Is 10.4:1 too high for my engine?

[Dino]

'71 440 hp cop engine.  Has six pack rods and a purple cam.  Currently running an edelbrock performer intake and 1407 carb.  Intake will be replaced with the stock '71 intake. 
Apart from having electronic ignition and headers I think everything else is pretty much stock.

When the previous owner had the engine rebuilt he installed forged TRW pistons bringing the compression up to 10.4:1.  Is this too much?  I run it on premium.

The car runs like a trooper, I put around 1000 miles on it since I bought it a few months ago and it runs awesome, cruising and wot.

When it comes out of storage I will swap the intake and install the valley pan with crossover block and fix the leaky header.  Should I be ok with leaving it there? 

I use it for cruising and as a grocery getter but I do like to gun it from time to time.

All gauges work and temp gauge reads around 170, never seen it go beyond, not even after a 4 hour drive. 

I 'think' everything works as it should but always wondered about the compression.  I don't want to find out a year from now that it's too much and I'm damaging the engine.

[elacruze]

10.4 is fine as long as the cam and ignition timing are correct...which you can only know by driving it. If it drives well with no perceptible detonation, you're good to go.

Why change the manifold?

[Dino]

10.4 is fine as long as the cam and ignition timing are correct...which you can only know by driving it. If it drives well with no perceptible detonation, you're good to go.

Why change the manifold?

Great!  Thanks for setting my mind at ease.

I have been told, by some very knowledgeable people here, that the stock '71 intake manifold was one of the best Chrysler ever made and it would actually flow better than the Edelbrock performer.  Now this is the plain performer, not the RPM.

Since I need to remove the manifold to install the valley pan it doesn't hurt to try.  The stock manifold came with the car so it's not costing me anything.  Well, actually I need to repaint it so I'll have to buy a spray can if I can find the good color. 

[Chryco Psycho]

10.4 :1 with iron heads can be touchy with pump gas , it depends if you are using the closed chamber heads or open , open chamber are far more likely to detonate .
If you are using alum heads it is no issues , your compression is low for pump gas .
the M1 dual plane intake sold for years was a a copy of the Iron 68 - 71 intake , the Performer is a Dog / poorly named , the carb is nowhere near the center of the intake even , it will cost you power .

[Chatt69chgr]

10.4 is the static CR.  You need to calculate the dynamic CR.  Look on the Keith Black piston site for the calculator.  Need cam info. 

I talked to a guy at local cruise-in that had a 69 440 that he said was stock rebuild at 10:1.  Said on 93 pump gas on a hot day he got detonation.  Claimed it ran OK the rest of the time. 

[BSB67]

Unless it has a really big cam, or aluminum heads, I doubt it is 10.4:1.  You would have detonation.  10.4 is a bit of an odd CR unless it was part of someone's strategic plan.  Which purple cam do you have?

[elacruze]

I ran a 440 for many years with a static 11:1 compression ratio, with open chamber heads. It had a .509 purple cam and MP distributor, and did show any signs of detonation. That engine does not compare to this discussion, but I challenge the notion that 10.4 is too much compression on pump gas with iron heads. Ignition timing causes detonation, not static compression.

[BSB67]

I ran one at 10.3:1.  Rattled like crazy. cold plugs, good cooling system, 160 Thermostat, and 25% race gas to keep it from rattling - smaller cam and heavy car w/3.23s.  My 383 w/ 11.0:1 with a 484 cam needs race gas.  My aluminum head motor w/ 10.8 and a intake closing at 77 degrees ABDC (which is later than a 509) is on the verge of rattle.  The factory original motors with CRs in the 9.7 ranges would not run on 93 either.  If the OP has 509 and 10.4:1, he would probably be okay.  I suspect that he does not have a 509.

[Dino]

I am finding myself in a situation where I need to rely on previous owner statements regarding the specs.  I do trust the guy but he may not have been given the actual facts either.

Supposedly the engine has a purple cam .474 / 280.  The headers are not coated and one of them leaks so they may not be the best in the world either.

Since it's a 1971 440 hp out of a cop car, it should have around 375 hp stock, this is gross rating.  Very likely the engine came out of a Polara.  I have a 71 dual snorkel that was likely on the engine that sports a Chrysler 440 TNT pie tin.  If I recall, stock comp is around 9.7:1 and these puppies ran on premium.

