NinjaNife

A quick disclaimer; I'm fairly new to the car world, and hence ask dumb questions lol. I'm trying to learn though, so any tips are welcome

As the title says, I'm wondering what size and thickness cylinder head gaskets I need for a 350 bored 0.040 over. I opened up the engine of my '87 GTA in order to see how the innards are looking, and found that the cylinders were bored out and quite a few things were upgraded by the previous owner...which is great in that my engine is upgraded, but now I don't get to use plain old "Chevy 350 gaskets" haha. I've found online that the stock bore is 4.000", so I'm assuming I would need 4.040" gaskets, but I'm not sure if the gaskets are supposed to be the exact size of the cylinder or slightly larger to give some installation tolerance (also the only 4.040" gaskets I've found are over $70/each, which is much more expensive than the standard 4.000" gaskets for some reason). Also, does the thickness matter for the gaskets? Most I've seen are 0.040" compressed thickness, but I'm not sure if that is the best thickness for these engines or not.

I was planning on just getting one of the better Chevy 350 gasket kits, but now I'm struggling to piece together the right components individually. Does anyone have any suggestions on size/thickness/brand that would be good in a somewhat-modified engine?

Any ideas would be greatly appreciated. Thanks.

Brendan "NinjaNife" West

Night rider327

iTrader: (13)

You can run any bore gasket that is the same size or larger than your bore and fire ring.

The common 350 chevy gaskets are 4.100" and 4.166" bore.

Yes thickness matters A LOT. You can stick what ever rebuilder gasket on it and it will work, but the correct thickness will help you to get better performance.

But at this point you need to know a few details so you can pick the correct gasket thickness...

What heads do you have on your engine? Brand and part # if aftermarket, or casting # if stock... This so we know the chamber volume size

What is the block deck height? You need to measure this by turning engine to bring a piston to true TDC (top dead center), then measure how far down the piston is in the bore from the top of block deck... You can measure this with a straight edge and feeler gauge or with a dial caliper.. The measurement will be in the 0.000" to 0.060" range

Then you need to know what volume your pistons are.. Being bored and aftermarket, they should have a part # on the top of them.. . Clean the top of one off with lint free rag and brake parts cleaner, maybe even a wire brush and see if you can find a #

Once you have all of that info you can figure out your compression and your deck height and that will then give you the info needed to pick the correct gasket to get your compression and quench height right.

The quench height is the space between piston at TDC and bottom of the head, counting the gasket.. You want to shoot for 0.038" to 0.045" quench height. With 0.040" being perfect.

So see if your pistons sits say .010" down in bore, you would want a .028" to .035" thick gasket

If your pistons sits say .025" in bore, you would want a .013" to .020" gasket. With the fel pro 1094 4.100 x .015 gasket being perfect here.

The thickness and the bore of gasket will also change compression.
Larger bore or thicker gasket adds space or volume which reduces compression.
Smaller bore or thinner gasket reduces space/volume which builds more compression

novaderrik

i'd run the thinnest gaskets you can find to try to maximize quench, especially if it has flat top pistons- Fel Pro and Mr Gasket have .015 shim gaskets that are dirt cheap.

Night rider327

iTrader: (13)

I agree, for most stock and even built engines but we should not tell the OP that just yet.

He is dealing with an unknown rebuilt engine. What if it's been 0 decked and he puts .015" gaskets on it?

He needs to check how far his pistons are down in the bore at TDC 1st

NinjaNife

Thanks for the response. Just so I understand this correctly, you're saying that most 350 gaskets are 4.100 or larger, even though the stock bore is 4.000? If that's the case, is 4.100 large enough for my 4.040 bore?


I'm afraid that I'm out of town for work for the next week or so, so I won't be able to check the cast number on the heads or measure the block deck height. As far as I know the heads are stock (I was just planning on doing a top-end rebuild, so I didn't take the engine completely apart); the only thing that I found was swapped out was the pistons, roller lifters (and I'm assuming an accompanying cam), roller rockers and aftermarket bolts for the innards. On that note, can you tell me where the cast # would be? I didn't notice anything when I took the heads off, but I probably just missed it.


