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  #1  
Old Feb 16th, 02, 03:44 PM
sheetmetal sheetmetal is offline
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do i need the 1.3/4 headers for this much hp or will the 1.5/8 be best for a street car. thanks
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  #2  
Old Feb 16th, 02, 04:28 PM
chevys4me chevys4me is offline

 
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If it's going to be a mainly street car, I'd say go with the 1-5/8 headers. The larger pipes would be good in the upper RPM ranges but you may sacrifice some low end torque which is good for a mostly street engine. I run the 1-5/8 Hooker headers on my 383 Nova and it screams.
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  #3  
Old Feb 17th, 02, 03:20 AM
onovakind67 onovakind67 is online now
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Primary size is just one consideration, how about the collector configuration? Most 1-5/8" headers have 3" collectors, not a good arrangement for secondary scavenging. If you are spending the money to develop a 500 horse engine, spend a little time researching modern exhaust systems.

------------------
1967 Nova coupe daily driver
406, 10:1, 224 cam, Q-jet, 700R4, 3465# w/driver
11.76 @ 116 thru the mufflers
18 mpg on the road
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  #4  
Old Feb 17th, 02, 03:49 AM
Eric68 Eric68 is offline
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Go with 1-3/4". 1-5/8" is too small for 500HP - street engine or not. I run Hedman 1-3/4" headers on my 383 and drive it everywhere. It makes around 450 HP and the larger headers don't kill any low end torque at all. With a 500 HP engine you'll need even more exhaust flow than me.

------------------
68 Camaro, 383 small block with TH350 trans. 11.98's at 111mph and never trailered.

[This message has been edited by Eric68 (edited 02-17-2002).]
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  #5  
Old Feb 17th, 02, 03:49 AM
boodlefoof boodlefoof is offline
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while a 1 & 5/8'' header will generally give a little more low end than a 1 & 3/4'', there have been cases when going up one size will yeild across the board increases. For example, the Goodwrench Quest series by CHP (the goodwrence crate motor with Vortec heads and XE268 Comp Cam) picked up something like 15 horses and 15 ft. lbs. at peak with 1 & 3/4'' headers with no loss anywhere.

American Speed recommends 1 & 3/4'' headers for most of their engines in the 380-500 horse range and most of their engines make peak horsepower no higher than 5500rpm.
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  #6  
Old Feb 17th, 02, 05:49 AM
onovakind67 onovakind67 is online now
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<BLOCKQUOTE>quote:</font><HR>Originally posted by boodlefoof:
while a 1 & 5/8'' header will generally give a little more low end than a 1 & 3/4'', there have been cases when going up one size will yeild across the board increases. For example, the Goodwrench Quest series by CHP (the goodwrence crate motor with Vortec heads and XE268 Comp Cam) picked up something like 15 horses and 15 ft. lbs. at peak with 1 & 3/4'' headers with no loss anywhere.

American Speed recommends 1 & 3/4'' headers for most of their engines in the 380-500 horse range and most of their engines make peak horsepower no higher than 5500rpm.
<HR></BLOCKQUOTE>


Making a blanket statement about header primary sizes has a few inherent problems. There are a lot of other considerations in header design besides primary tube size. My mild-mannered 406" SBC runs 1-5/8" primaries with 2-1/2" collectors, with no apparent loss of upper end power. The recent 383 GM crate motor test utilized some 1-1/2" Hedmans on a 450+ hp motor. It would be interesting to know the differences between the sets of headers used in the tests. Were the primaries the same length on both headers? Were the ports matched equally? Were the collectors the same size and shape? Here's an interesting critique by Ed Henniman about magazine header testing: http://www.headersbyed.com/info1.htm

------------------
1967 Nova coupe daily driver
406, 10:1, 224 cam, Q-jet, 700R4, 3465# w/driver
11.76 @ 116 thru the mufflers
18 mpg on the road
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  #7  
Old Feb 17th, 02, 05:38 PM
sheetmetal sheetmetal is offline
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one thing i did find was a build up of about 10 engines in one of Vizards books and all of them that made over 400hp used 1.3/4" headers. Im concerened about the clearance problems that may arise from this. anyone using this size header on a small block. also heddman makes a header this size but there square port flange, is this a problem?
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  #8  
Old Feb 17th, 02, 06:57 PM
onovakind67 onovakind67 is online now
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The header flange should match your port closely, as these ones do. Are you planning on using merge collectors?

