Happy holiday

Who knows the thickness of a stock vq35 head gasket?
I have a used set at of hg's at the shop but I was thinking
they might be off a .001mm since they are used.who knows
According to nissan stock CP= 10.3:1
According to HKS .7mm Hg= 10.3:1
FYI the Nismo HG=.7mm also
A local performance shop said .7mm=higher CP
The thinner HG=+CP
Thicker Hg=-CP

If you have a definite answer I would appreciate it
Thankyou

 

IIRC the stock headgasket for a 3.5 is .3mm. The thicker the headgasket the lower the compression, and vise versa.

 

thinner =higher CP
thicker = lower CP

 

.6mm according to charles at CJ motorsports

http://www.cj-motorsports.com/headgaskets1.htm

 

What's the significance?

 

I'm assuming this is for boost.

 

Doesn't really answer my question though...

 

Better sealing for the higher boost, and it *SLIGHTLY* lowers the compression, which is obviously good for FI.

 

Thicker head gasket ≠ better sealing. And who said these head gaskets lower the compression ratio?

 

OEM headgaskets "seal" well also.

Its common with other motors that a thicker headgasket will lower compression make the motor more boost friendly. Depending on how much boost your looking to run, or better yet if you need a lot of boost to achieve the desired power goals, use OEM gaskets and the Tune is where its going to count most.

 

Thankyou
You are correct

 

anyone using copper spray for the head gaskets?

 

Nope. Hows the build coming along?

 

Take that .6mm with a grain of salt. I've seen other figures floating around (.24/.25/.3). Also, none of these off-the-shelf head gaskets lower the compression ratio, FYI. Thirdly, if the head gasket thickness was different enough from stock to significantly affect the CR, you'd run into some fitment issues with the LIM and inner timing cover and altered cam timing. Lastly, lowering CR by using a thicker head gasket raises squish/quench volume and might contribute to MORE detonation than having a higher compression ratio due to a less efficient combustion chamber.

If you want lower compression you should do it right and install low CR pistons. Might not be what you wanted to hear, but there it is.

 

The "off-the-shelf head gaskets" dont change the CR Then Why are they sold in different sizes?... .05mm-.1mm from stock will affect the cr but not to the extent you have described above.I understand squish/quench as much as dodge did when they designed the original HEMI
combustion chamber.Not that crap They make now.Fyi imho I am doing it the right way. I am just clarifying thickness of said head gaskets.
Considering the fact that vq blocks dont have a "ring" option & sleeving is overkill I decided to go with a bead/stopper ring type gasket.
Yeah the nismo/cosworth heads are crazy expensive waaay over kill 4 me.
Thankyou for your input.

I'll make sure to let the org know final CR once my machinest gets to work.

 

IMO no good machinist/engine builder would suggest a thicker head gasket based on its affect on the squish area. It's not worth the ever-so-slight (if any) drop in compression.

In any case which HG are you going with?

 

The machinist did not suggest, the performance shop did & stated It would incrase the Cr. Like you said "with a grain of salt".lol
HKS Because its listed as stock CR & has Stopper ring type support, Also has 4 layers that should assist with the shear effect.

 

HKS = best HG out for the VQ35 as far as resilience under boost @ > 500WHP is concerned. Good choice. Which head fasteners you going with? Not standard ARP, I hope...


BTW, the shearing effect only applies to iron block/aluminum head engines since they expand at different rates. All-aluminum engines don't have to worry about that so much.

 

Yea I chose a .74mm cometic. We had to adjust the holes in the timing cover and LIM to compensate for the thicker HG. With the boost and power I'll be running, this gasket gives me peace of mind...along with the J&S of course

 

Agreed...As of right now yes. Standard Arp stud debate is uhhhh
controversial. I know you are gonna give me the look but.lol
We belive alot of the "headlift" issues have very little to do with the studs in most applications. More like improper install ie (over torque) thread cleaning/head prep.When N/A guys reported "headlift" I figured it could also be a "bad" tune (^cyl psi) preignition/detination etc...
I also made a few calls & asked around to see their real limit, With a proper install+tune=550whp according to injected performance & you know who works there I am still looking at the L19's but they seem to be overkill. You are right about the shear effect...Just figured I would be a bit more safe Stay tuned...

 

Ok seriously. The stock head bolts are good to over 500 WHP as well and I've never heard of "head lift" on an n/a VQ35 using them to boot.

Did I mention they're alot cheaper too?

 

I just measured my used stock HG, i got .8mm...

 

The measurement we're looking for here is the installed thickness.


Thanks for checking though...

 

doh, my bad ... I guess I should read a little more next time

 

I'm 99% sure its .3mm.

