This is interesting
I have read (on forums...) that there can be too high squish velocity when engines are under high boost.
NA engines not so sensitive i think? But if super much squish was of benefit, then would all engine makers already have it?
under boost the fuel/air mix must be significantly richer to avoid entering the detonation.
as compression increases ignition advance requirements tend to be reduced, as compression increases , the fuel/air ratio that generally produces the best peak torque needs to be marginally richer,
while a 14.7:1 ratio at between 8:1-10:1 may reduce emissions, you'll generally see torque improve with a richer f/a ratio near 12.5:1
while raising compression, generally results in increased torque, the percentage of that gain in torque tends to be reduced as you go closer to the ideal compression for the fuel octane used, thus a boost of compression from lets say 8:1-to-10:1 generally produces, a gain of about 7% -7.5% in HP boosting that same engine from 10:1 -to-12:1 might only result in a 6%-7% added gain and each boost requires a higher octane fuel.( usually a marginally richer F/A ratio, and more efficient engine cooling.
keep in mind the flame front burn speed is controlled to some extent by both the fuel/air mix and compression ratio, but combustion chambers with quench areas can significantly speed up the burn speed, as a significant volume of F/A mix it thrown across the combustion chamber significantly enhancing both burn efficiency and burn speed, thus less advance in the ignition timing is required and lower emissions are common.
spark plug info..SO!...read thru the links theres a ton of good info, but its spread over all the links, if you can get that skill mastered your well ahead of most guys who fail to take the time and effort to learn that skill guys frequently ask me what plug gap to use, Provided your ignition...
garage.grumpysperformance.com
1 cubic foot of air at standard temperature and pressure assuming average composition weighs approximately 0.0807 lbs. (at sea level) that simply means it takes 12.4 cubic feet of air to equal one pound, your best engine torque is generally found at a fuel/air ratio near 12.6:1 , thats 12.6...
garage.grumpysperformance.com you want a controlled burn (that generally takes 30-50 thousands of a second)
where a rapid increase in pressure above the piston forces it down the cylinder,
and you want to avoid detonation, that will rapidly damage a piston
A spark plug only functions completely when its center electrode temperature is between these temperatures of about 500°C and 950°C.
keep in mind just rapidly compressing the fuel/air mix rapidly raised the mixtures temperature enough that it can cause it to self ignite
(detonation) one reason you use quench & squish in the combustion chamber design to get the ignition to start and burn uniformly, and ideally starting in the near center of the combustion chamber and racing out toward the outer edges rather than self ignition near the edges that will rapidly result in piston damage from excessive pressure and heat. remember at 850 rpm (idle speed ) your compressing a new cylinder full of fuel/air , 7 times a second at 6000 rpm it is 50 times a second.
The following examples detail the typical temperatures of various combustion-related engine parts during normal operation:
Intake valve: 475° F
Exhaust valve: 1,200° F
Spark plug: 1,100° F
Piston face: 575° F
Cylinder wall: 375° F
"The most commonly known flammable liquid is gasoline.
It has a flash point of about −50° F (−65° C). The ignition temperature is about 495° F (232(232° C) [sic], a comparatively low figure." The temperature of the burning gases inside the combustion chamber is typically around 2,800° F. In a diesel engine, this temperature remains fairly steady. In a gasoline-powered engine, the temperature can climb to 4,500° F or more under certain circumstances. However, the vehicle's engine cooling system keeps the walls of the combustion chamber at a temperature of between 265° F and 475° F.
Hi guys, I NEED some advise here... I have a 350 sbc motor that has been bored out 40 over, 6" piston rods, dished out piston heads at 20cc, 3.750 stroke crankshaft, my deck clearance is -.006, Trick flow 175 cylinder head chamber size is 56cc, mild Elgin 923 cam, and an .042 head gasket... I...
Answer (1 of 9): As there appears to already be some engineering based answers, I will defer from a scientific answer, and give you my real world aviation experience. Flying my PA-31–325 Navajo, it being equipped with two turbo charged, air cooled six cylinder engines producing 325 horsepower eac...
