New 406 Build is Pretty Quiet

[RD_Racing]

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.

They are the 40 series and they came off the old motor.. They really didn't tone down the old motor but they did on the new motor..

[NormS]

With locked timing, you may not need butterfly holes. What carbs are you using?
In any event, the last thing you want to do is crack open the secondaries. If you're using Holleys, the proper butterfly position at idle is having NONE of the transition slots showing beneath the secondary butterflies, and no more than .030" of the slots showing beneath the primaries. If you have more showing than that, you may need some butterfly holes, but 1/8" may be too big. Start way smaller, like 1/16" in just the secondaries.

[RD_Racing]

With locked timing, you may not need butterfly holes. What carbs are you using?
In any event, the last thing you want to do is crack open the secondaries. If you're using Holleys, the proper butterfly position at idle is having NONE of the transition slots showing beneath the secondary butterflies, and no more than .030" of the slots showing beneath the primaries. If you have more showing than that, you may need some butterfly holes, but 1/8" may be too big. Start way smaller, like 1/16" in just the secondaries.

Im running a pair of Holley 450's mechanical secondaries (0-9776 4160).. I don't have the secondaires cracked at all, the screw adjustment on the bottom of these old carbs are frozen.. I will soak them with some PB blaster and try again.

[NormS]

No, you should not crack open the secondaries. That will make matters worse. The proper butterfly position at idle is having NONE of the transition slots showing beneath the secondary butterflies, and no more than .030" of the slots showing beneath the primaries. If you have more showing than that, you may need some butterfly holes, but 1/8" may be too big. Start way smaller, like 1/16" in just the secondaries.
Check to see how much of the primary transition slots are showing beneath the primary butterflies now. If it's more than .030", drill one small hole
(.052-.063") in each secondary butterfly.

[RD_Racing]

No, you should not crack open the secondaries. That will make matters worse. The proper butterfly position at idle is having NONE of the transition slots showing beneath the secondary butterflies, and no more than .030" of the slots showing beneath the primaries. If you have more showing than that, you may need some butterfly holes, but 1/8" may be too big. Start way smaller, like 1/16" in just the secondaries.
Check to see how much of the primary transition slots are showing beneath the primary butterflies now. If it's more than .030", drill one small hole
(.052-.063") in each secondary butterfly.

Wont adding holes lean out the idle circuit more? I remember back in the day we did that to help lean out the idle circuit on big dur cams.. I feel im already running lean at idle and have the idle mixture screws out about 3.5 turns to get maximum vacuum and it seems to be idleing pretty good where its at now and there is no eye burning exhaust fumes either (wish I had a wideband to check air/fuel ratio).. At 1.5 turns out (or less), it wont even idle.

[NormS]

What you need is 4 corner idle circuits on each of those carbs. What you have now, with only 4 idle circuits, is a lean idle mixture and poor distribution of fuel at idle. It's no wonder you have a ragged idle below 1300-1400. This needs to be addressed before considering anything about idle holes in the butterflies. The goal is to add enough idle fuel from the secondary ends, so that the idle mixture needles on the primary metering blocks are open
1-1.5 turns each, with the engine fully warmed up and trans in gear, if you have an automatic.

If you have an automatic trans,as things are now, I suspect the engine tries to die after you put the trans in gear. Putting the trans in gear lowers the manifold vacuum, and makes the idle mixture even leaner than it is out of gear.

[RD_Racing]

What you need is 4 corner idle circuits on each of those carbs. What you have now, with only 4 idle circuits, is a lean idle mixture and poor distribution of fuel at idle. It's no wonder you have a ragged idle below 1300-1400. This needs to be addressed before considering anything about idle holes in the butterflies.

Thanks, I was thinking about picking up a pair of Quickfuel SL600's, they are vacuum secondaries.. Skip White uses them on his 406 tunnel ram builds that dyno at around 580 and seem to work really good..

[rapidride2]

I myself would much rather have the ''stealthy -quiet yet more powerful/quicker'' approach versus the ''loud, obnoxious, look at me'' less powerful/slower approach.

[NormS]

Do the QFT carbs have four corner idle? If not , the improvement could be minimal. It's up to you whether you want to spend that money, but a pretty simple mod on your 450's is all that it would take to correct the idle mixture problem, and improve your idle quality and idle speed.
It would simply entail opening up the small bleed hole below each of the secondary transition slots(below the butterflies) .002-.003" at a time, until your primary idle mixture needles are at 1-1.5 turns each ,after re-adjusting the overall idle mixture, engine warmed up/trans in gear.

Drilling out those 4 bleed holes will be sensitive on those 9776 carbs, so be careful to enlarge them in small increments... .002-.003" at a time. Get yourself a set of #61-#80 drills, and a small pin vise.

And one more thing. If you have an electric fuel pump, and have been setting your float levels with the engine NOT running, that, all by itself, can make the idle mixture too lean. If you've been doing it this way, do it with the engine running before doing anything else. Reset your idle mixture, and then go from there with your secondary idle bleed holes, if necessary.

Always set fuel pressure and float levels with the engine running.

[RD_Racing]

Do the QFT carbs have four corner idle? If not , the improvement could be minimal. It's up to you whether you want to spend that money, but a pretty simple mod on your 450's is all that it would take to correct the idle mixture problem, and improve your idle quality and idle speed.
It would simply entail opening up the small bleed hole below each of the secondary transition slots(below the butterflies) .002-.003" at a time, until your primary idle mixture needles are at 1-1.5 turns each ,after re-adjusting the overall idle mixture, engine warmed up/trans in gear.

Drilling out those 4 bleed holes will be sensitive on those 9776 carbs, so be careful to enlarge them in small increments... .002-.003" at a time. Get yourself a set of #61-#80 drills, and a small pin vise.

Ok that sounds easy enough so I will give that a try first. It might be a while though because I don't have a trans in it yet. The motor is currently bolted to a front and mid plate only until I fab up a new trans mount.. Thanks again for all the help!!

[NormS]

And one more thing. If you have an electric fuel pump, and have been setting your float levels with the engine NOT running, that, all by itself, can make the idle mixture too lean. If you've been doing it this way, do it with the engine running before doing anything else. Reset your idle mixture, and then go from there with your secondary idle bleed holes, if necessary.

Always set fuel pressure and float levels with the engine running.

[MadBill]

...Always set fuel pressure and float levels with the engine running.

Yeah, I think someone mentioned that recently...

[RD_Racing]

...Always set fuel pressure and float levels with the engine running.

Yeah, I think someone mentioned that recently...

LOL, yes I did that already

[lefty o]

dont forget to set the floats with the engine running.................

[stealth]

Lean idle softens the tone along with more timing at idle