[d1mbu1b]

This is written from a tire kickers perspective.
I was hoping the pros can help folks like me, the back yard budget guys.

I see plenty of posts concerning compression ratios and head choices, and they all seem to boil down to fighting detonation while mismatching parts that we can get our hands on cheap.

Please view this as a starting point for discussion.
I am not asserting anything since, I am just learning.

Please feel free to criticize and debunk. I want to get it right.






detonation may be caused by one or more of the following:
1) temperature, 2) pressure, 3) velocity, 4) octane...




1) To reduce Temperature

1.a) quench (squish) - aerosol effect, cools cylinder??? reduces tolerances (good and bad)

1.b) enrich mixture - will this run cooler? If so I don't know why, just heard it somewhere. fuel consumption, soot.

1.c) de-burr combustion surfaces, jagged edges tend to heat up and glow; need to pull heads

1.d) use aluminum heads; expensive; what are the port volumes for E-heads? It seems the heat dissipation is offset by the large runner volumes for street use under 4500 RPM

1.e) there has to be better ways to keep the cylinder temperatures down; what are they.




2) To reduce Pressure

2.a) delay IVC event with bigger cam or retarded cam timing; moves power band to higher RPMs; fight this with wider LSA

2.b) retard ignition timing - pressure increase from combustion will happen when piston is further down the hole; lose power

2.c) change static compression ratio - need to rebuild engine and buy new heads and/or pistons

2.d) head gaskets and/or shims - eliminates squish/quench and may actually increase chance of detonation

2.e) can ring gap shed pressure at low RPMs?




3) To increase Velocity - does an increase in velocity actually reduce pressure and cool at the same time?

3.a) decrease head port volume; need to remove heads; aftermarket heads on street cars may have port volumes that are too large.

3.b) increase head flow; need to remove and modify heads

3.c) de-shroud intake valve to promote swirl; need to remove and modify heads

3.d) squish (quench) again; mixture is squished out from between piston and head surface at a high velocity; decreased tolerences




4) To increase Octane

4.a) alcohol, Is E85 101 octane?

4.b) additives; are these gimmicks

4.c) better fuel; more expensive (av gas, cam II)

4.d) sprayers, like the forced induction guys, what does water do to things?

[Jim Hand]

You will find a comprehensive discussion on the subject at:

http://www.pontiacstreetperformance....mpression.html

Incidentally, I run 10.17 static compression on my iron headed 473 cube street/bracket car on 92 octane pump gas using the techniques outlined in that discussion. And have for years with no detonation. And with pretty good strip performance (11/50's at 116+ at 4050# with 3.31 gears)!

Jim Hand

[66Mutt]

With regards to timing I might throw in that reducing the timing is a double edged sword in that you may get pinging to stop, but the retarded timing also increases the cyl head temps which could also contribute to the detonation. Where as before it might have been an early ignition event, after retarding the timing, the detonation may then be caused by a high temperature event.
Doug

[Half-Inch Stud]

I've done a bunch of effort to minimize ping for Street/Strip. Right or Wronng, these are the things that I pine for:

1. Y-Pipe Water cross-over for improved flow balance to Radiator.
2. Remote Oil Filter for Cooler oil.
3. Separated Auto-Trans fluid cooler.
4a: Well-contacted EXH Valve seat surface, and carefully-performed EXH Valve-guides (Valveguide part = Bronze-sleeve-in-Steel-Guide that gets pressed-in.)
4b: one-piece valves for a meager cooling benefit.
4c: Fill Exhaust crossover to keep central head zone cooler than if left open.
4d: port-match every bit of exhaust passage for sheer-flow, no cliffs or pockets for glow from heat.
4e: Run sandwich Exhaust gaskets to increase thermal resistance from header/manifold back to head.
5. (need critique--> Valve seal effort to promote oil in guide, rather than dry-guide, like Intake.

Street/Strip unique
5. Carefull MECH Advance effort for.
6. Reduced Idle speed.
7. Mech Fan for Idle, Stop lights, and bumper-bumper endurance "driving".
8. Whack-back the Spark-Plug lug for side-gap.
9. Cooler Plug until it shows evidence of mixture, then write-it-down and try next hotter range, write-down ping sensitivety differences.
10. Yea, Enrichen the Primary Rod/Jet, enrichen the Accel Pumps, YET attempt correct Power Mixture on Secondaries.
11. Be sure your Converter is hot-running, NOT nuclear-hot running. That heats the crank and Block.
12. Run the most-efficient Head (Combustion Chamber) you know of. Efficient is defiend as requiring the least timing advance to make the most power.
13. Allow crankcase to inhale cool air, not underhood hot air, nor exhaust gas from so goofy exhaust scavenging product that fails at idle & off-idle. PCV system still a good idea to promote draw.
14: Run a cam 2 sizes too large, and Rhoads lifters for benefits at low RPMs of dynamic compression includes some cam-induced EGR, and INITIAL timing needs bumped-up for cool running.

