Chambers and detonation resistance

[NickB]

I've come across only small bit of information that actually help explain how a combustion chamber is made more resistant or prone to detonation. I've heard that sharp edges can help promote detonation, as can mirror smooth chamber and piston surfaces.

What can be done to try prevent detonation without too much work? What about with lots of work?

I radiused the dish edges an valve reliefs on my pistons, radiused shar edges in the chamber, made everything about 320 grit texture, smooth, but not shiny, and took the chamber edges right out to the gasket opening -.015" to get rid of the sharp square edge of the head. By all theory my engine (Chrysler 2.2 turbo) should have blown apart from detonation long ago (based on previous experience from some well known turbo dodge guys) and yet it's kept together. Was it just luck, or did i do the right thing?

Comments anyone? Larry?

 

[MaxRaceSoftware]

What can be done to try prevent detonation without too much work?

Nick ...this is easy !!!

just joking !! ,..but seriously, the single most important thing you can do to prevent detonation is to choose
a race gasoline with enough motor-octane

a race gas with plenty of motor-octane will
cover some of the worst chambers .

it doesn't get any easier as pouring in a tank full .

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"What about with lots of work?" -NickB

The NHRA Stockers and Super Stock Classes are not allowed
even the tiniest of grind marks in the combustion chambers
any sort of polishing/unshrouding gets you instantly disqualified and maybe even suspended from NHRA Competion from 6 months to 1 year .

So the rough as cast chambers do OK in SS with 12:1 CR and less !!! some of it owing to cam specs (duration/centerlines/overlap) and engine operating RPMs

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Some relevant data ;
its very hard to detonate an engine turning 7000 rpms and upwards......its easy to detonate below 3500 rpms
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in the relatively short duration bursts of speed in drag
racing, and the fact that most racers come to the starting line with relatively cool water temperature , they can tolerate things like sharp edges , etc,...where in circle track, boat racing, etc. ..they might cause problems !

each kind of racing has special problems.

i'm saying that because some engine builders out there just very slightly radius piston domes...as not to loose Compression Ratio more than they have to .

You need a little surface texture for a light layer of soot to coat chambers/piston tops/valves/ports to sort of act as a "FREE" HiTech heat_insulating coating you don't have to apply or pay for !
Larry Meaux (meauxracing@mindspring.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

http://www.mindspring.com/~meauxracing/

 

[NickB]

I'm not limited by NHRA, or anyone elses rules, this is purely for fun. Detonation wouldn't be very fun though, hehe. Very good point you make about operating RPM. Didn't even cross my mind, but it makes perfect sense now that you've mentioned it.

I can't afford to fill up at the racetrack every day, though i do put in at LEAST 92 octane wherever i go.

 

[evelrod]

The old saying goes "with luck, s--- will do for brains" LOL

You did all right I guess. Did you determine what your final combustion chamber and/or compression ratios is?

Do you know what your boost curve is?

Are you using an aftercooler?

Do you know what your ign. 'curve/map' is?

Are you one of those 'hell bent to get to the next stoplight' drivers? (I would guess "not".)

You have done all the right things as I can see, and probably lowered your cr in doing so, quien sabe? Don't look a gift horse in the mouth---(I like them old sayins')


Rod

PS---I know a couple of "well known turbo guys" I wouldn't let near my pit wagon!!!!!

 

[NickB]

Stock CR is 8.1:1, i figure it's down to 8.0:1 at the lowest, as i didn't take much off. The head is coming off soon to replace a head gasket, i think i'll CC teh chambers when i have the chance to find out for sure.

I'll get full boost of 18psi as low as 3000 rpm under the right conditions. Depends on what gear it's in, and what i'm doing with the throttle.

Intercooler is a monstrous front mount i made from part of a freightliner 18 wheeler core. 30"wide, 10"high, 3" thick. It never gets more than warm after the most serious of beatings.

I can dig up the spark tables, i'm in the process of retuning the ECU, but from what i remember, they're not too aggressive. I'm planning on bumping it ahead a few degrees below 3000 rpm to hewlp get it out of the hole when not it boost. It feels like the car gets a big push at 3000 rpm, even when boost has been at 15 psi since 2500. I think it's the spark timing, but could be mixture as well. I'll compare the spark/fuel tables, and take some readings from sensors soon.

 

[nimpoc]

NickB,

You might want to consider a bigger turbine, turbine housing, or exhaust system. Backpressure is a big factor in detonation, and if you're getting 18 psi by 3000 rpm, you could probably handle a lazier turbo.

Obviously the exhaust will get the turbo to spool sooner, but is inline with the backpressure theme.

I was knock limited to about 14psi with my 0.63 A/R turbine housing, but can run 17 psi no problem on a 0.82 A/R. I wish there was something in the middle, as the big housing is kinda lazy with a stick.

MK

 

[NickB]

I just bolted on the new turbo, it's got a larger compressor wheel, and will be running at a hgher eifficeny area of the flow map than the old compressor, so that should releive a little backpresure fromt eh turbine.

The only turbine housing choices for the chrysler turbo motors is the stock .48, and the outrageously overpriced .63's. I've got s tock turbine right now, nothing like the nice flowing stage 2 and 3 wheels.

I'll be freeing up the exhaust some in the net little while, jut have to find the time to do it.

I'll just feed it plenty of fuel, and we'll see what happens

 

[MaxRaceSoftware]

Nick...how did the intake manifold you welded-up workout for you ???

any test results or comments yet ??
Worse ...Better ??

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what about SilTech with restrictor plate mods
any new test results ???
Larry Meaux (meauxracing@mindspring.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

http://www.mindspring.com/~meauxracing/

 

[NickB]

I'll find out in a few days, it's sitting on the motor right now, but the motor is on the garage floor, LOL.

I pulled the engine/tranny on thursday to do a bunch of work. One of the intermediate shaft bearings in the tranny is destroyed, i'm replacing all the bearings and seals, the syncros are fine. I just got the shift rails back in an hour ago.

Head gasket and head studs, turned out my compression problems was pitted exhaust valves from too much heat, i guess i've got to feed it more fuel. New turbo went on too.

Inspected the clutch while i had everything out, it looks good, no measureable wear, it's a carbon/kevlar "fibertuff" 4 puck disck and an insanely heavy pressure plate.

I should have it running tomorrow night or wednsday. I'll post results as soon as i figure out what it's done.