Jeep Strokers

So, given what I can figure for my engine I have these two options for the gasket and their resulting figures:
.051" gasket (stock):
SCR: 9.94:1
DCR: 8.48:1
Quench: .0645"

.043" gasket (MP):
SCR: 10.11:1
DCR: 8.63:1
Quench: .0564"

So, which gasket would work better? In the sense that I wouldn't run in to any other problems and avoid pinging, for a daily driver

Its a 4.6 with the 68-231-4 cam.

-Chris

I'm sure i have asked before but, what altitude do you live at?


Flash

Ranges from 2,103 FT to 123 FT

SilverXJ wrote:Ranges from 2,103 FT to 123 FT

Are you sure you SCR is that high?

IF so i would definitely go the the thicker head gasket, and try and get more CC from your syl head.

Attention to details, such as any place that could detonate (sharp edges bumps exc) Is something that is simple to address now and a pain in the butt latter if it pings.(Detonates)

I thing its going to want Premium pump gas.............Quench, is better then most, so that helps..........


Flash

Last I checked the MP head gasket were not in stock anywhere in the USA. Are they now?

No, I just found one of the MP gaskets.

As for the rest... I came up with the SCR with the info Titan gave me on the block... and my cc'ing the head.

This is what I got from Titan:
Hi Chris, The normal build would be.

P3071 Pistons
258 Rods
258 Crank
MLS Head Gasket .051
.025 Off Deck
.030 over


After searching I found that the P3071 piston is also known as the 3241HC. And this data:
Part Number Description Size
P3071(6) Piston Set STD, 020, 030, 040, 060
Dimension
Bore Inch 3.875 Bore MM 98.43 Comp. Ht 1.592
C. Ratio 8.7:1 Ring Top 1.5mm Groove 2nd 1.5mm
Width Oil 4.0mm Pin Dia. 0.9310

From the Piston info in the FAQ I found the following data: Piston 3241HC - Silvolite, 1.592 pin ht, 14.1cc **

So, I use the 14.1cc from the forum info, the comp ht I found on P3071
258 Rods 5.875"
258 Crank 3.895"
Bore: 3.905"
From calculations I found that the deck clearance is: 0.0135"
Head CC average: 58.3

I used that data and came out with the info posted above. And below. Also, I am running the Comp Cam 68-231-4 cam.

If you would like to check my calculations feel free to. Could have done something wrong.

.051" gasket:
SCR: 9.94:1
DCR: 8.48:1
Quench: .0645"

.043" gasket:
SCR: 10.11:1
DCR: 8.63:1
Quench: .0564"


Stock:
Stock deck heigth: 9.450-9.456"
Stock deck clearance: .0215"
Stock bore 3.8759 to 3.8775 in (3.875")
Stock rod: 6.123 to 6.127 in.
Sock piston pin bore: 1.599 to 1.603 in.
Stock stroke: 3.411"

Intake Closing Point (degrees)
ABDC @ 0.050 lift plus 15 degrees
56* IVC

Personal, I'd like to see you CC it. Them spec's tell you what it should be............If you do a actual cc of the piston at TDC.
And you already know you head cc....................

All of then ## are grate for preliminary figures or planning of a build. Yours is all but put together. Time for a final, accurate SCR figure.

We already know the head cc is 58, now if you can measure the CC of the syl at TDC ( this will figure in the dish and the volume above the piston to deck surface)

Apply a thin layer of grease between the edge of the piston and the bore, at TDC. And a piece of plexiglass on the block. using a thin layer of grease on the block surface to seal the plexiglass. With a hole to fill with, and a small hole for the air to escape from.....................................
If you can get me numbers i will give you a accurate SCR with a .043 and a .051 head gasket.
You really need to do this be for you decide on which gasket will work the best for you!


flash

I am planning on cc'ing the cylinder next weekend, but it will still have to be back together by Sunday.

But based on the numbers above, you would recommend the .051 gasket?

As it is now it will ping if I don't run premium. The gasket is has now isn't an MP, but it is .041" according to the maker of the last gasket set I was sent.

I thing i would rather have less compression if i had to guess....... but then again, quench is now more.

I would say thicker head gasket, and Attention to detail,.........were it comes to potential hot spots that will cause pinging in the combustion chamber!

When you get it together and it does or does not ping on X grade of fuel it would be helpful for those that are building similar to yours and especially your altitude..........................OK ok i just want you to do it(cc the Deck/piston) for my on research


Flash

A couple more thoughts here.

Sense compression is being raise, do to improvement of Quench.......................Usable octane level is going to be real close between the two head gaskets.........

Do you have both head gaskets available(051" or 043)

I thing i would install them both (one at a time ) and check your push rod install hight.................Us the head gasket that requires the least amount of shims or no shims to get the preload Correct!(lifter preload)

Don't do a final torque on the head gasket bolts...........20-30 pound feet of torque will be fine as the rest of the torque is for bolt stretch or tension.
This way you don't have to worry about replacing you bolts after testing is complete.

Reusing the head gasket is not a problem as long as you keep both surfaces completely clean between the gasket.


Flash

Push rod length is irrelevant as I have a set of HS adjustable roller rockers. And the head has been ported and polished by myself. It is pretty smooth although I may go touch up where the head combustion chamber meets the surface.

Got the head off the 4.6 Titan today. Measurements are as follows:

Piston dish: 13.4
Head chamber volume: 20.26 (piston dish + area above piston)
Deck clearance: .035
Bore: 3.909 (.040 over I think, as pistons have 40 stamped on them)
Head cc: 58.3

I'm leaning toward the mopar performance .043 Gasket

With the .051" gasket I am looking at this (Base on the IVC of 56 on the comp cam 68-231-4 cam):
SCR: 9.6
DCR: 8.2
Quench: .086"

With the .043" gasket I am looking at this:
SCR:9.76
DCR: 8.34
Quench: .078"h

Opinions?

Use the .043" HG. I have a 10:1 SCR and 8.54 DCR and it runs fine on 93 octane(I'm sorry guys--I still haven't tried 89 or 91 yet to see if it doesn't ping). However, my quench is .0605-.0625" so it can support a higher compression than a bigger quench can (unfortunately there are no absolutes as to what quench can support what compression using what octane). There are some guidelines as to optimal quench(.040-.060") and max DCR that pump gas can support(supposedly 8.5:1, and mine is right at it). In your case, I would try to get the quench down using the smaller gasket.