As for the pistons; I'll have to check those as well...I saw the "0.040" printed on the piston, but not an actual part number. I'll try to clean it off and see if there's anything else on there when I get home.



Another stupid question; is more compression better or worse? You're recommending maximum quench, which I assume equals more compression. What is the difference in an engine that isn't running any kind of supercharger/turbocharger (that's the main topic where I've heard talk about "lots of compression")?


Thanks for the help!


Brendan "NinjaNife" West

Night rider327

iTrader: (13)

Yes, most gaskets are larger than the bore. Most are 4.100" or 4.166" for the SBC.

Yes these will fit your 4.040" bore engine.

Stock heads will have the casting # in between the rocker arm studs. The number will be straight down in middle of head... Between the 6th and 7th rocker arms or the second and third rockers (heads are the same and can be used on eaither side of the engine so # stays in same place but its eaither at front or back depending on which side driver or pass. you look at)

If you can't find a part # on pistons, just post a picture of them on here. I can go from that.

Compression can be too little or too much... Not enough compression and you have lack of power, soft feeling low end torque, etc.

Too much and you can get detonation (ping/spark knock) that will damage the engine or force you to retard timing or run race fuel..

So you really need the compression in the right range to be best over all. That range is in the 9.0 to 10.0:1, with the closer you can get to 10:1 the better

86IROC112

I am also getting ready to install my newly rebuilt heads and found this a very interesting thread. I have the gaskets and will get the # off the pistons as well as measure the deck height. (Mine is supposedly bored .30 over)

I will post that info as well as what gaskets I have and if you can tell me if I got the right stuff I would greatly appreciate it. I don't want to have to tear this thing down again...Thanks!

Night rider327

iTrader: (13)

Sure thing man. Just post up the info and I will let you know

86IROC112

Okay, I don't have the exact tool to measure that deck height but based on my spark plug gap tool I estimate it at about 0.050-0.060. About the thickness of a medium Zip Tie. The number on the piston is: 534NP .020


I have attached photos of the head gasket to include the numbers on it as well as the whole kit my machinist got me. Also the head numbers are 14014416.


Thanks!

Night rider327

iTrader: (13)

1st off, Is yours suppose to be a 305 or 350? Cause it's a 305.

The .020 on piston means 0.020" over, it was not bored .030" over.

Whoever ordered your pistons screwed you up a little.

The 534NP's are good cheap cast pistons but they have a short compression height, which is very common for 'rebuilder' type pistons... These are the type you throw into the old farm truck with 400K miles on it to get it back on the road, or to throw in a engine and be able to sell it as a "rebuilt" engine.

The compression height is the measurement from center of wrist pin hole to top of piston.

The correct factory spec is 1.560"
With a factory spec 9.025 deck height (center line of crank to top of block deck), this would put the piston .025" in the bore at TDC.

The 534NP pistons has a 1.540" compression height, meaning they will sit .020" deeper into the bore...
If the block really is 9.025" then yours would sit .045" in... So your .050" to .060" is close.

The 8510PT head has has a 3.900" bore and .041" thick... Again just a 'rebuilder' head gasket. Will work fine if it's just to get car on road to go point A to point B.

Do not use this gasket if you are looking for performance!

That would put your quench height at well over .080"

With your parts as of right now with the 8510PT gaskets, you will have 8.75 to 8.93:1 compression (depending on your true deck height.

If you are building this for performance and have a larger than stock cam... Use the 350 steel shim head gaskets. Fel pro #1094 4.100" x .015"

That would put your compression up to 9.43:1 and gets your quench height as tight as you can with 1.540" compression height pistons and stock decks

86IROC112

Dang, you got this stuff down man! Yep, I know it's a 305. My top priority here is reliability. This is going to my son's car and it definitely does not need to be a hot rod. I just want it to be reliable and fun for him to cruise around.

The PO definitely was on a budget as evidenced by him rebuilding the bottom end then slapping the old heads back on so it doesn't surprise me he used cheap pistons.

So I guess my final question is this, will this set up make for a good daily driver for the kid?

Night rider327

iTrader: (13)

Thanks man... Yeah I been doing this for awhile now. It's like second nature now.

Yes with out question, the parts you have are 100% fine for a daily driver. It will be a good running engine. Run on pump 87 octane fuel and do what an engine needs to do..

