L- 88/L-89/LS-6 Exhaust Manifold Question

[SVO]

On the aluminum head big block engines, were the exhaust manifolds installed the same as the ones on cast iron heads? Did they use the same manifold bolts and were they torqued to the same torque value as the bolts on a cast iron head? And did they use a gasket between the aluminum head and the exhaust manifold?

I'm waiting for Hurricane Harveys water to recede and my mind is wandering all over the place at the moment...

 

[Vettehead Mikey]

In a given year all big block manifolds were the same part number irrespective of RPO, but the part numbers varied year to year. I don't have the torque values for the bolts, but know that there was no gasket between the head and manifold

Good luck with the flood water clean up.

 

[SVO]

Thanks for the info Mikey. Seriously planning a ZZ454 crate motor and want to use the stock exhaust manifolds.

Got lucky with the flood water clean up, only about 4 inches in shop, and cars were 18 inches above that. Have all kinds of crap that floated out of who knows where to pick up. Only casualty was a T/T steering column for my '69 that somehow ended up on shop floor in all the rush. All fresh water, so should clean up no problem.

 

[kpic]

Although I'd check what the "factory" states; typically cast iron and aluminum have different torque values.. Avoid dry torque and use engine oil on the threads as well as the friction surface.

Torque specifications for fasteners
Scroll down and you'll see a chart showing the differences..

Aluminum also requires more thread engagement than CI.

In the 70s, design engineering had charts; pick the thread, add length of engagement, 4 or 6 pitch clearance between the depth of the tap drill and the tap etc.. Today bolted joints are a science. There are two methods I'm aware of, torque to yield and torque to angle.

Threaded Fasteners Torque-to-Yield and Torque-to-Angle - Engine Builder Magazine

Good advice from the link is use new fasteners because the days of a coffee can filled with used fasteners are over..

 

[Hib Halverson]

BBC OE exhaust manifolds are all the same basic design but not the same part number. There are regular manifolds and then manifolds with AIR connectdions. Each has a different PN.

As for torque, I believe the thread sizes are the same for exhaust and intake manifold bolts.

Use the torque spec for intake manifold bolts going into aluminum heads.

 

[SVO]

Thanks to all for the input. This will give me something to research more.

 

[kpic]

SVO: There is a lot of sites with torque specs. The few I looked at had different values.. :confused

"High Temperature Effects
Most fastener materials are temperature sensitive; that is to say, their properties are influenced by a change in temperature. The strength of a metal fastener declines as temperature increases. At significant temperatures coatings may breakdown, high temperature corrosion, creep, or stress relaxation may occur, and differential thermal expansion rates between the fastener and the joint may cause failure."
Access Denied

Although there aren't answers to your questions in the above, it explains all the factors involved.

"Intake Manifold
(Cast Iron Heads)"
Big Block Chevrolet Engine Specs-Torque Specs-Cylinder Numbering-Firing Order-Distributor Rotation-396 402 427 454 Cid-BB Chevy V8

The above site states intake manifold (I assume aluminum) to cast iron heads.. The problem, they don't state aluminum heads or block. Different materials have different rates of expansion which affect torque.

 

[Vettehead Mikey]

BBC OE exhaust manifolds are all the same basic design but not the same part number. There are regular manifolds and then manifolds with AIR connectdions. Each has a different PN.

Not quite true. The only number that appears on the manifold is the basic casting number irrespective of AIR holes or not. GM did not always follow the fit, form or function convention for part numbers.

The line workers at Tonawanda picked the appropriate manifold in accordance with the engine code.

 

[kpic]

Not quite true. The only number that appears on the manifold is the basic casting number irrespective of AIR holes or not. GM did not always follow the fit, form or function convention for part numbers.

Correct.. Every casting and forging has its own part number which is cast or forged on the part. This insures manufacturing begins with the correct rough part to machine and logistics has the correct rough part number to provide to manufacturing.. What is made from either may have a different machining or finished part number. If a gear, crankshaft, or whatever had the same rough part PN as the finished PN, life would be impossibly confusing.. If the PNs were the same, assembly technicals would not be happy campers trying to assemble a rough part when they needed the finished part.

Some part numbers do not appear on the parts because they are an assembly or sub-assembly. For example, there is an engineering drawing of a transmission counter shaft assembly or a piston + rings (a sub assembly), pin and conn rod assembly. With a C'shaft in a transmission, it consists of gears, a key, a shaft and 2 tapered roller bearing cones (or whatever type bearing is used). The assembly technicians on the line don't build the assembly, they install it.
If the technicians built up the counter shaft assembly and installed it, production would be very slow.. It is common sense when we think about it..

 

[SVO]

What I really need to do is dig into the GM parts manuals and shop manuals to see if there is a difference in exhaust manifold bolts between a cast iron head and a aluminum head and if there is a difference in exhaust manifold bolt torque values between a cast iron head and a aluminum head.

Lots of good info presented here and I will be looking into the references provided.