Thread: Detonated Dreams

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Originally Posted by 63SSII

I do need to do a better job of reading the plugs consistently. They are usually tan/brown w a little black spotting.

If the black spotting is what looks like someone sprinkled pepper on the insulator of the plug, that is little particles of melted piston crown resulting from detonation.

So after talking to my dad last night, it's our car but right now it's his turn to have greasy hands, he had checked that the damper had not slipped and the timing was in fact correct. He did this some time before tearing into the motor. When the spark plugs were pulled this time they were heavily blackened due to some worn out valve guides seaping oil into the chamber. I'm sure this wouldn't help our cause, but this is a newer problem(last 500 miles) and its had the knock issue since it was built. In the past when i checked the plugs they were tan/brown with specks of black.

At this point it would seem there is no big "AAH HAA" problem with the motor like compression or cam timing. The biggest thing we've found is the head gasket is a bit bigger than the bore. We will get a snug head gasket, soften every edge we can find, get the coolest plugs, drop the thermostat, and fab up a cold air system. Am i missing anything? Once the motor is running we will verify fuel pressure, make sure the actual timing matches the computer and take it from there.

Hopefully all these tiny things will add up to a big change.

....also, i'm curious what some of these Virtual Dynos would rate this motor at for power. Anyone have access, or know of a good free one on the net?

Thanks for everyones help. You are all a wealth of information. I appreciate the posts.

Assuming your calculation is correct, a DCR of 8.6 is way to high for iron heads, in fact, it is too high for aluminum heads. That is why you are experiencing detonation. As a general rule, the DCR maximum is 8.0 with iron heads and 8.5 with aluminum heads. You can change the cam to one with a later intake closing point and more overlap to reduce cylinder pressure. Aluminum heads would also help, although you have a good set of iron heads. IMO, I would concentrate on a cam that reduces your cylinder pressures. You might look at one ground on a lobe center of 106 or 108 degrees. I have a feeling the one you have is probably ground on a 110-112 degree lobe center. These cams have less overlap and, as a result, more cylinder pressure. That is why blower engines have cams with a 114 degree lobe centers so they will not bleed off any of the boost due to overlap. PM me if you want any additional help.

Upon further review.....

RummRum wisely sugested a differant cam because my DCR was too high. After a little research on the net i was fairly convinced this was true. I've been shopping cams to get DCR below 8.0 to be safe(current DCR = 8.6). I called the tech line at CompCams and talked to a fellow that clearly didnt want to be talking to people about cams. He said that i should be fine with 8.5 DCR. He suggested Comp Cam p#12-404-4 which is the 268H and has an intake closing(.050") @ 41*. He also said that the higher lobe seperation would help reduce knock.

How does the brain trust @ CHR feel about this?

This seems to make more sense to me but i am curious how much DCR you can really get away with on pump gas in middle america. Also, is the KB.com calculator the best one on the net?

Originally Posted by 63SSII

Also, is the KB.com calculator the best one on the net?

I don't think it's a matter of being the best or the worst. It's a matter of using the same one every time and comparing results to known other results. For instance, I have seen motors that register 8.8:1 on KB's calculator, yet run fine on pump gas without detonation. I'm of the opinion, after thinking about it for a while, that the combustion chamber design has a great deal of bearing on whether the motor detonates or not on a certain grade of fuel. The chambers in those 441 heads are pretty old technology and may be part of the problem.

^^^so his plug spotting could be bits of combustion chamber and/or piston?

Everyone should read this thread about Dynamic Compression Ratio. It is the best explanation/discussion of DCR I have seen.

http://www.chevytalk.org/fusionbb/sh...php?tid/92966/

awesome link^^^ thanks

Originally Posted by 78c10

^^^so his plug spotting could be bits of combustion chamber and/or piston?

Highly likely.

I will apologize in advance if someone has already said this...

Hyper pistons do not hold/absorb heat like forged do, they send it to the head/chamber and top ring, yes this does increase temps at the top ring requiring more gap [to avoid butting] so the rest of the ring package is lowered to avoid having to increase their gap as well.

JMOanything beyond .042 thou quench distance from the head is a wash if trying to make use of quench benefits, like avoiding detonation...

I would like to know what the actual dynamic psi is-as in cranking psi ?

If you are over 185psi, then that explains it to me.



There is an old sbc x head that has more material around the plug to help centralize the ignition/burn and avoid uneven lighting off- 2 fronts colliding.

I like the the slipping balancer ring idea, just wonderer if since the efi set up retards the timing for you if that would matter?
that cam is a lil small for the compression on pump gas with those heads and their plug angle that is miles away from where it should be. .JMO

yep they reflect some heat not all hypers need more ring gap KB yes and i will stand by thinking they hold more heat around the top ring land were i seen many fail and NOT from lack of end gap if they fail and have much end gap you tell me why? if you can not get the heat out of the top ring thru the block then the top ring land as deep as the radial ring cut is going to run abit hotter ???? speed pro alloy seam to hold up better .i do not know if the machining on the fly cuts on the KBs are to sharp and need to be rolled (i roll most of my pistons if they are sharp) with there hi sil alloy to hard making them fail but i have seen many and i will stick to the 4032 or 2618 or for lower buck builds the speed pro hypers. even a HD cast piston before a KB hyper i used them ...i do not care for them.... if i am wrong its ok with me what i have been doing has worked very good for me

The KB have ridges above the top ring for heat dissipation.
Yes the the edges have to rolled/smoothed.
And I didn't say they didn't hold some heat, just said they absorb as much as forged pistons do, which translates into the pin/rod and into the oil temp.

Why do they fail?
Cause guys run too much timing with them for 1, for 2 people use these things out of app. when they should be running a forged piston, and then the ring gap factor...

I have heard many good things about the mogul/speed pro, too bad they don't expand their app's....

KB has many different head configured pistons to choose from.

btw..thats what it's about right? share our experiences and use what we like, but put the info out there for others to aid in making the right choice.

well KB are making a cheaper forged line and i have used them and will use them again . the KB s hypers i know about the ridges. there is sharp break on fly cuts with no radus. a good break off point. no big deal i use more forged piston stuff any ways just think there hypers are not that good for the money . and i bore just one or two blocks a year

So we ordered Comp Cams 12-366-4. Should give a DCR of 7.95 with quite a bit more duration. Hopefully it solves the problem.

Stay tuned for the outcome.

Intermediate update, with the heads back on and the previous cam still installed, we turned the engine over to see what the Pressure/PSI was in each cylinder. We are between 180-185 PSI. Sounds like a lot. Maybe we are on the right track. More to come....