After our first session with...
After our first session with the 950, we switched to the bigger 1050 Ultra HP carb. We use a Racor remote oil filter for all dyno testing since it lets us quickly examine the oil filter for any trash that might be circulating in the motor. You can also see the big K&N flow control air cleaner that we used during the dyno testing.
The Test Mule
The big-block that we're using to test this cam and the Ultra HP carbs were constructed for the "Modern Max Wedge" article that ran in our August '07 issue. This is a production 440 block with a 4.250-inch stroke crankshaft, 6.800-inch long rods, and forged Diamond Racing pistons with a healthy 13.5:1 compression ratio. The cylinder heads are Indy EZ units that were ported by Modern Cylinder Head. In the cross-ram dyno tests, this motor made 620 hp with a Mopar Performance cross-ram and 705 hp with the Indy cross-ram, so we know the basic combination is healthy. The only change we made for this test-in addition to the cam and the intake manifold-was installing a Super Stock-style aluminum oil pan. We filled the new pan with 8 quarts of Joe Gibb's break-in oil since the motor is still fairly fresh. we used our typical dyno combination of a remote screen-type oil filter and a Meziere electric water pump.
On The Dyno
It was a cold day when we unloaded the motor at Gray's Automotive in Tigard, Oregon. With the temperature reading in the low 40s, we knew the motor would be making plenty of raw power. Of course, the correction factor on the dyno output calculations take into account the air temperature, but it is always nice to see the bigger uncorrected numbers since that tells you how much power the motor is capable of making at the track.
After a normal warm-up period and a recheck of the valve lash, we started to make some dyno pulls with the 950 Ultra HP carb. The 950 carb calibration was very close right out of the box with the A/F ratio just slightly on the lean side. We only needed to make one jet change from 78 jets to 80 jets to richen the mixture up, and then saw our best power run of 705 hp at 6,000 rpm and 636 lb-ft of torque at 5,600 rpm.
After making enough dyno pulls with the 950 carb to ensure we had the combination tuned correctly, we swapped over to the larger 1050 carb. We could have bolted on a 440-3 intake manifold with a 4500 flange, but we decided to stay with the 440-2 intake manifold by adding a 4150-to-4500 adapter. According to the guys at Indy, the combination of the 440-2 intake with an adapter makes more power than using the 440-3 intake, so we used the adapter.
We used this Indy Cylinder...
We used this Indy Cylinder Head adapter to mount the larger 4500 flange carburetor onto our 4150-style intake manifold. We also used a low-profile merge plate under the Dominator carb to help smooth out the flow.
Be prepared to spend a few...
Be prepared to spend a few bucks to get a complete kit of tuning parts for these carbs. Not only do you need the normal selection of main jets, but you'll also want a selection of emulsion jets and air bleeds. It is also a good idea to have a selection of gaskets, power valves, pump squirters, and pump cams along when you go to the track.
Lately, we've been using NGK...
Lately, we've been using NGK sparkplugs in our dyno motors. The NGK-5238 is a nonprojected tip plug in a nine-heat range, while the NGK-7405 is a projected tip in the same heat range. We haven't noticed a power difference between these two styles of plugs, although most experts say the projected tip plugs should be worth a few horsepower.
The big 1050 Dominator carb was very rich right out of the box with an A/F ratio of 10:1, both at idle and during the early portion of the dyno pull. We were able to quickly lean out the idle A/F mixture by reducing the size of the idle feed restrictions in the metering block, but getting the fuel curve to stay at 12.5:1 during the entire dyno pull proved to be a bigger challenge. We eventually needed to reduce the size of the intermediate jets by 10 sizes, and we needed to open up the intermediate air bleeds before we got the A/F curve to flatten out during the dyno pulls. Once we had the A/F curve shaped up, the motor responded with a peak of 738 hp at 6,400 rpm and 641 lb-ft of torque at 5,500 rpm.
Well, there you have it. carburetor...
Well, there you have it. carburetor selection is crucial when trying to get the most out of your engine. If you're not sure what carburetor will work best for you, then you need to check out Holley's new Web site. They have an interactive program that asks you the appropriate questions, and then tells you which carb will work best for your application.
Wrap Up
The most obvious result of the carb testing was the 30-plus horsepower gain in switching from the 950 to the larger 1050. A motor like this 505 can really use the extra airflow that the larger 4500-type carb provides, although the 950 carb would still be the better choice for a dual-purpose-type vehicle.
What also impressed us was how easy these Ultra HP carbs were to tune. On a non-Ultra carb we would have had to plug the holes in the metering blocks with epoxy and then drill them back to the correct size in order to correct the A/F curve. Now that we've experienced the Ultra carb, we're tossing our tubes of carb epoxy into the round file!
Finally, we were stunned with how accurate the CamQuest 6 software was in predicting the power output of the two configurations. In both cases, the software was within just a few horsepower of our actual numbers. The torque values predicted by the software proved to be a little optimistic but only by a few percent. We would say this software package is a very good tool to help select cam profiles, as well as giving an engine builder a good idea of just how the motor will perform.