Plotting an L-46 homage

Discussion in 'Engine Combos and Dynometer Database' started by DorianL, Jan 8, 2018.

  1. DorianL

    DorianL solid fixture here in the forum Staff Member

    Hey All,

    My kids often rib me about how I spend months carefully plotting a long term vision months before I actually break ground. I know precisely where I want to go before I set the first stone.

    …and so it goes for the corvette. The concept of where I want to take my 1969 L-46 corvette is slowly percolating.

    In 1969, the L-46 put out 350HP/380TQ. The original L-46 powerplant is long gone. But nonetheless, puttering around with the iron lump that is in there, is kinda fun.

    This has led me to the conclusion that I don’t need or even desire tons of power.

    I have done the track days, exploded my trans and rebuilt it, did the centrifugal supercharger, the water/methanol injection… you name it…

    I definitely do not want to do that with this car. This will be 90% restoration, 10% modification. The 10% modification will include: rack and pinion (I need a precise feel to my steering) and a TKO transmission (I need a comfortable cruise at 70MPH). Tho’ I
    must admit, except on the highway, this close ratio is fun !

    My plan is to match or improve on the L-46. This car will clearly be spending most of its time under 4,000 rpm. I doubt it will ever see the track, but it certainly will see some casual spirited countryside backroad driving.

    I want to restore the engine bay’s original look (minus the AIR pump).

    The plan is:


    It will be a Quadrajet. I never really worked on those. I have done Holleys and AFBs. I always wanted a finely tuned Q that is nearly as smooth as FI. It also retains OEM looks. It can easily flow north of 750CFM. The small primaries will make for good throttle response… no real downsides that I can see other than the learning curve.

    I will be going for a low-rise Edelbrock Performer intake or similar. The OEM L-46 is quite a lump of iron on the front end. A Performer intake (along with aluminum heads, see below) seems like a good compromise sacrificing some of the OEM look for substantial weight saving in a critical location. I also suspect 1969 OEM cannot match modern intakes in terms of overall flow performance.

    OEM 186 iron heads are heavy, expensive, will need a lot of work and once again, cannot match aftermarket flow and weight saving. It is not worth seeing the camel humps on the end or the casting number underneath the valve covers. I suspect a pair of reasonable quality 195cc heads (blueprint seems to carry a nice, cost-effective pair) will do for my intended application.

    Here, I am clueless. I guess I have to worry about the vacuum at idle for the power brakes. I will probably go with a regular hydraulic cam swap on the block that I have and, when I do a rebuild, it makes sense to go hydraulic roller… with a 383.

    Here I want to go with a preproduction (maybe ported) ram-horn exhaust manifolds. These manifolds are more restrictive than the full length headers that I have. But it is a big return to what was OEM. They are quieter. And OEM manifolds did support 370 gross HP @ 6,000 rpm on the 1970 LT1. (Tho that might be a factory exaggeration.) Again, I know I am losing some performance points, but for my application, ram-horns will probably be fine for a 350/383 CID striving to match or improve upon the original L-46.

    For now it is a 350. Soon I will rebuild a 383 out of the numbers matching 4-bolt that is in my basement.

    My plan is to proceed in steps.
    Right now I have good oil pressure and good compression. My short block seems healthy. I’ll keep that for the moment and start with an intake and cam swap. Then I’ll follow up with heads and an exhaust manifold conversion somewhere along the way. Finally, car running, I will independently rebuild a 383 and when the time comes, swap it in with a roller cam.

    My questions are the following:
    - What insight do you gentlemen have to share regarding my stepped-plan ?
    - What would be good cam recommendations?
    - How much can we improve on OEM considering the restrictions I have set down? What should I expect with the 350 and the 383?

    MTIA !

    Last edited by a moderator: Jan 9, 2018
  2. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    for the parameters youve set out Id go this route, Id suggest the 383 be built with a 9.4:1 static compression
    make darn sure you get the full size corvette, rams horn exhaust manifolds and Id suggest you add an (X) pipe to a 2.5" exhaust with low restriction mufflers
    Id also use 1.6:1 roller rockers Hydraulic Roller_E/ERSE119815

    and select heads that clear a .550 valve lift clearance
    correctly tuned 380 hp-390 hp,( a bit more than 40-50 ft lbs more torque and hp than the original engine had for certain,) is certainly going to be reached due to the better heads and roller cam and roller rockers.

    Last edited: Jan 8, 2018
  3. DorianL

    DorianL solid fixture here in the forum Staff Member

    That sounds like exactly what I am looking for. Thanks. This car should be perfectly fun to drive.
  4. Indycars

    Indycars Administrator Staff Member

    This might help.
    Parameters :
    CID = 383
    SCR = 9.5
    Heads: Blue Printer 195cc, Flow Numbers: See Below
    Intake: Dual Plane w/700 CFM Carburetor
    Camshaft = Erson E119815




    DorianL likes this.
  5. Loves302Chevy

    Loves302Chevy "One test is worth a thousand expert opinions."

    Rick & Grumpy covered the future 383, so here are a few recommendations for upgrading the 350:

    Carburetor - Quadrajet from Cliff's High Performance Quadrajets if you don't want to mess with the carb yourself.

    Intake Manifold - Performer EPS

    Flat tappet camshaft - you said mostly less than 4000 rpm, so you will want to look at camshafts designed for torque. Crower has a nice category of these. Keep intake duration under 214 degrees at .050 for enough vacuum for the power brakes. Plan to change the timing set while you are in there. You might want to consider lifters with the EDM oil hole in the face for extra oiling directly on the camshaft lobes.
    BUT, you must change the valve springs and check for retainer-to-seal clearance. An easy and inexpensive and decent quality kit for doing this can be found at Alex's Parts
    Call and talk to Alex directly. He is a great guy and can set you up with a kit similar to the above with everything you will need, like shims and valve seals. You will not have to do ANY machining to your heads.

