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4.060 head gasket or 4.030

Old 05-15-2018, 07:11 PM
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Default 4.060 head gasket or 4.030

I have a stock lq4 and im fixing to put 243 heads and I have been told now by several people that i shouldn't run the 4.060 bore gasket and that I should run a 4.030 bore gasket. I did some research but still need a little clarification on this matter please, so I appreciate all the help

thanks
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Old 05-16-2018, 06:15 AM
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Originally Posted by LsxS10blazer View Post
I have a stock lq4 and im fixing to put 243 heads and I have been told now by several people that i shouldn't run the 4.060 bore gasket and that I should run a 4.030 bore gasket. I did some research but still need a little clarification on this matter please, so I appreciate all the help

thanks
if itís standard bore why not use the GM replacement piece which is 4.020Ē. Itís cheap as well
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Old 05-16-2018, 06:45 AM
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I was going to go with a thinner gasket and did not see a 4.020 but I will look into it. Thanks
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Old 05-16-2018, 10:42 AM
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If you go to a .040 your quench will be like .030-.033 which is really tight, have you considered milling the heads and running standard gaskets instead? Standard gaskets are far cheaper too.
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Old 05-16-2018, 10:47 AM
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Yes heads are milled to 60cc and going with a thinner gasket to get compression to 11:1. When I talked to cometic they said to run a 4.060 bore & .040 thickness. I'm just trying to see if people have ran the 4.060 or if I need to reconsider
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Old 05-16-2018, 10:58 AM
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Originally Posted by LsxS10blazer View Post
Yes heads are milled to 60cc and going with a thinner gasket to get compression to 11:1. When I talked to cometic they said to run a 4.060 bore & .040 thickness. I'm just trying to see if people have ran the 4.060 or if I need to reconsider
If you're set on running the .040 and only want to know 4.030 or 4.060, 4.030 is what you should use. The gasket should be as close to the bore size as possible. Obviously not under it though.

Technically you can run the 4.060 but I have no idea why you would want to. You can also technically use a wrench for a hammer, doesn't mean it's the right tool for the job just because it works.
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Old 05-16-2018, 11:51 AM
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I'm in the same boat with my lq4 and the closest thin felpro gasket is 0.041" with a 4.100" gasket bore diameter. The 0.040" with 4.060" gasket bore diameter unfortunately is just offered by Cometic at the moment.
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Old 05-16-2018, 12:01 PM
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Originally Posted by foxsl View Post
I'm in the same boat with my lq4 and the closest thin felpro gasket is 0.041" with a 4.100" gasket bore diameter. The 0.040" with 4.060" gasket bore diameter unfortunately is just offered by Cometic at the moment.
What keeps you guys from milling the heads another .010 and running standard gaskets?

And if yall are on 4" bore why do you wanna go with a 4.060?
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Old 05-16-2018, 12:05 PM
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If I end up having a piston to valve clearance issue then I can always go to a thicker gasket that's what I was always taught; if I was taught wrong then I guess I need to learn some new stuff.

Cometic was the company that told me to run a 4.060 that's why I was checking before I did order them
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Old 05-16-2018, 12:06 PM
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I checked Texas Speed website and they have a 4.030 so if that's what I need to order that's what I'll get
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Old 05-16-2018, 01:07 PM
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Originally Posted by LsxS10blazer View Post
If I end up having a piston to valve clearance issue then I can always go to a thicker gasket that's what I was always taught; if I was taught wrong then I guess I need to learn some new stuff.

Cometic was the company that told me to run a 4.060 that's why I was checking before I did order them
People get away with running 4.065 LS9 gaskets even on 3.78 bore truck motors but I don't see the point, I want the most gasket sealing surface possible. The larger gasket opening will cause a very minor drop in compression and affect quench as well. I just don't see why people do it. It can and has been done though and some people push it like it's god's word.

As far as going to a thicker gasket later.. You really should be measuring your PTV before you buy your gasket. It almost sounds like you plan on putting it together then finding out if you need a thicker gasket. If you go that route you'll need a whole lot more than gaskets. Yes you can always go to a thicker gasket later, but is that after the valves hit the pistons and break and take out the entire motor or is that after you spend a ton of money on custom gaskets and put them on and possibly find out they don't work then you've wasted money.

