What is the max boost on a 4 bolt head with a MLS gasket? Or a what point do you have to O-ring?

 

8.6456345634 pounds

boost doesnt matter at all...its overall power you make

 

Agree to some extent... It's actually cyl. pressure that determines it - you can make a ton of "power" if you spin the car to 11,000 rpm and the cyl pressures will still be low (honda guys do this all the time) and you won't hurt stuff. High cylinder pressures (read - torque on a dyno) leads to problems..

 

I pushed mid 20psi and ~1200 rwhp on GM 5-layer gaskets 2 yrs ago...

 

If you have a big cubed motor and make 1000hp with only 7psi, overall output would not be a factor. Cyl. pressure would be low. Higher boost psi would mean higher cly. pressure. I have good gaskets and arp head studes. There has to be a magic number that some one has hit that has lifted a head or blown a gasket because of lack of clamp pressure.

 

maybe this should have been asked a little bit differant....
on a great tune, at what boost # do you guys start to see the heads lifting

 

Agreed on the higher cyl pressure deal. There is no magic number. It all depends on the setup.

 

18-20 lbs. seems to be where most people see water start to push.

 

thats what i was thinking also.

 

That's a lot of boost. I'd think the majority of folks would be breaking other parts before they started to worry about lifting heads.

 

I think the assumption was the motor was built but has 4 bolt heads? I think there was a couple guys that reached around 20-22psi (I think Kyle being one of them) and around the 1200 whp mark when they pushed water on a 4 bolt head.

 

a thick deck head, new ls9 7 layer gaskets and arp studs with a good tune mine should see 1k to the flywheel

 

arent those ls9 gaskets for a bigger bore?

 

Agreed on the cylinder pressure thing. A centrifugal supercharged engine will hold more boost than a twin screw, roots or quick spooling turbo system for this reason IMO.

I'm running 18psi and going to turn it up in the not-so-distant future.

You can go with a larger bore head gasket, but you can't go with one smaller than your bore.

 

FWIW I was pushing water at 15psi on my previous engine (forged 346 LS6). It had ARP studs, and AFR 225 heads.

Dont forget also that timing plays a huge factor into lifting the heads as well!!!

 

So would it be safe to say that around the 800-900 crank hp level is when you should start to worry?

 

And RPM's

 

I don't talk much about my set up... but 4 bolt 317 heads... twins and gm gaskets well over all these boost numbers posted here and never push water.

a lot of it is in the tune and Jim from speed inc is the best around IMHO.

 

Tune is supposed to be the most critical part. Too much timing likely the main culprit.
I have no numbers yet for my combo. Running arp head studs with afr 225s but only gone up to 7.5psi so far.Plan to go to 15 plus with upgraded turbos shortly. I put in the ls7 head gaskets realize they are not supposed to be that great for lining up on the coolant holes.I will likley be switching over to ls9 head gaskets or some other head gasket likley over next winters layaway. Hoping to get buy this season with the ls7 in there but likely will keep boost 15 or under.

 

I've been running 19PSI for a couple of seasons and haven't had any issues yet. This season I'm going 23PSI. I actually made one pass with my wastegates stuck that resulted in 25PSI for an 1/8th mile before I shut it down. Pulled all the plugs and found two with the electrodes melted. Went real lean since I didn't have the injectors to support that. I still didn't push any water. Maybe lucky but in any case I'm going to see what happens this year.