LS3 / L99 Heads, Cams, and Intake Manifolds
part 1 : the mule
The test “mule” was a stock LS3 apart from a set of Diamond PN#11545 pistons with 2CC valve reliefs. This allowed us to experiment with different cam profiles and head combos without dealing with PTV during testing.
We baselined the set up with a stock intake, cam and heads. We calculated the CR at 10.36 on a 70 cc chamber using a stock .051 gasket and 11.1 with a 66 cc chamber and .040 gasket. We used the Holley Terminator controller and harness for our ignition and fuel management. This was done for not only its ease of set up but for its closed loop wide open power enrichment feature which maintained a spot on 12.8 to 13.0 air fuel ratio during over 70 dyno pulls to 7000 RPMs. Since we were making mechanical changes which effect volumetric efficiency we didn’t want to have to dial the VE in after each change. It also enabled us to display and log all our critical engine functions such as fuel and oil pressure without having to plumb extra analog sensors to the dyno. We had the engine on the Dyno and fired up in no time. We also used a 92mm mechanical throttle body which is a more compatible with an engine dyno than drive by wire.
…the old mule baselined at 493 @ 6000 RPMs and 500 Lb ft of torque @ 4600 RPMs. Remember, no accessory load, no induction or exhaust restriction and an ideal header configuration.
part2 : camshaft testing
Our first order of business was to dial in our SS3 three bolt product which runs a close second in sales only to our SS3 VVT. Our colleagues at Cam Motion supplied us with a selection of grinds featuring our GPI/GPX proprietary lobes ranging from 229 to 235 degrees’ duration on the intake side. The exhaust varied from 245 to 252 degrees’ duration. The lobe separation ranged from 111.5 to 116 degrees and all net valve lifts were in the mid 6s. We labeled these T-1 thru T-5 as shown on the charts.
At GPI we are constantly looking for opportunities to improve our products, making our customers faster and more reliable. If we ever stop doing this our customers should fire us.
The overlay resembles a piece of yarn at first glance but when we crunched the numbers we were able drill down what would be our latest greatest SS3 camshaft. All tools have their purpose and place, a chassis dyno is a great tool for tuning and measuring installed systems such as induction, exhaust. Spintrons allow detailed measurements of valve train systems and components not possible by any other means.
An engine dyno however is essential for measuring minute changes in power and power curve independent of chassis and environmental effects. Then certainly what happens at the track keeps us all honest and is the ultimate return on our efforts. T4 and T5 peaked within 3 HP of one another with T5 actually holding its head up a bit better after peak but the 11 lb ft of torque sacrificed in the mid- range makes T4 the best choice for the majority of our clients. Well over 100 HP gain with a camshaft you can daily drive isn’t a bad day’s work in any case.
…well over 100 HP gain with a camshaft you can daily drive isn’t a bad day’s work in any case.
part 3 : intake manifold porting & rod mod
We have often wondered and been asked if porting in addition to the radius rod addition would impove the LS3 manifold. We figured it would be a great time to find out – so Mike and Ryan quickly built 2 manifolds, one with just rods and the other with the stands removed and ported. Both we and our customers have tested the radius rods on chassis dynos and at the track many times and usually see from 6 to as much as 12 RWHP. We were quite frankly disappointed with the results but it is what it is and we pride ourselves on our brutal honesty. The most we saw was 11HP at 6600. Running no induction system and a cable throttle body which pivots the opposite direction may have some unknown effect we don’t understand but here it is look for yourself. You will also notice we left the T5 cam in for the remainder of the tests in the interest of time and we were sick of swapping cams. We thought we were going to be slick and cut a timing cover in two for quick change only to discover the Camaro balancer we were using would not allow the cam to clear. Epic fail! If anyone is in the market for a nice two piece cover we have one available.
We thought we were going to be slick and cut a timing cover in two for quick change only to discover the Camaro balancer we were using would not allow the cam to clear. Epic fail! If anyone is in the market for a nice two piece cover we have one available.
