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A Refresh and a Bigger Cam on This LS7 is Worth 661 HP

LS7 Rehab Program

Jeff Smith Sep 17, 2018
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There’s a muscle-bound world of used engines out there just waiting for deals to be made, but you should tread carefully to avoid being bitten. Efrain Diaz recently bought what appeared to be a really great deal on a used Katech LS7 engine. The previous owner was honest—his engine had been rode hard and hung up drenched multiple times and was nearing the point where it would need a rebuild. But Efrain opted to run the engine in his yellow ’69 Camaro for some events in the Optima series before doing a teardown.

After a season of more track thrashing, Efrain took the engine to EVOD Garage in Escondido, California, where engine builder Chris Pollock discovered this rehab was perfectly timed. There were a few damaged parts, but thankfully the rotating assembly was in good shape. Pollock suggested a complete rebuild for the LS7. His initial discoveries included a broken pushrod and lifter. This is not unusual since the LS7 was built to take advantage of a higher peak engine speed. It’s generally accepted that the pushrods on even a stock LS7 should be one of the first things swapped out for no other reason than the 0.080-inch wall performance aftermarket versions are much less prone to deflection and failure.

The next discovery was a hydraulic roller lifter that was trying to push its roller axle straight out the side of the lifter. The lifter bore prevented this cataclysmic event from occurring, but ended up requiring a sleeve. Other damage included loose/worn valveguides and a couple of titanium intake valves that would have to be replaced due to advanced stem wear.

Once the Katech short-block was fully disassembled, the only other surprise was a scored oil pump and the center three main caps appeared to have moved around a bit as evidenced by fretting between the main caps and the main web. With the block cleaned, the machine shop performed a simple line hone, after adding ARP main studs, which brought all the main caps into alignment. This also made setting the main bearing clearance easier. After the crank was polished it was time for reassembly.

Katech’s original pistons employed a gold-coated anodizing that did a great job of preventing wear in the piston ring grooves so the pistons were retained. For a better seal, EVOD selected a Total Seal 1.0/1.0/2.0mm ring package that ensured the cylinder pressure would remain in the cylinder where it will do the most good.

The heads were also slightly abused and required a solid cleaning followed by replacing several of the titanium intake and hollow-stem exhaust valves that revealed excess wear. The new valves were matched with new guides and the heads were checked to verify the installed height of the new valvesprings.

Because this engine would see plenty of abuse both on the street and on road courses and autocross tracks, Pollock spec’d a custom Comp hydraulic roller grind using a 235 at 0.050 intake lobe with 0.610-inch valve lift. The cam basically adds roughly 20 degrees of duration to both the intake and exhaust lobes while moving the lobe separation angle closer together. Factory GM cams for all LS engines tend to be very wide, which reduces the overlap and contributes to a very smooth and stable idle, which is important for a stock factory engine.

Adding duration tends to shift the torque curve higher in the rpm band as evidenced by this engine’s 6,600-rpm horsepower peak. It’s interesting that the stock LS7 cam makes peak torque at 4,900 as did the new, longer duration Comp version. However, the factory LS7 peaks at 6,300 with 505 hp and this new combination cranks the power up to a much stronger 661 hp at 6,600 rpm. This can be attributed to both the added duration and the tighter lobe separation angle.

One of the more interesting ways to evaluate an engine’s power curve is to see how far beyond the torque peak the engine carries maximum torque. One way to do this is to use the 90 percent rule, where we judge the power based on seeing how far beyond the torque peak the engine will maintain at least 90 percent of the peak torque. With a max torque of 585 lb-ft, 90 percent of that is 526 lb-ft of torque. Looking at the power curve, the LS7 is exceptional since it maintains no less than 526 lb-ft of torque from 3,800 to 6,500 rpm. This produces the somewhat flat torque curve you see in the graph.

This makes for a very tractable engine that is smooth and easy to apply the throttle because the power is always there. To put this into perspective, we plugged the power curve into the Quarter Pro dragstrip simulation program. In a 3,500-pound car with a five-speed manual trans, 3.55:1 rear gears, and a really sticky set of 26-inch tall tires, this package has the potential to run 11-flat at 128 mph! This simulation is designed for drag cars, so a Pro Touring car would likely be a bit slower, but low 11’s at 126 are certainly possible. That’s pretty stout for a street engine on pump gas.

While the LS7 isn’t nearly as common as 6.0 and 6.2L engines, it wouldn’t take much more to upgrade an LS3 to nearly these power heights with similar parts. Of course, the edge would go to the larger displacement of the 427 LS7 and the high-rpm potential afforded by parts like the titanium rods. But, with 661 hp potential from a naturally aspirated engine on pump gas these are great days to be a Chevy guy!

