Quote (FMX_89 @ Dec 30 2014 06:21pm)
What you need to be prepared for before you buy a C6 Z:
The good: The LS7 is a great engine. It's a 427ci (7.0L) N/A Gen IV V8 with titanium rods, a dry sump oil system, and really, really high flowing cylinder heads. Out of the box they flow the same air as a "good" set of aftermarket aluminum heads for a big block Chevy. The thing turns 7,000RPM safely. It is a monster. With a bigger cam and a set of headers you can make 550whp, run it on pump gas, and drive it every day.
The bad: The LS7 heads have a valve geometry problem from the factory. GM's official stance on the matter is that it only effected a small number of cars in the 2007 model year. The company that makes the castings for GM is at fault for the flaw, and GM is at fault for not catching it in QC or engineering and for refusing to acknowledge just how big of a problem it is. The severity of the issue varies from car to car. Over time the improper valvetrain geometry wears out the factory powdered metal valve guides. This allows the valve to wiggle and move in ways that it shouldn't. Once the guide starts to wear it accelerates rapidly. Some people notice noise at idle. Others do not. The end result if it goes unchecked is a valve will drop which will take out the piston on it's next up stroke and it will usually window the block (think put a big hole in it.) GM has been pretty good about replacing engines under warranty due to this problem. Once you are outside of warranty it becomes a battle with the dealership and the guys at the corporate level since they have never actually admitted it is an issue that effects all of the LS7's. Some people claimed they fixed the issue in 08 or 09. The fact is people have bought crate LS7's from 2013 and found the valve guide wear to be an issue after 15k miles.
The fix: This is a hotly debated issue. For a while the go to fix was to pull the heads off the car, ship them to someone well known for working LS7 heads like WCCH, and have them machine the heads for new bronze guides, replace or polish the titanium intake valves, and install aftermarket stainless steel exhaust valves. Most people opt to have them port the heads while they are there which adds around a grand to the price tag but saves a lot of time and money if you had planned on doing heads and cam later on down the road. Katech, who has been a developmental partner with GM for years in their endurance racing efforts posted Spintron results on corvette forum that turned this idea upside down. This is the hotly debated part. Their results showed that the extra weight of the stainless exhaust valves combined with the stiff aftermarket spring required to run that heavy valve with an aftermarket camshaft was NOT stable over 6000rpm. That is troublesome on a 7000RPM engine that people routinely turn 7500RPM with an aftermarket cam. Their solution is sodium filled hollow stem exhaust valves. They are much lighter. They are also much more expensive. That adds about $1500 to having the heads redone. Lots of people say it is unnecessary and many people are out there running the bronze guides and stainless valves. The worst part is we are starting to see that the guide replacement and machine work don't truly fix the problem. Guys are getting premature wear on their bronze guides. It takes a long time to see things like this because the average C6 Z gets driven 3-8k miles a year.
The "True" fix is to get rid of the stock heads altogether. This is expensive up front but there is a pretty big demand for factory LS7 heads from guys using them for drag racing or from those that don't care about the valve guide issue. You can recoup most of your money by selling them. The most affordable option is to buy a set of Brodix LS7 cylinder heads. They aren't well known in the LSX world but they make top tier SBC and BBC heads. They started producing an LS7 copy just a few years ago. It is almost identical to the factory head. The few minor differences allow for more aggressive porting. They do not suffer from the geometry problem of the factory casting. All of the valvetrain parts swap right over to the new heads. Going this route will end up costing you $3500 all said and done. Of course this depends on what valves and springs you choose. Most people that get the heads addressed right after buying the car do not cam it at the same time. Personally I would do it while the heads were off but vette guys are weird. To a lot of people an under rated 505bhp in a 3200lb car is plenty as is.
Thanks to all of this and the roaring road noise of the huge tires, complete lack of sound deadening, and balsa wood construction they really don't make good daily drivers. It's a purist sports car. Big N/A V8, RWD, 6 speed manual trans, as little weight as possible.
I'll have one one day.
Awesome info. I knew a little bit about the issue but it makes way more sense now.
And as far as a DD I completely agree. Here in California cruising one around in 100+ degree weather isn't all fun and games. Like you mentioned with the lack of sound deadening and insulation it gets mighty noisy and hot inside the car. The cup holders become useless unless you plan on keeping your hot chocolate warm.
That being said I believe I will own one someday just not as a DD.