New 406 Build is Pretty Quiet

[RD_Racing]

New member here
Just fired up my new motor for my 73 back halved Vega and was pretty surprised to find its way quieter than the old motor that was probably 1/2 the power or less.. The old motor that came with the car was a bone stock 350 short block (flattop pistons) with thumper cam, iron eagle 200cc heads and 1-3/4" headers.. The new motor is a 406 with 6" rods, 11:7-1 compression (wiseco pistons +8cc), Pro Topline 220cc heads and a Lunati cam (Dur @ 050 .258/.268, LSA/ICL: 106/102, .620 lift) and the "same" headers.. Both motors used the same tunnel ram, carbs and ignition.. This new motor is about as loud with open headers as the old low compression motor was with mufflers. LOL.. Is it possibly the cam profile or the Topline heads? My old 65 Chevy II that had a 406 in it was probably twice as loud.. It just seems really weird that its so quiet like something isnt right.. It seems to run and idle perfect, I just wont be able to drive it until spring

[fdicrasto]

Based on what info you have given, quieter could be better.

[gnicholson]

Sounds like a good problem to have. Probably has to do with a change in the exhausts resonant frequency

[RD_Racing]

Unless my 5" Autometer tac is off, I'm ideling at about 1400rpm, anything lower than that seems to low and almost sounds more like a extremely low compression gargling idle (it just doesn't sound right)

[RD_Racing]

Here are a few videos

The old 350 motor with 3" pipes and flowmaster mufflers
https://www.youtube.com/watch?v=-VeagXGo_0A

The new 406 motor with open headers
https://www.youtube.com/watch?v=5T-BOfcg4IM

It just seems like the exhaust pulses are weak with the new motor

[judgement_impared]

Did you degree the cam?
Who set the lash and at what?

[ptuomov]

High compression and retarded cams made my car much quieter and low compression and advanced cams made it a lot louder. It makes sense, but the change was larger than I expected.

[PackardV8]

Noise isn't power. A bit OT, but while at a vintage sports car race, a 911 Porsche was the loudest car in his class and was also one of the slowest.

[midnightbluS10]

Noise isn't power. A bit OT, but while at a vintage sports car race, a 911 Porsche was the loudest car in his class and was also one of the slowest.

There's a few Mustangs around here like that. Loud, overly obnoxious exhaust but they're hardly moving. Seems to be a common thing among the younger Mustang owners these days.


Only thing I can suggest is to compare it to the new motor with the mufflers back on and see how that changes it. It may sound more similar to the last motor and you don't even know it. Personally, I think it sounds better now.

[kimosabi]

I noticed the same with my 400. Cam is 2degrees retarded because of close to limit on pump gas and compression. The stock ~8:1 350 was equally loud with restrictive mufflers. Stepping on it is a differnet story though.

[RD_Racing]

Did you degree the cam?
Who set the lash and at what?

Yes ICL is 102 and it was degreed at 101.
Lash is set per cam card .022/.024

[RD_Racing]

Noise isn't power. A bit OT, but while at a vintage sports car race, a 911 Porsche was the loudest car in his class and was also one of the slowest.

Only thing I can suggest is to compare it to the new motor with the mufflers back on and see how that changes it. It may sound more similar to the last motor and you don't even know it. Personally, I think it sounds better now.

I bolted the same flowmasters on and it toned it way down, it almost sounds like a stock 350, lol

[NormS]

" Unless my 5" Autometer tac is off, I'm ideling at about 1400rpm, anything lower than that seems to low and almost sounds more like a extremely low compression gargling idle (it just doesn't sound right)"

I suspect that the duration of your new cam is considerably longer than your old thumper cam. That increased duration is going to need more initial ignition advance, and possibly small air bypass holes drilled in the butterflies to get them in the right position at idle. If you have less than 20° of initial now, try putting it somewhere in the 20-25° range, and see if that improves your idle, once you re-adjust your idle speed and idle mixture.
If that helps, then you would need to shorten the advance curve, so that you can run that increased initial and still have a reasonable amount of total advance.
Also, the thumper series of cams was meant to make noise, by way of their increased overlap, possibly putting more raw fuel into the exhaust.

[ptuomov]

Noise isn't power. A bit OT, but while at a vintage sports car race, a 911 Porsche was the loudest car in his class and was also one of the slowest.

Only thing I can suggest is to compare it to the new motor with the mufflers back on and see how that changes it. It may sound more similar to the last motor and you don't even know it. Personally, I think it sounds better now.

I bolted the same flowmasters on and it toned it way down, it almost sounds like a stock 350, lol

Why flowmasters and which models? I've been trying to get a low compression, early EVO engine quieter and I've ended up with different kind of muffler.

[RD_Racing]

" Unless my 5" Autometer tac is off, I'm ideling at about 1400rpm, anything lower than that seems to low and almost sounds more like a extremely low compression gargling idle (it just doesn't sound right)"

I suspect that the duration of your new cam is considerably longer than your old thumper cam. That increased duration is going to need more initial ignition advance, and possibly small air bypass holes drilled in the butterflies to get them in the right position at idle. If you have less than 20° of initial now, try putting it somewhere in the 20-25° range, and see if that improves your idle, once you re-adjust your idle speed and idle mixture.
If that helps, then you would need to shorten the advance curve, so that you can run that increased initial and still have a reasonable amount of total advance.
Also, the thumper series of cams was meant to make noise, by way of their increased overlap, possibly putting more raw fuel into the exhaust.

My distributor is locked out at 34 degrees. I did notice the new motor seems to burn allot cleaner at idle compared to the old thumper cam. I had a hard time keeping plugs clean at idle on the old motor. I don't see any adjustments for cracking open the secondaries on these old carbs so I may try drilling an 1/8" hole in the butterflies like we did back in the ole school days..