The ported version looked quite a bit better, this time we were disappointed with the positive result as the porting is very labor intensive and it’s probably going to be requested a lot going forward. We didn’t find significantly more peak power, but we got it everywhere and the midrange torque increase was worth the effort. The only negative is after the porting the manifold it is structurally impaired for any future forced induction applications.
part 4 : gpi Cylinder head testing
Our goal here was to determine how our heads responded back to back in comparison with some leading ported LS3 heads on the market as well as determining how much power our chamber work is worth since we consequently must increase the chamber volume. The third thing we wanted to determine was value of a little squeeze. Would working out the clearance issues be worth the gains on the average pump gas LS3?
Our objective here is not to make a competitive product look bad, as we respect the work of the good folks who bring them to market, so we have labeled the heads we tested with letters. We did note the approximate intake runner volume and tested like chamber sizes for a more valid result. If our heads suck we really wanted to know.
The first head we tested, which we will refer to as brand “Y’, was a nice looking 280+ cc runner GM casting using OEM LS3 valves. It has a CNC chamber measuring a tad over 71CC. We figured the midrange would be a little weak on a 378 cid engine due to the port volume. We find that when people start racing flow benches sometimes the end result isn’t as expected.
This head performs well on the bench and may well look better on a larger engine but didn’t do the LS3 much justice. It picked up about 10 HP at peak while losing 20 lb ft of torque thru the mid range. Now granted it was lower on compression by 1 cc than the stock head but we failed to find that equated to 20 lb ft of torque. Because we were dealing with varying chambers and compression ratios we bumped the timing in both directions up to 2 degrees to find the happy place. We also made sure the coolant and oil temperatures were the same within a few degrees. Again, this was to learn and improve rather than generate propaganda. If however at the end of the day we sell a few heads and cams I can live with that too!
We find that when people start racing flow benches sometimes the end result isn’t as expected.
The next head we tested we will refer to as brand X. It has a runner volume in the 270s and had already been milled to 66cc. We will never know how it might have fared against the brand Y on a level field, as we didn’t have an expediant way to find out. All the same it gave us our first real glimpse during our testing to see how compression sensitive our mule would be. We figured we could test our 268cc ported and chambered head at 70cc against our non-chambered version and the stock head. Then start milling to compare with brand X. Below are the results as compared to stock, of our GPI chambered and non-chambered.
What we learned here is that our heads on equal compression picked up an honest 20hp non-chambered and 25hp chambered without giving up any appreciable midrange, thus the beauty of a smaller intake runner which can maintain air speed on a smaller displacement engine such as a LS3. We also observed that the chamber work was paying off. We noted that the chambered head did not require more or less spark advance than the non-chambered, not what I expected. Below are the results of the GPI 268 chambered heads compared to the brand X at the same compression ratio.
What we learned here is that our heads on equal compression picked up an honest 20hp non-chambered and 25hp chambered without giving up any appreciable midrange…
The best power opportunity so far seems to be with our 268 cc runner with chamber work and some additional squeeze. This graph illustrates the gain over stock at 66cc. We netted 34 HP over the stock head while improving torque above 4200 RPMs without appreciable loss below.
We netted 34 HP over the stock head while improving torque above 4200 RPMs without appreciable loss below!
Now for the cathedral vs Rectangular port show down. We were fully prepared for this bad dude Trick Flow to do some damage and it didn’t disappoint. We have ran these things on some forced induction and nitrous builds that did the work. In our minds however, after the dust settles our good ol LS3 factory casting with a little GPI magic and an OEM intake is a great choice for the average LS3 owner! Our next step based on this testing will be to work out a solution to achieve improved compression on the SS3 equipped LS3 and L99 without fly-cutting valve reliefs or perhaps do a better job taking the mystery and tension out of the fly- cutting process.
…after the dust settles – our good ol LS3 factory casting with a little GPI magic and an OEM intake is a great choice for the average LS3 owner!
part 5 : in closing
I would like to take this opportunity to recognize and thank our team members and support network. To Ryan Stevens the best calibrator and envelop pusher I know. GPI would likely be bolting on headers, blowers and someone else’s camshafts without your passion and never ending persistance to reach higher and go faster. P.S. you still owe for those half dozen engines you destroyed trying to find another tenth! To Scott Sanders “Mister Corvette”, Mike Pestka who we can always count on, James Zajac, “Mister street rod”, to “where is my parts” Nathan Moore, and my right hand for a long time, John Sims. Thanks to Josh Hamilton for his efforts in parts sales and our soon to be launched new web site. To our friend and comrade Jim Kuntz for your wisdom and seemingly never ending intuition on air flow, port shape and all things that equal horsepower. A big thanks to the following great people and companies: Kip and the Cam Motion crew Rick Anderson and the Holley Team Randy Curtis and Diamond Pistons The Kuntz and company crew Lance Smith and Craft Performance engines Brian Tooley Racing Comp Cams Harold Gwatney, Jamie Cobb, and the Gwatney Chevrolet crew Everyone else I have forgotten!
