By Jeff Smith/Photos By Jeff Smith and CPR-Engines
It seems that the only engines that get any media exposure anymore in the popular media are 1,000-plus horsepower “street” engines. The problem with those big-power stories is that they do not represent what’s really going on. A turbo motor that can make 2,000 hp isn’t what the average street guy is all about. So we thought we’d follow along on a real street engine that was intended for a daily-driven ‘04 Corvette. Our pal Dan Livezey has been autocross racing for more decades that he cares to remember. Recently he picked up an ‘04 LS1 Corvette that supposedly had been rebuilt, but after a week or so, the motor started knocking heavily.
A subsequent teardown revealed that the LS1 had spun the Number 7 and 8-rod bearings. Dan took the dead LS1 to Martin Marinov at Custom Performance Racing Engines (CPR-E) with a plan to resurrect his engine. The combination they created would bump the displacement with more stroke, a touch more compression with forged pistons, some CPR-Enhanced CNC porting on the stock heads, a mild cam, and a better intake. Of course all of this was hinged on one other critical factor – they had to keep this engine at least appear to satisfy the smog police since Livezey lives in Southern California.
All of these points were essential factors for our build since loads of compression and a big cam just don’t play well when it comes to smog testing. It turns out that Marinov has some experience in this area and together he and Livezey hatched a plan that – because you’ve already cheated and jumped ahead to our dyno test – revealed this 383c.i. combination made an honest 550-plus hp on the dyno. Let’s see how they pulled this off.
Concept and Execution
The easiest way to make more power – even with an emission engine – is to pump the displacement. The only way to do that with any LS1 aluminum block engine is with stroke. The iron cylinder liners barely allow a 3.908-inch diameter bore so Marinov ordered a 4.00-inch stroke crank from nearby Scat to replace the original 3.62-inch version. Retaining its 24x reluctor count, Marinov then added a set of dished AutoTec 4032 alloy forged pistons designed to accommodate a set of 6.125-inch long RPM H-beam rods. The 4032 alloy contains a little shot of silicon to limit piston growth which allows a tighter piston-to-wall clearance, making these pistons much quieter than a typical 2618 alloy piston more commonly found in race engines. These pistons combined with a minor cleanup on the heads produce a 10.8:1 compression, which is pretty close to ideal for a pump gas LS engine.
CPR-E also does all its own machine work, which means the block was subjected to a line hone, simple decking, and a mild honing procedure using Rottler machines to make the block ready for assembly. Final assembly began with a set of King rod and main bearings and DuraBond cam bearings that can take the abuse of the mild increase in spring pressure without pushing out. Once the bearing clearances were set, CPR loaded up the COMP hydraulic roller camshaft and Rollmaster timing set to make sure the cam was where it should be. They also verified the valve-to-piston clearance since this cam is capable of over 0.600-inch valve lift on both the intake and exhaust.
Over their short period of time, CPR has developed a CNC porting package for the cathedral port heads that is pretty impressive. They start by adding a set of 2.02/1.60-inch stainless SI valves, machine the seats to this larger size along with their own multi-angle valve job again using Rottler equipment and then hand-blend the seats to the CNC porting to come up with some pretty impressive flow numbers. We’ve included a cylinder head flow chart that you can study at your leisure with some impressive intake and exhaust flow numbers. When you can squeak out over 300 cfm from a 227cc cathedral port head (200cc is stock), you’re achieving great flow plus maintaining excellent flow velocity, which usually pays off with great mid-range torque numbers as you will see. This LS head upgrade also includes of PAC springs set up with 130 pounds of load on the seat and 370 pounds of open pressure, just to make sure the valves stay where they are directed.
With the heads done, CPR-E wrapped up the engine build and bolted the engine on their in-house engine dyno. They began the test with the factory LS6 intake, stock 75mm throttle body and a pair of 1 7/8-inch primary pipe headers through open exhaust. As you can see from the power numbers, CPR-E’s very mild 383 made some fierce torque, which was exactly the plan. Even down at 3,000 rpm, the 383 thumped 446 lb.-ft of torque with a peak of 516 at 4,800 rpm. The 529 peak horsepower arrived at 6,100 rpm. That alone would have been newsworthy, but then CPR-E bolted on a FAST LSXr cathedral port intake manifold and a 104mm FAST throttle body. Both the new LSXr and the original factory LS6 intakes mounted a set of FAST 46 lb./hr. injectors to make sure the engine didn’t run out of fuel, since the stock injectors promised to be a little on the small side to feed this much power.
