With the head's intake ports...
With the head's intake ports opened up, we couldn't let the factory port size on the intake, so Modern Cylinder Head worked some magic on the Indy manifold and the heads.
Day One on the Dyno
It started out great, but ended well before we wanted. We started the testing with a small 750 Holley carb, and the timing was set at a conservative 36 degrees of total advance. On the first run, the dyno needle swung up to 600 hp, but we could see by the EGT readouts that the carb was a bit lean. After adding a jet size and bumping the timing to 38 degrees, we made a quick second pull. On this run, we saw 504 lb-ft of torque at 6,000 rpm and 625 hp at 7,500 rpm.
Feeling encouraged, we swapped on a larger carb and got ready to make some serious power. But the third pull of the day ended quickly when a serious stream of smoke started to come out of the valve covers. A quick teardown revealed a split cylinder wall in the number six hole, so our day was over.
We use the Cometic head gaskets...
We use the Cometic head gaskets on all the motors that have aluminum heads. They cost a bit more than conventional gaskets, but they sure work well. Also, you can get them custom-made in different diameters and thicknesses, so you can fine-tune your compression and quench height.
Even though we only got one decent dyno pull on this combination, it gave us a bit of insight into what the performance could have been. The second run showed 625 hp at 7,400 rpm, and the power curve was still climbing. Obviously, these Indy heads were working with the bigger camshaft to really make power at the higher speeds. The torque peak was about the same level as when the motor had Edelbrock heads, but the peak had shifted up the rpm band from 5,100 rpm to 6,000 rpm. This shift in the torque and power peak is due to the larger cross section in the heads as well as the larger cam profile. We're pretty sure we would have seen a good solid 650 hp from this combo if we had gotten a chance to wring it out with the larger carb. The Indy advertisement says, "take the iron 906 combo off and pick up 100 hp." On this combination we saw an increase of 125 hp over our 906 heads before we even got the combination tuned; it looks like the guys at Indy have hit the nail on the head.
What Went Wrong and Lessons Learned
A full autopsy of the motor showed the whole mess was started when the number six rod bearing spun. Once that bearing got chewed up, the piston kissed the cylinder head, then cocked in the cylinder, and split the block. We're not sure why the rod bearing spun in the first place, but it was probably due to our stock oiling system not being able to keep up at 7,500 rpm. For years, the Mopar racers have been telling people to upgrade the oiling system when spinning a big-block past 7,000 rpm. Our bottom end was dead stock with the factory 31/48-inch pickup, standard oil pump, and stock oil passages in the block. When we first built this motor we weren't planning on spinning it so high or making so much power, so we just didn't invest the time and money into the oiling system, and we paid for that mistake. Guess those Mopar racers knew what they were talking about all along!
 For oiling, we used a Milodon...  For oiling, we used a Milodon windage tray and oil pan. We used a stock 31/48-inch diameter pickup, and no oiling modifications were made to the block. We have since learned our lesson, and our failure was in no way related to any of the components. |  We filled up the crankcase...  We filled up the crankcase with Valvoline 50-weight racing oil. Since we would be spinning this motor over 7,000 rpm, we went with a racing oil that is designed for higher rpm use. |  The valvetrain is all Comp...  The valvetrain is all Comp Cams material; components include the stainless steel rocker arms and titanium valvespring retainers. The valvesprings are Comp PN 26094. They have 200 pounds of pressure on the seat and about 460 pounds over the nose. This kind of pressure works just fine with the Schubeck lifters. |