Vette Magazine L76 vs. L84 Fuelie Dyno Test / 30 30 Cam

[Loren S.]

Got the November 09 Vette Magazine in the mail today, with a very interesting dyno test. They used a 327 with 461 / 2.02 heads, and a 30 30 cam. They compared dyno results switching a Holley 750 Street HP carb (in lieu of a vintage 3310) with a 7380 FI unit supplied by Chuck Smith. The results were 355 hp at 5,700 rpm / 366 lb-ft at 4100 rpm for the carb, and 364 hp / 363 lb-ft for the FI. Peak torque occurred at a higher RPM for the FI. The most startling result was from the cam switch:

"Before pulling the 327 off the dyno, we couldn't help but try to improve the output of the L76 carbureted combination with a simple cam swap. Mostly, we wanted to demonstrate just how far cam technology has come in the last 40-odd years. Would it be possible to improve power while maintaining - or even improving - idle quality and driveability? To find out, we installed an XS274S cam from the Comp Cams catalog. This solid flat-tappet unit offered a 0.501/0.510 lift split and a 236/242 duration split (measured at 0.050). This represented a slight increase in lift but sizable drops in intake and exhaust duration (18 and 12 degrees, respectively) as compared with the original Duntov grind. Nevertheless, the more-aggressive ramp rates of the Comp unit increased the power output of our carbureted combination from 355 hp and 366 lb-ft to 370 hp and 380 lb-ft. The "milder" cam also improved power throughout the rpm range, offering improvements of as much as 20 hp and 20 lb-ft of torque over the factory Duntov stick."

[Joe C.]

Re: Vette Magazine L76 vs. L84 Fuelie Dyno Test / 30 30 Cam

Got the November 09 Vette Magazine in the mail today, with a very interesting dyno test. They used a 327 with 461 / 2.02 heads, and a 30 30 cam. They compared dyno results switching a Holley 750 Street HP carb (in lieu of a vintage 3310) with a 7380 FI unit supplied by Chuck Smith. The results were 355 hp at 5,700 rpm / 366 lb-ft at 4100 rpm for the carb, and 364 hp / 363 lb-ft for the FI. Peak torque occurred at a higher RPM for the FI. The most startling result was from the cam switch:

"Before pulling the 327 off the dyno, we couldn't help but try to improve the output of the L76 carbureted combination with a simple cam swap. Mostly, we wanted to demonstrate just how far cam technology has come in the last 40-odd years. Would it be possible to improve power while maintaining - or even improving - idle quality and driveability? To find out, we installed an XS274S cam from the Comp Cams catalog. This solid flat-tappet unit offered a 0.501/0.510 lift split and a 236/242 duration split (measured at 0.050). This represented a slight increase in lift but sizable drops in intake and exhaust duration (18 and 12 degrees, respectively) as compared with the original Duntov grind. Nevertheless, the more-aggressive ramp rates of the Comp unit increased the power output of our carbureted combination from 355 hp and 366 lb-ft to 370 hp and 380 lb-ft. The "milder" cam also improved power throughout the rpm range, offering improvements of as much as 20 hp and 20 lb-ft of torque over the factory Duntov stick."

Loren,

That is very true.
Vintage cams have exceedingly mild ramp rates. For example, the 30-30 has durations of 254/254 @ .05" lobe lift, BUT ITS SEAT TO SEAT DURATIONS ARE OF THE ORDER OF 300 +(measured @ .006" lift)!!!!! This gentle ramp rate bleeds off cylinder pressure and KILLS torque in order to produce power. The same is true of the LT1, and although it is milder at 247/254 the same gentle ramps are present. The hallmark of a cam with gentle ramps is the wide lash required. The Duntov cam, although it has less duration and lift, has more aggressive ramps as well (lash is tighter @ .012/.018), so it bleeds off less cylinder pressure.

[Duke W.]

Re: Vette Magazine L76 vs. L84 Fuelie Dyno Test / 30 30 Cam

Loren,

The hallmark of a cam with gentle ramps is the wide lash required.

First let's drop the vague and confusing hot rod term "ramps".

