Like it says why is my engines power dumping off after 4000 (see plot)? Even with the old 929 cam that came with my motor it would at least pull to 4500 or so. With the new one it just craps out after 4000. I assume its probably valve float thats doing it but why so early? Are the stock springs really that bad? Im assuming its what i previously mentioned but id like to get some more opinions before i start throwing parts at it.

 

Yes the stock springs really are that bad. So is that cam.

Get a better cam, you might be real surprised. Look at the Comp 12-402-4, aka 260AH-14, from their flat tappets for computer-controlled applications.

Although, another thing to think about.... your motor is essentially a duplicate of the 170 HP 350s of the late 70s. You bought it as a 240 HP motor. You're getting about 265 HP out of it. I'd suspect that in reality, the 929 POS cam you had was causing you peak torque to be at a lower value than you have now, but at about the same RPM; and your peak HP is about the same, at about the same RPM as it was. What you feel now though, is much like a TPI motor: good pull down low but nothing spectacular, giant rush of torque at 3600 RPM, everything disappears when you cross 4500. Having that taller peak makes it seems like it falls flatter than it did, when in reality it's about the same as it was above 4200, because there's more right before then.

Post your old dyno graph, I think you'll see what I mean.

Next, get rid of the "Hecho en Mexico" 993 heads, they're pitiful. Or at least port them.

 

The wierd thing is is that the rpm range at which the engine makes power is similar for both cams. I thaught that at least the new cam would at least pull till 4500-5000 because of the increased duration. I know its crappy but so is the rest of my setup: pos 700-r4 that only has second gear under WOT, small stock 2bbl tbi with 1-11/16 in bores,and a 2.73 one wheel peeler 10 bolt. Ill probably keep the cam untill i get more money but shouldnt it at least pull a little farther? Oh, here is the old one.

 

i guess your right... its pretty well mathced to what i have now but it just isnt made to pull up high. One of these days if i ever get some money ill buy decent parts to make power and get it to the ground.

 

Not if something besides the cam is choking it...

Think of each of the pieces of your induction system as being like a piece of garden hose, and you've got them all strung together in a series. Since power comes from flow, i.e. gasoline molcules burned per time, (which requires air molecules per time, which is just another way of saying "flow") you can equate changes you make to your engine to similar changes you might make to your garden hose array.

OK, let's say you take your garden hose sections; and that you have 25' of ½", then 10' of ¾", then 50' of ½", then 25' of 3/8", then 15' of ¾", just to pick some numbers out of thin air; and you turn your faucet on, and measure the flow (how long it takes to fill a bucket, say). Then you decide to change some pieces. OK, so what happens to the total system flow when you take out the 10' of ¾", and put in 2' of 1"? Nothing at all, right? OK, now you're mad, so you take out the 10' of 1" and put in 5' of 2". What happened then? Anything more? I doubt it. Now let's say you take out the 25' of 3/8", and put in 25' of ¾". What happened that time? It changed, didn't it?

Your engine is the same way. If you want to make it put out more power, you don't just keep buying different stuff and sticking it on and hoping the numbers will go up. Doesn't work that way. The right way is to find the weakest link, and change that one thing!!! Just like the garden hose, you can change every single other piece of that group of hoses, and nothing will happen until you change the restriction that's actually controlling the flow.... the 3/8" piece.

Your job is to find the restricted part of your intake tract. You say you haven't changed the TB; think that might be it? As long as it's the same weenie little thing that just barely lets through enough air for a 305, it doesn't matter what you put under it, it still only lets through the same number of air molecules per time.

Flow.

 

the tb+ stock air cleaner is somewhat restrictive, as well as the performer dual plane intake... theres about a 1.6 inHg drop (its rated at 570 cfm @ 3in Hg) across the tbi at around 4500 so those are just becoming restrictions. Im sure the heads are restrictive as well. Ill also need a better fuel pump as well as a prom if i want to make more power. Right now every part of my setup is restrictive in some way and thats why i chose the small cam. The biggest restriction is still my empty wallet, don thave money for better parts. Back to my origional question... do you think the crappy springs have anything to do with the sudden power drop off, RB? Or, is it just the series of small restrictions all coming together, including the valve springs, to cause the engine to fall on its face after 4000 rpms.