Our next series of tests will focus on the LS7 and LT1 so stay tuned…
Chevrolet Performance LS3 Camshaft Dyno Test
Uplifted: A few parts net big gains in our Chevrolet Performance LS3 crate engine
If you want a fresh powerplant, nothing beats the ease and value of a new crate engine. But, since many of us always crave "just a bit more power," it's nice to know it's only a few speed parts away. In this case, we started with a 430-horsepower Chevrolet Performance LS3 crate engine. Of course, 430 should be in quotes because it's conservative, very conservative. Part of this is because Chevrolet dynos to a different correction factor than the rest of the aftermarket world. So, right off the bat our dyno numbers are higher. Add in that they dyno through factory exhaust manifolds and the real-world power numbers are always higher than the advertised ones. But hey, under-promise and over-deliver always leads to happy customers.
Still, as good as the power output is, it is easy to extract more performance out of the LS3. One key area is the camshaft. The one provided by Chevrolet is on the conservative side at 204/211-degrees duration at 0.050 and 0.551/0.522-inch lift. Those specs are great if you're concerned about silky smooth idle and emission requirements, but if your Corvette isn't worried about those things then a more aggressive camshaft can really wake up the already potent LS3. To find out just how much power is waiting to be unleashed we decided to baseline the crate LS3 and then toss in a moderately aggressive camshaft. After all, it's a modification that's relatively easy to do and it doesn't require pulling the heads or cracking open the short-block. So, follow along as we attempt to squeeze a few more horses out of an LS3 crate engine.
01. Our starting point was a new Chevrolet Performance 376-cubic-inch (6.2L for the metric crowd) LS3 crate engine (PN 19301326). At $6,200 it's a lot of bang for your buck and the perfect upgrade engine for your earlier model Corvette.
02. The biggest problem with getting this new crate engine into a Corvette is that it shipped with a Camaro oil pan. We were able to order replacement parts and sell off the stock parts, so swapping to a C5/C6 Corvette oil pan only cost a couple hundred bucks. If you're transplanting into an older Corvette, then companies like Holley make oil pans to clear the various crossmembers.
03. One of our favorite shops for niche products is Improved Racing. In this case they had a complete oil pan swap kit that included a C6 oil pan, gasket, hardware, racing oil pan baffle, crank scraper, dipstick tube, dipstick, pickup tube, and oil filter bypass. In other words, the kit (PN EGM-464, $665) comes with everything you need to swap from whatever pan you have to one suitable for your C5 or C6 Vette. The included crank scraper replaced the windage tray (in this application) and helps reduce oil starvation by draining more oil to the bottom of the sump. As the name implies, it "scrapes" oil off of the crank, reducing parasitic drag, and can net an extra 2-5 horsepower. This one works with a factory (3.622-inch stroke) crank, but they just came out with a stroker version.
04. The key player in the kit was this badass bolt-in oil pan baffle. LS engines are prone to oil starvation at high g's. The main culprit is the GM oil pan baffling, or more accurately the lack of baffles. Improved's system adds track-tested directional trap doors and offers improved drainback and oil control over the stock baffle. According to Improved Racing, it's sufficient to prevent oil pressure drops at up to 1.4 sustained lateral g's. It simply bolted into the factory pan.
05. And here she is with the new C6 oil pan in place. With this done it was time to hit the SuperFlow 902 dyno over at Westech Performance.
06. We wanted to dyno the LS3 with a set of C5 headers from JBA Performance, but as you can see they fit a Corvette, but not a dyno. Hey, that's better than the other way around!
07. With a set of Westech's headers in place (with mufflers), we started tuning for a baseline number. The test was run on Rocket 91-octane gas and we used a Holley HP computer, along with their cable-actuated billet throttle body.
