Chevy Engine Build Part 26 - The Pinnacle Of Performance

Last month we started out by saying "it's been a long time since Danger Mouse (DM) has seen gains this big with only one bolt-on." Well, this month we're saying it again because the gains were even bigger than before, and we did it with fewer bolt ons this time too! In fact, this month's power gains were so impressive that we feel we've reached the pinnacle of normally aspirated performance for DM and we're going to go in a radically different direction from here. Yep, for a while at least, we'll be stepping it back, looking at power made with some really streetable combinations. Although finding this much power has truly been a fun experience, we need to get back into the real street game.

In this month's test, No. 43, we made almost as much power normally aspirated as we did with a blower way back in DM Pt 10/Test 20 (July, 2003). Back then we installed a Weiand Pro-Street mini blower and made 602-peak hp. Of course the blower added lots of torque as well, with DM making almost 575 lb-ft back in that test, all of it on 100-octane unleaded pump gas. Jump back to the present and we figured it would be fitting to return to Weiand, and its parent company Holley Performance Products, to see if we could make almost as much power without the blower now. We wanted to experiment with a combination that few people ever use on the street, but one that can make a lot of power.

Last month we felt that our cam choice was not quite in sync with our intake manifold/cylinder head package. So we asked Lunati to modify one of their catalog grinds for us and it turned out to be the perfect match.

Last month we felt that our cam choice was not quite in sync with our intake manifold/cyli

Test 42 from last month was our first trial with an out-of-the-box Weiand Hi-Ram, and the results were good, (see: DM Pt 25/Test 42; September, 2004). We knew the ramming effect of the long-runner Hi-Ram would make more torque, but we'd also expected more peak horsepower. When that extra top-end power didn't arrive, we consulted with George and Bob Vrbancic to select a new, more appropriate cam matched to DM's Hi-Ram intake manifold.

We also felt strongly that, although the valve springs on DM's Edelbrock Victor Jr. cylinder heads might still be in good shape, (a quick check in the valve spring tester confirmed they were holding up just fine), the entire valve train might be moving around a bit near our very high 7,000 rpm redline. So we dusted off some parts from DM's past that didn't work too well the first time out, but saved the day for us this time.

Way back in DM Pt 3/Test 08, (November, 2002), we tested a COMP Cams stud girdle to see if there would be any power added to the very mild combination we were running at the time. Power fell off, and we placed the girdle into semi-retirement. But, like any old pro, when the going gets tough, the coach needs something he can call on to shift the tide and the stud girdle was it. We bolted it on and were rewarded with more top end power and no losses down low.

Speaking of perfect matches... When we removed the Weiand Hi Ram to swap cams, we noticed that the Fel-Pro 1206 gasket was barely sealing. Notice the impression showing the top of the intake not even covering the silicone bead on the gasket.

Speaking of perfect matches... When we removed the Weiand Hi Ram to swap cams, we noticed

Heat Affects Power
Today was the first of June, and the heat in Speed-O-Motive's dyno cell was staggering. Hovering above 95-degrees most of the day, the air going into the engine was not conducive to making power. The problem was that with DM's new cam increasing cylinder pressure, all that hot air did was make DM detonate. If this had been a cool day we easily could've gotten away with running this test on pump gas.

But conditions forced us to run 105-octane VP race gas, which was a first for DM while running normally aspirated. Even when we tried to pull ignition advance out using MSD's timing computer, the power fell off and the detonation lingered on. There was no way around it this month, but heck, what'd be the fun of doing this thing the same way every single time?

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.

This month's conditions needed less jetting so we removed two jet sizes (from 70 to 68) on

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.

Note that the power for T42 does not begin until 3600 rpm. We had some difficulty loading the engine that low in last month's test. But this month, DM had no trouble pulling down there so we were able to get some power figures in the lower RPM range. As we said last month, "sometimes the dyno does not act like a car". But, now we know that if this engine were in a car, it'd be able to accelerate strongly from well below 3,500 rpm.

We're always looking for new ideas. Do you have a better one for Danger Mouse? Send your test suggestions to:

Super Chevy Magazine
Attn: Danger Mouse
720 Hundley Way
Placentia, CA 92870
Or e-mail: terry.cole@primedia.com