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Am I driving you nuts yet. Big D mustang shop is telling me 67 stangs are heavier than 65-66 and should use 720, he says 620's are to low, he says his springs are custom made for them at BIg D. Now I don't want to second guess this guy he's been in business awhile, butAnother mustang shop is saying 620 is a 1" drop and the #s do not represent spring rates but heights. Anyone buy coil springs from big D? If so which did you go with? I am thinking go 620 if its to low change them out.
 

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620's are stiffer than stock, even on a 67. What are you looking for? Lower ride height? Stiff suspension? Both? IMO, 720's will make you feel every crack in the road unless you are running a big block. A buddy put some 720's on a 68 years back, it was like having the freakin wheels bolted directly to the frame. Another buddy is currently running 620's with the 1 inch drop on a 67 with a 289 and says it's a rocket on rails. I plan on the 620's, 1 inch drop, graphite polly, 1 inch front sway, export brace and monte carlo (curved) bar on my vert. That ought to tighten it up!
 

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The numbers "620" and "720" refers to the diameter of the coil of the spring in inches, and not the load rating.

For example, the steel rod used to manufacture a 620 spring is 0.620" thick.

.620 and .720 springs are available with different load ratings. (usually 447, 500, 600, and 700 pounds).

447-pound and 500-pound load rated springs are usually recommended for small block applications. Springs rated at 600-700 pounds are typically recommended for big blocks.

The ride height of any spring is always assumed to be stock, unless otherwise indicated.

For instance, I'm running .720, 600-pound load-rated springs with a 1" drop from Maier Racing, but these springs are also available in stock height.

HTH,

Rick
 

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I've got 620 springs from Maier Racing and KYB Gasajust shocks and my 66 fb is plenty stiff .Just my 2cents worth .
 

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There's many factors that determine the spring rate, including the wire diameter, number of active coils, spring OD, etc. It is my understanding, though, that when you're buying a 620# spring (620 pound), that 620 is the spring rate, meaning it takes 620 ft. lbs. of force to compress the spring 1".

That being said (and wether or not I'm right), your guy talking about the '67 being too heavy for 620 springs has no clue as to what he's talking about, unless you've got a big block. I have 620# 1" lowered springs in my '69 sportsroof, which is even heavier than a '67/'68.
 

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We run 620's in our track cars and they are plenty stiff, I would not recommend a 720's on a street car unless you have steel balls and a kidney belt :)
 

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If the ads tell the truth, there should be three kind of 620 springs as I posted to some thread a couple of days ago.

-1" to 65-66
-1" to 67- or standard height for 65-66
standard height to 67-

So if you buy -1" springs to 67- some shops may sell -1" springs for 65-66 and then you have -2" spring in your 67-

This is because the 65-66 has an inch shorter shock tower, I have understood.
BTW, I have to check that diameter thing, I always thought that they are 620lbs and not .620". We'll see.
 
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