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comp 948 springs?
#529010
11/17/09 01:40 PM
11/17/09 01:40 PM
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Frostbitefalls MN (Rocky&Bullw...
gregsdart
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Anyone had experience running 948 springs, in tighter than the recommended 2.100? The best I can do if I go to a 948 is installed at 2.050. That yields 366 on the seat. I do have good parts, Manton 1/2 inch pushrods, jesel valve gear, lobe is a comp 1625b, .501 lobe lift. I was told their is good power to be had with my heads by going to a higher lift, as they keep increasing flow all the way to .900.
The jesel rocker I want to run is a 1.700, which will give a gross lift of .8500. Comments?
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: comp 948 springs?
[Re: HardcoreB]
#529014
11/17/09 04:19 PM
11/17/09 04:19 PM
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Frostbitefalls MN (Rocky&Bullw...
gregsdart
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Thanks for the response, HCB. My dilemma is not being able to get a correct spring to fit with a 2.050 max installed height, yet still allow .850 net lift. The 947 springs I have now are supposed to be in at 2.000 which only allows .810 max net lift if everything is perfect. My head porter set me up with +.050 locks and +.100 retainers(?) to get me as much room as he could. There are guys running faster than me with 440-1 heads, and I feel the need to catch up, maybe pass em  After reading a bit of the YB thread, I think I will go out to the shop and do a little measuring.!! 
Last edited by gregsdart; 11/17/09 07:47 PM.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Post deleted by Defbob
[Re: 451Mopar]
#529016
11/18/09 04:40 AM
11/18/09 04:40 AM
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Re: comp 948 springs?
#529017
11/18/09 09:32 AM
11/18/09 09:32 AM
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Frostbitefalls MN (Rocky&Bullw...
gregsdart
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This deal is maxed out. I have the max + retainers made, same for locks, can't cut the seats any more. Spring cups are as thin as they make. The retainers are TI, and I really don't want to change them. If the 948 would be stable without the inner third spring, that is definitely something to look into.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: comp 948 springs?
[Re: gregsdart]
#529019
11/18/09 10:54 AM
11/18/09 10:54 AM
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Shelby Twp. Mi
HardcoreB
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Quote:
I think I will go out to the shop and do a little measuring.!!
Honestly, that is the only solution. Measure actual NET lift with as-assembled loads and clearences. C/B varied from 1.137-1.116" on this set WITHOUT the 3rd spring. So, as you calculated 1.14"+.060"+NET=min. seat height. Don't forget your valvepocket clearences.
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Re: comp 948 springs?
[Re: HardcoreB]
#529020
11/18/09 11:05 AM
11/18/09 11:05 AM
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Las Vegas
Al_Alguire
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Greg have you looked at any of the springs from PAC yet? How big of a diameter can you go to? Maybe they have a spring that would be a good fit. FWIW I have Nexteks at 2.100 and 1.677 diameter.
"I am not ashamed to confess I am ignorant of what I do not know."
"It's never wrong to do the right thing"
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Re: comp 948 springs?
[Re: Al_Alguire]
#529021
11/18/09 03:15 PM
11/18/09 03:15 PM
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Frostbitefalls MN (Rocky&Bullw...
gregsdart
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Al, hoping to keep this somewhat low budget. The little bulb just came on, and maybe due to the fact I only run up to 7500 rpm, I could put my 947 springs in a touch high, say 2.020 if I need it. After reading the post on YB, I need to get my butt out there in the shop and start measuring true coilbind, true net lift, and do the math the right way. Then maybe I will have some more possibility's. Right now, it looks like mathematically a gross lift of .850, minus .026 lash, minus .010 deflection gives a true net lift of .814 . At .814 + .060 + 1.130 coil bind, I come up with a needed installed height of 2.004? Might just work. I can shim it from 2.050 to get back to 2.010, which would make me happier about the true seat pressure.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: comp 948 springs?
[Re: 64ssmax]
#529025
11/18/09 07:14 PM
11/18/09 07:14 PM
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Frostbitefalls MN (Rocky&Bullw...
gregsdart
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OK, got some relevant numbers!
Installed height, retainer to head--- 2.112
spring cup--- .037
True installed height of 947 with +.050 locks, +.100 retainers-- 2.075
Spring coil bind, measured with retainer 1.100
Max lift with checking spring, an inner from triple, .000 lash--.781
Max lift, with 947, .000 lash, .758 (edit ,in at 2.025)
Lobe, .501 lift
Rocker, 1.55 jesel
Pushrod, 1/2 inch manton
Loss due to compression, flex etc .023
Looks like I now have options I did not know of.
True net lift, as is, -.024 lash, .734 lots of room.
Theoretical numbers
1.7 jesel rocker
.025 lift loss (flex, etc)
lash .024
Gross lift, .852
Net lift at the valve, .803
Needed installed height to keep it all happy-1.130(comp cams spec CB) +.060 + .803 = 1.993
Seems a bit short, but those are the numbers I came up with.
Last edited by gregsdart; 11/18/09 07:46 PM.
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Re: comp 948 springs?
[Re: gregsdart]
#529026
11/18/09 07:59 PM
11/18/09 07:59 PM
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Long Beach, CA
Mike Swann
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The 948 is 0.015 less CB height than the 947 Higher seat pressures are better for RPM and lifter life.
I like the Comp pacaloy springs because they go soft but don't work harden/shatter when they fatigue life out like other manufacturer's springs.
0.02
8.30's @3400 lbs
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Re: comp 948 springs?
