Trying something different...

[KATwo40]

Spoke with my machinist today, who's going to be balancing the innerds next week (dropping off late this week) and boring the block and all that jazz. We were discussing the block O-ring option and he informed me that he wouldn't O-ring a block that's gonna get a non-copper headgasket. However, he did present to me another option.

Since I already have the Fel-Pro gasket (came with the head set) and I really don't plan on running any more than 20psi, he says that he can groove the block deck to accpet the fire-ring in the gasket, instead of installing an O-ring. This way, the ring will crush down into the block, decreasing the chance of lifting the gasket under high cylinder pressures. He says he's done this on numerous engines without any negative issues and this shop has been building high hp engines for probably 20 years now.

Any negative side effects come to mind? Ivan? NissanFanatic? Edub1? I think it's a great idea. I ran this past Chris @ AMS today on the phone after placing my order for bearings, but he said that was new to him.

[KATwo40]

Wow, this post has been up for days and no response.

Well, anyhow, doesn't matter. I've decided to abort the receiver groove idea. I think I would much rather use the Fel-Pro gasket in stock form (no head or block surface modifications) and have it act as a sort of "fuse" in the event of nasty detonation, that would otherwise result in a damaged rod, piston, ring, block, etc.

[fiznat]

I discussed this with my machinist as well when I was building my last motor, and pretty much decided against it for the same reasons. I went with a cometic MLS gasket instead though, I'm curious as to why you're skipping that too and going for the felpro? Seems a MLS will provide more of a middle ground between a regular HG and the all-out receiver groove + o-ring setup.

With either HG though, make sure you get the head and block both decked so that the surface is perfectly smooth for the gasket to seal against. This is even more important if you decide to go with a MLS gasket.

As far as the fuse theory, I'm not sure if it really is valid. Even though I admit I used this idea when I was making a HG decision as well, stuff I've learned and seen recently is kinda making me lean the other way. If you are pushing a significant amount of boost, knocking will pretty much destroy your engine instantly. The pressures are too great in the chamber at that kinda boost, if your timing goes out or your fuel drops- its going to be instant carnage. There will be no "blow the headgasket first and then the pistons will go." I have seen this happen a few times, and been told about this by a number of trusted, experienced tuners and machinists. The exact wording was something along the lines of "if that timing goes out, you wont even hear the detonation-- it will be over that quickly." Not sure if a weaker headgasket is really going to buy you any extra time if youre engine starts knocking at WOT.

Likewise, the "fuse" theory suggests that a blown headgasket can alert you to problems before further damage occurs, but there are other problems you need to think about. If you bust the headgasket in the wrong way, and start leaking coolant into the combustion chamber, you run a high risk of hydrolocking the motor and doing some VERY serious damage. The headgasket performs a very important job here, not only forming a seal to keep the compression in, but also to keep the coolant out. Sometimes the coolant will just burn if you let it in, but other times you can do much, much more damage. Something to think about as well-- I wouldnt want to use coolant burning as a diagnostic, its just too dangerous.

Not to scare you or anything. This is how it is with building motors that are going to run on the edge of their capability (more or less): you'll have to make some decisions based on what you think will work and what other people's experience tells you. In the end it is just going to come down to pretty much a guess and a choice, because neither way has been absolutey proven to work better than an other-- but hopefully we can help ya make a more informed decision. I too would like to hear what some of our experienced members have to say.

[KATwo40]

Holy crap...a well written post pointing out the pros and cons of a theory! Thank you!

I have a question, and I'd hope that some others would join in on this one as well...

It's well known that the KA24DE can make 350-375whp reliably on a bone stock, unopened, stock head gasket setup, running 15-18psi.

I maintain that the peak cylinder pressures in my engine running 15-18psi with 8.8:1 CR will be the same as or lower than those in found in the stock DOHC. So, assuming this rings true, I can't help but believe that a new Fel-Pro stock spec gasket along with ARP head studs for additional clamp force would hold this 400whp setup just fine.

Thanks again Fiz for the great reply. Please, add to this conversation again.

[fiznat]

I'm pretty sure that the peak cyl pressures will NOT be the same. Even though the compression ratio is slightly reduced, we are way overwhelming that with the boost pressure. I see where you're coming from, but think about it: this is why we have to run air/fuel ratios in the 11s and retard timing like crazy. We need the extra fuel to cool the mixture because pressures are so high, and the timing is reduced to compensate for the increased combustion rate at such high pressures. If peak cyl pressures were the same, we would not have to add fuel (beyond stoich) or retard timing.

I'm not so sure about stock KA headgaskets running "reliably" at those pressures, either. Then again, I'm constantly suprised at how well the KA does sometimes, and also at how poorly it does other times. Personally I would not trust the stock headgasket at ALL at anywhere close to 15psi/300rwhp. 375 is crazy-- my stock (forged) connecting rods bent in half at only 50 horse more. I cant imagine that the stock headgasket would last that long but again, who knows.

A cometic MLS has been used in almost all of the known high horsepower motors. I have never heard of one failing that was properly-installed, and reliability does not seem to be an issue here. For a (?) $30 price difference, I dont see any reason why not to use the MLS.

