30-30 Cam in a 400?

**Mike McKown** · February 13, 2006, 02:58 PM

I think that cam is a mistake in this engine.

You gonna' turn it off at 5500? That's where that cam starts to really work.

If you don't have to have the noisy lifters, the L-79 cam will run really well in this engine. I have this combo and it works extremely well.

I'm sure you'll get plenty of advice. Someone will no doubt recommend the LT-1 cam. There again, your rpm limit doesn't let this cam stretch out where it can work well either. If you want a Chevy cam, I'd go L-79. Not too sure that double pumper is a good idea either.

**Elm Zobens** · February 13, 2006, 04:11 PM

Re: I think that cam is a mistake in this engine.

Mike,
I apologize for my ignorace, but isn't the L-79 cam the same as the 30-30?
(254/254 duration @ .050, .485/.485 lift, 114 degree LSA, .030/.030 lash)?

I would like to try a mechanical cam just to get it out of my system-
I like the noisy lifer sound and lumpy idle (I know, no accounting for taste ;-)
Since this is not a daily driver, I don't have to worry about maintenance.

What are the specs of the L-79 cam you mentioned?
Thanks!
Elm

**John Hinckley (29964)** · February 13, 2006, 04:21 PM

Re: I think that cam is a mistake in this engine.

Elm -

The "30-30" cam is the LAST cam you want if you're looking for torque; if you simply HAVE to have solid lifters, use the LT-1 cam. If you want a maintenance-free setup, Mike's suggestion for the L-79 hydraulic cam is a good one. A double-pumper is a lousy setup for a daily-driven car; Jeg's and Summit know ZOT about what makes a good street engine.

**Mike McKown** · February 13, 2006, 05:12 PM

Re: I think that cam is a mistake in this engine.

Elm:

I don't have the specs handy for the L-79 cam. It is the 327-350 horse grind. It's all done by 6000 rpm. It has a nice lumpy idle and the torque curve starts down low but you won't have to worry too much about that with the 400 cubes and the 3.75 stroke. The 30-30 cam was in the 365/375/Z-28 engines. If you want lifter clatter maybe you could try Rhoades hydraulic lifters.

There's nothing at all wrong with the 30-30 cam if you use it for the purpose it was engineered for, high rpm and open exhaust. I'm putting one in a 327 engine I'm building up now but my expectations for the engine are different than what you described for your needs.

**William Voss (14291)** · February 13, 2006, 05:56 PM

Re: 30-30 Cam in a 400?

Elm

In 1st, 2nd & 3rd, the final drive line ratios with the 3.70 rear and m20 transmission, are almost the same as a close ratio m21/22 with a 4.11. The wide gap being between 3rd & 4th with the m20. I have a comp cam replacement for the 30-30 in my 64 327 e/w m20 and 3.36 rear. I'm quite pleased with the performance however I do have a nice 4.11 rear sitting on my work bench, I keep thinking how much fun it would be driving the 4.11 around town. 1st 2nd & 3rd are almost like a 4.56 rear e/w an m21/22.

Below are RPM to MPH figures the the 370 m20 and 4.11 m21/22. The spacing got compressed. The first figure is RPM and the other figures are MPH in each gear for that RPM

M20 with 3.70 & 26.5 inch tire dia
ENGINE MILES PER HOUR

RPM X1001ST GR 2ND GR 3RD GR 4TH GR

2.56 1.75 1.28 1
5 4 6 8 11
8 7 10 13 17
11 9 13 18 23
14 12 17 23 30
17 14 21 28 36
20 17 24 33 43
23 19 28 38 49
26 22 32 43 55
29 24 35 48 62
32 27 39 53 68
35 29 43 58 75
38 32 46 63 81
41 34 50 68 87
44 37 54 73 94
47 39 57 78 100
50 42 61 83 107
53 44 65 88 113
56 47 68 93 119
59 49 72 98 126
62 52 76 103 132
65 54 79 108 139

M21/22 with 4.11 rear & 26.5 inch tire dia
ENGINE MILES PER HOUR

RPM X1001ST GR 2ND GR 3RD GR 4TH GR

2.20 1.55 1.15 1
5 4 6 8 10
8 7 10 13 15
11 10 14 18 21
14 12 17 23 27
17 15 21 28 33
20 17 25 33 38
23 20 28 38 44
26 23 32 43 50
29 25 36 48 56
32 28 40 53 61
35 31 43 58 67
38 33 47 63 73
41 36 51 68 79
44 38 54 73 84
47 41 58 78 90
50 44 62 83 96
53 46 66 88 102
56 49 69 93 107
59 51 73 98 113
62 54 77 103 119
65 57 80 108 125

**Duke Williams (22045)** · February 13, 2006, 06:13 PM

Re: 30-30 Cam in a 400?

