63 340HP

BBC is a different animal.

​​​​​​​The BBC log exhaust manifolds were far more restrictive than headers (compared to the difference between SBC rams horns and headers). We used the BBC manifolds for thermal mass in the hobby shop beer freezer (where they worked well).

cv67

As said if your just driving it around leave the manifolds
Spending any more money on them is a complete waste!

Spent MANY hrs on a members ramshorns there was nothing more that could be done. Disappointed to hear there was no SOTP difference.
Very difficult to do much with some areas and obstructions..plus primary/collector length makes a huge difference cant change that. Would it make a few on the dyno or bench probably but in real life nope.

babbah

And the exhaust sound of headers vs. manifolds is much more intense.

Frankie the Fink

Just about every car I've had with them was a PITA....my 396 '67 Chevelle had them and you couldn't get the oil filter off they were so close; they overheated the starter motor and the installer actually banged a dent in them in a couple of places to clear in some areas....

PITA... There are prob some that fit perfectly but most of the ones I've seen required some Bubba mod or other for them to work

65tripleblack

The 2 biggest mistakes anyone can make when using headers is to wrap them, and/or use gaskets against the heads. No gaskets= metal-to-metal contact. Torque them to 25 ft-lbs and forget them forever.

In most cases they make spark plug removal a snap compared to using manifolds.

As with all things, if they are done "right" they are a pleasure, and add power and torque to any moderately cammed engine.

stratplus

Curious. Wouldn't a gaskets be better for sealing if the header wasn't 100% straight.

MikeM

Seems like it might be a good idea to make sure your header flange was straight.

There's lot's of leverage and vibrations just waiting to compress gaskets and start a leak.

65tripleblack

Well then you're talking about a system that has already been compromised.

Straighten the flange, then apply a thin film of RTV red or copper and torque the bolts. Then forget them forever.

If the bolts are squeezing a gasket, then they will never torque fully and never hold torque; they'll get loose once the gasket sets up.

If the gap is too big, the gasket usually blows out, so there's no cure for a bad header flange except straightening it. Start with a sturdy 3/8" thick flange.

RTV isn't necessary if the flanges are true. Any small leaks will "carbon up" and seal in a short time.

bpjon65

I installed a GM small block crate motor with angle plugs in my 1965. I used Patriot shorty hugger headers. I did need to refit the side pipe exhaust for proper fit. Plugs can be removed with the headers installed, but you need to use a wrench since the socket will not fit.

GearheadJoe

I think your estimates are pretty close. The OP asked if there was any factual data on this topic. When I was planning my engine build, I found that factual data was very hard to find. So, when I built my 383, I paid for an extra day of dyno time to get some actual comparison data. Keep in mind that this is just for one particular engine, but the comparison was for the exact same engine, with the only changes being to the exhaust system. I compared four different exhaust configurations:

1) Open long-tube headers
2) Long-tube headers with Corvette off-road mufflers
3) Open ram's horn 2.5" manifolds
4) Ram's horn 2.5" manifolds with Corvette off-road mufflers

My 383 stroker has 10.25:1 compression, a "medium" hydraulic roller cam (224/224, .525" lift), Dart Iron Eagle Platinum 200cc heads (disguised to look like stock '462 heads), and a 1967 Z28 intake.

The attached plot shows the results for all four exhaust combinations. Sorry that it's a bit hard to read, but if you zoom in it should be legible.

The plots show that with a stock exhaust, headers aren't much better than 2.5" ram's horns manifolds below about 4000 RPM. However, at 6000 rpm, headers add about 25 HP.

I'd like to make a few observations:

1) I think long-tube headers are the only type of header that will show much benefit over the ram's horn manifolds. The benefit comes from the wave tuning that only long-tube headers can provide. So, "shorty" headers probably add very little over ram's horn manifolds.

2) Open, long-tube headers will yield the most impressive power curve, but if your car is intended for street driving, open headers are not really an option. So, people should not use an open-header power number to compare with ram's horn manifolds running through mufflers.

3) As the test data show, adding mufflers behind headers will partially defeat the potential power gain. However, if the mufflers are low-restriction, headers will still provide some benefit above 4000 RPM.

Dr L-88

Thanks Joe. That's exactly what I was looking for. I've already made my choice and got the engine in the car, but your data just confirms that I made the right choice. My engine is very similar to yours except 355 inches.....................2.5 inch rams horns into NOS off road exhaust. I DID port match the exhaust manifolds slightly. I'm pleased.

63 340HP

​​​​​​​Very Nice.

Tom Heffernan

That is cool

PAmotorman

rex how did you connect the cold air intake to the dual air meters ??

Dr L-88

I haven't made the final connection yet Clem. I need a GOOD, and I mean REAL GOOD metal fabricator who can work metal like putty, to fab something for me.

PAmotorman

you could use something like the 57 air box setup with 2 hoses to the box and put the air filter out n front of the core support

Dr L-88

I would like to find another elbow section of the air cleaner, modify it and have a base plate made to fit over the two air meters (kinda like a Ford 2X4 base plate) and a lid over that connected to the modified elbow.