A
Anonymous
Guest
Read my article:
http://victorylibrary.com/mopar/otto.htm
http://victorylibrary.com/mopar/otto.htm
Good chart. I had a '69 Torino Squire with 351W 4V. When only the reduced octane was available in 1974, I had to retard the timing to keep it from pinging; and it ran like a dog. I installed dished pistons, from the 351W 2V. The car ran a lot better, because it could use the lower octane with more advance. In fact, it ran better with the lower compression than it did before with the higher octane. 
I think that does a lot to explain the diminishing returns you get from increaases at a certain point.
Does this calculation hold true for both iron and alloy heads?
Does this calculation hold true for both iron and alloy heads?
The point of diminishing returns!
I agree with what you have posted completely. There is never a time compression ratio increases produce disproportianately high gains. At about 14:1, volumetric efficiency tends to back down because of the other matters you excluded from the anaylsis.
Most people who can read listen to the overall statement, but not the conditions. I agree that the statement is conditional on some things never changing.
Lets objectively look at the chances of the four things staying the same. On the basis of my reading the chances are very,very small of the four item noted remaining the same. I assert that often, the changes made to create higher compression will aid the four factors positvely for the majority of American combustion chambers, negatively in only some of the high performance chambers.
My sources are mainly biased towards Fords and David Vizard books. I've only ever re-built four engines in my life, one GM, two Fords, and one Mini, so you can question my credentials if you wish, but I've spent lots of time arguing against the theories which Vizard exponds by reading Grumpy Jenkins, Clive Trickey, Rob McGavin and some of the Aussie guys who say hi compression is a waste (most Holden guys are in that camp)
The point I make is that
1. Other changes are always made when the compression ratio is altered.
Changes to:-
a)flame travel (its most often reduced with hi-po pistons),
b)valve shrouding (often increased, but is mitigated by gas flowing with a famous SuperFlow flow bench!),
c)piston dome masking (often, the dome is relief cut to suit flame travel and valve opening).
d)octane demand doesn't always go up with increased compression, as the whole reason for it is usually to raise opening duration to increase effective compression. When a racer bolts on a 320 degree cam, he can loose a huge amount of effective compression, which reduces the octane demand.
e)lastly, quench is often increased as at the 10 to 14:1 level, people go to alloy heads with closed chambers or welded iron or alloy production heads.
In some chambers, such as Mopar Hemis, some Pontiacs and certainly Porcupine Chevies, there is very little postive alteration to a) to e), and the results are counter productive has you always have to compromise on pistons popping up into the chamber.
On the 335/385 Martel Fords, the Pinto and Lima fours, A-series Austin/Mini I4's and the Geelong built X-flow I6, there are only positives.
Since there is no way to isolate a) to e), and that in 90% of the cases the mods are being done to rasie power, these aspects are improved.
Which is why we find 13:1 to 14:1 compression racers in all classes worldwide from sub 1 liter engines to those past 6 liters.
I agree with what you have posted completely. There is never a time compression ratio increases produce disproportianately high gains. At about 14:1, volumetric efficiency tends to back down because of the other matters you excluded from the anaylsis.
Most people who can read listen to the overall statement, but not the conditions. I agree that the statement is conditional on some things never changing.
Lets objectively look at the chances of the four things staying the same. On the basis of my reading the chances are very,very small of the four item noted remaining the same. I assert that often, the changes made to create higher compression will aid the four factors positvely for the majority of American combustion chambers, negatively in only some of the high performance chambers.
My sources are mainly biased towards Fords and David Vizard books. I've only ever re-built four engines in my life, one GM, two Fords, and one Mini, so you can question my credentials if you wish, but I've spent lots of time arguing against the theories which Vizard exponds by reading Grumpy Jenkins, Clive Trickey, Rob McGavin and some of the Aussie guys who say hi compression is a waste (most Holden guys are in that camp)
The point I make is that
1. Other changes are always made when the compression ratio is altered.
Changes to:-
a)flame travel (its most often reduced with hi-po pistons),
b)valve shrouding (often increased, but is mitigated by gas flowing with a famous SuperFlow flow bench!),
c)piston dome masking (often, the dome is relief cut to suit flame travel and valve opening).
d)octane demand doesn't always go up with increased compression, as the whole reason for it is usually to raise opening duration to increase effective compression. When a racer bolts on a 320 degree cam, he can loose a huge amount of effective compression, which reduces the octane demand.
e)lastly, quench is often increased as at the 10 to 14:1 level, people go to alloy heads with closed chambers or welded iron or alloy production heads.
In some chambers, such as Mopar Hemis, some Pontiacs and certainly Porcupine Chevies, there is very little postive alteration to a) to e), and the results are counter productive has you always have to compromise on pistons popping up into the chamber.
On the 335/385 Martel Fords, the Pinto and Lima fours, A-series Austin/Mini I4's and the Geelong built X-flow I6, there are only positives.
