1 5/8” headers and 500hp?

[GARY C]

Will a 1 5/8” header support 500+ HP without completely choking it to death?

Application will be a 408 sbf. Unfortunately for us truck guys there are no reasonably priced options for larger tubes (that I know of). SBF 1 3/4” tubes or larger typically go to a different flange bolt pattern, of which is available only for more typical performance platforms like mustangs.

This is kind of a bucket list type build for me...and I want to get it done before the arthritis in my hands gets to the point that I can’t do this anymore.

Richard Simmons did a header test for ya.
https://www.youtube.com/watch?v=9Lckpw_81PQ

[novadude]

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.

[travis]

Will a 1 5/8” header support 500+ HP without completely choking it to death?

Application will be a 408 sbf. Unfortunately for us truck guys there are no reasonably priced options for larger tubes (that I know of). SBF 1 3/4” tubes or larger typically go to a different flange bolt pattern, of which is available only for more typical performance platforms like mustangs.

This is kind of a bucket list type build for me...and I want to get it done before the arthritis in my hands gets to the point that I can’t do this anymore.

Richard Simmons did a header test for ya.
https://www.youtube.com/watch?v=9Lckpw_81PQ

I think you’re confusing “sweating to the oldies” with car stuff lol

[GARY C]

Will a 1 5/8” header support 500+ HP without completely choking it to death?

Application will be a 408 sbf. Unfortunately for us truck guys there are no reasonably priced options for larger tubes (that I know of). SBF 1 3/4” tubes or larger typically go to a different flange bolt pattern, of which is available only for more typical performance platforms like mustangs.

This is kind of a bucket list type build for me...and I want to get it done before the arthritis in my hands gets to the point that I can’t do this anymore.

Richard Simmons did a header test for ya.
https://www.youtube.com/watch?v=9Lckpw_81PQ

I think you’re confusing “sweating to the oldies” with car stuff lol

Oh, I thought he just took his wig off.

[NewbVetteGuy]

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?

What Calvin Elston calls "blowdown length" seems to be exactly this concept, implying that, "YES" high velocity exhaust flow has an anti-reversion / reversion reduction effect. -I THINK TRI-Y designs might reduce reversion further via dissipation of the reflected wave, too.

(I THINK the reflected waves although useful within a certain RPM range have to be counter productive in other RPM ranges if high pressure wave is coming in an open exhaust valve and going through the cylinder and up the intake at overlap; if it helps you within a certain RPM band because of the timing and the lower pressure area helps pull exhaust out of the cylinder, doesn't it HAVE TO hurt you at some other RPMs when the wave shows up at exactly the worst possible time? -So if you want a broad power curve you're better off reducing / avoiding the reflected wave entirely rather than trying to take advantage of it in one RPM range and having it effect you negatively outside that range?)

It would be SO INTERESTING to see a high-speed stepped 4:1 dyno graph vs a similar high-speed Tri-y side-by-side and see whether there's a power dip outside of the tuned rpm range in the 4:1 vs. the TRI-Y. (I'm sure the TRI-Y would have more torque down low in an ideal test, but would we see some sort of negative reversion effect on the 4:1 outside of the tuned range?!?)

-Anyone with the fancy pressure transducers ever compare pressure reading in a 4:1 vs Tri-y side-by-side test like that? That would be cool to see too...
http://www.exhausting101.com/?p=70



Adam

[NewbVetteGuy]

Would adding some exhaust duration reduce some of the loss?

... 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...

My understanding disagrees with this.
My understanding is that high-speed / small exhausts HELP THE MOST when you have cams with a lot of overlap by propping up the torque at the lower end of the RPM range and because they HELP REDUCE reversion by getting the majority of the volume of the exhaust as far away from the head as possible BEFORE the intake valve opens.

-That's assuming that you're not creating tons of back pressure by running the small pipe off the head for too long and you've got steps up in ID. (Seems like these really small tubes off the head have to be paired with stepped header designs to keep the length where it needs to be for HP / torque goals.)

---I've seen a few tests where it sure looks like a very fast tri-Y header is actually leading to OVER SCAVENGING and requires LESS duration. -A header test starts with a way too big header, and then moves progressively smaller and all of a sudden jumps to a really small header ID or a small TRI-Y and despite the low-end torque picking up for quite a while all of a sudden the LOW-END TORQUE DROPS-?!?! Sure the peak HP should drop, but if the low end torque drops off on the small fast header that's the exhaust volume being extracted rapidly from the cylinder and then incoming air and fuel being sucked out after the intake valve opens during overlap and being spit into the exhaust, to me. (If the velocity of the flow is FASTER you're removing a higher volume of exhaust from the cylinder in less time / fewer degrees of duration, right?)

How many CFM does the head's exhaust port with a small initial header ID flow @ 500PSI+ and 1300°F? (The Darin Morgan quote from his now lost-to-the-universe blog on 28" depressions and flow for exhaust ports being mostly irrelevant kinda seems like it looms large and might solve some of the mystery here, maybe.) Maybe a bigger ID primary pipe flows better at 28" depressions in CFM but at 500+PSI the high velocity of the small pipe flows way more Cubic Feet per Second / milisecond??? It would be amazing if someone had such a flow bench. Would a header with a small diameter for the power level for the first 10" off the head flow a lot more in this test than a big ID header primary right off the head? -I THINK so, otherwise none of this makes any sense to me...



Adam

[chimpvalet]

Suggest anyone not familiar with Calvin Elston's generously insightful postings get onto reading them as a starting point. Seems most folks imagine that their exhaust is bunging up the process in a manner something like constipation does a human. Jere Stahl used to make small diameter long tube headers that showed the way in IMSA production based cars and on the street. F3000 Formula cars ran 4-2-1 header layouts to 9000 RPM limited rules in top tier competition. Seems more harm is done throwing away the scavenge energy of exhaust flow with big tubes than any minor gain at the very top revs could possibly justify. Any vehicle accelerates in terms of its engine's output over a span, think of this in terms of the total area under a dyno curve. Also worth bearing in mind that horsepower is just a function of torque.

