Electrical cut outs on 383?

[euroZ06]

Hi guys,

I have a mint 68 charger. Car was restored to concourse, but... I'm a driver, and I don't like garage queens. I drive it all the time. Currently it is all stock.. sometimes I really miss the roar of my old 68 with a built 440.

I figured a cool solution to keep the car in almost stock shape by adding electrical cut outs. Someone told me that 383's don't like them (cause of the reduced back pressure). Is that true? Is there any harm? I wouldn't be cruising on highway with them open, just rolling around town and a few sprints now and then.

Also, can't figure out which size cut outs I'd need, I measured the exhaust and it's 19cm in circumference, but that doesn't clearly decide into inches... which size should I get...

[c00nhunterjoe]

In my opinion, you need lots of compression and a HUGE cam to sound good uncapped. Here is my 11:1 383 with essentially a purple 509 cam which is considered too big by most.... and in my opinion sounds terrible uncapped

https://youtu.be/vQazmSsG4sU

[c00nhunterjoe]

Vs high compression and a monster superstock cam in my current engine... big difference in sound open header.

https://youtu.be/p6kcOMgYxzY

[garner7555]

It doesn't "need backpressure".   The ideal situation for performance would be to have a vacuum sucking the exhaust out.   In my opinion don't put any value in people's opinion if they tell you an engine needs back pressure.           
As far as the sound quality, that is just personal preference.  I agree with coonhunter, the higher the compression= the better the sound.  I prefer the sound through deep rumbling mufflers over straight headers though.       
The all time best exhaust sound is wore out junk with straight pipes popping every time they let off the gas.           

[c00nhunterjoe]

I think it was kerndog who described it perfectly with the analogy of a 70s woodpulp truck. Lol.

Put a good sounding pair of mufflers on it.

[euroZ06]

I agree with you guys, a proper exhaust with properly built engine sounds the best. However, I'd like to keep the car stock, and I want it to be quiet when cruising or when starting it up at the house... plus I need to be able to pass NY state inspection. I figured cut outs would be perfect to rev up now and then...

[charger chris]

In my opinion, you need lots of compression and a HUGE cam to sound good uncapped. Here is my 11:1 383 with essentially a purple 509 cam which is considered too big by most.... and in my opinion sounds terrible uncapped

https://youtu.be/vQazmSsG4sU

That sounds good.

[Lennard]

https://m.youtube.com/watch?v=6uW0dJyMKsU

[BrianShaughnessy]

. plus I need to be able to pass NY state inspection. I figured cut outs would be perfect to rev up now and then...

NYS inspection for a '69 is $10 and a kid coming out with a scanner and a scrapper to take off the old sticker and put on the new one.    You hand him a $20 bill..  say thank you, keep the change. 

[c00nhunterjoe]

In my opinion, you need lots of compression and a HUGE cam to sound good uncapped. Here is my 11:1 383 with essentially a purple 509 cam which is considered too big by most.... and in my opinion sounds terrible uncapped

https://youtu.be/vQazmSsG4sU

That sounds good.

Thanks, but i was never a fan of that engine uncapped. Not radical enough to sound good to me. I prefered its sound through 3" mufflers.
https://youtu.be/9gpncCxfZ44
https://youtu.be/di8VIN6i6ok

[VegasCharger]

https://m.youtube.com/watch?v=6uW0dJyMKsU

Is that you Lennard behind the wheel? 

[Lennard]

https://m.youtube.com/watch?v=6uW0dJyMKsU

Is that you Lennard behind the wheel?  

in 2004.

[alfaitalia]

It doesn't "need backpressure".   The ideal situation for performance would be to have a vacuum sucking the exhaust out.   In my opinion don't put any value in people's opinion if they tell you an engine needs back pressure.            

Lol....well if you want the absolute maximum power at peak revs you are right...but if your cam has any sort of overlap and you want any torque at all at low revs (where you mostly drive it on the street I'm guessing)...then a bit of back pressures and correct length headers might stop all your un burnt fuel (fuel that produced no power at all! ) going straight out of the exhaust!

[Ghoste]

I agree, I think a lot of street cams are designed with that in mind also are they not?  I'm no engineer though.

[INTMD8]

Lol....well if you want the absolute maximum power at peak revs you are right...but if your cam has any sort of overlap and you want any torque at all at low revs (where you mostly drive it on the street I'm guessing)...then a bit of back pressures and correct length headers might stop all your un burnt fuel (fuel that produced no power at all! ) going straight out of the exhaust!

I believe you are thinking correctly but using the wrong terminology. No engine will make more power with backpressure.

It is concluded by many that backpressure is sometimes needed/makes more power when a larger than needed exhaust is used (or open headers/manifolds) and power drops.

The reason for this is not because it needs backpressure but you reduced scavenging efficiency by going too large, slowing velocity.

So, like anything else there is an -ideal- size which will give you maximum scavenging without inducing backpressure.

[alfaitalia]

You are correct...ultimately an engine with less back pressure (bigger headers, free flowing mufflers etc) will make higher peak power...but you will sacrifice power at the bottom end of the range (where us non racers want it). Lots of motorcycles have variable geometry exhausts that create slightly higher back pressure at low revs for this very reason. Yamahas EXUP is a good example. Due to packaging cars tend to go the other way and had the variation in the intake side.

[INTMD8]

Yes, my F355 has a variable exhaust (bypass valve on a secondary exhaust path).  A lot of the newer cars have dual mode mufflers and this does bolster low/midrange torque while allowing for higher flow at high rpm.

(and as you mentioned further yet many having variable intake manifolds as well)

Still, I think this is optimizing velocity/scavenging over a broader rpm range rather than inducing backpressure.

For example, with variable exhaust in it's most restrictive mode I think you will find it is optimizing velocity at low rpm but not so much that you would be measuring several+ psi backpressure.

[garner7555]

Yes, my F355 has a variable exhaust (bypass valve on a secondary exhaust path).  A lot of the newer cars have dual mode mufflers and this does bolster low/midrange torque while allowing for higher flow at high rpm.

(and as you mentioned further yet many having variable intake manifolds as well)

Still, I think this is optimizing velocity/scavenging over a broader rpm range rather than inducing backpressure.

For example, with variable exhaust in it's most restrictive mode I think you will find it is optimizing velocity at low rpm but not so much that you would be measuring several+ psi backpressure.

Yes, I agree,  Scavenging will increase power.   But in reality, scavenging is very much like vacuum that I mentioned above.  I have never seen a time when positive pressure in the exhaust created more power.   I also agree that too large of an exhaust can reduce scavenging which will hurt power.