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Old 02-14-2012, 01:35 PM
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Cam

My son has a 1985 Dodge D250 with a 360 and automatic trans.
We are rebuilding the engine and want to put a little hotter cam in that does not require additional parts. the truck will not be used for very much towing.
We just want a little more than stock without changing converter or valve springs
After researching on the web I am as confused as ever seems everybody has the answer but not the one i'm looking for.

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Old 02-14-2012, 05:28 PM
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Quote:
Originally Posted by GOODWRENCH
My son has a 1985 Dodge D250 with a 360 and automatic trans.
We are rebuilding the engine and want to put a little hotter cam in that does not require additional parts. the truck will not be used for very much towing.
We just want a little more than stock without changing converter or valve springs
After researching on the web I am as confused as ever seems everybody has the answer but not the one i'm looking for.
The simple answer is to keep the converter stall about 200 to 500 RPM above the minimum RPM of the cam's power range. An RV cam for example could read 1500 to 5500 RPM so you'd be looking for a converter from 1700 to 2000 RPM, which is pretty stock.

To keep lower end torque up you'd be looking for a cam with a lobe separation angle 110-114 deg to minimize overlap and duration of 200 to 210 maybe 215 degrees measured at .050 inch valve lift with a lift at the valve of .45 to.48 max lift at the valve. A cam in this range will keep you out of a high stall converter yet boost up lower, mid, and top end power quite a bit over the typical factory truck camshaft. What's important is to ingest and trap as much mixture in the cylinder as possible using mild timing and modest but increased lift. The long LSA keeps mixture from just running through the cylinder as the piston traverses from exhaust to intake stroke, this will inhibit top end power as you don't get any assist from the departing exhaust to start the intake cycle; but it helps fuel economy big time. However, you'd still want an effective exhaust system that minimizes taking power off the crank to pump exhaust out. The other feature of the timing is an early closing intake valve, again this hurts top end power as the engine can't take full advantage of ram filling due to high intake port velocity. Smallish valve sizes and ports can be used to pick the velocity up so the ram effect comes in earlier. The worst combination would be an RV type cam with large port heads and intake, this is a more common error than you might think which results in a disappointing engine all around. Since the valves spend a lot of time in the low and mid lift range with these type cams, the technique of back cutting the valves to remove the lip or ditch that separates the seat from the backside of the face is most effective toward helping to fill the cylinder. This is quite effective with a short duration, low lift cam in making up for some of the more exotic techniques of getting mixture into and out of the cylinder that are possible with a racier cam but not a mild cam. This technique proportionally has a larger effect on power output with a mild engine than it has on a full tilt race engine because the benefit just doesn't extend much beyond .4 inch lift. Basically these techniques are similar to what guys do to an engine that races in highly restricted classes where the engine must use mostly stock and unmodified components under a small 2 barrel carb. "Claimer motors" for lack of better term.

Bogie
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