Cam Specs
The following specs compare the original factory LS7 cam to a new custom grind that Pollock selected. This is worthy of attention since Comp can very quickly and easily build almost any cam you want based on selections listed in the Master Lobe Profile catalog that’s available online. In this particular case, Pollock selected a grind with an even greater spread between the intake and exhaust and also tightened the lobe separation angle (LSA) from 121 to 113 degrees. This increases the overlap and will add torque in the midrange and additional peak power, but comes at the sacrifice of reduced low-speed torque and a rougher idle.

CamshaftDur. at 0.050Lift (inches)LSA
GM LS7 intake2110.558121
GM LS7 exhaust2300.558 
Comp intake 13047R lobe2350.61113
Comp exhaust 3663R lobe2580.596

Power Curve  
RPMTQHP
3,200441267
3,400467302
3,600499342
3,800524379
4,000543413
4,200550440
4,400563472
4,600572501
4,800585533
5,000584556
5,200578573
5,400575592
5,600575613
5,800572632
6,000564644
6,200552652
6,400539657
6,600526661

Main Parts List  
DescriptionPNSource
ARP main stud kit234-5608Summit Racing
ARP head stud kit234-4317Summit Racing
ARP rod bolts, LS7 2000-series234-6302Summit Racing
ARP crankshaft bolt234-2504Summit Racing
ARP-stainless accessory bolt kit534-9605Summit Racing
Comp cam, custom grind54-000-11Summit Racing
Comp dual valvespring kit, Ti retainers26925Ti-KITSummit Racing
Comp short travel, tie-bar lifters15956-16Summit Racing
Harland Sharp 1.8:1 roller rockers, LS7 offsetSLS78ASummit Racing
Clevite rod bearingsCB663P-1Summit Racing
Clevite main bearingsMS2294-1Summit Racing
Clevite cam bearingsSH2125SSummit Racing
Fel-Pro MLS head gasket, left 0.053"1162L053Summit Racing
Fel-Pro MLS head gasket, right 0.053"1162R053Summit Racing
Melling oil pump, LS710295Summit Racing
Total Seal piston ring pkg 1.0/1.0/2.0mmCS1124125Summit Racing
GM titanium intake valve, 2.200"12591644Summit Racing
GM exhaust valve, sodium-filled12618110Summit Racing
FAST LSXr intake, LS7146202BSummit Racing
FAST 50-lb/hr injectors30507-8Summit Racing

002 427 LS7 Evod Rebuild Comp Dyno 2/26

1. The disassembly revealed several areas that needed attention, but no catastrophic errors were uncovered. The block was cleaned and only needed a mild hone on the mains to bring them back. The engine had been subjected to several seasons of very hard track action, so we expected it needed a freshening up.

003 427 LS7 Evod Rebuild Comp Dyno 3/26

2. The center main webs revealed where the caps had been moving slightly—despite the deep skirt block and cross-bolted mains, so a set of ARP main studs were added to improve the clamp load.

004 427 LS7 Evod Rebuild Comp Dyno 4/26

3. The rod and main bearings actually were not as bad as anticipated, and showed some signs of heat. They will be replaced with fresh Clevite pieces.

005 427 LS7 Evod Rebuild Comp Dyno 5/26

4. The valvetrain did not escape damage. The most obvious was this broken pushrod and lifter. This indicates perhaps excessive rpm or a missed shift that caused some valve float that took out the GM lifter and the corresponding pushrod.

006 427 LS7 Evod Rebuild Comp Dyno 6/26

5. There was also some lifter bore damage that needed repair as a result of a roller lifter axle trying to exit the lifter. This required a sleeve in the lifter bore.

007 427 LS7 Evod Rebuild Comp Dyno 7/26

6. Among the more obvious issues was significant exhaust valveguide wear that would need improving. The engine was running factory rockers and the high lift of the cam was more than likely side loading the valve, which increased wear.

008 427 LS7 Evod Rebuild Comp Dyno 8/26

7. The camshaft also exhibited some wear and would be replaced with a more aggressive Comp Cams version.

009 427 LS7 Evod Rebuild Comp Dyno 9/26

8. There was also a fairly significant amount of wear in the oil pump, so it was replaced with a performance Melling pump. This could have been caused by small metal pieces passing through from the broken lifter and pushrod. In any event, a new pump is cheap insurance given its critical nature.

010 427 LS7 Evod Rebuild Comp Dyno 10/26

9. Since the old cam showed signs of wear, engine builder Chris Pollock decided to change things up with a new custom grind from Comp. The new stick came in at 235/258-degrees duration with lift of 0.610/0.596-inch and an LSA of 113. The grind was 13047R/3663R HR113+2.

011 427 LS7 Evod Rebuild Comp Dyno 11/26

10. After the block was thoroughly cleaned and the bores lightly honed, the machine shop trimmed the main caps and honed the block to bring the crank centerline back in line. The mains were then fitted with new Clevite performance bearings and the clearances spec’d at 0.0025-inch.

