Exhaust Manifold Bolt sizes
 

Removing the headers from my '79 T/A...... Going back to iron logs.

Engine is a '76 Pontiac 350.
The engine code is: XR 0300605 with 6X heads.

The exhaust manifolds are:
LH 499624D dated Feb. 25 '77
RH 496002A dated Jan. 20 '77

I have no real good idea what size manifold bolts I need!!!!!!:noidea:

I have a service manual on CD....... A real pain in the butt to navigate, by the way.:confused:
So far, I've found a reference to several sizes..... section 3.275 shows:
1.05 3/8" 16x1 3/4 (what the heck does the 1.05 stand for?)
........... also 3/8" 16x2.70 for the LH.

I can deduce the 3/8" head size.... the 16x1.75 thread and length stuff.....

But HOW MANY OF EACH..... AND WHERE DO THE DIFFERENT SIZED ONES GO??????

I think I remember hearing stories of some folks busting into water jackets or something when torqueing down an exhaust bolt that was too long. Anyone help?

This is no concours restoration but I do want a trouble-free, long-lasting install. Love the performance of the headers but hate the leaks. The Pontiac heads have got to be the hardest things to get headers on correctly. Here's some pics of the car...... http://www.cardomain.com/ride/2678545

Measure them........................
 

Welcome to the Forums.

No one is likely to have this info handy; I would simply lay the exhaust manifolds flat on the bench and measure the bolt lengths, while noting their positions. The bolts are 3/8" diameter w/ 9/16" heads, unless you use the smaller head header-type bolts.

Les

The bolt passages through the manifolds obviously differ in height, but threaded socket holes in heads are different depths also. I measured my rebuilt 1968 GTO 400 engine, front and rear holes on both heads are 1.4" deep. The four holes next toward center go through but 0.5" thick. The central (dual port) holes on both heads are all 0.9" deep. I have decided to keep original manifolds, and finding all 12 holes in the heads, I intend to put a bolt in each before the engine is installed and steering is in the way. I measured the manifold passages and added them to the depths above and have determined bolt lengths for port #1- 2" front and 1", ports #3/5- 3", port #7- 2". On the even side port #2- 2", port #4/6- 2.5", and port #8- 2.5" and 2" in the rear. My list:
1 x 1.0"
2 x 3.0"
3 x 2.5"
6 x 2.0"
Grade 10.9 "car bolts" would be ideal replacement but not readily available (Ames has kits). The original hardware are standard hex head and torque spec is 30 pound feet so I am using grade 8 bolts and spring washers, and a smudge of copper grease (anti-seize for exhaust)

You'll want at least grade 5 and preferably grade 8. General rule of thumb is that you want 1-1/2 times the bolt diameter of thread engagement, or about 5/8" into the heads. You'll have to account for the thickness of any washers you plan to use and for the gasket thickness. Most hardware stores have a pretty decent selection of bolts, but if you can't find the exact lengths you need, you can order from www.mcmaster.com