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Discussion Starter · #1 ·
Hi
Looking for dyno sheets either showing ******individual tests or *******comparo 1 5/8 vs1 3/4 vs 1 7/8 . When compared the collectors need to preferably the same size eg all 3 inch .All mufflers fitted or all without . Need less to say on 383 ,,395,,400 410 sbc .

The reasoning behind this,
many magazine write ups compare but with no effort eg the collectors are different Doh !!!!!!!

Findings so far
On a 400sbc a 1 7/8 seems to be the largest pipe /or smallest cuin these can be fitted to .
What happens is the TQ curve slightly dips [ compared to 13/4 set ] in the mid range ,, a long collector seems to resolve this .
 

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Discussion Starter · #3 ·
hi
68chevelle cuin heads rpm cam ??

To all
seems true enough 400 dyno with small cam / small inlet manifold / small head flow and csa .Using 1 7/8 headers and no mid range dead zone WOW
Dart 400 SBC.wmv - YouTube
All sizes | Dart 400 dyno | Flickr - Photo Sharing!

427 Chrysler [stroked 383 wedge ] good for 2 inch primaries
Headers vs Manifolds - 426 Wedge on the Dyno! - YouTube

427 street strip 2 inch primary
Headers Dyno Test (hotrod.com)
The graph gives a good indication but the chart although labelling is incomplete shows torque well .Its always a trade want more above 5000rpm results in less 3500--5000rpm . How much do u want to lose . ??
 

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No header test will be accurate. They all have different primary lengths, different port exits, etc. and like any dyno operator will tell you it’s a full throttle test so it has no bearing on part throttle operation. Most headers are too big for the application anyway. Get the best fitting header for the car that fits the head port. I wanted 1 5/8” headers in my nova but found the 195 afr heads are better suited to seal on a 1 3/4” pipe. We dynoed my 1000 hp 565 with a 2 1/8” header and it went to 7500 on the dyno. This tells me that an average big block can get by with 2” or less and an average small block will be fine at 1 3/4”. Especially with the stock bolt spacing for the primary tubes.
 

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hi
68chevelle cuin heads rpm cam ??

To all
seems true enough 400 dyno with small cam / small inlet manifold / small head flow and csa .Using 1 7/8 headers and no mid range dead zone WOW
Dart 400 SBC.wmv - YouTube
All sizes | Dart 400 dyno | Flickr - Photo Sharing!

427 Chrysler [stroked 383 wedge ] good for 2 inch primaries
Headers vs Manifolds - 426 Wedge on the Dyno! - YouTube

427 street strip 2 inch primary
Headers Dyno Test (hotrod.com)
The graph gives a good indication but the chart although labelling is incomplete shows torque well .Its always a trade want more above 5000rpm results in less 3500--5000rpm . How much do u want to lose . ??
I ran the 1 5/8" headers last year with 062 Vortec's and the Elgin 1165P hyd cam. .488/.510 238° 248° on a 106 LCA.
 

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Discussion Starter · #6 ·
hi
HEader primary is in theory somewhere sized around the exhaust valve . In reality exh valve size is a guide ONLY. Easily decided by whatever part of the exh port /valve combo is the maximum restriction .Then overlay this with cam valve timing .
Header TQ curve production seems to occur in 3 areas
1/ up to 3000rpm
2/ 3000rpm to 5000rpm
3/ 5000rpm to 6500rpm redline

1/ area seems to be effected by pipe size, bigger sizes are better here .
2/ smaller pipes seem to work better here or larger pipe primary with longer collector ext .
3/ bigger pipes work here

summary
As with the example
A 427 favours 2 inch pri pipe.
What the dyno sheets show is going from 1 3/4 to 2 1/8 the midrange collapses .
The challenge is to get the just right sweet spot area is where the midrange is compromised as little as possible

Admittedly unless you can operate at full throttle the dyno figures are devalued . But good info for street driveability fuel economy ,throttle response etc etc
If your buying new 17/8 would be my choice
If u have 1 3/4 just use these
Almost every other engine around the 400 cuin benefits from 17/8 *****pending if you have a high flow cyl. head
The 400sbc with 23 deg heads are really poor flowing but a modern well matched head will give good results
Remember the 400 cu sbc is a very misunderstood engine heavily influenced by 350 thinking
 

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Discussion Starter · #7 ·
hi 68chevelle
The local 1 3/4 sets overlap ports a huge amount so 1 5/8 I would not consider . The local header makers are stuck in the 70`s eg port sizes and shapes ---small . No effort is made to enlarge /stretch the pipe at head flange plate.
I had to return my 1 3/4 for refund because of the failings in appearance and manufacture.
 

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If you've seen any of Calvin Elstons posts or talked to him, hell tell you most ex. ports are too big. He also says matching the header to the port is important. He seems to size by HP.
 

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To all A great street 396 BB
2 inch primaries ,very little TQ dip in the midrange

Storm Warning! - Quick Tech Inspection (archive.org)
Every time I have run 2" headers on my 396's and 454 BBC's so far the car has gone slower over the 1 3/4" headers. My buddy with his B/stocker Camaro swears by the 1 7/8" with a good merge collector and they spin them engines to the moon.
I did a back to back test on a weekend back in 2004 with my street 454 car. with the 2" Hookers the car ran the best of 12.09 and with the same everything on the car except for the smaller headers it then ran 11.91 and picked up 2 mph. I have read this over and over again and was told the same thing from Headers by Ed. He was one crabby guy but he knew headers inside out and knew what worked and what did not.
 

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Discussion Starter · #11 · (Edited)
hi
Yes I agree it seems little advantage in going 2 inch or greater . 1 7/8 seems like a sweet spot .I`m only talking 396/400 or bigger cuin . Yes I am awhere there are differences between SB and BB but the BB shows all the issues with sbc air flow.
Equip Sbc with a high flow head goes someway towards fixing the airflow problems .

To people who think big ports are bad ,this only occurs when incorrect for application.
Inlet and exhaust ports have been going higher and wider for decades.
 

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1968 Malibu sport coupe, 489 ci. 590 hp 600 tq, RV T-400 Freakshow 3200 stall, 3.73 12 bolt posi
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This probably wont help but my 489 with Brodix rec port 294's and 1 7/8 headers dyno'd 600 ft lbs from around 4200-4500, shop owner said I needed to dyno with his 2 1/8, he's a drag racer, but the flanges wouldn't clear my studs so really don't know but I'd think it would have moved the torque higher in rpm band, small hyd roller 231/239 .600 lift 107 lsa, 1000 cfm carb, I know it's a BB but might help ??
 

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This probably wont help but my 489 with Brodix rec port 294's and 1 7/8 headers dyno'd 600 ft lbs from around 4200-4500, shop owner said I needed to dyno with his 2 1/8, he's a drag racer, but the flanges wouldn't clear my studs so really don't know but I'd think it would have moved the torque higher in rpm band, small hyd roller 231/239 .600 lift 107 lsa, 1000 cfm carb, I know it's a BB but might help ??
What size exhaust valve are you using?
 

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66 El Camino 57 Chevy pickup 2004 Tahoe
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some things never change. most carbs, cams and headers are too big.
 
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