power vs detonation

[grumpyvette]

Detonation vs power

 

some of the major factors in your engines potential power, is the volumetric efficiency (how efficiently you fill and empty the cylinders) and the octane of the fuel used, compression ratio and detonation limits,

With detonation, prevention the main factors are

Ignition timing

Quench

FUEL OCTANE

DCR

and cylinder heat level

you’ll be fairly safe if you stay under

8.5:1 dcr at 170f degrees

8.25 dcr at 180f degrees

7.8:1 dcr at 210f degrees

and keep the quench in the .036-.043 range

heres some differant calculators

http://www.kb-silvolite.com/calc.php?action=comp2

http://www.wallaceracing.com/dynamic-cr.php

http://www.smokemup.com/auto_math/compression_ratio.php

http://not2fast.wryday.com/turbo/compression/cranking_pressure.shtml

average the results

 

the numbers are for 92 octane premium gas run at a 14.7:1 a/f ratio

 

BTW heres a VERY SIMILAR GRAPH

 

[

]

 

http://www.misterfixit.com/deton.htm

 

I won,t get into the extensive details of why, but heres what you can DO,

(1) retard the cam 4 degrees, (this tends to reduce your dcr and lower cylinder temps due to slightly lower DCR)

 

(2) add a pusher fan or in some way REDUCE your coolant temp, this tends to reduce the detonation tendency

 

(3) richen the air/fuel ratio to about 12.7:1 this tend to increase power and reduce the potential for detonation due to cooler cylinder temps)

 

(4) change the plug gap to .040, this tends (at least in theory)to reduce the plugs tip temp due to a lower electrical resistance of the spark jumping the gap)

 

(5) add some fresh coolant,and flush the radiator and install a 160 degree t-stat, some water wetter or purple ice ,in that coolant might help

 

richen up the mix to 12.5:1 for max power/tq vs low emmissions and you can cheat slightly as the cylinder temps go down slightly.

keep in mind ALUMINUM absorbs and allows the transfer of heat to the coolant at a much faster rate, so your less likely to have cylinder temps raise into the detonation range as quickly.

and it should be obvious that your igntion curve and spark strength will also effect results, personally Ive found the BETTER MSD multi strike ignitions keep the cylinders cleaner and less likely to detonate

 

btw, reading material

 

http://www.kennedysdynotune.com/Dynamic%20Compression%20Tech.htm

 

http://www.misterfixit.com/deton.htm

 

http://www.federal-mogul.com/cda/content/front/0,2194,2442_7359_7525,00.html

 

http://www.diabolicalperformance.com/hotrodoctane.html

 

http://www.sdsefi.com/meltdown.htm

 

http://www.procharger.com/intercooled.shtml

 

http://www.kb-silvolite.com/article.php?action=read&A_id=36

 

http://www.chevyhiperformance.com/techarticles/94138/

 

http://racingarticles.com/article_racing-10.html

 

http://www.popularhotrodding.com/tech/0311em_power_squeeze/index.html

 

1985,1992,1996 vettes

keep the rubber side down and the fiberglass off the guard rails

[jnewby]

Thats nice to know I am new to building hot rods and I thought I was leaning out at four grand, at least I wont have to tune the carb any more ( I wasn't having much luck any way) I just need to get it cooled down from 205 to about 170. Thanks grumpy.

[olie05]

 

 

 

Does this graph imply that an engine with excessive dynamic compression at operating temps will run perfectly fine if it has just been cranked up (cold engine), right before it reaches that critical temperature point on the graph for the octane used?

[grumpyvette]

"Does this graph imply that an engine with excessive dynamic compression at operating temps will run perfectly fine if it has just been cranked up (cold engine), right before it reaches that critical temperature point on the graph for the octane used?"'

