Header size? - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 07-19-2008, 02:03 AM
Registered User
 
Last photo:
Join Date: May 2008
Location: New Zealand
Age: 41
Posts: 165
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Header size?

Iv'e just finished making a new set of custom headers, it's the first time Iv'e made any and they were a particularly tricky set to make due to lack of room. They are a tri-y set up of 1 5/8" primaries into 2" secondaries then back to a twin 2 1/5" system. My engine is a 408ci sbc, 195 AFR Eliminator heads, Lunati cam with 241/249 @ 050 and 525/546 lift 110 lobe centres, victor jr intake, 750dp hp series holley or Demon (not sure on that one yet), HEI dizzy and MSD. My friend that works in an exhaust shop recommended the sizes that I used in fabricating my exhaust as he thought going any bigger could result in a loss of too much torque. Now that Im finished building them I think that could have been wrong thinking for this engine. The more research I do and more I read on this site, it seems torque loss in these 400+ci sbc's is the last thing I need to worry about! Your thoughts please!!!

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 07-19-2008, 07:21 AM
Notorious's Avatar
Hot rodder, not street rodder!
 
Last photo:
Join Date: Aug 2007
Location: Bakers Mountain, NC
Posts: 507
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I don't think you hurt yourself. I believe more people than not run too large of a primary tube for their application. I think your collectors should have been 2 1/2" though.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 07-19-2008, 07:41 AM
Member
 
Last photo:
Join Date: Nov 2004
Location: Lakeland FL
Age: 65
Posts: 4,110
Wiki Edits: 0

Thanks: 0
Thanked 3 Times in 3 Posts
Holden,
I plugged in a just roughly close to your combo into my DD (since you built your own headers design)...

1 7/8" could have gained you "up to" 6HP/6ft-lbs at the HP peak and lost 4HP/12ft-lbs at 2,000rpms (both at the flywheel) depending on motor details like cam advance/ign timing/etc....

in the "real world" that translates into "maybe" .05-.1 second difference at the strip and no difference you can feel on the street, so don't lose any sleep over it....

LOL...
using the correct stall convertor and deep gears needed by that big cam and parts combo.....
your motor is "NEVER" going to be at low rpms driving normal....
that's why "available" TQ/HP won't be a problem....

Last edited by red65mustang; 07-19-2008 at 07:58 AM.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 07-19-2008, 11:44 AM
ericnova72's Avatar
More for Less Racer
 
Join Date: Jan 2007
Location: S.W. Lower Michigan
Age: 47
Posts: 8,925
Wiki Edits: 0

Thanks: 19
Thanked 370 Times in 339 Posts
Like Red65mustang said, you're fine at the size you have and going bigger would only help above 6000+ rpm.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 07-19-2008, 05:05 PM
Registered User
 
Last photo:
Join Date: May 2008
Location: New Zealand
Age: 41
Posts: 165
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Holdon

Quote:
Originally Posted by red65mustang
Holden,
I plugged in a just roughly close to your combo into my DD (since you built your own headers design)...

1 7/8" could have gained you "up to" 6HP/6ft-lbs at the HP peak and lost 4HP/12ft-lbs at 2,000rpms (both at the flywheel) depending on motor details like cam advance/ign timing/etc....

in the "real world" that translates into "maybe" .05-.1 second difference at the strip and no difference you can feel on the street, so don't lose any sleep over it....

LOL...
using the correct stall convertor and deep gears needed by that big cam and parts combo.....
your motor is "NEVER" going to be at low rpms driving normal....
that's why "available" TQ/HP won't be a problem....
Ive got a 3000 stall and 3.25/1 diff ratio. I know the diff maybe a little tall but it is only a 3000lb car and I am intending to do a fair bit of cruising in it. I am still considering a new set of gears though. Out of interest did your program give any peak torque and hp figures? I would be very interested in those :-) I was thinking that might be a big cam for the street, but have been assured it isnt.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 07-19-2008, 05:16 PM
Registered User
 
Last photo:
Join Date: May 2008
Location: New Zealand
Age: 41
Posts: 165
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Holdon