The LT-1 cam provides the broadest torque bandwidth of any OE or aftermarket cam that can live with something in the range of OE valvespring force, which will guarantee a bulletproof valvetrain. The 80 pecent bandwidth extends from a mean piston speed of about 900 feet per second to about 3800 feet per second with heads that flow as least as good as a set of pocket ported 461Xs and exhaust backpressure of no more than 3 psi.

You can convert the above mean piston speeds to revs based on engine stroke, and, of course, a longer stroke engine's bandwidth will be shifted down the rev scale relative to a short stroke engine.

The top end of the bandwidth is determined by head flow and exhaust backpressure, so it is critical to include head flow and exhaust system flow in your system engineering.

The bottom end of the 80 percent bandwidth is primarily determined by valve timing, so you need to select a cam that supports a reasonable (not too high) beginning of the 80 percent bandwidth without chocking the top end, and the LT-1 cam is the answer. The 30-30 has too much overlap and even a modest amount of exhaust backpressure hurts the torque curve across the entire rev range, but it's and excellent cam to build a very reliable 7000 RPM racing engine with properly designed headers and open exhaust that won't eat the valvetrain.

For a long stroke engine the L-46 cam is a good choice if you want to run hydraulic lifters. It's a little weaker down low than the LT-1 cam, but is nearly as strong at the top end, and, unlike a short stroke engine which needs a mechanical lifter cam to reach the top of the 80 percent bandwidth at 6500-7000, a long stroke engine only needs to achieve 5500 to 6000, which is within the valvetrain limiting speed of the OE SHP hydraulic cams.

Duke

**Elm Zobens** · February 13, 2006, 06:22 PM

Re: 30-30 Cam in a 400?

Thank you for the info.
I'm pretty happy with the 3.70 and don't have any plans to go any higher (numerically) with the 400.

The specs for the L-79 cam don't seem to be a whole lot milder than the 30-30?
The duration is down a little but the overlap seems to be as bad if not worse than the 30-30?
To me, it seems that overlap is the biggest contributor to lack of low end grunt.
Can anyone enlighten me?
Thanks!
Elm.

**Elm Zobens** · February 13, 2006, 09:56 PM

Re: 30-30 Cam in a 400?

Duke,
Thank you for the info.
I am still somewhat confused as to why the LT-1 vs 30-30 would be so different?
Just looking at the specs on paper, they seem to be VERY similar.
It also would seem that the overlap is would be close as well- The 30-30 has 86 but I have to believe the LT-1 has at least 80?
Why the larger difference in low end performance?

I am also looking at 2 other Elgin grinds (E-1131-P and E-1133-P). Both of these mechanical cams have even 'tamer' specs than the LT-1, except for higher lift- Which I would think the 400 could use.
The 1131 specs are .521/.521 lift, 240/250 dur@.050, 75 overlap and 104/108 LC,
.024/.024 lash.
The 1133 specs are .498/.498 lift, 246/246 dur@.050, 65 overlap and 106/110 LC, .030/.030 lash.
Any suggestions?
Would either of these be better suited to my application?
Thanks!
Elm.

**Duke Williams (22045)** · February 14, 2006, 01:40 AM

Re: 30-30 Cam in a 400?

It's IMPOSSIBLE to compare mechanical lifter cams from typical published specs because the durations at .050" INCLUDE the clearance ramps and the valve doesn't even begin to lift until the clearance is taken up, so you CAN'T compare them to each other unless the clearance ramp designs are IDENTICAL (which is rarely the case), and you CAN'T compare ANY mechanical lifter cam to a hydraulic lifter came where virtually all the lifter rise is converted to valve lift. Apples and oranges!

For example, the L-72 lobe is "speced" at 242 deg. duration at .050" lifter rise and the 30-30 at 254, BUT if you compute the lifter rise from the tops of the clearance ramps (this requires that you have the detailed lobe design data, which I have for the OE cams) the durations are 231 and 239, respectively. Since the LT-1 cam is a L-72 lobe on the inlet side and a 30-30 lobe on the exhaust side (phased four degrees earlier than on the 30-30) you've got three cam designs from just two lobes that have proven reliable dynamics.

THESE durations, 231 and 239, are what you can compare to hydraulic lifter cams. The actual effective overlap of the LT-1 cam with 2.02/1.60" valves and actual measured OE rocker ratio behavior is about 4.2 square-inch-degrees and the 30-30 is a whopping 5.5 sq-in-deg. The L-72 is 6.1, but since it's a longer stroke engine, it can handle more, but it's at the practical limit for a good street BB with high flowing heads, and the effective overlap is greater for a given overlap under the lobe lift curves, compared to a SB, because the L-72 had larger valves and a higher rocker arem ratio. Nevertheless, since the OE Corvette exhaust system will generate about DOUBLE the exhaust backpressure (about 6 psi versus about 3 on a SHP SB), the L-72 cam would work better with less overlap.

