hi guys..

i will go g5x3 cam with afr 205..i already bought the comp 7.400 pushrod but i dont know whitch cometic gasket i buy there are two size:4.030 & 3.91 and olso it has diffrent thikness .040 or .030 or....??? plz i need help

 

You are going to want the 3.910 bore size if you have a stock LS1 block. The 4" bore size is for an LS2 or bigger.

On the thinkness you are going to have to decide based on what your goals are. If you want to bump your compression you can go with a thin one like the .040 cosmetic but its best to flycut.

I have the exact setup and I think i am going to go with the GM MLS gasket so I dont have to flycut. I may lose 5-10 HP but its worth it to me.

 

I run the G5x-3 cam with AFR'S AND 7.4 PR'S and cosmetic 40 gaskets.
No you don't have to fly cut the piston. Frank

 

I am running the same setup

 

When you get it apart, measure your PTV with the old gasket. Then figure out your thickness requirement. In the end, it will be how much do you want to push your luck. Because it clears doesn't mean its safe and there are recommended PTV clearances for a hydraulic roller cam. If I were a betting person, I would say that cam falls outside those recommendations. Thinner gasket will allow more timing, compression will give you better low end torque. You should sort it out prior to disassembly then decide on an approach.

 

Louis told me that it will clear and you can drive it but dont expect to over rev it and be safe. So Its best to flycut

 

ever seen the mess a valve makes when it contacts a piston

 

Have seen pics.....Thats why I suggested flycutting

 

That's my point

 

^ did you flycut or use a bigger gasket?

 

.040" or .045" are what most use. You really should be calculating your compression ratio, specifically dynamic compression to plan this sort of job. You can adjust it with the gasket thickness to a certain extent.

Your piston to valve clearance will probably be fine with AFR's, unless the heads were milled.

I wouldn't recommend anything thinner than .040" no matter what the compression is. Remember, your pistons are traveling out of the block around .006-.010", and if you had say only .030" separating the head and block...piston to head contact becomes a concern. ,023" quench is too little. Most recommend a quench of .030-.035" for best results. A .040" gasket minus say .007" out of the hole would net .033" quench, about ideal.


I'm using ,040" Cometics, 59cc milled heads, and a G5X4 cam. Yes, I flycut.

 

Tom,

What do you think about 59cc AFR's with the stock MLS gaskets? LG said I will lose maybe 5-10 hp but what about PTV clearence? Thanks

Chris

 

It would help a little, but we're only talking .012-.014" difference here. If you are borderline with .040" gaskets, maybe that'd make the difference.

I don't know what kind of p/v clearance your combo typically has. LG should certainly know, it's kinda their trademark h/c package.
But just using hypothetical numbers...say you had .060" clearance with the Cometics...bumping up to stock gasket will only get you to about .074" clearance. Is that a "make or break" proposition? Probably not, and I'd probably still opt for the thinner gaskets and risk it. If actual clearance is much tighter than that...then I'd flycut with either gasket, but certainly run the thinner ones.

So basically, I don't really see gasket thickness as a tool for adjusting p/v clearance.

Some of the newer "big" cams we all commonly see advertised as "clears stock heads" is a little deceiving, as you don't know by how much. A cam similar in size to mine from another vendor has been reportedly selling popular cams that take the p/v clearance as low as in the .040" range....that's absolutely ridiculous. My cam with stock heads/gasket was right around .050" clearance on the intake valve...I put a couple thousand miles on it that way, and never hit them, but I felt a little uneasy after learning I was running it THAT tight.

Safe p/v clearances for these engines is considered to be .080" intake, .100" to the exhaust valve. Going tighter than that will work, will clear, and you'll probably be fine as long as you don't severely overrev it or float the valves. That's when the contact problems occur.

With my setup as it is now, I would have had contact just bolting it together and spinning the engine by hand.
I cut .100" deep reliefs for the intake valve only, and ended up seeing about .090-.095" p/v clearance. My measured exhaust valve clearance was very good, well over .120", so I didn't have to cut for those.

 

I completly understand what you mean by not using the gasket size determine the PTV clearance. I just have so much trouble convincing myself to flycut.

 

Louis is the one I listened to that said, not a problem! Since they are the one's that have installed dozen's of these things I Did not fly cut.
Wish he would get his story straight. lol lol FRANK

 

Lots of tolerance stack-ups in the motors, so for a close one what works for one may not work for another. Only sure way is to measure. If you plan the time, you can measure and then determine a course of action. I have a much smaller cam than you guys, but I will still measure it during the installation process.

 

Always good advice.

 

While I am a strong supporter of using the stock GM MLS gaskets as I have seen how well they hold up under boost. I was unable to use them because my piston and rod combo, and the combination of my heads being resurfaced a couple of times, and the block being decked once...my deck height ended up being .014" out of the hole.

So I went with Cometic MLS gaskets...which have performed flawless over 1ks of miles running anywhere from 9-18#s of boost.

Great gaskets both the Cometic and GM...most important part is making sure the heads and block are straight prior to installing.

 

So you went with thicker-than-stock gaskets I hope?


Many may not know, but Cometic is a custom manufacturer, and will make you a set in nearly any thickness you could specify. Most of the vendors stock and advertise the most popular thicknesses and bore sizes used, ie; .040, .045, .060, .070, etc...but you can custom order a set any way you'd like.

The GM MLS gaskets are great...if their thickness suits your needs. They're cheap too. There are plenty of other thinner than stock gaskets out there, but for MLS, Cometic is about the only choice., and yes, you do pay dearly for them.

 

Yes my first build I had used .065" Cometics..which were custom ($100 per gasket). Subtract the .014" deck height from .065" and it is .051" which is very close to the GM MLS gaskets...except the factory pistons stick out of the hole about .007". So with factory deck height and stock pistons...assuming the GM .054" MLS HG thickness it's like .047". But knowing that the GM MLS's are really more like .050" compressed...its more like .044".

So this time when I did a refresh on the motor, I decided to go with off the shelf .060" Cometics....I wanted to tighten my quench up a little anyway and get it closer to stock...they were only $70 per gasket too.

GM are nice because they are like $30...but only come in the .054"....when I measure them I can only get .048-050" though.