Quote:
Originally Posted by Notorious
I don't think you hurt yourself. I believe more people than not run too large of a primary tube for their application. I think your collectors should have been 2 1/2" though.
Thanks for your reply mate. You think my first collectors should be 2 1/2"? What size would you make the final collector then? If you have a look at my photo album there is a good pic of my engine with the headers fitted. Photos have not long been added so you can also see them on the home page.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 07-19-2008, 05:39 PM
ericnova72's Avatar
More for Less Racer
 
Join Date: Jan 2007
Location: S.W. Lower Michigan
Age: 47
Posts: 8,925
Wiki Edits: 0

Thanks: 19
Thanked 370 Times in 339 Posts
I believe Notorious meant 2.5" final collectors. Power estimates w/CamQuest shows 480hp@6000rpm 485tq@4000rpm and , get this - 400tq@2000rpm and 440tq@3000rpm.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 07-19-2008, 06:12 PM
Registered User
 
Last photo:
Join Date: May 2008
Location: New Zealand
Age: 41
Posts: 165
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Holdon

Quote:
Originally Posted by ericnova72
I believe Notorious meant 2.5" final collectors. Power estimates w/CamQuest shows 480hp@6000rpm 485tq@4000rpm and , get this - 400tq@2000rpm and 440tq@3000rpm.
Yee ha mate, that is one wicked flat torque curve, sounds like its a pretty good starting point for a street/stip combo ay. Be a hard one to beat off the lights, if I can get that power down that is Thanks for running those numbers for me.
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 07-20-2008, 07:49 AM
Member
 
Last photo:
Join Date: Nov 2004
Location: Lakeland FL
Age: 65
Posts: 4,110
Wiki Edits: 0

Thanks: 0
Thanked 3 Times in 3 Posts
Holden,
Camquest is a free 20mb program on the Comp Cams site you can download and use.....

just a comment:
because that software is so limited for entering actual values for parts used and tuning/operating variables I wouldn't bet the bank on results accuracy....
I did chuckle at the 400ft-lbs @ 2000 results eric posted, (1ft-lb per cube with a 280+duration cam and open plenum at 2,000) because if that was true there is no need at all for a high stall/slip convertor and deep gears for decent acceleration from a stop light or at the strip!
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 07-20-2008, 12:39 PM
Registered User
 
Last photo:
Join Date: May 2008
Location: New Zealand
Age: 41
Posts: 165
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Holdon

Quote:
Originally Posted by red65mustang
Holden,
Camquest is a free 20mb program on the Comp Cams site you can download and use.....

just a comment:
because that software is so limited for entering actual values for parts used and tuning/operating variables I wouldn't bet the bank on results accuracy....
I did chuckle at the 400ft-lbs @ 2000 results eric posted, (1ft-lb per cube with a 280+duration cam and open plenum at 2,000) because if that was true there is no need at all for a high stall/slip convertor and deep gears for decent acceleration from a stop light or at the strip!
It does seem like a lot doesnt it, although Ive got the Virtual Dyno programe and mine shows 480ft/lbs @ 2750 and 500ft/lbs @ 3750. Still, they are only programes after all, not the real thing ay!
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 07-20-2008, 01:16 PM
ericnova72's Avatar
More for Less Racer
 
Join Date: Jan 2007
Location: S.W. Lower Michigan
Age: 47
Posts: 8,925
Wiki Edits: 0

Thanks: 19
Thanked 370 Times in 339 Posts
Red65mustang,
Yes, CamQuest is a simple and somewhat limiting but does allow you to input "custom" head flow figures so I used the AFR Eliminator 195 #'s from their site and their XE grind that is virtually the same as the VooDoo, and used the small tube open header option. While the HP #'s generated may be a little high, I've found them to be not far off from the fancier Engine Analyzer software I have, just faster, and will show the trends. Only bad thing is you can only test cams from CompCams, but all the major companies are pretty cookie-cutter in this respect.
As far as the high low end TQ #'s, Have you built many 400's with really good flowing heads?? I have, it's my favorite engine, TQ is the last thing to worry about,and you will usually have more than you can use from a dead stop unless you have a well-prepped suspension-- I practically won't give the time of day to the thought of a 350, it's a weinie engine-- 383 is my minimum even for a race engine. The 400 has plenty of TQ to spare, and a 280+ degree advertised camshaft is middle of the road to slightly small in a well prepped 400.
Holdon is using the new AFR Eliminators, and they are head and two shoulders above any other head company's off-the-shelf 23* head.
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 07-20-2008, 09:07 PM
Registered User
 
