I have finally collected most of the parts that I need for my 350 swap, but it has come to the time where I need to select a head gasket. The problem is, I have a new block and aluminum heads. This means the deck height is 9.025, putting the pistons .0239 " into the hole. Quench would be a perfect .04 with a .015 head gasket, but I have aluminum heads. The heads have 64cc chambers, putting compression ratio at 9.5:1 with the .015 gasket and the installed pistons. The pistons are 12cc D-cup style dished pistons. I originally was going with 64cc iron heads, so I needed the compression down, but I decided on aluminum, and thus my problem.

If I decide to go with a .020 head gasket that will work with aluminum heads, my compression will be around 9.4:1. This puts my quench at right around .045, which while not ideal, should work well with the low cr.

Should I use a .020 gasket compatible with my heads and deal with the lower CR, should I sell my dished pistons and get flat-tops and have the rotating assembly re-balanced, or should I use a .020 gasket and have the heads milled down to help boost the CR. This motor will be in a daily-driver, but I want the power to be there as well. Will the 9.4:1 CR be low enough to seriously affect performance? The engine is a standard 4" bore 350, with a standard 3.48" stroke crank and 5.7" rods.

 

Why don't you have the block decked. It does not cost that much. I would use the GM .028" headgasket and have the block decked accordingly.

 

The reason I don't want the block decked is because it has the cam bearings installed, along with all the freeze plugs, and its brand spanking new. Thats extra money I'll have to include in the price of getting it decked.

But theres probably no way around it. Without getting it decked, I'm going to be fighting something, whether it be less-than-ideal quench or low cr. It's just frustrating at the moment thinking I have to get the new bearings redone.

 

I just ran a few numbers, and it seems that even if I get the block 0 decked, and use an appropriate gasket for the .040 quench, I still get around 9.4-9.5:1 cr. The dished pistons and 64cc heads are keeping me in the 9.5 range, and without changing either, I'm stuck at that compression.

Is 9.5:1 compression with aluminum heads going to be a real issue? The car will never see a track, and unless theres a significant difference in upping the cr, I'm thinking just go with a .020 gasket and run it with slightly lower compression.

The heads are 64cc IK200s, and I'm using the LT4 hot cam, 1.6 rockers giving me .525 lift at the valve. Will my dynamic compression be too low?

 

ooh, IK200's? ie, 200cc intake port, or is that just the name brand? I forget...

I think that's a tad low on CR, with the HOT cam and somewhat big heads. It's not ideal, but it's ok. You might be down a few HP, but nothing to write home about. Mostly low end torque loss. I'd deck the block and use the .035" gasket or so. Or run the .015" gasket as is. Both options essentially get you to the same place.

The thin gasket route, and using different pistons would probably be the most ideal choice. Set yourself at around 10:1 or so with a 5cc valve relief piston (in that range).

Planing the heads, (and probably the intake) isn't ideal, due to the fact you'll have to machine the intake as well. Kinda boosts the price up.

Do you think you can return your pistons and easily swap to others? If you have to try to sell your pistons (good luck), and rebalance your rotating assy, ie, ~$600 when the smoke clears, i'd just leave it as is. You might be down 15-20HP, but you're in the clear when it comes to detonation. Just gap the rings large and plan on running some nitrous in the future. (Lets not rule anything out eh?)

 

Yeah, the rotating assembly was purchased as a kit, so I would have to sell the pistons outright. I think I'll just run it as-is. At least I'll never have to worry about detonation, and I can always run pump gas I found a .015 gasket by FelPro that a few have said will work fine with aluminum heads. The ring is pre-flattened, and is embossed in rubber for a good seal and to prevent etching in the head. The bore is 4.1" so that will give me slightly more compression which will help too. You can check it out here.

 

Anyone?

 

Do you have more questions? I thought you had decided?

 

I would put in flat tops and have it rebalanced and run the thin head gasket. Resell the dished pistons.

 

Sorry, I was wondering if anyone has had experience with the thin head gasket and aluminum heads. I should have specified! Brodix says you can use "new type o-ring gaskets," and they may imprint the heads, and this is usually acceptable. I assume that the .015 gasket posted above should be ok?

I really am beside myself with this issue. I have spent over 2 years getting this project ready, and I don't want to take the easy route out just yet. I think I will keep the block as-is and run the thin gasket, and sell the dished pistons. I can get the same type but with flat-tops for $180, 7cc instead of the dish 12cc, which pushes compression up to 10.05. I think, with all the time and money I have spent, I will be a lot happier in the end, even if I don't really notice the difference.

Thanks for the time and help Sonix, and Nighthawk. New pistons here I come!

