I am curious how much my factory exhaust manifolds might be holding my 1976 360 back.

Here are the specs:

• Stock bottom mid-70's 360
• Factory 2bbl was rated at 180hp @ 4,000 and 290ftlb @ 2400
• Milled [63cc] 2.02 J-heads, somewhere around 9.3:1 compression ratio
• Edelbrock Performer RPM intake
• Comp Hyd Flat Tappet, 0.470" intake lift, 0.480" exhaust lift @ 270/280 duration
• Comp 901 matching valve springs
• Stock rockers
• Holley Sniper EFI
• Stock exhaust manifolds with factory 2>1 single exhaust (2-1/4")

The truck runs decently well up to about 5,300rpm and it starts to fall off quickly thereafter. The cam and intake should pull pretty well up to 5,800, but I have a feeling my manifolds disagree.


I am not looking for a race truck, just something that is fun to cruise around in, how much are those factory exhaust manifolds holding me back at the top end?

I would think the single exhaust is holding you back a little.

I would say quite a bit. I would source a 68-70 340 HP pass ex manifold (might take some searching to find one seperate) & a drivers side early (has ~2&1/4 outlet) magnum exhaust manifold, the later ones are ~1&7/8 iirc.

I think Dulcich did a test on this, one a mild engine like yours the loss was pretty minimal on the dyno.

https://www.hotrod.com/articles/mopp-0307-mopar-crate-engine-exhaust/

Sounds like you enjoy tinkering and thats what the hobby is about. If I were you and money was available Id buy a good quality set of headers power output appropriate and install them with true dual exhaust and nice turbo mufflers. Dont do it in the chase for improved performance but do it for great sound and enjoyment. If you dont have the $$ for headers do a true dual exhaust with existing manifolds.

Interesting comparison, the cam they were using seemed to quit pulling at 5,000, but the power difference there wasn't all that substantial. I can't see another 500 rpm being a big jump for the headers.



It's not so much a cost thing as much as it's "I'd like to avoid headers" thing. Thin leaky flanges, steering clearance, starter clearance, plug wire routing etc.

You need duels or 3" single at least, and if you don't want to headers the best flow and fit is 92-3 magnum manifold, fit perfect. On one of my trucks I had roll the firewall/floorpan seam a little for clearance, duels on my 77, right one runs straight back, left one crosses under front of trans, parallel to the right one, mufflers vertical near stock location, over axle then off to the left, both pipes exit under bumper, balance tube just a head of the mufflers, pulls hard to 6500 with my 408

Really nice manifold design for the small blocks = the later model 318/360 Magnum manifolds. You'll have to grind the center webbing a little & probably have a new trans dipstick tube made. I installed mine from the top on my '73 Charger 340 Rallye & did not use gaskets. MUCH better fit & design than the OE manifolds.

I forgot about the Magnum series exhaust manifolds. Interestingly the first 2 years of the 318 Magnum used a larger opening I think 2.5". Then they went 2 1/4" for the rest of the prod run. Good choice IMO.

We used to build a bunch of low CR(8.5:1)350 Chevy oval track motors.
They had to use heads with 1.72” intake valves, stock 2bbl intakes, stock ex manifolds(and not the good ones), and under .500” lift hyd cams with stock rockers.
A pretty good one would make about 280hp.

I tried a set of 1-5/8” headers on one once...... just to see.
It picked up 42hp.