Chevy Engine Build Part 26 - The Pinnacle Of Performance

More Camshaft Gives DM 580 Hp And 514 Ft-Lb TQ!

Mike Petralia Oct 1, 2004 0 Comment(s)
Sucp_0410_09_z Chevy_engine_build_part_26 Carb_jetting 1/14

This month's conditions needed less jetting so we removed two jet sizes (from 70 to 68) on both primary and secondary sides of the HP650 carbs. Note: These carbs come with 6.5 power valves on both primary and secondary sides, which would not work well with such a large cam/intake manifold combo on the street. For street use, wed lower the power valve numbers to around 2.5 or 3.5, to compensate for the low idle manifold vacuum.

Big Cam Technology
The real deal this month is that we were able to properly match the camshaft to the intake package. This is something we've been preaching all along with DM and can't stress the importance of enough. While last month's power may have satisfied many players, we knew there'd be more if we had the right cam ground. But, unfortunately, no cam companies offer what could truly be considered the "perfect" cam for an engine like this, so we had to have one custom ground.

The process was simplified however; by selecting a Lunati catalog grind, and asking them to grind it with a wider lobe separation angle (112 degrees this month versus 110 degrees last month). We also asked Lunati to grind the intake lobes 4 degrees advanced, giving the cam a 108-degree intake centerline. Then, during testing we advanced the cam another 2 degrees, putting the intake installed CL at 106, which netted us the best overall power and torque of the day.

What all this effectively did was increase cylinder pressure by closing the intake valve a little sooner and the added duration of the bigger cam also helped pull more top-end power. Lift was increased as well with the new cam, but not so much to become a spring killer. Unfortunately, as you can clearly see from this month's dyno tests, power fell off slightly in the lower rpm ranges. That's to be expected when running a bigger cam. Besides, wouldn't you trade 51 extra hp up top for 5 lb-ft of lost torque any day?

We sure would, and although this engine would certainly be very radical on the street, (1,200 rpm idle with very low vacuum), it could still be driven everyday in the right car and since every part we installed is still unmodified from the factory, anyone that's bolted together an engine could build it. This engine could propel a well set-up, 3,500-lb streetcar to very low 11-second e.t.'s at 120-plus mph and still be driven home! And with the Hi-Ram's twin carbs poking through your hood, giving just a hint of the power that's beneath, we think it can't get much better than that.

Dyno Testing Part 26
We're comparing this month's test, T43, to the last test from last month, T42, in which DM was set up with the smaller camshaft and no stud girdle. Also, in T42 we were running locked-out ignition at 38 degrees and 91-octane gas, but T43's new cam increased cylinder pressure and the added heat of June in the dyno cell this month forced us to run on 105-octane race gas. So the comparison is not truly equal, but the power increase is truly incredible. Especially when you consider that it was achieved with just a cam, stud girdle, some tuning on the dyno, and a little more octane. This also proves that there's always power to be found when you devote some serious effort to trying different tuning options, instead of sticking with just one.

Danger Mouse specs for Part 25
- Test 42: Last test from last month 355 cid, 12.5:1 cr, 4.030-bore 4-bolt Motown block, 3.48-stroke Lunati crank, 5.7-inch Lunati rods, Lunati domed forged pistons, Total Seal ductile iron Gapless top rings, Edelbrock Victor Jr. heads (64cc chambers, 215cc runners, 2.08" intake valves, 1.60" exhaust valves), Weiand Hi Ram intake manifold and twin Holley HP650 carbs, COMP Cams XR286R solid roller camshaft installed @ 105 intake CL (248/254 @ .050, 286/292 adv, .606/.612 lift w/ COMP 1.6:1 rockers, 110 LS), 38 total advance, 91-octane. Tested on Vrbancic Brother's Racing DTS dyno.

Danger Mouse specs for Part 26
- Test 43: Same as above but with custom-ground Lunati roller camshaft installed @ 106 intake CL (259/266 @ .050, 294/300 adv, .636/.640 lift w/ COMP 1.6:1 rockers, 112 LS), 105-octane. Tested on Speed-O-Motive's DTS dyno.

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