Figuring compression

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1930

1930

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Whats the steps, 1978 440, I have my heads and Im going to guess I need to CC them and figure out where they stand first.

I know the pistons were way down in the hole and Id heard that in 78 the ratio was around 8.1, Id like to bump that up as far as I can and still run pump gas.

Engine is in pieces at the machine shop, still waiting for the shop to tell me how far they have to overbore and then I can get some new pistons coming but in the meantime Id like to start thinking about what I need to do to get an accurate measurement of what cylinder volume Id like to end up with and look at prices for any suggested pistons.

Thanks
 
To optimize compression you need to have a pretty good idea of what cam you are gonna run. The cam is kindof dictated by the head-flow, and to your intended useage, and horsepower target, and width of the powerband.
The rear gears stall and chassis weight all play into it as well.Other things to think about are altitude and available fuel.

Truth be; for a 440 in an A-body, unless you are building a drag-car, it almost doesn't matter; most especially if it is gonna be a streeter.
With a 440, zero to 60mph can be first gear; 3.23s and a 2.45 low will get you 60 with around 6000rpm. 30 will be around 1750 in second.and hiway will be around 2600. I just love this stuff.
Your cam can be quite small, and as a 1-gear deal the LDA is almost a non issue.
The 440 will have enough torque to easily spin the tires so the TC can also be small.
Knowing all this you might as well build it for 87 gas.So for iron heads you probably want to come in around a Dcr of 8.0.
Streeters is all I know, so if you are building something else, hang around, somebody will be around in a bit.
 
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Im guessing ( maybe Im wrong ) that I cant just order for instance a replacement piston for a 440 that offers a 9.1 compression because there are alot of variables that have to be considered.

I need to know what these variables are and go from there and yet I know guys are ordering these rebuild kits everyday and stating they have X amount of compression in their engine.

Ok so cam choice does make sense, is that the first step then ?

440 is going in a 4 wheel drive truck, truck is used mainly for show, I am going to do my best to build the 440 for torque.
 
If it won't run on pump gas without pingin, it has too much.
 
1930 said:
This helped, talked with machine shop today and in my case the only things needed are CC head, head gasket thickness and the bore/stroke. All easy to obtain
Click to expand...


Find a new machine shop. Evidently they don't know how to calculate CR. Unless they specifically down fill the bore, YOU WILL HAVE NO IDEA HOW MUCH COMPRESSION YOU HAVE.
I have seen way too many engines come in that we're 15:1 but when they were actually MEASURED, they would be lucky to be 13.5:1.

When you get the engine from the machine shop, all the math should be recorded on th build sheet, including downhill. If the math ain't there, you don't have a clue what your CR actually is...it will be and "ish" number.
 
yellow rose said:
Find a new machine shop. Evidently they don't know how to calculate CR. Unless they specifically down fill the bore, YOU WILL HAVE NO IDEA HOW MUCH COMPRESSION YOU HAVE.
I have seen way too many engines come in that were 15:1 but when they were actually MEASURED, they would be lucky to be 13.5:1.

When you get the engine from the machine shop, all the math should be recorded on th build sheet, including downhill. If the math ain't there, you don't have a clue what your CR actually is...it will be and "ish" number.
Click to expand...
 
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