Dished Pistons for 4v Quench Heads?

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detritusmaximus

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My Car
1973 Grande #1 looong time ago
1970 Sportsroof #2 almost as long
1971 Sportsroof M-code #3 needs money
2008 GT #4 where the money went
I've looked around for info that may already be out there, but no luck because everyone wants to go racing or drive it once a year...

I'm getting ready for a 351C rebuild and I want to use closed chamber heads (71 M or maybe Aussie or Trick Flow 72cc) but want to lower compression a bit. This is to be a conservative build for the street, no big cams or 4.11 gears.

Needs are:

commonly available pump gas 91-92 octane

3.55 rear tops (probably with 5 speed)

comfy street and highway driving (MPG...don't laugh, if I can get 20+ at 70mph I'm happy)

So the issue is this, 9.0:1 compression or so with quench heads, what pistons?

Somebody out there has an answer, I can't be the first person to go this direction.

 
Were buildin our sons cleveland now. Using his 62cc heads

We r goin with flat top pistons an dble thick head gaskets

In turn should get us dow to 10.5 to 1 compression

Good enough to run on 93 pump gas. Cam choice was just a

Touch above stock in lift an duration

 
Going to 2V heads would be the short road home IMHO.

Otherwise, you'd be looking for a 351M style, cast dished piston. And I don't think there's a market for that combo in a Cleveland (could be wrong, though).

Running a 4V with that octane and stock components, I imagine you'll be fine...

Stock advertised 4V-CC and flattop CR is 10.7, but I've read that most stockers actually calculate out to be a little less than that.

 
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Quench heads help reduce pinging, dished positions will reduce or even eliminate the effectiveness of the quench, depending on the depth of the dish. A mild cam will reduce the dynamic compression ratio, which actually makes the engine more friendly to pump gas, and still be streetable.

A 3.50 or 3.73 rear end with an AOD or AODE with lockup torque converter should give you decent gas mileage, how decent depends on how heavy your foot is.

 
I've looked around for info that may already be out there, but no luck because everyone wants to go racing or drive it once a year...

I'm getting ready for a 351C rebuild and I want to use closed chamber heads (71 M or maybe Aussie or Trick Flow 72cc) but want to lower compression a bit. This is to be a conservative build for the street, no big cams or 4.11 gears.

Needs are:

commonly available pump gas 91-92 octane

3.55 rear tops (probably with 5 speed)

comfy street and highway driving (MPG...don't laugh, if I can get 20+ at 70mph I'm happy)

So the issue is this, 9.0:1 compression or so with quench heads, what pistons?

Somebody out there has an answer, I can't be the first person to go this direction.
Click to expand...
You may want to look into the relationship between static compression, dynamic compression, octane numbers, and cam characteristics. Look at Mahle, SRP, or Diamond for pistons. The MPG may be possible but, major performance compromises will be made trying to get there. Think lots of lift, small durations and overlap, and a wide separation angle on the cam. Forget the trick flow heads. Spend the money elsewhere. How much do you want to spend trying to do this? Chuck

 
Simple -

Try not to over bore your block if at all possible and then find a good used set of used 1973 or newer 351C pistons. They are dished and have a really low pin location. I would bet several people on this site have them laying around.

Most lower mileage (70K range) engines that are running with no issues do not actually need to be punched to 30 over. It just gets done because they are buying pistons anyway.

If I had a set I would just give them to you.

Even with quenched heads you will be at or below 9:1

Nothing wrong with reusing pistons - If the skirts are clean then they are good to go.

- Paul

 
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Here is something to play with. Remember, GIGO. Chuck



Were buildin our sons cleveland now. Using his 62cc heads

We r goin with flat top pistons an dble thick head gaskets

In turn should get us dow to 10.5 to 1 compression

Good enough to run on 93 pump gas. Cam choice was just a

Touch above stock in lift an duration
Click to expand...
You may want to consider a different approach to lowering the compression. Especially true if block is not zero decked. See third paragraph in the link. Just trying to help. http://www.beckracing.com/page05.htm

 
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Here is something to play with. Remember, GIGO. Chuck
Click to expand...
Garbage in Garbage out (?)

He asked a very specific question about a conservative built good gas mileage getting Cleveland. No racing, no drama, and driven like a normal car.

Build a stock bore 4V Cleveland with good used 73 and up dished pistons and he can run even the cheapest ethanol mixed gas they sell.

Still will have the little 4's in the corner of the heads - good for the cool factor especially at a car show with the hood up and the engine off.