Perhaps:
12. Gear&Tire & Converter Stall to unload motor at low RPMS, as if Audible Ping is most prevalent.

[Schurkey]

Originally Posted by d1mbu1b

detonation may be caused by one or more of the following:
1) temperature,

of several items. Don't forget that intake air temp is going to make a difference, too.

Originally Posted by d1mbu1b

2) pressure, 3) velocity,

Velocity?

Originally Posted by d1mbu1b

4) octane...




1) To reduce Temperature

1.a) quench (squish) - aerosol effect, cools cylinder??? reduces tolerances (good and bad)

I don't know about aerosol effect; so far as I know quench does not cool the cylinder although there may be some meaningful cooling of the piston. I don't understand how squish has any effect on "tolerances". Quench/squish dramatically increases combustion chamber turbulence; thereby improving flame speed. I suppose that turbulence could atomize and disperse still-liquid fuel--is that what you mean by "aerosol effect"?

An engine with good squish/quench may have a cooler combustion chamber; it's less a result of the quench directly, but a result of the improved flame speed/burn quality.

Originally Posted by d1mbu1b

1.b) enrich mixture - will this run cooler? If so I don't know why, just heard it somewhere. fuel consumption, soot.

Used to be done a lot on aircraft engines; and certain race vehicles. You richen the mixture and the excess fuel evaporates and absorbs heat. It's a really poor way to cool the chamber; and leads directly to other problems. On the other hand, just having a "correct" fuel mix instead of one that's too lean can improve detonation resistance without being "overly rich".

Originally Posted by d1mbu1b

1.c) de-burr combustion surfaces, jagged edges tend to heat up and glow; need to pull heads

1.d) use aluminum heads; expensive; what are the port volumes for E-heads? It seems the heat dissipation is offset by the large runner volumes for street use under 4500 RPM

1.e) there has to be better ways to keep the cylinder temperatures down; what are they.

In general, CYLINDER temperature has little to do with detonation. And trying to lower the cylinder temperature means you may need to add additional piston-to-wall clearance. The piston tends to run hot no matter what; if the cylinders aren't at "normal" operating temperature they haven't expanded; therefore the clearance is reduced.

COMBUSTION CHAMBER temperature is another story.

Again, pay attention to intake air temp. The air cleaner should be ducted to pull in outside air, not the heated under-hood air. Reducing or eliminating the exhaust flow through the intake manifold crossover port will keep the manifold cooler; as will separating the water passage from the rest of the intake manifold casting.

There are those who want to remove the thermostat or drop in a lower-temperature 'stat. I consider this a poor way to drop cylinder head temperature.

Some folks add additional coolant passages--or even external hoses--intended to change coolant flow into or out of the cylinder head. Some work; some work very well; and some look good when you show off six feet of steel-braided hose to your buddies. Effectiveness varies with engine family; engine usage; and method chosen.

Originally Posted by d1mbu1b

2) To reduce Pressure

2.a) delay IVC event with bigger cam or retarded cam timing; moves power band to higher RPMs; fight this with wider LSA

2.b) retard ignition timing - pressure increase from combustion will happen when piston is further down the hole; lose power

Go to far with this and the fuel is still burning when the exhaust valve opens. Exhaust valve and cylinder head (via the exhaust port) absorb too much heat that could have been doing useful work. All kinds of problems result.

Originally Posted by d1mbu1b

2.c) change static compression ratio - need to rebuild engine and buy new heads and/or pistons

2.d) head gaskets and/or shims - eliminates squish/quench and may actually increase chance of detonation

2.e) can ring gap shed pressure at low RPMs?

If the rings are hot, they've expanded and the gap closes up. If they're not hot, the gap is larger. Even with a large gap--damn little is going past the ring gap. Don't look for big changes here.

Originally Posted by d1mbu1b

3) To increase Velocity - does an increase in velocity actually reduce pressure and cool at the same time?

