Compression too high?

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Steve, if you give me the following numbers I will be happy to calculate your exact compression ratio.

1) Bore
2) Stroke
3) Design volume of Piston (i.e. -3 ccm)
4) Design volume of Chambers quench (i.e. -58 ccm)
5) Extra quench (from top of Piston to Deck)
6) Head Gasket compressed thickness.
7) If you have a Cam Card with the specs of your Camshaft, I can also calculate the Dynamic Compression which is actually the more important one.

You can lower the compression ratio by using a thicker Head Gasket. So its not the end of the world ;-)

But judging by the Photos it looks like a high compression ratio.

Jan

Is the intake valve lift so great as to require that much valve relief cut into the piston?

The domes on the pop up pistons are usually hollow. If they were solid they would add a lot of weight to the piston.

The TRW pop-up simply can't cut this much off of the dome without holing through. I realize these are Ross pistons but specs are usually very similar.

The piston to wall clearance on the TRW is big. It is .0055".

The picture you posted looks like it is h-u-g-e!

.030" top, .005 bottom. I know the clearance is measured with a ribbon so the picture may be deceiving but it surely looks strange from my view from here in the cheap seats?

I think the number for piston to valve on the intake is .100" and .080" on the exhaust? I might have that reversed, I have to look that up to be sure. I haven't built a C in a while.

What are the lift specs on that cam? I want to say (offhand) that you are good to about .630" lift without having to cut the pockets?

You could use the lifter bushings installed too while it is apart.

You WILL pick up some free horsepower if you index those spark plugs.

I went into Clay Smith Engineering today with my cam, one of the cylinder heads, and pictures of the block and pistons. They gave me a cam card for my cam and recognized the springs and other components on the head as parts from their shop. They explained that the compression ratio is between 11 and 12, and also explained the problems would ensue. Specifically that the engine will ping on pump gas unless it is run very rich and timing is significantly retarded, and doing so will greatly reduce its power and general performance.

Their recommendation is to put in a set of dished pistons and thus reduce its compression, and continue with the rest of the configuration of the motor. They thought the cam was appropriate for my Pantera since I will not be racing it. The cam card is attached below.

They are comfortable working with this motor since it is their cam and related components. The plan is for me to disassemble the motor and take everything their shop next week. They will:
- measure combustion chamber volume in the heads
- measure cylinder bore
- check crank shaft stroke
- torque plate hone the block (unless already done)
- order the appropriate RaceTec custom dished pistons
- balance the updated rotating assembly

I find high compression in a Cleveland is not the cause of pinging and detonation like it is in many other engines.

I put this down to Ford's quench chamber.

I have a 351C bored 0.030" over, with flat top pistons, quench chambered 302 heads with 57cc chambers and milled .020" and felpro head gaskets.
I run it on 91octane unleaded and have no detonation problems.

The pop up on those pistons does not seem very high, I can't see that it would have compression higher than my engine. I don't see any problem.


Beware of mechanics and engine experts suffering "small block Chevy syndrome"

The only thing in common with a 350 Chevrolet and a 351Cleveland is they are 4" bore.

They have nothing else in common.

The domed pistons and the quenched heads, looks like 13 to 1 to me, be interested to know?
I would say it looks like a committed race engine,The cam is pretty radical for the street.Those look like steel heads? If so you would have to run retarded timing and race gas (110), cc the heads, If you go with aluminum heads, you can run a flat top piston, that's the standard for high performance street engines it will give you about 11 to one, and pump gas will work, run 34 on full advance.

Hi Steve

quote:

Originally posted by SteveBuchanan:

... It may be as high as 11.8 ... he said ... this motor was probably built at a time when high octane gas was readily available ...

The tech at Clay Smith must have been a young guy. Pump gas like that wasn't available when the 351C was new.

I'm pretty certain the piston domes are the standard Ross pop-ups for the 351C. The piston specs are listed on their web site. They are definitely the wrong choice to combine with D0AE heads and pump gas.

