2 Head Gaskets???

Dave Goob Cook · 12-26-2007, 04:01 AM

Quote:

Originally Posted by art leong

Has anyone tried doubling up on MKS headgaskets. Two of them would give me .080 thickness.
I'm trying to be able to change compression ratio with out doing the machine work all over again.

How much compression do you want to lose?

What are the bore/stroke, dome cc's, chamber cc's you're working with?

Solid or hollow domes?

I would never run a naturally aspirated engine with that much piston to head, unless it were a flat head or Hemi as mentioned.

You can work a chamber shape and volume, lose some dome (best option), sink the valves or use a tulip style.....????

Help us out here with as much specific information as possible....

art leong · 12-26-2007, 10:10 AM

Quote:

Originally Posted by Dave Goob Cook

How much compression do you want to lose?

What are the bore/stroke, dome cc's, chamber cc's you're working with?

Solid or hollow domes?

I would never run a naturally aspirated engine with that much piston to head, unless it were a flat head or Hemi as mentioned.

You can work a chamber shape and volume, lose some dome (best option), sink the valves or use a tulip style.....????

Help us out here with as much specific information as possible....

Bore is 3.484, stroke is 3.976. 7.5 cc dome, flat of piston(not dome) 0.010 above deck Head cc's 49.5. Stock head gasket is 0.040.
Using the stock gasket I come up with about 13.5 to 1 compression. The piston was sent back to the manufacturer to cut the valve reliefs as much as possible and shave the dome.
With the stock gasket I'll only have 0.030 piston to head clearance. 0.60 piston to valve with the smaller of the cams that are available to me at this time
Using an .080 head gasket will lower my compressiom ratio by over a point, give me 0.70 piston to head (quench area) and allow me to use a couple of larger cams.
The next motor I build I'll have a piston made without these froblems. But for now I'm going with these.
Called Cometic today and ordered a gasket from them 0.74 thick. I'll yrt 2 gaskets after I get the the running and dialed in. For now It's one less thing to worry about.

Dave Goob Cook · 12-26-2007, 12:12 PM

I see, it's a clearance issue more than compression.....

I get a difference of near 2 (1.9) points adding .040" on the gasket.

Gotta do what ya gotta do, watch your tune up on that one.

Good calculator tools here.... http://users.erols.com/srweiss/index.html#jcalc

art leong · 12-26-2007, 05:51 PM

Dave the calculator I used ( http://www.slowgt.com/Calc.htm ) gave me a slightly different reading (about a full point lower). Now I'm not sure which one is right?
I was under the thought that my compression was 13.58 to 1 with the 0.40 head gasket,
and about 12.16 to 1 with the 0.80 gasket.
Can anyone take a look at which calculator is correct?

There are only a few cams for the motor I'm using I don't want to go way up on the compression to start off plus the larger cams might have piston to valve issues. The overhead cam is probably more forgiving than a pushrod motor Due to very little weight. But I want to shoot for at least 0.060 The larger cam is .492 at the valve. The smaller one I'm using is .453

Tom Goldman · 12-26-2007, 07:00 PM

Art, I use the calculator Dave uses. ...I also use Challenger engine software. ... Both programs came out with similar numbers,altho higher than yours, using the specs you posted. . .....You didn't spec the gasket bore, but assuming it is 3.520"i.d., both programs indicate 14.25 to 1 compression with the .040" gasket,and 12.75to1 with an .080" gasket, if the 7.5cc dome volume is the net volume,including the valve reliefs ......Tom

art leong · 12-26-2007, 09:32 PM

The 7.5 cc number is the total dome displacement counting valve releifs and the piston flat area being 0.10 out of the hole. I poured the cylinder with the piston .500 down the bore. Got the volume of the bore and stroke times .500 then subtracted the volume from what I had measured. That was my dome volume.
The head gasket is 3.490.
I guess I'll have to run the thick gasket. 14+ comp ratio will be way to much for the cams I'm running but I can play with overlap due to 2 cams.

Dave Goob Cook · 12-27-2007, 02:13 PM

I think the Weiss calculators are pretty good, within a couple of tenths on the ratio.

You should be able to come up with a good number for the gasket, I didn't have the bore size on it, but catalog gaskets have the cc's calculated.

Don't forget to plug in the "-.010" for the piston out of the hole.

12-26-2007, 12:12 PM	#3
Dave Goob Cook Member Join Date: Dec 2006 Location: Indy Posts: 422 Likes: 0 Liked 0 Times in 0 Posts	Re: 2 Head Gaskets??? I see, it's a clearance issue more than compression..... I get a difference of near 2 (1.9) points adding .040" on the gasket. Gotta do what ya gotta do, watch your tune up on that one. Good calculator tools here.... http://users.erols.com/srweiss/index.html#jcalc

12-26-2007, 05:51 PM	#4
art leong VIP Member Join Date: Dec 2001 Location: Richmond Hill, Georgia Posts: 2,003 Likes: 0 Liked 1 Time in 1 Post	Re: 2 Head Gaskets??? Dave the calculator I used ( http://www.slowgt.com/Calc.htm ) gave me a slightly different reading (about a full point lower). Now I'm not sure which one is right? I was under the thought that my compression was 13.58 to 1 with the 0.40 head gasket, and about 12.16 to 1 with the 0.80 gasket. Can anyone take a look at which calculator is correct? There are only a few cams for the motor I'm using I don't want to go way up on the compression to start off plus the larger cams might have piston to valve issues. The overhead cam is probably more forgiving than a pushrod motor Due to very little weight. But I want to shoot for at least 0.060 The larger cam is .492 at the valve. The smaller one I'm using is .453 __________________ Art Leong 2095 SS

12-26-2007, 07:00 PM	#5
Tom Goldman VIP Member Join Date: Jan 2003 Location: Allentown,PA Posts: 2,477 Likes: 892 Liked 883 Times in 237 Posts	Re: 2 Head Gaskets??? Art, I use the calculator Dave uses. ...I also use Challenger engine software. ... Both programs came out with similar numbers,altho higher than yours, using the specs you posted. . .....You didn't spec the gasket bore, but assuming it is 3.520"i.d., both programs indicate 14.25 to 1 compression with the .040" gasket,and 12.75to1 with an .080" gasket, if the 7.5cc dome volume is the net volume,including the valve reliefs ......Tom __________________ Tom Goldman 1500 SG , 1506 STK

12-26-2007, 09:32 PM	#6
art leong VIP Member Join Date: Dec 2001 Location: Richmond Hill, Georgia Posts: 2,003 Likes: 0 Liked 1 Time in 1 Post	Re: 2 Head Gaskets??? The 7.5 cc number is the total dome displacement counting valve releifs and the piston flat area being 0.10 out of the hole. I poured the cylinder with the piston .500 down the bore. Got the volume of the bore and stroke times .500 then subtracted the volume from what I had measured. That was my dome volume. The head gasket is 3.490. I guess I'll have to run the thick gasket. 14+ comp ratio will be way to much for the cams I'm running but I can play with overlap due to 2 cams. __________________ Art Leong 2095 SS

12-27-2007, 02:13 PM	#7
Dave Goob Cook Member Join Date: Dec 2006 Location: Indy Posts: 422 Likes: 0 Liked 0 Times in 0 Posts	Re: 2 Head Gaskets??? I think the Weiss calculators are pretty good, within a couple of tenths on the ratio. You should be able to come up with a good number for the gasket, I didn't have the bore size on it, but catalog gaskets have the cc's calculated. Don't forget to plug in the "-.010" for the piston out of the hole.