Will PAC 1520s work?
Thread Starter
Race Director
Joined: Oct 2002
Posts: 16,477
Likes: 26
From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
Will PAC 1520s work?
Thinking about changing/upgrading valve springs soon, and considering the PAC beehives.
My heads have been machined for the larger spring pocket dia, but not deepened (that I know of). Heads were originally setup with 1.460" Comp 978 duals...now running with PRC/Patriot gold duals, and although I've not seen any float issues, thinking the pricey beehives might be better (and certainly less mass to move).
I know the 1.290" dia 1518s would work, and they are about the same spring rate/pressures as what I have now...but the 1.445" dia. 1520s are a little stouter, and diameter-wise, I can fit them.
But here's where I get confused... I see the 1520s are rated at .100" taller (1.900") installed height than LSx springs, and coil bind at ~1.181", and this initially caused me to think they might not work (without deepening the spring pockets), but now checking the Comp specs, the 978s coil bind at 1.195"...so that makes me think the 1520s might work? My valve lift is .610/.614" (XE-R lobes).
I personally haven't set up springs in these heads yet (TEA did it last time, and set installed height to 1.770" with coil bind of 1.050" with the golds), and don't know what the installed height would be w/o shims. Maybe the pockets were cut deeper? Or maybe there was previously zero safety factor to coil bind when the 978s were in them?..I don't know.
vettenuts and other PAC guys...what would you suggest? An $800 spring kit is not something to be guessing at.
My heads have been machined for the larger spring pocket dia, but not deepened (that I know of). Heads were originally setup with 1.460" Comp 978 duals...now running with PRC/Patriot gold duals, and although I've not seen any float issues, thinking the pricey beehives might be better (and certainly less mass to move).
I know the 1.290" dia 1518s would work, and they are about the same spring rate/pressures as what I have now...but the 1.445" dia. 1520s are a little stouter, and diameter-wise, I can fit them.
But here's where I get confused... I see the 1520s are rated at .100" taller (1.900") installed height than LSx springs, and coil bind at ~1.181", and this initially caused me to think they might not work (without deepening the spring pockets), but now checking the Comp specs, the 978s coil bind at 1.195"...so that makes me think the 1520s might work? My valve lift is .610/.614" (XE-R lobes).
I personally haven't set up springs in these heads yet (TEA did it last time, and set installed height to 1.770" with coil bind of 1.050" with the golds), and don't know what the installed height would be w/o shims. Maybe the pockets were cut deeper? Or maybe there was previously zero safety factor to coil bind when the 978s were in them?..I don't know.
vettenuts and other PAC guys...what would you suggest? An $800 spring kit is not something to be guessing at.
Team Owner
Joined: Mar 1999
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From: At the beach in little Rhody
Might be best to pull one spring and completely measure your current setup so you can run the calcs. You need shim thickness as currently installed, height from pocket to retainer and height from seal to retainer. You may have to use your stock retainers for initial measurements though since the Golds are duals.
Last edited by vettenuts; Jan 19, 2009 at 09:45 AM.
Thread Starter
Race Director
Joined: Oct 2002
Posts: 16,477
Likes: 26
From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
Thanks for the replies.
.