Just not parts for a "performance" setup, being for your kid you don't want that anyway.

What you have there is just as good if not better than any part store's rebuilt engine

86IROC112

Great news, Thanks! Besides if I want power I drive my Z06. The kid will not!


Another question regarding torqueing them down. The shop manual says to use a sealant like Locktite or something. My machinist told me to put plumber's thread tape on the bolts and he likes to torque them down then wait a few hours. Then he goes back and loosens each one, one at a time so I don't lose the torque, then torques them back down.


What do you do and how do you do it? Thanks again!

Night rider327

iTrader: (13)

I have always used Permatex #2 non hardening on head bolts. Don't go crazy with it but give 3/4 of the threads a good covering.

Torque heads to spec in 3 steps. 1st to 30 ft lbs, then 45 ft lbs, then 65 ft lbs.

And check some of the bolts after the 1st few days of run time.. Most builds will not need re-torquing these days with better gaskets and what not.

NinjaNife

So I finally am back home and was able to measure the stuff; it appears that the block deck height is 0.045", and I've confirmed the cylinder diameter to be 4.040". This makes me wonder though; how does one shoot for a 0.040" quench height if the block deck height is already 0.045"? And does that kind of block deck height say anything about the type/quality of pistons used? All of this is assuming that I measured it correctly...I measured from the top of the block to the top of the piston (the outer ring that was the highest point, since these pistons are dished). You can see what I mean in the pic below.

As for the pistons themselves, I wasn't able to find a part number on the top of the pistons and I don't really want to take them out if I don't have to..so I've attached a pic of the top of one in the hopes that you'll recognize the type haha. Does the piston volume actually depend on the piston itself, or simply the diameter of the piston? And does the rather large block deck height (assuming that the 0.025" mentioned is stock) mean that the previous owner built it badly, since a thicker quench means worse performance (which seems strange to me, since the previous owner went through so much trouble to bore it out and replace most of the innards)?

Thanks for the help.

Brendan "NinjaNife" West

-=Z28=-

iTrader: (3)

Is that block deck height with or with out head gasket? I see the gasket is still on the block.

NinjaNife

That's with the gasket off. It is actually off in the picture, but there are some tiny pieces that stuck to the block when I removed the gasket and I haven't scraped them off yet (it's definitely off though; I even went out and double checked to make sure there wasn't a second one after you said that haha). I measured in the places where there was only metal though, so it should be accurate. A picture of the gap itself is below (although there isn't any reference to show depth...it's just so you know where I measured).

Brendan "NinjaNife" West

Thirdgen89GTA

iTrader: (5)

You'll need to clean/remove all gasket material and measure again.

Remember you are looking at some very small clearances here, and even a little bit of gunk can affect your readings.

NinjaNife

Will it make any difference in this case though? I didn't measure where there was gasket material; I measured where it was the bare metal...the only thing I didn't do in that sport was actually scratch/grind it to make it shiny, since I am keeping everything oiled down. I am planning on cleaning the rest of it, but I'm not sure I understand if/how my current measurement would be different unless there was gasket material where I measured.

Brendan "NinjaNife" West

Thirdgen89GTA

iTrader: (5)

Pistons can rock in the bore so you need to take measurements in two different locations for an accurate read.

There are video's on youtube that show where to measure and how.

NinjaNife

Ah okay; I watched a video on YouTube and will try to replicate the measurement technique tomorrow.

Thanks for the help

Brendan "NinjaNife" West

Night rider327

iTrader: (13)

I don't think your re-measure will net much change.. Read post #10 that I typed to 86Iroc.

Most people don't know or understand piston compression height, most shops don't care, etc.

Cheap rebuilder's pistons are know to have 1.540" compression height and this sits the piston .020" deeper into the bore.. Stock spec puts piston .025" bore with a 1.560" compression height piston.. The 1.540" pistons will have you .045" in bore which is what you came up with and sounds right to me.

You will find MOST auto part store rebuilt engines are like this. You will also find that MOST repair shop rebuilds will be like that. Along with a lot of 1st timer back yard guys rebuilding an engine because the cheap rebuilder's pistons are much cheaper than brand name correct compression height pistons.