With D0AE heads, a flat top piston with the stock 1.65 pin height will give you 10:1 static compression. This is assuming the engine has a stock 3.50 stroke crankshaft. Combined with an intake valve closing around 70 degrees ABDC that nets 7.7:1 dynamic compression, the car will run on 91 octane pump gas reliably. You won't need a dished piston. You can take the dynamic compression up to 8:1, but I like to leave a little wiggle room. The cam's intake valve closes around 72 degrees based on the spec card.

I always recommend a round skirt piston, due to the thin cylinder walls of the 351C block, but the Ross flat top has a 1.668 pin height. The pin height of the good ol' TRW flat tops is 1.647, that would be a good match with the D0AE heads. I promise not to tell anyone if you were to make that choice.

That cam has 76 degrees overlap, based on advertised duration. The engine will be a lot more street-able with about 60 degrees overlap.

Flat top pistons and a cam swap are my recommendation.

I was tickled to learn that Clay Smith Cams is still in business.

Hi George,

The engine has a stroker crank, probably 3.750. I don't have the engine fully disassembled yet and can't see the stampings on the crank journal. The stroker crank is why he thinks it needs dished pistons. The plan is to bring the needed parts into the shop and then he will figure out how to get the correct compression for pump gas.

I was equally amazed that Clay Smith Engineering is still in business. I am also very fortunate that they are 8 miles from my house. There were three generations of family members in there working away and the business seemed alive and well.

Having run pretty much the gamete on Clevelands, my opinion is that you can stay in the 9.5:1 to 10:1 cr range and still make HP.

In MY EXPERIENCE aluminum heads don't help on octane need at all.
You are going to NEED 34-36 degrees total. 10.5:1 is PROBABLY the absolute limit to run with 93 octane gas.
Octane need is determined by the cylinder pressure. That is more closely related to static compression ratio than anything else.

Bleeding off compression through the exhaust timing does nothing in this engine. It simply does not work.



You also NEED to decide the nature of the engine that you want. That is mostly in the camshaft timing.

Although I like the timing on that cam, your cam, I don't use my car in any kind of an "every day" situation AND I wouldn't necessarily recommend my specs to anyone else.

I actually run a little more cam than yours but the end result is very similar. It's a lot of cam for the street and to make it work, you will need to deal with other factors as well such as putting in headers that actually work with that cam. That is not as simple as it sounds. PROBABLY 180's.

Your cam is very close to a race cam, mine too, but it is a cam that can be run on the street.

You do not want to have to row the car through bumper to bumper with it. No no.
If you are not suicidal now, you might become it being in traffic with it BUT it is very difficult to have a Pantera idle like a 428 Thunderbird, then run with 427 Cobras on the track.

You need to compromise one way or the other. Mild or wild.

I will say that if you get the opportunity to drive on an open track at WOT with it, you won't want to come off of the track. That kind of balances out the suicidal thing...sometimes?

Steve I re-read your original post. Sorry I glossed-over the stroker part the first time. Based on your stroke measurement I suspect it may be a stock crank offset ground for 3.7" stroke, that was the hot thing to do back before Chinese crankshafts came on the scene. The rod journals would be ground to 2.100 diameter and 6" Chevy rods were used with the big ends narrowed 0.550 to fit on the 1.66 wide Ford journals.

The other particulars were D1AE heads, 0.040 or 0.048 head gaskets, and flat top pistons with 1.320 pin height. The pistons and rods were available off-the-shelf a few decades back. The pop-up domes in your engine, well that's something else.

There's a pic of a rod below, showing the rod is narrowed on one side only, the rods would be assembled on the journal so that the narrowed sides faced each other. The big end width of Ford rods is 0.830, Chevys are 0.940,

Thanks George. I think you are on the right track about the stock crank with an offset grind. I say that because my crude measurements showed a 3.674 stroke which is quite a bit off from what is being sold today. I will pass this information along to Clay Smith Engineering.