012 427 LS7 Evod Rebuild Comp Dyno 12/26

11. The stock, forged LS7 crank survived the abuse intact, only requiring polishing of the main and rod journals before it was dropped back into place.

013 427 LS7 Evod Rebuild Comp Dyno 13/26

12. The original Katech forged pistons, which had been coated, were in great shape, as were the original LS7 powdered titanium rods. The only upgrade was replacing the original rod bolts with new ARP 2000 fasteners.

014 427 LS7 Evod Rebuild Comp Dyno 14/26

13. Rods take a ton of abuse and a broken rod bolt can end your day at the track in a dramatic way. Here you can see the stock GM rod bolts next to the stronger ARP replacements.

015 427 LS7 Evod Rebuild Comp Dyno 15/26

14. After the ring endgaps were custom set, the rings were properly oriented on the pistons and the whole assembly was gently slid in place using a tapered ring compressor.

016 427 LS7 Evod Rebuild Comp Dyno 16/26

15. Because the main caps had moved around, we upgraded to ARP main studs before the block was line honed. The rod bolts were carefully torqued using a rod bolt stretch gauge.

017 427 LS7 Evod Rebuild Comp Dyno 17/26

16. Even though only the rings and bearings had been changed, it’s always a good idea to verify piston-to-head clearance. Most LS engines protrude the piston out of the bore slightly to compensate for the usually thick MLS gaskets. In this case, the piston measures about 0.009-inch above the deck surface.

018 427 LS7 Evod Rebuild Comp Dyno 18/26

17. Next, the new Comp cam was degreed in place using the intake centerline method.

019 427 LS7 Evod Rebuild Comp Dyno 19/26

18. Because the stock lifters fared poorly, the decision was made to upgrade to a set of Comp reduced travel hydraulic rollers. These use tie-bars, eliminating the need for the plastic lifter trays.

020 427 LS7 Evod Rebuild Comp Dyno 20/26

19. The heads were fitted with new valveguides and seals. Whenever doing a rebuild on a high-mileage or hard-raced engine, this is a step you don’t want to skip.

021 427 LS7 Evod Rebuild Comp Dyno 21/26

20. Close inspection revealed that several of the titanium intake valves and a couple of the exhaust valves required replacement due to valve stem wear. Titanium valves are not cheap, but we consider it just the cost of driving hard!

022 427 LS7 Evod Rebuild Comp Dyno 22/26

21. Completing the valve installation is a Comp dual spring and titanium retainer package that should maintain stability through 7,000 rpm. People often choose springs that are too weak, which can lead to valve float and other performance-robbing issues. Chris at EVOD made sure to properly match our springs to the new camshaft.

023 427 LS7 Evod Rebuild Comp Dyno 23/26

22. To ensure all that sought-after cylinder pressure remains in the cylinders, the builders used a set of Fel-Pro MLS gaskets that measure 0.053-inch in compressed thickness. This puts the piston-to-head clearance at about 0.043-inch, which is just about perfect.

024 427 LS7 Evod Rebuild Comp Dyno 24/26

23. With a more aggressive camshaft, the stock factory rockers can have issues. A decision was made to step up to a set of Harland Sharp rockers, and both the intake and exhaust valve-to-piston clearance was verified. Remember, the increased ratio of the LS7 rockers will raise the lift numbers on the cam card quite a bit.

025 427 LS7 Evod Rebuild Comp Dyno 25/26

24. Final assembly included bolting on the FAST LSXr rectangular port intake manifold that is specific for the LS7 cylinder head port arrangement. The intake was finished off with FAST 50-lb/hr injectors and a set of their billet fuel rails.

026 427 LS7 Evod Rebuild Lifter Cross Pin Shift 26/26

Here’s the entire power curve from the test at Westech Performance. The LS7 performed admirably and made excellent power with 661 hp at 6,600 rpm and peak torque at nearly 585 lb-ft at 4,900. With the longer duration intake specs, you can expect the torque to be a little soft, but from 3,600 rpm on up, it never makes less than 500 lb-ft of torque. Those are big-block numbers. Also note that even though it makes peak power at 6,600 rpm it’s still making 651 hp all the way out at 7,000 rpm with zero sign of valve control problems.

Photos by Steven Rupp

Sources

ARP (Automotive Racing Products)
Ventura , CA 93003
800-826-3045
www.arp-bolts.com
Comp Cams
Memphis, TN 38118
901-795-2400
http://www.compcams.com
Summit Racing
800-230-3030
www.summitracing.com
Fuel Air Spark Technology (FAST)
Memphis, TN 38118
877-334-8355
http://www.fuelairspark.com
Evod Industries
760-737-0046
www.evodindustries.com
Federal-Mogul
Southfield, MI 48034
248-354-7700
www.federal-mogul.com
Total Seal
Phoenix, AZ
(800) 874-2753
totalseal.com
Mahle-Clevite
mahle-aftermarket.com

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