You can use your old gaskets to measure PTV and see what you've got PTV wise. Some people even use washers and the other day I saw someone say they use old CD's

One other thing on the gasket size, there is no benefit to running the larger gasket than necessary. If cometic was out of 4.030 that would likely be the only reason they told you to go 4.060
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Old 05-16-2018, 01:14 PM
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Originally Posted by A.R. Shale Targa View Post

if itís standard bore why not use the GM replacement piece which is 4.020Ē. Itís cheap as well
I want 0.040-0.041" thickness that's y
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Old 05-16-2018, 01:17 PM
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I wasn't going to start it with out checking for piston to valve clearance but I figured I could get away with a .040 and if not then order thicker but I understand that's money thrown away on gaskets doing it that way and after doing more research I saw exactly what you said as far as that would be to tight of a quench possibly and that i should go with a .045 or even back to stock
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Old 05-16-2018, 01:29 PM
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When I used to help maintain a Outlaw we had a set of copper test gaskets cut on a water jet out of .010 and .005 copper shim stock, they made us 6 of each, we used them for checking PTV clearance whenever we changed cams or pistons, or had the motor torn down.. I think they cost about 150 bucks to have made.. One nice thing is you could torque the head down on them. YMMV..
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Old 05-16-2018, 02:45 PM
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Originally Posted by LsxS10blazer View Post
I wasn't going to start it with out checking for piston to valve clearance but I figured I could get away with a .040 and if not then order thicker but I understand that's money thrown away on gaskets doing it that way and after doing more research I saw exactly what you said as far as that would be to tight of a quench possibly and that i should go with a .045 or even back to stock


People do get away with running .040 and having .032 or so of quench, but there's no margin for error there, one little oopsie and it's over, something isn't perfect with your setup it's over.... etc. And with stock gaskets you have around .041-.045 which is still good.. I haven't seen .045 gaskets, if they have them that would be cool, but honestly I think GM went to great lengths to get the quench about as tight as it can reasonably be already with long term durability in mind from standard components.

And honestly, going through all of that to gain about .2 points of compression and be on the ragged edge just doesn't seem worth it to me. We're talking a gain of probably less than 3 total horsepower and now you have no safety margin. I'm with you though, I want as much compression as possible, but trading a little safety for 2-4 hp or so..

All out max effort race motor with strict control and frequent rebuilds.. cool go for it. Daily driver that's gonna see some wear, things are gonna move, little incidents here and there we don't account for... not worth it, in my opinion.
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Old 05-16-2018, 02:58 PM
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Yes I agree and thanks for opening up my eyes a little bit more so I can realize that this is going to be a street vehicle and not a track vehicle and therefore should not be worried about gaining every little bit without considering the safety part of it

appreciate it
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Old 05-16-2018, 04:54 PM
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Originally Posted by LsxS10blazer View Post
Yes I agree and thanks for opening up my eyes a little bit more so I can realize that this is going to be a street vehicle and not a track vehicle and therefore should not be worried about gaining every little bit without considering the safety part of it

appreciate it
No problem man, I'd still shoot for compression, but I think you might be better off doing it through milling, to be on the safe side. And giant cams is where you normally run into PTV problems and also run into driveability problems. You can build a hell of a fun car that will out run your buddies donkey dick cams with a mild/big cam and have better driveabilitly too. I use to wear out my buddies that had cams with a bolt on only car, because they went for max power and sloppy builds. I was a full weight 200k mile car. The combo and how it performs at all times is far more important that peak numbers. Makes for a more fun car and a lot of times an actually faster car


good luck with your build man
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Old 05-16-2018, 05:02 PM
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Thanks
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Old 05-16-2018, 05:51 PM
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Yep. On the street, it's more about what's under the curve than its peak.
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Old 05-16-2018, 11:42 PM
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Originally Posted by foxsl View Post
I want 0.040-0.041" thickness that's y
sooo youíre not the OP and he did not even specify what quench he was looking for either.
Yes all aluminum engines can start as tight as .033Ē quench room temperature but time should be given to
warm up and expand before wacking it to seven grand thatís all
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