I really hate to post this question but I've reached the breaking point. I am looking for ideas on ways to prevent LS1 heads from lifting and losing cylinder pressure past the copper gaskets and into the cooling system. I have O-ringed the heads and am using 165,000 lb. ARP bolts torqued to 115 lbs. Cutting receiver grooves into the heads is the only other measure I have not yet taken. Ideas?

BTW, we have made over 1300 rwtq on a Mustang dyno last week by activating the NOS at 2800 rpm.

 

Not to go off topic, but I can't wait to see this thing run

 

What diameter head studs? I know some other shops that are making BIG power used like 1/2 head studs or something. You have to drill and retap the threads in the block and enlarge the holes in the heads, but you wont lift a large stud

 

I have been messing with engines for about 15 years now and have never had hands on experience with a powerplant producing cylinder pressure at that level. I personally would suggest contacting ARP and/or Lingenfelter for information.LPE has a great deal of experience with AL headed motors running massive cylinder pressure.

 

We are still trying to use stock diameter studs, and we just ordered 200,000 lb. L14 from ARP. (10-bolt heads are a curse).

We spoke with LPE, but they have not made this level of cylinder pressure with an LS1. They suggested receiver grooves.

 

One pitfall of the LS1 head is only having 4 bolts per cylinder. At least the Lt1 had 5 per. Have you considered heliarcing them down

 

We will speak with SCE and ARP today about the problem. We may even design some type of girdle or strap to see if that helps. I've tried to call Wade at ARE to see if he has any ideas.

Big HP and torque is no good if you lift heads.

 

i think Todd is right.. you're going to run into these kinds of problems w/ fewer head bolts. i think thats one design charachteristic that wasnt intended to handle that kind of cyllinder pressure.

best of luck,

 

We agree that 10-bolt heads are more of challenge that 15-bolt heads, but the 10-bolt Cleveland guys have figured a way to make huge HP, so it's possible.

 

I studied this mentally, but have no hand's on experience with the true problem. The true failure mode has to be found. Is the gasket being shot (extruded) out? Are the heads themselves deforming in between the fasteners? Is the pressure stretching the bolt/stud? Are the threads deforming? All of the above?

Here were my thoughts:

1) As mentioned, bigger diameter studs and nuts if the issue is associated with the threads or the studs. This will help somewhat if the head is deforming in between the fasteners, but not a whole lot.

2) Design a girdle, or run steel threaded inserts instead of relying on the threads in the aluminum and then "through-bolt" the head onto the block from the bottom if you can find the room.

3) If the head itself is lifting in between the fasteners, get ready for a shocker...

Switch to an iron head. Iron is 3 times as stiff as aluminum EVEN IF the aluminum has a higher ultimate tensile or yield strength (I HIGHLY doubt you are actually yielding the head, but most likely elastically deforming it). Stiffness is an inherent property related to the density of the molecular structure of the metal in question, and NO aluminum can match steel/iron alloys for stiffness. Matter of fact, it can't even come close.

BTW... titanium is HALF as stiff as steel/iron alloys.

4) Significantly alter the head design. What I mean here is that material type is only PART of the actual stiffness of a given design. The other part is shape. Properly placed gussets that deepen the section in the area that is deforming could allow you stiffen the head.

Be careful welding if this is the case, you'll ruin the heat-treating that gave the aluminum the desireable properties that it had in the first place. If you ALREADY welded on them, scrap them - they're junk.

5) Here's another shocker... Changing bolt materials from one type of steel to another without increasing the diameter WILL NOT stop this problem unless the bolts in question are actually permanently deforming. Again, ALL STEELS HAVE THE SAME STIFFNESS (slope of the stress/strain curve prior to yield). If you're not yielding the bolt, but just elastically deforming it, a higher material strength fastener WILL NOT HELP. You HAVE TO go up in diameter then.

 

PacerX
Thanks for your indepth analysis of the situation. Perhaps I should hire you to solve this problem for me!

1. No, the SCE copper gaskets are not being extruded or deformed. Gas is escaping past them at cylinders 3,4, 5 and 6 (middle two on each side) and entering the coolant system (bad). We overnighted SCE the gaskets last night and they are anxious to help solve our problem.

