Detonation?

[Joe C.]

Before I decide to go on a "wild goose chase" I thought that I would consult with you all. At this point, I am not certain about the source of the "percieved problem" , or whether or not it's a problem at all.
I can hear a rattle at highway speed. Of course, it is more pronounced when there is a reflective solid object next to my car (i.e. another car, a concrete road divider, an Armco barrier, or an overpass). The car does have sidepipes, and I have never heard this rattle before. I've hit the mufflers with a rubber mallet, but heard no response. I have put the car in gear, and "powerbraked" it to 3000RPM, with no discernable "rattle". What the hell could it be?

Joe

[Don 42616]

Re: Detonation?

Joe, If noise is more pronounced under load it may be preignition.Like high gear uphill @ 30 mph.. If so check your timing. You didn't say what compression your motor is or if it just started. I had preignition on my 11.1 comp. C2. I solved it be retarding timing to +2* TDC & using tetroethyle in our 91o gas. there are other & better remedys , But this worked for me. Don

[Rob Dame]

Re: Detonation?

Wheel covers, center caps, trim rings, splash shields, side covers

[Joe L.]

Re: Detonation?

Joe------

.....or, it could be a defective heat riser valve. If the anti-rattle spring has departed or become "disfunctional" due to long exposure to the high heat, they will rattle. To eliminate or confirm this possibility, tie the valve tightly open with wire. Then, see if the noise goes away.

[Richard S.]

Re: Detonation?

You could also check for the clutch anti rattle springs and the bolts attaching the belhousing shield....good luck.

[Joe C.]

Don,Rob,Joe,Rick

Thanks for all of your responses, especially you Joe, the sidepipe hater .
I have heard that sometimes the internal, perforated pipe baffle can rattle. I am assuming that this very, very rarely happens with new mufflers........mine have about 300 miles on them. I tapped them along their length with a rubber mallet, and heard nothing, so I have to rule that out at this point. Joe, I removed the "butterfly" from the heat riser, and cemented the shaft in place..........it is tight, solid and secure, so rule that out.
I have clear plastic protectors on the forward sections of the sidepipe covers, which may have been the problem. They fit loosely in place, and may have fluttered in the breeze, so I have temporarily removed them. I found a spot on the left side rear plug shielding that very possibly might have been causing a rattle against the clutch bellcrank.......I have bent it to obtain clearance. Right now I lean toward the ignition shielding as being the culprit.
The clutch anti-rattle springs are both in place on the bellcrank, and are new. I find it difficult to determine if the noise is actually detonation, because of the side exhaust note. It is a possibility, although I think, a remote one..........unless I got a tankful of "bad gas". I'm open to hearing any plausible ideas. When it gets resolved, I'll let you all know.
Thanks.

Joe

[John M.]

Re: Don,Rob,Joe,Rick

Joe,
A tankful of 110 octane or a 50-50 mix of ot with 93 would eliminate detonation if that's the problem. Also 100 octane avgas would eliminate it.