before/after 383 dyno results

[randy331]

That was dawning on me when dynoing project Dale. 1.875-2.00 3.5" collector , isn't that what the smallest dyno header there is? Anyway, I think Dale would have run better with a smaller header on it but who knows. Have you considered trying Ricks tri-y's on it? I also have my Chevelle headers you could try if they fit the dyno. They are 1.75, 32ish long 3 inch collector.

Joe has 1.75 x 1.875 x 3.5 headers up there. Think he has 1.875 x 2 x 3.5 too. He just bought a new set not long ago.
I have 1.75 x 1.875 x 3 inch that fit my Nova. Coated and Still new in the box.
It may be more sensitive to header changes now.

This 383 has a Jesel belt drive on it now, so moving the cam is faster than changing jets. LOL

Randy

[CGT]

What size do these look to you Randy?

Resized_20190309_130759.jpeg

I didnt see a smaller set and these look 1.875 to 2 inch to me.. I wonder if i overlooked them. This thing definitely didnt need that size of header on it, damn wish I would have looked harder or tried a passenger car header on it.

[77cruiser]

Resized_Screenshot_20190320-134546.jpg

You can try these if i have them finished in time. Its turning in to quite a project

Better get those Jet hot coated you don't want those to rust & turn ugly.

[zums]

That was dawning on me when dynoing project Dale. 1.875-2.00 3.5" collector , isn't that what the smallest dyno header there is? Anyway, I think Dale would have run better with a smaller header on it but who knows. Have you considered trying Ricks tri-y's on it? I also have my Chevelle headers you could try if they fit the dyno. They are 1.75, 32ish long 3 inch collector.

Joe has 1.75 x 1.875 x 3.5 headers up there. Think he has 1.875 x 2 x 3.5 too. He just bought a new set not long ago.
I have 1.75 x 1.875 x 3 inch that fit my Nova. Coated and Still new in the box.
It may be more sensitive to header changes now.

This 383 has a Jesel belt drive on it now, so moving the cam is faster than changing jets. LOL

Randy

Do you have a straight 1.75x 3 header to test with
Tom

[randy331]

Do you have a straight 1.75x 3 header to test with
Tom

Just a old rusty set off the Nova that got some damage when it landed hard.
Is that the size you think will run best ?

Randy

[cgarb]

If your going to run it up there in the rpm's...my bet it on the 1.875 tubes. Got any fancy collectors to try? My standard 4-1 collectors made more peak HP but the tri-y's made more average Hp and the torque jumped up there a couple hundred rpm quicker.

[paulzig]

1.875 x 2 x 3.5 in the useable RPM range if I was a betting man...

[cgarb]

Sorry for the side track...but why is it that they step the tubes larger as you go down the primary? Wouldn't stepping the tube smaller gain velocity as the gas travels down the pipe? I think about things in ways that relate to what I do...if you step water pipe down in size you gain pressure. I guess back pressure is not your friend in some cases...but as the hot exhaust gas cools wouldn't you need less pipe for it to travel out?

[paulzig]

Sorry for the side track...but why is it that they step the tubes larger as you go down the primary?

I would think its because each step up creates an anti-reversion barrier ...

[zums]

Do you have a straight 1.75x 3 header to test with
Tom

Just a old rusty set off the Nova that got some damage when it landed hard.
Is that the size you think will run best ?

Randy

Ive seen that standard size run real good on enough combos that i would try them if they were available, dented and rusty i would probably pass
Tom

[John Wallace]

Sorry for the side track...but why is it that they step the tubes larger as you go down the primary?

You want the exhaust out of the chamber.

Pressure goes to lower pressure.
Going to outside atmosphere is lower pressure than in pipe.
It wouldn't go to more pressure if smaller diameter?

Then there is the volume situation.

[cjperformance]

Sorry for the side track...but why is it that they step the tubes larger as you go down the primary?

I would think its because each step up creates an anti-reversion barrier ...

Every step up or increase in diameter provides a negative pressure pulse. The small diameter start to the primary keeps each gas 'parcel' at high velocity , not allowing the gas to slow down right after the port helps the chamber scavenging process,, but keeping the pipe at this diameter for too much length then becomes a restriction, a 'small' step up gives a controlled reduction in gas velocity (losing to much velocity causes the rapidly decellerating gas become a restriction to move) and a controlled reduction in pipe restriction.
Yes the gas cools as it moves thru the pipe and in the process of cooling becomes denser and loses velocity, common sense would say reduce pipe size to keep velocity high and keep the gas moving but prior to the collector where the cylinder scavenging process of the header as a unit is not complete this does not work.
Remember as the gas cools and becomess denser it also has more molecules per sq" to become a frictonal loss against the pipe wall which creates a slower moving boundary layer of gas near the pipe wall and a faster moving area of gas nearer the center of the pipe.
So the stepped primary is a juggle of keeping velocity high off of the port for long enough to creat high scavenging potential but not for so long that it then becomes a restriction, and then stepping the pipe up enough to allow good flow and create a negative pressure wave to help the proceeding pipe but not slow the gas so fast that it becomes a slow boggy mess and is consuming so much energy from the proceding pipe/gas velocity just to keep it moving that its scavenging potential is lost/reduced.
Then there may or may not be be another step up,
Then the collector will also still function properly and enhance the benefit of the stepped pipe and create its own negative pressure pulse.. that is just the basics and there is so much more to this. Extremely interesting stuff and each engine combo will respond differently, some will really benefit from a stepped primary, some not so much.
Going on after the header pipe and collector process is complete is then another matter and this is an area where some pipe reduction to enhance gas velocity can work very well.

