L-46 Dyno Runs Part 2

[Duke W.]

Re: L-46 Dyno Runs Part 2

Duke,

Why does your EA 3.0 calculations for the EX262 show Peak torque 374 lb-ft @ 4000, and Peak power 339 @ 5000? The actual peaks were attained at 3400/5600 rpm.

Thanks,
Mike

I quoted the peaks that EA showed in the data table from 2000 to 6500 in 500 RPM increments. Being as how the torque and power curves near their respective peaks are fairly flat, there is little difference in the predictions plus or minus 500 revs from the peaks, and you can also see that this is the case in your test results data table.

EA predicted torque at 3500 was 368 lb-ft and predicted power at 5500 was 338.

Simulation programs will not produce exact results to three significant digits, but if they are accurate within a few percent they can be a very useful tool. The best way to use them is by establishing a baseline. I've used test data I've gathered over the years on known OE configured engines to tweak the input parameters to give the best correlation. Then from this baseline changes can be made - like head flow or valve timing to see their effect on the performance curves. The absolute numbers may be off a little, but the errors apply to both cases equally, so the DIFFERENCES, expressed in percent are usually quite accurate.

Duke

[Duke W.]

Re: L-46 Dyno Runs Part 2

I do know that GM spent millions on research to get it right and Duntov's favorite small block was the L46. What is being said is that regardless of the cam selection the head work is more important to increasing power than any differences in the two cams.

While I am a TOTAL novice head flow seems to be the key to making more power. Unfortunately, it also seems like getting the head work done on cast iron heads can cost a pretty penny. If I were to have the work done, my heads would be sent to DUKE if he does such things.

Mike, that is excellent advice to have my motor tested before doing anything. It runs great. I just wish it had a little more power that could be felt in the seat of the pants.


Bill

You got it! I've been harping about head flow on the TDB since day one. It is the most effective way to get "more power" without losing low end torque or screwing up idle behavior with an aftermarket cam. Valve timing is really just a tuning parameter - like the spark advance map - to achieve desired performance characteristics, and I have one strict criterion for a road engine - 80 percent peak torque at 2000 for SHP engines and 90 percent at 2000 for base engines or any engine coupled to an automatic transmission. Any less and the engine will feel soggy and unresponsive in normal driving. Most guys would find that "racing engines" perform very poorly and are gas guzzlers in normal around town driving.

Head massaging is a labor intensive task, so it's expensive if done professionally, and some shops won't even do this work on cast iron heads. The basic procedures have been out there for several decades in books like "How to Hotrod Small (or Big) Block Chevys" and the various books by David Vizard. The work itself is not complicated. I just takes a lot of time. I don't do work for others, but I've done this work on both my '63 L-76 engine and my Cosworth Vega. I can tell you that aluminum cuts much faster than cast iron, but I've also said that every enthusiast should have the experience of massaging a set of cast iron heads. Once you've done one set, you will never want to do another.

The cost can be offset by reusing reusable parts like oil pumps and valve train parts (other than valve springs, but the OE replacement small block springs cost about a buck each) Most of these parts can be reused if they pass simple visual inspections. You can also save money by using OE equivalent parts like timing sets that are inexpensive relative to the high dollar "roller chains" and work just as well. OE equivalent valves are very satisfactory. Stainless steel, especially on the inlet side are way overkill and a waste of money. Even OE Morraine 400 bearings are reuseable, and IMO superior to the current "tri-metal" replacement bearings.

Everything you save by judicious selection of what needs to be replaced and what to replace it with can be allocated to head massaging. Even though it can be expensive if done professionally, if it's done properly, it's the best bang for the buck to get "more power" without altering the engine's normal idle behavior or sacrifice in low end torque.

So, if you rebuild your '70 L-46 with massaged heads and the OE cam and both you and Mike get chassis dyno tests, we will have a direct comparison of how the XE262 performs relative to the OE L-46 cam.

