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What header primary tube dia. for 427 strokers?
This is for a street/strip setup 550-575 FWHP with 6000-6200 max RPM.
Will a 1 3/4 O.D. tube header handle this? |
A 427 will benefit from 1 7/8 pipe. A 1 3/4 will help a 408 and smaller.
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1.75 is really too small. I reccomend equal length 2" down to the a 3"collector, 3.5" muffler and 3" turn out. A 4" muffler has shown a loss in HP. I gained 7 hp to over 40 over 4500 rpm with this exhaust.
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You'll never get 2" pipes out of small block header flanges and still be able to mount them due to header bolt clearance. And those will only work if you have someone who can form the flange tubes to fit the exhaust ports and leave room for the bolt heads to fit.
1 7/8" will be very tight, but will probably be your best bet for flow/horsepower as long as you use the rest of the recipe Kevin recommended above. I went through this before I built my headers with a couple engine builders and this seems to be the consensus for small blocks except for extreme flowing heads and big cubes on the aftermarket blocks. Bob |
don't know what your specs are but for a 427 using specs for a healthy 406ci (3.80x4.125) exhaust program shows
--- Single Primary Pipe Specs --- for 427.650 CID from 4600 to 7100 RPM Diameter= 1.873 to 1.998 Length= 29.9 to 32.7 inches long --- 2-Step Primary Pipe Specs --- 1st Dia. inches= 1.873 Length= 15.0 to 16.4 2nd Dia. inches= 1.998 Length= 15.0 to 16.4 --- 3-Step Primary Pipe Specs --- 1st Dia. inches= 1.873 Length= 15.0 to 16.4 2nd Dia. inches= 1.998 Length= 7.5 to 8.2 3rd Dia. inches= 2.123 Length= 7.5 to 8.2 --- Header Collector Specs (Conventional Straight Tube) --- Diameter= 3.422 to 3.672 Tuned Lengths= 17.2 best and also 8.6 or 34.4 --- Header Collector Specs (Megaphone or Diffuser Cone Shape) --- Diameter= 2.922 taper to 3.922 Megaphone/Diffuser Length= 17.2 inches Best HP/TQ Tuned Collector Lengths= 17.2 , 34.4 , 68.7 , 137.5 inches long Worst HP/TQ Loss Collector Lengths= 25.8 , 51.6 , 103.1 , 206.2 inches long Note-> all Pipe Diameters are OD and based-off .0625 inch Pipe thickness ---- Primary Pipe's Harmonics ---- 1st Harmonic = 131.8 inches long ... typically never used 2nd Harmonic = 50.0 inches long ... longest recommended 3rd Harmonic = 29.9 inches long ... highly recommended , best Torque Curve 4th Harmonic = 20.8 inches long ... shortest recommended 5th Harmonic = 15.7 inches long ... typically never used 6th Harmonic = 12.3 inches long ... typically never used 7th Harmonic = 10.0 inches long ... typically never used 8th Harmonic = 8.3 inches long ... typically never used ---- Collector's Harmonics (includes Intermediate, Muffler , TailPipe) ---- 1st Harmonic = 137.5 inches long ... longest with Mufflers and TailPipes 2nd Harmonic = 68.7 inches long ... longest recommended with Mufflers 3rd Harmonic = 34.4 inches long ... more bottom-end Torque 4th Harmonic = 17.2 inches long ... highly recommended , best Torque Curve 5th Harmonic = 8.6 inches long ... reduced Torque , more top-end HP sometimes 6th Harmonic = 4.3 inches long ... reduced Torque , not recommended |
Some of the heads Bob is referring to are AFR 205's. I have them on my 427 cubic inch Windsor based stroker. I use 2" primary tube headers and attach them to the engine using studs screwed into the head which makes header installation much easier.
These heads have a dual bolt pattern. I use the wider pattern which are 3" apart center to center. I can use a 9/16" box end wrench to tighten the nuts that hold the headers on and reach all of the nuts from the top side. Jody |
I saw a 427 Windsor w/ 1 7/8" make 706HP and 630 TQ at 13.5 on race gas.
Also saw 460 Windsors make 630 to 647 HP and 630TQ on pump gas w/ 1 7/8"-every week-dozens of them. Both types of builds ran 1050 Dominators also. You will lose torque w/ 2" and have the fit problems described by Peaks. |
I have 2" primaries. Firefly Performance Products headers and the only 2" set. Current production is 1 7/8" which may make more sense for street motors.
My 427 runs well at 7k rpm and makes power to the upper 6k range. I'm also running AFR 225s and using the 3" bolt spacing. I can easily get to 9/16" nuts on studs. Jim |
Thanks for all the great info.!!
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