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Bill Hartman (aka Streetrodder007) [ View ] [ hartman@comcast.net ] [ Car Ads ] [ Blogs ] Port Huron, Michigan

Does anyone know a formula to change compression ratio by altering the compressed cylinder head gasket thickness? Such as changing from the usual .040 to .065 or .080. Great question for all you technical rodders / builders. Any thoughts ?

Comments

Posted by BigAlBre  -  02/10/2007 07:15 PM The thicker the head gasket the lower the compression ration because you are moving the head away from the picton and combustion chamber... remember in the old days we use to "shave" the heads (i.e., take metal off) to increase the compression and power.... Big Al sittin back in paradise. [ View ] [ Email ] [ Blogs ] [ Car Ads ] St Pete Beach, Florida Charter Member since June 1999   Posted by dixie  -  02/12/2007 12:41 AM YOUR JUST WASTING YOUR TIME IF THAT ALL YOUR GOING TO DO TO THE HEADS. jim grace [ View ] [ Email ] [ Blogs ] [ Car Ads ] dade city, Florida Charter Member since January 2006   Posted by Streetrodder007  -  02/12/2007 12:29 PM These heads are 555 Hemi heads, they do not make these anymore, and are extremely hard to come by, and very expensive. These have had professional light port and polish in the quench throat, and you are slightly limited by what pistons are available for these motors. After you deck the block and mill the heads, that all changes your compression ratio, therefore, altering the cylinder head gasket will help bring compression back to where I want it, and it will help the intake manifold line back up so you do not have to elongate the mounting holes. Making a long story short, its not a waste of time, its just a math formula for a big dollar motor thats needed, you do not want to just guess. Streetrodder007 [ View ] [ Email ] [ Blogs ] [ Car Ads ] Port Huron, Michigan Charter Member since April 2006   Posted by Woody2B  -  02/12/2007 01:06 PM Try car.race-cars.net/calculators/compression I'm running 58cc vette heads and have been playing around trying to lower my compression also. This one worked pretty easy. Woody2B [ View ] [ Email ] [ Blogs ] [ Car Ads ] Arnold, Missouri   Posted by tlp1968  -  02/12/2007 01:19 PM I can remember in the past putting a thick gasket on for that reason. I just cannot remember who made it. I think I got it from Wise Performance in St. Louis MO- but that was 20 years ago so not sure if they still have such a creature. Certainly some other old racers on this site have done this too. Mine was for a set of double hump heads that had been shaved before I got them. StreetRodding.com Marketing Director [ View ] [ Email ] [ Blogs ] [ Car Ads ] Springfield,, Illinois Charter Member since August 2003   Posted by Streetrodder007  -  02/12/2007 03:15 PM Thanks for the help guys ! I perfer to keep my compression at 11 to 1 and below on all my motors. Thats why I am buying bigger gaskets, I am too far above, after all the machine work, and $500 pistons, a thicker gasket is a cheap and eay way to bring the compression back down. When buying Hemi pistons, $400-$600 is an average price, you can go up to $2000 for special sets, $300 for cheapest set. SBC is definately much cheaper ! And you have alot of choices available to you. Streetrodder007 [ View ] [ Email ] [ Blogs ] [ Car Ads ] Port Huron, Michigan Charter Member since April 2006   Posted by bigdude  -  02/12/2007 05:02 PM What in the hell are you doing with that Hemi? resident know it all [ View ] [ Email ] [ Blogs ] [ Car Ads ] Three Rivers, Michigan Charter Member since January 2004   Posted by Streetrodder007  -  02/12/2007 05:14 PM Building it for a friend. I did a 331 bored .125 to a 354 for myself a couple of years ago also. I also have an old Poly Hemi, Just sold a broken 1968 426 Hemi Block I took in on trade for doing some Electrical work for a friend, sold that 1 on E-Bay to a guy in Sweden for $1800, he paid $1830 just to have it shipped ! He wanted it in 4 days. Crazy Eh ? My friend also has 3 more 426 Hemi blocks he is thinking of selling. Anyone need a 426 Hemi or Poly Hemi, let me know, I can deal and sell and / or build . Streetrodder007 [ View ] [ Email ] [ Blogs ] [ Car Ads ] Port Huron, Michigan Charter Member since April 2006   Posted by dixie  -  02/12/2007 08:26 PM STREETRODDER YOU SEEM TO KNOW ALOT ABOUT THESE ENGINES SUPRISED YOU DON'T HAVE THE HEAD GASKETS