Regarding cam specs, I think I will proceed with what I have for now. Clay Smith is saying that the cam is appropriate for the car. I plan to test the engine on a stand and will scrutinize manifold vacuum. If it is too low then I may change cams right then. Otherwise, maybe try it in the car once it is rolling. If it precipitates suicidal thoughts then I will go back to Clay Smith for something different. They might be able regrind what I have now.

quote:

Originally posted by SteveBuchanan:


Regarding cam specs, I think I will proceed with what I have for now. Clay Smith is saying that the cam is appropriate for the car. I plan to test the engine on a stand and will scrutinize manifold vacuum. If it is too low then I may change cams right then. Otherwise, maybe try it in the car once it is rolling. If it precipitates suicidal thoughts then I will go back to Clay Smith for something different. They might be able regrind what I have now.

You won't get suicidal with the engine on a stand. Not at all.

You could do what I do if caught in traffic, close the windows and put the a/c on high. Put on your favorite music and ignore the Ferrari guy behind you who has his windshield wipers on because of your exhaust.

That alone will boost the happy button. Especially when he runs out of windshield wiper fluid.

Don't worry about him threatening you. They are mostly pussies.

Yes, I missed the extra stroke as well.
It's a little unclear how much extra stroke you have though. It would be good to calculate the cr and compare it to 3.5" stroke with flat tops.

Also what is the volume of the dome on the pistons?

DOAE heads are closed chamber and have a 63cc +- combustion chamber. The engine shop is doing an actual volume measurement of my heads since they have been milled and also have aftermarket valves.

I do not have the proper tools or skill set to accurately measure crank shaft stroke myself. The aftermarket stroker cranks are stamped with stroke length. If my crankshaft is stock with an offset grind as George suggested then the shop will have to measure its stroke length.

When I measured cylinder bore with my telescope gauge and digital micrometer, I came up with 4.025 which seems unusual. Most rebuilt Cleveland engines have a 4.030 bore. I am glad the professionals will be looking at it.

It takes special equipment to measure volume of the dome on the piston. At this point most of us are thinking that the domed pistons will cause a higher compression ratio than is incompatible with today's pump gas. I am not sure what the engine builder was thinking when he ordered those pistons since the engine would need high octane gas. The engine may have been built 15 or 20 years ago.

Depending on the pin height in those pistons, you MIGHT be able to just go back to a standard crank and rods, without reboring the block and changing the existing pistons, leaving the heads alone.

You need to consider that even just honing the bores might make the bores .002 or .003 too big, then you are back into custom pistons and rings.

From the era, most shops rebored right to .030 over, because those simply were off the shelf pistons. You don't want to go over that with a stock block.

Just a thought.

Steve, if those pistons you have are forged, they can successfully be run with as much as 0.005" clearance- often done with thinwall Clevelands by cylinder honing rather than boring. Cast or cast/hypereutectic need much less clearance since such pistons often have steel struts cast inside to control the heat expansion. Someone should look at the underside of the pistons to see if the small dome is hollow or solid; I've seen them both ways. The piston mfgr mark & model number should also be there since its not visible on the tops. That will define a cast vs a forged piston.

If there's enough meat, the dome can be machined off to lower compression. Cheaper than another $500 set of pistons. Alternatively, use a thick composite head gasket. Your builder can advise you on what's available and how much it will change the C.R. on your particular engine combo.

You're going to quite a bit of trouble for a car that will be sold when completed. Or have you changed your mind? If so, congratulations!

Doug, Aluminum heads allow higher compression ratios, you know that? every point of compression is good for about 50 horsepower, a 500 h.p. engine with 9 to 1, will make 600 with 11 to one. 700 at 13 to one. The higher octane along with cam header etc all play a part, but compression is horsepower.

quote:

Originally posted by pantera chris:
Doug, Aluminum heads allow higher compression ratios, you know that? every point of compression is good for about 50 horsepower, a 500 h.p. engine with 9 to 1, will make 600 with 11 to one. 700 at 13 to one. The higher octane along with cam header etc all play a part, but compression is horsepower.

Agree to disagree.