What else influences your car's octane requirements? IF YOU DON,T LIKE READING SUB-LINKS, AND LOOKING AT CHARTS , AND DOING A BIT OF MATH 'AND INDIVIDUAL CALCULATIONS, YOUR UN-LIKELY TO BENEFIT FROM MOST OF THE THREADS, ON THIS WEB SITE! LIKE IN MOST AREAS ITS KNOWLEDGE AND THE ABILITY TO THINK...
garage.grumpysperformance.com
Whether you're a weekend DIY mechanic, a diehard gearhead, or just a vehicle owner curious about how your car works, you may want to know more about how the engine burns fuel to create power. Many common questions center on what causes engine overheating. You may be wondering just how hot it...
This is interesting :like: I have read (on forums...) that there can be too high squish velocity when engines are under high boost. NA engines not so sensitive i think? But if super much squish was of benefit, then would all engine makers already have it?
What else influences your car's octane requirements? IF YOU DON,T LIKE READING SUB-LINKS, AND LOOKING AT CHARTS , AND DOING A BIT OF MATH 'AND INDIVIDUAL CALCULATIONS, YOUR UN-LIKELY TO BENEFIT FROM MOST OF THE THREADS, ON THIS WEB SITE! LIKE IN MOST AREAS ITS KNOWLEDGE AND THE ABILITY TO THINK...
it helps a great deal to know what your working with ,ID suggest starting, by verifying TDC and having the correct timing tape on your damper then,start with 8 degrees btdc and verifying the full advance of 36 degrees total is all in at 3200rpm as a base line, once youve got that, as a standard...
when your setting up your cars fuel delivery system, you'll obviously need to know the physically requirements of the engine your about to feed, For your older carburetor, equiped muscle car, this will generally be for most performance cars 5-6 psi of fuel pressure at the carb inlet port, a fuel...
Gasoline is produced in oil refineries. Material that is separated from crude oil via distillation, called virgin or straight-run gasoline, does not meet the required specifications for modern engines (in particular octane rating; see below), but will form part of the blend. The bulk of a...
What else influences your car's octane requirements? IF YOU DON,T LIKE READING SUB-LINKS, AND LOOKING AT CHARTS , AND DOING A BIT OF MATH 'AND INDIVIDUAL CALCULATIONS, YOUR UN-LIKELY TO BENEFIT FROM MOST OF THE THREADS, ON THIS WEB SITE! LIKE IN MOST AREAS ITS KNOWLEDGE AND THE ABILITY TO THINK...
Opinions are like assholes and everyone has one. Look on a forum, blog, Instagram or YouTube account and you can find a number of “engine builders” sharing their thoughts and feelings on the best compression ratio for a particular engine or application. If you take away anything more than the […]
theres a long list of factors that have to be considered and balanced for the internal combustion engine to make better power ,one major factor is the type of fuel used and the fuel/air ratio and its efficient combustion, if you want to boost power you need to more effectively increase...
In today's video we're talking about your engine's compression ratio. First we'll explain the theory behind the compression ratio, so what it is and how it ...
I've been using this calculator some http://www.torqsoft.net/squish-velocity.html but I also have an XLS based calculator that was given to me by a Dr. with an automotive research company that is very similar and uses bowl diameter directly instead of using %Squish Area, it gets SUPER interesting because the 2nd tab of that particular XLS takes the squish velocity calculations as input, and then lets you measure the "Flame Path Radius" (basically measure from the spark plug electrode to the furthest reach of the chamber), the initial laminar flame speed (which it says depends upon what fuel you're using your air fuel mixture and especially IATs), then your engine's ignition delay (.2 - .8 ms range) and at what crank angle you're targeting to have peak cylinder pressure occur at and it tells you your engine's expected turbulent flame speed, burntime, burn angle, and ignition firing angle required in your timing table. (You could theoretically recalculate the squish velocity at multiple RPM points and use the resulting ignition firing angle for an initial engine base tune...)
I am pretty certain the author doesn't want me widely distributing that XLS, though..
I've been collecting recommendations for max squish velocities over the past week and Professor Gordon Blair says max squish velocity shoudl be 15 - 20m/s at your desired peak HP RPM, the Dr. who gave me the XLS says 25-35 m/s at hp peak is ok on many NA engines, and TSR which I guess is a big professional automotive engineer software suite recommends a max squish velocity between 15-30 m/s.
