One of the most critical measurements you will make is the valve-to-piston clearance. Clea
Lube It Or Lose It
Last month, we detailed our lubrication plan, and modified the stock internal block passages leading to the new Milodon high-volume pump. With the front cam drive and cover installed, we were ready to button up the bottom end. We weren't straying too far from factory issue in the lubrication system, shying away from exotica such as external pump feeds or swinging pickups. Putting a lid on the lubrication system came down to a windage tray and pan selection. We went with the Milodon tray. Similar in concept to the excellent factory offering, this tray offered more complete coverage of the spinning crank at the front of the crankcase, and two more rows of louvers/baffles to aid in drain-back.
With that part complete, it was just a matter of choosing a sump for the task at hand. Hard-learned lessons have taught us that any kind of potential for street use virtually excludes the traditional drag race asphalt plows. The Milodon wide sump street pan fit our need for increased capacity, with much less of a penalty in terms of ground clearance than a full deep sump, drag-type pan.
While thumbing through the Milodon catalog, we spotted a nifty adjustable oil pump pressure regulator, which we couldn't resist. It allows the dialing-in of the oil pump relief valve with a turn of an Allen screw.
The above method will indicate how much lift you can handle, but won't give you a clue of
If you followed our series on porting Mopar big-block heads, you've got a handle on the porting tricks we employed. For our initial dyno testing, we are running a set of 915s, ported exactly as described in "Going With the Flow, Part 2," (Feb. '99). We chose the 915s, which share the same basic intake ports as the 906, because they are the only late-model heads that offer the combustion advantages of closed chambers as described in "Going With the Flow, Part 1" (Jan. '99).
To recap, getting big improvements in high-lift flow from the 915/906 intake is no picnic. We found the later 346-452 heads to be much more responsive to porting and large valve modifications on the intake port. Unless the earlier head is precisely reworked-preferably with a flow bench at hand-the modified smog heads will outflow them hands down. Ultimately, we were able to best the late castings with the early port (albeit with much more development time on the flow bench) by close to 6 percent at max lift. For us, it required more than twice the porting time just to equal the flow of the ported late casting, and four times the porting time and constant progress checks on the bench to gain that 6 percent edge. Our ported 915s moved 34 percent more air at max lift than the stock port, with no welding, brazing, sleeving, or epoxy.
Pop the heads back off, and with a razor, slice sections of the compressed clay, then chec
The exhaust valves on our test heads are common oversize replacement Manley units in a 1.81-inch diameter, modified with a radius margin for better flow. On the intake side, things are a bit more unconventional. Looking at the heads, flow guru David Vizard's first question was, "What size valves are you running?" "2.14," we told him, "it's what everyone runs." The next question was, "Why? It looks like a 2.25-inch valve would drop in." After the ensuing session at the Serdi seat machine for a 30-degree seat in the 2.25-inch diameter, we were testing the head with a Hemi-sized 2.25-inch valve (a big-block Chevy unit). Top-end flow picked up a few cfm, but lift from right off the seat through the mid-lift ranges was fattened up over our already great numbers by up to 10-12 cfm.
We arranged for Manley to make us a custom set of cut-down big-block Chevy 2.25-inch valves, with the keeper groove at the stock Mopar height. A peculiarity in valve manufacturing is that the tip must be indivi-dually hardened to a much higher level than the rest of the valve to withstand the rocker's action. Our special cut-down and regrooved valves from Manley would, of course, lose the hard tip, which is not a problem if a lash cap is installed. We ordered the semicustom valves with a tip length .080-inch shorter than a stock Mopar valve, so we would have a stock length with a .080-inch-thick lash cap in place. With the improved low to midrange flow, we set up our test 915s with the custom 2.25-inch Manleys.
We wanted to know the exact compression ratio of our combination, as well as equalize the
Ironically, after slaving over the math to determine if the .080-inch-shorter tip length would enable the lash caps to clear the Comp Cams locks with the recessed lash cap groove (it's quite close), we found that the added .080-inch lash cap thickness actually would have worked fine with a stock-length tip when using the Comp rockers (the geometry is actually slightly better). Next time, we'll specify the standard tip length and run lash caps on the intake and exhaust.
The Manley 2.25-inch valves feature an 111/432-inch stem diameter, which reduces weight and assists us in our goals toward a lightweight valvetrain. The exhaust valves are standard 31/48-inch stem units, which actually is a benefit for critical heat dissipation in an exhaust valve. The guides were replaced with corresponding 111/432-inch silicon bronze inserts on the intake, and 31/48-inch inserts on the exhaust. With extremely high-lift cams, a top-quality guide insert is mandatory, if any reasonable guide life is to be expected. For longevity, forget about cast-iron guides. Our silicon bronze guides were sourced from APT. Rounding out the head mods, the spring seats were machined to take the dual valve springs, and the guideboss cut down for positive stop guideseals (a must for oil control with the high-vacuum Total Seal rings installed previously).