Is there a way to determine the seat pressure from a known spring rate, and visa/versa.. a spring rate from a known seat pressure?

I have a cam that that specs a matching spring rate at 357 lb/in. with a max lift of .490". No data on seat pressure.

I'm looking to buy a set of aftermarket heads (pro-filer) that if purchased assembled, come with 100lb. seat pressure springs with max lift @ .550". I called and they do not have the spring rate, only seat pressure.

It is more cost effective to buy the heads assembled if I can confirm the supplied springs work with the cam. This is all mild hydraulic flat tappet (for now). ..and I plan to run 1.6 rockers to utilize the extra flow of the new heads. (which would otherwise exceed the .490" of the recommended springs)

Any help?

 

In both cases measured is better but;
If they have the seat pressure for installed height and the seat pressure open at .550" then you could figure out the spring rate.

For instance if the spring pressure is 100 lbs on the seat at installed height and 220 lbs @ .550 inches. then you can figure it.

220 - 100 = 120.
120lb rise in .550 inches.
You take the lift (.550) and divide 1.0" by that.
In this case 1.0/.550= 1.81818. Or you can round it to 1.82.

1.82 is the number you will multiply the difference between seat and open at .550 to get your spring rate.

1.82 X 120 = 218.4

The spring rate is 218 lb/in.

If the rise from seat to open @ .550 is 143 lbs. Then;

1.82 X 143 = 260.26 lb/in spring.

You could then figure your over the nose pressure by taking the calculated spring rate and multiplying it by the lift of your rocker/cam and adding that to the seat pressure.

IE, .490 in lift X 260lb/in = 127.4 lb

127.4 + 100 = 227.4 lbs over the nose.

Seat pressure needs to be measured to know what it is as far as I know.

But I suppose the same calcualations could be applied if the spring rate is known and taking the free length of the spring minus the installed height to get the amount compressed and multiplying that out.

IE, free length 2.5" installed height 1.8"

2.5-1.8 = .70"

.70in X 260 lb/in = 182 lbs on the seat.

It's accuracy may be questionable however.

 

That was a bit much to take in but it sounds like I still need more info then what I have. Only further info is on the recommended spring (357 lb/in) which is installed at 1.70" and max lift, like stated above, is .490".

 

I called pro-filer when I ordered my heads and asked if they used plus .100 valves.They also let me send the matching springs and retainers for my cam and assembled the heads with my parts.The phone call was well worth it to make sure everything is properly matched.If winter ever ends I'll get back to work on the car!

 

You know I thought the simple solution was to order them bare with a set of valves and just assemble them myself with the matching springs, but then I go back to thinking that I really need to run the 1.6 rockers to utilize the flow of the new heads. The matching valves do not support the lift of the 1.6.

 

If you'd post your cam card info, or at least the lobe lift and duration numbers, we'd have a lot better chance of recommending a suitable spring.

 

.295 intake @ lobe .442 w/ 1.5 and .472 w/ 1.6
.310 exhaust @ lobe .465 w/ 1.5 and .496 w/ 1.6

214 / 224 @ .050 on a 112

This is a mild motor I've had that I'm going to use to get the car going, adjusted, and dial in the chassis, etc. giving me some time for funds to build my roller motor. It was planned around a bowl blended set of stock cast heads but upon assembling them I found they had several worn and non concentric seats. Rather then put money into machine work, I'm going to get the pro-filers that I plan to use on the new motor and use them on this for now.

 

This one should fit the bill for a SBC hydraulic cam of your duration and lift (1.6) range.

CompCams # 983-16 (set) - single coil, 105# installed @ 1.7", 410#/in, .500 max valve lift.

Hope that helps you out of a bind, so to speak.