Nothing much you can really do at this point.. Other than leave it, or change pistons, or have block milled.

If you leave it as is, your best and only good head gasket option would be fel pro #1094. Clean those decks really good, and spray the 1094 gaskets with copper spray a gasket and install.

This will give you .060" quench height, but that's the best you can get with what you have.

And don't fret too much, the .060" quench will not make or break the engine. It is just not optimize for best performance, but neither are those dish pistons lol. It is not like the wide quench will kill of 20 HP or anything crazy like that.

"Does the piston volume actually depend on the piston itself, or simply the diameter of the piston?"
YES.
Yeah the piston CC volume depends on any part of the pistons crown (top) that can hold liquid (and air). Like the dished portion below the high ridge around the top, plus the 2 valve reliefs (eye brows) The depth, size, dia. of those recessed places adds to the piston CC size.

Your pistons looks to be about a 12 to 14 cc volume

The larger the dia. of the piston is (bore size) the more compression you have, but the bigger the recessed portions are on the piston the less compression you will have

I can't remember if you said what heads you are running or what chamber size they are but here will be your est. compression using the fel pro 1094 4.100 x .015" gaskets and using 13cc piston volume as a base line

58cc heads = 9.58:1
62cc heads = 9.18:1
64cc heads = 9.00:1
67cc heads = 8.74:1
70cc heads = 8.50:1
74cc heads = 8.20:1
76cc heads = 8.05:1

novaderrik

those dished pistons kill off all your quench- so it won't really matter what head gaskets you use from that standpoint... so get the thinnest ones you can to get the compression up to try to squeeze the air/fuel mixture just a little harder, slap the heads on, and drive the hell out of it using the cheapest 87 octane swill you can find..

if you don't understand what "quench" is or how it affects things, i'll just relate my own personal tale about quench: when i built the vortec headed/HOT cammed 355 for my 71 Nova back in early 2000, i used the thick head gaskets that came with the cheap gasket set i picked up locally because i wanted to get it in and running, while also being told that i needed to do that to keep the compression down to run on pump gas with the 2 valve relief flat top pistons i was running... it ran good, but always rattled and detonated under part throttle on 93 octane if i put the timing where it made any power. it was fun, but i knew it was supposed to be better. so when i pulled the car apart to rebuild and upgrade the suspension and brakes, i pulled the heads off and put in some .015" Mr Gasket steel shim gaskets that i had laying around. when i got it back together, i noticed that it was snappier off idle and just generally felt better all around. after some tuning, i got it to where it pulled hard without ever detonating, and i could even start the car in third gear (lugging it like crazy) without any rattling... so i tried 89 octane, and never a rattle and more power... then i tried 87 octane, and got a little bit of ping on really hot days but still made good power...

so in some engines, quench can make it less prone to detonation despite the higher static compression ratio. those dish pistons you have pretty much kill all the quench, so your results will differ from mine even if you swap to vortec heads... but slide a set of 2 valve relief flat tops in it along with some vortecs and some shim gaskets, and it will totally change the character of the engine and make it better in every way..

NinjaNife

I re-measured it anyway, just to be safe, and got the same result. When pushing on the sides of the piston the readings varied, but the average is still approximately 0.045".

I think for now my plan is to just get it back together and get it in the car; this project has taken much longer than anticipated since I'm rarely home due to work and school, so I'd rather spend the time and money on getting the car running before I decide to do a performance rebuild. With this in mind, I would like your opinion on which gaskets I should get to put it back together:

Head Gaskets: http://www.summitracing.com/parts/fel-1094
Intake Gaskets: http://www.summitracing.com/parts/fel-ms93318 OR http://www.hawksthirdgenparts.com/ga...-5-0-5-7l-set/ (is one better than the other, and if so, how do I tell for the future?)

Originally I was going to get a full kit so that I would have everything (like this one: http://www.summitracing.com/parts/fel-2812/overview/), but now that the head gaskets have to be more specific and I don't know what thickness the kit ones are, I'm not really sure what the best option would be for the remaining gaskets. The only other thing I took off is the distributor; I left the timing cover and such on since I just wanted to inspect the cylinders and see what was under the heads.