Compare the above to the effective overlap of the new 505 HP, 4" stroke LS7 cam, which is a mere 2.1 sq-in-deg - half the LT-1 and barely a third of the L-72.

Do you think there is a message here?

Notwithstanding the above discussion, the lobe separation angle is a rough indication of effective overlap, and, for a street engine, as duration increases, LSA should actually INCREASE if you want to avoid excess overlap. Once you reach the maximum effective overlap you can only close the inlet valve later and/or open the exhaust earlier, and these two effects will increase LSA, which keeps effective overlap essentially constant. Closing the inlet valve later can increase top end power at the expense of low end torque, but once you achieve an inlet Mach index over 0.5 the cost in low end torque for a little more top end power is HUGE! The LT-1 LSA is 116 degrees and the 30-30 is 114. The two cams you profiled are 105 and 108. Talk about too much overlap! Those timing numbers are like my Cosworth Vega. Chevrolet indexed the cams (218 degrees .050" duration above the tops of the clearance ramps) at 106 and 110. It had to idle at 1600 and the 80 percent torque bandwidth didn't start until 3000. The exhaust system generated about 12 psi backpressure, which combined with the overlap meant there was more exhaust gas left in the cylinders than fresh charge when the plug fired. Can you spell D-O-G! Chevrolet established this goofy timing to create a high exhaust gas residual to control NOx, but it really screwed up the engine.

After a lot of simulations I retarded the inlet cam 8 degrees and advanced the exhaust cam 8 degrees to end up with a LSA of 114. Sound familar? The L-79 cam has the same points of max. lift/LSA on 221 degrees at .050", and since it has about the same stroke as a 327 it makes makes about the same low end torque bandwidth as a L-79, but revs much higher because of the free flowing head. Now it idles butter smooth at 900 (any lower and the voltage falls off) pulls from 1000 revs in fifth, and the 80 percent torque bandwidth is 1900-7200. I've never experienced such a flexible engine. I can drag it down with the brake to 200 revs in first, floor the throttle, and it just takes off. Try doing that with even a modern digital EFI car. Part of this flexibililty is due to the CV's the analog EFI system. Digital systems get "confused" below about 500 RPM.

It would probably take me at least a one-semester 3-credit hour course to teach what I have learned in the past 35 years on "Valvetrain Dynamics and the Effects of Valve Timing on Engine Performance", assuming you had all the basic engineering prerequisites including thermodynamics, fluid mechanics, and dynamics.

Being as how it's impractical to do this on this Board, I will provide you with the following "bottom line" insights. If you buy the Enginer Analyzer simulation program, figure out how to use it and interpret the outputs, you will come to the same conclusions as applied to a STREET engine.

1. There is a limit to the amount of valve overlap an engine can effectively use, with or without headers, in the presence of ANY exhaust backpressure, and the more exhaust backpressure the more DETRIMENTAL excess overlap is to torque bandwidth.

2. Aftermarket cams of similar duration to the OE SHP cams typically have TOO MUCH overlap for a street engine, even with a relatively low restriction exhaust system.

3. Corvette OE SHP cams (except the 30-30) have about as much overlap as the engine can effectively use (in the presence of the OE exhaust system, which is quite good), which is why they produce better torque bandwidth than typical aftermarket cams.

4. Racing engines where you can design a zero backpressure exhaust system that exploits exhaust wave dynamics are a completely DIFFERENT animal and will require signficantly different valvetiming (including more overlap) to maximize average power in the upper third of the rev range, compared to maximizing torque bandwidth on a street engine.

5. You pick the cam to achieve 80 percent peak torque at no less than 2000 revs and work the inlet and exhaust system to get as much top end power as you budget affords. If your cam meets the low end torque bandwidth spec an you achieve an inlet Mach index of over 0.5 at peak revs, you have extracted as much broad bandwidth output from the particular architecture as is possible in this universe. (DISCLAIMER: Results in a parallel universe with physics different than ours may vary.)

6. Head flow is CRITICAL!!! And, especially on a carbureted engine you want a relatively small port with HIGH flow efficiency, which is the actual flow rate compared to an "isentropic" ("perfect" to a layman) duct of the same average cross section area. OE heads can be massaged to achieve close to 50 percent on the inlet and 60 percent on the exhaust, which is pretty good for a pushrod design where the inlet port has to snake around the pushrod passages. A run of the mill modern production DOHC 4V engine inlet port is rarely better than 50 percent, but the best DOHC 4V racing engines are probably over 70 percent. As another point of reference, the new LS7's CNC ports are about 60 percent efficient on BOTH sides, which is remarkable for a pushrod design. (Did GM Powertrain sweat the details? You bet!) Relatively conservative valve timing and VERY HIGH head flow efficiency is the key to the LS7's broad torque bandwidth and very high specific output, which is comparable to many DOHC designs, which would be MUCH heavier and bigger to achieve 7 liters - basically wouldn't even fit in the C6's body envelop. With good engineering and a generous manufacturing budget you CAN have your cake and eat it too!