 

The springs pro-filer has specified should be fine.They normally use a plus .100 valve and a 1.900 installed height.The lighest tall spring I have seen is a howards 98515 1.88 install ht,350 in lb with 100 lb closed and 275 open and coil bind at 1.300.Most springs are rated with .06 clearance above coil bind also.I believe pro-filer uses pioneer products springs and 3/8 rocker studs in the assembled heads.I replaced my studs
with arp 7/16 due to the roller cam and stud girdle.Pro-filer gives you a pretty generic spring in their assembled heads to cover a wide range of cam choices.That is why I sent the springs and retainers that are spec'd for my cam.If you go with a shorter spring they will have to go with a standard length valve.If you really want all the technical data on this head give Chad Speier a call,he will answer any questions you have and give you a straight answer.The springs that pro-filer spec'd should work fine with the cam you listed.If need any help finding parts for the pro-filer head feel free to send a pm a give me a call,I'll be more than happy to save you some time.
Good luck,
Dave

 

Yes, I would defer to verifying exactly what you have before making the assumption that you actually need alternative solutions such as the springs I have suggested. The menu is quite limited for .500" lift at 1.7", installed.

 

Thanks Dave. I thought it was going to be a simple call to pro-filer for the detailed specs, but the guy could only provide that the valves provided are qualcast / qualfast and the smallest .550 lift springs had a 100lb seat pressure. I thought for sure they would be able to easily spit out the specifications. I was almost tempted to call back another day and hopefully be connected with someone else. I find it doubtful that this information is not available.

But, sounds pretty accurate that the supplied spring may work just fine. You are right about the .100 valves, it does show that on the website. Skunkworks - thanks for the help as well. I may run it past chad for a 100%.

Dave - How'd the carpet set work out for you? ...and do I recall you saying you possibly had a hookup on the heads from someone?

 

Chad Speier is a great source for pro-filer heads and he sells any and everything you could ever want.He will also take them back and port them if you want more power.I went thru pro-filer on mine because Chad did not have the casting I needed in stock.Bailey engines in michigan is also a dealer and he is on ebay.Chad can get you stud girdles,sportsman shaft rockers(lgm)and any particular valve set up you want.I went with roller rockers and stud girdles due to the fact that 6500 rpm will be my limit and I could not justify the shaft rockers.It is not always easy to get a hold of someone at pro-filer and I had the best luck in the morning.The carpet set is in my house waiting for better weather.I have original driveline out and would like to clean and paint before the new engine and transmission go in.I may dyno the new engine and break it in there to avoid leaks etc... Are you still going to supercharge your roller motor when it's done?

 

Sounds good. Just started our bathroom remodel this week so my focus has changed for the time being, but I do plan on calling Chad. Yes on the blower, and I even plan to play around with it on this motor since the combination works with the exception of not being forged . The ignition is already setup for the FI with the programmable MSD, and I'll have a wide band air/fuel, so I should be able to get the tune right and keep it real conservative. If I blow it up then that much more motivation to get the good short block done. ..but that's the "now" plan. I've had the motor so it's here and available if the time comes that the car is ready and I need it (the virgin roller block is sitting in the corner just wanting machined too). This build has been ever changing as time goes on. There's a chance that it'll be too nice by the time it's done to want to mess around with a temporary motor, but all $$ dependent. I've already went from a basic frame replacement to a full on resto-mod.

Your car going to be ready this season? I thought I had a chance, but rebonding the front end and body work/paint was suppose to start at the beginning of the year and it's still sitting here. My hopes are diminishing

 

I hope the have the vette on the road late spring or early summer.My plan is to get the suspension and driveline dialed in before paint.I want to make sure the car hooks properly to limit the chances of damaging the new paint job.Hopefully your remodel will go smoothly and save some time for your vette! If I dyno my engine I'll post the results on my build thread.

 

What you need is the springs the cam calls for. You need seat pressure, installed height and open pressure. Next you measure for pushrods. No "Looks close enough for me" these parts are critical to avoid a catastrophic disaster.

Most of the time you can get away with adding 1.6 rr on mild engines without swapping springs because the lift difference is relatively small but the pushrods have to be checked again and make sure they don't rub the block and don't go into the safety margin of coil bind.