1 5/8” headers and 500hp?

[hoffman900]

When I hear that, or how mufflers added power, first thought is that everything is way too big and the muffler is attenuating waves / atmospheric pressure

[n2omike]

Would adding some exhaust duration reduce some of the loss?

Cam design likely plays a significant role. Cams that rely on a lot of overlap would likely suffer more with the small tubes, as there would be more reversion. Opening the exhaust valve sooner by spreading the LSA and advancing the cam to compensate might yield the best results. Adding a little exhaust duration to go along with it probably wouldn't hurt. Someone can correct me if they disagree...

I wonder about this. Would the smaller tubes actually reduce reversion (in the range they are "tuned") due to the higher velocity pulling harder on the intake? Would this even apply outside of the "tuned" RPM range due to smaller tubes not allowing as much back-flow? Maybe I am out to lunch on this... just thinking aloud.

Velocity comes from restriction. As you constrict a passage, the velocity has to increase in order to move the same amount of fluid/gas. Scavenging effects are indeed real, but if the port is too constricted, the resistance to flow FAR outweighs any scavenging going on.

A sized header tube can only support so much flow in a given amount of time. My thinking is that if a tube is too small to properly evacuate an exhaust cycle in a given duration of time... extend the duration of time. Opening the exhaust valve sooner and holding it open longer would be one way to crutch a 'too small' header tube. This would be done by spreading the LSA, adding more exhaust duration and advancing the cam. This way, the intake events are left pretty much alone.

When the discussion of 'scavenging' is brought up on a 406, and the debate is between 1-7/8" or 2" tubes... it turns into a scavenging discussion. If the pipes are too small, capacity is the limiting factor.

[exhausted]

I just need to step in here. There is a world of difference between a 1.63 straight tube header and a header that leaves the head at 1.63 but is stepped and maybe many times to reach a given power level. A PS Australian 4into1 header may leave the head at 1.88" but it is stepped every 5 or 4 inches and is at 2.25" in 18".
If you are buying headers in a box that hopefully fit your street car or truck, I'd be more worried about ground clearance than how much power I was loosing at 5800rpm.
And just to add, a 421 header offers decidedly more ground clearance as a bonus.

[steve cowan]

I just need to step in here. There is a world of difference between a 1.63 straight tube header and a header that leaves the head at 1.63 but is stepped and maybe many times to reach a given power level. A PS Australian 4into1 header may leave the head at 1.88" but it is stepped every 5 or 4 inches and is at 2.25" in 18".
If you are buying headers in a box that hopefully fit your street car or truck, I'd be more worried about ground clearance than how much power I was loosing at 5800rpm.
And just to add, a 421 header offers decidedly more ground clearance as a bonus.

Mr Elston is back

[travis]

There is a tri-y option available from Dougs. I’m a bit dubious though as they say that they fit both 302’s and 351’s in these trucks.

[digger]

A random combo i put together
383
11:1
2.05/1.6 valve
320@700/240@700
XR292R 254/260/110/+2
0.66"/0.67"
single plane

some sims (so not an actual dyno test)

the primary 30" and colletor 17" lengths came from pipemax and remain same

some preliminary runs
1.625 to 1.875" and increments
2.5 and 3" collector

all runs (refer to legend)



best and worst 1-875-3" vs 1.625-2.5"



A quick diagnosis comparing at 7,000 rpm where there is ~4% difference 678hp vs 650 hp (my first interpretation atleast)

mass flow (smaller header has more reversion at IVO due to cylinder pressure higher than intake pressure see pressure grpah)



pressure ( cylinder pressure at BDC to IVO much higher with smaller header, despite smaller smaller header making higher peak suction quite a different shape though, note at this rpm the intake pressure is far from ideal at IVO)



this is delivery ratio/VE (so a small 1% difference due to the reversion at start)



so there is a 4% loss of power at 7000 with smaller header, essentially all caused by higher pressure BDC to IVO resulting in 1% loss of intake fill and 3% pumping loss

There are lots of things you could do to improve things, stepped size on the small headers, different length, more/less duration etc, better intake geometry but each and every change that improves at a given rpm the consequence at other rpm need to be considered so it comes down to bunch of compromises.

it illustares that while scavenging is great it needs to be balanced against pumping losses

[travis]

A random combo i put together
383
11:1
2.05/1.6 valve
320@700/240@700
XR292R 254/260/110/+2
0.66"/0.67"
single plane

some sims (so not an actual dyno test)

the primary 30" and colletor 17" lengths came from pipemax and remain same

some preliminary runs
1.625 to 1.875" and increments
2.5 and 3" collector

all runs (refer to legend)



best and worst 1-875-3" vs 1.625-2.5"



A quick diagnosis comparing at 7,000 rpm where there is ~4% difference 678hp vs 650 hp (my first interpretation atleast)

mass flow (smaller header has more reversion at IVO due to cylinder pressure higher than intake pressure see pressure grpah)



pressure ( cylinder pressure at BDC to IVO much higher with smaller header, despite smaller smaller header making higher peak suction quite a different shape though, note at this rpm the intake pressure is far from ideal at IVO)



this is delivery ratio/VE (so a small 1% difference due to the reversion at start)



so there is a 4% loss of power at 7000 with smaller header, essentially all caused by higher pressure BDC to IVO resulting in 1% loss of intake fill and 3% pumping loss

There are lots of things you could do to improve things, stepped size on the small headers, different length, more/less duration etc, better intake geometry but each and every change that improves at a given rpm the consequence at other rpm need to be considered so it comes down to bunch of compromises.

it illustares that while scavenging is great it needs to be balanced against pumping losses

If it’s not too much to ask, can you try these sims with another 6* or so of exhaust duration? Or maybe the same setup but with say a 112 lsa?