Since there is no way to isolate a) to e), and that in 90% of the cases the mods are being done to rasie power, these aspects are improved.
Which is why we find 13:1 to 14:1 compression racers in all classes worldwide from sub 1 liter engines to those past 6 liters.
A
Anonymous
Guest
Ex;
I'd have to agree with you: altering CR in most engines also, by default, alters other items. In the case of our 200 engines, for instance, milling the head also reduces the height of the combustion chamber, but it does nothing to the quench band height. However, after milling the head past the point where the round shape becomes the 'bathtub' wedge instead (about .030" or so on the D78 head), the acceleration of the flow across the center of the chamber rises dramatically. This can actually 'blow the fire out' in the center of the chamber, making it necessary to either re-ignite it with the rest of the burning charge or add another spark, like with the multi-spark systems. To prevent this situation, one must then reduce the deck height so that the quench becomes more universally oriented toward the center from all edges, not just from one side. It can become a pain.
In the realm of pop-up top pistons, the issue of quench is a little easier to direct: the pop-top blocks the quench, period. The acceleration becomes mostly upward, toward the edges of the chamber, on compression. Most pop-up engine types I've worked on (Ford's FE, Hondas, Suzukis, Yamahas, BMW bikes) all have zero or near-zero deck heights. This gives enormous accelerations of the upward flow on compression. The net result is a longer burn time, because the flamefront is somewhat snuffed or inhibited in the fastest-moving portions of the flow, being re-ignited later by the other burning gases. Evenly-dispersed heat is the result: the heat is, in effect, 'moved down' further into the cylinder to push a little longer on the piston. This usually yields better MPG and a wider powerband. The higher the popup (in Honda bikes, for instance), the longer the burn and the wider the powerband, all else being equal (until octane becomes a problem).
I have, however, had to use airplane gas once or twice for having gone too far 'up'...
I'd have to agree with you: altering CR in most engines also, by default, alters other items. In the case of our 200 engines, for instance, milling the head also reduces the height of the combustion chamber, but it does nothing to the quench band height. However, after milling the head past the point where the round shape becomes the 'bathtub' wedge instead (about .030" or so on the D78 head), the acceleration of the flow across the center of the chamber rises dramatically. This can actually 'blow the fire out' in the center of the chamber, making it necessary to either re-ignite it with the rest of the burning charge or add another spark, like with the multi-spark systems. To prevent this situation, one must then reduce the deck height so that the quench becomes more universally oriented toward the center from all edges, not just from one side. It can become a pain.
In the realm of pop-up top pistons, the issue of quench is a little easier to direct: the pop-top blocks the quench, period. The acceleration becomes mostly upward, toward the edges of the chamber, on compression. Most pop-up engine types I've worked on (Ford's FE, Hondas, Suzukis, Yamahas, BMW bikes) all have zero or near-zero deck heights. This gives enormous accelerations of the upward flow on compression. The net result is a longer burn time, because the flamefront is somewhat snuffed or inhibited in the fastest-moving portions of the flow, being re-ignited later by the other burning gases. Evenly-dispersed heat is the result: the heat is, in effect, 'moved down' further into the cylinder to push a little longer on the piston. This usually yields better MPG and a wider powerband. The higher the popup (in Honda bikes, for instance), the longer the burn and the wider the powerband, all else being equal (until octane becomes a problem).
I have, however, had to use airplane gas once or twice for having gone too far 'up'...
A recap of the details. I'm getting a characteristic curve set up for the 8 typical combustion chambers
Firsty, Jeffery Diamond, at http://victorylibrary.com/mopar/otto-c.htm, has some generic data which shows that compression ratio rise reaches a point of fastly dimishing returns.
Secondly, we discussed it broadly a while ago, and I promised to spill the beans on data I had acess to.
It still isn’t done yet, but I'm very close. It is as significant as:-
a) Flame Travel due to plug placement (its most often reduced with hi-po pistons),
b) Valve Shrouding (often increased, but is mitigated by gas flowing with a famous SuperFlow flow bench!),
c) Piston Dome Masking (often, the dome is relief cut to suit flame travel and valve opening).
d) Effective Compression (cam related octane demand). Doesn't always go up with increased compression, as the whole reason for it is usually to raise opening duration to increase effective compression. When a racer bolts on a 320 degree cam, he can loose a huge amount of effective compression, which reduces the octane demand.
e) Quench is often increased as at the 10 to 14:1 level, people go to alloy heads with closed chambers or welded iron or alloy production heads.
f) Intake Heating
g) Fuel Distribution
h) Head Material (iron or alloy)
i) Inertial Ramming (Carburation, efi, vee engines have better thermodynamic properties)
j) Piston Deck Impinging , Flat or Recessed.
k) Head Gasket Material and Thickness in relation to Piston Deck
l) Sharp edges and loose tollerances or
blue printed to 0.1 c/r or
C/R balanced on all cylinders accept the detonation prone ones. (If they are reduced by half a point, you can go up another 0.5 points on the other cylinders)
all these have a bearing.
