Odd Sound on Decel

[rwantin]

Hi, please lend me your ears if you would.

It may or may not be a big deal, but wanted to bounce this off of some more experienced (probably most of you) than myself.

I have a Mark IV with an Engine Factory 393 (351 Windsor) with Edelbrock Performer heads and intake. It's my second Roadster, and reluctant to admit it is bought not built. I do all my own work (I guess you could say I am Advanced Shadetree), and have been sorting things, but having a tough time pinning this down.

On decel or off-throttle, both static and driving, there is sort of a gravelly, almost rattle from the exhaust. I don't think it is physically something with the pipes themselves, and it is even on both sides. The car runs great, and again, maybe this isn't anything, but if it IS something I can fine tune out, I'd love to try. Someone that heard it mentioned cam overlap? In any event, I have no idea. I went through the paperwork, not much there in terms of specs (and I didn't consign this engine).

I hope this link works, if not, I'll try uploading to Youtube or something.

https://share.icloud.com/photos/0S-t38kYMMwItDqlAOhuYnDKA

Thanks (in advance) for your time.

-Robert

[mike223]

My 393w, carburetted - has a funny "rattle" on decel too - only when its running "perfect" otherwise.

[rwantin]

My 393w, carburetted - has a funny "rattle" on decel too - only when its running "perfect" otherwise.

Thanks much for the reply, it is possible my Vehicular OCD is getting the best of me. That definitely helps.

[NAZ]

People spend a lot of $$ to get that sound on your video.

[rwantin]

People spend a lot of $$ to get that sound on your video.

And someone assuredly did just that. Thanks, appreciate it. It DOES sound great, just on decel does it seem a bit odd. I should just enjoy the thing.

[frankb]

A really looong time ago during my motorcycle days, I installed a 4 into 1 exhaust system on my motorcycle and I noticed a similar sound during engine deceleration. One night during a tuning session, I placed my open hand close to the exhaust outlet and revved the engine a couple times and noticed that the exhaust developed a vacuum (pulled my open hand against the outlet) during engine deceleration. It is this vacuum that was causing the sound change. After that I didn't think about it any more until I read your question above! ;)

[NAZ]

Yes, enjoy the sound. But if you're still worried, ship the car to me and I'll drive it around for a couple weeks and let you know what I think.:)

[Papa]

Burble, not rattle. Sounds fantastic to me.

Dave

[rwantin]

Thanks a ton guys. Puts my mind at ease. It seems really hard to hear in the video, very subtle on the back end, but it is there. It is far more pronounced on the road, but hey, it runs great.

And again, many thanks!

[RBachman]

These engines have a history of noises like this. Do a Google search and you'll find a lot of stuff on it. There was even a tech bulletin on it at one time, but that also failed to fix it and I didn't find a resolution when I searched. Some have said reprogramming the EFI helped. Seems to be non-issue, but do your research.