When I say I'm reusing the same block, I mean as-is. I was not intending on pulling pistons, etc... It has 55k miles.

The mechanic with check the deck for flatness. If a problem exists, then the story will be different.

So, if the block is O.K., I assume this post does not apply. And, to be honest, I don't understand parts of this post.

The only honing I've seen in my life was hand-honing on a 1968 block when I was young. I don't understand using the same gaskets as the block was honed with. Do you mean reuse the same kind of gaskets as the original installation? How does one hone with a gasket?

I'm not sure I'd be bumping compression. DCR should go down with a bigger cam, I'm shooting to keep it near the same DCR as stock. OTOH, I understand more air will be filling the cylinders (has to for a power increase). I understand there's a risk of blow-by on a stock bottom end (maybe more w/o honing?) Letting compression drop a bit might lessen that risk.

That's part of the argument.

Another part is wanting to keep it lively with street response. And, to pull well in 6th gear on the hwy. I have to assume compression helps acheive that.

I'm also hearing good quench controls knock. Squeezing combustion up into the head chamber decreases detonation. My first choice is to use an intake w/o EGR. So, won't the extra quench help compensate for loss of EGR (by reducing possibility of detonation)?

 

I ordered a set of this for my LT4.

 

I know that ratios around 11.1 to 11.7 are doable. When I asked Lloyd Elliot about head gaskets this is one of the responses I got back regarding head gasket thickness and compression. I was initially concerned about the using the thinner Impala SS gasket, but on my setup he recomended and this raises factory compression a bit.

 

My appologies, I thought you were in the process of building an engine. I see now you are working on the engine in your C4. I should try to explain what I wrote earlier though because I think a good understanding of what happens when you start swapping parts is important.

Since you are obviously not rehoning the block and fitting new pistons and rings it will be important to put the same head gasket back on or you could easily cause the tops of the cylinders to distort when you torque the heads back on. Anything that creates different stresses in a used engine during re-assembly where these parts are mated and seated is inviting bore distortion and increased cylinder leakage. This is especially true in the case of the Small Block Chevy.

Below is a picture of a SBC being honed with honing plates torqued in place and the machine is a Sunnen Products Company model CV-616 Automatic Cylinder Honing Machine.

Engine builders discovered long ago the importance of good block preparation by simulating distributed stresses around the tops of the cylinder bores that result from torquing on the heads. These bolt stresses pull on the bores about 1/2" down from the top adjacent to each of the five head bolts causing around .0015 - .002 out of round which will allow a lot of blow-by and this hurts power. Using a different style head gasket than the one the engine broke-in with causes distributed stresses at the top of the block to be different as well and introduces unwanted bore distortion. Changing to studs when you broke in with bolts will too. If you plan to change something in this area you want to simulate those conditions the block will see in the honing process so you have good straight round cylinders when the heads are installed.




Performance Honing- copied from the Internet

Maximizing Torque Plate Performance
While just bolting on a torque plate is enough to put you ahead of a standard production machine shop's bore quality, paying attention to the fine points can increase the degree of accuracy substantially. Fastener loads and type, as well as the lubricants and thread engagement, torque plate stiffness and surface finish, and even gasket type can all vary the bore distortion replicated by the torque plate. It is important to mimic the final engine assembly as closely as possible. Sunnen has done extensive research in this regard, with precision bore measurements showing that these factors can materially affect the final bore quality.

True bore distortion cannot be measured with a dial bore gauge since it only measures length without considering an axis. The Inner Contour Meter is a precision device that can map the actual bore shape. This is an important tool at Sunnen in developing tooling and techniques, which closely replicate an ideal cylindrical shape. With it isometric and radial plots of the bore are generated under various conditions, allowing comparative evaluation of the cylinder bores. This is useful in solving complex distortion simulation problems, and allows compensation or correction that can lead to a better finished product.



...In the isometric above notice how dramatically the bore distortion changes at the upper portion of the bore with the variation in clamping loads imposed by the two different gasket types.

 

I'm a believer in tight quench on SBC engines and I'd worry more about quench than compression ratio especially with a relatively tame CR in the 11:1 ratio

(caveat this is with aluminum heads)

 

So, in short, you're saying any head gasket pulls up/in on the deck. And, that "distortion" throws the deck/bores out of perfection.

Using different types of gaskets magnifies distortion by pulling the deck in multiple directions/ways. Therefore changing gasket types increases the chance for gasket failure and other "failures".

The question I have is what constitutes a different gasket type. Strickly speaking, I have to assume different thickness(es) of the same type could be considered different types. That means using the SAME stock gasket minimizes chance of problem.

