What to do

[hans]

I need a little help here deciding on what to do. I'm concerned that my spring pressure will not be enough and was wondering what the best option is to do. I have the following combo going into a 20ft circle race boat that will be used as a lake rocket. I'd like to keep my RPMs to 6500.
Merlin II block 4.6" bore.
Crower 4.25" crank.
Lunati 6.8" Pro-billet rods.
JE pistons.
CR = 8.68:1.
Pro-topline 360CC heads.
Pistons, chambers and exhaust ports coated.
1071 BDS Blower
Whipple Intercooler
2 x 1150 dominators (gas)
Cam is a custom roller 283/292 @ 0.050, 0.799/0.765 on 114 centres
1.7 Roller lifters
Isky toolroom springs 9955
With the springs and the cam I will have around 285-295lbs seat pressure and around 700lbs open.
Also, there is only 0.060 clearance before coilbind.
There is a Comp Cams spring that will give me 305 / 830 lbs and over 0.100 before binding.
Should I:
a) See how the current springs go.
b) Get the new springs
c) Get a smaller lift cam
Thanks
Paul

[Infomaniac]

What seat pressure does the cam mfg recommend?

[Fiat48]

Anytime I have ever had the seat pressure drop to 220 lbs or below I find evidence of the valve bouncing and beating the seats up. I keep 240 lbs of seat pressure or more at all times. High lift pressures of 700 would be fine.
6500 rpm is not asking much. That camshaft has got a big lift. If it were me, I'd run the springs I had, perhaps even backing them down on the seat pressure and maybe .125 away from coil bind. When you run that close to coil bind, the springs life is shortened.
Then I'd see how they hold up and take it from there. Smaller lift cam probably would extend spring life.

[hans]

Thanks for the replies. Called the cam mfg and they reccomended 280 and 700 (what I've got now!!). I'm sure last time the figures were higher. Anyway, I'm feeling better now, except for the coil bind issue. The problem with that is I can't go any higher on the installed height as the spring seats can go no deeper and I've got the best combination of locator/retainer/lock to give me the highest installed height now. I'll go with these springs untill they drop 20?? pounds, then redo with a spring with the same pressures, but greater margin before coilbind.
Thanks again.
Paul

[Slyder]

For your application it is actually good to have the springs closer to coil bind than further away.
We found on the endurance applications as well as radical lift drag applications, if we were too far from coil bind, a harmonic was produced in the spring and that would kill the springs almost immediately.
Always consult with the tech. from your cam company before making a decision.
Paul

[Snowboat]

Since we're talking about spring pressures. What is the best tool for checking the seat pressure while the springs and heads are on the engine? Can it be used with ot's or do you need zoomies or the pipes off?

[hans]

Rio, I could get longer Inlets, exhausts are already +.100 but the exhaust lift is 0.030 better off anyway. Can you get +.150 exhaust valves? I'm currently using Crower severe duty stainless.
Slyder, thats interesting. I've always been told that for durability you should have .100+ before binding. I guess I'll see. I plan on keeping a close eye on the pressure. Am going to get a Rimac spring tester. $$$$
Anyone used the Isky 9955 springs before?? and, any estimates on how long they'll last?
Paul

[Fiat48]

Measure your actual lift at the valve. Remember from the claimed(Lift spec) lift of the cam, your actual lift will be less due to:
Valve lash must be subtracted.
Actual rocker ratio (some are 1.7, some are 1.72)
Push rod deflection.
So take that .799 lift and you may find .750 or a whole lot less at the valve. Now how far are you from actual coil bind?
Want more fun? Start measuring all your lifts at every valve. Deflections, rocker ratios do vary.
Springs are in batches. Good and bad. You never know if you're on a good batch or bad.

[GofastRacer]

Originally posted by Snowboat
Since we're talking about spring pressures. What is the best tool for checking the seat pressure while the springs and heads are on the engine? Can it be used with ot's or do you need zoomies or the pipes off?
These from Moroso are the shit, they also have one for tight quarters!..:cool:

[GofastRacer]

Originally posted by hans
Rio, I could get longer Inlets, exhausts are already +.100 but the exhaust lift is 0.030 better off anyway. Can you get +.150 exhaust valves? I'm currently using Crower severe duty stainless.
Slyder, thats interesting. I've always been told that for durability you should have .100+ before binding. I guess I'll see. I plan on keeping a close eye on the pressure. Am going to get a Rimac spring tester. $$$$
Anyone used the Isky 9955 springs before?? and, any estimates on how long they'll last?
Paul
Longevity depends a lot on cam profiles, some are easy and some are hard on valvetrain parts. One of the main things that kills valve springs is not backing them off while not in use, and rotating the motor don't get it because there's always some that are compressed. If mine sits for a week, I back them off!!..