[KATwo40]

I'm pretty sure that the peak cyl pressures will NOT be the same. Even though the compression ratio is slightly reduced, we are way overwhelming that with the boost pressure. I see where you're coming from, but think about it: this is why we have to run air/fuel ratios in the 11s and retard timing like crazy. We need the extra fuel to cool the mixture because pressures are so high, and the timing is reduced to compensate for the increased combustion rate at such high pressures. If peak cyl pressures were the same, we would not have to add fuel (beyond stoich) or retard timing.

I'm not so sure about stock KA headgaskets running "reliably" at those pressures, either. Then again, I'm constantly suprised at how well the KA does sometimes, and also at how poorly it does other times. Personally I would not trust the stock headgasket at ALL at anywhere close to 15psi/300rwhp. 375 is crazy-- my stock (forged) connecting rods bent in half at only 50 horse more. I cant imagine that the stock headgasket would last that long but again, who knows.

A cometic MLS has been used in almost all of the known high horsepower motors. I have never heard of one failing that was properly-installed, and reliability does not seem to be an issue here. For a (?) $30 price difference, I dont see any reason why not to use the MLS.

Good points here, but let's look at the peak cylinder pressure theory again...

For example, an engine built to make 300whp with F/I using 8.8:1 CR would certainly have lower peak cylinder pressures than an engine built to be N/A, using 10:1 pistons and making 300whp with N2O. Same power, but different peak cylinder pressures.

However, you make a good argument...why risk it over $30? I think you might have just made my decision clear. Thanks again for this conversation, it's much much appreciated.

[DammitBobby]

I am in the same boat as far as power goals and boost level. Although I think I may keep it around 15 psi instead of 20 psi. Last friday I took my stock rebuilt engine out and yesterday we set the engine on the engine stand. Today I hope to see what happen to cylinder number 2. I posted a question to Ivan and asked him about his basic rebuilt kit which includes felpro gasket set. He told me that the felpro gasket would hold those power levels. I am leaning towards that route since the kit all ready comes with Felpro head gasket and I won`t have to worry as much about having a perfect surface.

[KATwo40]

To add to this conversation, I just hung up the phone from talking to a very very good friend of mine, of several years. He used to drag race on a semi-pro level in Chicago. His setup was as follows:

512cid big block V815:1 static CR forged pistonsForged rods and crank 300 wet-shot nitrousFel-Pro stock gasketsHead studsMain studs

He made a little more than 1,000 bhp on this engine using those Fel-Pro gaskets. I would venture to say that his peak cylinder pressures were certainly in the neighborhood of 3500psi or more. He said in all the years he ran that car (8.50's in the 1/4mi...3500lb car) he NEVER blew one of those gaskets. In fact, he re-used them sometimes, just to see if it would work...and it did.

I think I might just use the Fel-Pro. If it blows, it blows. When that happens, if it's because of actual gasket failure, I'll upgrade to a better gasket. Until then, let's ride in suspense!

[klattr1]

He made a little more than 1,000 bhp on this engine using those Fel-Pro gaskets.

ask him what size head studs/bolts he was using...

as far as the stock vs metal HG thing goes, if you plan on surpassing on 400 whp and 20+ psi, then go with the Cometic HP headgasket...the stock headgasket can work at that level, but it takes more octane, better tuning, etc...all it takes is for the head to lift a little and destroy it...

but on the same note, about the "fuse" issue...i usually tell people to go with the Cometic if they are confident in their tune...if the tune is too much on the edge and/or octane used, etc, then it could damage the bottom end sooner than compared with the stock HG...

[KATwo40]

ask him what size head studs/bolts he was using...

as far as the stock vs metal HG thing goes, if you plan on surpassing on 400 whp and 20+ psi, then go with the Cometic HP headgasket...the stock headgasket can work at that level, but it takes more octane, better tuning, etc...all it takes is for the head to lift a little and destroy it...

but on the same note, about the "fuse" issue...i usually tell people to go with the Cometic if they are confident in their tune...if the tune is too much on the edge and/or octane used, etc, then it could damage the bottom end sooner than compared with the stock HG...

I'll ask him, but I'm betting they weren't larger than 11mm.

I really don't want to run more than 20psi boost (but you know how that goes...starts with 250whp...next thing ya' know, you're at 300whp...and so on, and so forth ).

I really have a hard time believing that the head will lift on 20psi using 10mm headstuds. That's a substantial increase in clamping force, plus the lower static CR MUST help with peak cylinder pressures (when compared to say, a 9.5:1 CR), or no one would bother using low comp. pistons.

As for the tune, I plan to make it like the perfect female...really rich and pretty retarded. No, seriously, I'll do it by the book...start with AFR's in the 11.5:1 range and timing pulled further than necessary and work my way up until I reach MBT...then back everything off just a tad for safety.

Thanks again for all the help on this. It's great to have such a vast knowledge base here at our disposal. I hope I can give back as much as I've received on this forum. Whatever my final decision, I'll be sure to keep everyone updated as to the progress of the project.

Cheers!

[klattr1]

I'll ask him, but I'm betting they weren't larger than 11mm.Cheers!

and he'll be like "what the hell is a mm?"...hehe-gotta love domestic guys