[Re: gregsdart]
#529028
11/19/09 07:44 PM
11/19/09 07:44 PM
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Shelby Twp. Mi
HardcoreB
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You may assume some error in Jesel's 1.7 ratio as well. From what I have seen .02-.03(+). How much room do you have between the retainer bottom and valve seal? Also are you sure the rocker change will use the same pushrod length? What about a camshaft change with the same base circle height?
Last edited by HardcoreB; 11/19/09 07:49 PM.
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Re: comp 948 springs?
[Re: HardcoreB]
#529029
11/19/09 09:24 PM
11/19/09 09:24 PM
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Frostbitefalls MN (Rocky&Bullw...
gregsdart
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Good points all. Pushrod length combined with base circle and rocker configuration will have to be checked. Thanks for the great input. Will get this put in my VT post!
I don't run valve seals, alky motor. Lots of lift room there.
If I go with a 948 in at 2.075, and getting the spring within .060 of CB is not needed, that would seem to be my best option? I here there is a PAC-1347(?) spring that fits also?
Last edited by gregsdart; 11/19/09 09:27 PM.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: comp 948 springs?
[Re: gregsdart]
#529030
11/19/09 09:57 PM
11/19/09 09:57 PM
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Minnesota
Barnstorm
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mopar
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Love my 948's. Ran K1000h's and they would break over winter sometimes. Mine in at 2.10.
The little old lady from Pasadena is back!
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Re: comp 948 springs?
[Re: gregsdart]
#529033
11/20/09 11:02 AM
11/20/09 11:02 AM
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Joined: Jan 2003
Posts: 19,363
Las Vegas
Al_Alguire
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Pardon my ignorance but what is the largest diameter valve spring you can use? Isn't the 948 a 1.650? I ask becuase if you can squeeze in a larger diameter it opens up more possibilities.
"I am not ashamed to confess I am ignorant of what I do not know."
"It's never wrong to do the right thing"
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Re: comp 948 springs?
[Re: gregsdart]
#529034
11/20/09 11:57 AM
11/20/09 11:57 AM
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Sonora CA
Mopar_Rich
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Quote:
My dilemma is not being able to get a correct spring to fit with a 2.050 max installed height, yet still allow .850 net lift.
As much as I like Comp, I'd switch to a PAC spring.
The PAC-1248 will handle a .900 lift easily. Its specs are:
PAC-1248: 350 lbs @ 2.050, 950 lbs @ 1.20
This spring is spec'd to .900 lift
The PAC 1246 is a little less pressure and although this spring is spec'd to .800 lift, I have run them many times with .850 lifts with no problems.
PAC-1246: 250 @ 2.050, 830 @ 1.20
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Re: comp 948 springs?
[Re: Mopar_Rich]
#529035
11/20/09 01:08 PM
11/20/09 01:08 PM
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Shelby Twp. Mi
HardcoreB
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Quote:
Quote:
My dilemma is not being able to get a correct spring to fit with a 2.050 max installed height, yet still allow .850 net lift.
As much as I like Comp, I'd switch to a PAC spring.
The PAC-1248 will handle a .900 lift easily. Its specs are:
PAC-1248: 350 lbs @ 2.050, 950 lbs @ 1.20
This spring is spec'd to .900 lift
The PAC 1246 is a little less pressure and although this spring is spec'd to .800 lift, I have run them many times with .850 lifts with no problems.
PAC-1246: 250 @ 2.050, 830 @ 1.20
Pieces like this (among others)makes the thread better...people adding their personal experience data. The post on YB was lengthly back and forth. I summed-up that unless your running specific parts with a spintron, laser and stress instrumentation, confidence in valvetrain dynamics comes from correctly evaluating experience(just like anything else I guess ).
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Re: comp 948 springs?
[Re: HardcoreB]
#529039
11/21/09 04:25 PM
11/21/09 04:25 PM
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North Sweden
RT540
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My B1 heads came with PSI-1248 installed at 2.100"
DR1248,Triple,diam1.660",375lbs@2.100",1045lbs@1.200"
coil bind 1.130"
Maybe PSI-1247 would fit at 2.050" installed height ?
DR1247,Triple,1.660",340lbs@2.070",940lbs@1.270"
coil bind 1.130"
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Re: comp 948 springs?
[Re: Mopar_Rich]
#529040
11/21/09 07:26 PM
11/21/09 07:26 PM
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Joined: Feb 2004
Posts: 1,093
Long Beach, CA
Mike Swann
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Quote:
I don't agree. Here's the data from PAC.
It shows an installed height of 2.1, but in this case the installed height would be 2.050. Even at .900 lift that puts the spring at 2.050 - .900 = 1.150, with stated coil bind not occurring until 1.130.
Rich, if you are really going to lift the valve .900, the installed height should be 2.15-2.2. Even then, you would have infinitesimal performance gain and a lot of heartache with anything short of a late 90's or later series PS head, IMO.
8.30's @3400 lbs
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Re: comp 948 springs?
[Re: Mopar_Rich]
#529042
11/22/09 11:48 PM
11/22/09 11:48 PM
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Frostbitefalls MN (Rocky&Bullw...
gregsdart
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Thanks guys, I really appreciate the input. My choice is for a cost reason; I put so few runs on the car, the 948 would be my choice if I need them. I will check the 947 springs I have to make sure they are close to spec, and am starting the season with the same rocker ratio I have to keep things simple. I can install them at less than 2.00 and still have room.
If i decide to go for this extra lift, the comp 948 springs can be installed at 2.050 and give me 355 seat pressure, and would allow a NET lift of .860 which is .050 more than my proposed change. As mentioned, a larger cam core might be needed, as I run a stock bearing sized cam, and lose a lot of lift just rolling it over on the stand. So not knowing enough about possible consequences at this point, I will wait to make my move.
Last edited by gregsdart; 11/22/09 11:50 PM.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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