L-46 Dyno Runs Part 2

[Mike F.]

Had the detuned L-46 rebuilt and brought back closer to the original specs. Forged pistons .030, Comp cam, heads ported, .........
(L-46 Dyno Runs Part 1 here, https://www.forums.ncrs.org/showthre...ight=l-46+dyno )

Engine Lab dyno results
Before - 285hp @ 4900rpm / 336tq @ 3400 / Comp 8.7:1
After - 341hp @ 5600rpm / 387tq @ 3400 / Comp 10.4:1

Here are the Engine dyno numbers. I'll get chassis dyno results when weather permits.

[Duke W.]

Re: L-46 Dyno Runs Part 2

Why did you use the Comp XE262 rather than the OE cam?

When you run on a chassis dyno please start the pulls at 1000 RPM, so the bottom end torque and power characteristics can be seen. We actually spend more time down low that up high, so those number count.

Before you run on a chassis dyno you should put the lightest springs into the centrifugal advance that the engine can tolerate without detonation. The quicker you can get it all end, the better the low end torque. Best power usually occurs with 38 degrees total WOT advance.

Thanks for posting the data.

Duke

[Mike F.]

Re: L-46 Dyno Runs Part 2

I went back and forth on the cam. When I dropped the engine off at the machine shop, I instructed them not to deck the block, externally the engine must look stock when completed, give me as much compression as possible for 93 octane pump gas, and a parts lists/recommendations from you (Duke) and Joe Ciaravino.

The machinist building the engine suggested the 262 cam over the stock one, said he had seen some better results with it. So with my engine rebuild experience at zero and his at 42 years, I went with his suggestion. He also mentioned (prior to disassembly) that 350hp would be about all I would see with the original cast iron manifold.

I was there for the dyno tune. They either replaced/adjusted as needed (using various combinations), the carb (Q-jet metering rods), spark plugs, timing, etc., to get the most power.

Prior to the rebuild I spent hours on the world wide webulator looking for dyno results for comparison. The best I could find is a Super Chevy article that included a stock L-46 build. They got 351hp/393tq. http://www.superchevy.com/technical/...g/viewall.html
Mine was pretty close. Was the difference caused by the build, cam, dyno's used, compression, fuel, etc., .... I don't know?

As for dyno runs, seems like everyone I know avoids them like the plague. I've even offered to pay for the runs, but no takers. I've searched here in the forum, but haven't found any other "stock/original" dyno runs posted. Would love to see some comparisons.

[Bill L.]

Re: L-46 Dyno Runs Part 2

Hi Mike,

Seems pretty close to the factory claims.


Bill

[Duke W.]

Re: L-46 Dyno Runs Part 2

As-built by Flint the true SAE horsepower was closer to 300 than 350. It's the head massaging that gets it up to the factory advertised ballpark.

The OE cam has less overlap and will make more low end torque with about the same peak torque and power. The Comp XE series has more aggressive dynamics than OE cams, which requires higher rate valve springs that place far greater loads on the valve train without any significant improvement in return, which is one reason why I don't like them.

The flat power curve is typical of OE exhaust manifolds and massaged heads and the useable power bandwidth likely extends up to the lifter pump up speed. With an OE cam and properly set up valve spring installed height it's about 67-6800.

The increase in peak torque is significant - 15 percent - and I would attribute about two-thirds of this to the nearly 2 point increase in compression ratio and one-third to the head work, and the nearly 20 percent increase in peak power is about equally divided between the two. This example shows what high compression and head massaging can do to a low compression OE built engine like the the L-82, which is basically a low compression version of the L-46.

Other than less low end torque and a lumpier idle, this engine has very good performance characteristics, and should be very strong and linear from the mid range to lifter pump up speed. The owner will be amazed at the seat-of-the-pants improvement when he drives the car.

We can predict the approximate SAE corrected rear wheel performance data within a few percent by applying the empirical conversion factors I developed from the data I've accumulated over the years. Manual transmission driveline efficiency in direct drive is 0.85 and the net/gross conversion factor for a small block with no front end accessories and the 2.5" under-the-car-exhaust is 0.89.

