If you're interested in a pump gas, big-block Chevy street driver that makes a very stout 1.3 lbs-ft of torque per cube along with enough hp to put a John Deere tractor into the 9's then this build might be for you. Add its cost conscious budget and good looks, and it could be just what you want to see in your street machine.
The beginnings of this engine came when Kevin Feeney, RHS's expeditor of all good things related to cylinder head production, called and asked if I would like to test its then-new street big- block Chevy head. I had this feeling that I could get pulled, even against my better judgment, into just about anything that looks exciting, so before engaging my brain my mouth is already up and running. "Sure, just send me a pair and I will take it from there." Well about the time the heads arrive I realize that it takes a little more than just having a dyno-I also needed an engine.
That was the not so good news. Fortunately this was countered by the fact that I know a ton or more of top-notch engine builders. Lloyd McCleary of T&L engines, who is a bonified NASCAR engine builder who has had great success on the track at the top levels of competition. Lloyd had a line of dyno proven big-block Chevy crate motor builds that range from 454 to 640 inches so the plan was to use the heads on one of these. The RHS heads targeted big-block Chevys in the displacement range from 454 to about 540 inches so to be as near representative of both ends of that spectrum a 505 inch engine was chosen.
Block & Rotating Assembly
To get 505-inches with the planed 4.25-inch inch stroker crank required a block that would bore safely to .100-inch-over, bringing the finished bore size to 4.350 inches. Lloyd had a block in his inventory that, after sonic testing, showed it would go to this size with meat to spare. Unfortunately it was a 2-bolt mains block so the first job here was to install 4-bolt steel mains caps. After this the block was decked true to the mains then bored and deck plate honed. When all the machine work was done the block went through a detailing procedure to remove casting flash before being finished in high-gloss engine enamel. The last step was to install the Calico-coated cam bearings and the block was ready to start accepting the rotating assembly.
The engine was destined to go in a street rod that also needed to be capable of fast passes down the strip. For this build the owners also needed 650 hp and 7000 rpm capability. This requirement meant that a very cost effective rotating assembly could be specced out. For the crank, a Scat 9000 series cast steel 4 1/4 stroker crank was chosen. These have proved more than reliable in such applications to power levels of 750 or so horses. Because they use so much Scat stuff, T&L can do a good deal on rotating assemblies, either cast or forged. With their hollow journal, windage-reducing aero design, the Scat 9000 series cast cranks represent a very viable performance upgrade for any 454.
After balancing the rotating assembly, the crank went into the block with Calico coated main bearings and the caps installed using ARP 6 point mains bolts. The rods used were Scats street/strip forged H beam 6.385-inch-long (0.250-inch longer than stock) rods featuring all the goodies seen on race rods. These were chosen in part for their high strength and for having less weight than may budget orientated H beam rods. With less weight in both the rod and the chosen piston, from Ross, the bottom end balanced up without the use of expensive heavy metal slugs.
For the pistons it was necessary to have Ross make us up some custom items so we could nail the 10.5:1 compression ratio with the RHS heads right on the money. We were rewarded with a nice looking set of pistons that weighed in at a very respectable low weight. By using the 250 long Scat rod with the 4-1/4 inch stroker crank the stock rod/stroke ratio was almost maintained and left a compression height of 1.165 inches. With the 1/16 - 1/16- 3/16 Total seal ring pack being used, the pin bore intruded into the oil ring groove necessitating the use of a steel support rail type oil ring assembly. The rings used for this engine were from Total Seal.
Cam and Cam Timing
When it came time to select the cam for this engine, the heads were already ported and the flow characteristics throughout the lift range known. Using the latest version of the Cam-Master program the valve opening event timing was computed for the 6200 rpm to peak power called for. To give an idea of how accurate this program is the dyno tests showed peak power to be within 100 rpm of this computed value.
As for the profiles themselves, this was decided after it was learned from Comp Cams math whiz kid Billy Godbold that some of his relatively new NASCAR Busch series solid roller profiles would meet our needs. Top of the "need-to-have" list was reliability with high lift. This meant the use a moderate spring so the dynamics would have to be something special if the high lift requirement was to be met. We also needed a reasonably quiet valvetrain because it is a street rod we are powering here not an open exhaust Busch Grand National car.
The eventual profiles chosen were not of overly long period but they did get with the program in terms of opening and closing rate. For the intake, an SP-series roller with an advertised duration of 279 degrees was chosen (profile #4788); for the exhaust a slightly less aggressive RP profile of 284 degrees advertised duration was selected. These, with 1.7:1 Comp Cams rockers, delivered a gross valve lift of 0.653- and 0.648-inch respectively. As short as these profiles look at the 0.020 lifter rise used for the quoting advertised duration, they are longer by about 14 degrees at the lash point. This makes the seat duration, at 293/298 look a little on the long side for a street cam.
This would be the case if big-block Chevys had more appropriate valve sizes for the displacement involved but the truth is they are grossly under-valved. This makes them less sensitive to the negative effects of long duration cams or, putting it another way, any duration figure looks a lot smaller (by typically 10-15 degrees) in a big-block than in a small-block.
With the lobes selected, Cam-Master was used to determine the Lobe Centerline Angle. With the figures input a result of 106.5 degrees was called for so we settled on 107. This was ground at 4 degrees advance. Motion from the cam profile was transmitted to the valves via a set of Comp Cams Endure-X solid roller lifters, 3/8th Magnum pushrods and aluminum 1.7:1 rocker arms.
After loading the cam into the block it was timed in. An important fact is that the more accurately a cam is specced out the more it can lose by being incorrectly timed into the engine. To make sure the cam could be timed right on the money a Comp Cams fully adjustable cam timing set was used. This allowed us to hit the required 103 degree intake centerline required right on the money.