Fitting an Air Gap manifold to my 340 (with pics!)

[MilesnMiles]

This isn't for all the old hands who do these jobs before breakfast, but it might be useful for some of the newer guys who want to make some simple upgrades to their motor.

It's well documented that the 360 small block is a great torque builder, but it's more sought after cousin the 340 needs to rev to build power. To try and introduce more torque to my near stock 340 i'd fitted a Holley 670 Street Avenger with very immediate and obvious power range improvements, but I still wanted more torque as i'm pulling a B body with this motor.

Every review/comparison I could find indicated that the Edelbrock Air Gap manifold would increase mid to high end torque and horse power.I'd previously fitted one to my Dart and its 360 and enjoyed the extra grunt so it was time to treat the 340!

[MilesnMiles]

Comparison pics.
The original 1972 340 is cast iron. The Air Gap is aluminium and half the weight. It is also 1.5" taller so make sure you have space. Even under my B body hood it looked tight.

As the pics show, the air gap is evident and the runners look to be larger as is the plenum area. You can see that the Mopar manifold is cut exactly to fit the original Thermoquad carb.

When buying one of these manifolds do note that there is no fitting kit. This means that you ave to salvage parts of the old manifold if they will come off!
As ever. Ade W bailed me out in particular by supplying the 1" pipe that the by pass hose connects to as the old one would not shift from the cast iron manifold.

[MilesnMiles]

Removing the manifold is easy. 12 x 9/16 bolts hold it down. Ease back the rocker covers to allow access, remove carb linkage and pull the bugger out! I even left the distributor in place.

Before replacing check everything ail fit.
My block has dowels in it to locate the manifold. I didn't want to drill my new manifold as it would mean drilling into the water passage at the front, potentially. Therefore i used the thick cork gaskets that come with the manifold. This raised the manifold slightly out of kilter with where the bolts hold it to the head. It took some time manipulating and using the bolts to slowly pull the manifold down and it all went well in the end. Edelbrock say to discard the cork manifolds at either end, but the dowels gave me no option and RTV wasn't going to do it.

[MilesnMiles]

Once I had bolted it all down it is a simple process to reconnect the wire to the temp gauge, ensure all hoses are refitted and carb is fully connected. I then offered up the original 340 air breather and was pleased to find that it cleared the hood.

Additionally, the kick down linkage and throttle cable despite being higher still connected and work well as the pics show without further modifications.

[MilesnMiles]

Finally, the road test! I warmed up the car and went for a blast. Whilst the carb was off the car I upped the jetting as the manifold was going to flow better and need more jetting. I went for mains at 68 on the Primary side and 74 on the Secondary mains and it pulled really well.
There is a clear improvement in torque and at 3,000 rpm the cam comes on song, the secondaries are firing and it really pulls much harder than before going by the 'seat of the pants' test.
All in all a good £300 worth of improvement

[Carl]

Great you got one too Miles I put one on my 340 Stroker along with the 850 DP but never felt the full benefit of it due to the 850 bogging problem. But we will see once I get the car running again.

[Guy]

My block has dowels in it to locate the manifold. I didn't want to drill my new manifold as it would mean drilling into the water passage at the front, potentially. Therefore i used the thick cork gaskets that come with the manifold. This raised the manifold slightly out of kilter with where the bolts hold it to the head. It took some time manipulating and using the bolts to slowly pull the manifold down and it all went well in the end. Edelbrock say to discard the cork manifolds at either end, but the dowels gave me no option and RTV wasn't going to do it.

The reason Edelbrock say discard the cork gaskets and use RTV is because you are meant to take out the dowels to allow the manifold to sit sightly lower for correct port alignment. Hopefully you did remove them and not torque down the manifold on them as this could end up warping the manifold and maybe give you some air leaks .

[MilesnMiles]

Guy, i realised that, but the dowels were not shifting. the cork gasket lets the dowels go pretty much flush, although in truth I will probably remove the whole lot and check again over winter.
In the past when there have been no dowels there is no way that a line of RTV would seal the ends up despite what Edelbrock recommend. I usually re-used the original cork gaskets which were sufficiently depressed.
The dowels would not come out which does leave a future question to deal with.

[Guy]

If the dowels wont come out Miles you should now have a witness mark on the manifold which would allow you to drill the intake with the appropriate size drill bit for clearance. You would not need to go right through the manifold so externally it would still look good.

[MilesnMiles]

ok mate, I will return to this. Suspension and front end set up is now on the agenda