The first set of aluminum heads I used was in 1983 on an iron Cleveland block. They are not a stranger to me.

What you are stating is a mis-interpretation of the iron head to aluminum head power production comparison or ratio.

To not sound like a physics nerd, what it says in laymen terms is that with all things given equal, in order to produce equal horsepower, an engine with aluminum heads on an iron block, the compression ratio needs to be 10% higher with aluminum heads then the iron heads have.

Aluminum transfers heat faster to the water jacket then iron heads do. It's roughly 1.1:1 faster, or 10%.

Heat generation or captivation contributes to horsepower production.



Fuel can be ignited by compressing it. There is a chart for that also, i.e., known compressible properties of fuel that gives it an octane rating.

The higher the number, the more difficult the fuel is to ignite by compressing it.


Diesel engines work without any ignition. They compress the fuel to the point of igniting. This is called dieseling.


In a Cleveland with the production quench heads to run 11:1, you need 103 octane gas.

Changing the heads from iron to aluminum will not change that. It will still need the same octane to prevent detonation.

You will just make 10% less horsepower with aluminum heads on the same engine unless you increase the compression ratio to 12.1:1.

Then you will likely need even more octane. Maybe 106?


There are other ways to make horsepower with almost all of the available aluminum aftermarket heads other than raising compression.

I find in a Cleveland 9.5 to 10:1 is enough. What's wrong with over 600 streetable hp on 93 pump gas?

quote:

Originally posted by PanteraDoug:

quote:

Originally posted by pantera chris:
Doug, Aluminum heads allow higher compression ratios, you know that? every point of compression is good for about 50 horsepower, a 500 h.p. engine with 9 to 1, will make 600 with 11 to one. 700 at 13 to one. The higher octane along with cam header etc all play a part, but compression is horsepower.

Agree to disagree.

The first set of aluminum heads I used was in 1983 on an iron Cleveland block. They are not a stranger to me.

What you are stating is a mis-interpretation of the iron head to aluminum head power production comparison or ratio.

To not sound like a physics nerd, what it says in laymen terms is that with all things given equal, in order to produce equal horsepower, an engine with aluminum heads on an iron block, the compression ratio needs to be 10% higher with aluminum heads then the iron heads have.

Aluminum transfers heat faster to the water jacket then iron heads do. It's roughly 1.1:1 faster, or 10%.

Heat generation or captivation contributes to horsepower production.



Fuel can be ignited by compressing it. There is a chart for that also, i.e., known compressible properties of fuel that gives it an octane rating.

The higher the number, the more difficult the fuel is to ignite by compressing it.


Diesel engines work without any ignition. They compress the fuel to the point of igniting. This is called dieseling.


In a Cleveland with the production quench heads to run 11:1, you need 103 octane gas.

Changing the heads from iron to aluminum will not change that. It will still need the same octane to prevent detonation.

You will just make 10% less horsepower with aluminum heads on the same engine unless you increase the compression ratio to 12.1:1.

Then you will likely need even more octane. Maybe 106?


There are other ways to make horsepower with almost all of the available aluminum aftermarket heads other than raising compression.

I find in a Cleveland 9.5 to 10:1 is enough. What's wrong with over 600 streetable hp on 93 pump gas?

Notes on compression:

Cleveland pop-up dome pistons, as best as memory serves me, have 12cc to 14cc domes. In regards to a 4" bore, every 0.005" change in clearance is equivalent to 1cc. So to use a head gasket to correct the dome volume of a pop-up dome piston would require increasing the thickness of that gasket by 0.060 to 0.070. The net result would be a gasket that is kinda too thick.

Horsepower increase based upon compression is not linear, it is logarithmic. There is a law of diminishing returns. Increasing compression from 10:1 to 11:1 does not increase horsepower as much as increasing compression from 9:1 to 10:1. And increasing compression from 9:1 to 10:1 does not increase horsepower as much as increasing compression from 8:1 to 9:1.