Finding the right valve timing for the application is a matter of system engineering, however, in your case, my recommendation is that you choose between the L-46 and LT-1 cams. (And spend some budget massageing the heads, whatever you use.) All the zillion aftermarket cam choices are just noise!

Duke

**Elm Zobens** · February 14, 2006, 10:28 PM

Re: 30-30 Cam in a 400?

Wow-
That's a helluva write-up Duke!
Thank you so much for your patience with my somewhat lame questions.
I really am trying to understand how all this fits together.
Obviously, you have much more experience and background on this topic than I will ever have. If you could humor me just a little longer I would GREATLY appreciate it!
The specs that I have quoted are directly from the Elgin Industries master catalog, so I apologize if these are somewhat dated or inaccurate.
I followed most of your information above except for the whole 'Square-inch-degree' thing, which still has me baffled.

From my limited knowledge of camshafts and what works better than others, overlap has always been the determining factor I've been able to use to 'eye-ball' what will be acceptable. Since my background is basically big block Oldsmobiles, that is what I try to relate everything to (good, bad or otherwise).
In my 442s, anything over about 57 degree overlap in the auto or 68 degree in the 4-speed is just too much. And these are 455s. The factory W-30 4-speed cam is just INSANE with 328/328 adv duration and 108 overlap! Unless you have a 4.88 gear and open headers, don't even bother. Even the W-31 (350 CI) cam at 308/308 adv duration and 82 overlap was too much for a street car.
Currently, I have the best performance with the 285/287 adv duration, 57 overlap in the auto and 294/296 adv duration and 68 overlap with the stick.

I guess my confusion comes from what the published overlaps are compared to what you are calculating. In my mind, overlap is more than just the LSA and duration, it's also the (for the lack of a better term) the pitch or steepness (is that a word?) of the lobe itself. Couldn't you have 2 lobes with the exact same duration and LSA but different overlap based on how 'fat' the lobe itself was?
Again, with my primitive logic, the LT-1 cam with 316/336 adv duration compared to the 30-30 with 314/314 would make the lobes on the LT-1 seem 'fatter' and therfore more overlap- Moving the LSA to 116 from 114 would tend to even that out. So again, with my limited logic here, both cams still seem awfully similar to me- And probably too much for my 400 with both having 80+ overlap.
The other 2 cams I mentioned had much less quoted overlap and that was my main reason for entertaining them. Quite honestly, I didn't even pay much attention to the LSA since it seems that any SBC cam falls anywhere from 104-116 LSA.

Please don't be offended of take it that I am questioning your knowledge or ability- I just want to understand.
Thank you for your time.
Elm

**Duke Williams (22045)** · February 14, 2006, 11:00 PM

Re: 30-30 Cam in a 400?

Forget "overlap degrees"! You have to rid your mind of this fluff.

LSA is a more meaningful measurement of overlap than degrees overlap, but if the two cams have signficantly different duration the picture gets foggy, and "duration" is often undefined or ill-defined. The old GM specs are meaningless. They were measured at an undefined height above the base circles, and the "346 degrees" duration of the 30-30 lobe (and 317 for the L-72 lobe that was used on the inlet side of the LT-1 cam) along with the "108 degrees" overlap for the 30-30 cam can't be compared to any other manufacturers measurement. These numbers include a lot of the clearance ramp. If you want the equivalent of the W-30 cam go with the 30-30, but I don't think that's what you want, and I certainly don't recommend it.

Effective overlap in square inch degrees is the total "curtain" area for both valves (curtain area is valve diameter times lift, which is the actual total flow area) during overlap event times overlap duration. Curtain area is square inches (pi x D x lift). Multiply by degrees and you get square-inch-degrees.

Stay away from those Elgin cams if you want a good performing engine with broad torque bandwidth and choose either the L-46 or LT-1 cam.

Duke

**Clem Zahrobsky (45134)** · February 15, 2006, 10:59 AM

Re: 30-30 Cam in a 400?

the aftermarket cam copies of the GM cams have their "true" specs listed at the manufactures so they can give you a truer picture of what is what,check with them. make sure to use 5.7 GM PM rods,or after market in your 400 because the stock 400 rods are not that good.

30-30 Cam in a 400?

30-30 Cam in a 400?

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