BBC Valve spring help!

I know this has been discussed sometime back, but this is our first go around with a blower motor. We are putting togeather a 540 BBC with a 12-71 @ 20psi boost at 8000 rpm max. We are using a set of Sonny's BB5's with 2.300 SS intakes and 2.19 SS exhaust valves. The cam is .748/.748 lift and 286 @.050. Pushrods are 7/16, .165 wall, .904 Morel lifters. We have PAC springs that are 425 lbs. on the seat and 1000 lbs. open. My concern is this to much spring for our combo?? I had a great deal of confusion from guys saying it's too much and others actually saying it should have more. Lets here what you guy's think before we button this thing up. Thanks!

 

You didn't tell us how hard you were planning to twist it. With that cam, lifters, and push rods you should be good to 8000 rpm. Your set up looks good to me.
Joe

 

We are going to twist it to 8000 max. We will shift at 7800 and go thru the top end at 7800. We are looking at trying to make this live without being real hard on valve train items.
Thanks

 

A little more seat pressure than I run on a Chevy with titanium valves and a small cam but should be fine. Not sure what rockers you are running but make sure you have the longest stand bolts you can use on the intake and EXHAUST.

 

At that pressure he should be using the ARP2000 bolts. Anything less you will start breaking rocker bolts. That's my experience anyway.

Blessings........Ron Clevenger

 

That not far from what I run. I have Jesel pro shaft rocker system and did break a stand bolt once. But its got a bunch of runs on it. works great. I would run it.

 

Assuming you have a shaft rocker system, are the intake and exhaust bars hooked together somehow?

As said before, make sure the holes in the heads are drilled/tapped as deep as possible.

IMO and experience for your combo 425 is great plenty seat psi.

 

A little more info

We have a T&D shaft rockers with the stands all bolted togeather and then tig welded. We also added onto the exhaust stand, on the end and bolted that thru the end of the head to give that exhaust rocker more support. I could go with a +.100 retainer on the valve that would get us at 360 on the seat. Again it seems at 20 pounds of boost, some guy's are getting by with 270 on the seat. But the real question is we want enough spring to not "bang the blower" but still easy on our valve train. Any thoughts would be appreciated

 

I had that exact setup. Stay off a 2 step. It will destroy your combo. Been there done that. Ti intake valves would be better safe than sorry down the road. 425 on seat is what I ran for years until I did the 2 step. Destroyed a bunch of parts in a season and decided a hemi was much more fun.

 

Do you mean #1 and #8. If you did, that is a great modification. If you can get 9/16" pushrods on the exhaust and 1/2" pushrods on the intakes it would be closer to bulletproof. You don't have a lot of boost but we have found with a lot of boost (like 50-60 LBS), the pushrods are swinging around ALOT! Lost two motors over this exact issue. We ran 350 LBS on the seat for years at up to 48 LBS of boost with no issues and no tie in on the #1 and #8 cylinders. We also ran straight 7/16" .188 wall pushrods. This was with titanium 2.350 intakes and 1.90 titanium exhausts. With all that said, I think you could dial down the pressure to 375-400 and be okay.

 

springs

I like the setup. Get a valvespring pressure checker and keep an eye on them. If they are happy the pressure will be stable.
I went through the same deal with a chevy and a lot of times low pressure bends and breaks stuff that appears to be high pressure.
When I ran that kind of boost and rpm we left the valve covers on between rounds...lol.
Those were the days!!!