Thread: Detonated Dreams

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At first, I though NAAAA, this fellow has figured the SCR and DCR incorrectly. I refigured it and he's right on the money, so the cam and cylinder pressure match up, the squish looks ok at 0.051"/0.052" depending on whether he's using a 0.039" or 0.040" gasket and the motor absolutely should not be detonating on 91 octane fuel. I have a Crane catalog right in front of me that has the Cam Facts for this cam....."Good low end and mid range torque and horsepower. Daily useage and off-road, towing, performance and fuel efficiency. 8.75 to 10.75 static compression ratio advised."

OP, I'm gonna take you at your word when you say better fuel makes it a little better and go out on a limb here. I'm betting the inertia ring on the damper has slipped circumferentially in relation to the hub and you are getting incorrect ignition timing figures when you put a light on the motor. Here's a tutorial I wrote for the Crankshaft Coalition Wiki a couple of years ago. It explains how to correct the condition.
http://www.crankshaftcoalition.com/w...op_dead_center

The other long shot I was thinking about is that the noise is not spark related at all and is a mechanical interference noise. What made me think of that is the 1.6 rockers. Did you check for piston to valve clearance, spring coil bind clearance, retainer to guide/seal clearance and rocker slot to stud clearance at full lift? I know with the other things you said, it is unlikely, but just asking if you checked this stuff.

I run a lot of DynoSim combinations and the usual improvement I have seen going from 1.5 to 1.6 rockers is a single digit improvement in hp and torque. When you consider the extreme additional pressure that is generated at the lifter/lobe interface with these higher lift rockers, it hardly seems worth it. You want more lift, use more cam that is designed for more lift from the gitgo. That's just my opinion.

Glenn offered a reasonable explanation also, with hot spots in the chamber/piston crown, so clean all that up and round off everything while you have the motor apart. As Pat said, use a head gasket with a large enough I.D. so that it doesn't overhang the bore and glow red hot. The bore of the gasket should just exactly match the counterbore at the top of the cylinder. Using a bore that is too large is just as bad as one that is too small in my opinion. A very large bore gasket leaves a crevice where unburned gases can hide.

OP posted:
"In no way is this engine fast enough to warrant the need for race gas."
If the ignition timing is advanced as far as I think it is, that would explain the general lack of performance. Peak cylinder pressure could be occurring at the wrong piston position.

OP posted:
"I've heard that some things can happen to make your engine "see cylinder pressure" that rivals that of 11:1 even though you are only at 9.5:1. Not sure i understand how that would happen or what to do about it but i am VERY open minded at this point."
I think what you're alluding to is the DCR, which you already understand, apparently.

Thanks to everyone for all the great posts/ideas.

Glenn S-
I am cleaning up my chambers to rid the hot spots and am also looking at different valves to eliminate those edges, but i never thought of the piston. Makes sense. Is there anything i can do about those w/out pulling them from the motor to get them rebalanced/machined?

Cold air intake is def in the works.

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

Jerry C-
.012 is the distance from the top of my piston to the top of my deck @ TDC. Is this to little?

Pat M-
Water temps are steady at 185-190 in any weather. I have a great radiator. The thermostat is a 185. I could go lower.

I am shopping cams as we speak. I would love more power as long as it stays between 1000-5000 rpm. Any suggestions???

TechI-
The damper was new when i built the motor. I will definitely look into that scenario.

The heads were machined to be used with 1.6 rockers, but no i didnt check the other stuff you mentioned. Would those things be load/heat sensitive? Either way those 1.6's are gone. I already have a set of 1.5 rollers to eliminate the question mark.

You're right about the power being limited by my retarded(in every sense of the word) timing. Unfortunately predetonation doesnt make power either HA.

How do you guys feel about my DCR? Is 8.6 a good number?
How much HP/Torq do you think i can get out of this combo with the current cam?
Could i get more usable power(1000-5000rpm) from a bigger cam w/out using a hi stall converter?

Louey-
Engine temps are steady at 185-190
Vaccum idles at 12"+
I never actually checked the timing with my light. I just took the control modules word for it (and i don't even have those numbers written down for you), that's how you all know I'm an inexperienced hack.

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.