3.a) decrease head port volume; need to remove heads; aftermarket heads on street cars may have port volumes that are too large.

3.b) increase head flow; need to remove and modify heads

3.c) de-shroud intake valve to promote swirl; need to remove and modify heads

3.d) squish (quench) again; mixture is squished out from between piston and head surface at a high velocity; decreased tolerences

Again, I don't know about port velocity making any difference in detonation resistance. Some ports are designed to "Swirl" the mixture; apparently dizzy fuel mixtures can burn better--but I don't know that detonation resistance is the object of swirl. I thought it was emissions/fuel economy concerns. But I could be wrong. Quench increases turbulence; makes for a faster and more complete burn; so I guess "in-cylinder velocity" can result in reduced detonation. Squish/Quench can also provide some heat transfer from piston to head--but I wouldn't say it's a lot of heat transfer. You also talk about squish and "tolerances" and I don't know how squish can change tolerances of anything except maybe the engine's tolerance of lower octane rating fuel. It does reduce piston-to-head clearance; but clearance and tolerances are not the same thing.

Originally Posted by d1mbu1b

4) To increase Octane

4.a) alcohol, Is E85 101 octane?

It is higher-octane; but also lower-energy. Better have a LOT of compression, and your own still, 'cause you're going to use a lot of fuel.

Originally Posted by d1mbu1b

4.b) additives; are these gimmicks

almost all of them are useless. The ones that actually work are expensive and/or dangerous--including highly poisonous and absorbed through your skin. Mr. Liver will not approve. You do not want your liver to jump out and run down the street in disgust.

Originally Posted by d1mbu1b

4.c) better fuel; more expensive (av gas, cam II)

4.d) sprayers, like the forced induction guys, what does water do to things?

The merits of water injection (directly into the fuel/air mix) have been debated since WWII. Some folks say it works; others say it just masks the problem. I tried it; years ago. But my self-fabricated system was overly crude--it wasn't a good test of the concept.

Spraying water on a heat exchanger--the radiator, for example--or applying it to the engine itself; including applying it as a bag of ice on the intake manifold--is much less debatable. It works. Spray enough water on the radiator, and you'll remove a lot of heat. Spray it long enough, and you may build up scale on the OUTSIDE of the radiator (from minerals in the water being sprayed) or promote corrosion of the air fins (although I've never seen this from water deliberately sprayed on; it's extremely common for radiators in parts of the country that use salt on the roads to fail because the air fins corrode from road splash and no longer make contact with the coolant tubes.)


Another item you'd want to note is combustion chamber SHAPE. Some chambers are more prone to detonation than others due to their shape--sharp edges; poor flame travel; or lack of turbulence.

[blaktopr]

To this day, I still love your car Jim. To look more closely at "quench/squish", take a look at 2 stroke head design. The end gasses that end up between the piston and quench pad are cooler on the surface of the head. When the area between the two are reduced, the "cooler" gasses are left over. Sink the piston a little, and there will be an area of hot gasses between the surface gasses. Thats another way to look at the positive effects of a reduced "squishband"

Chris.

[amcmike]

Engine coatings help a lot too. You can go crazy coating the intake bottom, the entire combustion chamber, the piston top, the intake and port runners, and even the valve stems. But the cost will add up fast.

However, keeping in mind the exhaust valve is one of the hottest parts of the combustion chamber, coating the exhaust valve face should help a lot and cost less than $100.
http://www.swaintech.com/store.asp?pid=10971
"Face Only (TBC)…………………………….......... $10.00 each "

Here's some more good information:
http://www.popularhotrodding.com/tec...ech/index.html

[d1mbu1b]

Thank you everybody for helping me out.
Great stuff, everybody mentioned something I was not aware of.
This is a pretty steep learning curve for me.

Originally Posted by Jim Hand

You will find a comprehensive discussion on the subject at:
http://www.pontiacstreetperformance....mpression.html
Jim Hand

Thanks for the article. It is very helpful. What is a safe distance using a cast factory rotating assy? I see recommendations from 030 with expensive connecting rods up to 050 for marine engines.

Originally Posted by 66Mutt

With regards to timing I might throw in that reducing the timing is a double edged sword in that you may get pinging to stop, but the retarded timing also increases the cyl head temps which could also contribute to the detonation. Where as before it might have been an early ignition event, after retarding the timing, the detonation may then be caused by a high temperature event.
Doug

Please explain why. I am just trying to get a better handle on whats going on. It seems the combustion is continuing as the piston is further down in the cylinder. When the ignition is retarded, is it still burning on the exhaust stroke? What causes the heat to linger on a late ignition timing? At what crank angle do you want the combustion complete? Is it the other side if the exhaust valve we are worried about?

