max boost on a 4 bolt head.
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..
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.
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.
Last edited by ryarbrough; Jan 14, 2010 at 11:01 AM.
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Launching!
Joined: Jul 2008
Posts: 205
Likes: 10
From: Newville, PA
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.
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.
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.
8 sec potential, 12 sec slip
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Joined: Apr 2002
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From: Savannah, GA
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!!!
Dont forget also that timing plays a huge factor into lifting the heads as well!!!
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.
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 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.