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Discussion Starter #1 (Edited)
Freshening up the top end of a 665 BBC brodix aluminum with big duke 18* heads and found valvesprings low on pressure. I believe they are 1248 PAC springs. They are installed at 2.1 height and are 1.645 diameter triples. Says 332 lbs at 2.1 installed height and 950 lbs open. Good for 900 lift.
Based on some measurements I am coming up with .875 lift intake and exhaust for camshaft.

I have no stats on this engine ( got it used in the new car) so it has been a treasure hunt to find what all it has lol not!

I have a set of 221448p-16 new Manleys on the shelf I want to put in. They show the same max lift. I know they are .032 diameter bigger so I will need to change the locators. The heads have cups in them right now that are for the 1.645 springs. But have the same installed height, and retainer fits, as well as inner diameter of inside spring. Will the additional 20 lbs at installed height and 60 lbs when open create problems though? 332 lbs installed vrs. 350 lbs for the manleys, 950 lbs open vs. 1010 lbs open with the manleys. It does have .904 lifter bore.

Was going to call Manley on Monday and get the correct part number for the cup or locator they recommend.
 

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Discussion Starter #3
7500 or so, steel valves, has two n2o kits on board. I will have to measure/ look at the pushrods again. Don't have it right in front of me. They are large smith bros though.
 

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Discussion Starter #4
Really haven't run the car enough to know where she runs out of steam, without a cam card I am unsure. Looked like previous guy had this shift setup around 75-7600
 

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If you haven’t done it already, before you take it apart measure lift on both sides at the retainer with the PAC 1248’s on it, and the lash you intend to run, THAT is your actual lift. Coil bind EVERY one of your Manley springs, record those numbers, set up the springs to be .120” from coil bind at the net lifts you measured at the retainer and race it.
 

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Discussion Starter #6
I did measure it off the retainer, that's where I came up with my measurements of .875 lift but also that was cold it will have .020 lash when warm (cold it has very little lash, like .05 with aluminum block and heads they sure grow. Shocked at the growth.) So that said Manley says coil bind at 1.142. PAC shows 1.130
So 2.100 installed - .875 so .083 from coil bind I am getting. I was told to keep the spring .060 to .90 for best results? This also means the PAC is around .090 from bind...
There is shims under the locators, so I could move them to .120 to coil bind if needed but this would change the installed height....
 

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It's best to actually measure coil bind, don't trust what's on the box. The little extra spring pressure will be welcomed with the steel valves. Personally,...I would run a little bit more, but don't know anything about your setup. I assume it's got a 5" stroke,....so the 7500-7600 is realistic .
 

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I have found the Manley springs to bind lower than stated. You must bind them in a vise. Set mine up at .080" to .100" as per Manley tech.
 

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Discussion Starter #10
It's best to actually measure coil bind, don't trust what's on the box. The little extra spring pressure will be welcomed with the steel valves. Personally,...I would run a little bit more, but don't know anything about your setup. I assume it's got a 5" stroke,....so the 7500-7600 is realistic .
Thank you for your input Ron!

I will be sure to measure the springs at bind to make sure that they measure correctly. Sounds like this setup would not be way out in left field though based on the responses.
 

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The pressure isn’t a concern, you could get away with less, but the Manley spring has more rate than the PAC so you’ll be fine,
Rate is Your control, not big seat pressure.
 

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Any concerns with pulling the intake rocker stud/shaft mounting threads from high spring pressure because of limited threads after full porting? On BBC there are only 4/5 threads left on 2 ports per head. On my Dart Pro 1 365 heads and my AFR/ Mamo 360 heads I have one piece intake rocker stands to hopefully spread the load. Don't know if that helps any though. 310# seat pressure.
 
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