I have an 83 z28 with the LU5 CFI. once upon a time a bought a cam and am just now getting around to putting it in. I was wondering if someone would help me find the right valve springs. preferably by specs not just comp cams are awesome or whatever.

The cam I have is the SUM-1104. summit brand. The lift is .465" for intake and exhaust and the actual duration is 224º for both. While the advertised is 282º, why thats on the cam card is beyond me.

Point being its considerably more than the stock .269 (intake) & .276 (exhaust) and i don't know what i'm looking for exactly.

someone told me to look for one with around 450lbs open pressure? is this enough? too much? anything else to look for? Thanks.

 

450 lbs is WAY WAY WAY WAY too much.

The reason the "advertised" duration is so large but the .050" is so low, is because that is a PITIFUL weenie old obsolete cam from days back when there was very little available for valve springs besides either stock, or all-out racing. No in-between. That cam is "more" than stock, but it's pretty lazy and light-weight, in the grand scheme of things. It has long, slow, gentle, inefficient ramps that just kind of mosey the valves up off the seat slow and leisurely, and let them gently and sleepily drift back down; wasting all kinds of time in the process. They spend ALOT of time just barely cracked open, not flowing much, compared to modern ones, which snap the valves open FAR more enthusiastically and hold them as far open as possible for as long as possible, to allow as much cylinder fill to occur as possible. It's not even as aggressive as alot of modern stock ones. Consequently, you don't need to get all wrapped up in super high-$$$ hot-rod stuff, just for that thing.

You need an entry-level stock-diameter spring. Better than stock, but the requirements aren't too extreme. Look for numbers around 110-115 on the seat and 285 or so over the nose. Just about anything matching that description from any of the cam mfrs would work: Comp 981, Crane 99848, or the equivalvent from Lunati, Isky, Crower, or Manley. With the matching retainers and keepers of course, and properly set up at the correct installed height.

Your stock cam, incidentally, actually has LOBE lifts slightly less than those numbers that you quote, which are for the L69 cam, not the LG4/LU5 one; the VALVE lift is then that number, times the rocker ratio (1.5). Yours in the neighborhood of .400" at the valve; something like .384" / 394" if memory serves me right. The ones you quoted, for the other cam, are something like .403" / .415" or so.

If I was you, and going to all the trouble and expense of a cam swap, I'd sure get something more .... to the point, and suitably OPTIMIZED for your application (a fuel-injected 305), than that ancient generic POS.

 

If you're on a budget, the el cheapo "Z28" springs that Scoggin-Dickey sells would work just fine on a cam with the mild specs you posted. You'll probably need the matching retainers too, and you can get the whole setup for roughly $65 the last time I looked on their website.

 

brand new stock Z-28 style springs will work.....you can shim them to the sddired seat pressures....you want no less than 90 on the seat with a max of 105 on the seat......and around 300lbs. open.......cam is similar to a comp 270 magnum.....an an isky 270 mega cam......nice cam 1 in my old small block.

 

Comp cams #981-16 Lunati #73943 Isky #205D Speedpro #739R Pioneer/Elgin
943 are all "just right"

The sum 1104 is not all as bad as Sofaking makes it out to be. In the right application, it works very well and makes very good power and torque.
This cam is the wrong cam for a near stock 305.
Spend $59 and get the right summit camshaft for your motor.
Sum-1102 or sum-1103 is the right camshaft for you.
All use the same valve spring.

Sum-1104 being 224-224@.050 needs 10:1+compression and a very high stall converter (3500-4000rpm) and 4.10+ gears when used in a 305. You don;t have this stuff to support this camshaft in your 305.

Unless you're making those mods, use a smaller camshaft like Sum-1102 or Sum-1103 at the most. They will give you the performance increase you're looking for without getting carried away.

 

And even WITH that, will STILL get beat easily by a modern cam that makes the same OR MORE power, with FAR LESS "big cam" drawbacks.

He's right... I'm too harsh on those old junk cams. They're not really THAT bad.

They're WORSE.

Although, the smaller ones in that series, such as the "RV cam" (Summit sells it as the 1102) or the "mild cam" (1103) will work AHELLUVALOT better than that one you're asking about; and do pretty good in a motor that it doesn't really matter whether it runs as good as it can or not, just as long as it runs at all. That's about where those cams are on the food chain: not for use if the car has to be competitive or efficient or optimized.

Even better than getting one of those though, would be to get one that's actually DESIGNED to work with EFI.

Here's a MUCH better one for the application at hand than any of those old generic ones. http://store.summitracing.com/partde...2D12%2D249%2D4 Crane also has some that work well, in the series they used to call their CompuCams.

 

http://store.summitracing.com/partde...1&autoview=sku
this is the crane camshaft I would use. I would remove and fully port the heads with larger 1.94" intake valves. Mill 'em a bit to bump up the cr. And do a nice shorty header, custom Y pipe and Cat back exhaust change.
I would change the converter for a 3000stall and add 3.73:1 rear gears.

 

ok i think i should add some more to this post before a fight breaks out. the motor is not quite stock, nor does it have the CFI on it anymore. it has a dual plane intake and a carb, a high stall converter, an msd and other stuff thats less concerning to the cam.

but as i said ive had the cam for ages and dont plan on buying a new one if this is worth any time at all, subjectively. when i put the springs in a buddy of mine offered to port polish and mill the heads for me. so what im hearing is mill the heads to raise the 9.5 to 10:1. and look for valve springs with around 100 seat and 300 open give or take. and the crane 99848 were the ones i was looking at.

as for the gear ratio im not that into it yet unless i find a salvage part or this shows some promise without it. but thats a later conversation.

 

No fight breaking out here... we'll just keep it as a hockey game between us. F-Bird and I regularly disagree regarding that series of cams: this isn't the first time, and won't be the last, I'm sure.

That part # of Crane springs is perfect. Should fix you right up.

I'm sorry to hear that you are determined to slow your car down like that. But that's OK by me, I always like to see somebody like that in the other lane. Post us up some before/after time slips, so the next guy that bites on those low-bid cams, will know what it does, and how it really performs. Sometimes it's hard to tell about "worth" except in hindsight.