And remember, PLEASE START THE PULLS AT 1000 REVS. Torque/power from off-idle to 3000 revs is REALLY IMPORTANT We spend most of our driving time in this rev range!

Duke

[Joe C.]

Re: L-46 Dyno Runs Part 2

Joe,

If you have the time, what does 3.5 show?

Thanks,
Mike

Mike,

EA 3.5 (now updated to v3.9) is the "Pro" version of EA 3.0 (now updated to v3.4), and it costs $469.00 versus $109.99. It has quite a bit more detail, the most important of which are as follows:

1. Allows head flow data inputs at multiple valve lifts (i.e.: .100, .200, .300, .400, .500, .600, .700.......) , so that actual bench test numbers can be entered. The base version only allows a single lift input.

2. Allows three cam duration inputs which very accurately charts cam dynamics. Generally, durations at J604d and .050 valve lift are used although .200 valve lift may also be used. The base version uses estimates for valve acceleration rates, e.g.: mild/aggressive/solid/hydraulic.

Joe

[Joe C.]

Re: L-46 Dyno Runs Part 2

I do know that GM spent millions on research to get it right and Duntov's favorite small block was the L46. What is being said is that regardless of the cam selection the head work is more important to increasing power than any differences in the two cams.

While I am a TOTAL novice head flow seems to be the key to making more power. Unfortunately, it also seems like getting the head work done on cast iron heads can cost a pretty penny. If I were to have the work done, my heads would be sent to DUKE if he does such things.

Mike, that is excellent advice to have my motor tested before doing anything. It runs great. I just wish it had a little more power that could be felt in the seat of the pants.


Bill

You may do so, although I should tell you that I follow Vizard's procedures to the letter, with one very special and important addition of my own. I have been able to achieve better than 250 cfm flowrates @ .500" - .600" lift out of 2.02/1.60 valved iron, double hump heads. You couldn't pay me enough to do a set for you, because it takes too many hours and the labor rate simply wouldn't pay off for me. I only do this job for friends.

It is very important, no matter who ports your heads for you, to have them pressure tested before and after the porting. DO NOT, DO NOT have anyone try to sell you hardened exhaust seats. The procedure weakens the casting, and almost guarantees penetration into the water jacket. You should have your three (or five) angle valve job done before porting. The port profile must be matched/blended into the entry and exits to the valve throats.

[Joe C.]

Re: L-46 Dyno Runs Part 2

"The OE cam has less overlap and will make more low end torque with about the same peak torque and power."

If both cams have the same valve acceleration rates, ie: the same degree of aggressiveness of the opening and closing flanks, then this would be a true statement. The Comp "XTreme Energy" cam has significantly more aggressive opening and closing rates than the OE cam, thus, the effect of its longer overlap is more than compensated for on the bottom of the rev range by the fast ramps. Among other benefits, this means that there is less pressure bleed-off during the compression stroke because the "delta" between SAE J604d duration (the duration at which the valves are EFFECTIVELY closed), and 0.050 duration is smaller, which results in higher DCR for a fixed SCR, leading to higher BMEP, which equates to more torque. Furthermore, the Comp cam has about 0.010" more lift on both intake and exhaust. The increased lift, faster actuation rates, and increased overlap will absolutely, positively result in higher peak torque, as well as a flatter torque curve with peak torque extended further in both directions.

This, of course means higher horsepower as well, since: Horsepower = RPM x (Torque/5250)

One reliable indicator of this is my own .030" over 327, which made 430+ (derived) flywheel horsepower using ported cast iron fuelie heads, and a high lift cam with fast flanks and very similar .050" durations as the 30-30. This engine makes significantly more torque at 1500 RPM than an L75,
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[Robert K.]

Re: L-46 Dyno Runs Part 2

Joe & Duke,

You guys always talk about pocket porting, what about port matching? Is that included in your head massaging or was that just understood by everyone except me? I've got my re-done 461x heads sitting on the bench just staring at me, but they have harden seats. What do I do? Sell them and start over with the other set? I didn't read about the harden seats until after I had them installed.