[CGT]

Do you have a straight 1.75x 3 header to test with
Tom

Just a old rusty set off the Nova that got some damage when it landed hard.
Is that the size you think will run best ?

Randy

Ive seen that standard size run real good on enough combos that i would try them if they were available, dented and rusty i would probably pass
Tom

My headers for my Chevelle are in very good condition, and they are 1.75 x 3". You are more than welcome to those if you want. If they aren't in the shop. I just dug them out. Im putting some O² sensor bungs in along with some different collectors and V-band connections. Not sure when your planning on dynoing so. .

[cgarb]

Sorry for the side track...but why is it that they step the tubes larger as you go down the primary?

I would think its because each step up creates an anti-reversion barrier ...

Every step up or increase in diameter provides a negative pressure pulse. The small diameter start to the primary keeps each gas 'parcel' at high velocity , not allowing the gas to slow down right after the port helps the chamber scavenging process,, but keeping the pipe at this diameter for too much length then becomes a restriction, a 'small' step up gives a controlled reduction in gas velocity (losing to much velocity causes the rapidly decellerating gas become a restriction to move) and a controlled reduction in pipe restriction.
Yes the gas cools as it moves thru the pipe and in the process of cooling becomes denser and loses velocity, common sense would say reduce pipe size to keep velocity high and keep the gas moving but prior to the collector where the cylinder scavenging process of the header as a unit is not complete this does not work.
Remember as the gas cools and becomess denser it also has more molecules per sq" to become a frictonal loss against the pipe wall which creates a slower moving boundary layer of gas near the pipe wall and a faster moving area of gas nearer the center of the pipe.
So the stepped primary is a juggle of keeping velocity high off of the port for long enough to creat high scavenging potential but not for so long that it then becomes a restriction, and then stepping the pipe up enough to allow good flow and create a negative pressure wave to help the proceeding pipe but not slow the gas so fast that it becomes a slow boggy mess and is consuming so much energy from the proceding pipe/gas velocity just to keep it moving that its scavenging potential is lost/reduced.
Then there may or may not be be another step up,
Then the collector will also still function properly and enhance the benefit of the stepped pipe and create its own negative pressure pulse.. that is just the basics and there is so much more to this. Extremely interesting stuff and each engine combo will respond differently, some will really benefit from a stepped primary, some not so much.
Going on after the header pipe and collector process is complete is then another matter and this is an area where some pipe reduction to enhance gas velocity can work very well.

You got what I was thinking about right...a merged collector or a tri-y set up. The Venturi effect they have, I was thinking that step smaller would have that effect also. You make a good point about reversion, I did not think about that. Also about pressure moving to negative pressure. Makes sense now...or at least is a little easier to understand. I'm sure there is a million scientific reasons behind it which I will probably never understand, but I'm working on it. Thanks.

[cjperformance]

You got what I was thinking about right...a merged collector or a tri-y set up. The Venturi effect they have, I was thinking that step smaller would have that effect also. You make a good point about reversion, I did not think about that. Also about pressure moving to negative pressure. Makes sense now...or at least is a little easier to understand. I'm sure there is a million scientific reasons behind it which I will probably never understand, but I'm working on it. Thanks.

To have a very effective venturi effect you need squeeze the gas down which loosly has the effect of beginning to dampen pulses as well as straightening gas flow and then effectively allow this 'organised higher velocity gas' have a path into a lower pressure area (bigger diameter) that will maintain this 'organised' flow. If you dont allow the gas to expand it becomes a restriction and consumes energy to move it, or if you dont allow the gas to expand in a minimally turbulent/organised fashion it loses too much velocity and again becomes a restriction and consumes energy.

A good and basic example of this is simply the working range of 2 different diameter collectors, a smaller collector comes on at lower rpm because the smaller diameter of the collector compared to the pipe entering it allows the gas flow become efficient at a lower rpm (less gas) which allows the collector to enhance engine performance accordingly.. The bigger collector comes on at a higher rpm as it requires more gas flow to reach an efficient flow point. And on the flip side the smaller collector will kill power production off at a lower rpm because it gets to the point if becoming a rectriction to gas flow due to its smaller size.

As i said earlier is very interesting stuff. Dont feel alone trying to understand it all, no one knows everything, i probably only understand .001% of whats actually going on, and the more I learn about anything the more i realize how much I didnt actually know anyway!! In the grand scheme of things within this universe I know next to nothing about next to nothing !!