bolting on X-heads to my 340, can i use my exhaust manifolds?

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djais1801

djais1801

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Over the winter I am going to be changing the cam. I picked up a set of complete X heads ready to bolt on. I am running stock exhaust manifolds and don't want to go with headers. Should there be any issues bolting up stock exhaust manifolds w the X heads?
motor has stock heads, a 474 lift purple cam. Eddy performer intake, I am switching to a Weiand (idle to 5000) powerband, holley 670 street avenger, 4spd and 355 sure grip

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Lelo Dart said:
My friend just switched from 318 heads to X heads on his 340 with 273 manifolds and no issues.
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They will work but that's choking things down quite a bit. Smaller ports, smaller tubes, and smaller outlet. That combination will work just not nearly as good as it could.
 
Agreed. 66 Barracuda so until he can get some headers there's not a lot of options. Was just pointing out that the exhaust bolted back up.
 
Ok, if you have 340 manifolds and want to use x heads, thats how 340's came until 69. I would recommend flatout graphite manifold gaskets. Yes headers would give you more hp, the more all out the motor the more benefit. That being said I run 12.10 at 113 through stock 340 exhaust manifolds. With the bump in compression high 11's definitely in ball park. point is you can get a bunch out of the 340 manifold.
 
furrystump said:
Ok, if you have 340 manifolds and want to use x heads, thats how 340's came until 69. I would recommend flatout graphite manifold gaskets. Yes headers would give you more hp, the more all out the motor the more benefit. That being said I run 12.10 at 113 through stock 340 exhaust manifolds. With the bump in compression high 11's definitely in ball park. point is you can get a bunch out of the 340 manifold.
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Copper or GPC?
 
I have looked at the copper just never used them. The silver graphite with the metal inner core. They don't leak and i have reused them a couple of times without issue. I still dont throw the old ones away, just in case I need an emergency one! Also is that an air gap intake?
 
furrystump said:
I have looked at the copper just never used them. The silver graphite with the metal inner core. They don't leak and i have reused them a couple of times without issue. I still dont throw the old ones away, just in case I need an emergency one! Also is that an air gap intake?
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The one that is on there now I believe so… It is rated for 1500–5000 RPM power band… I want power band from idle-5000 rpm... so I picked up a weiand
 
The 68-69 exhaust manifolds are supposed to be a bit better that the 70's but in practice I haven't seen it. I run against a duster that runs the 70's manifolds and he runs 11.73
 
The 318/360 air gap rpm is 1500-6500. Assuming your valve train is up to snuff. It is going to want more that 5000rpm
 
If you are worried about the 1500 starting point. 4 speed will make that not a factor. Idles at 800 feather the throttle as the clutch comes out, your at 1000 or higher. I like to run a high idle just to make sure the cam gets enough splash lubrication.
 
furrystump said:
If you are worried about the 1500 starting point. 4 speed will make that not a factor. Idles at 800 feather the throttle as the clutch comes out, your at 1000 or higher. I like to run a high idle just to make sure the cam gets enough splash lubrication.
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Maybe the carburetor needs to be tuned … I don't feel it's crisp at 1500… It kicks in for 3 to 5000 RPMs ...I feel it bogs down off the line
 
Not real familiar with the street avengers. The accelerator pump must start squirting the moment the throttle moves. I believe the it is adjustable through different cams. The vacuum secondaries may be slow or to fast. I believe they are adjusted by canister springs. Dollars to donuts it's in one of those not the intake. If the intake was a huge single plane maybe, but not the air gap dual plane.
 
What does the exhaust look like as it bogs from idle to 3000rpm? Black rich or no color. Does it ever pop in that rpm range?
 
furrystump said:
What does the exhaust look like as it bogs from idle to 3000rpm? Black rich or no color. Does it ever pop in that rpm range?
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I have a valve tap which started me down this road of rebuild...motor came w car-I replaced: lifters, rockers, springs, cam was inspected when intake was off and lobes looked okay...tap still there-so I'm thinking cam is only thing I didn't replace-which I will do so when I do the heads. I have good oil pressure and no smoke
No smoke when I get on it...I know when idle to warm up condensation spits out the pipes
 
A lean pop is unmistakable and irregular. Not consistent. Probably wait until its back together to tune. You don't know how good the mechanical state the engine is in.
 
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