Mechanical lift cams have constant velocity clearance ramps that are typically in the range of .0002 to .0005 inches per crank degree. The basic lash setting is a function of the height of the clearance ramp and has absolutely nothing to do with the dynamics of the opening and closing flanks of the lobe.

If lash is set at clearance ramp height times rocker ratio then clearance is taken up at the top of the clearance ramp where acceleration begins. This is the beginning of the opening flank. The Duntov inlet lobe has a .0002"/deg clearance ramp. which is .008" high. The 30-30 cam has a similar velocity clearance ramp that is .017" high. The LT-1 cam inlet lobe has a .012" high clearance ramp with similar velocity on the opening side, but it's slower on closing side, and the approach to clearance ramp velocity is very gentle, which makes the lobe is highly asymmetrical.

In hard running if the valve stems heat up. clearance will be taken up before the end of the constant velocity clearance ramp and the valve will be opened and seated at no more than clearance ramp velocity, which will minimize valve bounce on seating and minimize valve train shock loading. If the lash is too loose the valve is yanked off and slammed back into the seat at higher than clearance ramp velocity, which will increase valve train loading and cause the valve to bounce when seated.

There is nothing "modern" about aftermarket camshafts. Most have symmetrical lobes. In fact, very little "engineering" went into most of them. The basic physics that governs valve train dynamics hasn't changed since Newton explained it over 400 years ago, and Chrevrolet had a good understanding of valve train dynamics by the mid-sixties. In fact, they began designing asymmetrical lobes in the fifties!

All the aftermarket does is push valvetrain dynamics beyond what GM considered acceptable for OEM reliability/durability because they require much higher valve spring forces to yield the same valve train limiting speed as OE.

Why do you think there are so many "wiped lobe" threads about Comp Cams on the Internet?

Duke

[Stuart F.]

Re: Vette Magazine L76 vs. L84 Fuelie Dyno Test / 30 30 Cam

I gave up on Vette Magazine recently due to their 90% + C-5/C-6 content so it is interesting that they are doing tests on old iron again. But I am confused; was the test on the L-76 done with a 30-30 cam or a 097 Duntov? In your quote of the article, it says "Duntov", but you say it was a 30-30 cam. Was it a 63 L-76 or 64/65? Did they say the engine had 461 heads or 461-x?

Stu Fox

[Jerry G.]

Re: Vette Magazine L76 vs. L84 Fuelie Dyno Test / 30 30 Cam

I have a 65 FI car and freshened the motor a few years back. While it was apart I pocket ported the heads. everything else in the motor was OEM spec components including the 30-30 cam. I do quite a bit of dyno work because of the racing work so I wanted to see what my fuelie would do. After fooling around with normal timing adjustments and using race gasoline , the motor produced 381 HP. Seems like GM had it right. Jerry

[Joe C.]

Re: Vette Magazine L76 vs. L84 Fuelie Dyno Test / 30 30 Cam

First let's drop the vague and confusing hot rod term "ramps".

Mechanical lift cams have constant velocity clearance ramps that are typically in the range of .0002 to .0005 inches per crank degree. The basic lash setting is a function of the height of the clearance ramp and has absolutely nothing to do with the dynamics of the opening and closing flanks of the lobe.

If lash is set at clearance ramp height times rocker ratio then clearance is taken up at the top of the clearance ramp where acceleration begins. This is the beginning of the opening flank. The Duntov inlet lobe has a .0002"/deg clearance ramp. which is .008" high. The 30-30 cam has a similar velocity clearance ramp that is .017" high. The LT-1 cam inlet lobe has a .012" high clearance ramp with similar velocity on the opening side, but it's slower on closing side, and the approach to clearance ramp velocity is very gentle, which makes the lobe is highly asymmetrical.

In hard running if the valve stems heat up. clearance will be taken up before the end of the constant velocity clearance ramp and the valve will be opened and seated at no more than clearance ramp velocity, which will minimize valve bounce on seating and minimize valve train shock loading. If the lash is too loose the valve is yanked off and slammed back into the seat at higher than clearance ramp velocity, which will increase valve train loading and cause the valve to bounce when seated.