08. After nine tuning pulls we nailed down a best run of 494 horsepower and 482 lb-ft of torque. The numbers might sound high, but remember that we're running long-tube headers, aftermarket EFI, and we picked up a few ponies from the oiling system improvements. Also, there's the legendary GM "under rating," which is mostly due to the different correction factor they use.
09. The plan was to add a bigger cam, but to keep everything happy that meant we needed to upgrade our springs as well. After a little math we came up with COMP's dual valvespring kit (PN 26926TS-KIT). This valvespring kit came with tool steel retainers, 7-degree steel valve locks, valve seals (which we didn't use), and spring seats. Max lift for these springs was listed at 0.675-inch.
10. After pumping the cylinder full of air to keep the valves from dropping we started removing the stock blue springs and installing the COMP pieces.
11. Trust us, the air method is the way to go and much faster than raising up each piston to hold the valve up. For extra peace of mind, we upgraded the stock LS3 rockers with COMP's LS trunnion kit (PN 13702-KIT) and added Hi-Tech 7.4-inch hardened pushrods (PN 7955-16) to the mix. These two parts don't add any power, but they do add reliability if you're going to be running the engine hard.
12. To swap cams, we had to remove the timing cover, and to do that we had to pull the damper. Remember that the crank bolt is torque-to-yield and shouldn't be reused, so pick up a spare from GM (PN 12557840, $6) or buy a reusable one from ARP (PN 234-2405, $32).
13. The stock single-bolt LS3 cam was then removed from the crate engine.
14. What stick you decide to stuff in an engine will ultimately determine its personality. Go super aggressive and you'll make more power, but it won't be happy cruising around town. We consulted with the cam gurus over at COMP and came up with a profile that should yield gobs of power and have nice enough manners for a Sunday cruise. The final specs on the cam were 227/243-degrees duration with lift numbers of 0.613/0.623-inch on a 113 LSA (PN 54-454-11). LS3 heads just love these big-split cams.
15. Our new cam was a three-bolt style, so we hit up Improved Racing for the proper four-pulse timing sprocket (PN 12586481, $20). With this installed we buttoned up the engine and started tuning for the extra power we were expecting.
16. Seven pulls later we were rewarded with a best pull of 555 hp and 507 lb-ft of torque. The new cam made a ton more power, especially over 5,000 rpm.
17. Actually it made more power and torque over the entire pull with peak gains of 61 hp and 25 lb-ft of twist. The cam, spring kit, pushrods, and sprocket set us back $1,050 and we feel the performance gain. Put this in the good bang-for-the-buck category.
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Why were we so excited about swapping cams on the all-aluminum L92?
The first was that we had previously run the Summit Stage 4 Pro LS cam (SUM-8711) successfully on a smaller 5.3L. In fact, we broke the 500-horsepower mark with that cam on the little LM7, so we naturally had high hopes for the larger 6.2L.
We also liked the fact that the cam test on the 5.3L was run with ported cathedral-port heads, while this 6.2L L92 featured factory rectangular-port heads.
There is a lot of misinformation about cam profiles favoring one head design over another and it would be interesting to see how well these cam specs worked on each application.
In addition to the difference in displacement and cylinder head design, we enjoyed the refreshing change from running another junkyard 5.3L. The all-aluminum LS engines are hard to come by in the junkyard, as they are quickly snatched up by savvy enthusiasts and resell companies. Most of all, we were excited to see if the extra displacement and head flow allowed the healthy Summit cam profile to shine.
Full disclosure, the L92 test mule did not belong to us, though our good buddy Jason Trejo at Fort Meade, FL-based JTFab, gave us permission to go wild with it.
We’re sure he had boost and/or nitrous in mind, but we decided to start on the mild end of the destructive scale, with a simple cam test. After all, even though the L92 offered plenty of displacement and head flow, it, like all LS motors, was in dire need of a cam swap. Even if nitrous and boost happen to follow, every motor deserves to produce decent power before the adders come into play, right? To prep for our test, the loaner L92 required a few changes, namely removal of the VVT and DBW throttle body.
