Cometic Head Gaskets $139.99

[3400-95-Modified]

Bore opening would be whatever you wanted it to be, stock 3500 was 3.720 and you can go up to .060 over, I checked...

There was no question in my mind that these were made for performance or not... Cometic is a VERY reputable company... It just sucks that this first run was not biased on the right gasket and that just put their completion of the fix too far after when I needed them. Otherwise I would have definitely used them.

I don't think these had a stopper bead from what I'm reading about what one is. I do not remember seeing something like that, but I could be wrong.

[chri0029]

Thanks. That is really good if they had 3 embossed layers. That means they were designed for performance. 4 would be better (that is what the LS9 has), but sometimes that is not possible due to design constraints.

Now I am just wondering now how high the stopper is (or if it has one). That would most likely be on the only layer without embossed beads (the thick center layer) between where the embossed combustion bead sits and the bore. I assume the bore opening is probably around 95 or 96 mm to work on the newest LX9's, LA1's, LG8's, etc.

[3400-95-Modified]

They were 4 layers for a .060 set, three were stamped, two back to back, then the thick and one more stamped one... I do not know what the thicknesses were.

[chri0029]

Can anyone with a set of these still tell me how many layers they have and the height of the center layer stopper (the thing between the combustion bead & the bore)?

[chri0029]

Yea, I know. When the motor was upgraded after 05, they went MLS. So there was not a business case to retrofit the old LA1 back to MLS. I wanted to replace my CHG with MLS ones, but it was the tooling that cost too much. I would need to order over 100 of them to even begin to amortize the tooling. Otherwise I would have ordered some prototypes. I'm not saying the GM composites aren't good, but I know the limitations of them when used with stock bolts. I'm just skeptical of adding boost to it stock. I am very familiar with the newest MLS designs, even the highest hp ones for D.I. & even blown engines that are more than capable. I'm not sure about the older 3.4 engines, but I know the newer ones have too high of a fan cal for the coolant flow. From the posts, it sound like at least the gaskets from the older engines can handle boost. But I know a few people with newer engines with bad stock gaskets under 100k mi. I'm just trying to identify the weakest link since I'm looking into boosting my 2004 engine as well in a few years.

[1988GTU]

Ran over 20lbs for over 10K miles in a 3.1 on stock gaskets. Only hiccup I have had was lifter failure.

[IsaacHayes]

For the record, I got my car with 104,000 miles in 99, and have been daily driving it in the city only ever since. So it does sit idling in hot weather, stop/start etc etc.

[3400-95-Modified]

Yes but these newer MLS gaskets you speak of do not exist for the 3400 or 3500, GM won't go back an improve the gaskets for a dead engine.

And right now these current MLS gaskets are not available on a time frame that many had hoped for, so in the end the best possible solution for us to use in the mean time would be the 2004 GM Graphite 3400 head gaskets.

I ran a set on my last motor for 15k and hit it a few times with a 100shot and never had an issue... I was also using ARP head studs which kills stock GM bolts as far as even clamping force and bolt load.

In the end MLS yes is an option that I would rather go with, but I cant keep my car on blocks till they are ready. This is just something that will have to wait till next year or the year after that, depending on when I pull the engine apart again.

Also I'm guessing that the new GM gaskets that are MLS are being installed on DI motors where the compression is also in the area's of 10.5:1 to 11.5:1 for example their 2.4L motors are 11.4:1 compression.

[chri0029]

Interesting ....

My stock 2004 ones went out at 70k miles. And they looked horrible after inspection. I know the fan temp is set too high for the engine. I guess it depends on how much you idle in traffic and let the engine temp rise.

I know for a fact the newer MLS gaskets are good for 600+ hp and > 150k miles. You just have to have good head structure and adequate bolt load along with a good CHG design.

[IsaacHayes]

Mars man has been running his cammed, headered boosted CSC setup for several years now. He peaks over 10psi I want to say he has seen up to 16-17 but I can't recall for sure. No failures yet.

My stock 94 head gaskets are working fine (no power adder) and I have more than 3x 70,000 miles on the motor.

[chri0029]

I'm not too familiar with the Felpro gaskets since I never used them. I just know that the GM design is marginal on the stock engine (during GM validation and even in my own vehicle at 70k miles), so I am curious what experience people have with GM 3.4L head gaskets (the later graphite ones) in their boosted engines. The latest GM designs ALL use MLS gaskets which can be designed for any application and perform far superior to both the graphite and composite gaskets. Graphite is more forgiving but won't hold up to the constant head lift of high boost for the long-term. Maybe you'll get a couple of years depending on how often and how hard you boost.

[3400-95-Modified]

I would believe you if every failure I had was not a result of the gasket decomposing behind the fire ring right next to the coolant port which then would negate ANY gasket compression in that area which would in turn blow out and release coolant in to the cylinders.

Sorry but thats my experience with Felpro, the gasket literly melted away... Its not the same quality as a GM gasket.

[chri0029]

No, the gaskets aren't the critical part of boost .. the bolts are. The higher the boost, the higher the head lift. The higher the head lift, the more the bolts are worked. That's where you see which gasket is designed the best. It doesn't matter which gasket you use if it's designed right - the bolts keep the engine together. What I'm saying is the bolts are far more critical to the equation than the head gasket (if it's designed correctly). Although MLS gaskets are far superior to the composite ones, your bolts are the weakest link. The GM stock gasket design is marginal but obsolete compared to MLS designs. It won't survive a lot of boost for the long haul. But I have seen Cometic's work before, and it's less than marginal on a different application. Somebody needs to look at a cross section of the Cometic MLS gasket (probably center layer) and measure the height of the stopper - the thing in front of the combustion bead (if it even has one). The higher the stopper, the more you can leverage against your existing head bolts. Otherwise you increase your bolt load and can use the existing GM head gasket but face bore, piston, and other problems. If you can make this combination work, you can add all the boost you want until you break the next weakest component.

[IsaacHayes]

Stock bolts with GM gaskets hold up to 9psi on a lot of engines. The felpro's just seem to not like boost.

[chri0029]

You need to be looking more at bolt load than your cylinder head gaskets. It doesn't matter if you have Felpro or Cometic gaskets; they will both fail eventually unless you control head lift. Look for bolts with higher plasticity or higher yield.