L46 Dyno Runs

[Mike F.]

I made some dynojet runs today!

70 Coupe, 350/350, M21, 3.70 gears. Engine, drivetrain, and exhuast are stock except flat top pistons and cam.
See https://www.forums.ncrs.org/showthre...87716&uid=4514 for cam and flat top pistons.

93 oct. pump gas, Timing 16 degrees initial, 36 degrees @ 2500rpm.

(Graph 1) Air filter on, 213hp @ 4750, 276tq @ 2750rpm

(Graph 2) Air filter lid removed, 217hp @ 4750 282tq @ 2750rpm

Good article in Super Chevy L79 vs L46 vs L-82.

http://www.superchevy.com/technical/engines_drivetrain/cams_heads_valvetrain/sucp_1003_classic_chevy_small_block_dyno_testing/index.html

If anyone else has dyno run information for their engine please post.

Edit: For some reason I can't attach the photos in this thread because the graphs were already up-loaded in the L46 Cam thread. I've tried changing the file names, still no luck.

[Duke W.]

Re: L46 Dyno Runs

...almost as good as the "Special 300 HP" 327 in the Fall 2010 Corvette Restorer.

A real 350/350 should do better, especially on the torque side - more on the order of 300 lb-ft. The low compression yields no more torque than a high compression 327 despite the larger displacement. That's the effect of low compression, and it also reduces top end power by about the same percentage.

Low end torque 80 percent bandwidth is probably very good, but why didn't you start the pulls at 1500 or less, so you can see what it is? Getting all the spark advance in as quickly as possible, as you have done, helps low end torque.

Inlet duration 10 degrees less and POML indexing 7 degrees earlier than the OE L-46 cam helps the low end torque, but costs some top end power and revs. If the heads have no massaging, then the numbers are pretty good for the configuration.

The curve shapes are fairly typical for OE or mildly modified engines with the OE exhaust manifolds. Both torque and power curves are quite flat, which makes for a good, responsive road engine that has a very "linear" feel to it - not at all "peaky".

Duke

[Duke W.]

Re: L46 Dyno Runs

I'm surprised this thread has so few views.

...just thought I'd add that I recommend all OE equivalent components for L-46 restorations, including the OE cam and Speed Pro (Federal Mogul) OE replacement forged/domed pistons with a not to exceed true, measured CR of 10.5:1, which should be achievable with proper head gasket thickness selection.

Head massaging is optional and will increase top end power and the useable power rev range to the valve train limiting speed, which is about 6500 with proper OE spring setup.

This massaged OE configuration might be slightly down on low end torque compared to the stated configuration, but will have more top end power and revs.

Duke

[Dennis D.]

Re: L46 Dyno Runs

I'm surprised this thread has so few views.

...just thought I'd add that I recommend all OE equivalent components for L-46 restorations, including the OE cam and Speed Pro (Federal Mogul) OE replacement forged/domed pistons with a not to exceed true, measured CR of 10.5:1, which should be achievable with proper head gasket thickness selection.

Head massaging is optional and will increase top end power and the useable power rev range to the valve train limiting speed, which is about 6500 with proper OE spring setup.

This massaged OE configuration might be slightly down on low end torque compared to the stated configuration, but will have more top end power and revs.

Duke

I let a pro rebuild my 70 L-46 a few years back. Mostly original parts. New stock GM cam. TRW stock pistons. He did message the heads,(be lying if I said exactly what was done). Did change to manley valves with comp cam 1.52 roller tip rockers with spring to match. Lastly went to a MSD billet distributor. Runs very well especially at top end.

Only negatives... Had a nasty pinging so I blocked the heat crossover, got rid of the heat riser valve with a spacer. Although that was to keep the right muffler from rusting out. Also 2 1/2" style exhaust. Does take forever to warmup, but I live with that in the NE and don,t drive the cold months

[Joe C.]

Re: L46 Dyno Runs

I made some dynojet runs today!

70 Coupe, 350/350, M21, 3.70 gears. Engine, drivetrain, and exhuast are stock except flat top pistons and cam.
See https://www.forums.ncrs.org/showthre...87716&uid=4514 for cam and flat top pistons.

93 oct. pump gas, Timing 16 degrees initial, 36 degrees @ 2500rpm.

(Graph 1) Air filter on, 213hp @ 4750, 276tq @ 2750rpm

(Graph 2) Air filter lid removed, 217hp @ 4750 282tq @ 2750rpm

Good article in Super Chevy L79 vs L46 vs L-82.

http://www.superchevy.com/technical/engines_drivetrain/cams_heads_valvetrain/sucp_1003_classic_chevy_small_block_dyno_testing/index.html

If anyone else has dyno run information for their engine please post.

Edit: For some reason I can't attach the photos in this thread because the graphs were already up-loaded in the L46 Cam thread. I've tried changing the file names, still no luck.

[Don C.]

