Bigger head studs than stock?

434nova

Active Member
#1
Who here has drilled there 109 blocks for bigger head studs? What size did you end up going with? I know on the fords they drill the blocks out to 5/8 size. Same with Oldsmobile. Has me thinking that the stock 7/16 size head bolts can’t keep the heads on at the higher boost levels.
 

earlbrown

runs with scissors
#2
The heads don't lift because the fasteners are too weak. It's just a design limitation that shows up when you more than double the output of the engine. (or detonate the crap out of it)
 

Mike T

Well-Known Member
#7
I know a machinist/builder who has put 1/2 studs in a 109 block. Didn't ask for details or why but he usually has a good reason for his upgrades.

Would guess it's not just a grab the drill and tap process either.

Now this is just me thinking out loud ......
If were asked to do this at home I wouldn't go crazy with a drill, maybe just knock the crest off of the threads and try to follow the original threads with the 1/2 tap.

How you go about it would also depend on the thread pitch.
 
#8
I know a machinist/builder who has put 1/2 studs in a 109 block. Didn't ask for details or why but he usually has a good reason for his upgrades.

Would guess it's not just a grab the drill and tap process either.

Now this is just me thinking out loud ......
If were asked to do this at home I wouldn't go crazy with a drill, maybe just knock the crest off of the threads and try to follow the original threads with the 1/2 tap.

How you go about it would also depend on the thread pitch.
If you don't run a drill through there is a very high risk of breaking the tap. Also the holes need to be as square to the desk as possible to get the most benifit.
That said the deck and number of bolts is the limiting factor more so than the bolts or studs.
 

Mr.Spool

Well-Known Member
#12
If you really think about it the bolts surrounding cylinders 3&4 are subjected to more stress.
the most stress is inside the cylinder and there is just no getting around that.its not just the extra bolt holes you pick up on a stage block there is more nickel content and the ta block looks even stronger.you can make a ton of power on a 109 with the right builder and tune but in the end it is still a stock block and that is the limitation. the number or size of the head bolts are not.
 

Mike T

Well-Known Member
#13
@ 6000 rpm the cylinder is firing 50 times per second. At that rate ( if the heads lift) the fasteners would have to recover from stretch at an unbelievable rate. The center cylinders are dealing with the added stress from the adjacent cylinders firing as well. While not firing at the same time I believe the speed at which it occurs would factor.
 

Mr.Spool

Well-Known Member
#14
ive spun a 109 to 7500 rpm never lifted a head.now start moving over 90lbs a minute regardless of rpm and see what starts happening.here is the answer, since i have done,not read about it or heard about it, small cracks from cylinder pressure will start to form and eventually the cylinder gives way,head gets torched,cometic torched,deck torched.i had alot of time on my last 109 so i got another one built the same way i was very happy.however 800+rwhp, 900 to 1000 fwhp these things will happen.hard fill,bigger studs etc you cant get around the fact the cylinder walls will go away and thats if its built right and tuned right.noticed i used cylinder pressure not boost pressure since a killer set of heads lowers the boost pressure, it doesnt change the fact that cylinder pressure is what will kill it eventually
 

Mr.Spool

Well-Known Member
#15
Has me thinking that the stock 7/16 size head bolts can’t keep the heads on at the higher boost levels.
i ran bolts on previous build with a 109 that made over 80 lbs a minute with a hpc bb 64/68 turbo. over 35psi spun routinely to 6600 rpm with an .85 3 bolt.
 
#16
Something that isn't being realized in this discussion about going to a larger stud or bolt is the fact that when you do this you are going to have to put alot more torque on the larger bolt to get the extra clamping force you are looking for which will also distort the deck surface. Gm engineers already did their homework on this just look at the stage blocks, when they built those most of those engines were not designed to make 1200 horsepower or even 1500 horsepower they were meant for Indy and NASCAR around the 7 to 800 horsepower range back then and you'll notice they didn't just leave the four Head bolts and go to larger studs they put more holes in the block for more clamping force ,not larger, more you can do what you want and try what you want this is not the correct way to go about it the only correct way is to use good grade studs or go to a stage block
 
#18
Not huge but pretty big you have to understand that when you put a bolt in it you are not only stretching the bolt it is also being twisted( torsional Force) which pulls harder on the threads in the block, with a stud you are not doing this you are screwing it in until it bottoms out lightly then all you are doing is putting a tension( pulling force )on the stud which does not distort the block. Now I'm not saying you can't use bolts because the ARP bolts work great but it is kind of a loaded question as depends on what kind of power (cylinder pressure )you are going to be putting on them
 

rag231

Well-Known Member
#19
Bolts will never achieve full thread engagement of the surface that it is going into where as a stud can literally be bottomed out if done correctly. It ultimately depends on the material that it is being screwed into. I know of several stage 2 blocks that had been terminated on assembly due to improper torquing of studs cracking a main stud mount in a crank location or at one of the cylinder head stud locations.