The Edelbrock heads and cam combo achieved great torque, but it was apparent that a larger cam, at the very least, was needed to achieve our goal of over 450 ponies in an effort to keep up with our LS1 brethren. But to make good power naturally aspirated, we couldn't simply slap a few random parts together and call it good. Dart's Platinum Pro1 LT1 180cc heads were relatively new and untested, yet looked to be a formidable cylinder head for smaller cube motors. Dart's flow numbers had it on par with some of the best small runner CNC-ported stock castings and even some 195cc aftermarket castings. When we decided to give these $1,080 (bare) beauties a whirl, a call was placed to COMP Cams for its recommendations for a slightly aggressive street roller that would match the heads. After going back and forth a few times, it was decided that a custom grind 224/230-duration XFI roller should pair well and have good street manners. Naturally we would also have to use COMP's complementing 918 beehive valve springs (p/n 26918-16), to eliminate the valve float we were getting with the previous double springs, R-series lifters (p/n 875-16) and 1.6 ratio Pro Magnum roller rockers (p/n 1318-16). Follow along as we head back to RaceKrafters in Lancaster, PA to ring the last ounces of power out of our top-ended LT1.
|DART PRO1 LT1 HEAD FLOW (CFM)* |
|Inch Lift ||Intake ||Exhaust |
|.100 ||71 ||69 |
|.200 ||139 ||102 |
|.300 ||190 ||136 |
|.400 ||231 ||158 |
|.500 ||254 ||175 |
|.600 ||263 ||186 |
|*Tested using SuperFlow SF-1020 flow bench with 28 |
inches of water and 4.030-inch bore.
|Peak HP ||459.4@6100rpm |
|Peak TQ ||422.7@5200rpm |
|Avg HP ||326.66 |
|Avg TQ ||401.16 |
With all of our tweaks, the...
With all of our tweaks, the RaceKrafters 355 LT1 test motor had reached 422 horsepower; impressive enough, yet we thought it was time to take it to the next level.
Our new weapon of choice is...
Our new weapon of choice is the Dart Platinum Pro1 heads, which go for about $540 a piece (in bare form) and $756 assembled (with springs to handle over .600-inch lift). Quality materials are used throughout, including Manganese bronze valve guides and ductile iron valve seats; there is even an available optional DC2 thermal coating on the chambers and exhaust port. Since we had intended to use COMP's revised 918 valve springs for better high rpm stability, we chose the bare version and had Dart send us the stainless steel 2.02 intake and 1.60 exhaust valves separately. A four-angle valve job was performed on the intakes and three-angle on the exhaust.
The smaller runner version...
The smaller runner version (advertised at 180cc) comes as cast with optimized intake and exhaust port shape (note the squared not D-shaped exhaust) for excellent flow wet and dry...
...The chambers are designed...
...The chambers are designed to move the spark plug as close to the top and center as possible for more efficient combustion.
COMP Cams sent us an ideal...
COMP Cams sent us an ideal set of valvetrain components from the custom grind cam and 918 beehive springs to the R lifters, 1.6 Pro Magnum steel roller rockers as well as steel retainers (p/n 787-16), seats (p/n 4705-16) and locks (p/n 648-16), these should really help optimize our combo and add reliability for around $1,000. Initially I had been dead set on using an off-the-shelf XFI grind, but after much consideration I felt a 224/230-duration roller would better bridge the gap between Comp's largest street grind and its smallest race/stroker grind. Using the new designed lobes with .574/.569-inch lift and 113LSA seemed to be the best way to take advantage of these new heads, and still have some street manners.
Off came our 1.5 ratio aluminum...
Off came our 1.5 ratio aluminum Summit roller rockers, these would not be reused since 1.6s were needed with our new cam...