DOWN PAT. IF IT WAS ME AN I WANTED TO BRING THE COMP. DOWN I WOULD GO WITH ONE OF THE THICKER ONES.IS THIS A RACE MOTOR WHERE YOU NEED TO KNOW THE COMP. RATIO FOR SOME REASON? OTHER WISE IS IT REALLY THAT IMPORANT TO KNOW EXACTLY WHERE YOUR AT. HEY JUST MY 2 CENTS. jim grace [ View ] [ Email ] [ Blogs ] [ Car Ads ] dade city, Florida Charter Member since January 2006   Posted by Streetrodder007  -  02/13/2007 09:52 AM I am fairly knowledgable about engines, always have more to learn, but I like to know exact formulas. DIXIE you are correct , its really not that important to have a difference of 10.5 or 10.65 compression, I am just really perticular about how I build motors, and I feel when I sell one to someone, that attention to detail shows how much thought and care goes into building one of these. I am very anal about little details . When I get into a topic, I try to learn as much as I can, just interesting to me. I dont build engines full time, just as a little side job. But if my name is on it, I will stand behind it always. Streetrodder007 [ View ] [ Email ] [ Blogs ] [ Car Ads ] Port Huron, Michigan Charter Member since April 2006   Posted by tlp1968  -  02/13/2007 11:39 AM Compression is important if you want to run pump gas, add a blower, or make some serious horsepower. I look at it this way, anyone who builds his own engines is cool to me. I like building them for the experience, and the sense of accomplishment. StreetRodding.com Marketing Director [ View ] [ Email ] [ Blogs ] [ Car Ads ] Springfield,, Illinois Charter Member since August 2003   Posted by dixie  -  02/13/2007 04:32 PM NOT TRYING TO B A SMART ASS .BUT WHY IN THE WORLD WOULD YOU WANT TO BUILD A STREET MOTOR THAT COULDN'T RUN ON PUMP GAS. ========JUST CURIOUS========= jim grace [ View ] [ Email ] [ Blogs ] [ Car Ads ] dade city, Florida Charter Member since January 2006   Posted by tlp1968  -  02/13/2007 08:17 PM Just looked at my post, what I meant is, if you have a purpose high compression can be necessary. I didn't mean that you need high compression to run pump gas....just typing faster than I was proof reading. Around here guys love the way the high octane stuff smells and they will build high compression engines that they occasionally drive off the trailer and into the show. StreetRodding.com Marketing Director [ View ] [ Email ] [ Blogs ] [ Car Ads ] Springfield,, Illinois Charter Member since August 2003   Posted by sixguns  -  02/13/2007 09:18 PM Quench area has always been a concern when I build an engine, the head gasket compressed thinkness is part of the formula too acheive the correct Quench, to prevent detonation. Installing a thicker gasket to lower C/R on an engine ,with the correct Quench can do more harm than good. this may or may not apply to your engine. Enjoy the Ride [ View ] [ Email ] [ Blogs ] [ Car Ads ] Woodland, Washington Charter Member since June 2002   Posted by Streetrodder007  -  02/13/2007 09:27 PM For my daily driven hotrod motors I like about 9.75 -10 to 1 compression, radical for my own stuff is 10.5 to 11.5 tops. But I do love the sound and smell of a 600 inch motor on AV gas! And how can you beat hearing a .850 inch cam makin noise! Streetrodder007 [ View ] [ Email ] [ Blogs ] [ Car Ads ] Port Huron, Michigan Charter Member since April 2006   Posted by dixie  -  02/14/2007 01:54 PM TIP LAST SENTANCE IN YOU POST TALES THE TAIL. IHAVE ONE THATS 9.0 THE OTHER IS 10.5 BOTH ON PUMP GAS. AND YOU GUSSED RIGHT THEY BOTH DON'T SMELL GOOD.BUT I'M ALWAYS UP WIND. WATCH OUT WHEN I GO BY AN HOLD YOUR NOISE. =============== jim grace [ View ] [ Email ] [ Blogs ] [ Car Ads ] dade city, Florida Charter Member since January 2006   Posted by maniac  -  02/14/2007 08:36 PM Also remember that a thicker head gasket will RAISE the intake manifold up also, could end up creating other problems as well maniac [ View ] [ Email ] [ Blogs ] [ Car Ads ] Bethel, Connecticutt   Posted by Streetrodder007  -  02/14/2007 09:05 PM Good point, But I have already decked the block .010 and milled the heads .012, it needs to go up a little to fit right. Streetrodder007 [ View ] [ Email ] [ Blogs ] [ Car Ads ] Port Huron, Michigan Charter Member since April 2006   Posted by Jaybird  -  02/14/2007 09:09 PM The design of the Hemi headlets you run a higher compression ratio on pump gas without ill effects. Bill, I have some of the data that you are looking for at