Cascade Crew

[blue89]

Does anyone have any experience with the vortec heads? I'm trying to source a long tube header for my dad's project truck and all we seem to find are round tube headers. Here's a pic of the headers so you can see. Most of the headers summit recommends are round tube as well. Just wondering if anyone else has experience with these heads/headers.

[chevymad]

There's no difference on teh exhaust side between regular heads and vortecs. They all have square holes.

[Quasi-Traction]

[blue89]

So are most header manufacturers not concerned about port matching? I appreciate your help, I've never owned a run of the mill sbc, oddly enough.

[chevymad]

For some reason headers almost never match the shape of the port in the head. They do sometimes make their sealing rings fit the shape though. You have to watch for that and buy the appropriately shaped gasket.

[blue89]

Alrighty then. Just odd to notice that my dad ordered 3 different headers for his truck and none of them were a matching square port. Wouldn't that port mismatch cause a reversion right at the head?

I drew a square in autocad that was 1.3x1.3, the rough size of the port
. Then drew a circle with a diameter of 1.3 (circle fits in the square), a circle of diameter 1.838 (fit the square in the circle), then a circle of diameter of 1.467 (circle area equals square area). Then noted the area's.
Big circle area= 2.654
Medium circle area = 1.69
Small circle area = 1.327
Square area = 1.69
Seems like the best header tube to use would be the 1.5" round, being that it has the same area as the square port vortec head. The other two sizes are around a 30% area change which isn't great for exhaust design. The 1.5" tube will overlap the sides of the port by .08", shouldn't be terrible? Guess I don't have much choice. I'd appreciate some comments on my logic.

[chevymad]

If 1.5 is the tube size that will cut into your hp but tq will be up slightly. I like 1 5/8s tube headers myself. I think its a sweet spot for tq vs hp. For high hp motors some like the 1.75. None of this has anything to do with the opening size, just an in general the way sb headers work thing. If a guy was building a race car, I guess one could weld and shape the hole in the flange to match the head, but the transition would still be pretty short.

In practice port matching hasnt shown alot of benefit. Even on the intake side people with BB's have found very little loss using a rectangle port intake on oval port heads, which is a gigantic mismatch.

[blue89]

With the BB stuff being mentioned, I can see how the port mismatch would be less critical than the area. My dad is trying to get more torque at cruise speed to eliminate downshifting while towing. I'll let him know what you guys think, maybe it'll make him less concerned about the port mismatch.

He's using the corvette ramhorn cast manifolds at the moment so I told him to go long tube headers as that would be the best possible bolt on solution. He's at 2500RPM at 65MPH running an edlebrock eps intake and a 650 edlebrock thunder carb with a cold air inlet on a tall large k&n filter.

[chevymad]

Cam is the biggest thing. Cam it for that app. That carb will be dependable but not best at anything. For a tow rig I'd be looking for a good quadrajet or thermoquad. Dad used to tow a backhoe and equip trailer(about 20k lbs) with a 350 powered 75 3/4 ton. Did it for years and years. That truck was basically stock except for dual exhaust and a thermoquad. Pulled very well for what it was.

If you're towing something heavy your exhaust manifolds/headers are going to take a real beating. Get some very free flowing exhaust to get the heat out of them. If you ever look at used motorhomes almost all of them have leaking manifolds...The heat buildup just warps the hell out of the things.

[blue89]

Thank's for your advice. I'll see if I can talk to him about it and we'll get a plan together.

What makes the quadrajet or thermoquad better? Spread bore?

[chevymad]

Spreadbore is a major part of it. At least the carb you have has adjustable secondaries which helps. The regular edelbrocks dont.

The 2 spreadbore carbs were basically the last 2 stock carbs to be designed. They were made to work under a broad spectrum of applications and do it with a good tq curve/mpg. The edelbrock is basically a carter afb or in your case avs. The afb came out in the 50s.. avs i think late 60s. I know i've got an old original one off a 71 charger anyway.

I think you'll find the quad to just be alot more advanced. The thermoquad was chryslers answer to it. It's usually a bit bigger then the rochester. Thermoquad is made of phenolic though and good cores can be hard to get.

There's alot of tech I just don't know or remember. Like how the boosters work etc. But its the reason why holleys perform more crisp and make more power, quads perform better all around, and afb's usually come in last.. even though the afr's are the same.

Btw.. I hate holley.. but have one on my truck because it performed the best. I've had all of these carbs except the thermoquad on it.

[QwkTrip]

Actually, the best thing you can do for towing is use the right gears in the axles. A little more aggressive gear can go a long ways toward making the truck feel more powerful and not down shift.

[chevymad]

Ah. Jon's right about that too. A sb is only going to go so far no matter how well built if you're running 3.08s.

[blue89]

With all things considered, this is the header he's going with.

http://www.jegs.com/i/Hooker/520/2827-1/10002/-1?CT=999

Looks good, tuned, 1-5/8, nice collector. We'll see how it goes! Next we'll do carb tuning.

[chevymad]

Hooker's supposed to be a quality header. Usually considered a step up from the hedmans. Those are some spendy pieces. I've always used hedman or cheaper.