 

either I don,t understand the QUESTION,(which is easily possiable) or YOU DON,T UNDERSTAND exactly what DYNAMIC COMPRESSION IS!.........what I THINK your asking is can an engine with enought extra durration run fine with high compression at higher temps ,than an engine built identical compression levels with a lower durration cam when both have exactly the same STATIC compression ratio....., the answer is YES, if you bleed off enought cylinder pressure by delaying the intake valves close point you can run much higher static compression levels...........but Id also point out that that increased durration tends to make the engine run like crap in the lower rpm ranges and idle badly if its taken too far, and you need a higher stall speed and higher NUMERICALLY...IE , like swapping from 2.57:1 to 4.11:1) rear gears to opperate effectively in that cams effective rpm band DUE to that extra durration and overlap

 

 

 

you need to understand it before selecting a combos components

 

the differance between STATIC COMPRESSION RATIO AND DYNAMIC COMPRESSION RATIO is where the piston is in the cylinder when the valves close and the piston can accually start compressing the REMAINING VOLUUM IN THE CYLINDER VS the STATIC COMPRESSION THAT ASSUMES THE PISTON STARTS COMPRESSING THE INSTANT IT LEAVES BOTTOM DEAD CENTER AND STARTS UPWARD ON THE COMPRESSION STROKE!

 

let me try and explain, the short version is that the PISTON COMPRESSES NOTHING untill BOTH VALVES ARE CLOSED, .......thats the only compression ratio that matters,.... since its the only compression ratio the engine ever sees.

 

static compression is simply the differance between the cylinder volume at BOTTOM DEAD CENTER(BDC) and its compressed volume at TOP DEAD CENTER (TDC), into the combustion chambers,... dynamic compression takes into account that on the pistons upward compression stroke the valves have not yet closed and nothing gets compressed by the piston untill they do, that of course depends on the cam and rockers, pistons and connecting rods, the cylinder voluum, the rod/stroke ratio, ETC.,used, in the combo, and the rpm levels to some extent BTW, ALUMINUM HEADS can usually operate at a higher dynamic compression simply because ALUMINUM releases heat to the coolant much faster than iron, its the lower heat levels that remain in the cylinder that help prevent detonation..when you increase the dynamic compression the heat levels in the heads combustion chamber rise , the differance in the RATE heat leaves the cylinder allows a slightly higher dynamic compression level from aluminum before the same HEAT levels are REACHED & MAINTAINED in the combustion chambers

 

heres a calculator for static cpr, which you need to figure first

 

http://www.rbracing-rsr.com/compstaticcalc.html

 

or

http://users.erols.com/srweiss/calccr.htm

 

or

http://not2fast.wryday.com/turbo/compression/compression.shtml

let me point out a few things

first look at this chart

 

http://www.iskycams.com/ART/techinfo/ncrank1.pdf

 

then lets assume your 350 sbc engine has a static compression ratio of 11:1 but youve installed this cam

 

http://www.cranecams.com/?show=browsePar...lvl=2&prt=5

 

looking at the cam specs we see that the effective stroke is not the 3.48" that the static compression ratio is measured from ,at BDC, BUT from about 2.6 inches from tdc where the valves close as the piston moves upward, so your true working compression is closer to 8.1:1 NOT 11:1

 

heres a longer more detailed explanation and access to the software to figure dynamic cpr with the cam your useing in your engine

 

http://cochise.uia.net/pkelley2/DynamicCR.html

 

http://www.diamondracing.net/cocalc.htm

 

heres some differant calculators

 

http://www.kb-silvolite.com/calc.php?action=comp2

 

http://www.wallaceracing.com/dynamic-cr.php

 

http://www.smokemup.com/auto_math/compression_ratio.php

 

http://not2fast.wryday.com/turbo/compression/cranking_pressure.shtml

average the results

 

keep in mind that you can easilly run a stattic compressio of 11:1 with aluminum heads if you keep the cam timing in a range so that the DYNAMIC COMPRESSION is CLOSE TO 8:1

take the time to understand the concept,it VERY IMPORTANT

 

read this

 

http://www.diamondracing.net/cocalc.htm

 

 

 

http://victorylibrary.com/mopar/cam-tech.htm

 

http://victorylibrary.com/mopar/otto-c.htm

 

http://victorylibrary.com/mopar/cam-tech-c.htm

 

http://kb-silvolite.com/article.php?acti...3117842f4eb4c49

 

http://victorylibrary.com/mopar/rod-tech-c.htm

 

http://victorylibrary.com/mopar/piston_position-c.htm

 

http://www.iskycams.com/techtips.html#2003

 

http://victorylibrary.com/mopar/rod-tech.htm

 

http://www.zhome.com/ZCMnL/PICS/detonation/detonation.html

 

http://www.chevytalk.org/threads/showfla...true#Post397334

 

if cams are a mystery please take the time to read these, it will get you a good start

