Here is our finished block...
Here is our finished block prior to assembly by T&L. The precision applied to the bores, decking, and align honing is the same that T&L uses for top-series NASCAR engines. Block prep for a production 350-inch cylinder block-a late-model 880 casting in our case-takes on added importance when it's being taken out to 408 cubic inches. We detailed that process in our May 2008 issue (search "Stretching The Limits" at popularhotrodding.com).
Let me ask a question: How would you like to make a cam selection for your engine at least as good as Jon Kaase or Warren Johnson? Also, how would you like to select it in 30 seconds or less? The new V range from Comp allows just that. The way the catalog is structured means that, in essence, you have a top pro engine builder in your corner working exclusively for you. This allows you to select a cam that is very specific to your engine, not just a generic grind for a small-block Chevy engine. To give you an idea as to how easy and accurate this new selection method is, try this for size. My 12-year-old daughter selected this 408's cam in under 20 seconds. The outstanding torque and horsepower results we got amply demonstrate just how effective that cam proved to be.
So what exactly was this "wonder" cam from Comp? The part number was V280-05RSX. All these numbers actually mean something. The "280" signifies the duration at 0.020-inch lift (at 0.050, it was actually 242 degrees). The "05" signifies the last two numbers of the lobe centerline angle (105), and the RSX signifies a Roller, Solid, and Xtreme. This cam is very specific to our requirement. It's intended for a small-block Chevy of 400 to 420 inches in displacement, with cylinder heads having an intake valve between 2.02 and 2.08, and a compression ratio of 9 to 10.5:1. In addition, it also assumes a decently flowing intake and exhaust system. Now if my 12-year-old daughter can pick a cam for an engine that will have its results shown in a national magazine, just think how smart you can look by using this new catalog selection system. (By the time you read this, it will hopefully be up on Comp's website.)
For the rest of the valvetrain, we used a set of Comp's new Gold rockers having a 1.65 ratio. These, when the lash was figured in, delivered the necessary big lift number of 0.600 inch so as to allow the filling of those big, stroked cylinders. The pushrods where Magnums, and the solid roller lifters where Comp's Endure-X design. All this made for a dynamically sound and reliable valvetrain. One last point here is that many hot rodders are shy about using a solid roller on the street. Here you need to know that the opening and closing ramps on Comp's street rollers are such that they will often go as much as 80,000 miles before needing relashing. On top of that, they are way quieter than the roller cams your father used.
Here is our Scat four-inch...
Here is our Scat four-inch stroker kit that turned our 350 into a 408 (Scat PN 1-40576; $2,358.95, Summit price). This kit features Mahle high-tech pistons and Scat's stroker-friendly rods, which offer far greater internal clearance than most rods. This kit comes complete with rings, and as an option from Scat, can be had as a balanced assembly for $250 extra.
Heads, Intake, And Carb
To make power, it's necessary to have heads that flow a lot of air and have good wet flow and combustion properties. Give up anything on any of these counts and the results will be less than you hoped. The heads we wanted to use for our 408 were the 210 Comp Eliminators from Air Flow Research. Part of the rationale driving this choice was the fact that one of my more advanced students from UNC-C built a 350 and achieved nothing short of outstanding results on pump gas using the smaller 195cc runner version of these heads. So working on the premise that reinventing the wheel is somewhat futile, the 210 heads from AFR seemed like the obvious choice. Since there is a lot more to these heads than just another CNC port job, the info for it and our flow tests was gathered together and put in sidebar form, so read all about it there.
After installing the heads with ARP six-point head bolts, the rockers were installed. The Gold rockers are a new line for Comp, with supposedly superior trunnion bearings, pushrod, pivot point, and roller geometry. They are available in the usual 1.5, 1.6, and 1.65 ratios. The ones we used with our single-pattern cam were 1.65:1 ratio, which delivered the 0.600-inch valve lift we sought.
When used correctly, the current crop of air-gap-style intakes are nothing short of highly effective, and the grand daddy (and one of the top players) of them all is the Edelbrock RPM Performer Air-Gap two-plane intake. When fed to full carburetion capacity (which most often it is not), these intakes will deliver some really great street performance figures. But that's not all they do. Allowing for the less-than-direct route the airflow must take, this Performer Air-Gap does exceptionally well. The end result is a top-end not far behind a race intake. But the key to making it all work as we did here is a carb that delivers both at low speed, and has sufficient flow to make full use of this great intake manifold. The carb we used was an AED carb based on the Holley 950-series race carb. With boosters built expressly to deliver a strong signal for good low-speed calibration and mixture atomization (which also helps mileage), our AED carb flowed a wet 900 cfm. The carb was ordered from AED specifically for our application, and came with the jetting so close to ideal (on the dyno), that it defines the real meaning of plug-and-play.
Exhaust
All our efforts toward building power will be to no avail unless the exhaust system is up to scratch. Remember, this is a street motor, and therefore will need to be muffled. For headers, we used a dyno set that T&L's boss, Lloyd McCleary, had previously found ideal for a similar spec 408. This proved to be a stepped header as follows: primary 1 3/4-inch diameter by 9-10 inches in length to the step. From there it was 1-7/8-inch diameter by 22-24 inches to a 3.5-inch collector. Using this as a starting point, our plan was to get the secondary length (the most critical) tuned on the dyno. So that all this length tuning would not be overridden by the effect of a muffler, which the exhaust might see as additional tuned length, it was decided that we would go with a big pair of Flowmasters (PN 953541-10). These 3.5-inch-diameter mufflers have sufficient open volume for the exhaust pressure waves to act as if they have hit open atmosphere. What this means is the header/collector length tuning sees almost no impact, so the engine largely responds as if the muffler was not there. This, combined with a respectably high muffler flow, means the engine can produce near open exhaust power with noise levels more commensurate with street requirements. And since we'll be building a custom side-exit exhaust NASCAR style, we won't really have to deal with snaking a 3.5-inch pipe over the rear axle.