[aronhk_md]

Can anyone shed light on how boost and compression play a part in the life of cylinder head to block seal? In other words, at what point does one need to o-ring block, heads, or both? In one of the threads recently posted Bruce mentions a 406 chevy that was boosted all the way up to 28 psi, with pump fuel at lower boost, then race fuel later, and it made me wonder at what point our pontiacs need these mods. I realize that cam design plays a part here too, but would just like to hear some thoughts on the matter.

Also, take a boosted application designed mostly for the street and an occasional foray to the track.

Is it safer for a stock 455 block to make X hp and torque at 10 psi boost(just a relative # here), but allowing the engine to spin higher to say 6500 rpm (again, just a relative #), versus the same block tuned for a lower rpm range (say 5800 rpm max) and 15 psi in an attempt to maximize mid range. Assume the rotating assembly was well prepared but mostly stock.

Hope to get everyone's input on one or both questions.

[thadeal4real]

its all about cylinder pressure and clamping force

[aronhk_md]

uhuh......that much I realize......but what are some people's thoughts on when o-rings might be a wise choice?

[thadeal4real]

mls gaskets work well imo vs o ringn for 15psi 40 on the same motor mabey i dont know??

[Steve Barcak]

O-ringing a blown motor is a wise choice at any boost level. Get it done, do it right and you are done with it. Why be so hesistant to O-ring a blown engine? So many seem scared to O-ring a supercharged engine though hot rodders have been doing it probably since the early 50s.
O-ring the block and put a reciever groove in the head and have some more confidence that it'll hold better. Then you can turn the wick up instead of futsing around scared and wondering if your gaskets will hold or not.
For the amount of time and money one spends on supercharging an engine, O-ringing is not a big deal to do.

Steve

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[aronhk_md]

Hi Steve,

Thanks for the reply. I can see your point. In my case, I am buying a boosted car that the block was o-ringed, but the heads were not. They are cast but ported. So my plan was to run it as is for the summer, and possibly next winter replace the heads with a better flowing aluminum set. My main use will be street, with an occasional visit to the track. Thoughts were to limit the boost to 10 psi for now anyway.

My other question was to get ideas on what I might change next winter. After changing to aluminum heads (and grooving them as you say), do I set the car up to run toward a 6500 rpm limit with say 10 psi, or a 5800 rpm limit and perhaps use more boost (15 psi?)

Obviously I want to get the best performance from it, but this question was based more from a safety perspective keeping in mind the stock bottom end and the desire to keep it in one piece, and wondering if higher rpms with less boost is more stressful than lower rpms with more boost???................(it is zero decked, balanced, forged pistons, aluminum rods, nodular crank, early style block). It is already in the 1000hp range with 10 psi, intercooled. So far peak HP was made at around 5500 rpm, peak torque at around 5000 rpm.

[bad69bird]

Originally Posted by aronhk_md

uhuh......that much I realize......but what are some people's thoughts on when o-rings might be a wise choice?

For 10-15lbs of boost, IMO, it's not worth it. A Cometic MLS will do you just fine. Especially for an application that is "mostly for the street use." Plus, if you are looking at re-sale value, it's easier to sell a head that doesn't have a receiver groove in it, versus one that does, again IMO.

I have no direct experience with o-ring/receiver groove stuff. I have always had a hard time embracing that if that head lifts (and it will) that it's going to settle back down in the same exact spot as it was originally. Keep in mind that you have a copper head gasket in between the o-ring and receiver groove. If it's off a couple of thousands, it's going to crush the gasket in a new place and possibly not re-seal properly. Again, I have no real world experience, just my theory. Take it for what it's worth and if I am wrong someone please correct me.

Originally Posted by aronhk_md

Hi Steve,

Thanks for the reply. I can see your point. In my case, I am buying a boosted car that the block was o-ringed, but the heads were not. They are cast but ported. So my plan was to run it as is for the summer, and possibly next winter replace the heads with a better flowing aluminum set. My main use will be street, with an occasional visit to the track. Thoughts were to limit the boost to 10 psi for now anyway.

My other question was to get ideas on what I might change next winter. After changing to aluminum heads (and grooving them as you say), do I set the car up to run toward a 6500 rpm limit with say 10 psi, or a 5800 rpm limit and perhaps use more boost (15 psi?)

Obviously I want to get the best performance from it, but this question was based more from a safety perspective keeping in mind the stock bottom end and the desire to keep it in one piece, and wondering if higher rpms with less boost is more stressful than lower rpms with more boost???................(it is zero decked, balanced, forged pistons, aluminum rods, nodular crank, early style block). It is already in the 1000hp range with 10 psi, intercooled. So far peak HP was made at around 5500 rpm, peak torque at around 5000 rpm.

