In my effort to start understanding what I'm doing to my car, I came across my cam card, which I totally forgot about.

The engine has a set of RHS heads ( P# 12306) 5.7 Rods, Flat Top Pistons, Stroker Crank, 2.02/1.60 Valves, etc.

After looking at it for 10 minutes, I realized that I had no idea what the numbers meant A picture of it is enclosed.

 

There's a thread about cam tech on the FAQ forum.

 

You know, I ALWAYS forget about that board...

Sorry for the out of place post, and thanks for reminding me

 

It means you need to do a cam swap RIGHT AWAY.

You have the Crane replica of the GM "151" cam.

If you feel like the car has no "leave" whatsoever, no bottom end "grunt", sounds slightly mean but has no .... cajones, is hard to get to ever idle right, seems like it will rev forever and is just about to get to a RPM where it will start producing power but never quite does, drinks too much gas, and loses races to the most unlikely things (Hyundai Sonatas hurt, don't they? ) then the reason is that cam.

What would you like to know about it that you haven't already figured out?

 

When I finally get the motor back into the car, I'll let you know if there is no "leave"

And the word is "cojones" I should know, spanish is my first language hahaha.

I read the tech article, so I have a pretty basic understanding on it, but why exactly wouldn't it have any low end power?

 

You don't have to "let me know"; trust me on that. I'm "letting you know", up front. Been there, done that, learned the lesson already. Many times over. Learn from my experience I'm sharing with you.

It's just a terrible cam. It's been building cars with "no leave" for almost 50 years now. I lost count probably about 30 years ago of how many I TOOK OUT for people that couldn't stand it any more, and then couldn't believe how much better their car ran with something decent in it instead. Although, when it came in the motors it originally came in, in the cars it came in, it wasn't so bad; but put it in a heavy car (over 3000 lbs or so) with what we would consider "normal" gears nowadays (3.73 or lower) with an automatic transmission, and it's REAL disappointing.

If you haven't put the motor in yet, do yourself a favor, and swap that POS out NOW, while it's still easy.

Its problem is WAY WAY WAY too much "advertised" duration for its .050" duration; and WAY not enough lift. Basically, if you look at the valve motion produced by a modern cam, the valves stay closed until the last possible instant, they snap open as quickly as possible, they stay open as far as possible for as long as possible, and they close as quickly as possible when the time comes. That old thing, OTOH, starts to crack the valves open WAY early which produces in effect a compression leak, opens them in a very slow leisurely way, doesn't open them very far, doesn't hold them fully open at all but rather starts to immediately let them back down again, lets them mosey and amble back toward the valve seat, and then holds them open just barely cracked and leaking compression for a LONG time when they should be closed. It's those long compression leaks that bleed off cyl pressure at low RPMs that make it run so lazy. Just an altogether obsolete, ineffective design. You'll hate it if you leave it in there, you can believe that.

Thanks for the Spanish lesson. I don't speak that language very well, although I know Latin, French, German, a little Greek, some Chinese, and some Italian, plus however much Spanish I had to learn from living in California. I'm an American though, so English is my first language. I was just looking for a "politically correct" way of saying that.

 

Mhmm, I see. If i get any money soon, I'll see what I can do. I wish I knew that before the shop built the engine. As far as I know, they got it dialed in pretty well, but worst comes to worst, I'll swap it out. What cam would you suggest? I'm not racing this car at the track, maybe once or twice, but I'll be DD it for the forseeable future.

 

Look at modern cams in general; especially the series that have come out in the last few years.

The Comp XE series and Lunati Voodoo are good places to start. Without details about the car, I can't be real specific about which ones; but there is no doubt that both of those product lines cover what you'd be likely to do, as broad as they are.

Avoid:

• Edelbrock cams
• Summit cams or other generic cams from Melling, SpeedPro, etc.
• Single-pattern cams (ones with the same lobes on both int & exh)
• Any replicas of factory cams, regardless of how romantic the names of engines they came in might sound

You have a relatively large CID (383) for your platform (small block Chevy). This argues in favor of a larger exh lobe. Likewise, your heads have relatively poor-flowing exh ports, as a percentage of their int port flow, which argues in favor of a larger exh lobe. That's why you DON'T want a single-pattern cam: both of the most significant factors in that relationship say a single-pattern cam, such as the 151, is a poor match.