    With your somewhat restricted exhaust system (rams horns), your camshaft should have the approximate 10 degree longer exhaust duration vs intake duration.
    Last edited: Jan 8, 2018
  6. DorianL

    DorianL solid fixture here in the forum Staff Member

    Thanks Rick, that really helps ground the project in reality. Thanks!
  7. DorianL

    DorianL solid fixture here in the forum Staff Member

    I liked the torque curve...
  8. DorianL

    DorianL solid fixture here in the forum Staff Member


    You also mention the Edelbrock EPS intake... a square bore. So with an adapter? I don't think it is available spread bore...

    Yes, I may well outsource the Q-jet setup...

  9. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    and that the wider 114 LSA will smooth the idle,
    and extend the torque curve slightly, also increasing the engine vacuum available for the brakes booster, reducing friction, and taking full advantage of the more modern and effective roller cam and roller rocker technology has both the potential to reduce wear, oil temps and increase air flow rates
    notice its right where the roller cams lobe design maximized the extra air flow potential that is the most effective flow area during the whole valve flow curve
    and yes it frequently helps to match a roller cam to roller rockers as the reduced friction further helps the engines durability and ability to easily cope with faster valve train component acceleration, that tends to reduce heat and wear.
    The following equation mathematically defines the available flow area for any given valve diameter and lift value:
    Area = valve diameter x 0.98 x 3.14 x valve lift
    Where 3.14 = pi (π)
    For a typical 2.02-inch intake valve at .500-inch lift, it calculates as follows:
    Area = 2.02 x 0.98 x 3.14 x 0.500 = 3.107 square inches, thus it makes a great deal of sense to push the valve lift a bit over .500, and have an intake port that is at least 3.2 square inches in cross sectional area, if you want to maximize flow on a 2.02" intake valve


    Last edited: Jan 9, 2018
  10. Indycars

    Indycars Administrator Staff Member

    Taking one of the Crower camshafts that Loves302Chevy suggested for SBC 350, I get the following results.

    One thing I didn't mention last time and is also true this time..... the simulation is run with mufflers and
    without Cats. The flow numbers for the heads are based on the Vortecs.


    Interesting how the torque did not drop all that much, but the HP did. This is because the peak torque
    occurs at a higher RPM.

  11. DorianL

    DorianL solid fixture here in the forum Staff Member

    These simulations are interesting...

    As I expected, the 383 roller easily matches and outperforms the L-46 (350HP/380TQ) with, what looks like: 375HP/5500 and 430TQ/3500.

    The 350 simulation surprised me. I would have thought it would at least get close to L-46 OEM, but rather I seem to read: 275HP/4250 and 400TQ/2750. All the way up to 3500 rpm, the torque curve is crazy flat at around 400ft/lbs after which is falls off dramatically.

    I am assuming this is because OEM does not specify where in the rpm range peak HP and TQ occur. I am assuming this is because the L-46 had a static compression of 11:1 and probably a wilder camshaft...

    (Not necessarily a desirable thing, considering my application, BTW.)
  12. Indycars

    Indycars Administrator Staff Member

    BTW, the Erson 383 motor had a SCR of 9.5, the Crower 350 had a SCR of 8.5. Should I run
    that 350 motor again with a SCR of 11:1, it's only a few click???
  13. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    in 1968 high test leaded gas like sunoco 240-260 was about 36 cents a gallon,
    allowing 11:1 compression engines to run decently,
    todays, current unleaded pathetic fuel won,t allow the same performance with ,
    the same 11:1 compression in an iron 350 SBC without a higher risk of detonation issues.

    I don,t know if dorianl can do this but many of the members in the U.S.A. might.
    theres also the option in some areas of boosting compression to 12:1, if you have a constantly available E85 fuel supply,
    and your willing to make the required changes to run that fuel

    Last edited: Apr 7, 2018
  14. DorianL

    DorianL solid fixture here in the forum Staff Member

    If you would... I am surprised at the shortfall.

    Interesting also on the fuel limitations.
  15. DorianL

    DorianL solid fixture here in the forum Staff Member

    The plan remains a good one - I like this "2-step" idea.
  16. Indycars

    Indycars Administrator Staff Member

    Ok, below is a graph with both curves plotted. A very noticeable difference.

  17. DorianL

    DorianL solid fixture here in the forum Staff Member

    Thanks !!!!! Interesting difference.

    So GM must have been running a hotter cam.
  18. Indycars

    Indycars Administrator Staff Member

    I found some specs for the L46 camshaft, it does have better numbers.

    Intake duration @ .050- 222
    Exhaust Duration @ .050- 222
    Intake Lift- .450"
    Exhaust Lift- .460"
    Lobe Centerline- 114
  19. Indycars

    Indycars Administrator Staff Member

    Since I don't know the details about the intake manifold, I chose a Dual Plane-Std Flow. If I chose
    a Dual Plane-High Flow, the HP jumps by 30. If I chose the best called the Dual Plane-Max Flow,
    then HP jumps by 45. So you see the graphs are only really good for COMPARISON and not so
    much about ABSOLUTE numbers.

    The manifold and camshaft could easily make the up difference and bring the HP to 350.
  20. Loves302Chevy

    Loves302Chevy "One test is worth a thousand expert opinions."

    I would love to have E85 around me because I have a 12.8:1 compression 350 SBC that I would love to play with.
    But it will sit in the basement and collect dust because there is no way I economically run that thing on racing fuel.

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