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73-87 Chevy _ GMC Trucks => Performance => Topic started by: lukieg on December 23, 2011, 02:57:50 am
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I have a 366 which is stock aside from an rv camshaft.. I was going to try my hand at a simple port matching and glean out the rrunner some.. I dont wish to spend much cash at all.. as this is being done at the same time as the cam swap, Im not sure what it has for head gaskets.. but could I use some thin steel shim gaskets to add a few points of compression also? Thanks
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Are you drag racing? If not I would not recommend. Use FelPro or Victor gaskets
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No im thinking of boosting my comp ratio a bit.. just a bit of added efficiency.
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It's not added efficiency to go to a steel shim gasket. In stock car racing you would try to pull off anything to gain small advantages. In reality what you gain from different head gasket thickness is miniscule and if you are not racing you are better off with a better quality gasket as opposed to something that may give you an imaginary performance boost.
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if my old crusty memory serves me, i think going from a .040 composite to a .015 shim will only get you about 0.1 compression extra. on a mild engine build that will net about 1 or 2 horsepower. my $ would run a stock felpro personally.
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Your other concern with polishing and porting and using thinner gaskets, if you do all that and susceed at raising your compression you will more than likely have to run premium gas to avoid the dreeded engine ping. That is one reason why racers use high octang fuel.
In the long run you will end up spending more money.
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other reason for using shim gaskets is to get you clearances right so you get a good mixture in the cylinder. you would want the quench ( distance from the top of the piston to the bottom of the head ) around .040 - .050
here is a good read
http://www.chevyhiperformance.com/techarticles/94138_piston_head_clearance_guide/index.html
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Thank you for the concern with pinging.. but i believe that comes from high compression?? I think the engine currently runs an 8:1 compression.. i was hoping to get around 9:1 nothing beyond the range of pump fuel.
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if you're at 8-1 right now the best you could get would be more like 8.3 or so with the shim head gasket. you're only looking at losing about 5-7cc of volume in the cylinder. nominal change at all.
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Out side of the minute compression gains you will experience you said that you would like to spend as little money as possible, right. Well switching to a thinner gasket will cost you more money in machining than many people anticipate. Heres why i say that..almost all thinner gaskets have a certian raiting of how even your deck and head surfaces are...I can't remember the actual termenology that measures, basically the smoothness, but chances are that with out decking the block and heads you will never get a good seal...just a little more to think about.
Static compression...this isn't the cheapest way to gain HP. Dynamic compression is what you will want to look at and oddly enough you are but probably don't realize it. Dynamic compression is basically functioning compression of your engine while it's running. It takes into account intake/exhaust duration as well as over lap, valve openin and closing events. Key word CAM...
Porting...With the RV cam you have there is a huge nono you will want to avoid. Do not blend the intake runners to perfectly match the intake manifold runners. You want to do whats known as step porting. Basicall,y you will open up the runners on the heads to match the gaskets and blend it into the rest of the bolw...don't over due it in the bowl area! Now the intake manifold runner should be slightly smaller where it meets the head. This is where you create the step. What this does is maintains the air velocity and creates a low pressure area just behind the runner which adds to the atomization of fuel. Plus if you try and push too much air through it will exceed the rpm range of that cam which is made for low-mid range torque.