 

http://www.newcovenant.com/speedcrafter/tech/camshaft/1.htm

(read LESSONs 1-8)

 

 

http://www.wighat.com/fcr3/confusion.htm

 

http://www.chevyhiperformance.com/techarticles/95298/

 

http://www.idavette.net/hib/camcon.htm

 

http://www.centuryperformance.com/valveadjustment.htm

 

http://www.totalengineairflow.com/tech/valvelashing.htm

 

http://www.chevytalk.com/tech/engine/Cam_Selection.html

 

http://www.chevytalk.com/tech/101/Cam_Theory.html

 

http://www.babcox.com/editorial/ar/ar119736.htm

 

 

 

http://www.symuli.com/vw/camp1.html

 

http://www.symuli.com/vw/camp2.html

 

http://home.wxs.nl/~meine119/tech/camqa.html

 

http://www.chevytalk.org/threads/showfla...true#Post200511

 

http://www.crower.com/misc/valve_timing_chart.html

 

http://www.speedomotive.com/Building%20Tips.htm

 

]

 

http://chevyhiperformance.com/techarticles/94138/

 

http://www.aera.org/Members/EngineTech/engine.htm

 

http://www.zhome.com/ZCMnL/PICS/detonation/detonation.html

[olie05]

I understand dynamic compression. I will restate the question clearly.

 

An engine with slightly excessive dynamic compression (i.e. low durration cam, relatively high static compression) detonates once it reaches operating temperatures. Does this same engine run perfectly fine before it reaches the critical temperatures depicted by the graph?

 

example, 11:1cr L6 with a STOCK cam!! (not my setup, but an extreme example) If you look at the graphs, does this engine hold off detonation until the engine temperature goes beyond the corresponding slope on the graph?

 

I hope that made sense!

 

Edit:

I may have figured out why there is confusion. In the graph it shows that the higher the temperatures are, the more octane the engine needs to prevent detonation. If this is true, then can one also assume that a detonating engine is less likely to detonate at temperatures far below operating temperatures, such as those seen when first starting up the engine from ambient temperature?

 

sorry for the run-on.

[grumpyvette]

detonation is usually the result of BOTH the effects of pressure and HEAT, combined, that allow the pressure rise in the cylinder from either the flame front,(spark plug ignition) moving across the cylinder to self ignite the far edge of the combustion chamber in an uncontrolled burn resulting in a sudden pressure spike. or just the combined effects of heat and pressure to ignite the a/f mix (like a diesel)

so while the cylinders cool (below certain ignition thresh hold limits, due to octane) the mix won,t normally detonate. so yes, if the cylinders cool enought you can normally run compression levels that will not detonate untill the heat level build sufficiantly, but keep in mind that HEAT builds FAST.

one method of controlling detonation is to COOL the cylinders temp, (water or alcohol injection, added to the a/f mix lowers the burn temps) or retarding the ignition(lowers the cylinders pressure curve)

 

 

http://www.motorcycle.com/mo/mcrob/rt-fuel2.html

[Michael]

Here’s an effort at clarification…

 

Olie’s point, I think, is what might happen during the first few seconds upon starting a cold engine.

 

Consider an average temperature over some number of cycles – large enough to smooth over intake-compression-combustion-exhaust variation, but small enough so that the engine block is still cold to the touch. Well, if the temperature in the combustion chamber somehow happens to be similar to the temperature in the water jacket, then things in the combustion chamber are happening at maybe 70 deg F – and if that were true, then hypothetically detonation would not be a problem even for a very high SCR and low octane.

 

However, this condition does not exist! Immediately upon starting the engine, combustion chamber temperatures climb to something like 300 deg F (probably much more, but this is just guess for illustrative purposes; and note that this number is much lower than the flame temperature itself), while the water jacket and exterior of the block are still cold to the touch. When the engine “warms upâ€, the ratio of temperatures at the combustion chamber walls to those in the water jacket approach equilibrium.

 

So, there are two points of confusion. First, one can not correlate the water temperature to the combustion chamber temperature until the engine warms up. And second, the combustion chamber temperature is what effects detonation, BMEP, etc. – and not the water jacket or block temperatures. But we measure water temperature, and hence the rules of thumb are based on water temperature.