Thanks,
Bob

[Duke W.]

Re: L-46 Dyno Runs Part 2

I refer to "head massaging" because it includes more that pocket porting. The other operations are port matching (both inlet and exhaust side) and chamber relieving.

See the Fall 2010 Corvette Restorer for a more detailed discussion of "head massaging".

Duke

[Joe C.]

Re: L-46 Dyno Runs Part 2

Joe & Duke, You guys always talk about pocket porting, what about port matching? Is that included in your head massaging or was that just understood by everyone except me? I've got my re-done 461x heads sitting on the bench just staring at me, but they have harden seats. What do I do? Sell them and start over with the other set? I didn't read about the harden seats until after I had them installed. Thanks, Bob

Robert, Since your seats have already been replaced, then you should have the heads pressure tested, and preferably by the person who installed the seats, WHILE YOU WITNESS THE TEST. In most cases, if sealant is used on the inserts, along with a proper pressed-fit, then leakage should not be a problem. This is not a guarantee that (if core shift resulted in the inserts breaking through to the water jacket) the integrity will be maintained after numerous heat/cool cycles, but it certainly gives you a certain amount of peace of mind at the outset. Any possible weakening in the seat area between the intake and exhaust valves, and subsequent cracking in this area, which is the vulnerable area with these heads, is not as critical because your engine will likely not see much severe duty, plus, the fact that it has "small valves".

In your application, port matching can be done, although not extensively, on the rooves of the ports, as well as on the side of the port adjacent to the cylinder wall. The biggest flow gains are always made within 1/2" both upstream and downstream of the seats. Your heads currently have 170cc (nominal) intake ports compared to 160cc (nominal) ports on all of the other "double humps", and enlargement in conjunction with the 1.94/1.50 valves won't result in significant flow improvement, and I DO NOT recommend it. Your maximum flow with port match as described and significant reconfiguration in the bowl areas is all that should be done with a "small valve" iron head. Your '62 engine has a 097 cam, whose lift is not high enough to take FULL advantage of bigger valves and a full-race port job. A multiangle valve job followed by a thorough bowl cleanup and port match as described above should be sufficient.

A full race port procedure, as I did to my 2.02/1.60 valved 461 heads, and others requires a 5 angle Serdi Cutter valve seat profile, contouring of the intake and exhaust valves themselves, narrowing of the seats on both intake and exhaust, relieving the chambers, and related procedures on the block decks, unshrouding the valves, and cc-ing the chambers for equalization, streamlining the valve bosses, sealing the exhaust crossover with steel plate, widening the restricted cross sectional areas at the pushrod and lower head bolt locations of intake ports, raising the rooves, smoothing short turn radii, and streamlining the cylinder wall sides of the intake ports, and enlarging the intake ports to maximum safe size, which is quite a bit more than the "as cast" size. This must be done with care, and continual wall thickness measurements must be taken. On the exhaust side, raising the rooves and streamlining the cylinder wall side as well as significant enlargement of the port volume is accomplished. Intake ports should not be highly polished, and port floors should be left rough-cast as this helps keep fuel droplets suspended. Exhaust ports should be highly polished, as this somewhat retards the buildup of carbon in low velocity areas. Port floors may be left rough, as polishing these areas have no value. Gasket matching should be done carefully on both intake and exhaust sides. If headers are used, the port shape may be changed to match that of the header flanges (after the header flanges are properly enlarged, cleaned of flash, and dressed). Exhaust ports are best fashioned into a raised "D" shape. The worst mistake that one can commit, is to make the exhaust ports in the head too large, as a significant amount of turbulence will develop. A step should be provided at the base of the ports, and this becomes more important as the cam's overlap and exhaust duration increases. Intake ports should have a similar step at the interface to the intake manifold.


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