 

did you ever look into the cosworth head studs? http://www.cosworth.com/shop_item.php?productid=509

they are $314 + shipping..might want to call them monday and ask them about the torque specs...

my build is coming along slowly...lol..i ll be working on it more monday since i was pretty close putting in the rod bolts...got tired and it was getting cold.

my head gasket of choice is cosworth but its .6mm

Few speed shops that i know recommended these head gaskets over HKS, but I will give them a call monday and ask why. I will also post up the info their reasons why as well...

here's some of the specs if you or anyone else is interested:

"Individual die cut layer of stainless steel with superior consistency compared to laser cut gaskets

Pre-coated stainless steel using nitrile rubber that is exactly 0.25 microns thick

Manufacturing dimensional tolerance of .00001”

Die cut manufacturing process ensures smooth edges, unlike laser cut gaskets

Cosworth head gaskets are manufacture from pre-coated material ensuring consistent distribution of coating with no high or low spots

Coswoth gaskets feature a “stopper” layer for additional torque around each cylinder

The width of sealing area is specific for each application thereby providing ultimate sealing properties

Every Cosworth high performance head gasket has been engineered to ensure absolute perfect distribution of torque around each cylinder. Gaskets that do no include the feature may have torque “spikes” around each head bolt along with torque “valleys” between the cylinder bolts resulting in uneven and or poor sealing"

 

having built several motors.... including 98MaxedOut's

the stock gasket size is 0.3mm... for those that do not understand it's about 3/10 of a millimeter.

by using a thicker head gasket.. you are creating more surface area between the head and block.. thus LOWERING compresion..
HKS HG is .7mm (about twice as thick) (made in Japan)
Cosworth makes them .6mm and (made in UK)
Cometic makes them in any thickness you want.. from .27 to like .80mm.. (Made in the USA)

as far as OEM Head studs holding up to 500hp.. nismology why don't u take that chance.. I would not.. and i would not recommend that to Anybody..

I HAVE seen a n/a 02 max vq35 block with rear head lifted on one side... car was overreved to 7200. i tihnk i even have a picture of it on that kid's camera.. head was lifted about 1mm.. you can clearly see where the oil and coolant started seeping out from the gash.. the Rod Bolts were Fine..

ARP head studs will cost you $90 over OEM.... heh I'd REALLY hate to rebuild a motor because someone decided to save $90 I can understand if they cost $400

u can only learn so much from reading.. the rest (i.e. experience) u have to learn by Doing.

 

I understand the theory. As of yet no one has calculated the resulting CR with just these head gaskets since most people raise or lower the compression at the same time. The gasket companies aren't advertising the fact that their head gaskets lower the compression so the difference must be negligible. Got numbers?

65 lb-ft isn't much. There's no proof that standard ARP's are any better than oem bolts.

FWD 3.5 oem gaskets are two layer, RWD 3.5 gaskets are 3. Who's to say that it wasn't just a HG breach that got worse over time? It's no secret that the FWD gaskets are junk. My bud bought a 3.5 to put in his max and the head gaskets were blown. We threw some OEM Z33 gaskets in there and no problems since. I used to work at a nissan dealer...there were quite a few cases of head gasket failure on the transverse mounted 3.5's. In any case there are RWD VQ35's out there making 500+ reliable WHP with the stock gaskets AND bolts. Guess they're flukes.

As for standard ARP studs, a road racing Z33 over on my350Z comes to mind. Aftermarket head gasket, standard ARP studs, head lift. On an n/a car......

Haven't seen that happen with OEM bolts and Z33 headgaskets.

L19's or OEM for me. I just don't buy into the fact that just because something is made by ARP or is a stud/nut as opposed to a bolt it is categorically better than stock. Sorry if that upsets you...

Interesting. What a concept....

 

Well I stopped pass the shop yesterday & measured the used oem Hg and the new hks Hg
Oem .6mm-.7mm depending on where I measured
Hks .7mm
Fyi I used a digital micrometer
Are we confusing mm's with inches?
.7mm=.027"
.78mm=.030"
.3mm=.011" About the thickness of 3 sheets of paper.
Thankyou all for your input.

Vipervadim are you measuring the hg out or installed?
I am not doubting anyones input just wanted to know how you come up with these measurments.

 

Keep it comin' fellas.

 

as for the cr talk per the hg it is pure physics that if you alter the size of the hg that alters the clearance volume and the displacement volume and that will alter the cr.

compression ratio is calculated as max volume/min volume

a change in hg directly changes the clearance volume and will have an effect on the cr.

i'm sure you motor gurus would have the volume figures laying around and can figure out how much the cr will change based upon a hg change.

 

Understood but the problem is that we don't know how the installed thickness of these aftermarket HG's differs from the stock one, if at all.