how much are headers with 2 inch primaries better than 1-7/8 primary headers?

how about 1-7/8 stepped to 2 inches over full 1-7/8 headres?


are 2 inch primaries even beneficial with our exaust ports? ( port/gasket smaller than 2 inches??)

this is assuming boosted motors and/or big cubed ones.

 

good luck making them fit.

 

heads are coming off any way... so it should be easier.

 

Bigger is not always better. What ever happened to port-matching? I'm not a header expert but 2 inch primaries seems too big to me.

<small>[ January 29, 2003, 07:06 PM: Message edited by: Gary Z ]</small>

 

I know someone make some 1 3/4" to 2" steped header i cant thin of who it is off the top of my head but on a big cube motor thay gained like 20hp over a set of 1 3/4" LT.I will have to find a link real quick.

 

i was wondering about port matching too....

 

just out of curiosity , how much do the exaust ports measure in diameter??

 

Miss match is important between head and header. 2" is too big for almost all of our motors because it supports flow at too high a rpm. 1 3/4" is sized for good flow at rpms up to 7000.
2" would trade torque at 4500 to 5500 and add power at peak. Heavier med. rpm cars would lose perf. especially 346" LS1's.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by 1dirtyZ:
<strong> just out of curiosity , how much do the exaust ports measure in diameter?? </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">The diameter of the exhaust ports mean little when picking primary tube diameter. The massflow of gas through the exhaust is much more decisive when picking header dimensions.

 

Anti-reversion.

If the header, where it meets the head, is somewhat larger then the port, especially at the bottom, gasses have a harder time backing into the exhaust port during the overlap period. It doesn't seem to effect flow outward.

The same thing can work in reverse on the intake side: intake manifold port smaller than head port helps stop intake reversion. I've seen it work.

Primary header diameter is most directly related to horsepower which is airflow. 1-7/8 can support well over 600 hp in a V-8. If you are below this, you might suffer some low-mid torque (and therefore power) loss depending on the head/intake/cam/exhaust combination.

 

cool , thanks for the info.
how about blown motors??

 

Forced induction puts larger demand on exhaust flow, but header pipes diameter doesnt set flow it sets gas speed thru it. More important to have better flowing exhaust port than bigger header with blown application.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Old SStroker:
<strong> Anti-reversion.

If the header, where it meets the head, is somewhat larger then the port, especially at the bottom, gasses have a harder time backing into the exhaust port during the overlap period. It doesn't seem to effect flow outward.

The same thing can work in reverse on the intake side: intake manifold port smaller than head port helps stop intake reversion. I've seen it work.

Primary header diameter is most directly related to horsepower which is airflow. 1-7/8 can support well over 600 hp in a V-8. If you are below this, you might suffer some low-mid torque (and therefore power) loss depending on the head/intake/cam/exhaust combination. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Very well said!

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Fenris Ulf:
<strong> </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Old SStroker:
<strong> Anti-reversion.

If the header, where it meets the head, is somewhat larger then the port, especially at the bottom, gasses have a harder time backing into the exhaust port during the overlap period. It doesn't seem to effect flow outward.

The same thing can work in reverse on the intake side: intake manifold port smaller than head port helps stop intake reversion. I've seen it work.

Primary header diameter is most directly related to horsepower which is airflow. 1-7/8 can support well over 600 hp in a V-8. If you are below this, you might suffer some low-mid torque (and therefore power) loss depending on the head/intake/cam/exhaust combination. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Very well said! </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I agree step affects reversion on intake, but this is not a good idea.When intake valves close and intake charge bounces of closed valve, it flows back into intake manifold, if there is a step at manifold opening it causes disruptive turbulence that affects next incoming charge of air. Max flow and power comes from smooth un disturbed air, as close to laminar flow as possible. Back when carburetors were the rage this same turbulence may have helped atomization and torque, not worth it now!

 

Originall posted by LS1derfull:

I agree step affects reversion on intake, but this is not a good idea.When intake valves close and intake charge bounces of closed valve, it flows back into intake manifold, if there is a step at manifold opening it causes disruptive turbulence that affects next incoming charge of air. Max flow and power comes from smooth un disturbed air, as close to laminar flow as possible. Back when carburetors were the rage this same turbulence may have helped atomization and torque, not worth it now!

It's always good to have different views expressed.

IMO, there's not a lot of laminar flow in an inlet tract cycling 50 or more times a second.

Also, as I recall, the Reynolds number of a typical engine inlet is 2000+, so it's turbulent, not laminar flow.

Yes, keeping the wet flow from a carbed engine atomized is one of the reasons for anti-reversion. So, if the injector induces fuel about at the head/manifold junction, and the now wet charge bounces off the intake valve, isn't that similar?

My $.02

 

You have a good point about wet flow, but i still believe in smooth transition in intake tract whenever possible. To be honest i am a follower of Bill Jenkins and his way of thinking, i hold on to lots of ideas that i have learned from him and other Pro Stock engine gurus that i have personal training from.