Originally Posted by Half-Inch Stud

8. Whack-back the Spark-Plug lug for side-gap.

Please explain this, I don't understand.

Originally Posted by Schurkey

Velocity?

Well I just assumed... As you say "turbulance" is probably the key and not velocity.

Originally Posted by Schurkey

In general, CYLINDER temperature has little to do with detonation.
COMBUSTION CHAMBER temperature is another story.

Thanks, I didn't understand the difference before.

Originally Posted by Schurkey

Some folks add additional coolant passages--or even external hoses--intended to change coolant flow into or out of the cylinder head. Some work; some work very well; and some look good when you show off six feet of steel-braided hose to your buddies. Effectiveness varies with engine family; engine usage; and method chosen.

This looks like something a backyard tire kicker can do relatively inexpensive and get great benefits. I am interested to learn more hear.

Originally Posted by Schurkey

Again, I don't know about port velocity making any difference in detonation resistance. Some ports are designed to "Swirl" the mixture; apparently dizzy fuel mixtures can burn better--but I don't know that detonation resistance is the object of swirl. I thought it was emissions/fuel economy concerns. But I could be wrong.

Just thinking out load, while trying to understand...
I hear port velocity is the key to throttle response, and you should have as small of ports that will flow the required amount based upon RPM and displacement. Please correct me here if this is not right.

increased velocity decreases surface pressure (like a wing or like a venturi) and decrease in pressure decreases temperature.
hopefully this is right.

if the air/fuel; has a given mass then it has more momentum at increased velocities
maybe this will increase turbulence?

I don't understand the differences and results of velocity, turbulence, and swirl.

Originally Posted by amcmike

Engine coatings help a lot too. You can go crazy coating the intake bottom, the entire combustion chamber, the piston top, the intake and port runners, and even the valve stems. But the cost will add up fast.
However, keeping in mind the exhaust valve is one of the hottest parts of the combustion chamber, coating the exhaust valve face should help a lot and cost less than $100

Is this something a do it yourselfer can do?

[66Mutt]

I may have to ask around to find out the mechanism that causes the higher Cyl head and exhaust temps with retarded timing. I don't think the combustion event drags on into the exhaust stroke. But since the timing event is late, I suspect that less of the heat that is generated is actually converted to pressure. It may be heating up the air, but since the piston may be falling or may not be rising at the optimum time relative to the max temperature generated, the net result is the gas heats up but generates less pressure. When more pressure is generated the engine can dissipate more of the energy as actual work. If less of the energy is consumed in work/pressure, then a greater portion of the total energy is unused and is rejected as heat. If your distributor is hooked up to a manifold vacuum source, disconnect and plug the vacuum line and watch the temperature climb rapidly. An IR thermometer pointed at the exhaust manifolds will show a temp rise of a few hundred degrees.
Doug

[d1mbu1b]

Originally Posted by 66Mutt

then a greater portion of the total energy is unused and is rejected as heat.
Doug

I think I get it. The energy is converted to heat instead of kinetic energy since the slow piston movement at the bottom of the stroke acts like a brake; the v in E = 1/2mv^2 is limited; so the rest of the energy is converted to heat. Thanks for the insight.

[66Mutt]

At what crank angle do you want the combustion complete?

I stumbled across this article last week by Steve Davis of DUI Performance Dirstibutors and David Vizard. It stated that the goal of ignition timing is to get peak cylinder pressure to occur at about 15 deg past TDC on the power stroke.

Here is a link to it.
http://www.classicinlines.com/spark.asp

Doug

[67'7F6'Bird]

http://www.snowperformance.net/news_item.php?prk=88

[screamingchief]

Originally Posted by d1mbu1b

2.a) delay IVC event with bigger cam or retarded cam timing; moves power band to higher RPMs; fight this with wider LSA

FYI,as it's stated,this line of thought is somewhat incorrect.

If you've delayed the IC event via additional duration,and you were wanting to keep the new powerband "in check" (ie: the same as before),you would then need to tighten the LSA,not widen it,as widening the LSA would just tend to "extend" the powerband further,and likely move the peaks to a slightly higher RPM as well for the longer duration now being used.