Run a simple 600 cfm carb

Put in an Crane h260 or similar cam for mileage.

Keep the rear end gears as high as possible - 2.75's actually are quite "peppy" behind a Cleveland. Maybe "peppy" is a stretch but still not a total dog. 3.25's are good for what he wants.

Save Big $$$$ and use it for other items such as a Nasa hood and an aftermarket ram air set up. (again - hood up engine off coolness)

Get 17 to 20 mpg and save more big $$$$ and use that money make sure everything works such as having ice cold AC.

Decide to run 351C 2V heads with a more modern 2V carb and he could get 25 mpg and still have the Ram Air set up.

Have a classic car that is almost as easy to drive as a new Honda for the win!

- Paul

 
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Paul seems to know where I'm going with this. I'm not looking for getting MORE out of the Cleveland, but I want the parts to work really well together and not be a dog. At the same time, it is a 71 M code and should look like one....with the addition of the Ram Air for coolness, as Paul said.

It's too easy to get distracted with things that make more hp and end up with a car that you never drive because it either costs too much or becomes impractical for the street. That being said, a straight stock rebuild on this motor might not be happy with the ethanol and would require compensating efforts (backed off timing, octane booster along with the 92octane ethanol) to get it happy again. Since I have to rebuild it, lower compression pistons seem like a good alternative to shelling out for octane booster and fussing with it every time they change the alcohol content.

Doing some research says that the open chamber heads are more prone to detonation and such than the closed chamber. Does the closed chamber with dished pistons still have this problem or is it related to the cylinder head combustion chamber shape/size rather than the actual compression ratio? Haven't found an answer to this yet, since most reasons for the dished pistons are to control compression/detonation issues in strokers or other motors looking for more power with smaller combustion chambers.

Paul- are you talking factory 73 and later pistons? Same as in a 351M or are those different? I have quite a bit of info on the Cleveland specs, but almost nothing on factory dish cc.

 
I have 350 gears and I would say go with 3 or 275 if you are going to drive every day. My car may get unmodded on the rear end back to stock. I have no tach but it seems to wind higher than I like on the highway since I drive mine daily.

 
Paul seems to know where I'm going with this. I'm not looking for getting MORE out of the Cleveland, but I want the parts to work really well together and not be a dog. At the same time, it is a 71 M code and should look like one....with the addition of the Ram Air for coolness, as Paul said.

It's too easy to get distracted with things that make more hp and end up with a car that you never drive because it either costs too much or becomes impractical for the street. That being said, a straight stock rebuild on this motor might not be happy with the ethanol and would require compensating efforts (backed off timing, octane booster along with the 92octane ethanol) to get it happy again. Since I have to rebuild it, lower compression pistons seem like a good alternative to shelling out for octane booster and fussing with it every time they change the alcohol content.

Doing some research says that the open chamber heads are more prone to detonation and such than the closed chamber. Does the closed chamber with dished pistons still have this problem or is it related to the cylinder head combustion chamber shape/size rather than the actual compression ratio? Haven't found an answer to this yet, since most reasons for the dished pistons are to control compression/detonation issues in strokers or other motors looking for more power with smaller combustion chambers.

Paul- are you talking factory 73 and later pistons? Same as in a 351M or are those different? I have quite a bit of info on the Cleveland specs, but almost nothing on factory dish cc.
Click to expand...
Here is a cast piston with flycuts and dish. https://www.uempistons.com/index.php?main_page=index&cPath=6_25_26&sort=5a&filter_id=6&page=2

The don't list the volume of the dish and flycuts. The do list the compression height of 1.630" or 1.635". The standard early compression height was 1.647. One of the things Ford did in later years to try to meet emissions standards was to lower the compression height, which moved the piston down the bore and lowered the compression ratio. It also made the engine more prone to detonation. Large quench distances (the distance from the top of the piston to the bottom of the head) contribute to detonation. Opinions vary somewhat as to what optimal quench distance is but generally about .040. If the piston stock is .015 down the bore and the compressed head gasket thickness is .041 you have a quench distance of .056. Add the .012 from the piston above and now the distance is .068.

The Compression Ratio calculator on the Diamond piston site will allow you to change some of the variables and see what happens to compression.

As near as I can tell, the volume of the factory dished and flycut pistons was 16cc.

Chuck

 
RottenRalph:

I'm looking at a 5 speed with overdrive, so the 3.0:1 in it now might be as low as I would want to go. I have an idea for an Explorer 8.8 and those are typically 3.55 or 3.73. The 3.55 is usually not a lsd, so if I have to install a lsd/locker, then I could swap to 3.23 also.

