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When statements are made like shim your valvesprings until you're .060" from coilbind, does that factor in hot lash or no? How about deflection?
Like...is that .060" from bind cold with a checking spring, or .060" from bind with .014" hot lash and probably .010-020" of deflection - IE more like .045" from bind when cold with an actual valvespring in there.
My cam is .775" gross lift and I'll be spinning the engine 8000-ish. Should run in the range of .014 hot lash. It is really making it tough for valve spring selection and this last little bit of installed height is making a difference when shopping around. The 1209x is probably not enough, and the 1238x I'm worried about for a number of reasons.
If anyone has some input - I'd appreciate any other options you know about too for springs. I need dead stable valvetrian up to 8000rpm for standing mile stuff. I'm using ported LS7 heads with the stock pedestal mounts cast into the heads and T&D steel roller tip rockers with lash adjusters.
PAC - 1209x - Comp thinks these will probably only be good to 7500rpm with my cam and valvetrain
Seat pressure at 1.800 - 160 pounds
Open pressure at 1.050 - 535 pounds
Spring rate - 515 lb/in
Coilbind 1.000"
PAC 1238x - I bought these already. Comp thinks they're good for 8500rpm or more with my setup. I'm concerned with spring life, broken springs, and my biggest concern is ripping the top of the intake port out with the ls7 pedestal mount rockers. Probably really ought to be using a shaft rocker. I've read about guys being successful with this setup drag racing, but ruining a cylinder head is not my goal. I also have no interest in machining these heads for shaft rockers.
Seat pressure at 1.800 - 250 pounds
Open pressure at 1.050 - 700 pounds
spring rate - 600
Coilbind - .985
Manley Nextek - an interesting choice that may work slightly better than the PAC 1209X? When shimmed up, same open pressure as the 1209x but a bunch more seat pressure.
1.800 installed height - 165 pounds
1.000 open height - 515 pounds
spring rate 435 pounds/in coilbind - .900" If shimmed up to 1.700 - 208 pounds
.950 open - 535 pounds
Lastly - Comp recommended these PAC circle track springs as a tweener option, but these are astronomically expensive and I can't justify it. $700 for springs only - still need seats retainers etc all bought separately. I'm trying to use this as a reference to get as close to these performance specs as possible without spending nearly a grand on springs.
PAC 1529
1.900 installed height - 180 pounds
1.150 open - 600 pounds
rate 560 pounds
coilbind 1.085
So I found and ordered some PAC-1237x, .700 lift spring - but I can install it at 1.850.
Installed height 1.850" - 173 on the seat
1.100" max lift - 585 pounds open
spring rate 585 lb/inch
coilbind - 1.045"
This gets very close to the expensive PAC1529 recommended by Comp.
Still curious about distance to coilbind lol
.050 out of max theoretical lift is a safe minimum. We would keep lash out of the equation because it’s hard to know the expansion rates of everything in the system. Better to be .015 too loose than .005 too tight.
.
Coil bind clearance is a loaded answer. It should be calculated off your net lift, and works good between .060-.100”depending on application. I would never suggest run anything less than .060”, and only run that little if I can’t get anymore.
Without knowing your cam lobes and valve weights, Your safest spring option is the 1238x installed at 1.830-1.840”
I'm using Comp's new low shock LGW/LGX lobes .775/.754 lift and 258/274 duration at .050, 289/258/180 duration .020/.050/.200" and 303/272/192 duration exhaust.
Valves are Ti 2.200 intake and stainless 1.59 exhaust - 77g and 101g exhaust. I'm using the T&D LS7 pedestal mount rocker arms.
I want to set my limiter to 8200 and try never to hit it - maximum revs likely 7800-8000 but will be decided by the powerband.
My concern with the 1238x is running them on the ported stock ls7 casting and either pulling the threads out or breaking the top of the intake port since I'm using the pedestal mount rockers and not shaft rockers.
My concern with the 1238x is running them on the ported stock ls7 casting and either pulling the threads out or breaking the top of the intake port since I'm using the pedestal mount rockers and not shaft rockers.
Unfortunately there aren’t a lot of options for stock casting heads and valve springs for that much lift. I’ve personally never seen either of those two things happen on something like you’re doing.
Lastly - Comp recommended these PAC circle track springs as a tweener option, but these are astronomically expensive and I can't justify it. $700 for springs only - still need seats retainers etc all bought separately. I'm trying to use this as a reference to get as close to these performance specs as possible without spending nearly a grand on springs.
PAC 1529
1.900 installed height - 180 pounds
1.150 open - 600 pounds
rate 560 pounds
coilbind 1.085
There is a reason for the price, it is not just for WOW factor....
There is a reason for the price, it is not just for WOW factor....