You guys can do the math.

And to the OP: PLEASE START THE PULLS AT 1000 REVS, SO THE LOW END TORQUE DATA CAM BE CAPTURED!!!

Duke

[Bill L.]

Re: L-46 Dyno Runs Part 2

As-built by Flint the true SAE horsepower was closer to 300 than 350. It's the head massaging that gets it up to the factory advertised ballpark.

The OE cam has less overlap and will make more low end torque with about the same peak torque and power. The Comp XE series has more aggressive dynamics than OE cams, which requires higher rate valve springs that place far greater loads on the valve train without any significant improvement in return, which is one reason why I don't like them.

The flat power curve is typical of OE exhaust manifolds and massaged heads and the useable power bandwidth likely extends up to the lifter pump up speed. With an OE cam and properly set up valve spring installed height it's about 67-6800.

The increase in peak torque is significant - 15 percent - and I would attribute about two-thirds of this to the nearly 2 point increase in compression ratio and one-third to the head work, and the nearly 20 percent increase in peak power is about equally divided between the two. This example shows what high compression and head massaging can do to a low compression OE built engine like the the L-82, which is basically a low compression version of the L-46.

Other than less low end torque and a lumpier idle, this engine has very good performance characteristics, and should be very strong and linear from the mid range to lifter pump up speed. The owner will be amazed at the seat-of-the-pants improvement when he drives the car.

We can predict the approximate SAE corrected rear wheel performance data within a few percent by applying the empirical conversion factors I developed from the data I've accumulated over the years. Manual transmission driveline efficiency in direct drive is 0.85 and the net/gross conversion factor for a small block with no front end accessories and the 2.5" under-the-car-exhaust is 0.89.

You guys can do the math.

And to the OP: PLEASE START THE PULLS AT 1000 REVS, SO THE LOW END TORQUE DATA CAM BE CAPTURED!!!

Duke

Hi Duke,

Just so I understand. If I massage the heads on my original 70 L46 there will be a significant increase in usable power as well? Mine has the higher compression of course as well as the original cam.

Hmmm - Now you really got me thinking

I do not want to go crazy but more power would be nice. What could I expect in the way of increased power and does it make sense to clean up the runners on the intake a bit too?


Thanks, Bill

[Mike F.]

Re: L-46 Dyno Runs Part 2

Hi Duke,

Just so I understand. If I massage the heads on my original 70 L46 there will be a significant increase in usable power as well? Mine has the higher compression of course as well as the original cam.

Hmmm - Now you really got me thinking

I do not want to go crazy but more power would be nice. What could I expect in the way of increased power and does it make sense to clean up the runners on the intake a bit too?


Thanks, Bill

Bill,

If your car is original and running, do some chassis dyno runs before you change anything. (PM me before you do)

If I understand Duke correctly, I believe my engine makes more power than a stock Flint built L-46. I also believe that our compression ratios (yours/mine) are probably pretty close to the same.
With head massaging, your L-46 should make as much power as my rebuilt engine.

A great comparison would be some chassis dyno runs on your stock L-46 and then some engine/lab dyno runs on your rebuilt/head massaged engine with original cam.

Regards,
Mike

[Joe C.]

Re: L-46 Dyno Runs Part 2

Mike,

Impressive dyno sheet on your build! I agree with what was said about your engine's performance, and the reasons for the increase. One thing that was not said, however, is the fact that your cam has .010 more valve lift on both sides than the stock cam. The more aggressive dynamics, additional 8 degrees of overlap, and the very small increase in lift, all combine to allow a flatter torque curve and an extension of the output in the high RPM direction. Any sacrifice in low end torque due to the increased overlap is more than compensated for by the faster valve actuation rates. Net result is bottom end torque virtually identical to stock, with an extended useful RPM range and higher overall torque throughout the rev range.