Many of the recommendations I believe come from 2 cycle engines where it's more important and where squish is more plentiful.
I've also heard some nitrous-focused engine builders who try to get squish near ZERO so that they don't accelerate the burn speed any more than it already is with tons of nitrous and knock engines to death.
All the Nitrous and forced induction tapered quench pad / "chamber softening" enhancements SEEM TO BE focused on reducing squish velocity (when you change the squish area taper angle using the calculator above you'll see that even VERY SMALL tapers like the "chamber softening" folks recommend DRAMATICALLY lowers the max squish velocity). -Taper angle changes the max squish velocity the most, then the squish distance, then all the other factors. Changes in the % area I haven't played with much because I don't want to waste my time with junk numbers; I'm hoping to get some decent numbers to model some actual engines.
-I THINK the reason that we don't hear about Squish Velocity being too high on 23 deg SBC engines is because squish area is so much harder to come by. -That's actually why I wanted a calculator, I wanted to be able to model typical SBC engine combos and se what the max quench velocity looks like, but I can't get good enough quality data on actual chamber diameters or quench area percentages to get good results out of the calculator.
(I could see a really big bore SBC like a 4.165" bore with a small chamber and a D-dish or a mirrored piston dish with a close piston to head clearance actually exceeding 35 m/s max squish velocity, but I just don't know as I don't have real data on the critical quench area %...)
-The most interesting thing that I've learned in all of this is that there's actually 2 squish events: the one we normally talk about where the air-fuel mixture in the quench area gets forced rapidly into center of the cylinder, mixing it well, and evening out any hot spots, but then after ignition occurs and after TDC as the piston is traveling down, the quench area then actually pushes the burning air-fuel mass back out towards the cylinder's extremities and increases the burn rate and cylinder pressure (it dramatically increases the turbulent flame speed that's responsible for the actual rate of burn largely).
This idea that because the max quench velocity drives the rate that the flame front spreads and is a / the major factor driving timing requirements was something that I was missing before...
On the discussions I've come across so far, many folks coorelate the max quench velocity with the rate of pressure rise in the cylinder due to combustion and it becomes one more variable that they try to control -I believe that's why these calculators look at the timing of the exhaust valve opening event -if they have an early exhaust valve open I believe they try to push the rate of pressure rise to be faster to get more work done on pushing the piston down the bore before the valve opens -but the engine and bearings take more of a beating, if you have the luxury of the exhaust valve not opening for a while then you can run less on the ragged edge with a super fast rate of pressure rise and have a slightly slower pressure rise that isn't as hard on parts and bearings -that's my current best guess understanding like a week into this and reading way too much about it in a short period of time...
Interesting idea: Maybe pushing the quench velocity as high as you can get it is a good thing for someone running a CompCams Thumper cam with it's stupid early exhaust valve opening so you can lose slightly less torque with one! ;-)
This is interesting
I have read (on forums...) that there can be too high squish velocity when engines are under high boost.
NA engines not so sensitive i think? But if super much squish was of benefit, then would all engine makers already have it?
Yep, the same thing I keep coming across and it seems to be why the forced induction / nitrous guys do "chamber softening" and go with tapered quench areas.
The 2 cycle motorcycle guys seem SUPER OBSESSED with it- not just getting enough, but avoiding too much and getting it "just right".
-Then I start to run into the "super geeks" on this subject who start to hint about changes that improve the quench velocity going "outbound" after TDC and forcing the burning fuel air mix out into the larger chamber. I also vaguely remember a Darin Morgan video posted on his youtube channel that touched on this that I want to go and find again, when I get the time. (I've got a pretty major dental surgery on Thursday morning and I need to go get some work stuff closed out today and tomorrow before I'll be able to try and track any more of this down...)
I've been collecting recommendations for max squish velocities over the past week and Professor Gordon Blair says max squish velocity shoudl be 15 - 20m/s at your desired peak HP RPM,
I think it was detonation/knock control, it was a couple of years since i read it, im not sure, could been combustion speed vs rod angle, it was a "hot debate" from "both sides", no real conclusion.
Its a complex thing, but so interesting.
I think it was detonation/knock control, it was a couple of years since i read it, im not sure, could been combustion speed vs rod angle, it was a "hot debate" from "both sides", no real conclusion.
