i158.photobucket.com/albums/t102/PlainBrownR2/DSC00009.jpg?t=1171153019[/img=right]
[img=left]http://i158.photobucket.com/albums/t102/PlainBrownR2/DSC00002.jpg?t=1171153180[/img=left]
[img=right]http://i158.photobucket.com/albums/t102/PlainBrownR2/DSC00005.jpg?t=1171153370[/img=right]

[Chucks Stude]

When they were available, I was always told, years ago, that the thick head gasket left a 289 with a cr around 7 to 1, and the thin shim gasket gave you about 7.75 to 1. Was I being fed a line?

[Chicken Hawk]

Don't know if this will help much but here's what I've found over the years. First, to tell if the heads have been milled or not, measure the thickness of the head from the machined surface where the valve cover gasket sets to the machined surface where the head sets on the block. If it has not been milled, it should read 3.563".

Of course the best way to tell what the cc's are is to cc it. Since you are having R 3 intakes installed, this would be the only way to know for sure what the cc's are.

If you tell us what the numbers on the heads are, this will help give a reasonable estimate what the cc's are assuming they have not been milled. If they have been milled you can figure about 1.5 cc's for each .010" milled off. Since these heads may be 50 years old, it's hard to tell what's been done during that time as far as milling, how many valve grinds they may have had, etc.

My guess would be to use the "cup" pistons Phil suggested (these are about half the cc's as the original "dish" pistons) and use the composition head gaskets (which are more readily available than the beaded steel at this time).

The composition gaskets will give about four tenths of a point compression less than the beaded steel. This should keep your ratio under 9.0 which should handle the 87 octane pretty well and if you want to use 89 octane, I think you could use the beaded steel gaskets. My '62 Cruiser is about 8.25 and with the timing set up to about 12 degrees instead of the factory 4 degree mark, I can run 87 with no problem.

If you use the composition gaskets, remember to re-torque the heads and re-set the valve lash after it has been run to operation temperature a couple times. These gaskets will compress more after they get hot.

If you find the actual headd cc's, let us know and we can pretty will dial in what your compression would be with various pistons and gaskets.

Ted

quote:Originally posted by studelover

I have started getting my parts from Mr. Harris, next week I will be ordering my pistons. The pistons that are in my engine are dished.My question is how much compression does a stock 289 stude motor have? If I got flat top pistons and bored the cly to 60 over how much compression would it have? Mr. Harris suggested the semi dish piston. It is important to have a compression ratio that can run on mid grade gas. can anybody help?

Studebakers forever!

[Mike Van Veghten]

Good notes Ted.

I'd guess...most engines do not have the "advertized" compression ratio.

The big three engines I've "measured" have always been on the shy side of advertized...so there's no reason to believe Stude didn't fudge a bit also.

Plus with all the head swapping....deck milling, head milling, cylinder boring over...what 40 years..nothing is what it may have been "advertized".

As Ted notes...the only way to "KNOW" what your compression ratio actually is.......is to actually measure it!
Or the easy way out is to keep guessing.

Mike

[Dick Steinkamp]

quote:Originally posted by StudeRich

Wow Dick, those numbers must have been created by the Co. that makes Engine Management Computers!

It is common knowledge, and people have stated here that ordinary 87 octane works great with up to 9-1 compression, but they say you need 96? Not even available! Is $6-8.00 a gal. race gas that high even?

Probably the RON (research octane number) MON (motor octane number) difference. This from Wikpedia...

In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in the United States, Canada and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 8 to 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, would be 91-92 in Europe. However most European pumps deliver 95 (RON) as "regular", equivalent to 90-91 US (R+M)/2, and even deliver 98 (RON) or 100 (RON).

http://en.wikipedia.org/wiki/Octane_rating

So, 96 octane in most countries would be about the same as US midgrade. You could probably run regular but you also might have to shave a couple of degrees of initial advance.

[John Kirchhoff]

One needs to keep in mind that the compression ratio figure we all know and love is the volumetric compression ratio of the engine on a strictly mechanical basis. 8:1 means your squeezing the volume of the cylinder and combustion chamber to 1/8th its orginal volume. This has little to do the volume the intake charge is being compressed into compared to normal atmospheric pressure. More on that later. The mechanical c.r. definately has an influence on the octane rating required to prevent detonation, but there are a lot of other factors that come into play as well. There are motorcycle engines out there that are running 12.5-13:1 straight from the factory and run great on regular pump gas. Several things make this possible. One thing is combustion chamber design; those engines have what comes very close to being a true hemispherical design, a shape that is devoid of nooks and crannies that trap some of the fuel-air charge and burn unevenly. At the opposite end of the spectrum are L head designs like the old flathead 169's. Instead of having a combustion chamber shaped like an orange, it's shaped more like a ham sandwich with one end having been stepped on. Not exactly a shape that promotes even burning.

Many combustion chambers have what's called a squish band or squish ring. Basically, most have a cylinder that's larger in diameter than the combustion chamber. As the piston goes up, the intake charge gets "squished" between the piston and the obstructing ring and is then squirted out. Kind of like pinching a watermelon seed between your fingers. This helps cause turbulence in the combustion chamber, mixing fuel rich parts of the charge with lean parts and helping chase charge out of those nooks and crannies mentioned earlier.

Something else that greatly effects the allowable compression ratio is the camshaft design. Long duration cams with a lot of overlap let some of the incoming air-fuel charge go straight out the exhaust valve at lower rpm's. In effect, this is like opening the petcock on old John Deere 2 cylinder engines or the compression release that holds the exhaust valve open slightly to release some of the compression on single cylinder Kohler engines...less volume to compress made them easier to crank over and get started. My 6 cylinder Kasawaki touring motorcycle engine has a half point less c.r. than the earlier, more sporting version. Everything is exactly the same on the two engines...except the camshafts, compresion ratio and the horsepower output. My touring engine has 10 degrees less duration and something like 12 & 14 degrees less overlap. This enhances (increases) the low rpm power characteristics (compared to the more sporting version) by trapping more of the intake charge. The exhaust valve closes earlier and the inertia of the moving intake charge actually compresses the charge once inside the cylinder (kind of like a mini supercharger). While increasing low rpm power, this design does hurt high rpm power. As a result, my engine is rated 117 hp while the sportier version is 120. The c.r. on the touring engine was lowered because capturing more intake charge (at lower rpms) has the same effect as increasing the c.r., which in turn would increase the possibility of detonation. The effect of trapping more intake charge is familiar to anyone who's ever started the old 6 volt JD tractors with the petcocks closed. The starter has a heck of a time cranking them over.

Having a good healthy spark also helps. The higher the compression pressures in the combustion chamber are, the more powerful the spark must be jump across the spark plug electrodes. High combustion pressures with weak ignition usually means no-go. Recently some auto manufacturers have bragged about their engines having twin spark plugs. To me, twin plugs translates into crappy combustion chamber design with poor burn characteristics. By poor I mean the flame front doesn't burn evenly from the plug outward but instead leaves unburned areas that superheat and then explode (the ping you hear) rather