1 5/8 Header vs. 1 1/2 Header for 79 3.0
 

Hi,

I have been searching and searching. I see different opinions. I will hopefully be picking up a 1979 large port engine next week. I want to buy headers.

Stock is just 180hp, my plan is to eventually do the cams and pistons.

Question; Do I want the 1 5/8 header?

Cheers
James

I suggest that 1.5" will suffice with a relatively stock 3.oL in most all instances. much more appropriate for a 3.2

point of reference. the spec911 class allows 1.5" max for 3.oL and a 1 5/8" for 3.2s. the header upsizing helped the stock intake by rule 3.2 to run a bit faster in testing after requiring 1.5" across the board rule was lifted for them after a number of years. at the same time the 3.oL cars on carbs or ITB's out HP the 3.2s by a long shot even with the 1.5".

1.5" we have done extensive behind the scenes testing of this on a clients car that runs a racing program with 3.0 engines only .. Tried it multiple ways.. Racing only 1.625. Street/track 1.5"

+1
Bigger is not always better

Thanks everyone!

Just to confirm:
more hp with carbd motor and lap faster?

If you like your low end torque, go small.

For the bone stock 3.0L engine there is no advantage increasing the header primary tubing size to 1.63"OD. Exhaust port size and volume coupled with C/R and cam profile work best with 1.5"OD primary size. Engine modifications that improve breathing and flow will benefit from larger pipes.

the spec911 class requires stock pistons, although you can use the higher compression euro units and stock cams on both the 3.oL and 3.2 motors.


the 3.2 motors can be chipped, but must use stock intake and injection.

a 3.oL motor can be carbed up to a 46mm weber/pmo or some dam fancy ITB injection systems. I ran 46mm pmo for the last 4 years I raced with PRC as the injection systems were waaay beyond my tax bracket and were in most cases having greater HP than carbs.

so to answer your question the 3.oL motors have traditionally been the superior motor from a HP standpoint with either the carbs or ITB injection systems. the rule changes to aid the 3.2's in being more competitive have been the larger headers and some years ago they allowed the more robust G50 3.2's to participate with a somewhat greater minimum weight where as all 3.oL must use a stock geared 915.

Need to clarify whether inside diameter vs outside, e.g. 1 5/8" outside diam. is 1 1/2" inside diameter.

measured by inside diameter. differing tube material thickness can skew the OD.

I always assumed it was outside diameter.

A what point does a 3 L get the larger header? Their must a point in hp?

For a stock and even lightly modded 3.0, headers such as SSI are going to be the best bang for the buck, they have 1 1/2" OD, 1 3/8" ID, They are well designed, fit well and can use more varieties of mufflers than most anything else out there. The ss material helps retain heat which helps flow, the sizing is oriented to maximise torque/hp in the 4500 to 7000 rpm rev range of a stockish 3.0. The use of almost any muffler negates the possibility of acoustic tuning w/ any header, use of cams w/o a good deal of overlap further reduces the possibility of acoustic tuning.

When a bit too small a header is used it is less harmful for most operating regimes than when a bit too large is used.

Thanks to all who contributed. I will probably get the 1.5 headers. I can always get bigger dependent on the future pistons, cams, twin plug AND the money needed!

Yes but ID depends on wall thickness your assuming it's .065 wall.


Note for everyone.. Tubing is ALWAYS measured OD.. Pipe is measured ID(infrastructure materials))

ALL exhaust is Tubing..

Thanks Ben. I Really like your products. Nice to know What the standard of measurement is.

No, measured by O.D.

Yes!

How did that come to be? It makes no sense, considering the outside diameter has nothing to do with the flow of gasses.

It's because piping is meant to have either liquids or gases flowing through it, so I.D. is important. Tubing was originally meant for structural applications, so O.D. was important.

First, it is tubing not piping. Tubes are always measured by O.D. Wall thickness varies by application.

For headers used in competition, diameter is often limited in the class rules packages. Think about measuring for compliance. How do you measure the inside of something you have no access to? You can't. So the rules stipulate the O.D. because that can be easily measured. This is convenient as the O.D. is the only measurement that will equate to standard dimensions.