On the engine id pad I think it says its .20 over or something, I'll have to check tomorrow.  Definitely an F code 440 HP.  Again supposedly with six pack rods but who knows if this is true?

Apart from the headers and edelbrock bolt on stuff, it all looks pretty stock to me.

The engine is by no means slow, it's definitely not a race engine, and with the 2.96 gears and 14" tires it won't win any races, but it's still one peppy sob on the road and I can make it go sideways real easy.

It also idles nice and steady and doesn't sound overly aggressive, just a nice fat rumble.

I think this engine is barely anything more than stock and likely a well machined and tuned stock 440 might perform better, but since it's so reliable I'm not too eager to take it apart to find out what's in there.  I haven't done anything to this engine and it's as reliable as anything.  At one point I would love to take it apart and make it a bit more powerful or at the least more efficient, but right now I want to enjoy it.

I asked the question about the comp because if I'm likely to damage anything then I need to do the work now before it's too late.

Is there a way to test compression easily?

[elacruze]

You can get some idea about your combination by testing the cranking compression with an inexpensive gauge that screws a hose in place of the spark plug.

You can also test to see if a recurved distributor will help. Use a timing light and a friend to help, record your timing at idle, 2000rpm, 3000rpm, and full advance. Don't bother with the vacuum, disconnect it. After recording these, drive the car and note the RPM and conditions when detonation is worst. Retard the timing 5* and drive the car just long enough to see if the detonation goes away. If not, back up another 5*. You'll find a setting where the engine stops detonating, but keep in mind that the timing will not be optimized for idle or high rpm-you're only looking to get rid of the timing where necessary. Once you find the advance that doesn't detonate, record it alongside the first data set and have a distributor recurved to match your needs.

Two things that cause detonation other than too much timing are carbon buildup and poor oil control.
Carbon buildup can cause pre-ignition due to glowing coals when cylinder pressure goes up, and if bad enough can actually raise compression significantly.
Poor oil control in either rings or valve seals can introduce oil into the combustion mixture, which lowers the effective octane rating and lowers detonation resistance.

[Dino]

I recall seeing those things that screw into place of a spark plug when I started work in a body shop and watched the mechanic play around with all that.  I may just give that a go.

For the rest you mentioned I will have to go read a book or two!   

I feel like I'm getting speed courses on a lot of subjects since I've gotten this car so it's time to sit down and really learn something so it'll stick.  Engines are pretty challenging for a novice like me.

[firefighter3931]

A compression test will give you the info you need. I doubt that you have a true 10.4:1 unless the cam is very large bleeding off cylinder pressure. 

Personally, i wouldn't worry about it at this point. Have a look at the plugs for signs of detonation ; small specs of black or silver on the porcelin will indicate a problem. 



Ron

[HPP]

I recall seeing those things that screw into place of a spark plug when I started work in a body shop and watched the mechanic play around with all that.  I may just give that a go.

Make sure you wire the throttle open, then turn it over several times and write down the reading. This is your dynamic, or cranking pressure. Once you know your cylinder pressure, collect the cam specifications for intake valve closing degrees, plug in your altitude, and zero out the boost mulitiplier, then you can back in to potential compression numbers using this caclulator:
http://www.rbracing-rsr.com/comprAdvHD.htm

Altitude is a big one that A LOT of people forget about. It kills compression fast and can be as big a factor in detonation as cam size and timing.  Where I live, 12:1 engines can live on pump gas with the right combination of ignition and valve timing and make tons of power. First hand experience; I had an 11:1 set up that had such a big cam shaft with long duration events, that I only had 7:1 dynamic compression ratio. I had to swap out to a much smaller cam to get the squeeze back up and even though I gave up some top end performanc with the change, the over all results were a HUGE improvement.

