Header size

Post by **demo2** » Mon May 09, 2011 1:21 pm

Ive finally bort the tina out of hibernation, 3 yrs of collecting dust. Im re-makin the headers, as its a 5.0ltr what is the best size header? was running 1 1/2inch 4-1, wondering if 1 5/8 would be better? would be tight 4 room with the weld comin close to the bolt holes,also i have very little room 2 play with so 1 1/2 wud be better but is it strangling it?

kiwicar · Post by **kiwicar** » Mon May 09, 2011 3:09 pm

Hi
Unless you can do considerable work to open up the exhaust ports in the head then the 1 1/2 headers will be best. When I say considerable work I am implying opening up into the water passages and welding in material to let you make them much bigger and raise them 1/4 inch or so. 1 1/2" headers should see you past 350 or 400 BHP easily N/A and alot more if it is forced induction and the 1 5/8 will hurt torque off idle, which if you have built a 5 litre engine based on a rover would be logically what you are after.
Best regards
Mike

mgbloke · Post by **mgbloke** » Mon May 09, 2011 7:59 pm

Demo2
I can only speak from personal experience. I have a 4.6 Rover V8 with the merlin heads and it makes good power, 326bhp (see merlin head thread).
I had a complete new exhaust system made by Maniflow in Salisbury
primaries are 1.75 inches and it makes good torque too.

Mark

ian.stewart · Post by **ian.stewart** » Mon May 09, 2011 11:18 pm

Why does Demo2 ring a bell, LOL, how are you mate long time, I am running 1-5/8"on my primaries, seems to work ok, dont forget the CSA of 1-3/4 against 1-5/8 is around 40% more if I am guessing correctly,

Post by **demo2** » Tue May 10, 2011 12:40 am

Hi Ian, yes its been a while, life has been busy. I figured 3 yrs of being used as a storage shelf it was time to start work on her, 4got what a pig 2 work on she is, no room at all lol. Any chance u can take a pic of ur drivers side header area showing the column as well. Im redoing my steering too so need some ideas.

sidecar · Post by **sidecar** » Tue May 10, 2011 4:44 am

I run a stage III 4.6 with 1.75" headers, it will pull top gear from 1600 RPM without any problems. I made the headers and I squared off the last 1.5" of each pipe by hammering them round a former so that it matched the port shape and gave a bit more room for the nuts. (I fitted studs to the heads). I also left a step at the top of about 3mm to help stop exhaust gas reversion.

Finally watch out to the exit angle of the exhaust tracks, they are not at 90 degrees to the gasket flange, the tracks point down slightly.

Post by **demo2** » Tue May 10, 2011 8:50 am

Hey sidecar, did u make the former? would solve the problem of the hole clearance.

stevieturbo · Post by **stevieturbo** » Tue May 10, 2011 9:19 am

I doubt bigger would hurt much, but also dont see it offering any benefit.

But bigger will be harder to fit if you are tight for space.

1 5/8" would be more than adequate.

sidecar · Post by **sidecar** » Tue May 10, 2011 10:00 am

demo2 wrote:Hey sidecar, did u make the former? would solve the problem of the hole clearance.

The word 'former' that I used in my post may have been slightly inaccurate! Really it was just a big lump of square section steel bar that I had sticking out of the side of my vice! I practiced on a few off cuts of exhaust tube, in the end I got quite good at judging where to hammer the metal in order to get the correct rectangular cross section pipe. I then cut the end of the pipe at the correct angle so that the pipe pointed slightly downwards. I 'whittled' up a piece of wood that stuck out of the exhaust port to help judge the angle!

My exhaust flanges were all 'individuals' made from 8mm steel, each one was opened out to match the stage III heads. The step that I created was between the square section pipe and the back of the flange.