OTOH. If sticking with a composite gasket that still has a stainless fire ring may be reasonably similar -- and therefore low-risk. (Especially if it also has a lock wire (as does stock). I feel some latitude has to exist -- otherwise modifying a motor would always require the use of a new block and new heads!

So, going from a composite to a shim is what's really risky. (Because it's a totally different type of gasket). Another company makes a solid copper gasket as well. Though considered reusable, it may be better if used on a new motor from the outset.

There are several types of gaskets listed on any retail site. From what's being said here, it seems sticking with a composite gasket is best. There are a decent number of responders who say a .029" gasket has worked for years. I wonder if that was on a new block or reused factory block.

 

Gregg -- Sorry for the minor hijack, but it is on topic .......

I'm finalizing the choice of head gasket for my 383 Gen 1 build. I have 65 cc heads, and 5 cc flat tops .005 in the hole. I was originally planning on a FelPro 1010 (.039 thickness) which puts me at 10.8 static, 8.05 dynamic with .043 quench. If I move to a .028 gasket, I will have .033 quench distance with 11.15 SCR, 8.30 DCR. My question is this -- will the tighter quench offset the increased compression from a detonation resistance perspective?

 

My comments were not suggesting that your choices might be inviting possible head gasket failure. I was trying point out installing a different gasket type than the engine has run with this long would be inviting likely bore distortion by disturbing the piston ring to cylinder wall seal.

Examples of different gasket types would be FelPro MLS, FelPro composition with stainless steel wire inside the armor, preflattened stainless steel wire inside the armor, copper wire inside the armor, Cometic MLS, and thin shim type gasket. Testing bore distortion with different head gasket types using special equipment points out each gasket style caused different stress distribution at the tops of the bores. This is why the better engine shops hone blocks using honing plates torqued to the block decks with the same style gasket the engine is to be assembled with. If the engine work does not include a complete teardown for rehoning, new pistons and rings the the same style gaskets should be installed again.

For best results and to prevent introducing unwanted bore distortion.

 

I have to claim ignorance here, Greg. Even if I called a Chevy dealership (which I did), Mr. BudWieser Parts Counter Guy doesn't know what the stock gasket "type" is. They can't tell me bore, compressed thickness, nothing. And, 20 yrs after manufacture, I wouldn't bet two dollars they'd sell the same gasket as used when built by the factory!

So, what type did they use? I would have assumed composite with a wire inside the firing ring. And, I've read (inconsistently), that it is a .051" gasket. (Chevy Performance parts makes this thickness/configuration, but maybe it's not stock. Hell, I don't know.)

I would assume any composite gasket would be similar (and minimize) the risk of gasket failure. I'd also assume a .051" with a wire would be better -- but this is all a GUESS. Knowing what to use/why vs. what not to use would be helpful.

Todd,
FWIW, Tony recommended I shoot for 10.8-11.0 compression on my build. Assuming he read my plan correctly, I have to assume a new build could easily tolerate another couple of tenths. And, since racing/power is your goal, why not? From the threads I've read on the subject, I'll predict feedback will support the higher number...

A poster earlier in this thread uses more quench successfully too. But, maybe the reverse cooling of the LT1 makes higher compression w/o knock easier?

 

Would the result be blow-by only or even a broken ring?

 

Absolutely no danger of a broken ring. Concern is only for increased blowby which will negate any small increase you sought with the thinner head gasket. Any gains you are trying to get by swapping to thinner or smaller volume head gaskets will probably be more than offset by screwing up the ring to cylinder wall seal regardless what the wizard behind the local parts counter thinks.

 

Uhhhh, Greg. Those "wizards" are in here and 3rd gen. Something about quench they say....

The idea is getting to the ideal burn configuration within the cylinder. What I don't get is how real this quench issue really is. Since you're technically versed, maybe you can help.

TPiS describes it as a "secret making HP". Others describe quench as being necessary to avoid detonation. And, we all know detonation can be very harmful to a motor!

Practically though, we're talking about a minute sliver of space. For example, getting L98 factory quench from .076 to .040 is a change of .035". That's 35 thousanths of an inch!! That's only 1/3rd of 1/10th of an inch.

From what I understand, a stock L98 piston sits .025" down in the hole. With the factory gasket, it's face is .076" away from the head deck. But, some magic, somewhere, has determined that .040" is "THE" distance where power is maximized. And, people seem to associate this with a more complete burn.

There are also characteristics of intake runners, piston tops, and chamber designs that promote swirling of AFmix for more complete burns. What I find odd is this aspect has typically been ignored in discussions about "the" best cylinders heads. I've even seen the topic brushed aside (maybe because head designers have all dealt with that issue equally well????)

Todd asks the question about higher compression ratio. I ask it about lower numbers.