 

Here's what a set of cam bearings for a SBC costs. Big whoop.

Cam bearings

Not enough to pork building a "brand spanking new" motor over.

Get the block decked. Do it right. Cheeeeeping out at a critical moment isn't worth it, in the long run. And in this case, I suspect you'll find out that the long run isn't even very long.

 

The cost of getting the block decked and new cam bearings will be less than new pistons and the hassle. Just do it right. You will be glad you did.

 

Yes it would be, but I would still be stuck at my 9.4-ish compression. I have to change either the pistons or the heads to get a better cr. I understand that a lot of people get the block decked, but why should I get it done when I can run a .015 gasket? As long as I use the appropriate gasket and keep the head bolts properly torqued, would I really see a longevity issue? Is there any definitive answer as to whether it will make a difference?

From what I can tell, the embossed head gasket from Fel-Pro (#1094) should work just fine with aluminum heads and iron block. A few guys on hotrodders.com and camaros.net have done this without any issues. The 2 surfaces appear to be VERY straight and flat since they are new and unused. I checked using a machinists straight-edge and I could not see any gaps.

 

That is a way to go if it works. I would think that there would not be much room for error and both the block deck and the heads would have to be dead nuts flat.

 

I think they're talking about racers that do a yearly rebuild. If the gaskets imprint the heads they would have to be resurfaced at each teardown. If you pull the heads off this engine every 100k miles and have to have them resurfaced I don't think it's going to be a big deal...

 

i run brodix racerite 200's.. the IK heads are like a little brother to the racerites.. but anyway, i run the gaskets you are looking at.. 4.100"x.015" embossed steel shim and I JUST SPRUNG A LEAK.. i get a smoke show for a minute after start up.. i even installed the gasket with a copper head gasket spray.. i would just deck the block, and run a regular felpro gasket.. now i have to pull the topend and install a new head gasket for both sides..

 

not telling you what to do TA or trying to hijack anything but with high cylinder pressures like your engine is seeing i would think that the copper spray wouldnt be a good idea maybe try another shim without the spray i think sofa mentioned that the copper spray would act as a nice lubricant and cause that type of failure...

 

Just wondering, how many miles/months or whatever do you have on those gaskets? I checked your VBgarage for your buildup, and I noticed that you are running 11.1:1 compression. Do you think that may have contributed as well? I don't plan on running more than 10.1:1 (i typo-oed 10.5 in an earlier post), and the car will never see a track (pure street car).

 

i only got about 750 miles on the gaskets.. i guess you could say a combo of 11:1 and that copper spray contributed to failure.. i shoulda used a real gasket sealer.. something thick.. but whatever.. i wont be using those gaskets anymore.. 0.7:1 compression loss wont be a whole lot.. maybe 20hp at the most..

now i can safely spray it for real.. before i sprung the leak, i was considering a 100shot with the 11.2:1 on 92 pump.. not gonna happen anymore..

 

Alright guys, I had a birthday recently and was away for a while. I have decided what I am going to do. Since I have to get the block decked and cam bearings installed, I am going to go ahead and get some flat-tops and have everything balanced. Since everything will be at the same place anyways, I am going to take the cam as well and have the short-block assembled for me. This way I can save some time since it has to be done and installed by late May.

Over out.

 

good choice..

 

How did the build go?

Flat tops are good for big chamber heads. Reverse domes make more power with a smaller chamber. On my setup, I used reverse domes and angle milled the heads to 55cc. I set the pistons down .005" in the hole.

-- Joe

 

Oh! ge!

I am lost now!
Reading this post I get scare of my setup.
I have work on it for the last two years or so and now here has been mentioned a head gasket failure with the one I have, (FEL1094) on top of that some of you guy's say don't use the copper spray sealant.
You know I did use the VHT copper sealant in combination of this gasket.

I will to start the engine in several weeks and wonder if there are other good experiences with this combination.

What I have is as follow:
AFR 180 heads milled down to 58 cc (to get some decent compression)
New engine like "Phatfiddler" with a deck height of 9.025"
The result compression is 10.2 and the DCR is 8.26

"Phatfiddler" like "anesthes" say I wonder how the build runs and did you any change to your last decision mentioned here above?

So what do you say?

Regards,
Cobra289

 

Hey,

I forgot about this post! lol. But anyways, the engine was never built. I moved to Florida in the middle of the whole thing and had to get everything shipped down by truck. With my new job, finances are a lot easier to manage, so I changed plans. Same intake and block, but I'm selling the pistons and crank to go all forged. I bought the S400 BW turbo to go on it. Still havent got the block decked, but w/e. It'll happen in time.