Re: L46 Dyno Runs

Mike
The attached graph shows the results of a recent dynojet run on my 65 L79. It was built using the knowledge so freely imparted on this website by Duke and Clem, plus a bunch I've learned over the years, plus info from Vizard's book's.
The engine is an L79 using OEM parts - valvetrain, rods, flat top pistons, intake manifold etc. but has the smaller 1.94/1.50 valves. SCR is 10.05/1. I installed the L46 cam advanced 4 degrees. The 'aftermarket' stuff is a larger carb (730 CFM, mechanical secondaries), and 1-3/4 inch headers. I 'massaged' the 461 heads as well as did quite a bit of work on the Allen under car 2-1/2 inch exhaust system to reduce the back pressure to under 1 PSI at full power. The engine pulls hard to about 6800 where it experiences valve float. It runs 107+ MPH and low 13's in the quarter. Overall I am pleased with results but am still fine tuning to get a little more. It surprises a lot of C5's!

This is my first attempt at attaching something, so hope it works.

[Duke W.]

Re: L46 Dyno Runs

Very impressive! The headers and very low exhaust backpressure push peak torque to over 300 lb-ft from the approximate 280 that I would expect with manifolds, but they cost down low, which why the curve has a hole between 2500-3500, but the mechanical secondary carb may be an issue, too.

I have Don's head flow data and they outflow all data I have for 2.02/1.6" valve heads with similar preparation.

Now, Don, if you install a LT-1 cam peak power should hit 300 and useable revs will increase to 7200!

It would be interesting to see how the OE 585 CFM carb would do. I don't think it will cost too much top end power, but it might help fill in the low end torque hole.

Duke

[Don C.]

Re: L46 Dyno Runs

Thanks Duke

The only comparison info I have on the effect of the smaller carb is quarter mile performance data collected a year apart. With the change from a generic 0-1850 Holley (600 CFM rated) to the present carb, speed increased by 3 MPH. Now to muddy the waters I was still playing with the exhaust system during that period and it also probably contributed to the increased power. I am thinking the mechanical secondaries are more than likely causing the slow ramp up in the torque curve and am playing with some carb changes to improve the A/F ratio. Right now it goes too rich at WOT for the first couple of seconds. We did run the carb on my son's similarly built 350 LT1 and collected some dyno comparison data using a Vac secondary 750 during the same test session. In that configuration the vac secondary carb produced a steeper initial torque curve as we expected with no significant difference in top end power.

[Duke W.]

Re: L46 Dyno Runs

Assuming you have the data files and WinPrep software to view the tests on your computer, what is peak power if you use smoothing level 5?

Using the Flywheel HP = weight x (MPH/234)**3 empirical formula the 3 MPH increase in trap speed indicates an eight percent power improvement, which is signficant.

Duke

[Don C.]

Re: L46 Dyno Runs

288.93 at smoothing 5 vs 290.34 at smoothing 0

[Duke W.]

Re: L46 Dyno Runs

I think it's fair to call it 290. My goal is to see a "327 LT-1" make 300 with all OE exterior components including the exhaust manifolds. So far I'm about 10 HP short.

With your head flow and low restriction exhaust system, I think it's doable!

Just a reminder to anyone who gets a Dynojet test - do it on a cool day with plenty of external cooling to keep the fan clutch from tightening. It can cost 15 lb-ft and 10 or more HP at the top end. Use a garden spayer to spritz down the radiator and fan clutch themostatic spring, and PLEASE, PLEASE, PLEASE, start the pulls from less than 1500. With the OE carb if it won't pull smoothly from 1000 there's something wrong with the tune.

Duke

[Mike F.]

Re: L46 Dyno Runs

Update,

Pulled the engine for rebuild and had it run on an engine dyno before disassembly. This L-46 had been detuned in the 80's with flat top pistons (Comp. 8.7) and a pretty weak cam. (See first post)
The engine dyno (Stuska Dynamometers) was with open headers/velocity stack. The chassis dyno was a Dynojet with stock exhaust manifolds, 2 1/2" undercar exhaust, power steering, and air cleaner installed. Just about a 25% total loss from Gross to RWHP.

[Duke W.]

Re: L46 Dyno Runs

Okay, so the latest dyno test was on a lab dyno with the freshly rebuilt engine.What is the configuration - CR, cam, head work?

Unless the configs are identical, there's no valid comparison.

You should run it again on a Dynojet chassis dyno after you have it debugged and broken-in.

Start the pulls at 1000 revs.

Duke

[Mike F.]

Re: L46 Dyno Runs

Duke,

My update was to show the lab dyno results for the same engine that was run on the dynojet.The engine was run in the old, low compression, bad cam configuration.
Old engine, lab dyno = 285hp, dynojet = 213hp.

I'll get the rebuilt engine back in January with lab dyno results, once installed in the car I'll get some Dynojet runs/results (weather permitting) or it'll have to wait till Spring.

[Bob I.]

Re: L46 Dyno Runs

What are the plans, for the configuration of the rebuild. Will it include, using the cast iron intake and exhaust manifolds.

Bob