In the end maximum compression is largely based upon fuel octane, and next upon combustion chamber dynamics. Since the combustion chambers of iron quench chamber heads and SVO aluminum heads are identical, I would not expect there to be much difference in power or maximum octane. I would hope calm minds see the logic in that.

I have heard the arguments for iron heads expressed by Pantera Doug expressed previously (decades ago) by experienced practitioners of the dark hot rod arts. Such anarchic ideas were expressed by folks smarter than I. There appears to be many advantages to iron. We in the world of small automobiles (sports cars) tend to appreciate elimination of weight above other priorities.

There are three types of compression. The static compression, the dynamic compression (which used to be called effective compression), and the operating compression (which if you think about it, is actually the dynamic compression). We can measure static and dynamic compression, operating compression is only learned by empirical data (experience).

Finally, I jumped on the net and looked quickly for info about compression. Here are the thoughts regarding compression by John Maher, proprietor of John Maher Racing. They seem to be right in line with what I have learned. So of course that's what I posted, seeing how I'm so starved for validation.

Compression - John Maher Racing

wow really Doug?, I run 11 to 1 and have aluminum heads, that allows me or anyone to run on 91 octane. Aluminum does disperse the heat from the combustion chamber, that keeps the charge of fuel from early combustion, pre- ignition knock (pinging) that is why all modern performance engines use aluminum heads, Dieseling can be caused by to hot a plug, to a vacuum leak, or to much timing.the production of horse power is a product of efficiency in air flow through the head, the iron to aluminum head equation? where did you get that? it is not what I have experienced in building many engines. Finally, for guys trying to figure out a way to achieve horsepower, in a street able set-up, some of this can be confusing to say the least, and I would say read, building engines are done everyday without the stuff I have read in this thread and Doug if you can get 600 hp out of a 9 to 1 streetable naturally aspirated 351-C engine your dyno's broken.

As I said Chris, agree to disagree. Glad you are happy with your engine.

And I said, "all things given equal".

Thank you Doug, but, the reason I am perusing the idea of big horse power is to help set a realistic goal for NEW owners and engine builders,
In the April 2016 issue of "Hot Rod" their is a excellent and illustrative article on building "big" horse power, The "AMS/OIL" "Engine Masters Challenge". In this contest the builders achieved some incredible h.p. numbers building small blocks from Ford to Chrysler, Chevy to Hemi. The winner in the small block class was our beloved Cleveland! At 415c.i. Chris Thomas from John Kaase Racing engines used the following parts, Edelbrock (Aluminum) 2V heads, Scat rotating assembly, milling the heavily modified heads created a 44cc combustion chamber so to meet the rules on compression, it runs dished pistons to attain 10.84 to 1, Edelbrock air gap intake, Diamond pistons,Comp flat tappet cam 251/255 , a 1050cfm Holly carb, finally running through Hooker 1 7/8 primary headers. This engine has 64 more cubes 11 to 1 (not 9 to 1) compression and is filled with innovation from the top Ford builder in the U.S. How much drive able power did it make? 575h.p. and 553lb-ft. The point? Bench racing and real word are two different things.

My engine,396ci 11 to 1, Ford racing modified C302 B heads comp cam, high rise Ford racing intake, Electromotive crank trigger ignition, Pro-Systems 750 double pumper, Scat rotating assembly, balanced blue printed roller motor and how much power does it make?
517hp and 507lb-ft, I have the dyno sheet to prove it.

quote:

Originally posted by pantera chris:
My engine,396ci 11 to 1, Ford racing modified C302 B heads comp cam, high rise Ford racing intake, Electromotive crank trigger ignition, Pro-Systems 750 double pumper, Scat rotating assembly, balanced blue printed roller motor and how much power does it make?
517hp and 507lb-ft, I have the dyno sheet to prove it.

Congratulations. You are my hero. Your medal is in the mail.

Many examples of modern high compression engines being built today & using octane rated fuel considerably lower than Doug's claimed 103 octane required fuel.

Here is just one example with the compression ratio being 11 to 1...