What kind of mpg do you get and what kind of driving mix (city/highway)?


Chuck-

I've looked at the S1159 with a supposed CR of 7.9. I've also read that Ford rated the CR higher than it was, so how do the aftermarket/replacement CR specs compare? More questions....

 
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These are the factory '73/74 pistons:

IMG_0299_zpsdb0d6782.jpg


 
Yep - those are the dished low octane wonders. The 351M/400 engines (modified not 4V) use a taller piston and can not be used in a 351C. It is very confusing with 351w, 351C M Q R code, and the totally different but similar 351M (modified or Michigan).

Questions:

Are you going to do the work yourself?

Do you already have the M code quench heads?

Do you have a Cleveland engine of any type and what have you done with it?

I have not done the exact math but dished pistons with quench heads should be 8.5ish to one and about 8.0 to one with open 4V heads. With an economy cam and conservative timing it won't ping if you hit it with a hammer even on the cheapest gas. It will run just fine and will sound great through Flowmasters.

A re-ring kit is about 150 bucks

Cam and lifter another 150

Odds and ends another 150

Most importantly you will have a blast and will be able to drive it rain or shine.

- Paul

 
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I have flat tops and quench heads (see sig for details). Pings on 91 octane which is the highest commonly available here. Currently I have it mixed to just over 93 octane and it pings just a little. Next tank I am going to bump it up to 94.

I don't drive the car much so I don't mind fussing with the gas. I don't get good gas mileage either, 9 or 10 mpg tops. Except for the pinging it is streetable, idles well but that's because of the Rhodes lifters and they do make a lot of noise.

I am just providing this as reference. I can see that your goal is to avoid some of this (mixing gas, pinging, etc) so it's a good example of what you do not want to do.

 
RottenRalph:

I'm looking at a 5 speed with overdrive, so the 3.0:1 in it now might be as low as I would want to go. I have an idea for an Explorer 8.8 and those are typically 3.55 or 3.73. The 3.55 is usually not a lsd, so if I have to install a lsd/locker, then I could swap to 3.23 also.

What kind of mpg do you get and what kind of driving mix (city/highway)?


Chuck-

I've looked at the S1159 with a supposed CR of 7.9. I've also read that Ford rated the CR higher than it was, so how do the aftermarket/replacement CR specs compare? More questions....
Click to expand...
Most show a Compression Height/Distance of 1.660-1.662 which is about .013-.015 higher than stock. I believe that is because they know that Ford built the engines with the piston down the bore .015 or more. They want to have the piston at or near the top of the bore (close to zero deck). If you have the heads off you can use a dial indicator to determine how far down the bore your piston are. Zero deck is desirable to minimize the quench distance (see previous post). With that information you can do the math to determine what the best piston match is. Plan on having the block decked to get at or near zero deck. Which machine shop you use is absolutely CRITICAL. Find one that has experience building Clevelands, with good outcomes, if possible. Seemingly small things like how deep the front cam bearing is set matter. Nothing about engine building is as simple as some might believe. Do all the math yourself. Verify everything is compatible before you buy parts and measure the parts before they are used. Verify everything as the engine is being assembled. Trust but verify.

As far as detonation goes shoot for a dynamic compression ratio of about 7.75-8.1. Dynamic compression ratio is not the "end all" of predicting resistance to detonation but, it is a good indicator.

Use a cruising speed vs. rpm calculator to figure out cruising RPM and use that as one consideration when choosing a cam. Chuck

 
Yes - Flat top pistons and quench heads will ping on anything less than 93 octane.

No - Dished pistons and quench heads will not ping even on 87 octane.

Having the block zero decked will raise the compression and get you closer to pinging and will cost $ that you do not need to spend to reach your stated goal.

I did some simple math and came up with 8.3 compression on quench heads and 1973 dished pistons. You will be building a 140hp M code 4V Cleveland and I wholeheartedly approve! You might even crack 20mpg with a well tuned carb and distributor.

Your 140hp 20mpg M code 4V Cleveland will run great and pull your Grande down the road just peachy.

If you want it to sound tough then run dual glass packs and it will sound like a NASCAR plus you will pick up another 1/2 mpg or so - FUN!

There is a term for this - it is call ecomodding. Some ecomoders have built "drivable" cars that get 90 plus mpg and they are every bit of a motor head as I am - all be it quite a bit more strange.

Build it! You can do it! Come on build it!

- Paul

 
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