There is nothing "modern" about aftermarket camshafts. Most have symmetrical lobes. In fact, very little "engineering" went into most of them. The basic physics that governs valve train dynamics hasn't changed since Newton explained it over 400 years ago, and Chrevrolet had a good understanding of valve train dynamics by the mid-sixties. In fact, they began designing asymmetrical lobes in the fifties!

All the aftermarket does is push valvetrain dynamics beyond what GM considered acceptable for OEM reliability/durability because they require much higher valve spring forces to yield the same valve train limiting speed as OE.

Why do you think there are so many "wiped lobe" threads about Comp Cams on the Internet?

Duke

Here is a quote from a technical paper which you co-wrote:

"The traditional method of adjusting valves one or more cylinders at a time with each cylinder at TDC is fine for hydraulics and for most solid-lifter cams, but NOT for the factory "30-30" solid-lifter cam used in '64-'65 L-76 365 HP and L-84 375 HP (FI) Corvette engines (and in '67-'69 Camaro 302/290 Z/28 engines); this cam has VERY long clearance ramps that are .017" high, and at TDC for any cylinder, both the intake and exhaust valve for that cylinder are still on their ramps, NOT on the cam's base circle, which is why the Service Manual for all cars so equipped says specifically to set them "hot and running".

What you say about lash having nothing to do with the cam's flanks is technically correct; however, short of having lift/angle data, which would be a great help in evaluating camshafts, one fairly reliable way to judge the aggressiveness of a cam's flank is to look at the required lash. As you say, lash is strictly a function of the clearance ramp height; however, cams with large clearance ramps are almost always ones with lower opening and closing velocities. Those with smaller (shorter) clearance ramps (i.e.: tighter lash requirements) almost always have higher values (velocity).

Some relative lash numbers for Chevrolet solid lifter cams:

Duntov (3736097): .010/.016 (283); .008/.016 (327)
30-30 (3849346): .025/.025 (design); .030/.030 (production)
LT1 (3972178): .024/.030

Chevrolet was well known for applying some serious "band aids" in order to economize rather than redesign. Notice, above, that the lash settings for the Duntov cam were specified tighter for the 327 than for the 283. Reason for that was because the 327 would tolerate more effective duration. So, effective duration was added by tightening the lash spec. The 30-30 was designed with .025/.025 lash appearing on the engineering drawing, but speculation has it that the Rochester fuel injection unit would have had poor idle stability with the design lash specs, so Chevrolet engineers, in their infinite wisdom (well, actually can't blame them fully, because they were continually hamstrung by the bean counters) shortened the effective durations by loosening the lash setting.

I suspect that the vast majority of the folks who install those aftermarket camshafts in their engines have no clue as to the importance of the camshaft in determining engine operating characteristics, let alone having an interest in protecting their investment as we do. As far as aftermarket camshafts are concerned, there are ways to deal with any supposed durability issues. Some of you go to great pains in taking care of your lacquer paint, so why not take good care of your camshaft by using the proper oil with sufficient phosphorous levels? Another is to make the cam more robust by having it gas nitride treated. Finally, the use of "beehive" springs greatly lowers the installed height and compressed height forces required to control the valves when using camshafts with higher ramp velocities. The main reason for this, is that loss of valve control is, among other things, a function of spring resonant frequency, which is a function of its weight. "Beehive" springs, being lighter, having less inertial mass, will resonate at higher frequencies than conventional springs. They also do not require dampers and/or inner springs in order to achieve the same amount of valve control, thus saving more weight and greatly reducing heat generated by the valvetrain.

[Duke W.]

Re: Vette Magazine L76 vs. L84 Fuelie Dyno Test / 30 30 Cam

I have a 65 FI car and freshened the motor a few years back. While it was apart I pocket ported the heads. everything else in the motor was OEM spec components including the 30-30 cam. I do quite a bit of dyno work because of the racing work so I wanted to see what my fuelie would do. After fooling around with normal timing adjustments and using race gasoline , the motor produced 381 HP. Seems like GM had it right. Jerry

The data I have supports the conclusion that OE engines, especially SHP/FI will make near the advertised gross power numbers if the heads are "massaged" and compression is increased to the actual advertised value, but as machined by Flint the engines come up 10-15 percent short of the OE gross power ratings. Base engines like the 327/300 come up about 20 percent short!