The 5.0 L (4948 cc, 302 cid)[10] "Coyote" V8 is the latest evolution of the Modular engine.[11] Ford engineers needed to design a V8, specifically for the Mustang GT, that would compete with the GM 6.2L LS3 used in the new Chevrolet Camaro, and the new Chrysler 6.4L Hemi ESF in the Charger, Challenger, and Grand Cherokee. This engine had to remain close to the same physical size of the outgoing 4.6, and share other specifications with it such as bore spacing, deck height, bell housing bolt pattern, etc. in order for the engine to utilize existing Modular production line tooling. The result was the 5.0 Coyote, which produced roughly the same amount of power as its competitors, but with a much smaller displacement. To strengthen the block enough to handle increased output, webbing was extensively used as reinforcement in the casting, rather than increasing the thickness of the walls. The intake plenum was also situated low between the two cylinder banks to meet the height constraint, thus the alternator traditionally placed low and center was moved to the side of the engine. It shares the 4.6 L's 100 mm (3.937 in) bore spacing and 227 mm (8.937 in) deck height,[12] while bore diameter and stroke have increased to 92.2mm (3.629 in) and 92.7mm (3.649 in), respectively. The engine also retains the 4.6 L's 150.7 mm (5.933 in) connecting rod length, which produces a 1.62:1 rod to stroke ratio.[13] The firing order has been changed from that shared by all previous Modular V8s (1-3-7-2-6-5-4-8) to that of the Ford Flathead V8 (1-5-4-8-6-3-7-2).[13] Compression ratio is 11.0:1, and despite having port fuel injection (as opposed to direct injection) the engine can still be run on 87 octane gasoline.

Another example with 10.9 to 1 compression ratio & requiring just 91 octane, 12 octane points lower than Doug's claimed as required 103 octane rating...

2013 Dodge Challenger SRT8 392
SPECIFICATIONS
All dimensions are in inches (millimeters) unless otherwise noted.
All dimensions are measured at curb weight with standard tires and wheels.
Note: Information shown is correct at time of publication, and is subject to change without notice.
GENERAL INFORMATION
Vehicle Type Two-door coupe
Assembly Plant Brampton, Ontario, Canada
EPA Vehicle Class Intermediate car
Introduction Date Summer 2012 as 2013 model
BODY
Layout Longitudinal front engine, rear-wheel drive
Construction Unitized steel body
ENGINE: 392 HEMI® V-8 (6.4 Liter)
Availability Standard
Type and Description 90-degree V-type, liquid-cooled
Displacement 392 cu. in. (6,417 cu. cm)
Bore x Stroke 4.09 x 3.72 (103.9 x 94.5)
Valve System Pushrod-operated overhead valves, 16 valves with sodium-filled exhaust
valves and hollow stem intake valves, 16 conventional hydraulic lifters, all
with roller tips
Fuel Injection Sequential, multi-port, electronic, returnless; automatic features Fuel
Saver mode
Construction Deep-skirt cast-iron block with cross-bolted main bearing caps, aluminum
alloy heads with hemispherical combustion chambers
Compression Ratio 10.9:1
Power (estimated SAE net) 470 bhp (351 kW) @ 6,000 rpm (73.4 bhp/liter)
Torque (estimated SAE net) 470 lb.-ft. (637 N•m) @ 4,200 rpm
Max. Engine Speed 6,400 rpm (electronically limited)
Fuel Requirement Premium 91 octane (R+M)/2 — recommended

can we all agree on one thing?

The engine bay of Chris' Pantera is gorgeous.

Chris, I'm also running C302B heads (427 ci, Fontana aluminum block) with 11.25:1 CR without any detonation issues. It will run on 91 octane but Chevron self-serve gas stations in Western Canada have 94 octane, so that's what I use.

Doug, better get some more medals ready.

quote:

Originally posted by pantera chris:
Doug, better get some more medals ready.

Thats whats causing all that pinging, Medals!!!

This is a good, practical discussion of this topic by David Vizard. I have found it helpful and accurate.

http://www.hotrod.com/articles/0311em-power-squeeze/

Jack