Comp ZS II Lobes.

[paulzig]

I am looking at the ZS II Lobe #2950

280@.020 250@.050 172@.200 .420 lobe lift using with a 1.65:1 rocker arm.

120g steel valve, steel retainers.

PAC-1243 spring 240LBS seat, 625LBS Open, 550LBS spring rate.

Would this setup control this lobe at 7500RPM or more?

[blykins]

I'd rather see 275/700.

[paulzig]

I'd rather see 275/700.

I also have a PAC-1225 spring with Ti retainers here.

Installed Height (in): 2.000 in.

Seat Pressure at Installed Height (lbs): 250 lbs.

Open Height (in): 1.200 in.

Open Pressure (lbs): 765 lbs.

Rate: 644LBS.in

Installed height can be 1.9 so seat pressure will be around 315lbs

[1972ho]

I use to run the rz lobe at 264 @050 272 exh. with a .428 lobe lift with a 1.7 rocker and 550 # on the seat and I ran that engine up 7600 rpm shift point 8100 cross the stripe with no floating,But that was in a v-6 if that means anything to you.But that was with titanium stuff.

[blykins]

I'd rather see 275/700.

I also have a PAC-1225 spring with Ti retainers here.

Installed Height (in): 2.000 in.

Seat Pressure at Installed Height (lbs): 250 lbs.

Open Height (in): 1.200 in.

Open Pressure (lbs): 765 lbs.

Rate: 644LBS.in

Installed height can be 1.9 so seat pressure will be around 315lbs

Where do those coil bind?

[paulzig]

Where do those coil bind?

1.15... But the seat pressure at 315LBS probably not required.. I'll have .673 lift with .020 lash so no need for 2.0 install height

I emailed comp re the required pressure last week but still no response.

[Neal Arnold]

With 120g valve and steel retainer. I would not use anything less than a 600 rate.

[blykins]

Where do those coil bind?

1.15... But the seat pressure at 315LBS probably not required.. I'll have .673 lift with .020 lash so no need for 2.0 install height

I emailed comp re the required pressure last week but still no response.

Well, for all intents and purposes, the guys that answer the emails probably won't have a good idea. There are guys there that can help, but you need to know who to ask for. I tried to get an appointment down there for a Spintron for a pulling truck engine, but Kaase took his block back (thanks Jon) and so they didn't have a block with the cam journals that I needed (Trend didn't have one either). Instead, we had a conference call between me, my sales guy, and a couple of higher ups. I gave them all the lobe numbers, valve weights, retainer weights, lash cap weights, locks, lifters, you name it, and we had a good discussion about it....then came to a consensus.

I have a general rule of thumb that I like to use for bracket engines, which I assume this is, and then tweak from there.

So getting back to the 1225's....

Is that where you have measured coil bind, or is it what they have labeled them to be? I have found that most spring manufacturers document a coil bind that's completely different than actual.

If it's accurate, then if you install .060" from coil bind, then you have an install height of 1.880". I assume that will put your spring pressures a lot higher than necessary. If you go .100" from coil bind, then you're at 1.920". Doing the calculations, with a 1.920" height, you'd be at 300 lbs seat, with 730 lbs open.

I think that's a little higher than what you need, but if you're determined to use something that you have, I like those better than the first set you posted.

[paulzig]

Yeah thanks for that, I'll measure actual CB before hand.

I was thinking doing a mix' n match with the 1225 springs on the intake and the exhaust lobe is a softer RZ lobe and using the 1243 on those..

[blykins]

I *personally* would not run a softer spring on the exhaust side. If the exhaust valve bounces off the seat, you're tagging a piston.

[KnightEngines]

Paully - use tool steel retainers, that'll shave some weight.
You'll still want 250-260lb on the seat, make it 260 so the springs can loose 10lb & not be an issue.
Rate around 530-550lb/in is enough, 630-650 over the nose is plenty.

I run the Crane .438" lobes at 260 on the seat, 540lb rate with steel valves & TS retainers, Isky gold stripe springs. I've run the .450" lobes at the same, but with Ti retainers.

Spend real $ on springs, Isky, Manley Nextek or the good Pac springs - cheaper stuff just costs more down the track.

[paulzig]

Paully - use tool steel retainers, that'll shave some weight.
You'll still want 250-260lb on the seat, make it 260 so the springs can loose 10lb & not be an issue.
Rate around 530-550lb/in is enough, 630-650 over the nose is plenty.

I run the Crane .438" lobes at 260 on the seat, 540lb rate with steel valves & TS retainers, Isky gold stripe springs. I've run the .450" lobes at the same, but with Ti retainers.

Spend real $ on springs, Isky, Manley Nextek or the good Pac springs - cheaper stuff just costs more down the track.

The PAC-1243 and PAC-1225 (which I have) looks like they share the same retainer I have the R-505 Titanium retainer here as well, the tool steel I'd have to check but I cant find anything close.

I'd have to physically check bind like Mr.Lykins said but the 1243 specs:

Installed Height (in): 1.900 in.

Seat Pressure at Installed Height (lbs): 240 lbs.

Open Height (in): 1.200 in.

Open Pressure (lbs): 625 lbs.

Rate (lbs): 550 lbs.

I dont have quite .700 lift more like .675 with lash so the seat pressure will end up closer to 270 if I shim it up around .050, so its only .050 from bind.. Will check

[KnightEngines]

Watch those 1243's - they tend to loose a bit of pressure pretty quick, give em an extra 10 on the seat or watch em & shim when they sag.
Not great springs, but the installed height, pressure & rate is great in a stock valve length holden.

[paulzig]

Not great springs, but the installed height, pressure & rate is great in a stock valve length holden.

Yeah I took a guess at that when I bought them. I have the option of the 1225 spring.

[MELWAY]

Watch those 1243's - they tend to loose a bit of pressure pretty quick, give em an extra 10 on the seat or watch em & shim when they sag.
Not great springs, but the installed height, pressure & rate is great in a stock valve length holden.

Spot on Tony. PSI have a new spring similar to the 1243 that should fix this problem