On the basis of simulations, the '64-'65 spec L-84 doesn't make much more top end power than the L-76, but once head flow is improved, the higher flow efficiency of the FI manifold and single plane architecture allow it to make significantly more top end power, but it loses on low end torque.

I assume your engine was tested on a lab dyno with open exhaust - basically an "SAE gross" test. Did it have the OE exhaust manifolds or headers?

The test data presented by Loren leaves out some critical information. Were the heads "massaged"? Flow numbers? Actual compression ratio? The carburetor was "bigger" than OE, but what really counts is what inlet manifold was used? Headers or manifolds? Were the tests started at low enough speeds to determine the beginning of the 80 percent torque bandwidth?

Maybe he can fill us in.

Duke

[Joe C.]

Re: Vette Magazine L76 vs. L84 Fuelie Dyno Test / 30 30 Cam

I gave up on Vette Magazine recently due to their 90% + C-5/C-6 content so it is interesting that they are doing tests on old iron again. But I am confused; was the test on the L-76 done with a 30-30 cam or a 097 Duntov? In your quote of the article, it says "Duntov", but you say it was a 30-30 cam. Was it a 63 L-76 or 64/65? Did they say the engine had 461 heads or 461-x?

Stu Fox

A few details:

*** The heads installed on the engine as shown on the dyno look like 3927186, not 3782461.

*** For some strange reason, they decided to use Probe Sportsman pistons rather than the FM parts. This change necessitated the use of a 6" rather than a 5.7" con rod.

*** The cam specs as stated appear to be those of the 3849346 ("30-30"). Some people refer to the 346 cam as the "30-30 Duntov" .

*** They used a 750 cfm carburetor on the L76 rather than the 585 cfm 2818. The big 750 certainly increased peak power by a slight amount. I say "slight" because the potential of the carburetor was severely limited by the shortcomings of the 461 intake. By the way, a 750 Holley will not fit on a stock 461 intake because the throttle bores are not large enough. You can see from the photo that the test 461's plenum was modified by removing the divider between the upper and lower plenum halves (which the authors replaced with a piece of sheetmetal). What you may not notice, is that the individual bores on the 1-7-4-6 (lower) plenum side were eliminated, and these were combined into a single oval shape like in a more modern intake. While they had the die grinder out, they certainly enlarged the plenum to accommodate the big 750.

*** They used a large journal crankshaft for the build. The article states that the journal size will not influence power production. That is not true because the small journal crank will have slightly less parasitic loss than the big journal piece because of its lower journal velocity.

Joe

[Joe C.]

Re: Vette Magazine L76 vs. L84 Fuelie Dyno Test / 30 30 Cam

The data I have supports the conclusion that OE engines, especially SHP/FI will make near the advertised gross power numbers if the heads are "massaged" and compression is increased to the actual advertised value, but as machined by Flint the engines come up 10-15 percent short of the OE gross power ratings. Base engines like the 327/300 come up about 20 percent short!

On the basis of simulations, the '64-'65 spec L-84 doesn't make much more top end power than the L-76, but once head flow is improved, the higher flow efficiency of the FI manifold and single plane architecture allow it to make significantly more top end power, but it loses on low end torque.

I assume your engine was tested on a lab dyno with open exhaust - basically an "SAE gross" test. Did it have the OE exhaust manifolds or headers?

The test data presented by Loren leaves out some critical information. Were the heads "massaged"? Flow numbers? Actual compression ratio? The carburetor was "bigger" than OE, but what really counts is what inlet manifold was used? Headers or manifolds? Were the tests started at low enough speeds to determine the beginning of the 80 percent torque bandwidth?

Maybe he can fill us in.

Duke

Duke,

"GOOGLE is your friend", so find the article Loren referred to online, and READ it.
The answers to all of your questions, and more, will be found in the article.
Read my "bullet points" on the article, above. Those are just a few discrepancies that can be found within a short time. If you want to continue digging, there are probably more. I've looked at the article long enough. Right now I'm going out to the garage to install the heads on my engine.