[Challenger340]

IMO,
I think whats missing here in the discussion about static and dynamic compression, is the failure to properly account for ABOVE 100% Volumetric Efficiencies that are part/parcel of all performance Camshaft design criterions ?
especially, once different parts/combos are factored in to assist the particular Engine's breathing ?
Factoring in a bleed off of Cylinder Pressure at low rpm's works fine in Theory, but once the Engine hits the powerband and starts to see 107%, 110% or whatever, all you are really doing is "hoping" it won't have TIME to detonate at the higher rpm ?

secondly,
I fail to understand how "Timing" affects "Detonation" ?
since,
the MOST destructive forms of "detonation", are occuring when the Air/Fuel is "Self-Igniting", due to too much Heat Load of Compression...
waay before...
any Spark gets there to set it off ?

WTF is the point "backing" up the Timing/Ignition Spark gonna do, when the Air/Fuel is detonating all by itself before the spark ?

The only time backing the "Timing" can reduce Compression, is if the Engine is "just on the Edge" of the Fuel Load range....
which, again IMO....
a Guy is FAR BETTER served to fatten beyond Stocchiometric range and DROWN it, than backing up the Timing ?
It's only the leaner mixtures than Burn "Fast & Erratic" under too much Timing/Compression.

[elacruze]

IMO,
I think whats missing here in the discussion about static and dynamic compression, is the failure to properly account for ABOVE 100% Volumetric Efficiencies that are part/parcel of all performance Camshaft design criterions ?
especially, once different parts/combos are factored in to assist the particular Engine's breathing ?
Factoring in a bleed off of Cylinder Pressure at low rpm's works fine in Theory, but once the Engine hits the powerband and starts to see 107%, 110% or whatever, all you are really doing is "hoping" it won't have TIME to detonate at the higher rpm ?

secondly,
I fail to understand how "Timing" affects "Detonation" ?
since,
the MOST destructive forms of "detonation", are occuring when the Air/Fuel is "Self-Igniting", due to too much Heat Load of Compression...
waay before...
any Spark gets there to set it off ?

WTF is the point "backing" up the Timing/Ignition Spark gonna do, when the Air/Fuel is detonating all by itself before the spark ?

The only time backing the "Timing" can reduce Compression, is if the Engine is "just on the Edge" of the Fuel Load range....
which, again IMO....
a Guy is FAR BETTER served to fatten beyond Stocchiometric range and DROWN it, than backing up the Timing ?
It's only the leaner mixtures than Burn "Fast & Erratic" under too much Timing/Compression.

If compression and heat alone are the root of detonation, then you would never be able to hot-start a detonating engine.
Detonation occurs _after_ spark ignites, and as cylinder pressure rises due to combustion, at some point the remaining unburned mixture detonates-not the entire package. Retarding the timing reduces cylinder pressure because the piston is retreating faster as the crank angle increases, effectively 'running away' from the dynamic compression and cylinder pressure increase.

The reason that over-rich jetting (usually) improves detonation is because it burns slower-effectively retarding timing. I think it more appropriate to have an efficient mixture and timing that produces optimal pressures.

Mixtures are only 'erratic' when they are too rich or too lean. Fast burn is efficient, and efficient is good.

Let me differentiate "Detonation" from "Pre-ignition" which is what occurs when hot spots in the cylinder ignite the mixture before the spark from the plug. They are not the same in symptoms, causes, or cures.

[Nacho-RT74]

 

[flyinlow]

When you do a compression check aren't you doing dynamic compression ratio check at 200 rpm. (cranking speed) ?

If you left the compression gauge in a cylinder and drove the car (on 7 cylinders) and ran wide open throttle to red line, would the compression gauge read your peak dynamic compression ratio pressure after you stopped?... I was not planning on doing this.

What readings indicate 10:1 compression .   air pressure at sea level, standard day ( 59*F, barometric pressure 29.92 in.hg.)  14.7 psi.   
14.7 times 10 = 147 psi?   I did a cold compression check on my 446 when new , 170 -175 psi. I thought it was a 10.5:1  engine , 10:1 dynamic with Vodoo 60303 cam

.

[flyinlow]

.

:
http://www.rbracing-rsr.com/comprAdvHD.htm




Ran my numbers with this calculator. 9.5 dynamic CR. Eddy heads so minus 1 CR for aluminum heads. I guess I have a 8.5 CR engine.  Oh well ,it runs well.  Maybe I can run regular in it instead of premuim.