Oh, and one more question..do you happen to know what sensors and such I would need to change if I swap a 350 engine from a digital dash GTA to a body with a 305 analog dash (I know the digital cars have a few extra sensors, but I'm not sure which are different on the engine itself)? Are the dashes even compatible at all, since the original engine sizes are different? I'm having to swap car bodies due to a crushed brace on the underbody, and was going to swap my digital dash in right away but now (due to the timing thing) I'm thinking about leaving the interior analog until I get it running. I'm not sure if I should make another thread or something for this question, so please let me know if I need to ask elsewhere

Thanks for the help.

Brendan "NinjaNife" West

-=Z28=-

iTrader: (3)

+1 for Night!

You are gong to want to clean the deck surface and head surface so it is spotless. careful on what you use. Dont want to disturb the deck or head surface. The best way to remove gaskets is with a sharp scraper and/or a can of aerosol chemical gasket remover. Spraying the gaskets with a chemical remover eliminates hard scraping and the risk of scratching or gouging the surface, especially on soft aluminum heads and blocks. The chemical does most of the work by softening the gaskets. The residue can then be easily scraped off the surface.

Another thing you should check, although there is nothing you can do about it, is check how flat/true the deck/head is. This is out of my machinist book, Flatness specifications vary depending on the application, but on most pushrod engines with cast iron heads, up to .003″ (0.076 mm) out-of-flat lengthwise in V6 heads, .004″ (0.102 mm) in four cylinder or V8 heads, and .006″ (0.152 mm) in straight six cylinder heads is considered acceptable. Aluminum heads, on the other hand, should have no more than .002″ (.05 mm) out-of-flat in any direction. On a performance engine, the flatter the better.

And one more thing, if you use those thin metal gaskets, As a rule, the recommended surface finish for a traditional composition style soft-face head gasket in an engine with cast iron heads and block is 60 to 120 microinches Ra (roughness average). But the recommended surface finish for the same type of head gasket in an engine with an aluminum head on a cast iron block is smoother, typically 20 to 50 microinches Ra. On late model engines with multi-layer steel (MLS) head gaskets, the OEM surface finish recommendations tend to be even smoother, say 20 to 30 microinches Ra or even 7 to 15 Ra. But the aftermarket also sells MLS gaskets with special coatings for many of these same applications that can handle surface finishes in the 50 to 60 microinch Ra range. So you have to know your gaskets and the surface finish recommendations for them by the gasket manufacturer, or the OEM if you are using a factory-style replacement head gasket. The only way to accurately determine if the surface finish is within the correct range is to check it with a profilometer.

Now, I took it to the extreme with all this. Mainly posted it for you to read and learn. Biggest thing for you is making sure everything is clean before assemble. I'd check for flatness too.

-D

NinjaNife

Thanks for the tips. I scraped it clean with a razor blade scraper, and plan to wipe it down with Acetone or a similar chemical before installing the gaskets. Hopefully that will be good enough haha.

What's the best method to check for flatness without having fancy equipment to do so? Just put a straight edge down or something?

I had never heard of a "profilometer", so I Googled it and most of the stuff that came up was over $1,500..is this a common tool for you guys, or was that just an example? How do you make sure you get it smooth enough for your gaskets (or do you just do the "clean it as best as I can and hope it's good enough" approach)?

Thanks for the help.

Brendan "NinjaNife" West

-=Z28=-

iTrader: (3)

LOL, Yeah, just an example. I wanted you to see/learn more.

Yes, use a straight edge and a set of feeler gauges. (metal straight edge or a piece of glass, has to be true)

I have used a straight board, must be really straight, and put like 80 grit paper on it and can use that gently to clean the deck. If there isnt a lot of junk, use a finer grit. coat the paper in wd40 or something. Ive actually straightened out a block doing that.
It will have to be paper for sanding metal tho. not wood.

Just make sure the surfaces are spotless. both the heads and block.

You will be fine.

-=Z28=-

iTrader: (3)

They use that profilometer to check cylinder wall RA too. Different rings need different finishes. the profilometer will tell how rough the surface is.

This is a magnified pic of cylinder crosshatch using a profilometer.



And this is from a lathe tooling marks. Pretty crazy. This lathe is accurate to .0002