How to fix your V8 (Understanding Engines, Part 2)
After you’ve added an aftermarket exhaust and intake, upgraded the factory valve springs and had a tune done, the next step in NA performance for an LS V8 involves swapping the cam to something spicier than the factory’s bumpstick that has all the duration of a broom handle.
But, when it comes to upgrading the cam don’t just go for the biggest number. In the same vein as yeeting a turbo from a bulldozer onto your mostly-stock two-litre four-cylinder, going “full send” on a race cam in your street car will end in tears and sadness, just like that time Moog made a tuna milkshake.
If you haven't ever looked at camshafts or V8s and wonder what the heck this story is about, maybe start HERE.
While most V8 guys want their car’s idle to sound like the intro to Van Halen’s epic song “Hot For Teacher”, the worst way to pick a camshaft upgrade on your car is by looking at videos of cars idling on YouTube or Facebook and blindly copying them. Too big a cam can push the car at traffic lights, or buck and hop under 2000rpm, so tell your cam supplier about your car’s weight, how it is driven, other engine and drivetrain mods, and how you drive it (in traffic, etc) before you blindly pick a grind.
I had a Holden VF SS-V ute (see above) as a daily and upgraded the cam in the factory 6L LS V8 to a VCM #883 unit (the same unit the boys have fitted to Black Chops in THIS EPISODE). With the factory 6-speed manual it was perfect in the horrible LA-style traffic that Sydneysiders know all about, but it also was great fun at track days, and made over 400rwhp through a restrictive twin 2.5in exhaust.
Since then I have had half a dozen friends cam their Gen IV LS engines in their daily drivers or primarily street-driven cars, and all have ended up with the #883 as the 228/238/113° specs give you a tough-sounding chop at idle with a fat mid-range that pulls hard from 4000rpm up to 6500rpm, and this was one of the big reasons Marty and MOOG chose this spec cam for their Black Chops LS3 E30 BMW.
In LAST WEEK'S EPISODE the lads brought Black Chops back to Brintech, partly to fix some rust they discovered under the brake booster when swapping the LS3 in, and while they had the engine on the bench they decided to throw some extra ponies in there to fatten up the mid-range. They hit up VCM Performance in Melbourne to get a full kit from them, which includes the cam, timing set, lifters and buckets, pushrods and more.
Thankfully because the lads chose to use a 6.2-litre LS3 Gen IV engine this means they didn't have to go through the process of deleting the dreaded "AFM" (Active Fuel Management) or "DOD" (Displacement On Demand) the Gen IV 6.0-litre V8s (L76 andL77, and the 6.2L L99) had for emissions purposes. The good news is VCM sell a full "DOD Delete" kit which provides all the parts required to get rid of this terrible tech, preventing your LS from eating a failing lifter... which often means a full engine rebuild.
The hot sauce for street-driven LS engines, even ones making four-digit power figures, are the factory LS7 lifters. These high-quality short-travel hydraulic roller lifters were fitted by the factory in their 505hp 7-litre track-focussed LS7 V8, as found in the C6 Z06 Corvette, and they’re actually pretty cheap.
Pictured below, you can see why these are called "roller lifters" as the round end rides on the lobes of the camshaft for a lower-friction, smooth transfer of the camshaft's circular motion ("around and around") into a vertical motion (ie: "up and down").
The lifters push the pushrods up and down in their bore, which operates the rocker arms and opens and closes the intake and exhaust valves, so lifters are an integral part of the valvetrain system, and overall engine performance.
When updating the camshaft and lifters, checking the length of your pushrods is mandatory - or using the pushrods which come in the kit, as the lads did. These can come in different lengths (and thicknesses), as the longer the pushrod the more pre-load it places on the valvetrain. However, too long a pushrod and it will hold each valve open (not allowing the engine to start), while too short won't open the valves far enough.
Because the pushrod's fit needs to be so careful, checking the preload on the pushrod is key. The preload is the amount of tension on the pushrod, so don't just bolt it all together and make sure nothing moves any more!