2. We are working on a girdle design.

3. Yes, our best guess is that we are actually lifting both heads off of the block, and yes we have discussed changing to the CI heads, which retain more heat and would require three times more machining.

5. ARP is sending us a new, less elastic bolt.

I am trying to get Wade to help me with this problem since he is one of only a few who have solved it or something similar.

 

I cant wait till I get to that horsepower level..

 

Someone has to pave the way, unfortunately it seems to be me.

 

You're very welcome.


K, that's good.


Sounds good - don't weld on the heads though. Welding heat treated aluminum anneals it. That's bad. Machining heat can do it also, so be careful if somebody fires up a milling machine on your heads.


That's true, iron heads are going to need more machining, and they are going to retain more heat. BUT - what really matters is the heat that is conducted to the intake charge - and you can stop that nonsense dead in its tracks with a ceramic thermal barrier coating... I'm making an assumption here given the impressive work you have done, but I bet you could swing the cash to do the runners and the combustion chamber.


They're the experts, but I really hope "less elastic" means "larger diameter" or I'd be worried.


As soon as this gets sorted out (I'm sure you'll nail it down), you're the benchmark. I envy you, I really do.

 

2. No welding of heads will take place.
3. CI heads, maybe.
5. No, ARP is staying with the stock diameter.

 

I'm having the same problem at about 700 rwhp (250hp shot) at 5 to 7 o-clock position on cyl's 3 and 5, 4 and 6. I don't think it's a fastener problem. I think it a head material problem and not enough headbolts. I think the aluminum used in the C5R heads are t-6 or better where as stock castings are T-5 like the stock block.

 

Joe,
If we solve this problem, I promise to tell you how we did.

 

Joe,

I know this is arcane, but you have to follow me here to understand fully how to fix the problem.

Metals have many properties. I'll list some of them:

Density
Stiffness (also know as Young's Modulus)
Yield Strength
Ultimate Tensile Strength
Elongation Percentage
Hardness
Thermal Conductivity
Electrical Conductivity
etc...

The CRITICAL properties for your problem only fall into one of two areas.

Stiffness and yield strength.

Lots of folks use incorrect terms to describe the "strength" of a metal. "Strength" means lots of different things, depending on what is being described.

If I am talking about the maximum load a fastener can take before it breaks - I'm talking about ultimate tensile strength.

If I am talking about the maximum load a fastener can take before taking a permanent set (elongating permanently due to the load) I am talking about yield strength. Any elongation that the fastener can take BEFORE yielding (permanently deforming) is called ELASTIC DEFORMATION.

If I am talking about the amount of load it takes to stretch a fastener a given amount BEFORE yielding, I am talking about stiffness.

Now, there are properties that can be effected by heat treatment or other manufacturing processes. Yield strength and ultimate tensile strength are two of these. Stiffness is NOT. No matter WHAT I do to aluminum, the stiffness of the alloy stays the same.

This is the question you have to ask to solve your problem:

Are my cylinder heads ELASTICALLY DEFORMING enough due to cylinder pressure to cause the failure I'm seeing?

If the answer to that question is "yes" then no matter what you do with the heat treatment of the aluminum heads, you will never solve the problem.

Your only options at that point are to switch to a steel/iron alloy OR stiffen the head by changing it's shape - which means a girdle or added material at critical areas. Adding material to the head is VERY difficult. Once you weld on it, you ruin the heat treatment (which is important in other areas). Furthermore, it's a casting, and castings and welding is a risky proposition.

An iron head might be the quickest, most economical answer.

 

Much of the problem lies in the design of head... look at the areas around the top bolts... not a heck of a lot of support there, I would think that a girldle like stealth is saying would be the only cure, short of a custom made aluminum head or an iron head.


And Joe... congrats on the explosion!

PS: Detonation and heat transfer to the intake charge not withstanding, who here thinks the aluminum head would make more power than a 100% identical iron head?

 

After much discussion with those in the know, it seems increasingly doubtful that an LS1 can live very long in the >1000 hp ranges. If I back-off of the NOS, it might work with 9/16" custom studs, 140 lbs torque, wire rings in the block, and reduced timing (+/- 20 deg.).

My project might have just died, and have to be scaled back to lower hp levels. Shoulda started with a SBC.