On port matching - IMHO you make the sides maybe a little bigger than the head's port, the bottom smooth as you can, and open up the top of the manifold runner to create that reversion step. Go through and clean out all the boogers the best you can. Open up the exhaust opening to match your headpipe.

If you have another $600 - $900 to burn, the extrude hone process will make you feel like you've done something, but I bet there's not more than 5hp in it.

R.

Good question... I did not consider that but I think you are right! Thinking about using the TTI down pipes in the 3" size and then 2 1/2 after the x-pipe to the tailpipes... If I have to grind out the head pipes to 2 1/2 than I guess I will have too..... I will get with TTI tomorrow and ask them the inside diameter of there headpipes.... I already opened up the exhaust flanges to the 2 1/2" size so I may have to fire up the ole makita die grinder and let it rip on the headpipes when I get them! TBF

I am going to measure the exact distance from the exhaust bolt holes to the edge of the exhaust port on the edelbrock heads and trace an exact outline on the manifold face to see where I stand. Iam going to do some exhaust port cleanup on the heads first so I need to get that done. Just some light work with sanding rolls..... My goal is to eliminate every restriction that I can and get these manifolds to work as efficiently as possible..... Hey BSB, I did not really pay attention to your car until now and that thing is awesome!! 11's with exhaust manifolds and mild gears is quite a feet of engineering!!! What cam are you using? PM me if cant divulge the info, I can keep a secret!! TBF

After a bit of research it looks like the max gain to expect from porting the HP exhaust is a few peak horsepower gain...... However, there was a gain of 10ft/lbs of torque in the mid rpm range so every little bit helps! TBF

I dont think it will hurt to de burr and smooth them out some but as has been stated it wont do much for horsepower. I would gasket match the exhaust ports as well as the manifolds to ensure there are no blockages or blind ledges. Thats about all that can be done. The big exhaust pipe will help clear out the back pressure. Really people scream about headers all the time but once you bolt them to mufflers HP is down. Headers are for equal pressure per cylender and are at their best un corked!!!

Here is my opinion. You are doing yourself a disservice HP-wise by sticking with manifolds. I understand the argument for manifolds on the street. They're cheap, reliable, and you already own them. That, and headers are known for being a PITA. Then there's the installation, the scraping, the leaking... blah

What is the argument FOR headers? properly sized, better HP and toque all across the range. In your scope, for something around 500HP, you're almost assuredly giving up 40-60hp (this is dyno proven) by not using a good header and appropriately sized exhaust.

So the question becomes: do you care? if not, stick with what you got, and you'll never have to worry about exhaust until rust eats a hole in it somewhere. If you want the reliability, don't hog out the outlets for reasons stated. You won't feel the gain, but the cast iron will feel the loss. By all means gasket match if you feel there is enough meat there, and take off the sharp edges. beyond that, I'd live with them as-is.

or find some of those nice max-wedge cast iron headers

You will lose power. I did comparison on a dyno in August. 502hp with headers at 5800 rpm and climbing to 468 hp at 5400 rpm. About a 7% loss is that enough to deal with headers that you can only decide. This motor is stroker 400 w/ aluminum heads and intake exhaust not matched.

If you select a camshaft to maximize hp with headers, you will see a larger drop in hp when switching to manifolds than if you selected a camshaft to maximize power with manifolds.