There are characteristic curves I’ve seen for most combustion chambers, so you don’t have to run these factors into a program. The two curves I have are for the Pinto 2000 and Austin A-series engine. These have very accurate additional data about the 11 items listed above.
There are many chambers. I haven’t listed the huge range of vintage flat head and inlet over exhast combos, thank the dear Lord.
Steep included angle Mopar Hemi’s, Jag XK 6, Alfa Romeo
Steep Wedge Porcupine Chevies.
Steep Reverse Wedge the Pinto and Lima fours,
Shallow Compound Vetrtex Hemi
Shallow included Pontiac’s, Holden’s, Olds, Wedge, Chev, Ford’s ohv non Clevo, Lima
Shallow porcupine 335/385 Martel Fords, Geelong built X-flow
Flat bathtub Weslake A-series Austin/Mini I4's and the , there are only positives.
Flat Heron head Kent, XKE 12, Y-block.
Cosworth narrow Angle Pentrooof (Sierra, Toyota 4AGE, Ford BDA, etc)
Back soon!
Firsty, Jeffery Diamond, at http://victorylibrary.com/mopar/otto-c.htm, has some generic data which shows that compression ratio rise reaches a point of fastly dimishing returns.
Secondly, we discussed it broadly a while ago, and I promised to spill the beans on data I had acess to.
It still isn’t done yet, but I'm very close. It is as significant as:-
a) Flame Travel due to plug placement (its most often reduced with hi-po pistons),
b) Valve Shrouding (often increased, but is mitigated by gas flowing with a famous SuperFlow flow bench!),
c) Piston Dome Masking (often, the dome is relief cut to suit flame travel and valve opening).
d) Effective Compression (cam related octane demand). Doesn't always go up with increased compression, as the whole reason for it is usually to raise opening duration to increase effective compression. When a racer bolts on a 320 degree cam, he can loose a huge amount of effective compression, which reduces the octane demand.
e) Quench is often increased as at the 10 to 14:1 level, people go to alloy heads with closed chambers or welded iron or alloy production heads.
f) Intake Heating
g) Fuel Distribution
h) Head Material (iron or alloy)
i) Inertial Ramming (Carburation, efi, vee engines have better thermodynamic properties)
j) Piston Deck Impinging , Flat or Recessed.
k) Head Gasket Material and Thickness in relation to Piston Deck
l) Sharp edges and loose tollerances or
blue printed to 0.1 c/r or
C/R balanced on all cylinders accept the detonation prone ones. (If they are reduced by half a point, you can go up another 0.5 points on the other cylinders)
all these have a bearing.
There are characteristic curves I’ve seen for most combustion chambers, so you don’t have to run these factors into a program. The two curves I have are for the Pinto 2000 and Austin A-series engine. These have very accurate additional data about the 11 items listed above.
There are many chambers. I haven’t listed the huge range of vintage flat head and inlet over exhast combos, thank the dear Lord.
Steep included angle Mopar Hemi’s, Jag XK 6, Alfa Romeo
Steep Wedge Porcupine Chevies.
Steep Reverse Wedge the Pinto and Lima fours,
Shallow Compound Vetrtex Hemi
Shallow included Pontiac’s, Holden’s, Olds, Wedge, Chev, Ford’s ohv non Clevo, Lima
Shallow porcupine 335/385 Martel Fords, Geelong built X-flow
Flat bathtub Weslake A-series Austin/Mini I4's and the , there are only positives.
Flat Heron head Kent, XKE 12, Y-block.
Cosworth narrow Angle Pentrooof (Sierra, Toyota 4AGE, Ford BDA, etc)
Back soon!
A
Anonymous
Guest
Can you articulate on your definition of efficiency. You write that it is "the relative use made of the energy contained in the fuel". I assume you're following a fraction of work produced by a unit mass of fuel?
Just curious. Thanks for your sharing.
Just curious. Thanks for your sharing.
tetraruby":2jhhhii2 said:
Efficiency is work done (Force time distance) for a given consumption of existing energy, less engery loss via heat. If 778 BTU's has l hp of energy in a closed system, then it only has goes into making about 0.25 hp in the internal cumbustion engine. 75% is wasted.
The formula panic used is his from a source book, and, I don't know what one.
There is no way to radically improve the efficiency of an engine via just adding compression. A stock engine may be 18% efficient , but 25% efficient with all the blue printed in hipo tricks. The point I think is that at around 13 to 14:1, the effort in time and expense isn't warranted.
While I was reading through toe Vizaed text books today, I found that Heanium coatings, valve guide seals, and the fuel air alteration needed, and exhast back pressure also figure in detonation resistance. From some of the issues some guys have here with having to run hi test on their Fairmonts, I'd say there are heaps of avenues for improvement. Best one was seeing that intake charge heating adds a need for an extra 3 to 8 octane numbers to an engine.
The heat out put on a