Double-check the pushrods have seated properly as catastrophic damage can occur when they haven’t seated fully in the lifter, often showing up as a bad misfire. VCM’s 7.400in pushrods are used in this application, while tie-bar lifters often require a 7.350in as they are taller, but there can be differences with each combo of cam, lifter and pushrod combo.
Thankfully the LS is a modern pushrod design with hydraulic roller lifters so there is no “break in” period. If you're wondering about the difference between a "tappet" and a "roller" cam, check the image below, which was borrowed from THIS COOL STORY BY SUPER CHEVY
The pushrods work on a "roller rocker", which pushes down on the valve to open it and either allow fuel/air mix into the cylinder, or expel burnt gases out. The cam's lift relates to how far open it pushes the valves, while the duration is how long it keeps that valve open - and the rocker arm can affect this by changing the operating ratio.
For every millimetre of travel from the pushrod, the rocker arm pushes down a larger amount as the tip of the rocker acting on the valve is further away from the centre-line (pivot point) of the rocker than where the pushrod is acting on. The standard LS3 rocker is a 1.7-ratio piece, while many other older engines ran 1.5-ratio and could be upgraded with 1.65, 1.7, or even 1.8-ratio rockers to suit a high-RPM cam.
Fitting the cam and lifter hardware is most easily done by stripping the engine down to almost a short motor, with cylinder heads, valley plate, timing cover, water pump, intake and exhaust manifolds needing to be removed to access the stock lifters and buckets. Upgrading the cam bolts and harmonic balancer bolt to ARP items at the same time, and putting upgraded valve springs in are almost mandatory items, too.
Ensure you have the correct cam gear as some engines need four-lump trigger wheel while earlier engines run a half-moon trigger. If this is wrong the engine can’t pick up the correct firing signal and could start on the third hit of the key or not at all.
Following a cam swap you should have your car retuned before even trying to start it. This is especially true if you’re using a stock GM ECU as there are protections for misfiring built into the factory software which are triggered by an un-tuned cam swap.
With a high-performance cam upgrade most tunes will need some more ignition timing advance and more air-flow, which is why many cammed LS engines end up with a “MAF-less” tune as the air required by the engine with its new cam is outside the scale of the factory MAF sensor.
- Head bolts on some Gen IV engines (L98, L77, LS3, L99) have a lot of sealant on the threads and can be difficult to remove. Chase threads before installing new head bolts as old sealant can cause new bolts to bind and cause incorrect torque settings for heads
- Put a piece of wire through the timing chain and into the guide to hold it in place if you aren’t changing the whole chain and bottom gear piece.
- The cam is always pre-oiled to ensure it slides home without causing any damage to the stick or the cam bearings.
- When playing with Gen IV pistons note the small indent on the front of the piston. This always needs to face the front of the motor, so you know you have it installed correctly.
- It’s easy to crack the timing cover and sump if you don’t fit the timing cover correctly. Loosely seat the case using two side bolts, then tighten the two bottom bolts, followed by the front bolts. The bottom bolts pull the cover down into place and if you tighten the front case bolts first it pulls the bottom of the timing cover off, or snaps the front of the sump.
- When removing the DOD/AFM hardware you change the valley cover to an L98 item without the solenoids underneath. Due to the new plate having an oil breather line out the front this removes the need for the stock breather line from the rear of the passenger rocker cover to the front of the intake manifold. The breather on the rocker cover is capped and a rubber U-line is fitted between the L98 valley plate and intake manifold.
- It can be a good idea to tie-wire the ARP balancer and bolt to ensure they will never come loose or fall out, even after using thread-locking sealant on the bolt.
- A stock LS1 runs a 198/209/119.5 LSA cam, while the L76/L77 twins apparently use the same 200/208/116.5 LSA bumpstick. The supercharged LT4 Gen V motor uses a 189/223/120 cam to increase exhaust duration, allowing the boosted air fully out of the chamber.
- Watch the cam duration on older motors otherwise you’re revving the engine too hard and the pistons and rods won’t like it.