PAC Valve Spring advice needed

[jmendlik]

I'm looking to upgrade to GN-1 Heads for my new 250CU Stroker motor I have built. I have max ported Irons on it now with Big Valves and want to order a set of GN-1's .

Im struggling with what valve springs to get.
Here is my set up now

3.820 Stage1 Block, BMS crank,crower rods, Diamond pistons, JW plate, BJH Balancer
Comp cams 218/224 billet roller (.545 intake/.553 Exhaust) .330 Lobe lift intake--.335 Exh
Comp cams 885 Roller lifters
Going to purchase Tom's scorpion roller rocker setup 1.65 ratio
Full race port on Tom's GN-1s
Champion ported intake also
PTE 6466 DBBB CEA Turbo
Jimmys stage 3 full billiet trans
Dusty PTE NL Converter
E85 with TT 6.1 W/B Chip

my question

should I run PAC 1203 springs or PAC 1201 140 seat@1.750 410 open @1.200

are the PAC 1203 too much pressure? 145 seat @1.800 511 open @ 1.200
PAC 1201 140 seat@1.750 410 open @1.200

Street car with limited track time

open to suggestions...

Bison---your thoughts??

 

[David Husek]

You cannot get enough seat pressure with the 1201's for the GN1 head. Everything is heavier, so more seat pressure is needed. If you shim more pressure, you will coil bind the spring. The cam is not very aggressive and needs on an iron head about 410-420 open pressure. I would look for 440 on the GN1's.The 1203 are way to much pressure for that setup. Also, you are using a non billet cam so excessive spring pressure should be a concern. The comp 26926 springs would be a good choice for that setup. You could also use the comp 26056 beehive springs, they will have 180 on seat and 420 open which will be more than enough pressure for your cam as you dont need as much presssure open with a beehive. Any questions, you know how to get in touch.

 

[jmendlik]

Dave- I do believe it's a billet cam...

I talked to PAC Tech person this morning and they make a "1201X" that has 150 lb seat @ 1.750 and 430 open at 1.200

Maybe an option

What is the plunger travel on those 885's I got from you again?

 

[David Husek]

Dave- I do believe it's a billet cam...

I talked to PAC Tech person this morning and they make a "1201X" that has 150 lb seat @ 1.750 and 430 open at 1.200

Maybe an option

What is the plunger travel on those 885's I got from you again?

With the lift of your cam, you cannot go tighter than 1.730 installed height. You will need more seat pressure with the 1201's on GN1's, so to shim to 160+ seat pressure needed, you will be in coil bind.

The 885's have a .093" reservoir, so on the GN1's, I would look for .030-.035 preload per manufacture spec.

 

[jmendlik]

so you suggest the Comp cams 26926 Spring then....what would the numbers be installed at 1.730 or 1.750 ?? seat/open pressure with these 26926

how do you figure out coilbind?

sorry for all the questions...

 

[David Husek]

1.750 - 170
1.200 - 450
coil bind 1.100

coil bind is listed on the manufacturers specs sheet, but I use my tester to check it.

 

[TurboTdr3.8]

looking

 

[jmendlik]

Dave-

Can you expalin why my cam needs such high--170lbs seat pressure and 450 open with GN-1's ?

 

[BEATAV8]

http://www.turbobuick.com/forums/threads/comp-springs-wtf.383720/

 

[David Husek]

Dave-

Can you expalin why my cam needs such high--170lbs seat pressure and 450 open with GN-1's ?

The valvetrain is heavier with the GN1 heads, so you need more spring pressure to control the valvetrain, If you were running an aggressive cam, the spring pressure would need to be even higher.

 

[TurboBuRick]

Dave gives great advice. The only thing I don't agree on are the beehives. I have never had any luck with those..

Rick

 

[TurboTdr3.8]

The only thing I don't agree on are the beehives. I have never had any luck with those..

You got that right