If you used the recommended springs to compliment your cam, then I suggest that you use motor oil with at least 1200 ppm phosphorous content. Ordinary Rotella CK oil is OK for OEM cams, but not for the XTreme Energy series flat tappets. I recommend Mobil 1 15W-50 full synthetic, which will run about the same price as Joe Gibbs or Brad Penn mineral based oil.

Did the machinist give you the flow data for your heads after porting? If he didn't achieve at least 250 cfm @ .500 valve lift, then there's potential for more. Chevy cast iron intake can be massaged by Brezinski to produce flows comparable to an Edelbrock Performer.

[Duke W.]

Re: L-46 Dyno Runs Part 2

Hi Duke,

Just so I understand. If I massage the heads on my original 70 L46 there will be a significant increase in usable power as well? Mine has the higher compression of course as well as the original cam.

Hmmm - Now you really got me thinking

I do not want to go crazy but more power would be nice. What could I expect in the way of increased power and does it make sense to clean up the runners on the intake a bit too?


Thanks, Bill

The single most effective way to make "more power" and 500-1000 more useable revs without screwing up the low end and idle quality and taking a chance on reducing valve train durabilty with an aggressive dynamics aftermarket cam and high rate springs is to massage the heads. See the Fall 2010 Corvette Restorer article "A Tale of Two Camshafts" for a more compreshensive discussion of the subject. I also discussed this in my San Diego presentation last summer. Google my name with San Diego and Corvette to find it on the Web.

The OE L-46 cam has less overlap, but a later closing inlet valve than the XE262. The OE cam will make more average power across the rev range. At best the XE262 might make slightly more peak torque, but it's the average torque/power across the rev range that counts for a road engine.

The '70 L-46 is a very good configuration. Other than head massaging NOTHING needs to be done. The OE "pink" rods can be reused without any work as long as they pass dimensional checks - no resizing or new bolts. The OE valvetrain needs nothilng other than new OE equivalent (Sealed Power VS-677) valve springs. Speed Pro OE replacement pistons should be used if boring the block is required and CR should be managed to a NTE level of 10.5:1 (See the Fall 2009 Corvette Restorer "Compression Ratio Explained")

I have a technical support paper on restoring vintage engines for "more power" without affecting idle behavior or normal operating characteristics. Email me if you want a copy.

Duke

[Duke W.]

Re: L-46 Dyno Runs Part 2

After expressing my off-the-top-of-my-head opinion, I ran both cases through Engine Analyzer 3.0. In the last several years I have used this as a primary engine system engineering tool. Most of the jobs were for small block Corvette engines, but also included big blocks and other types of engines.

Most of these engines were tested on lab or chassis dynos, which gave me a good feel for how accurate this program is.
As a general rule, it is quite accurate at the top end - often within one to two percent on top end power. Peak torque is usually in the ballpark to a few percent high, but low end torque predictions are usually substantially low - up to 20 percent.

The EX262 cam has similar durations to the L-46 cam, but significant differences exist. One is the LSA -110 deg. for the 262 and 114 for the L-46 cam. This results in about 36 percent more effective overlap for the 262, and increasing overlap reduces low end torque, especially in the car with the production exhaust system, even though it is relatively low restriction.

The other difference is that the L-46 inlet valve closing at .050" is about 11 degrees later than the 262. As a general rule, all other things equal, retarding the inlet valve closing point shifts the torque curve up the scale, which increase top end power and top end useable power bandwidth, but reduces low end torque.

As a basic configuration I used a .020" overbore 350 with typically massaged heads that flow 220/165 CFM at 28" H2O depression, 0.5" valve lift with a true compression ratio of 10.5:1 and a 750 CFM carb on a typical production manifold. The only difference was the two different camshafts.