With the FAST manifold and larger throttle body bolted on, the 383 again pushed through the power curve and after a little WOT-tuning on the stock ECU, the numbers surged. All you have to do is look at the graph to see how the FAST manifold bumped the power curve up across the entire rpm span from 3,000 to 6,400 rpm. There aren’t too many aftermarket parts that can pull of that kind of broad power magic across a 3,400-rpm span. As for the specific numbers – the most important really isn’t the peak torque at 528 lb.-ft at 4,800 or even the 556 peak horsepower number. The most impressive number is the average 14 lb.-ft improvement across the entire power curve. Add to this a minimum of 500-plus lb.-ft from 3,800 rpm to 5,600 rpm and the fact that the torque never dropped below 450 lb.-ft over the entire curve and those are some outstanding numbers. True, all this comes at a price. The induction package comes to more than $2,000 for the manifold, throttle body, fuel rails and injectors. But short of a supercharger or nitrous, it’s hard to come up with something that can add power across such a broad power band.
That means this engine will deliver excellent drivability and fantastic acceleration while still delivering near-stock idle characteristics. This engine should also be able to pass a California emissions test even with the LSXr manifold in place since it has a California Executive Order (E.O.) number, making it a legal manifold with the smog police. Owner Livezey is currently hunting for a set of headers that also offer the same E.O. clemency. Of course, there’s bound to be a minor power loss when the engine is bolted in the car since it will have to breathe through the Corvette’s street exhaust system but that should present only a minor decrease. Frankly, the torque will probably suffer the least, and that’s exactly what Livezey intends to rely on the most. As we said, Livezey is an autocross racer, so you can expect to see his ’04 Corvette at more than its share of local Los Angeles autocross challenges. Be prepared to discover he is quick behind the wheel!
CPR-E Flow Numbers
This chart compares the stock 243 LS1 cathedral port head with CPR-E’s CNC-ported , 227cc version with 2.02/ 2.160-inch valves, a CPR-E valve job and some minor hand blending. The E/I column is the exhaust-to-intake flow relationship. Generally, the higher the percentage of exhaust flow compared to the intake, less additional exhaust lobe duration is required to help the engine make horsepower.
|Valve Lift||Stock Intake||Stock Exh.||CPR-E Intake||CPR-E Exh.||E/I|
Cam Specs Chart
|Camshaft||Dur. at 0.050” lift||Valve Lift (inches)||Lobe Sep.Angle|
|Stock ’02 LS1 Intake||196||0.479||116|
|Stock LS1 Exhaust||201||0.467||—|
|COMP LSr Intake||219||0.607||112|
|COMP LSr Exhaust||227||0.614||—|
|RPM||TQ1||HP1||TQ2||HP2||TQ +||HP +|
The two tests plot the power difference between the stock LS6 intake and the major torque and horsepower gains offered by the FAST LSXr intake and 102mm throttle body. But don’t overlook how much torque this 383 makes. How many street 383’s on pump gas have you seen that make 500 lb.-ft of torque at 3,800 rpm?
|Scat 4340 steel crank, 24x||4LS140062||Summit Racing||$1,097.97|
|RPM LS H-beam rod, 6.125-inch||LG3-6125LSH||RPM||$388.00|
|AutoTec ring pack. 1.5/1.5/3.0mm||AT4905||CPR-E||$Call|
|King main bearings||MB5013XP||Summit Racing||$135.00|
|King rod bearings||CR807XPN||Summit Racing||$ 67.50|
|DuraBond cam bearings||CH10||Summit Racing||$ 20.97|
|COMP 269 LSr hyd. roller||54-456-11||Summit Racing||$373.97|
|GM LS hyd. roller lifters||12499225||Summit Racing||$124.97|
|COMP rocker trunnion kit/tool||13702-KIT||Summit Racing||$139.90|
|SI Valves, 2.02” Intake||SL-2095||SI Valves||N/A|
|SI Valves, 1.60” Exhaust||SL-1168||SI Valves||N/A|
|PAC valve springs||1211X||Summit Racing||$243.82|
|Romac Rollmaster timing set||CS1135||CPR-E||$135.00|
|Melling Oil pump||10295||Summit Racing||$128.97|
|FAST Intake, LSXr||146302B||Summit Racing||$951.97|
|FAST 102mm||54102||Summit Racing||$509.97|
|FAST LS6 fuel rails, black||146032B||Summit Racing||$247.97|
|FAST fuel line kit||54028KIT||Summit Racing||$124.97|
|FAST fuel injectors, 46 lb-hr||30462-8||Summit Racing||$410-.97|
|Fel-Pro head gasket, left, 0.041||1161L041||Summit Racing||$67.97|
|Fel-Pro head gasket, right, 0.041||1161R041||Summit Racing||$65.97|
|ARP main studs||234-5608||Summit Racing||$266.38|
|ARP head bolts – different lengths||134-3609||Summit Racing||$199.93|
Custom Performance Racing Engines (CPR-E)
Fuel Air Spark Technology (FAST)
Melling Automotive Products
PAC Racing Springs
RaceTec Pistons (Auto-Tec)
Racing Parts Maximum (RPM)