SBC exhaust manifold comparison.

[rfoll]

I have an 84 El Camino with a 305 and the stock manifolds, (the rusty ones). It has a single pipe going to a Flowmaster with dual outlets. It sounds pretty good at idle and the 60+ mph noise is remarkably quiet. I have a wrecked El Camino with the common 350 manifolds. This system has a true Y pipe going into a single 2 1/2" pipe. If or when I pull the engine at a later date, will the older style manifolds offer any improvement hooked up to the existing system? It's possible I might use a 350 in place of the 305 at this time

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[travis]

I don’t know if the ones in the top pic are better, but they are great at baking the valve cover gaskets and causing leaks

I’m willing to bet that the bottom design is actually a bit better. When GM trucks went from the TBI engines (with the top pic style manifolds) to the Vortec engines, they switched back to the bottom design type manifold (slightly different but close).

Realistically there probably isn’t much difference in performance between the 2...I just never liked the gasket frying design. The outlet size may make the biggest difference here.

The top design seems to be more prone to cracks as well.

[Brian W]

I did a bunch of testing on this about 20yrs ago... The top picture 305 style are one of the worst performance wise...
Best of the rear dump manifolds are the LT1 style.

[novadude]

TPI 80s Camaros had a larger outlet version of the El Camino manifolds (2.25" vs 2"). I know the 350 cars did, but not sure if ALL TPI cars had the large manifolds.

Don't know how much of a performance improvement they would offer, but I do know for sure they fit the 78-88 Malibu / El Camino Chassis just like stock, as I used a set on an 81 Malibu once.

[mag2555]

Good is a relative word!
If a bigger type Exh Manifold area wise has more heavy rust scale in it as compared to a non rusty smaller area one , then give me the smaller one to bolt on every time please!

A number of months ago I took on a dinner bet from a buddy, and won a nice meal!

I flow tested a rusted up normally carbon scaly 3 inch long Exh port in a head and I kinda polished it up for two minutes worth of time.
It was by no means fully cleaned up , nor did I roll over the top of the air injection boss as my photos show , yet the port when slapped back on my flow bench picked up 8 cfm of flow.
Imagine how a 12 inch long run thru a rusty carboned up exh Manifold will murder flow numbers!

[Carnut1]

The bottom exhaust manifold is a better flowing design. That is what the old work truck had when new in '88. They got ported when the original swirl ports got ported. When the truck got the 383 they went back on for a while till I got some slp stainless shorties. I couldn't tell the difference after the shorties went on. Except it was way louder. 383 was 6000rpm max engine. Thanks, Charlie

[chevyfreak]

Between those 2 i would use the bottom style log type .
Never liked the other units that goes up next to valve covers.


Chevyfreak.

[rfoll]

The bottom manifolds came from my 79 Impala. When I did an engine swap, I cleaned them up as far as I could reach with a grinder. My exhaust guy installed the Y pipe where the cat used to be. 2 1/2" pipe to a stock muffler.

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I do have headers that fit the chassis, but they tend to cook starters, and when you change oil the filter dumps right on the collector. The reason I am worrying this so much is there is a chance I will stick with a 305 engine, (19.5 mpg freeway), and I am searching for ways to help the torque. The engine does fine for what it is, but a few more ft. lbs. couldn't hurt. If I stumble across LT1 manifolds beforehand, I might go that direction. This is a daily driver car, and I will likely drive it until they take my license away for old age.

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[HDBD]

I had an 85. Swapped the short block to a 383 with the 305 heads ported and the stock E quadrajet crane 260. It ran great and got fantastic mileage with stock manifolds a performance cat and bigger pipe and muffler. 20+ mpg on the highway with no more maintenance than stock.

[rfoll]

My car had the electronic QJ system, but someone removed so many parts the car barely ran. This car has a 3.08 rear gear, which helps the torque. The lockup converter helps economy. If I put a 350 in the car I will likely use the 2.73 gears from the other car. 2.41 gears were the most common ratios for 70s and early 80s GM automatic trans cars. It takes some serious low end torque to make that work.

[HDBD]

Leave the gears alone, if you don't have an OD trans consider a built 200r4. Not sure they would fit but the old Corvette center dumps rams horns would be a big improvement on manifolds.

[rfoll]

I actually like the 2.73 gear, but the 305 wouldn't like it. I have a 700r4 and a 3.73 gear if I wanted to go down that path, but there's much to be appreciated about the simplicity of a TH350C and a reasonable highway gear.

[travis]

You might consider the 1 1/2” tube mid lengths with 2.5” collectors made by dynomax. Supposedly they fit and clear much better than a full length header.

I have yet to see a situation where small tube headers haven’t helped in mileage and off idle torque, even with stock or near stock smogger motors.

Although there is a lot to be said for the rock-like reliability and simplicity of iron manifolds

[rfoll]

I'm tempted.

[pdq67]

What about the later P/U SS pipe shorty header/manifolds that came out stock back then? Or maybe later??

pdq67