Then, to see just how pitiful that 151 replica is in just a general way, apart from its very poor match to your motor, compare its numbers to the Comp XE268. The XE268 has 268° of "advertised" duration (duh) on the int, and 224° of duration between the .050" lift points, and .480" of lift on the int (more than that on the exh). The sucky stock cam has 306° of "adv" duration but only 222° between the .050" points, meaning it's "leaking" compression for 40° more, without actually flowing anything during all that time. And, its peak lift is only .447" compared to the XE's ..480", but even more so, if you look at the duration between the .200" points (large valve opening), I'd bet the XE has AT LEAST 20° more that the valve is open that far. But since its .050" int duration is about the same as the 151, the peak torque and peak HP RPMs will be similar; i.e. no monster gears required, no additional "big cam" trade-offs, and you don't have to run itup to 6000 RPM just to begin making power.

It's pretty easy to see how bad the 151 is. Now it's not entirely fair to directly compare those ""advertised" durations, because they're not measured exactly the same way; but that's only about like saying that someone that's only been dead for a week isn't as dead as somebody that's been dead for a month. They're still dead. The 151, by its numbers, even when compared strictly apples-to-apples, comes up woefully short.

What's the rest of the car? Intake manifold, exh system, gears, converter, weight, usage? That'll help zero in on the correct cam choice.

 

It's kind of sad to see my expecations for my first engine shot down b/c I didn't know much

Would I have to change anything else besides the cam? Like the lifters? And I guess that I'd have to break the engine in again wouldn't I?



It has an Edelbrock Performer RPM Air Gap intake, gonna get the exhaust system done w/ shorties and a full 3 in pipe all the way back, until I can find a posi rear end around here, it's gonna stay at the stock ratio. It's stock weight, I haven't done any stripping or weight reduction, this is my DD. I'm shooting for 2800 stall on the converter also.

 

¿ And that would be .... ???

There are lots of those. One of my cars has a stock ratio of 3.73. (a couple of them actually) One of them it was 2.41. Most of these cars it's 2.73, 3.08, or 3.23, or the 9-bolt equivalents. It makes a BIG difference.

Good all-around gears with a 700 are 3.23 and 3.42. 3.73 is about as far as you want to go. 2.73 is just ... worthless. 3.08 not much better. What have you got?

 

Silly me, I thought I had mentioned that I had a 91 Rs

I have the 2.73 gears, as I highly doubt the PO changed them out. I'm in the process of looking for a posi out of a 4th gen, but it's slow going.

 

You did... however that doesn't define a gear ratio, as it could be anything from 2.73 (305 TBI) to 3.42 (6-cyl 5-spd or B4C 5-spd).

But that's OK, at least it's out in the open now.

With those gears, if you plan on keeping them, I'd keep the cam small. Probably not the XE268. The XE262 would be a better choice, or the Voodoo that's similar, I think it's the 60101. If you can find a decent gear such as a 3.42 which is actually pretty common, you could step up to the XE268. Or even, I had a XE274 not too long ago in a 400 with 3.73s, which ran GREAT; in the words of somebody who heard it, it sounded "angry", "like it wanted to jump up out of there and kill something". Mostly Mustangs. (which it ate several of before it failed and got replaced with a hyd roller)

Don't get too discouraged. Back in the Stone Age, back before AlGore invented the Internet, we all made lots of mistakes and bad decisions and whatnot, and just kind of learned from them. It's a process. Much easier nowadays if you can manage to cut through the drivel and the repetition of the same old tired hot-rodder myths that just won't die.

As far as your lifters, when you take them out, keep them CAREFULLY numbered or whatever so they correspond to the cam. If all you've done is just broke them in on your existing cam, odds are you can re-use them, if you have a certain tolerance for risk. If they were all spinning (you can tell if they have a circle drawn on them as opposed to a bar) the odds are good. If you don't feel like taking the chance, then ebay the cam and lifters as a set, you might be surprised how many "greater fools" there are out there. For all I know, you might be able to get more for them as a known good broken-in set than new out-of-the-box; I don't know that of course, but I wouldn't rule it out.