Cheers,
Joe

[Duke W.]

Re: Vette Magazine L76 vs. L84 Fuelie Dyno Test / 30 30 Cam

The results were 355 hp at 5,700 rpm / 366 lb-ft at 4100 rpm for the carb, and 364 hp / 363 lb-ft for the FI. Peak torque occurred at a higher RPM for the FI.

Here's another example of "magazine dyno tests" showing better results than the test data I have for guys like us who blueprint and massage our OE engines.

A case in point is a "327 LT-1" configuration that started out as a '65 L-79. It received typical head massaging including valve and seat work to a very good set of flow numbers and a LT-1 cam. All other parts were OE equivalent other than Crower Sportsman rods. The true CR averaged 10.35:1 across the range with a spread of a little less than 0.1.

The best runs on a lab dyno with standard (sea level) temperature and pressure air density correction (STP), which is essentially SAE gross follow.

With OE 2.5" exhaust manifolds:
338 lb-ft @ 4400
356HP @ 6400

With headers:
358 lb-ft @ 4500
369 HP @ 6500

Headers increased peak torque about 5.9 percent and peak power by 3.6 percent. In the chassis, even with the modest backpressure of the OE 2.5" exhaust system, the header advantage likely narrows.

A similar "327 LT-1" (with OE exhaust manifolds) that started life as a '65 L-76 was tested on a chassis dyno and with suitable empirical conversion factors the results generally jibed.

The data from this article shows similar peak power numbers, but at nearly 1000 revs lower and higher peak torque at lower revs. Why? Torque is basically a function of displacement and CR., but where it occurs is highly influenced by valve timing. The 327/250 has the same advertised peak torque rating - 350 lb-ft as the 327/375FI, but the FI engine's peak torque is nearly 2000 revs higher. Both are somewhat "optimistic", but not as much as the power ratings. The peak torque data presented in this article is closer to what I would expect for a 350, most of which had advertised peak torque at or near 380 lb-ft.

Also, recall Taylor's "similar engines" - all other things equal, two identical engines other than stroke will make about the same peak power at about the same mean piston speed. The data in this article and a previous article discussed a week or two ago just don't jibe with anything I or my collaborators have seen with massaged OE appearance 327s.

I would expect a "stock" (Flint-built or equivalent rebuilt) SHP/FI 327 with a 30-30 or LT-1 cam to achieve peak power in the 5500-6000 range, but less than presented in this article - something on the order of 310-330 gross HP. Massaging the heads not only increases peak power, but pushes the power peak higher up the rev scale and extends the useable rev range to the initiation of light valve float at about 7200.

I have STP corrected lab dyno test data for a .040"-over "stock rebuilt" '63 L-76 (340 HP/Duntov cam) - no head work other than a standard valve reseat and no attention to optimizing CR .

It made very near the advertised peak torque figure (344 lb-ft @ 4000) - 343 lb-ft @ 3800, but peak power was only 295 HP @ 5500.

Regarding camshafts there is a "Duntov cam", which was the OE mechanical lifter cam from '57-'63. Various stories have it that Duntov designed this cam (including calling in the basic specs from the Arizona proving ground), but he probaby didn't do the actual computations - just gave the engineer who did the detail design the basic accleration profile and timing points.

There is no such thing as a "Duntov 30-30 cam" - just the "30-30 cam". This design was based on data Chevrolet gathered about valve train behavior with the Optron machine. There is no evidence that Duntov had a direct hand in designing this cam, but he probably had oversight. His original cam design from 1956 was purely intuitive. The 30-30 was based on engineering research, and this shows in the lobe dynamics. The Duntov overall is mild, but harsh just above the tops of the clearance ramps, where peak jerk occurs. Beginning with the 30-30 lobe all subsequent hydraulic and mechanical lifter lobes had much lower peak jerk, and it was further above the tops of the clearance ramps.

It's all in the details!


Duke

[Jerry G.]

Re: Vette Magazine L76 vs. L84 Fuelie Dyno Test / 30 30 Cam

The data I have supports the conclusion that OE engines, especially SHP/FI will make near the advertised gross power numbers if the heads are "massaged" and compression is increased to the actual advertised value, but as machined by Flint the engines come up 10-15 percent short of the OE gross power ratings. Base engines like the 327/300 come up about 20 percent short!