The question is whether quench is important (and effective) enough to consider taking risks. It may not be to add power (though a side-effect). More specifically, it's to acheive optimal burn. This can avoid detonation in high-compression applications. For me, I'm also hoping it would help alleviate the need for an EGR valve. Most aftermarket intakes don't have EGR provisions, so from that aspect, I believe this issue to be very important. Unless it's total B.S.....

 

i put .029 on mine when i installed Edelbrock heads. I did have a slight leak and i had to have it re-done, but i'm pretty sure that was more about attaching aluminum heads to a cast iron block. I don't know how those guys did it, but the seal is solid as a rock now.

As for the compression, I've heard of it gaining a decent amount with the thinner gasket. More compression is good compression as long as you don't end up launching anything through your valve covers....

 

The difference in compression and detonation resistance wont really matter with aluminum heads on that level. 10.8 to 11.15 isnt a huge difference and those DCR's are within range of acceptable pump gas limits. General quench guidelines is between .035-.045 so your on the tighter side, which still should be fine. I know i've run 11 to 1 with 8.3 dynamic with 93 octane and havent seen knock counts or spark retard for timing values from 32-39 degrees WOT and air fuels from mid 14's to 12 to 1



As for the gasket thing, i dont think you'll beable to use the stock gasket again good luck trying to do that and it be dumb to try to reuse a factory 10+ year old gasket. I think the gain in compression will be greater than any blow by losses with different gaskets, with your intended goals/power levels

 

It's not total BS, just not at the top of the list for what you are trying to accomplish. The .040 figure you are being quoted as gospel is because someone heard most performance engine builders strive for a zero deck and since the gasket typically measures .040 compressed they guess this must be the secret to optimal quench when this is actually not true. Quench is not really what you design on purpose first, it is what is left over after you have designed the ideal combustion chamber. A good combustion chamber wants to occupy as little real estate as possible but this is counter productive to good port flow because a tight small chamber shrouds the valve. So an acceptable compromise must be reached by spreading out the chamber walls which promotes mid-lift flow without presenting more surface area to the combustion process to burn across than is absolutely necessary. Actually the correct figure for quench is whatever it takes to run the piston close to the head without hitting it. There are several things that decide this; one being piston to wall clearance, another being piston skirt design and yet another being peak operating RPM of the engine. Potential for gain no doubt does exist for a piston .076 away from the head but in your example more gain will come from the boost in compression as you move the head closer to the piston. I would have to recommend changing to better pistons machined to run closer to the deck as the right approach and you could also incorporate some of the better 1mm rings while you are at it. There is no question a better choice would be to upgrade to a good head which will improve performance far more than monkeying with head gasket thickness. When it comes to planning your engine build start with a clean sheet of paper and draw a vertical line down through the middle. Title the left side of your list "It's a Big Thing" and title the right side "It's a Little Thing." Spend your money on the big things first.

 

Yep, rpm and weight of the rotating assembly factor in with rod stretch from heat and forces from being thrown around in the cylinder. .035-.045 is not a bad place to be. Biggest thing i mentioned is with a cam, and aluminum heads, keeping static compression up will help keep dynamic up depending on the cam he uses, so that will help keep the streetability up as it wont be a dog on the low end

 

Thank you. Sounds like common-sense to me. Not a big mystery. Squeeze the air tightly w/o smacking pistons and valves....

Knowing there's a lot of hype in sales-prose, please comment on this...

From TPiS website: "This (.029") head gasket is designed to raise the compression ratio 1/2 point (vs. the stock .051" gasket). But more importantly, it tightens up the quench area which is one of the major secrets to making horsepower without being octane sensitive. "

So, is there any truth to the advertisement shown above? If tightening up quench is synonomous with increasing compression, doesn't this statement really say increased compression avoids octane sensitivity!? Where's the logic in that?

Note: The gasket being advertised is designed (from my understanding) as a replacement for an L98 stock small block.

And, could you rephrase the statement above? I'm unsure of your point. More gain than what?... knock suppression? I don't get it.

 

Their advertising is correct in that it does tighten up the quench and increase compression ratio at the same time but the power increase will be more attributal to the compression ratio increase than the change in quench. It is impossible to quantify changes relating to how quench affects knock without special equipment. Knock comes about when some adverse condition forms or is present which interferes with the otherwise controlled rate of burn in a properly operating combustion cycle. Oxygen count in the exhaust is worth looking at. Oxygen count will always increase when an engine is knocking because oxygen is not uniting with carbon and hydrogen to form Co, Co2, and h2o (and others) because of the disruption in the combustion process.

Causes of knock is a tough parameter to nail down. The usual remedy is to retard spark advance but the usual culprit is combustion chamber design and layout and of course fuel quality.