The Holley HP management system did not allow us to run the variable cam timing so it was replaced by a fixed LQ4 cam. Likewise, the DBW throttle body was ditched in favor of a manual 92-mm FAST throttle body. The final two changes prior to testing included replacement of the factory exhaust manifolds with long-tube headers and the installation of a dual valve spring kit from COMP Cams. The healthy Stage-4, Pro LS cam certainly required a spring upgrade.
After our changes to the stock engine, the rest of the test was a breeze.
All that was necessary was to dial in the tune on the LQ4 cam, then perform the same procedure after swapping in the Summit Stage 4 cam.
Speaking of the Stage 4 cam, the Summit grind was a healthy customer with a .625/.605-lift split, a 234/247-degree duration split, and 113+3.5 LSA.
Summit offers two different Stage 4 LS cams.
Compared to the slightly more aggressive Stage 4 LS grind (SUM-8709), which offered .625/.605-lift split, a 237/246-degree duration split and 113-degree LSA, the Stage 4 LS3 cam (SUM-8711) offered slightly more (.015) piston-to-valve clearance.
This is important for LS guys looking to mill their heads.
Initially, we chose the Stage 4 LS3 cam to ensure adequate piston-to-valve clearance and to work with the LS3-style heads. The increased piston-to-valve clearance was a given but, given the success of the LS3 cam on the cathedral-port 5.3L, our concern for matching the cam profile with the respective port style seemed all but unwarranted.
Could it be possible these cams work well on both heads? There we go, opening Pandora’s box!
By no means was the LQ4 cam an exact replacement for the stock VVT cam.
First, the fixed cam didn’t benefit from the extra power offered by the advance/retard features of the VVT, but we needed a starting point for our cam test.
The Holley HP ECU wasn’t able to control the VVT cam, so we swapped it out for the LQ4 to establish our baseline. Run with the 1 7/8-inch headers feeding the 3.0-inch exhaust, the LQ4-equipped L92 produced peak numbers of 445 hp at 5,600 rpm and 460 (459.9) ft.-lbs. of torque at 4,600 rpm.
With our baseline established, it was time to upgrade the cam.
With the Summit Pro LS Stage 4 cam, the peak power numbers jumped to 568 hp at 6,700 rpm and 510 ft.-lbs. of torque at 5,500 rpm.
Note that the wilder cam timing pushed peak power higher in the rev range, but did so without a loss of low-speed torque. The Summit cam out-powered the LQ4 cam even down at 3,200 rpm.
This doesn’t imply that the more-aggressive Summit cam will offer the same idle vacuum or torque production at 2,000 rpm, but it does show the versatility of the bigger cam.
Upstaging a stock cam with big power gains is always welcome, and adding 123 hp certainly qualifies as big, but the gains are even more impressive when they come with no loss in power down low.
Author: Richard Holdener Richard Holdener is a technical editor with over 25 years of hands-on experience in the automotive industry. He's authored several books on performance engine building and written numerous articles for publications like Hot Rod, Car Craft, Super Chevy, Power & Performance, GM High Tech, and many others.
Originally Posted by kevin2323
noob question do all states have emission laws?
I don't agree with the rules, but they state the the factory catalytic converter(s) must remain intact and in the factory position(s). The converter are so far forward on most cars that there isn't room for long tube without breaking that rule.
The reason the rule exists is so that cold-start catalyst light-off is not delayed by the additional exhaust tubing length between the heads and converters. Also, the oxygen sensor has to be in the flow post-collector. Long tube headers require that the sensor be moved further downstream since the collector is further downstream. The further from the head ports the oxygen sensor get the more "lazy" they get since they're measuring the output from operating conditions "too old". Basically you end up with bad data and that affects emissions too.
So, YES - long tube headers absolutely fail visual inspection by definition.
Long tube headers themselves have minimal effect on actual emissions, the problem is the latency induced by the greater exhaust gas travel to the O2 sensors. Generally, they WILL pass the sniffer because there is very little affect at constant sustained throttle conditions where these test take place at on t he dyno.
Of course, legal headers must acommodate all factory emissions eguipment like EGR, A.I.R., O2 sensors, etc.
Hey big man let me hold a dollar
Cam dyno ls3
.Dyno Tuning my Camaro SS with the GPI SS3 cam- New Power Numbers!!
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