1 5/8" headers vs 1 3/4" headers on a 347cid

Depends on what your doing with it. Street car......Probably just stick with the 1 5/8", Strip or Street/Strip go with the bigger tubes' (but spend the money on Good ones not all headers are created equal !!
[addsig]

A lot of this has to do with the camshaft as well. Too large of a primary may not provide enough backpressure which can lead to overscavenging if the cam has excessive overlap, this can cause a loss in power.

No enough exhaust duration can cause too much back pressure in the exhaust if coupled with a restrictive exhaust system, this leads to reversion and a loss in power as well.

Larger headers won't always mean a loss in power if the 1 5/8 headers were too small to begin with. I would base the decision on the cam and whether or not your 1 5/8 headers are actually port matched to the 205's exhaust port

Dude, one thing is 4 sure ......BBK headers are a pice of ****!
Ok now to the header subject, I had BBk 15/8 headers on my 347 stroker with AFR 185's. Now the car was making as little as 330 at the wheels, i think it was way off cause the guy never let the motor cool down under 200 degrees. Well now i have Mac 13/4 with 3'' collectors and 3'' prochamber with 3''ssflowmaster mufflers and dumps.I dont know how much more horsepower i got out of that combination but damn does it pull alot harder! I can easely brake the tires loose in 3 gear just by stomping on the throdle. Couldnt do that before!

I ran a pretty strong 347 on the dyno a while back,and he had 1 & 5/8 Hooker headers on his car,So after we got it to make 554 HP at 7200 RPM with my 1.75 dyno headers, we put his smaller headers on and it LOST 23 HP at the peak, BUT, the smaller headers were better up to 57 or 5800 RPM. Remember, this was a pretty good 347.
JOE SHERMAN RACING

I for got to mention, this 347 runs 10.98 at 122.5 in a 1965 Falcon. with a C-4 with 4.56 gears and a 10 by 26 inch slick. He goes through the lights at 76-7700 RPM(and the small headers)
JOE SHERMAN RACING

you need to look at tube size for the max torque rpm
there is a formula to help determine what size of header to run
cross section of header pipe x 88200 / cubic inch size of one cylinder
example 1.875 header minus wall .040 1.835 x pie /2 x 88,200 / cubic inch of one cylinder .....this will tell you max rpm torque


Mike S

The AFR205 heads have exhaust ports thay may be wider than the port on your 1 5/8 headers. This was the case with my hooker SC 1 5/8 headers. It caused a big power loss. I found the FPA 1 3/4 headers to fit perfectly with the AFR exhaust ports.

Originally Posted by seefour

you need to look at tube size for the max torque rpm
there is a formula to help determine what size of header to run
cross section of header pipe x 88200 / cubic inch size of one cylinder
example 1.875 header minus wall .040 1.835 x pie /2 x 88,200 / cubic inch of one cylinder .....this will tell you max rpm torque


Mike S

More importantly you need to match them to the inlet flow of your cyl heads, It's no use getting flow in without getting flow out. On a 347 with any sort of decent heads you need at least 1 7/8

I forgot to mention, camshafts are also play a deciding factor in pipe diameter and and lenght not just cylinder capacity.

I have tested this several times and the higher you can rev the engine, the bigger the gains will be. Below 5700 RPM, the smaller pipes are better, If to can rev up to over 7000 RPM, the big pipes are worth 30 or more HPAt 7500 RPM, the big pipes are 35 to 40 better. It is true that the port match is important, BUT , the flow in the exhaust port comes right down the center of the exhaust port. I ALWAYS remove any weld beads, ect and put a small chamfer on the inside of the headers port.
JOE SHERMAN RACING ENGINES