Yeah they say they're the best valvesprings they manufacture and I don't doubt it. I'm not upset at the price it just isn't for me. I now own two sets of higher end PAC springs lol so they're still getting my business. I guess I have some flexibility now when screwing the thing together to decide what to use. I like that the 1237x is described with drag race + street/strip application whereas the 1238x is drag race only. I assume that comes with a longer expected service life.
Last edited by spanks13; Dec 14, 2020 at 04:09 PM.
Yeah they say they're the best valvesprings they manufacture and I don't doubt it. I'm not upset at the price it just isn't for me. I now own two sets of higher end PAC springs lol so they're still getting my business. I guess I have some flexibility now when screwing the thing together to decide what to use. I like that the 1237x is described with drag race + street/strip application whereas the 1238x is drag race only. I assume that comes with a longer expected service life.
I see about 5000 miles out of the 1238X on the street with 774 lift CM lobes
I see about 5000 miles out of the 1238X on the street with 774 lift CM lobes
👆
when purchased 🤔. Main❓I asked: 😉 This is intended for 98% street use.
Perfect choice for the lift and spring rate.
If considered your cam lift is what? That's before Lash Subtract'$ from what's: said / advertised 🤔. Does the 1237x fit the bill? 👉💸💵
👎PAC-1237X RPM Series RACE ONLY Dual Spring Open Load 585👈
Recommended Valve Lift 0.700👎
Spring Rate (lbs/in)550👈
👍PAC: 1238X RPM Series RACE ONLY Dual
Spring Open Load 700👈
Recommended Valve Lift0.750👍
Spring Rate (lbs/in)600👈
👆
when purchased 🤔. Main❓I asked: 😉 This is intended for 98% street use.
Perfect choice for the lift and spring rate.
If considered your cam lift is what? That's before Lash Subtract'$ from what's: said / advertised 🤔. Does the 1237x fit the bill? 👉💸💵
👎PAC-1237X RPM Series RACE ONLY Dual Spring Open Load 585👈
Recommended Valve Lift 0.700👎
Spring Rate (lbs/in)550👈
👍PAC: 1238X RPM Series RACE ONLY Dual
Spring Open Load 700👈
Recommended Valve Lift0.750👍
Spring Rate (lbs/in)600👈
👌
Same price around $25 ea.
The distance to coil bind is what you look at. 1.800 is not a rule just the standard. Published coilbind numbers aren't always exact either it is best to measure each spring.
With LS7 valves you can set up taller installed height 1.960" is stock. 1237x at 1.850" installed height makes room for .750 lift and lightens up on the spring pressure a little.
That's awesome news. Hard to find much info about these.
I had the same issue when I was looking for springs. 774 is advertised lift subtract lash and deflection and the running engine is likely to see about 750. I have mine set up at 1.825 installed height with a all steel heavy valvetrain. Limiter set a 8100
I had the same issue when I was looking for springs. 774 is advertised lift subtract lash and deflection and the running engine is likely to see about 750. I have mine set up at 1.825 installed height with a all steel heavy valvetrain. Limiter set a 8100
Bitchin! Yeah I was between 1209x and 1238x when selecting springs and went with the heavy guys I knew would run up to ~8k rpm but started getting worried about the pedestal mount rockers. Sounds like I was worrying about nothing. I still feel better using the 1237x if I can get away with it. I'll see how everything looks screwing it together. I'm running Ti intakes and I'm not worried about the stainless exhaust valve at all.
Which lobes are you running? The low shock from comp I selected are also 774 gross lift with a 1.8 rocker, .430 lobe lift. .756"/.420 exhaust lobe lift.
The extra lift ought to be a significant performance bump. I'm excited to see what it does. For the RPM range 5000-8000 I don't think you can utilize much more duration than a 258 intake lobe, so more lift makes sense to me to get more out of it. I also want a fighting chance of driving it on the street and 33 degrees overlap hot is already pretty rowdy even for a 429.
Bitchin! Yeah I was between 1209x and 1238x when selecting springs and went with the heavy guys I knew would run up to ~8k rpm but started getting worried about the pedestal mount rockers. Sounds like I was worrying about nothing. I still feel better using the 1237x if I can get away with it. I'll see how everything looks screwing it together. I'm running Ti intakes and I'm not worried about the stainless exhaust valve at all.
Which lobes are you running? The low shock from comp I selected are also 774 gross lift with a 1.8 rocker, .430 lobe lift. .756"/.420 exhaust lobe lift.
The extra lift ought to be a significant performance bump. I'm excited to see what it does. For the RPM range 5000-8000 I don't think you can utilize much more duration than a 258 intake lobe, so more lift makes sense to me to get more out of it. I also want a fighting chance of driving it on the street and 33 degrees overlap hot is already pretty rowdy even for a 429.
253/270 113+3.5. Ls3 heads on a 468. 2.20 intake valves 1.5 exhaust 13.7 compress on E
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Valvespring distance from bind 