Is this 1000hp documented? What size blower and type? At 10lbs (even intercooled) I would be skeptical. Now I would think that it would be in the 750-900hp range.

As far as spinning the motor to 6500 or 5800, 700rpm ain't gonna kill you...it's the cylinder pressure/heat/tune that are gonna tear chit up. I'm not trying to pi$$ on your parade, you just need to think everything through before you pull the trigger.

[screamingchief]

I'd be more concerned about losing water via the headgaskets than the cylinder pressure sealing.

Pump some coolant into the cylinder,,,and trust me,,,bad things are gonna happen...

Pumping coolant into the crankcase aint much better than that either.

So I for one would wanna dry deck it more-so than O-ringing it.

Then yeah,use the cometics without the cooling holes in them & leave the pistons down in the hole somewhat.

Probably look into reverse cooling it as well,not to mention adding some aux. cooling lines to the center "siamesed" cylinders area if at all possible (depends on heads though).

That should hold all but the most serious boost builds.



Bret P.

[aronhk_md]

Originally Posted by bad69bird

For 10-15lbs of boost, IMO, it's not worth it. A Cometic MLS will do you just fine. Especially for an application that is "mostly for the street use." Plus, if you are looking at re-sale value, it's easier to sell a head that doesn't have a receiver groove in it, versus one that does, again IMO.

I have no direct experience with o-ring/receiver groove stuff. I have always had a hard time embracing that if that head lifts (and it will) that it's going to settle back down in the same exact spot as it was originally. Keep in mind that you have a copper head gasket in between the o-ring and receiver groove. If it's off a couple of thousands, it's going to crush the gasket in a new place and possibly not re-seal properly. Again, I have no real world experience, just my theory. Take it for what it's worth and if I am wrong someone please correct me.




Is this 1000hp documented? What size blower and type? At 10lbs (even intercooled) I would be skeptical. Now I would think that it would be in the 750-900hp range.

As far as spinning the motor to 6500 or 5800, 700rpm ain't gonna kill you...it's the cylinder pressure/heat/tune that are gonna tear chit up. I'm not trying to pi$$ on your parade, you just need to think everything through before you pull the trigger.

Thanks for the reply Bad! I dont think you are in any way urinating on my parade...lol. I put the info out here for comments, thoughts, etc.

So......at what point do you consider o-ringing a benefit? Or do you?

The HP figures are documented, but I should have added that the 10 psi 1000hp results were calculated from rear wheel results around 800hp accounting for approximately 20% drivetrain loss. Its an 80mm turbo, and obviously the intercooling plays a part in those numbers.

Regarding the higher rpm/lower boost vs lower rpm/higher boost idea....I appreciate your input, but are you thinking more about the top end grenading with heat/pressure/detonation or the boosted stress on the somewhat stock lower end.........which is where I was going with the question?

Thanks,
Aron

[thadeal4real]

go 15psi at 5800
not 6500 at 10 its NIGHT and DAY

FWIW I RAN 16PSI ON A 455 6X COMBO WITH FELPRO BLUES NO PROBLEMS
good luck sounds like you need lots of help j/k

[70 bird]

I have been running up to 15psi. on the street with felpro 1016's on a undecked block. Keep the rpm's under 6k and a good tune you will be fine. If you detonate you will kill any head gasket/o ring seal. jmo.

[aronhk_md]

Originally Posted by screamingchief

I'd be more concerned about losing water via the headgaskets than the cylinder pressure sealing.

Pump some coolant into the cylinder,,,and trust me,,,bad things are gonna happen...

Pumping coolant into the crankcase aint much better than that either.

So I for one would wanna dry deck it more-so than O-ringing it.

Then yeah,use the cometics without the cooling holes in them & leave the pistons down in the hole somewhat.

Probably look into reverse cooling it as well,not to mention adding some aux. cooling lines to the center "siamesed" cylinders area if at all possible (depends on heads though).

That should hold all but the most serious boost builds.



Bret P.

Screamingchief - thanks, but I am looking at a street machine as mentioned, and my barebones understanding about drydecking is its a race only application. I'm not really trying to go with max boost here, rather to understand at what points people feel modifications might be necessary on the pontiacs so I can make solid decisions. I'm not interested in putting together an engine that needs to be torn down after every race, or after every season either.

I'm aware that any performance mod is a risk, and if I damage something, its because I went beyond what the engineers ever considered these blocks and really engine design would be used for. Still, I know there are things that can be done to help prevent failures, and I want to understand them better.



thadeal........lots of help needed, which is why I'm asking questions.


