I'm thinking of doing some fine tuning using heat range and tip length to maximize the advance curve.
i'm thinking of short tip R44T in the leanest cylinders, to reduce compression, and R45TS, extended tip pugs in the rich cyl's to raise CR. So the question is how much, in CC's do the longer plugs displace?
Also, how much hotter, in degrees is a 45 vs. 44,
and 46 vs 45?
This is just an experiment, not sure if this idea will actually work

 

"extended tip pugs in the rich cyl's to raise CR."

Your serious, arnt you? :skep:

 

About as much as carboned up plugs do.

 

i've got the plugs here side by side, and the extended tip plug will no doubt displace air, raising CR. :cool: ..
.
you know how the instructions to cc a head say to use the spark plug you intend to use? i just never thought to try different plugs to see how many cc's the difference would be. i'm thinking 1 or 2 cc's. enough for some tuning. But if it is 1/4 cc that would be too small, that is why i am asking the question.


[Modified by Matt Gruber, 9:59 AM 5/23/2003]

 

I'm sure SOMEONE here will actually sit down and run some numbers for ya, but for now....."Put Down The Plugs And Back Away From The Car!!" :lol: :D :lolg:

 

:lolg: had a good laugh, took a 5 min. bike ride.
.
Studied the lean plug with a 5x loop. saw 1 tiny ball on the insulator, possibly heat related.
Will replace that long reach plug with a new short plug R44T.
Who else could make a simple plug change a controversial experiment? :eek:

 

it will change the CCs a couple of tens of a CC but it will change the timing in that cylinder. every .020 you move the plug tip the timing will change about 1 degree. adding more plug washers and moving the plug out farther is a way to change the timing to prevent detonation in certain cylinders on race engines. you can run a hotter range extended tip plug because of the fuel wash make the hotter plug look colder. chevy

 

Wow Clem,
I am impressed!
have .080" difference, short plug in the 3 leanest cylinders. So that is taking out 4 degrees of advance. May have to use the long plug with washers as this may be too much.
Now i am tempted to lean out the leanest to 13.5:1 rather than 13:1, this would help bring the rich ones closer.
Any idea what the degrees difference would be between a 12:1 vs. a 13 or 13.5:1 cylinder?
Thanks for your help!
:cheers:
Matt

 

without EGT probes in each cylinder it would just be a crap shoot to know what is happening. this is not somthing you can just calculate. :chevy

 

I just knew SOMEONE was gonna calculate it, fully expected SWCDuke though. :lurk: :D

 

I'll just have to give it my best guess; it really is hard to do this while driving around WOT. :crazy: i do have oxygen sensors in the 2 leanest cylinders on my 72 that i am now working on.
my 61 has probes in all 8 :eek:

 

i would hope i had learned something in 40+ years of race engine building. :chevy

 

This is one of the few times that someone has asked a question that is below the level of detail that I have paid attention to ;), but if I wanted to measure the difference in volume between a normal tip and extended tip spark plug, I would dip both plugs into a suitably sized calibrated burette filled with mineral spirits or alcohol (less surface tension than water to give more accurate measurements), and record the amount displaced by each. The difference in displaced fluid is the difference in tip volume. Since the upper shell is probably identical for the same brand, you could submerge the entire plug. Otherwise dip them in just to the top of the thread, or do it both ways and see if the difference is consistent.

Duke

 

Duke
if i had a burette i would have just measured it. That is why i asked.
.
The topic turned out to be badly worded; wrong. I should have asked HOW DO I RETARD THE TIMING IN A PINGING CYLINDER.

Thanks again Clem! :D

 

The only burette that I measure alcohol into is a shot glass. As usual Duke and Clem have turned my brain to mush. :p: Matt, I understand your problem now. Sorry bro, it was funny though. I'm gonna go do a fill/drain test on my burette now. :cheers:


[Modified by MasterDave, 1:27 PM 5/23/2003]

 

i have an engine building book that states a long tip plug will move the flame front closer to the piston, thus acting to increase CR. i'll have to dig around to find the explanation in the book. i've wanted to do this same type of experiment, just have never gotten around to it.

i was surprised to see that the plug dukes recommends has a shorter tip than the AC's i've been using. on my FI engine (which is bored .060 and using flat tops instead of domed), i've been able to set the base timing WAY advanced without any audible detonation. it runs much stronger now than it ever has in the past 4 years. however, it loses some coolant after shut down, which it has never done before. my total advance is something like 55*, and i use juiced-up 93 octane. i've read that you can have detonation without hearing anything.

i'd like to know if inaudible detonation is will cause a failure, and if the aggressive timing is contributing to the coolant leaks.

anyone have any opinions/ideas????

 

[QUOTE] I'm gonna go do a fill/drain test on my burette now. [QUOTE]

Good idea. Think I will try that on my brunette later.
OOPs.....you said burette. Nevermind.


:jester

 

if the coolant is coming out the over flow your cap may not be holding the pressure. get it tested or just buy a new one. also if you corvette does not have a expansion tank you my be filling the rad too full and if you have a expansion tank you should only fill it 1/2 full when cold. the difference in CCs of the plugs is a couple of tens of a CC. i have a listing here somewhere of the difference and i will look for it when i have time.:chevy


[Modified by clem zahrobsky, 4:54 PM 5/23/2003]

 

Bearvet, you mean 55º including vacuum advance, right? The normally used definition of "total" is the maximum amount of advance the engine achieves at with the vacuum advance disconnected when all of the centrifugal advance is in. With vacuum advance connected, 55º might be on the high side for many engines but not for all. Check your total with the vacuum advance disconnected. Different combinations work best with different total timing but about 34-38 is optimum for most. Can you give us some info about what your initial is set at and how much centrifugal your distributor adds, and at what rpm it peaks?

Too little timing is more likely to increase coolant temps than too much timing. Is your temp guage indicating higher temps? If not, maybe your cap just happened to fail at the same time you increased the timing?

 

clem & vetterodder,
thanks for the responses. i have a new expansion tank (nice clean seal for the cap), new 180* stat, new coolant, new 13# cap but right now it has a relatively new 15# cap with a tight spring and clean rubber. you're right, i may have filled it a little more than half. it overheated unexpectedly about 2 weeks ago, and blew the neck/cap off the tank (it had been JB Weld-ed a couple of years ago). that's why i've just replaced everything. i drove it a couple of nights ago, and it lost a tiny bit on the garage floor. made a puddle about 2 inches in diameter.

55* advance is the sum of my base, initial and vac. i may be doing the procedure wrong as i'm a newbie at it, but the base timing is something like 26*. i didn't mention it before, cause i know it's almost an insame #. mech adv doesn't add as much as it should, i think due to a bushing issue on the shaft, only about 10* maybe. vac adv is from the can duke recommends. i have light springs, starts about 1100 and all in around 2300. TheOman and i worked on it a couple of months ago. we couldn't get enough advance out of it before the vac can hit the FI intake. so he pulled the dist and advanced it one tooth on the gear.

now, i have the dist turned all the way retarded, and it still reads 26* advanced (base). i couldn't retard it anymore before the vac can hit the coil. i was driving it without the vac adv, but even with it in place, the car runs great under all conditions, all rpms, all loads & throttle positions. i've never been able to get it to knock. cruises well. thermostat is now locked on 180*. it has MUCH MUCH more mid range pull now. i'm afraid i'm going to bust a cylinder wall or something.

i can recheck all the numbers over the weekend. i've been wanting to start a post about how i've got it setup. i'll do that over the weekend.

:flag