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1974 620 Ultra Quiet Exhaust: Adapt 720? or?


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#1 Cardinal Grammeter

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Posted 17 December 2017 - 01:13 AM

I do interstate driving over 4500 rpm and do not want any kind of exhaust drone - seems like I have an OE muffler on mine an it gives off only the faintest hum at that speed.

 

Even sticking with OEM style mufflers is not a guarantee.  For instance, the Suzuki Swift variants Walker SoundFX is terrible - very noisy mufflers.  Only the Walker stainless steel mufflers are quiet.

 

I was looking at Ranger and S10 exhaust parts and it looks like both are RHS systems (620 is LHS.)

 

The 720 might be good for the muffler/tailpipe?  Bosal has a welded 283-903 for about $110 shipped from RA.  (muffler has a front flange, but that could be cut off or welded.

05838380.jpg

 

 

I don't want to go to a muffler shop and get something bent because I would be really

pissed for a $300 job for muffler/tailpipe that was loud - which is what most people want. 

I could weld up a tailpipe but that leaves the muffler.

 

So that leaves me sourcing a muffler.

 

I looked at a lot of threads and one referenced a quiet muffler choice for a King Cab.  It didn't have much in the way of responses.

 

NOTE on PIPE SIZES:  The S10 and Rangers use a 2.25 exhaust and 2.0 tailpipe for their 2.0 liter engines.  I'm guessing they are 100 hp, so the 70 hp L18 could manage with a 2.0 and 1.75/1.50 pipe sizes.

 

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EDIT:  I'm guessing 520/521 exhaust might be a direct fit more or less.  Yes, older, but past discoveries would apply.

 

NOTE:  It doesn't seem like there is any attempts to find modern parts that will fit w/minor modification.  Everyone is getting loud / performance stuff either DIY or from muffler shops. 

 

I admit working on exhaust is a RPITA and virtually impossible if you don't have the tools/equipment.  I have all the tools/welders but not the lift.  I've done fabbed exhaust working off jack stands and I just don't have the stomach for it anymore.  But it backed into a corner, I guess I'll have to submit...



#2 G-Duax

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Posted 17 December 2017 - 08:20 AM

Add a good thick layer of sound deadening, like DynaMat, to underside, doors, back of cab, and under the whole bed.

These trucks were not made to be as quiet as a Lexus while driving.

All that tin amplifies any noise made by the engine.

 

Either that, or remove the dirty, noisy internal combustion engine, and replace it with a Green Planet electric motor, then fill the bed with 1000 lbs of batteries.


"All of a sudden it started making noise, then started losing power. I limped the car home and tried to get it up the driveway, the engine just died."

 

Why do people do this?

A $100 tow bill is never as much as the extra damage you cause by trying to "limp the car home".

 

Don't be that person !


#3 Stoffregen Motorsports

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Posted 17 December 2017 - 09:31 AM

I just built a new exhaust for my Land Rover and I wrapped the muffler with some sound deadener from DEI.https://www.summitra...0455/overview/  I ran the truck before and after I installed the muffler wrap and it was both quieter and cooler with the muffler wrap.

 

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Rover_Exhaust_Small_03_zpsd0m5fj0m.jpg

 

Rover_Exhaust_Small_04_zpshyqhgu6u.jpg

 

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#4 wayno

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Posted 17 December 2017 - 09:47 AM

Your going to struggle to quiet the engine noise itself, the exhaust is a different noise all together.


 

 


#5 datzenmike

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Posted 17 December 2017 - 09:50 AM

To be silent the exhaust can't come out of the pipe in puffs, it has to come out in a steady stream all slowed down. The very explosive pulse has to be spread out and released over a longer time. This requires a lot of resistance to flow through the muffler and is impractical as the engine has to work harder to push it through. If you were running at a set RPM the muffler can be designed (tuned) to cancel out the exhaust pulse frequency but this is also impractical. Exhaust sound can also be lowered by absorption into a sound deadening material lining the inside of the 'muffler'.   