Anybody else have thoughts? Steve believes it should be o-ringed. Bad69bird thinks for 10-15 psi boost it should not need it. Any further input?

Bad69bird - I wanted to ask..........if the heads lift and come down in any way moving on the gasket, arent we basically talking head gasket failure anyway? Pressurized gases will take advantage of ANY opportunity, and coming "back down" in a slightly different spot would be a moot point once that happens.......or so I would believe?

[PONTIAC DUDE]

I have been 0-ringing blocks and heads for over 30 years and found a solution that seems to hold up better then most others that I have seen or tried.


I 0-ring the block and heads, but offset the one 0-ring from the other about .030. The ignition is now trying to make an S shape out past the gasket and harder to do over a trying to compress 2 .012 protrusions (one over the other) while the head is trying to lift. Less of an issue with a cast head too.
The cometics or multi layer gasket works great, but still has limits. A normal gasket will control lift in the .002 area. The multi layer steel gaskets can go upwards of .004/.005 and still hold a seal. Add a 4 bolt per cylinder Pontiac block and now you have more issues you are trying to control. But the 0-ring deal has the 0-rings protruding .010/.012 out of the block and controlling the seal slightly better.

You can dry deck and heads to keep water from intruding into the cylinders. No issues.
I also like to run the piston down in the hole a little to take the flat flame propagation away from the head gasket sealing area. Ya might give up a little hp but that can be made upo with more pill or more boost.
Any boost over 15 and nitrous over 300hp I recommend 0-ringing.
I have had success with my steel on one side/fiber on the other copper coated head gaskets at the lower levels of a power adder combo. But once you reach a certain point, then it's solid decks and copper coated gasket time with 0-rings.

RPM doesn't affect cylinder pressure. Boost/hp does and is what you're trying to contain.

Just from my experiences.

[PONTIAC DUDE]

Originally Posted by aronhk_md

Bad69bird - I wanted to ask..........if the heads lift and come down in any way moving on the gasket, arent we basically talking head gasket failure anyway? Pressurized gases will take advantage of ANY opportunity, and coming "back down" in a slightly different spot would be a moot point once that happens.......or so I would believe?

Shouldn't come down in a different spot. Dowel pins center and align the head, not the head bolts. The head lifting is a norm. that's why 0-ringing (.012) allows more vertical movement without issues.

[aronhk_md]

[SIZE="3"]Thanks Ken for giving me some understanding there, and thats where I was headed with this thread.

The higher rpm/lower boost vs lower rpm/higher boost question wasnt really aimed at longevity of the top end of the motor, but to longevity (and making power as a secondary but still desireable idea) of a somewhat stock BOTTOM end under boost.[SIZE]

[thadeal4real]

thats why its all about cyl pressure and clamping force
just imo with your goal of 10-15 psi under 7000rpm you should be honkey dory with a mls gasket unless your running like 13:1 static(ie cyl pressure) witch i dont think based on your "street" goals. like two have said even a std felpro would even be sufficent with 0 detination.
good luck

[PONTIAC DUDE]

Here ya go; This gives a rough idea of your final compression ratio with static and boost together.

http://www.angelfire.com/fl4/pontiac...owerboost.html

[aronhk_md]

Thanks Ken, thats a good chart. How would that chart be affected by pulling out more timing........would it move the racing gas line to the right allowing one to use more boost before requiring higher octane? In other words, if you are at 10 psi on pump gas, but the chart shows to go to 15 psi you'd need race gas......can you get away with the 15 psi on pump gas by removing some timing, and still have gains? Or would you be better off with the 10 psi and more timing?

[taff2]

You can run o ring wires in the block without reciever grooves being cut in the heads,with a copper or composition head gasket,just make sure the o ring wires don't stand up so high-0.004" instead of 0.010". If using composition gaskets you would have to check where the o ring wire sits in relation to the fire ring of the gasket. This way will work with iron or ali heads,easily at just 10-15 psi of boost,though ultimately double o ringing is better for serious boost.

[cgeise]

The "tune up " will have as much to do with how it lives as anything - to much timing or to lean - trouble - Cylinder pressure is the key and how violent the combustion process is. the felro 1016 or the butler gaket seem to give it up around 12 to 13 to one - I personaly run copper and an o-ring on the supergas car at 15 to 1- and drydecked - One little trick is to o-ring your block and use a SCE Tiatan gasket with intrigal o-ring - make sure they are off set a bit and it makes a good dual ring type set up. Cometic seem to live for me ok - BUT you must have the heads and block machined to the proper rms.