Valve sizes...
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I am at about sea level in so cal. All I have right now is a stock 73 914 2.0. Most of the parts are good. It stopped running because of a burned valve (according to the previous owner). Im going to have the heads remachined, and im thinking of either headflow masters or rimco.
As of now, I am thinking of going with stock cylinders and KB 96mm pistons. I dont have those yet though (the pistons). I want to run about a 9:1 cr, maybe a little bit more. Im not set on that, but that was some advice I got a while ago. I have a pair of 40 IDFs that I need to rebuild. If they are too shot I will go with 44s, but they should be fine, just some jets and stuff.
Any advice? I hate to ask for free advice like this because I know it costs (i spend time at work answering questions sometimes), but I would really appreciate your help.
As of now, I am thinking of going with stock cylinders and KB 96mm pistons. I dont have those yet though (the pistons). I want to run about a 9:1 cr, maybe a little bit more. Im not set on that, but that was some advice I got a while ago. I have a pair of 40 IDFs that I need to rebuild. If they are too shot I will go with 44s, but they should be fine, just some jets and stuff.
Any advice? I hate to ask for free advice like this because I know it costs (i spend time at work answering questions sometimes), but I would really appreciate your help.
Last edited by MattR on Fri Mar 19, 2004 11:46 am, edited 1 time in total.
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Okay, so it looks like a 494 with an 8.8 cr and 42x36 valve combo. Thanks so much!
What has to be done to the 96x71 kb pistons to get 8.8 cr if anything? I plugged in my info on the aircooled.net engine calculator and I got a deck height of .359. How does that differ from stock? Sorry if this is a stupid question, Im just not sure what they mean by deck height. Is that a figure I tell to the machine shop?
What has to be done to the 96x71 kb pistons to get 8.8 cr if anything? I plugged in my info on the aircooled.net engine calculator and I got a deck height of .359. How does that differ from stock? Sorry if this is a stupid question, Im just not sure what they mean by deck height. Is that a figure I tell to the machine shop?
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- A_67vdub
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OK, that sounds much better. The deck height is the distance from the top of the piston when it is at Top Dead Center to the top of the cylinder plus the width of the gasket (if you are using one). The combustion chamber volume is the space between the top of the cylinder and the valves (kinda). This is measured on the head with a special tool. The tool can be made with simple around the house stuff. I don't have one, but I've seen pictures. What people do is put a plastic disk, thats the same size as the top of the piston, into the bore of the head. It must seat on the same surface that the cylinder does. Also there needs to be a hole in the middle of this disk. Then you fill this area with water or some other liquid until it gets to the disk. You then use a syringe of some sort to take the fluid out and measure it. That is the volume of the combustion chamber.MattR wrote:I messed around with the numbers a bit and I got the deck height at .05", and to get an 8.8 cr I need 57cc combustion chamber. What do these figures mean? I know bore, stroke, and compression ratio. But where is deck height measured from? And how do I check/modify my combustion chamber volume?
To calculate the compression ratio, you have to know the volume inside the chamber when the piston is at Top Dead Center, and the volume when the piston is at Bottom Dead Center. This basically tells you how much the air/fuel mix is going to be squished when the piston compresses it.
Hope this helps.
Steve
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What would change if I am altering these numbers? In other words, if I dont mess with it and keep it stock, will I keep about an 8.8 cr? Or would i be better off going with the 86a and letting the cr go up to 9? In other words, the bigger pistons will naturally up the compression, right? So if I just assume it will go up a few points from stock and go with an 86a will I be safe?
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- A_67vdub
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Assumption is the mother of all evils. You need to measure it either way you go.MattR wrote:What would change if I am altering these numbers? In other words, if I dont mess with it and keep it stock, will I keep about an 8.8 cr? Or would i be better off going with the 86a and letting the cr go up to 9? In other words, the bigger pistons will naturally up the compression, right? So if I just assume it will go up a few points from stock and go with an 86a will I be safe?
Steve
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