68 - 340 Cam Specs
Mopar
Like to tease you with these Magazine Ads with 'advertised specs'.
http://img.auctiva.com/imgdata/1/0/4/3/2/5/3/webimg/513650195_o.jpg
That's gotta be a tease , cuz my 70 Swinger340-4spd didn't idle like 60*lumpy. Nor did any of the other 69 to 71s of my classmates back in highschool. But yeah, I remember the 68M/Ts were advertised with slightly hotter cams than 69ups, and they were all still chebby killers!
Also IIRC those cams had incredibly long clearance ramps, making a 276advertised into something like 220 or
[email protected]? (Ima guessing).
There's better cams out there for teeners. A lot better.
This 276er on a 114LDA(in at 112) leaves just 110*of compression distance to make the charge hot enough and dense enough to make power. Well in a LC teener this works after the torque peak, but not so much at rpms that it spends most of it's street life at. And the 102* of extraction means there's still a lot of energy in the cylinder when the exhaust valve opens. Energy that could have been used to propel the vehicle.So with this energy going out the pipe, hey you paid for that! and now it's wasted. It comes out the end of the tailpipe as sound and withturn-downs, ends up making little dust-devils in the graveldust on the road when idling,stopped.
But if you take that same 276er and tighten up the LDA to108 and install it at split overlap of 106*, the you will get116* of compression, with the ICA falling to64* from 70*. This leaves the Dcr up and the cylinder pressure probably 10 or more psi higher. Furthermore the extraction moves this same 6* to 108* delivering more energy to the crank, and less out the exhaust. The "penalty" for this is the extra 6+6=12* of overlap which is now 64 degrees. At this point the overlap is beginning to become a 5th element to the 4-stroke principle. If headers are now used, this element can be exploited to increase engine output by virtue of bringing the V.E.
closer to 100% during a portion of the powerband beginning from around the torque peak and up. 64* ain't much yet, but the effect is better than at the previous 52*. The real penalty is the slightly lumpier idle(which most guys like) and a wee bit of a tuning learning-curve.
Anyhow, I don't know what got me going, but If anyone read this far, have a great day!!
