After the second short pull,...
After the second short pull, we decided to play with the carburetor's idle mixture screws a little to see if we could clean up the idle, as it was a little rich. We may have had the Promax jet plates to help tuning, but we should have also gotten the outboard base plates to make the idle adjustments easier. A mistake we won't make again.
The visual impact of the original 340 Six Pack was, well, the Six Pack intake and carburetors. Harking back to the previous version, Mopar again decided that history needs to repeat itself, and the Six Pack is again the induction of choice. The intake, PN P4529054, is the same intake used previously, and is ready for you to install the carburetors on top of. Nope, carburetors and linkage are not included but are readily available. Finishing the engine is a stock style oil pan and cast aluminum valve covers. We're glad to see the LA-style heads and valve covers used in this case. Sure, the Magnum-style heads work great, but the 10-bolt valve covers would detract from the vintage look of a true 340 Six Pack.
Well, we told you what's in it, but how does it run? Remember we told you that we proved Mopar was a little off in their horsepower and torque ratings? Well, we'll get back to that. Anyway, after our engine arrived, we contacted Holley because as we said earlier, carburetors are not included. To finish the engine, we got the linkage kit and air filter assembly from YearOne.
As we hooked the engine up to the Dyno, we were concerned about this 340 living up to the reputation of its predecessor. We were still a little concerned after we initially primed the oil system, checked for fuel leaks, and finally fired the engine, as it sounded like a very mild engine. The idle seemed to be fairly smooth, and after some mild tweaking, it idled at around 850 rpm. Like we said, it sounded like a mild, basically stock, small-block. We made some initial pulls to around 5,000 rpm, just to get an idea of how it would act and to get some initial tuning requirements. It sounded like a good engine, and at 5,200 rpm, we ended up with 295.1 hp and 292.1 lb/ft of torque. We weren't sure what to expect after that because 5,200 rpm isn't that far away from what we thought to be peak rpm. We gave it another short pull for good measure and didn't notice much change.
Our initial pulls were short...
Our initial pulls were short because we wanted to make sure all sounded good before we spun it tight. It sounded good and even a little docile.
After the second pull, we decided to spin the engine up to 6,000 rpm and see what happened. We got a decent number--320.4 hp, which was just shy of Mopar's stated number of 330. We decided to add a little timing and see if that helped boost our numbers any. Our initial pulls had the timing set around 32 degrees. This was an initial setting deemed safe to start with. After the fourth pull, though, we bumped the timing up to 34 degrees, and it liked it. We now had more power than Mopar claimed--335.3 hp, and all we did was adjust the timing.
We decided it was time to do some jet changing. Thankfully, before our test session, we installed a set of Promax Carbs' jet plates in the outboard carburetors. Normally, changing fuel delivery in the outboard carburetors required drilling/enlarging the fuel delivery holes in the metering plates. The problem with this is two-fold. First, you physically have to drill the holes. Second, drill the holes too large, and you need to find another metering plate and start over. The Promax plates allow the use of standard Holley carburetor jets, meaning you can change to your heart's content.
After our first pull to 6,000...
After our first pull to 6,000 rpm, we still felt that the idle was not quite right and decided that the power valve must be the culprit. We changed the center carb's power valve from a 6.5 to a 4.5. After that, we ended up changing it again to a 2.5--man, did that help.
After a few more jet changes, upping the timing to a final setting of 35, and a couple more dyno pulls, we finally hit the end of our power climb--we found all there was to be had from the 340. At the end of the session, our new 340 Six Pack crate engine netted a total of 388.5 hp at 6,800 rpm, and 397.3 lb/ft of torque at 4,200 rpm. Like we said, Mopar wasn't exactly rating this engine correctly. The fact that the tried and true flat-tappet "Purple Shaft" cam willingly spun to 6,800 rpm impressed us. Finally, if we go by Mopar's numbers, we got an additional 58 hp, and little over 63 more lb/ft of torque than they claim. It's always good when you get more than you expect.
With the idle cleaned up,...
With the idle cleaned up, it was time to make some more pulls.
We now felt it was time to...
We now felt it was time to make some jet changes. Thanks to the help of the Promax jet-able metering plates...
...tuning was much easier...
...tuning was much easier than it could have been with the factory plates. With the factory plates, adjustments are made with a drill bit.