On the basis of simulations, the '64-'65 spec L-84 doesn't make much more top end power than the L-76, but once head flow is improved, the higher flow efficiency of the FI manifold and single plane architecture allow it to make significantly more top end power, but it loses on low end torque.

I assume your engine was tested on a lab dyno with open exhaust - basically an "SAE gross" test. Did it have the OE exhaust manifolds or headers?

The test data presented by Loren leaves out some critical information. Were the heads "massaged"? Flow numbers? Actual compression ratio? The carburetor was "bigger" than OE, but what really counts is what inlet manifold was used? Headers or manifolds? Were the tests started at low enough speeds to determine the beginning of the 80 percent torque bandwidth?

Maybe he can fill us in.

Duke

Duke the heads were "pocket Ported to unshroud the valves. A good multi angle valve job was done and the heads were cc'd and compression was brought up to spec. The exhaust was 1 1/2 inch tube headers.

By the way I just put back together my black death racing motor and I used real 461 heads that were heavily worked on. I was amazed to see 248 CFM on the intakes. and the mid range torque is up about 10% from the larger aftermarket heads I was using before.

[Duke W.]

Re: Vette Magazine L76 vs. L84 Fuelie Dyno Test / 30 30 Cam

Thanks for the details on the heads in the magazine test. So the power numbers make sense and are in the same ballpark as the "327 LT-1", but the peak torque numbers still seem high and both torque and power peaks are way lower in the rev scale than they should be for those configurations based on all the test data I have. I'm still suspicious.

Of course the LT-1 cam will also show much better low end torque than the 30-30, but I doubt if they presented any data below 3000-3500 were road engines spend most of their time. Typical! Magazines are all about "gee whiz" numbers.

Contrary to popular belief, 461X heads are really quite good. As OE machined the flow numbers are nothing impressive, but pocket porting with careful attention to valve seating can get the 0.5" lift, 28" H2O depression flow up into the 230 CFM range, and with full "race porting" the kind of numbers you are seeing.

It's also my understanding that the cast iron alloy has higher nickel content, which makes the material tougher and more resistant to cracking. If you've ever hand ported a set of these heads, you'll understand.

Well into the seventies after Chevrolet began offering "bow tie" heads, there were still a lot of sprint car engine builders who preferred to start with a set of "seasoned" 461X heads.

Rebuildable core sets can usually be picked up for $100-150 because nobody wants them, nowadays.

Duke

[Duke W.]

Re: Vette Magazine L76 vs. L84 Fuelie Dyno Test / 30 30 Cam

Okay, I found the online article and because I'm such a good guy, here is the link.

http://www.vetteweb.com/tech/vemp_0911_l84_fuelie_motor_on_engine_dyno/l76_carbureted_combination.html

There was no head work other than new aftermarket valves. The quoted flow numbers (205/140) are about what a set of Flint-machined 327 or early 350 heads will do.

Knowing this really strains the credulity of the performance data presented compared to what I have in my test dyno test library. But, what do I know? Maybe they were using a surplus sixties vintage GM dyno!

Now the low peak torque and power revs make sense, but the torque and particularly power are way too high for the level of head flow, despite the 1.75" primary tube headers.

The modest head flow means the inlet port "chokes" long before you "run out of cam" at these duration levels, which is why it takes head massaging to get the kind of power quoted, and it will occur 500-1000 revs higher.

BTW, I know the author. "Rick" and I competed in the 1989 Silver State Classic Challenge and bumped into each other occasionally for the next few years. He ran his supercharged 5.0 Mustang Sedan, and I drove a buddy's Saleen. (Yeah, his average speed was higher, but he was the only eighties vintage Mustang that beat me, which included a wet road for the first third of the 90 mile distance. After holding it at 130 MPH I got up to the 150-160 range when the road began to dry out.)

He's a good guy (and good driver), but he's about 20 years younger than me and "cut his teeth" on eighties Mustangs, and I doubt if he has any other experience with vintage Corvette 327s, so he was willing to believe the data.

Duke