Mitsubishi MLS headgasket thickness, CR issues.

[SaulHudson]

I've been searching for a total of about 3 hours now, it seems this is a relatively untouched topic on here which Is very surprising.
I am using mitsubishi MD 349347 with wiseco 10.5:1 pistons.
Currently I have been unable to find mitsubishi published compressed headgasket thickness or more than 1 person stating the thickness. One vendor lists it at .051" one reply on this forum says .054"

When measuring my own gasket I get .051" on the edges and .065" in the center. The center has a shim and doesn't seem like it compresses any more but then again that is not putting the clamping force the head would. If it is indeed .065" that would put my CR at 9.5:1 which is far from where I want to be of 10+


Does anyone have a definitive answer as for the compressed thickness of the oem MLS headgasket?

 

[RvlutionMtrsprt]

.051"

 

[bud09]

pretty sure if you even used the .054" gasket it wouldn't change the compression by a full step. and just because the pistons are said to be 10.5:1 doesn't mean that's what you're going to get, there are other factors to take into effect. the compression could even be higher than the advertised number.

 

[Boosted6]

I measured my headgasket before installing it and the center is indeed bigge, outer edges are the real thickness compressed #'s to go by. I would not worry about your compression changing more than .2-.3 with a thicker headgasket.

 

[Kapok6]

doe not answer your question, but it's related to the same topic.

http://www.dsmtuners.com/forums/articles-engine-fuel/468895-how-figure-compression-ratio.html

 

[SaulHudson]

pretty sure if you even used the .054" gasket it wouldn't change the compression by a full step. and just because the pistons are said to be 10.5:1 doesn't mean that's what you're going to get, there are other factors to take into effect. the compression could even be higher than the advertised number.

Actually, if its .051" my CR would be 10.17:1 if its .065" it would be 9.5:1.
While I know it's not a full step 9.5 is too low while 10 will be fine.



Thanks for all the answers, much appreciated.

 

[BogusSVO]

You can not measure the bead roll of the gasket, it will flatten out when the head is torqued on.

So if you use the .051 or .054 you will be close to correct compression thickness.

Now here is the info for the Felpro 1153-1 MLS HG

Federal-Mogul eCatalog Resource Center

It has a volume of 8.3cc

The thickness is .055

Since most info used is based off the OE info, this gasket should be very close to figure your CR.

 

[SaulHudson]

You can not measure the bead roll of the gasket, it will flatten out when the head is torqued on.

So if you use the .051 or .054 you will be close to correct compression thickness.

Now here is the info for the Felpro 1153-1 MLS HG

Federal-Mogul eCatalog Resource Center

It has a volume of 8.3cc

The thickness is .055

Since most info used is based off the OE info, this gasket should be very close to figure your CR.

Thanks for the awesome info!

 

[99gst_racer]

Actually, if its .051" my CR would be 10.17:1 if its .065" it would be 9.5:1.
While I know it's not a full step 9.5 is too low while 10 will be fine.

I think your math of incorrect somewhere. Wiseco's "10.5cr E85 series" pistons are actually almost a full point lower in a DSM. Here's my numbers that I used to calculate my CR using these same pistons with a Felpro MLS:

Bore: 3.366"
Stroke: 3.465"
Gasket bore: 3.425"
Gasket thickness: .051"
Deck height: 0
Dome volume: -4.5cc
Chamber volume: 48cc

Compression ratio = 9.4:1

Even with an untouched chamber and the piston hanging .015" out of a .040" overbore, you wont get over 9.8:1.

 

[BogusSVO]

Racer, I will have to agree.

When I ran the math, I came up with a 9.51 CR

I used a 46cc head, with a thickness of 5.191

The gasket thickness was .055

Now with a composite HG with a .039 thickness it works out to be 9.88 CR

 

[lasthope05]

The only true or close to 10.5:1 pistons at zero deck are forced engineerings custom spec Wisecos that has better quench zones then the standard 4g63 dished pistons. If you wanted more compression you can also switch to a 42cc head.

 

[99gst_racer]

The only true or close to 10.5:1 pistons at zero deck are forced engineerings custom spec Wisecos that has better quench zones then the standard 4g63 dished pistons. If you wanted more compression you can also switch to a 42cc head.

Yup, and they can spec out pretty much any reasonable compression ratio.

A flat top would be around 10:1, so it would take a dome to get beyond that.



BTW, I've spoken with Wiseco reps on more than one occasion about the E85 series pistons have incorrectly listed estimated compression ratios for the DSM and EVO applications. They didn't seem to care much. So I hope that anyone who actually cares about compression ratio is crunching the numbers themselves prior to ordering anything.

 

[SaulHudson]

STM told me aswell they run low but they thought only .5

Here are my specs.
Stock stroke
Stock bore
Deck height 5.189
Piston with valve relief 4.5cc
Chamber 45cc

 

[bud09]

so on a completely untouched n/t engine i would be around 8.5ish?

 

[99gst_racer]

Deck height 5.189

Typo?

 

[SaulHudson]

Typo?

Rechecked, 5.191

 

[BogusSVO]

Racer, Looks more like a head thickness measurement.

 

[99gst_racer]

Here are my specs.
Stock stroke
Stock bore
Deck height 5.189
Piston with valve relief 4.5cc
Chamber 45cc

Using those specs (assuming 0 deck clearance), you'd be at 9.73:1.

 

[SaulHudson]

Yeah that's head thickness sorry.

Thanks Racer.


Thanks for all the replies. Awesome info in this thread