Does anyone know what material is used in dual plenums on the G8's V6? If it is composite plastic, I am definitely sticking with the V8 or nothing.

I owned a '99 Bonneville with the 3.8 V6. It was a great car for me. I loved the 3.8 engine except the plenums were made of a composite plastic. I had to replace the upper plenum twice at about 40,000 mile intervals. I think this design sucked. I am lucky that the lower plenum did not warp on me because that one was expensive to replace.

GM says;

Intake manifold : aluminum ( 319 Upper, and Lower )

Also interesting tidbit, this same engine is capable of 275hp in the crossovers (Acadia, Enclave, Outlook) and even pumps out 263 in a CTS. Easy exhaust and ecm upgrades for a quick 20+ hp boost.

I've had enough 3800 V6's and put on a lot of miles and reading up on the engine on wikipedia was the first I knew of problems.

GM says;

Intake manifold : aluminum ( 319 Upper, and Lower )

Also interesting tidbit, this same engine is capable of 275hp in the crossovers (Acadia, Enclave, Outlook) and even pumps out 263 in a CTS. Easy exhaust and ecm upgrades for a quick 20+ hp boost.

I've had enough 3800 V6's and put on a lot of miles and reading up on the engine on wikipedia was the first I knew of problems.

It depends on the years your 3800 was built, earlier engines used metal.

I am not a car guy but know enough to know what a manifold does why do they now call a manifold a plenum?

I'm pretty sure the V8 is plastic. The LS1, LS2 and the LS6 were all plastic.

Why plenum? Partly becasue they are cast or molded into tighter shapes sometimes with internal baffling or other changes. The plenum on this engine has a valve internal that changes the size of the air chamber. Also plenum is a foreign-sounding word to make you think you are getting more than you pay for.

Okay, real reason. Plenum is used in HVAC and refers to air handling. In teh days of cast iron inytake manifolds with carburetors on top (or under) teh maniufold transported an air/fuel mixture taht was mixed insode the carburetor. Now with port injection, mostly, teh air and fuel are mixed just before teh intake valves and is not premixed and distributed along the runners. Plenums carry for the most part just air, not air/fuel. But don't confuse plenum with airbox (which is on list of 2009 accessories for GT)

Yes, the V8's intake manifold is composite, and comes straight from the Corvette's LS3.

Yes, the V8's intake manifold is composite, and comes straight from the Corvette's LS3.

I hope GM has fixed the warping problem with plastic plenums?

The biggest problem with the 95-00(ish) 3800 Series II plastic upper intake manifold was that the EGR port was to close to a major coolant path. The heat (and possibly the DEX coolant) degraded the plastic until the coolant path burst open into the EGR port, dumping coolant into the engine. GM improved the design, and other kits were released to modify or replace the involved parts.

I doubt they are gonna make that mistake again anytime soon.

Warping is not a common problem I've heard on the 3800 manifold. Is it on LSx engines?

The biggest problem with the 95-00(ish) 3800 Series II plastic upper intake manifold was that the EGR port was to close to a major coolant path. The heat (and possibly the DEX coolant) degraded the plastic until the coolant path burst open into the EGR port, dumping coolant into the engine. GM improved the design, and other kits were released to modify or replace the involved parts.

I doubt they are gonna make that mistake again anytime soon.

Warping is not a common problem I've heard on the 3800 manifold. Is it on LSx engines?

I believe that they have done away with the EGR valve in the LY7 and doing its job with the VVT, so you should be pretty safe.

The biggest problem with the 95-00(ish) 3800 Series II plastic upper intake manifold was that the EGR port was to close to a major coolant path. The heat (and possibly the DEX coolant) degraded the plastic until the coolant path burst open into the EGR port, dumping coolant into the engine. GM improved the design, and other kits were released to modify or replace the involved parts.

I doubt they are gonna make that mistake again anytime soon.

Warping is not a common problem I've heard on the 3800 manifold. Is it on LSx engines?

Each time I had this problem with my Bonnie, coolant leaked on the ground not in the engine. The service manager told me that if the coolant had leaked into the engine, it would be very expensive to repair. My Bonnie was the entry-level, I think it was called the GS model.

And he said the UIM was leaking? I don't know where it woulda come from other than the TB-UIM mating surface (which could be from warping I guess) or there is an elbow on the accessory end that routes coolant through the accessory bracket that commonly cracks.

ps: Regals come in GS form, Bonnevilles had SE, SLE, and SSE trims that came with 3800's.

And he said the UIM was leaking? I don't know where it woulda come from other than the TB-UIM mating surface (which could be from warping I guess) or there is an elbow on the accessory end that routes coolant through the accessory bracket that commonly cracks.

ps: Regals come in GS form, Bonnevilles had SE, SLE, and SSE trims that came with 3800's.
It was an SE. Thanks for the reminder.

I hope GM has fixed the warping problem with plastic plenums?

The v8's all have plastic plenums. The diference is this isn't a 80's engine design. The coolant doesn't flow through the intake like the 3.8 did.

The v8's all have plastic plenums. The diference is this isn't a 80's engine design. The coolant doesn't flow through the intake like the 3.8 did.

:mswerd:

These aren't 1980s' plastics either.