Thread: Stock L36 + Boost =

Thought you guys would get a kick out of that picture so I just had to post it. But it does tend to bring up heated debates.

I've been to college for this stuff, specifically hi-performance automotive. But beyond that, there's logic; and there's an understanding of what impact the bean-counters and emissions standards have on automotive design, materials usage, and build quality. Combine these factors and it's not hard to conclude that if an engine didn't come from the factory with boost, it probably won't be able to take much before buying the farm.

One very important thing I learned in college was there are two ways of doing things: the cheap way and the right way. I have seen a lot of people in the 3800 community try to do things the cheap way; but in the end they end up spending a lot more money just to be disappointed and would have saved money in the long run if they would have just done things the right way from the start. I'm sure trannyman can attest to this when it comes to people trying to put highly modded engines onto stock trannys.

Specifically what I'm talking about in this thread is the tendency of some people to want to put boost on their stock L36's. The L36 is a fine engine, but to put it bluntly, it just isn't designed for boost. Sure it shares the same block, crank, and same casting heads as its boost-friendly counterpart, the L67. But the L36 has much weaker connecting rods, pistons, and piston pins than the L67. These parts were simply designed to be as light (and cheap) as possible to meet emissions and get the job done (without boost). Having said that the stock L67's parts aren't perfect either. They are also a compromised design in order to meet emissions.

Emissions standards have forced auto manufacturers to make compromises for years when it comes to engine design. One of those compromises is in piston design; specifically sealing ring placement. On BOTH the L36 and the L67 piston, the ring package is very tight and located very close to the top of the piston. This helps keeps as much of the combustion gases above the piston (and not around its sides) as possible. But the drawback here is it exposes the top sealing ring to more heat. And when you throw in a very tight ring gap and tight piston-to-wall clearance to further improve emissions, you are left with a recipe for disaster if you try to add too much boost. Plus when you factor in the L36's already higher static compression ratio, you are really asking for trouble.

Basically the biggest factor at work here is cylinder pressure. Higher cylinder pressures = higher combustion heat. So it's not so much a factor of charge air temp; but more so it's the amount of air you are trying to pack into the cylinder. If the parts aren't designed or the clearances aren't set optimally for the application, then you are basically working with a ticking time bomb.

Now for my application I started with a L67 shortblock (engine w/o heads/intake) and had the cylinders honed to open up the clearance between the piston and cylinder; as well as open up that sealing ring end gap. I'm still using stock L67 pistons, and I've been able to put up to 15lbs of boost on them without failure. But I just don't feel comfortable pushing it any harder than that. Keeping my boost in check is probably what has allowed my engine to survive for the past 5 years.

Just some food for thought.

-ryan

Sinister Im glad both you and Turbocharged403sbc post here because you both bring a ton of smarts to the game and a lot of practical insight. Not just saying you cant or shouldnt but breaking it down into simple laymen terms for everyone to grasp.

I was speaking to another member here via IM that there is modding and there is durability and you have to weigh a particular mods gains vs. its affect on overall durability. You can slap just about anything you want on a motor, but how long before that performance level results in you puking parts on the highway or something.

When I first started modifying vehicles, no one ever talked to me about durability and how an engine was constructed, the mentality was that if it resulted in a performance boost, well then you needed to do it. As time wore on and I grew a bit wiser I kinda came to the conclusion you spoke of. If its not designed from the factory to handle extreme mods like boost from the factory, chances are you are going to make a big dent in durability and reliability.

I think we keep hoping that the manufacturer has 'over engineered' the car to the point we can have fun and quite the opposite is true. They have engineered it just enough to be reasonably durable and reliable. Their focus is expense vs. durability and reliability. Make it cheap enough to be affordable, but durable enough that the consumer has the perspective they got their money's worth.

Some people never think of the future though, and the longitivity of there motor. When it breaks they'll ***** and cry and call the 3800 a POS. There are alot of people out there like this, i've seen them for years on Club GP. There are many improvements that can be made on both the L36 and L67.

There are other people too that have the mindset "ZZP does it" we can too. Comparing our cars to there race cars that are not daily drivers isn't a good idea. Anybody can just throw in a short block when it blows up, sure thats cheap and easy on a race car that gets limited miles. When your talking about a driver being pushed to the limits all the time, gets tens of thousands of miles yearly, realibilty should be a factor there too. No stock L36 and L67 is going to last with extensive power and be a realible daily driver and constant High HP levels. You have your fair share of risks running a "built-up" motor as well, don't get me wrong. Oiling improvements and forged slugs goes a long ways! These motors ain't that costly to build up either to have a SOLID motor.

In the end it comes down to the old saying... "You gotta pay to play" But my point is, if you're gonna pay, do the proper steps and do it right the first time.

I know i'll get rants from this, i'm just speaking the truth, thats all...

To add...

These motors do hold up good for what they are, so do the trannies for that matter. There always is a weak link, no matter what motor is mass produced or home built. I do believe some people push these motors a little too far sometimes though, thats my opinion. Also, every motor is different from the other, for example No two L67s will be alike, many things factor in this... Tolerences and even how the motor was initially broke in factors in this situation.