 

 

Stick with the 620 pipes, you know they fit and work. Good news is it's a truck with lots of clearance under it so there is leeway for a larger muffler. If you can afford it a 2" 620 system custom bent at a muffler shop. A larger pipe diameter will be the first step in slowing down the exhaust speed. If the 620 pipe is 1 3/4" going to 2" is a 30% larger cross section. I would put a resonator up behind the down pipe under the cab. A glass pack 'Cherry Bomb' style will work, but they don't last the life of the system. A better choice is a newer car resonator that is a straight perforated pipe inside an empty shell. This allows the high pressure spike a place to expand and slow down without too much turbulence in the flow. For a muffler the largest 2" inlet you can find. Does not have to be for a truck. Look inside as some makers have 2" on the outside but it necks down inside the muffler. It's just a generic muffler with different inlets welded on. You could even go 2 1/4 inlet with a pipe adapter. This is what I did on my 710. A muffler with extra outside layers or internal sound absorbing materials will also reduce sound in the muffler casing. These 'mufflers' tend to be surprisingly heavy. As mentioned wrapping might be an option too. Definitely run a tail pipe to get the sound as far to the rear of the truck s you can.


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#6 thisismatt

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Posted 17 December 2017 - 10:31 AM

I'd look at a sedan setup, eg a 4 cylinder Honda Accord. Anything 4th generation up should be fine as those were 2 liters. They are quiet up through 7k rpm, so shouldn't be a problem.
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#7 DanielC

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Posted 17 December 2017 - 10:43 AM

See this thread, I made an exhaust system for a 521.
http://community.rat...tsun-521/page-3

To be honest, I have not yet had this truck on on the freeway yet, it is a too long term project that I am currently working on.  I also put a new exhaust system on another 521 that is running, but not really good, it burns too much oil.  I used a similar muffler on it, both trucks use a baffled design muffler.

 

I believe the drone at certain RPM ranges is caused by a specific length of pipe.  I do not know if it is the length of pipe before or after the muffler.  For example, the truck that is running not really good had a drone at about 1900-2000 RPM, then again at 3800 -4000 RPM. 

 

Like Mike said, a resonator between the engine and muffler may prevent the drone.  I might try it someday.  If you do try a resonator, I would try to place it so the length of pipe between where the runners on the exhaust manifold come together, the resonator, and length of pipe to the muffler are different.



#8 Cardinal Grammeter

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Posted 17 December 2017 - 06:29 PM

Thanks for the tips.

 

FYI, the exhaust on the truck is just fine as far as quiet goes - and that is with a rotted off tailpipe.  My Suzuki Swift references are probably not completely comparable since that system has a mid-resonator and a muffler at he very end (no tailpipe.)

 

RE:  Large Case Mufflers:

 

Another thing I learned about mufflers from my 1989 LS1 Z28 which had a long tube header system made by a company I can't remember, 3 initials, Txx, and not TSP which is Texas - I think this outfit had a misleading name like "turbo marine" or something - they had the first 1/2in flange long tubes you could buy for the LS1.  But the crux was that when they designed the system, they discovered mufflers with a small case did not have strong resonances  - an example of the worst muffler you could choose would be a Walker school bus muffler.  Does anyone remember "racking off?"  Some loved it, but it was really the worst possible exhaust sound out there.

 

So a large case muffler might be problematic, however, the current muffler on my 74 is a big round one (no dimensions at this time.)

 

I do like the idea of getting Honda pieces - or even S10 or Ranger mufflers.  But it might be best to find a muffler from something with 70 hp instead of over 100hp.

 

Off to check out that 521 thread...  wow, lots of nice work!  The exhaust crosses over to the RHS?  Is the 521 tank on the RHS like the 620?



#9 datzenmike

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Posted 17 December 2017 - 08:26 PM

521 tank is behind the driver.


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#10 Cardinal Grammeter

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Posted 07 January 2018 - 05:41 PM

Does anyone have copies of the Walker parts book picture of the 620 exhaust components?



#11 distributorguy

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Posted 08 January 2018 - 03:50 PM

1.  Run a cast iron manifold at the head.  

2.  Have a custom front pipe made of VERY heavy wall tubing.  

3.  Run a cat under the driver's floor 

4.  Run very heavy wall tubing to a rear mounted muffler - as far back as you can.  The further back it is, the more "high notes" it removes

5.  Ask your local muffler shop for a suggestion on a very quiet muffler.  They likely either know what you need.  Its what they do for a living (if its not some douche-bag Midas type shop.)  

Around here you're talking about a $300 system including a cat.  A smaller 2" system will be quieter than larger - maybe even choke down to a 1 7/8" tailpipe.  

 

The resonance you normally here is through the pipe.  Thin 14 or 16 gauge pipe is loud.  OEM systems are a little heavier, and the pipe is softer so it absorbs more noise (like cast iron manifolds).