Had posted in tbi but I think this is the right section.

Ok so here's the specs. I have a 94 k1500 pickup. Put a new longblock from jegs about 10,000 miles ago. Stock replacement with 193 heads and flat tappet cam. Before install I replaced cam and lifters with sum k1102 but not springs. I have a custom tune. Intake edelbrock 2104, exhaust hooker full length headers dual with crossover, plus new distributor, icm, pickup, ignition coil, and wires.
So the problem. I think I am experiencing valve float. Truck runs fine until Around 4,000 rpms. Then feels flat and sounds like crap too. It climbs through the rpms quickly until then.
I have read to get "z28" valve springs in several places. But I am unsure of exactly which ones to get. And a little confused why they are just outers. I seem to remember having dual springs stock. Thanks in advance.

 

Install springs recommended for the camshaft. Don't use used springs unless you know what the installed spring pressures are and if they're good enough for the camshaft that's in the engine.

Valve float is caused by springs with not enough seat pressure. As the lifter is coming down off the lobe, the valve is being pulled down towards the seat. At higher rpms, this happens so fast that if the seat pressure isn't high enough, the valve will bounce off the seat which loses cylinder pressure for the next cycle.

According to Summitracing, the K1102 camshaft is a very low lift camshaft and only has an operating range of 1500-4800. I don't think you have a valve spring problem as stock springs should be more than enough. I think you have a very under spec cam. Looks like a low rpm towing camshaft for a truck, not a high rpm performance camshaft.

Change the camshaft.

 

If this is how the cam is going to perform I will get back with my tuner and have him move my shift points down to 4,000 rpm. After all it is a 4wd pickup truck. Thing is to me it just seems like around 4,000 rpm it loses compression. It even starts sounding bad through the exhaust. I'm happy with the camshaft i do tow regularly and the truck is heavy. I just think power would wind down over a few hundred rpm not just fall on its face and sound bad like this. The rev range is 1,500 to 4,800 and it seems like it would make that extra 800 or so rpms until it sounds that way. Maybe it's lifter pump up???

 

It's possible your valve springs are weak but that cam only needs stock spring replacements. Stock springs usually have around 80 pounds of seat pressure which isn't very much.

I doubt a 4x4 truck would see more than 3500 rpm anyway under normal driving conditions.

 

Sounds like a loss in valve train control however as Alky points out, that cam shouldn't take much spring. That said, check the specs on the springs and what's needed for the cam. It wouldn't hurt to pop a spring or two off and have them checked at a machine shop.
As for lifter pump up, that's what happens when the spring can't control the valve. There's component separation (the valve floats as opposed to bouncing off the seat) and with that, the oil pressure fills the lifter and closes the gap. Then the valve gets held open by the "pumped up" lifter until such time that the valve is back under control and the spring the spring compresses the lifter to it's lash point. Speaking of lash, or lifter pre-load in this case, be sure you have it adjusted properly and that it's within spec.

 

Sir you are exactly right. It doesn't see over 3,500 rpm in normal circumstances. But I still want to correct the issue and I have been chasing this solution unsuccessfully. The valve springs are stock but the lifters came with the cam which I installed before I ever started the engine. The motor came from gm just through jegs. It is not a reman. It is a brand new engine. It's done this ever since I first ran it. Any other thoughts???

 

Thanks and by the way. I did set the preload properly. Don't exactly remember the specs but remember doing it when I set the valves

 

Well, if it's not valve springs (and I think you owe it to yourself to have a couple of them checked) then you have to check out the usual suspects.
Is the ignition up to the task? Perhaps the module is weak (not sure of your ignition setup. HEI?). Often RPMs and insufficient spark go hand in hand. How about fuel? Is pressure being maintained?
You have to hope too that the cam and lifters are still sound. I'm sure you're aware of the problems associated with flat tappets and their longevity these days.
You may have already gone through a list like that but if not, there's food for thought.

 

I have all brand new ignition components. All ac delco except for coil. Which is a dui. Any specific way I should test for spark failures? I guess I'll have to add a fuel pressure guage as well.

 

Individually testing is a tough one. Short of pulling the plugs and observing the spark, there's not a lot that can be done unless you have access to a distributor machine. Even the plug observations won't indicate much if it's a combination of RPM and cylinder pressure that's blowing out the spark.
Is your spark module an over the counter stock replacement? I understand DUI makes an excellent upgrade.

 

I had a dui dyna mod icm and coil. Icm lasted 6 months. I still have the coil. I replace with an ac delco icm. Pn ACDelco D1943A. Still using dui coil.

 

I'm guessing you still had the RPM limitation with the DUI ICM?

 

Yes

 

Yes and as for as ignition the only things that aren't ac delco are the cap and rotor. I knew I should've changed the rotor when I swapped the pick up for an ac delco last week.

 

I ran a basically stock large cap HEI for years. MSD cap and rotor. Stock GM module and main distributor and an aftermarket coil. Easily spun the engine to 7000 rpm with no rpm limitations in the module.

 

I have a tbi truck distributor. Is that considered large or small cap??hei??? Do you think I should change the rotor

 

Technically the TBI distributor is small cap HEI but really, there's nothing in it. An ignition module. Even the coil is externally mounted. The computer controls the spark advance etc so there's no weights, springs etc under the cap to change the mechanical/vacuum timing.

You disconnect the EST wire behind the cover on the firewall, set the base timing, reconnect the EST and forget about it.

 

My wire was under dash notice it behind glove box. When I changed the prom chip. Thank God for that otherwise j doubt I would have found it. I had told yall false earlier that all my ignition was ac delco. It is a cardone distributor that I have been swapping parts to try to make this high rpm miss disappear. The rotor and reluctor are still not ac delco. You think that could cause this miss at 4,000 rpm

 

Certainly a faulty ignition could cause a misfire. Whether it's causing your misfire is another question.
If in doubt, swap it out is an old saying although I much prefer a diagnosis first.
As for Alkys' no trouble HEI module, some have luck, others don't. I'ts a common upgrade to the HEI. 7000 RPM is a lot for the HEI in it's stock form. But your (malachilou) RPMs aren't excessive so it's a safe bet to conclude that if the module is in good condition, then the trouble lies elsewhere. The easiest chance at repair would be a complete replacement drop-in distributor but that's a large expense unless you can get a loaner somewhere. Perhaps a local speed shop has a distributor machine? Then you could do a test in it's entirety.
And the valve springs still haven't been ruled out entirely.

 

Thanks. I will keep these 3 at the top of my list. Try to find a good distributor to swap in. Check valve springs. And fuel pressure at high rpm.
If I find an hei with vacuum or mechanical advance what do I do with my wires that go to coil and icm??

 

When you installed everything did you check to make sure your springs were not close to binding? The lift is low but I am running out of ideas. Good news is new springs are fairly cheap and the rope in the spark plug hole works well. Other than that if you do end up changing them get a good tool not one of those crank type.