Compression stuff - i've lost a point...

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My ignitor system is on its way and hopefully i'll have it installed by the end of next week. It will be my 1st step towards success 8) umm... :?

But, since i'm still on my 1st step i have some very basic questions that i need sorting out. I've got a '72 250 and it's rated 99 BHPs in my chilton manual, not much, the earlier 250s was at 145. Ok, so i know that the measuring is net and that matters (dunno how much though :roll:). But i still got 1 point less compression (8.0:1) compared to earlier 250s (9.0:1), doesn't that make me a bit disabled? Isn't the comp a major deal when it comes to boosting my engine, i know i can mill my head to increase comp - but will such a thing make up for that whole point lost?

What did Ford do to lower the compression on the engines, is it something i can do something radical about without to much effort? I have a '66 head on it if that makes any big difference. I do not know if earlier owners have done something to the engine.

Ok, as you see these are newbie questions. But i would appreciate if someone explained the compression stuff to me, i know in general what it's all about - but i'm only scratching the surface - i would love to do some calculating comparing what different comp.ratios does, can you guide me to a website explaining this to me (not the howstuffworks, i've been there :wink:) or give it a shot yourself?
 
How about this article
http://e30m3performance.com/myths/more_myths1/comp_ratio/comp_ratio.htm

And once you got the basics down head over to an engine calculator
http://falconperformance.sundog.net/compcalculator.asp

Change the stroke to 3.91"
and start playing

In order to get a real handle on what your motor is running at you need to tear it apart and get some critical measurements, like how far is the piston down from the top of the block, how thick is your headgasket, etc.. But the calculator will give you an idea of what could happen as you change things.

-ron
 
Howdy Fossil:

The big engine difference that took place was that early Pre-70 heads have a combustion chamber volume of about 52 ccs. '69 "M" and later head, low compression heads have a volume of 62.

Another variable on the 250 was a horribly hige deck height- anywhere from .100" to .150".

Your '66 head with a 52 stock chamber (not milled) with an aftermarket composite head gasket will yeild a CR of about 8.6:1. But the early head is down on intake tract volume & carb hole diameter equaling less flow. What carb are you using?

"Gross" to "net" is worth about 25%. The loss of CR is worth somewhere between 4 & 10%. The rest is due to advertizing hipe. Prior to 1970 more was better, after 1970 less was better. I guess they never heard of Dolly Parton!

Check out the CR calculator on our website. Click on the link below my signature.

Adios, David
 
David,
I agree.
Saw her in a TV ad the other night and thought to myself,
Boy she sure does have big beautiful eyes! :-)
DaveP
 
Thanks for answers, i'll dig into that article today. So, if i get you right im not all that crippled with my setup as it is?

CZLN6: my carb's an autolite 1100.
 
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