Last photo:
Join Date: May 2008
Location: New Zealand
Age: 41
Posts: 165
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Holdon

Quote:
Originally Posted by red65mustang
Holden,
Camquest is a free 20mb program on the Comp Cams site you can download and use.....

just a comment:
because that software is so limited for entering actual values for parts used and tuning/operating variables I wouldn't bet the bank on results accuracy....
I did chuckle at the 400ft-lbs @ 2000 results eric posted, (1ft-lb per cube with a 280+duration cam and open plenum at 2,000) because if that was true there is no need at all for a high stall/slip convertor and deep gears for decent acceleration from a stop light or at the strip!
Just in reply to what you chuckled at before, perhaps you might want to have a look at the AFR website and some of their dyno figures. Even a 383ci with the same heads as mine, 9.5/1, 93 octane and a very similar cam was making 450ft/lbs at 2500rpms. It was running performer rpm, but in saying that I have got more cubes and higher comp. So I dont really thing 400ft/lbs at 2000 is out of the question after all. Having a high stall does get you up into a better hp area though, even if there is loads of torque everywhere.
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 07-21-2008, 10:44 AM
Member
 
Last photo:
Join Date: Nov 2004
Location: Lakeland FL
Age: 65
Posts: 4,110
Wiki Edits: 0

Thanks: 0
Thanked 3 Times in 3 Posts
Holden, eric,
to clarify why I chuckled:
yes you can/do have 400ft-lbs+ TQ actual at 2,000 with your motor combo....just lock out the timing at 36* and stomp the peddle to the floor for WOT 13/1 A/F ratio from a stop sign.....
(hard to do with stop and go intown traffic!!!!)

accelerating from a stop at anywhere near a normal rate the TQ is maybe possibly/approx 300ft-lbs (max?) due to that cam's overlap low Hg signal causing exhaust reversion into the open plenum intake at low piston speeds....
(simply stated the mix quality and quantity of actual cylinder fill for making best TQ power is yuch )

if it did make just 250ft-lbs at 2,000 (very probable) "at part throttle" that is still a tremendous amount of acceleration force applied to the tires from a stop sign:
250ft-lbs at the flywheel x 2.46 first gear(?) x 3.25 rear gears = 1998 ft-lbs twisting the hides!!!

so I do chuckle when people use WOT dyno results for describing a street cars actual driving performance.....

just a difference of perspective on the subject....
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 07-21-2008, 03:29 PM
ericnova72's Avatar
More for Less Racer
 
Join Date: Jan 2007
Location: S.W. Lower Michigan
Age: 47
Posts: 8,925
Wiki Edits: 0

Thanks: 19
Thanked 370 Times in 339 Posts
Red65mustang,
I agree with your last post, and I can be a little blind-eyed as I'm a drag racer(part throttle?!?!? oh ya, that's what I use up return road ) and I don't really place a total trust on software programs, but they are more useful if you use them to plot the trends that show as you play with different parts specs in the same engine.
Your example is a good one, and also don't forget that the torque converter is multiplying at a rate somewhere between 1.8 to 2.3 the engines torque at rpms below stall. (I can't remember if this is a WOT issue tho)

Last edited by ericnova72; 07-21-2008 at 03:29 PM. Reason: spelling
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 07-21-2008, 08:57 PM
Registered User
 
Last photo:
Join Date: May 2008
Location: New Zealand
Age: 41
Posts: 165
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Header size?

Thanks guys, needless to say it sounds like the 1 5/8" or 1 3/4" headers would have been fine which ever I used. Just wanted to make sure before getting them HPC coated.
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
What size header gasket do I need for my SBC? (Pic) Porschev Engine 4 02-10-2007 05:20 PM
header gaskets markzepp820 Engine 5 12-14-2006 05:42 PM
Dumb Header Reducer Question Mustangsaly Hotrodding Basics 6 10-19-2006 08:05 PM
Is 2 1/2 pipes big enough? Mustang_Killa66 Engine 7 02-12-2004 08:04 AM
Exhaust Header wrap...No! No! No1 Dave E Shank Engine 5 07-09-2003 08:50 AM


All times are GMT -6. The time now is 06:28 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.