Hi all,

i had a post where I suspected my flowmasters restricting the flow of the engine, now I gave it another look and I believe it actually might be my headers.

What I'm experiencing is plenty of power around 3000-4000 but then it drops. I can rev it to 6000 and probably above but I have to push it there. accelleration slows down at 5000. with the rpm heads and camshaft I expect this thing to make most power between 3000 and 6000 ...
so i checked on the edelbrock website and they say that the exhaust ports in the heads need felpro 1415 gaskets, and it would be great to have the headers the same size.
I checked on the felpro gasket (as i couldn't find any port size reference on edelbrock) and it says the ports are 1.5" tall and 1.25" wide.

I tried to measure the header tubes (outside), but even with a caliper it's hard to get to.
two inches away from the port they seem to be big enough, but when I manage to measure directly at the flange they seem to be same size or smaller on the outside compared to what they should be on the inside.

Could this cause my problems? I (stupid) never checked when I put the headers on.
Would this cause any other easy to identify problem so I'd now that this is the cause?

Unfortunately I have _no idea_ what headers are on it. I'm currently trying to match up the routing with pictures from summit.
But I guess the only way to find out is to remove one of them (which is a huge PITA, even on passenger side).

btw: if summit sells 1.5" primary tube diameter, is that measured inside our outside?

Any opinions?

Kalli

 

found partial answers:
tubes are always measured outside, and pipes inside ... kinda makes sense.
Further there's a chart: http://www.usaindustries.com/tube_gauge_chart.htm

from this I need 1-5/8" tube (to cover inside dia of 1.5" up to 18 gauge)
if it's 1-5/8" OD tube I have then it's the crappiest manufacturing on the planet, if it's 1.5" I'll order ....

any opinions welcome. I have no experience in header selection whatsoever ...

Kalli

 

I don't think that it will continue to make power much over 5k or so. Mine doesn't. Actually, my engine builders recommended that I not take it over 5200, if I remember right. They said that after that it will make less power anyway.

 

hmmm what cam/intake/heads do you have ?

 

I seriously doubt that a small difference in header size will make a noticeable difference in power. By that I mean something you can feel while driving it. You may see a few HP on a dyno but not by driving it. If you have noticeable power drop above 4000 you more than likely have a tuning or ignition timing issue, or your engine is just running out of air (cam, intake, carb). The only way to know for sure it to dyno it (or at least put it on something to analyze the timing and mixture). Tuning by the seat of the pants is not very accurate.

 

my main (and only) concern is that the header ports are smaller than the ports in the head. which would not only restrict flow but cause backpressure or whatever it's called (huge turbulences from pushing against header and back against exhaust stream)

 

I would think header flanges that are too small could ruin your day. Why are your headers so hard to pull? For me it's as easy as changing my underwear.

 

What headers do you have? Also, keep in mind that the engine will pull hardest to peak TORQUE, after that it won't pull as hard up towards peak hp, and actually since torque is dropping off it will pull less and less....you just stay in gear towards peak power to take advantage of the lower gearing. 1st gear at 6k is still putting more torque at the wheels than 2nd gear at 4k, because of the lower gearing in 1st.

 

oxford: it's the most tedious part in my car. i have to kinda loosen all bolts, then go over them again, again .. and again. out of those 8 bolts per side i can only pull about 4 straight out. the rest is kinda between head and pipe. but with the passenger side at least I won''t have to worry about the equalizer bar.

602m302: not the foggiest idea which headers I have. i think the seller claimed hooker competition headers and looking at summit pictures that kinda matches (the routing). all of the ones seem to have 1-5/8 tubing, but as said at the very front just behind the flange they are slimmer outside to what they should be inside.
I believe I'll just have to pull one and check

as for your description: thats very true, the power drops again at 4 grand (torque), i probably just expected more to 6+ grand.
But then again I have no experience, nothing to compare to. It's not much quicker than my old 289 was though. so there's definetly something I'm doing wrong .....
it's advertised to 350HP, wouldn't surprise me if it wouldn't make more than 300, but I believe am rather like 275-ish at engine.

what keeps me at it is that when i installed engine with that holley it ran like a rocket, but had a massive lean bog and the cruising mixture was way too low. so i went to the edelbrock, no help, changed around 3 disdtributors, rejetted carb .etc etc etc ...


might as well start from scratch again ignition, a/f etc ... *******

 

Large tube and small tube headers are a big topic of power for people playing at levels where it counts. Header size classification is based on size with relation to exhaust valve diameter, not port size. Small tube headers are 95-105% of exhaust valve size while larger tube headers are 120-140%. These numbers change slightly when you start talking about multiple valves per cylinder like the newer OHC stuff. There are also step tube headers, but those are really entering into the tuned exhaust world.

Small tube headers are designed for optimum power slightly higher in the rpm band than peak torque. Large tube headers are really for high reving or high displacement engines.

I would say any engine including a 289/302 could be adversely affected by too small of a header tube. Given a 1.6 exhaust valve, that means you need a 1 5/8 (1.625") primary tube. If you are running 1.5" primary tubes or less, you could very well be hurting the engines performance at higher rpms.