A question on valve springs

Blown BBC 468 ci 12 to 1 comp aluminum head Dart 345 heads 2.4 intake 1.88 ex 14-71 std blower 240# springs. My question is are these springs sufficent or should I go to a greater # and if so how much? DAVE

 

I'm not a valve train expert but I would tend to think you may want to increase your seat pressure a bit. I have a BBC also and I'm running 350# on the seat and some have said thats even a little light. I'm going to run it as is but I would think 400# would be better. What is your installed height?

 

2inches, is there a formula to determine seat pressure,or trial and error.Thanks for responding.

 

The springs will have different a psi. for a certain installed height, it will also have a lbs. per inch. You can take your installed height of 2", their height/psi, spring rate (lbs per inch), do some simple math and compute to see where you're at psi. wise. I personally believe that you are way too low on seat psi., and have performance to gain by increasing the seat psi.. You should figure out your piston to valve clearance as well as actual lift on the valve (not what the cam card says). If you need help doing this, I can tell you how (just don't want to type it all out if I don't need to). Once you have all that info you can figure what spring/installed height/seat psi. is right for you. Good luck and let us know what you find.

Respectfully,



Brandon Booher
NHRA TAD #34

 

Among other things the springs come with a pressure@installed height number. The spring manufacturer will tell you what that number is. When you install them at that height they should be close. Best way to confirm is a Rimac spring tester. Unfortunatly with only a 2" installed height you won't get much more seat pressure because those springs hover around the 250-275# range max. You will have to go to a 2.100 or 2.200" installed and then you have lots of selections of springs. What is your cam lift? You have to be aware of your coil bind dimension also, because you can shim your springs a bit to get your seat pressure up, but your max lift before bind will suffer. Its all a bit of a balancing act.

 

Brandon I have heard using oil restrictors in my block (dart iron) may cause the early demise of valve springs, any thoughts on this? DAVE

 

Chevy's pump a lot of oil to the top. Without restrictors you'll have broken rods and burned bearings.

 

Yes they pump a lot of oil, depends on your pushrods/rockers etc, I'd speak to Dart and/or your valvetrain manufacturer on this. On a hemi, we run .105 restrictors in the block.

Brandon Booher
NHRA TAD #34

 

Valve Spring Pressure

I had a lot of wear in the valve keeper groove until I took Noel Manton's advice and increased the valve spring pressure.....the radial lock groove would become sloppy as the keepers were not held tight against the valve stem....I'm not gonna suggest a number on pressure, seems like I was around 350# seat with the BBC....now over 400 on the hemi...but make SURE you get the correct length rocker shaft bolts into the head - must thread deep into the hole or they can break the bosses off of the Dart aluminum heads (ask me how I know)

 

I will say I very rarely disagree with a manufacturer of anything but if you contact Dart and ask them about restrictors in the BigM blocks they will tell you to not use any. I disagree with this, in a drag situation with shaft rockers restrictors are a very good idea. I lost a crank because I filled the valve covers with oil and lost pressure, I believe if I had restricted the oil to the top end this wouldn't have happened. Plus on a Chevy put in drain lines from the heads.

Just my opinion.

 

The number I got from Dart was .187" drill in the blank they supply with the block.I just got back from IMIS today and got some information from all the valve spring mfgs. So between IMIS and my fellow racers on ITA I think Im going to be alright,thanks to all who respond.DAVE

 

Formula

Yes there is a basic formula that will help.If you give me a call I will be happy to give that to you and I will explain a few other things.

Noel Manton
Manton Rockerarm phone 951 674-2212

 

for one material of the valve makes a difference also, whether it be titanium or stainless steel, but in your case for either the pressure you have is not enough. cam profile, engine rpm, piston to valve clearance, boost pressure, all of these play a big factor in spring setup. You can have a higher installed pressure but the open pressure may not be sufficient enough also, I keep mine at about 400 lbs. of seat pressure and about 1100 open, probably overkill for my application, but oh well. be sure that the spring rate is correct for the cam profile. A 2.400 dia. valve in stainless is pretty heavy, titanium is not but you dont want a titanium valve bouncing off the seat as it will concave the face faster.

 

springs

If you give me a call I will be happy to explain a few other things.

The subject needs more than opinions.

Noel

 

Noel I will give you a call soon,just trying to get things ready for the holidays. I want to thank you all for responding.DAVE MOLDENHAUER RACING

 

oil restricters

We have been running bbc pretty long time and have used restricters and not used them.I prefer to not use them and just add more oil capacity.Usually 15 quarts for the quarter mile and 12 quarts for the 1/8. hope this helps in some small way.overthehill.....

 

I wont give anymore opinions, thats for sure.