Its a complex thing, but so interesting.
That's essentially what I've heard reported, too. When the quench velocity gets too high, it causes the rate-of-pressure rise to get too high and it can induce detonation itself. Makes sense anyway.
No. And I'm afraid of what it would even cost. I've seen it largely quoted as the source of the 15-20m/s max quench velocity quote, in a number of places, though.
I've got only one hobby where I'll buy and collect academic text books, and this one isn't it...
It's really interesting to look at some of the calculations that go from Squish Velocity to Turbulent Flame Speed and ultimately the ignition timing requirements / firing angle and then think about how that compares to Plasma ignition and how they seem kind like focusing on 60 ft time vs. "back half" 1/4 mile times.
The quench velocity dramatically increases the turbulent flame speed -which really helps after the initial flame kernel is present and the flame front is starting to move across the cylinder.
My current understanding of how Plasma ignition decreases ignition advance requirements is that it reduces the ignition delay and essentially reduces the flame path radius because you're starting with a larger flame kernel. (Kinda like 60 ft times it gets the initial burn started much sooner so you don't need as much advance but I'm not sure how much it changes the rate of pressure rise.)
Now if someone would just release a plasma ignition system that doesn't EAT plugs...
These guys only seem to care about working directly with big OEMs AND have all the patents locked, up, unfortunately, but maybe it will eventually trickle down: https://www.transientplasmasystems.com/applications/#ignition
I know that Quench Velocity and Plasma ignition seem like HUGE tangents to each other, but I think they really occupy a similar space; two different approaches to burning more of the air and fuel mixture faster with less ignition advance so you put more of the air and fuel to work AND two technologies that help reduce knock when the engine is octane limited because they leave less TIME for preignition or knock to happen. (Apparently if you don't let the rate-of-pressure-rise get too out of control.
Recent NewsGround-Breaking Ignition Technology from Transient Plasma Systems Proven to Make Gasoline-Powered Vehicles Cleaner and More EfficientJune 8, 2022Transient Plasma Systems Reports Significant Breakthroughs in Ignition TechnologyDecember 15, 2021Experts Are Divided on the Best Way for...
www.tpsignition.com
Look at the flame front development photos comparing standard ignition to the TPS "transient plasma" ignition:
The transient plasma flame front looks kinda like a strange mushroom cloud growing in the cylinder!
its been my experience that quench distances tighter than about .035 tend to allow the piston to almost or marginally contact the cylinder head under high heat and high load conditions.
now admittedly I mostly built BBC engines, and mostly with the longer 6.385" or with the stock 6.135" connecting rods,
keep in mind the steel used or alloy , length and cross section of the rod design has some effect,
on the connecting rods elongation under high stress and as the heat is increased.
heres a couple rather interesting videos that answer several common questions
you should keep in mind every choice made is a compromise in some areas, planning is critical, but reality can bite you in financial the ass.
incremental gains through minor mods while surely possible and yes proven, to work,but adding those mods,
are at some point ,mods to the engine,or transmission, that are becoming rapidly more, expensive and thus restrictive to completion of a durable & functional engine than the benefits are to the overall build, those mods may produce minor and documented gains, but the minor gains produced are far out weighted by the cost of the mods, especially in a daily drivers engine, things that make sense in a formula 1 or NASCAR engine build, are cost prohibitive to do on a street car, simply shedding weight on the car or improving the aerodynamics, may be far cheaper and result in greater performance.
I've built a few dozen 489-496 BBC engines in the past for guys with novas, camaros chevelles etc, that had visions of having a 10 second or faster car on the street, and the results of having a significantly more powerful engines always resulted in the need for mods like suspension mods,
like traction bars, air shocks, bigger tires, bigger brakes, better engine cooling systems, new stronger differentials, etc. that they may have never considered, that were required to make the car handle correctly, this is never a cheap hobby, but at some point there's a limit to what your wallet will tolerate and how long you want to deal with a car who's engine is (STILL UNDER CONSTRUCTION SO I CAN'T DRIVE IT YET)
you can start with this, the SIX cam manufacturers POSTED OR LINKED BELOW that have proven to be dependable, the soft ware below might prove useful, so use it to get a base line INFO YOU NEED IF YOUR selecting the correct cam for YOUR combo FIRST!!>>>>>>ANY AND ALL CAM MANUFACTURERS WILL need...
you might want to read thru these links for info also first lets point out how you calculate 4000 Feet Per Minute, in piston speed, which in most chevy v8 engines is a reasonable durability limit in one revolution a piston moves from TDC (top dead center )TO BDC (bottom dead center)and back to...