Remember,a narrow LSA usually shortens the power band & tends to lower the power peak,it closes the intake earlier in most cases,and thus it tends to "mimick" a slightly smaller cam for a given duration.

Wide LSA is the opposite,widens the power band & tends to raise the power peak,it also closes the intake later,and thus tends to "mimick" a slightly larger cam for a given duration.

What confuses a lot of folks is the fact that added overlap from the tighter LSA tends to help high RPM breathing for a given duration,but that effect is often over-shadowed by these other influences.

But that added overlap is part and parcel to why a tight LSA often tends to make higher peak numbers than an nearly identical wide LSA cam,but also understand that it often does so at the expense of some measure of average power.

Play around with the cam numbers enough,and almost anything is possible.

But you better be watching the "big picture",not just one or two small pieces of that picture.

The debate becomes which would be more detonation resistant,the longer duration cam with the tight LSA,or the shorter duration cam on a wide LSA,that deal can & will be argued endlessly,as often you can easily get exactly the same IC event doing that sorta "cam numbers game",and in doing such understand that the DCR will compute to be exactly the same for both,despite the other obvious differences in the two cams,thus this is one big reason why DCR will never become the "be all/end all" answer some would like it to be,there is just too much it does'nt account for,or take into consideration.

HTH.

["QUICK-SILVER"]

Originally Posted by d1mbu1b

I think I get it. The energy is converted to heat instead of kinetic energy since the slow piston movement at the bottom of the stroke acts like a brake; the v in E = 1/2mv^2 is limited; so the rest of the energy is converted to heat. Thanks for the insight.

Some thoughts on this that might make things a little clearer.
Timing too slow, ATDC, and fuel wont be completely burned when exhaust valve opens. Ends up acting like a torch on exhaust valve. Seen heads and exhaust manifolds turn cherry red from it, even at low rpm or idle.

Way too high of an octane fuel, on a low compression engine, tries to do the same thing. Fuel doesn't burn fast enough and ends up torching the exhaust.

When it gets hot enough it starts acting like a diesel.

[bobzdar]

Originally Posted by screamingchief

FYI,as it's stated,this line of thought is somewhat incorrect.

If you've delayed the IC event via additional duration,and you were wanting to keep the new powerband "in check" (ie: the same as before),you would then need to tighten the LSA,not widen it,as widening the LSA would just tend to "extend" the powerband further,and likely move the peaks to a slightly higher RPM as well for the longer duration now being used.

Remember,a narrow LSA usually shortens the power band & tends to lower the power peak,it closes the intake earlier in most cases,and thus it tends to "mimick" a slightly smaller cam for a given duration.

Wide LSA is the opposite,widens the power band & tends to raise the power peak,it also closes the intake later,and thus tends to "mimick" a slightly larger cam for a given duration.

What confuses a lot of folks is the fact that added overlap from the tighter LSA tends to help high RPM breathing for a given duration,but that effect is often over-shadowed by these other influences.

But that added overlap is part and parcel to why a tight LSA often tends to make higher peak numbers than an nearly identical wide LSA cam,but also understand that it often does so at the expense of some measure of average power.

Play around with the cam numbers enough,and almost anything is possible.

But you better be watching the "big picture",not just one or two small pieces of that picture.

The debate becomes which would be more detonation resistant,the longer duration cam with the tight LSA,or the shorter duration cam on a wide LSA,that deal can & will be argued endlessly,as often you can easily get exactly the same IC event doing that sorta "cam numbers game",and in doing such understand that the DCR will compute to be exactly the same for both,despite the other obvious differences in the two cams,thus this is one big reason why DCR will never become the "be all/end all" answer some would like it to be,there is just too much it does'nt account for,or take into consideration.

HTH.

DCR coupled with the rpm it occurs at can give good insight into detonation propensity. If you have 2 cams with the same DCR but one had peak cylinder pressure 1000rpm higher than the other, it will have lower tendency to detonation due to increased turbulence at the higher rpm. Unfortunately, I don't know what DCR at what peak pressure rpm will cause problems with a given fuel, but it's something to look at and maybe a general trend will emerge if enough people give their cam specs and detonation propensity.

Take a look at the very high compression being used in factory cars now and look at what cam specs they're using - the ls7 for example has something like a 120.5 lsa and 11:1 compression without detonation or emissions problems, has nice idle and power to 7000rpm. This should give an indication which direction to go for good manners and detonation resistance in a street motor...

[70 bird]

Look into water/meth injection, I run it on two boosted vehicles.