[baddriver]

I've never seen numerical values assigned to 'quench' before. I always thought it was just an abstract concept that had to be determined experimentally. I know that it is related to the shape of the compressed charge, and the bore / stroke ratio, but I don't really know what it is.

 

Can someone tell me how it is measured/calculated and what are the variables involved?

[grumpyvette]

QUENCH??

http://www.100megsfree4.com/dictionary/car-dicq.htm

 

quench area:

A zone in the combustion chamber where the piston at top dead center is very close to the cylinder head. Because the piston and cylinder head is cooler than the unburned part of the fuel-air mixture (i.e., end gas), they pull the heat from the end gas. Because the end gas is now cooler, detonation is quenched or reduced. However, the process does form unburned hydrocarbons.

 

SQUISH

An area in the combustion chamber of some engines where the piston squishes or squeezes part of the fuel-air mixture at the end of the compression stroke. As the piston approaches top dead center, the mixture is pushed out of the squish area and this promotes turbulence, further mixing of the fuel-air mixture and more efficient combustion

 

run less than about .035 thousands and at high rpm levels the pistons might hit the cylinder heads, run more than about .044 thousands the QUENCH effect of forceing the fuel air mix to the center of the cylinder from the cylinders edge area looses both speed and effectiveness, remember the quench area must be so tight that virtually all the fuel/air mix is forced (squished) into the center area and none is allowed to burn untill its squirted into the burn area increaseing turbulance and burn efficiency

in theory the much better quench, combined with the shorter more compact area the flame front needs to cover and the far higher turbulance combine to allow more of the pressure to build AFTER the crank passes TDC on the end of compression and begining of the power stroke

 

its mostly an advantage in that you get a more even and FASTER burn in the cylinder and less chance of detonation, simply because both the lower time and faster pressure curves favor the ignition flame front vs detonation

look, it takes approximately 40 thousands of a second for the flame from the ignition to cross a 4.25" bore,at low rpms and still takes about 15 milliseconds at high RPM due to the much faster movement of the compressed fuel air mix in the cylinders, lets look at what that means

if the chevy plug is located 4/5ths of the way to one side thats a time of about 32 thousands for the pressure to build as the flame travels 3.4" in the chevy but in a compact combustion chamber it could only take the cylinder flame front less than 10-20 thousands of a second to travel acrossed the combustion chamber for a complete burn at low rpms, this of course speeds up as the swirl and turbulance increase with increased engine RPMs but the ratios stay similar. this results in more useable energy WORKING on the piston AFTER IT PASSES TOP DEAD CENTER ON THE POWER STROKE. BUT MODERN WEDGE combustion chambers use increased QUENCH to speed the flame front and lower the burn time combined with a smaller combustion chambers.

the differance may be easier to grasp if you think of the quench area as a significant part of the total combustion chamber voluum,thats forcing its potential fuel/air mix into the central combustion chamber as a jet of highly compressed F/A mix, like the differance between lighting a cup of gasoline by simply placing it next to a camp fire vs throwing it violently into a camp fire

 

look at this chart

http://www.iskycams.com/ART/techinfo/ncrank1.pdf

 

keep in mind that the cylinder pressure starts, builds to a peak and drops off all before the piston moves more than about 1/2 inch away from TDC and that if your wasteing 10-20 degrees of rotation compressing the burning mix in a slow to ignite combustion chamber your wasteing engine power

http://chevyhiperformance.com/techarticles/94138/

 

http://naca.larc.nasa.gov/reports/1939/naca-tm-914/

 

http://www.me.gatech.edu/energy/ICEngines/8_CylinderCombustionProcesses.pdf

 

 

http://www.nedians.8m.com/Comp_IC.html

 

http://mb-soft.com/public2/engine.html

 

 

[

 

LOOK CLOSELY AT THESE PICTURES

you only have QUENCH if theres a flat area on the piston that mates to a matching flat area on the combustion chamber roof, on these pistons dual quench areas throw the compressed fuel/air mix to the center from the twin quench areas

notice, if used with this head, that only one side would have a fairly large and EFFECTIVE QUENCH area ,(the side away from the spark plug)

 

 

things to read

http://chevyhiperformance.com/techarticles/94138/

 

http://www.theoldone.com/archive/quench-area.htm

 

 

 

http://racehelp.com/article_racing-10.html

 

 

 

http://members.uia.net/pkelley2/DynamicCR.html

[baddriver]

Thanks Grumpy!