Steve

[GARY C]

Suggest anyone not familiar with Calvin Elston's generously insightful postings get onto reading them as a starting point. Seems most folks imagine that their exhaust is bunging up the process in a manner something like constipation does a human. Jere Stahl used to make small diameter long tube headers that showed the way in IMSA production based cars and on the street. F3000 Formula cars ran 4-2-1 header layouts to 9000 RPM limited rules in top tier competition. Seems more harm is done throwing away the scavenge energy of exhaust flow with big tubes than any minor gain at the very top revs could possibly justify. Any vehicle accelerates in terms of its engine's output over a span, think of this in terms of the total area under a dyno curve. Also worth bearing in mind that horsepower is just a function of torque.

Steve

True! Yet none of these examples would apply to an average performance street engine with a non step header made to fit a stock chassis application with a full exhaust system.

[digger]

Based on 1D calcs i think length is more important than diameter on the power curve, i still think you only need diameter as you need which is smaller than most think and its easier to package a smaller system. With a lot of header tests many times there are multi variables changed. This then leads people to hypothesize the reason for the difference which is often done to fit with their beliefs rather than understanding the underlying physics and details happening. its human nature to simplify extremely complex systems

[Tom Walker]

Maybe we get the very best header for our application and now we need to re cam the engine to take advantage of the new exhaust efficiency, now the new cam might benifit from a change in the intake port area, which requires some carb massaging which might lead to some timing finessing which might lead to a header change, which might lead to any and everything. The envelope constantly gets improved and progresses. Just time and money I quess, it makes the world go around.

[Caprimaniac]

YES.... according to the guys at my local speedshop- in fact the only speed shop in this part of the country- a set of 1 1/2’’ Doug T. Tri-Y headers were good for 500Hp in a SB Mustang.

Not my data.... Never been too keen on very large primaries. A customer once said he wanted 2’’ primaries on 4 cyl 500cc cyl engine. I asked why. He came up with «You’re stupid and don’t understand shit»....
However 1 3/4’’ Stepped to 1 7/8’’ on the new 371 cui V8 for 8500+ rpm shiftpoint should be perfect...

[englertracing]

Not my data.... Never been too keen on very large primaries. A customer once said he wanted 2’’ primaries on 4 cyl 500cc cyl engine. I asked why. He came up with «You’re stupid and don’t understand shit»....
However 1 3/4’’ Stepped to 1 7/8’’ on the new 371 cui V8 for 8500+ rpm shiftpoint should be perfect...

LOL

[hoffman900]

Not my data.... Never been too keen on very large primaries. A customer once said he wanted 2’’ primaries on 4 cyl 500cc cyl engine. I asked why. He came up with «You’re stupid and don’t understand shit»....
However 1 3/4’’ Stepped to 1 7/8’’ on the new 371 cui V8 for 8500+ rpm shiftpoint should be perfect...

LOL

Those people are the worst.

[maxracesoftware]

Will a 1 5/8” header support 500+ HP without completely choking it to death?

Application will be a 408 sbf. Unfortunately for us truck guys there are no reasonably priced options for larger tubes (that I know of). SBF 1 3/4” tubes or larger typically go to a different flange bolt pattern, of which is available only for more typical performance platforms like mustangs.

This is kind of a bucket list type build for me...and I want to get it done before the arthritis in my hands gets to the point that I can’t do this anymore.
==========================================
I’m thinking somewhere in the 2500-3000 range.
That’s another downside to the weight...it makes a looser converter feel even looser under normal driving.
I have a heavy duty Hughes 11” in the ‘83 that is rated at 2500.
It took a bit of getting used to but it isn’t bad at all.

Travis ,
here's some Engine Specs + Dyno Sheet for SBF352cid engine
its the closest Dyno Data to what you are asking about that i could find .

438.6 / 352cid = 1.246 HP/CID Ratio
1.246 HP/CID Ratio * 406cid = 505.9 Peak HP

Peak TQ = 429.2 @ 4800 RPM
Peak HP = 438.6 @ 5500 RPM

Chris_SBF352_May_9_2014
4.060x3.400
Edelbrock Performer RPM Heads out the box 1.900/1.600 valves
Edelbrock RPM Air Gap intake manifold .750 angle spacer
Stock Ford Mustang oil pan Shell Rotella 15/40 6 qrts
Power Products Balancer
Ricks Dirt Track Schoenfeld Headers 1.625 3.000 Collector
Scat Crank and IBeam Rods 5.400
Keith Black Hyperutectic -6.5 CC flat top valve reliefs = 10.1:1 CR
Chevron 93 prem pump gas
Total Seal Rings 1/16,1/16,3/16
Holley Street Avenger 770 CFM vac carb
Scorpion 1.60 Rockers
Howards Hyd Roller Cam 235/241-112 on 110 CL .581/.581
----------------------
30 btdc from 28
Carb light-Silver vac diaphram spring

[chimpvalet]

Based on 1D calcs i think length is more important than diameter on the power curve, i still think you only need diameter as you need which is smaller than most think and its easier to package a smaller system. With a lot of header tests many times there are multi variables changed. This then leads people to hypothesize the reason for the difference which is often done to fit with their beliefs rather than understanding the underlying physics and details happening. its human nature to simplify extremely complex systems

Agree! Brings to mind how often one hears the old saw about how back-pressure is needed to make the exhaust right. Heard that one most recently on holiday lakeside when a nephew who's into drifting trotted it out .