HG Thickness Question

[Sside]

Hi guys, im wondering about the HG thickness i need, i asked my machinist to measure the Head and Block, however i think he may have gotten the Block height wrong, as its bigger than the 198.5mm spec. However the head height came to be 115.443mm so i know im already looking at a 1.8mm thickness just from that alone. So im wondering if the minimum was taken off the block can it be safe to say a 2.0mm MHG will work just fine. My block was also bored out .020 over and i was also wondering if the Titan MS MHG had a HG bore size bigger than 83mm.


Thanks for taking your time to read this.
~Sside

 

[IJ.]

Block needs to be measured from the Main bearing tunnel to the deck.

 

[GC89]

You want to choose the thickness that gives you the optimum quench area and compression ratio. You should shoot for a quench area around .8-1 mil and you'll have to calculate your compression ratio. what pistons are you using?

 

[JDMMA70]

Filling in for Sside as hes in the garage putting the last bits together.

Hes running NPR .020 Piston, pretty much OEM pistons i guess you could say

 

[Sside]

Thanks JDM, and like he said I am running stock quality pistons just .020.... I will go ahead and call the machine shop today and try and get more information on exactly what they did. Ij and Gc89, thanks alot guys... Ill keep yall updated...

 

[Sside]

Okay guys, I measured 198 mm on block and on the head 115.443 mm... So would a 2.0 mm with 86 mm bore hg be okay... (I am bad with compression ratio calculator) and I will not be going over 400 hp......

 

[jdub]

I assume the above values are with the head/block decked and prep'ed (RA spec wise) for a MHG?

To maintain stock CR (assuming stock CR pistons), you need a 2.427mm thick MHG. Stock bore is 83.0mm...if you bored 0.020" over, the MHG needs to be 83.5mm for the cylinder bore.

A 2.0mm MHG should be ok as far as CR goes, but you do need to get the cylinder bore as close as possible...an 84mm would work. Why not order a custom made Cometic MHG? The Titan MHG is made by Cometic after all...you could get the exact thickness and bore you need for basically the same cost.

BTW - That is a lot of material removal for the block/head.

 

[Sside]

Thanks alot Jdub.... I been looking for one and nobody seems to have a 2.00 mm thickness and 84 mm bore... I am looking at ordering a custom one from Cometic right now... I did find one that is currently in stock, brand is Titan but its a 86 mm bore. Would this happen to work?

 

[jdub]

Ummmm....

but you do need to get the cylinder bore as close as possible...

I wouldn't use an 86mm MHG on a 83.5mm bore. Not unless you want a 2mm gap that will accumulate carbon (making for some nice hot spots) around the base of your combustion chamber.

Cool your jets and order the Cometic....2.4mm thickness and an 83.5mm bore.

 

[Piratetip]

Intriguing info.

Titan lists
Cometic - All 84mm
Greddy - 83 & 85
HKS - All 86

Why would anyone run an HKS?

 

[IJ.]

Blown everything on that list excluding the Greddy

I use a HKS Stopper now so far no failures.

 

[Piratetip]

An 86mm bore Ian?
Or do they have multiple bore sizes per thickness / per stopper or bead type?

 

[IJ.]

Stoppers are 86mm only Nick.

 

[grimreaper]

^ im assuming you bore it out with the block and tq plate when stepping up in piston size?

 

[Sside]

Hey guys, I ended up talking to the machine shop and thye said my block was never machined before... They took off 7 thousands.... I gave that number to JDM7 and he came up with my thickness being 2.0 mm. So now I need a 2.0 mm thick and 84 mm bore. Closest gasket I can get within two weeks is a Greddy at 2.0 mm thick and 85 mm bore. Cometic would be 7-8 weeks for a custom MHG. I am scared to go with with Greddy because I am not sure if the deck job will do. Ive heard Greddy gaskets need to have a really good block deck job to seal. Wht do you guys think?

 

[InFrnt0fU]

P A T I E N C E. Wait for the custom cometic. The smallest things can hurt you down the road. I overtq'd the head less than 8% over ARP specs and a year later I'm having to do it all over again. Save your money over the 2 months and buy your car something nice for letting it be patient haha.