------------------
1967 Nova coupe daily driver
406, 10:1, 224 cam, Q-jet, 700R4, 3465# w/driver
11.76 @ 116 thru the mufflers
18 mpg on the road
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  #9  
Old Feb 17th, 02, 07:05 PM
sheetmetal sheetmetal is offline
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yes i plan on the merge collectors.ive followed your posts on both sites and respect your oppinions. i have afr heads and was concerned about the square flange. does the 1.3/4 heddman header with the s&s collectors sound right for this power range thanks
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  #10  
Old Feb 18th, 02, 12:22 AM
1NAST69 1NAST69 is offline
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Please pardon my ignorance, but what are merge collectors?
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  #11  
Old Feb 18th, 02, 02:17 AM
Eric68 Eric68 is offline
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The 1-3/4 Hedmans I am using fit very good. I trimmed about 1/4" of thread off the driver's side upper control arm stud to clear the #1 cylinder pipe but that's about it. I use ARP 12 point bolts and they all went straight in with the exception of the #1 cylinder. My #1 cylinder has an alternator bracket (swp setup) bolted on top of the header. I put a 3/8" x 1-1/4" long stud in place of the very front bolt. The other bolt on #1 (the one behind the pipe) was a bear, but I got it after grinding down the bolt shoulder just a hair. The headers seal well and I ran them for 6-7k miles with the same gaskets.

The Trick Flow heads have a D-shaped exhaust ports and in general, the header opening was bigger than the exhaust port. I did grind just a little off the header flange to port match my heads - there was about a 1/32"-1/16" lip that protruded into the port exit. There was enough material in the flange to do this easily and it was pretty minor - about 10 minutes per header.

I've had 1-1/2" and 1-5/8" tube headers that were harder to put on.

Hope this helps.

------------------
68 Camaro, 383 small block with TH350 trans. 11.98's at 111mph and never trailered.

[This message has been edited by Eric68 (edited 02-18-2002).]
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  #12  
Old Feb 18th, 02, 07:18 AM
onovakind67 onovakind67 is online now
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<BLOCKQUOTE>quote:</font><HR>Originally posted by 1NAST69:
Please pardon my ignorance, but what are merge collectors?<HR></BLOCKQUOTE>

These are merge collectors by S&S headers, about $60 each. Burns Stainless also makes some pricey ones. http://www.burnsstainless.com/MergeC...ollectors.html

Sheetmetal -
1-3/4" headers will work fine, it's the little details that make the difference. We bought some Stahl primaries for a road race car last year and they were flawless. Brazed header flanges, perfectly matched ports, equal-length primaries, etc. A lot of off-the-shelf headers need finishing, like brazing up the outside so you can grind the inside to match the port, or adding tube to the primaries to better match your engine's torque curve. You can build a much better set of headers than you can buy off-the-shelf.
One of the major shortcomings of the ordinary 1-5/8" headers is the collector size, usually 3". A 1-3/4" header with the same collector will work better in most cases due to the increased scavenging ability. Another shortcoming is the port shape, usually round and unfinished, providing a large discontinuity in the exhaust flow.
Ed Henniman has a fairly extensive package on header design, and one of the points he dwells on is 'peak power and peak performance are usually not synonymous'.

------------------
1967 Nova coupe daily driver
406, 10:1, 224 cam, Q-jet, 700R4, 3465# w/driver
11.76 @ 116 thru the mufflers
18 mpg on the road
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  #13  
Old Feb 18th, 02, 07:22 AM
gheatly gheatly is offline
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Go to this thread:
http://www.camaros.net/forum/Forum4/HTML/003709.html

Header and exhaust system design were discussed and several articles are linked. The article by Vizard was excellent and discussed header design in detail. There is a chart that you can use to select the proper primary tube diameter. The selection criteria is exhaust port flow at the maximum cam lift on the exhaust side.

My supercharged engine made 500 HP with 1 5/8 headers and a 2.5 inch exhaust system, but after reading the articles, my system is probably a little smaller than optimum.

I wnet to the Headers by Ed site. He has some good info and is not accepting additional header orders until August 2002!!! I guess it goes to show that there are many people who would pay for a better product if someone would actually take the time to design and manufacture it.

[This message has been edited by gheatly (edited 02-18-2002).]
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