[Challenger340]

IMO,
I think whats missing here in the discussion about static and dynamic compression, is the failure to properly account for ABOVE 100% Volumetric Efficiencies that are part/parcel of all performance Camshaft design criterions ?
especially, once different parts/combos are factored in to assist the particular Engine's breathing ?
Factoring in a bleed off of Cylinder Pressure at low rpm's works fine in Theory, but once the Engine hits the powerband and starts to see 107%, 110% or whatever, all you are really doing is "hoping" it won't have TIME to detonate at the higher rpm ?

secondly,
I fail to understand how "Timing" affects "Detonation" ?
since,
the MOST destructive forms of "detonation", are occuring when the Air/Fuel is "Self-Igniting", due to too much Heat Load of Compression...
waay before...
any Spark gets there to set it off ?

WTF is the point "backing" up the Timing/Ignition Spark gonna do, when the Air/Fuel is detonating all by itself before the spark ?

The only time backing the "Timing" can reduce Compression, is if the Engine is "just on the Edge" of the Fuel Load range....
which, again IMO....
a Guy is FAR BETTER served to fatten beyond Stocchiometric range and DROWN it, than backing up the Timing ?
It's only the leaner mixtures than Burn "Fast & Erratic" under too much Timing/Compression.

If compression and heat alone are the root of detonation, then you would never be able to hot-start a detonating engine.
Detonation occurs _after_ spark ignites, and as cylinder pressure rises due to combustion, at some point the remaining unburned mixture detonates-not the entire package. Retarding the timing reduces cylinder pressure because the piston is retreating faster as the crank angle increases, effectively 'running away' from the dynamic compression and cylinder pressure increase.

The reason that over-rich jetting (usually) improves detonation is because it burns slower-effectively retarding timing. I think it more appropriate to have an efficient mixture and timing that produces optimal pressures.

Mixtures are only 'erratic' when they are too rich or too lean. Fast burn is efficient, and efficient is good.

Let me differentiate "Detonation" from "Pre-ignition" which is what occurs when hot spots in the cylinder ignite the mixture before the spark from the plug. They are not the same in symptoms, causes, or cures.

I think you may be making my point for me here ?
But we are talking about 2 different things.....one being an Engine with too high Compression for the Fuel being used, and the other on an Engine assuming the Compression pressures are NOT too high for the fuel....
The problem may be the definition of two VERY different Combustion events, under differing air/fuel mixture conditions, being lumped under the same "detonation" term...on two Different Engine conditions...

You are absolutely correct in that air/fuel charge will self-ignite elsewhere in the chamber, as a result of the "increased pressure" wave from the spark ignited flamefront, happens all the time, and "Detonation" is the most CORRECT recognized term.....where the Comp. Ratio is NOT too high for the fuel....

Just zip the Timing ahead on any Engine, and eventually you can hear it "Ping" ?

But the above also occurs, while the piston is moving UP, and INCREASING cylinder pressure towards TDC from the Timing being ignited 30-36 degrees BEFORE TDC., and PEAK pressures are still within the After TDC range where they can be used
It is not simply the Ignited fuel increasing pressure, but the Piston also, that is still going up and reducing chamber size and increasing pressure.

The Target with ignition, is to provide maximum burn pressures AFTER TDC, so the "rate of burn" has to be conduscive to waiting, and allowing the mixture's maximum pressure to occur later....when the piston/Rod is at the BEST angle for 'push"
A "fast" burn being efficient, is relative to "within" a range still considered a "controlled" burn, where the pressure increase linear to full pressure....
An "EXPLOSION" outside that range is not only destructive, but offers poor "pressures' to be exerted after TDC, where best push on the Crank is helpful.

What I am talking about....and I thought was the context of this thread on 10.4:1 with iron heads ?
is when the Compression ratio is too high for the Fuel being used, and indeed, it is SELF-IGNITING by itself  at a point ahead of Timing Spark, the Timing Spark then accelerating the uncontrolled EXPLOSION with even Higher pressures....
Backing the Timing at that point, does little to provide best pressure after TDC, and is BEST controlled by "Drowning" it with fatter mixtures FIRST.....then applying/moving the secondary Spark wave back up for best "Push", albeit still after TDC.

long Story short...
the Engine condition/Compression Ratio/Fuel being used is gonna dictate this discussion...
but,
back to the 10.4:1 with Iron heads......
IMO,
probably gonna be too high for "pump Gas" for most applications/people with iron heads, and simply "Backing" timing is a BAD Band-aid to the root problem....
Just cause you ain't hearing it, don't mean it ain't there ?