[digger]

here is power curve with

1-875-3" as shown before
1.625-2.5" as shown before

with two new ones
1.625 with two equal steps and 2.5" collector (lengths same)
1.625 with two equal steps and 2.5" to 3" divergent 7 degree cone (lengths same)



so it brings back a decent chunk but it doesnt offer any real midrange improvements so you might ask why not just use the larger single pipe size and parallel 3"

pressure of 1.625"-2.5" vs 1.625-2.5" with 2 equal primary steps

the stepped primaries drops the exhaust and cylinder pressure BDC to IVO but also lowers the strength of the suction/scavenge slightly




pressure of 1.625-2.5" with 2 equal primary steps vs 1.625-2.5" with 2 equal primary steps with collector divergent to 3"

the divergent section broadenss the width of scution wave but doesnt really alter the cylinder pressure or exhaust pressure from BDC to IVO

[blown265]

This thread is very relevant to a dilema/choice I have, so apologies for the slight sidetrack. The engine in this case is a supercharged 4.3lt 2V I6 making approximately 65hp per cylinder (approximately 500hp in V8 terms) on a 1.63 primary pipe at 6000rpm. The drive ratio on the M122 is being increased soon, with a target of 85hp per cylinder, and the question for us is whether to step up to a 1.75 primary pipe? It'll be an expensive upgrade - around $1000- so we're at odds to whether there'll be any reasonable gains.
Exhaust is currently a Pipemax spec, straight 1&5/8 long tube header, and open exhaust after the collector.
Thanks in advance
Paul

[digger]

A random combo i put together
383
11:1
2.05/1.6 valve
320@700/240@700
XR292R 254/260/110/+2
0.66"/0.67"
single plane

some sims (so not an actual dyno test)

the primary 30" and colletor 17" lengths came from pipemax and remain same

some preliminary runs
1.625 to 1.875" and increments
2.5 and 3" collector

all runs (refer to legend)



best and worst 1-875-3" vs 1.625-2.5"



A quick diagnosis comparing at 7,000 rpm where there is ~4% difference 678hp vs 650 hp (my first interpretation atleast)

mass flow (smaller header has more reversion at IVO due to cylinder pressure higher than intake pressure see pressure grpah)



pressure ( cylinder pressure at BDC to IVO much higher with smaller header, despite smaller smaller header making higher peak suction quite a different shape though, note at this rpm the intake pressure is far from ideal at IVO)



this is delivery ratio/VE (so a small 1% difference due to the reversion at start)



so there is a 4% loss of power at 7000 with smaller header, essentially all caused by higher pressure BDC to IVO resulting in 1% loss of intake fill and 3% pumping loss

There are lots of things you could do to improve things, stepped size on the small headers, different length, more/less duration etc, better intake geometry but each and every change that improves at a given rpm the consequence at other rpm need to be considered so it comes down to bunch of compromises.

it illustares that while scavenging is great it needs to be balanced against pumping losses

If it’s not too much to ask, can you try these sims with another 6* or so of exhaust duration? Or maybe the same setup but with say a 112 lsa?

here is an extra 6 degrees and 0.010" more lift

[RevTheory]

Travis, apologies if I missed it but what are your current cam specs?

[RevTheory]

Shoot, I lost my opportunity to edit. Do you happen to know your hot, cranking pressure?

[travis]

Shoot, I lost my opportunity to edit. Do you happen to know your hot, cranking pressure?

I’m just in the planning stages at this point...kicking around a few ideas. I’ll probably start on this build this winter

[maxracesoftware]

Shoot, I lost my opportunity to edit. Do you happen to know your hot, cranking pressure?

I’m just in the planning stages at this point...kicking around a few ideas. I’ll probably start on this build this winter

Travis ,
i don't know if you missed this Post ?
viewtopic.php?p=874899#p874899

but this Combo should get you an honest 505.9 Peak HP out of a 406cid
it has a Dual-Plane Manifold , should make excellent low RPM Torque as well

[travis]

Shoot, I lost my opportunity to edit. Do you happen to know your hot, cranking pressure?

I’m just in the planning stages at this point...kicking around a few ideas. I’ll probably start on this build this winter

Travis ,
i don't know if you missed this Post ?
viewtopic.php?p=874899#p874899

but this Combo should get you an honest 505.9 Peak HP out of a 406cid
it has a Dual-Plane Manifold , should make excellent low RPM Torque as well

That combo is right in the ballpark of what I am thinking.

I’ve been playing with Engine Analyzer 3.4. It looks like an 8-10 degree I/e split on the cam definitely minimizes the loss between a 1 5/8” header and a 1 3/4” header under 6000 rpms. Typically shows about a 10-12hp difference from 5000-6000 rpms, but the difference certainly grows past that point...but I’m not worried about that.