Simulating a lab dyno test with the production manifolds and no exhaust restriction (no mufflers) and standard air density correction, which is how the OP's engine was tested the following is the summary data, which is effectively SAE gross:

XE262 camshaft

Torque @ 2000 = 274 lb ft
Peak torque 374 lb-ft @ 4000
Peak power: 339 @ 5000
Average power from 2000-6500: 259

L-46 camshaft

Torque @ 2000: 258
Peak torque: 377 @ 4500
Peak power: 367 @ 6000
Average power from 2000-6500: 271

Note that the peak measured power of the OP's engine with the XE262 was 341, which is within one percent of the predicted value. Peak torque was about 3.5 percent greater than predicted, but there is no way to compare the EA prediction with test results at 2000 since the dyno pulls started at 3200. (If you're going to pay for dyno time, PLEASE start some pulls at 1000 so you capture the low end torque characteristics!)

But this is not the end of the story - not by a long shot.

I adjusted the simulations to predict SAE net with the engine installed in the car - production water pump and clutch fan, 500 CFM exhaust flow @ 1.5" Hg, and SAE air density. This is what really counts, not SAE gross on a lab dyno.

The results are as follows:

EX262

257 lb-ft @ 2000
Peak torque: 340 lb-ft @ 4000
Peak power: 304 @ 5000
Average power from 2000-6500: 232

L-46

Torque @ 2000 241 lb-ft
Peak torque: 342 @ 4000-4500
Peak Power: 326 @ 5500
Average power from 2000-6500: 244

Because EA 3.0 is significantly low on low end torque prediction, the actual difference is likely marginal, and could probably not be felt SOTP.

The higher overlap of the XE262 is offset to some degree by the significantly later L-46 inlet cam closing event, but this creates a substantial improvement in top end power in the 5000-6500 range which is the operating range of the engine when shifted at 6500 except the 3-4 shift with the WR four-speed.

As I've said before, all other thing equal, the L-46 cam makes about the same top end power as the LT-1 cam. The difference is that the LT-1 cam allows a valve train limiting speed of about 7200 versus about 6700, both with careful valve spring set up. The additional useable revs are more important on a short stroke 327 because there is very little rolloff from peak power at 6500 to the 7200 valve train limiting speed. All other things equal a longer stroke engine will make about the same peak power at the same mean piston speed, so a longer stroke engine doesn't have to rev as high.

About 15 of the 20 extra horsepower rating of the LT-1 was due to the more efficient inlet manifold - my engine system engineering opinion based on simulations.

The L-46 cam is so good that I recommend it for L-79 rebuilds, but installed with an adjustable timing set to advance it to an inlet POML of 110 deg. ATDC, which matches the OE L-79 cam. Installing it at the producton 114 deg. ATDC, will push the useable power bandwith beyond the valve train limiting speed of a 327, and advancing it as above on a L-79 will maintain the low end torque at OE level.

The L-46 cam was designed in the 1967-68 time frame at which point Chevy engineers had a good handle on both valve train dynamics and what kind of valve timing produces the broadest torque bandwidth in a high performane road engine. The L-46 cam was the result, and it is still used, today, in a GM crate engine.

Duke

[Mike F.]

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

[Joe C.]

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

Mike,
One reason is that EA 3.0 is not as accurate as 3.5, which is what I use. 3.0 does not allow for accurate input of cam dynamics, a critical element.
Joe

[Mike F.]

Re: L-46 Dyno Runs Part 2

I appreciate the input and help I've received from all members, but can everyone please stop the bickering (at least on my thread)!

My only goal was to get as much HP out of a stock looking L-46 as possible. Could I have done a little better? Maybe, maybe not. The only true way to find out is if I pulled the engine, installed the OE L-46 cam and made some dyno runs for comparison using the same engine, same dyno, same conditions, ........

What I would really like to see is actual engine/chassis dyno run sheets for a stock L-46/LT-1 or any of the other 69-72 small blocks.

Thanks,

[Mike F.]

Re: L-46 Dyno Runs Part 2

Mike,
One reason is that EA 3.0 is not as accurate as 3.5, which is what I use. 3.0 does not allow for accurate input of cam dynamics, a critical element.
Joe

Joe,

If you have the time, what does 3.5 show?

Thanks,
Mike

[Bill L.]

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