Do the mfg's advertise their weights with or without bolts? I have a set of 6" h-beams that weigh 715grams with 1.75 long ARP bolts. Without they weight about 645g empty They look like Scat, Callies, Carillo and others but they dont have the chamfered edge at the bolt end like all of those...
garage.grumpysperformance.com
btw 301c- about 574F
now consider you measure the piston to deck clearance at lets say 80F degrees and oil temps generally run under 275F
BUT PISTON TEMPS CAN EASILY EXCEED 400f, SO LETS SAY THE CONNECTING RODS ARE EXPOSED TO A 240f INCREASE IN TEMPERATURE
now , you can generally expect a length extension, of perhaps .06% elongation per 100f rise in temp
thus .006x2.4=.00144 or maybe .00919" over a 6.135 inch long rod, due to thermal expansion alone so a .035 quench is reduced to about .026 , now remember that piston,
is under stress from inertial loads, especially on the exhaust stroke , that easily reduces quench by about a further .006, your down to maybe
.0020 quench, add slack in bearing clearances and your easily down to less than .0020 quench, that is ignoring thermal expansion of the aluminum piston, and your lucky to have .017 with effective quench clearance at 6000 plus rpm.
Id also point out that when the piston deck to cylinder head quench surface is less than about .040,
and if you use a fairly RICH F/A mix, you retard or prevent detonation simply because you don't allow enough HEAT to be generated to allow ignition to be maintained as the two surfaces in very close proximity will not allow combustion to continue, as they absorb a good deal of heat while the surfaces are adjacent, but remember theres only about 12-20 degrees of the 360 degrees of rotation while the two surfaces are in close proximity.
doing a quick check on the math,
the piston will be within 2mm off the cylinder head surface for a full 20 degrees,
of rotation from 10 degrees before to 10 degrees after tdc
its been my experience that quench distances tighter than about .035 tend to allow the piston to almost or marginally contact the cylinder head under high heat and high load conditions.
now admittedly I mostly built BBC engines, and mostly with the longer 6.385" or with the stock 6.135" connecting rods,
now consider you measure the piston to deck clearance at lets say 80F degrees and oil temps generally run under 275F
BUT PISTON TEMPS CAN EASILY EXCEED 400f, SO LETS SAY THE CONNECTING RODS ARE EXPOSED TO A 240f INCREASE IN TEMPERATURE
now , you can generally expect a length extension, of perhaps .06 per 100f rise in temp
thus .06x2.4=.0144 or maybe .00919" due to thermal expansion alone so a .035 quench is reduced to about .032 , now remember that piston,
is under stress from inertial loads, especially on the exhaust stroke , that easily reduces quench by about a further .006, your down to maybe
.0023 quench, add slack in bearing clearances and your easily down to less than .0020 quench, that is ignoring thermal expansion of the aluminum piston, and your lucky to have .017 with effective quench clearance at 6000 plus rpm
Wow! I SO appreciate this individual component breakdown on WHY the quench recommendations on a typical steel rod SBC land at .040" "for safety" or "as close as 0.035" if you are VERY accurate at measuring and really know what you're doing".
I've never seen anyone break down the per-component reasoning behind that recommendation before.
This is the kind of content that's so hard to find elsewhere.
Doesn't piston rock and piston-to-bore clearance also play at least some small part when trying to run tight quenches without having piston to head contact?
And if I remember right, a longer rod combo dwells longer at TDC vs. a shorter rod combo? (If we're thinking about the time dimension of those 20 degrees where the piston and head are close together). -I heard one nitrous engine builder express a preference for shorter rods for that reason.
Kieth Black engines in AA/F and Top Fuel Dragsters seem to have this whole thing worked out when even using a blower.
See if you can get any info from them.
from "both sides", no real conclusion.
