Valve Spring Clearance From Coil Bind

[Procharged 434]

I will be running the PAC 1356 spring, and was going to set it up at a 2.00" Installed height, but it would have around .120" from coil bind with the camshaft I will be running. I have read bad things can happen (spring surge) if you have too much clearance before coil bind. Should I install the spring at a 1.950" Installed Height instead? That would get me to .070" clearance from coil bind, but it would raise the seat pressure. The lift of my camshaft is .776" on both, the Intake and exhaust, minus the .025" lash, so the actual valve lift will be around .750". The coil bind of the spring is at 1.130". So 1.950" I.H. - 1.130" C.B.= .820", .820" - .750" lift = .070" clearance. What would my Seat Pressure be at a 1.950" Installed height with this spring? They advertise is at 300lb seat at a 2.10" Installed height, Bullet Cams told me they would have around 375 lb installed at 2.00" installed height, so what would it have installed at 1.950" Installed height? Here are the specs of the spring


PAC 1356
Seat Pressure 300 lb.@2.100"
Open Pressure 1002 lb.@1.200"
Coil Bind@1.130"
Spring Rate is 780 lb/in.

These will be on a N/A 18* 436 SBC, max RPM 8000, 1/8 mile drag race application. What installed height would you set them up at, stick with the 2.00" I.H. along with .120" Clearance before coil bind, or set them up at a 1.950" I.H. to bring the clearance down to .070"?

Thanks

[Straight8]

Do you need that much psi? Why not use another spring? 1326 maybe?

[superpursuit]

From the information you have given at 1.950 installed height you will have 417 pounds pressure.

[Procharged 434]

Well... I bought these springs because Mark at Bullet recommended them for my application, it will be turbocharged in the future, but N/A for now. I don't really want to buy another set of springs, I would rather use what I've already got.

[Procharged 434]

From the information you have given at 1.950 installed height you will have 417 pounds pressure.

Thanks, that's exaclty what I figured too, just didn't know if my math was correct. I think we might just stick with installing them at a 2.00" I.H. and live with the .120" clearance, so we can keep the seat pressure more reasonable....

[cgarb]

I have never ran my springs within .070 of coil bind. Most of my set ups are at least .100 off coil bind. I have not had any trouble to date. I am not making the kind of power you will be though. My engine it turn to 7K with a steel retainer and stainless undercut 11/32 valve. Nothing special.

[In-Tech]

I guess it's always good to ask around as to other peoples experiences... I would think your best bet would be to ask PAC and have all your valvetrain weights at hand.

[Racerrick]

Springs without dampers should always be run less than .100 and .050 -.070 is prefered. If the spring has a damper then I might go to .125 If I was you I would use less spring until I put the turbos on

[Newold1]

Too much clearance at full net lift at 2.00" installed height.
Too much spring pressure at open and closed at 1.950" installed height

Return springs to PAC and replace with better spring rating for your use.

[groberts101]

I will be running the PAC 1356 spring, and was going to set it up at a 2.00" Installed height, but it would have around .120" from coil bind with the camshaft I will be running. I have read bad things can happen (spring surge) if you have too much clearance before coil bind. Should I install the spring at a 1.950" Installed Height instead? That would get me to .070" clearance from coil bind, but it would raise the seat pressure. The lift of my camshaft is .776" on both, the Intake and exhaust, minus the .025" lash, so the actual valve lift will be around .750". The coil bind of the spring is at 1.130". So 1.950" I.H. - 1.130" C.B.= .820", .820" - .750" lift = .070" clearance. What would my Seat Pressure be at a 1.950" Installed height with this spring? They advertise is at 300lb seat at a 2.10" Installed height, Bullet Cams told me they would have around 375 lb installed at 2.00" installed height, so what would it have installed at 1.950" Installed height? Here are the specs of the spring


PAC 1356
Seat Pressure 300 lb.@2.100"
Open Pressure 1002 lb.@1.200"
Coil Bind@1.130"
Spring Rate is 780 lb/in.

These will be on a N/A 18* 436 SBC, max RPM 8000, 1/8 mile drag race application. What installed height would you set them up at, stick with the 2.00" I.H. along with .120" Clearance before coil bind, or set them up at a 1.950" I.H. to bring the clearance down to .070"?

Thanks

PAC has a spring pressure calculator on their website for those springs. Entering the spec's you gave the seat pressure shows 417 lbs @ 1.95" installed. Seems pretty excessive considering there's probably a slightly shorter thinner stemmed valve weight involved. With lighter weight valvetrain components controlling 8,000 rpm is pretty easy beans these days. Probably the wrong spring for this application, IMO.

[engineguyBill]

The most important elements of valve springs are installed height (and pressure at installed height); compressed spring dimension at full valve lift (with recommended coil bind clearance). Use the springs that are recommended by the camshaft manufacturer, install them correctly and insure that there is plenty of coil-bind clearance and you are ready to go.

Side note. Compress all of the springs all the way to coil bind, several times then check each spring on a spring tester at several different compressed heights. The valve spring pressures should be very close to each other at each of the different compressed heights when new. If not, reject them.

[Walter R. Malik]

Well... I bought these springs because Mark at Bullet recommended them for my application, it will be turbocharged in the future, but N/A for now. I don't really want to buy another set of springs, I would rather use what I've already got.

SO, in other words you are of the opinion that valve springs never wear out and do not lose any of what they had when they were new ...?

[Procharged 434]

Well... I bought these springs because Mark at Bullet recommended them for my application, it will be turbocharged in the future, but N/A for now. I don't really want to buy another set of springs, I would rather use what I've already got.

SO, in other words you are of the opinion that valve springs never wear out and do not lose any of what they had when they were new ...?

Uhh, no, that's not my opinion of valve springs at all, I been around this stuff a few years, I know they have a life cycle, and have to be replaced.... what I am saying is, our orginal plan was to build the turbo motor from the start, but plans have changed in the middle of the build, and we will be running it naturally aspirated for awhile, but we are going to be using the same camshaft, and already have the springs as well. I was just simply stating that I would like to use the springs, since I already have them.