work. Sixguns is right on the mark about quench. Don't worryabout being anal on your build. I have some aerospace engineering buddies and you should see the detail that they go ito on this subject and related subjects. Then again, you should see their motors run.....on pump gas. I'll dig this up for you tomorrow for wehad this discussion week and they where crankin' numbers faster thanI wated to listen if you know what I mean. Jaybird [ View ] [ Email ] [ Blogs ] [ Car Ads ] Cincinnati, Ohio Charter Member since December 2003   Posted by Streetrodder007  -  02/15/2007 04:45 AM Sounds great, thanks. Streetrodder007 [ View ] [ Email ] [ Blogs ] [ Car Ads ] Port Huron, Michigan Charter Member since April 2006   Posted by Jaybird  -  02/15/2007 06:23 PM Ok, I got with my buddy today and here is the "disertation" that I recieved from him. I also have an excel spreadsheet that will calculate compression ratio with inputs of bore, stroke, rod length, block height, piston height, gasket thicknes.....you get the picture. Anyway, here's Ralphies' input" Subject: Quench, Squish, and Compression Definitions: Squish and Quench are both result of the piston coming within close proximity to the head. Accepted minimum for steel rod engines is about 0.035 inch. I had an old Mopar magazine article on quench that quoted a maximum of 0.055 to get sufficient quench. Quench and squish are part of the design of conventional wedge and modern bathtub combustion chambers. Squish refers to the "squirt" of air and fuel that jets into the combustion chamber as the piston goes through TDC. Squish promotes mixing and improves efficiency and reduces emissions. Mixing reduces lean and hot spots and makes the engine more resistant to detonation, or more tolerant of higher compression. Quench refers to the transfer of heat from the top of the piston to the water cooled head that results in a cooler piston top. Cooler piston tops help piston life and also again reduce detonation as a result of lower temperatures. Either requires that the top of the piston be flat where it is closest to the flat part of the head. A dished piston where the dish covers the entire piston top will have poor quench. A completely open chamber head also has poor quench. Gaskets: Most head gaskets are about 040 to 050 when compressed. Thinner head gaskets, as thin as maybe 0.020 are sometimes available, but for most engines only on a special order basis from a custom head gasket manufacturer. Embossed steel shim gaskets used to be readily available for some applications, and some still are, but again availability is limited. Deck Height: Best way to get quench is to adjust the deck clearance to near zero and run a modern gasket with conventional thickness. Deck the block or change the length of the rods, or use pistons with more compression height, or increase stroke. The quench distance is the deck height plus the gasket height. Compression: Thinner gaskets, or less deck by any of the methods listed reduce combustion volume and increase compression. For a 4 inch bore, combustion volume is reduced 2 cc for each 010 of gasket or deck reduction. As an example, a 350 with 9:1 compression with 020 less gasket would have a compression ratio of 9.4:1 Hope this helps Ralphie!!!! Jaybird [ View ] [ Email ] [ Blogs ] [ Car Ads ] Cincinnati, Ohio Charter Member since December 2003   Posted by Streetrodder007  -  02/15/2007 06:46 PM Hey Ralphie thats a good disertation on combustion chambers ! Well done, That last paragraph is exactly what I was looking for. thanks, Bill Streetrodder007 [ View ] [ Email ] [ Blogs ] [ Car Ads ] Port Huron, Michigan Charter Member since April 2006   Posted by Streetrodder007  -  02/15/2007 06:50 PM Another thought. I have always been told that on all Hemi heads, you should not do much polishing at all on the intake runners, you want the fuel and air to mix efficiently, so you should have small turbulent rough areas, not too rough that you have bad flow, but also not polished like a mirror, where the mixture will not tumble and mix evenly, so you do not get wet or flat spots on the intake stroke. I suppose in theory, that would apply to all motors, but I have especially heard this for Hemispherical combustion chambers. Streetrodder007 [ View ] [ Email ] [ Blogs ] [ Car Ads ] Port Huron, Michigan Charter Member since April 2006

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