Just on the very "edge" of what we are calling "Detonation" WITH Timing Spark, makes GREAT POWER on the Dyno, especially when cheating C.R. for the fuel with iron heads, but it is a very narrow range best found on the Dyno, and NOT simply a "do this" type way to build or Tune ?

[elacruze]

Challenger340, I think we merely have a slight difference of descriptive terms, and agree fundamentally. Sticking particularly to this thread's engine combo, I don't think that unsparked early detonation is possible, but sparked detonation is likely-and I believe that is controllable with corrected timing. We don't really know enough about the engine to say for sure, nor even if it is detonating at all until the owner investigates. I do know that my 11:1 .509 440 drove like a dream when it had a CH4B manifold on it, and never indicated detonation on the plugs or in my ears. It does have polished combustion chambers in the Stage IV heads, but that is a pre-ignition preventer rather than detonation.

The real question is what cam is in there? 10.4:1 should be very drivable and detonation free with the appropriate camshaft and timing, on pump premium.
Another question is how is the car driven? An engine that is prone to detonation at WOT may never exhibit signs if the driver never opens the throttle wide enough.

[Challenger340]

Challenger340, I think we merely have a slight difference of descriptive terms, and agree fundamentally. Sticking particularly to this thread's engine combo, I don't think that unsparked early detonation is possible, but sparked detonation is likely-and I believe that is controllable with corrected timing. We don't really know enough about the engine to say for sure, nor even if it is detonating at all until the owner investigates. I do know that my 11:1 .509 440 drove like a dream when it had a CH4B manifold on it, and never indicated detonation on the plugs or in my ears. It does have polished combustion chambers in the Stage IV heads, but that is a pre-ignition preventer rather than detonation.

The real question is what cam is in there? 10.4:1 should be very drivable and detonation free with the appropriate camshaft and timing, on pump premium.
Another question is how is the car driven? An engine that is prone to detonation at WOT may never exhibit signs if the driver never opens the throttle wide enough.

Agreed !
A ton of variables here to be known, and user tuning capabilities against the variables must be known as well.....
You obviously have alot of continuity/experience with your combo to be able to run up at 11:1 on pump fuel with the irons..... NOT saying it cannot be done...Obviously it can, you are doing it...
just........
THAT, takes some talents....not always present with others ? and, it can be a very steep learning curve for many ?

I myself used to Drag Race a 10.6:1 440 on pump gas Irons as well...no problems back 25 years ago....
But Today,
I tend to look at things from the Business perspective as an Engine Builder, and what not only "Fits" a particular Customer, but what is "safe" longterm for the expected environment after it's Dyno'd, and leaves my Shop.....
That "Environment", for me anyways, has to include not knowing the Fuel the Guy make stick in it, Elevation, even the dam exhaust which can change scavenging...just a TON of unknowns....and usually the "Guy" whose gonna drive it like he stole it...
and,
that pretty much dictates 9.75:1 max with Irons, about a point Higher for Aluminum Heads on pump fuels....for me to stay safe anyways, against the user environment.....

One thing is for sure, with the advent of newer fuels, e85, etc., people are bound to revisit the "accepted" C.R. parameters....

[flyinlow]

33 years ago I assembled a .030 over 1972 440 Cop engine. Steel crank, sixpac rods , TRW forged sixpac pistons and 67 440 heads. All the "Hot" items back then. CR in the low tens, Crower Monarch cam ,don;t remember the specs ,but a midrange hydraulic street cam. In a 68 RT with 3.55 gears, headers,intake and a TQ. I remember only being able to run about 32* of timing with premium unleaded. Ran well as a daily driver. I sold the car , last I knew it had about 50K on the engine.
This is similar to your engine, so I would think if you match the timing to your fuel ,you should be good to go.