DuPuis Family Cobra Build

Discussion in 'Hangar Talk' started by Ted DuPuis, Aug 3, 2018.

  1. ElPaso Pilot

    ElPaso Pilot Cleared for Takeoff

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    BTW, Just yankin' your chain. I appreciate lopey idles and old school mechanical stuff, too.
     
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  2. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    Oh I know you are. And even if you didn't appreciate the old school mechanical stuff, that's fine. It's what I'm doing anyway because I don't care what anyone else thinks. :)
     
  3. 455 Bravo Uniform

    455 Bravo Uniform Pattern Altitude PoA Supporter

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    If it’s lope you want, look for overlap. One way to get it is by using tighter lobe centers. The other way is by increasing either exhaust or intake duration, or both.

    A good example is an old 1960s grind for a big block Buick called the “Window Rattler”. 107 LC with low lift. The other end of the spectrum is wide LCs and that’s what I run in my BB Buick; 118 LC with 1 degree of overlap. Total sleeper at idle. Great nitrous cam. It was called a cheater cam back in the early 70s.

    You’re gonna get your tuning chops tuned, with the carbs, solid cam, and roller rockers. You’re gonna need to put in a points distributor to get the full effect, lol!

    Jonesin’ for more pics from you, when the time is right.

    Sorry, can’t resist. You’re making me want to build something. Gotta throw theses up...I probably have already...I sold the green one (drag only); white one is street car, bench seat, column shift, I toy with selling it once in a while.

    D331A693-5D04-4AAA-878A-1EA8054A82DD.jpeg 56E4D5D1-C135-4ABB-87D0-4174A93B03CC.jpeg 5D330713-37F7-4AEE-AACA-99DA2B78407B.jpeg B56850F1-8583-431D-AF0B-E773BECB6A9F.jpeg
     
    Last edited: May 15, 2019
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  4. tmyers

    tmyers En-Route

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    IMAG0381.jpg Ted, If you don't want to worry about the vacuum for brakes, just install a 12 VDC Vacuum Pump. That is what Chris had on his 68 Chevelle.
     
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  5. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    That's part of what I like about this cam that I'm considering. It's got good overlap, duration, and lift, without having too much to be "too big" of a cam for what I want. I want the engine at idle to give the visceral feeling of an engine that is jonesin' to go, and don't want to sit around loafing at idle. With no catalytic converters it should make a great sound.

    Yeah, the tuning on it will be a lot of fun and getting everything set up right and tuned correctly. I am going with electronic ignition so I'll at least have that for me, but I do need to decide which setup to go with. I'm thinking of buying a complete ignition kit from MSD since I like MSD stuff and have had good luck with it. Vacuum and mechanical advance is what I'm planning there, but vacuum advance is really probably not required since this isn't a car where I care about fuel economy too much.

    Right now there's really not much to show pictures wise. All I've done is pull some parts out of the parts car. I'll probably have some more pics this weekend after tearing apart the engine.

    The reality is this car doesn't need power brakes, and if the booster is working right (which it should since I'll be putting in a brand new one) it "holds" a few brake presses from vacuum. So really the thing to do is let it rev enough (or coast enough) to get some vacuum to the booster from a higher RPM and then it should be fine from there. I'm not going to install the electric vacuum pump.
     
  6. MIFlyer

    MIFlyer Line Up and Wait PoA Supporter

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    if you really want to make it your own, put an as removed wet vacuum pump from an aircraft in it for your brake booster. :)
     
  7. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    That would be adding complexity for no real benefit. Any engine will make vacuum given the right conditions, and the booster will hold some level of vacuum. The goal is simplicity with complexification only added to achieve a noted benefit.
     
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  8. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    Also to add on to my response to this, now that I have an engine plan pretty solidly figured out, I'm really getting the itch to start ordering parts and building an engine. Of course the fact that the thing won't be driveable for a good while longer is irrelevant, I want to hear those ponies sing. :)
     
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  9. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    I haven’t made any real progress on the car itself, but a few comments.

    I’d previously cut 1.75” off the inner tie rod ends per the manual, and there was a massive toe in from that which didn’t look right at all. Turns out the step I missed was that there’s rack extensions that you have to put on. So I need to put those on, easy enough.

    A friend of mine also suggested I consider doing a tri-power (3-carb) setup instead of the Webers. My general thought is that is a bad idea. The 6-pack carb setup was more of a big block muscle car thing and while it looks cool and might help with low end torque a bit, it doesn’t do anything for responsiveness and won’t do anything for power. The only manifold I can find that would support that is from Edelbrock and they define it as an idle-5,500 RPM manifold. It would save a good bit of money vs Webers, but if it doesn’t meet the goals then what’s the point? If anyone else has experience using the tri-carb idea I’d be interested in hearing thoughts, and specifically regarding the goal of responsiveness.

    This weekend I hope to get some work done tearing into the engine and/or transmission, but I don’t think I’ll do anything else. The E55 got flooded during the recent rain storms and I have to look into that some...
     
  10. Zeldman

    Zeldman Touchdown! Greaser!

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    Tri-carb.....if it is the street version that uses vacuum to open the other two carbs, then it just operates as a vacuum secondary carb. Easy to set up and maintain as the center carb is the one to adjust. (once the jet sizes and, if Holley, the metering block sizes are determined) Using the single carb for normal daily driving should be responsive enough for a light car, and help with fuel mileage. And when it is time for fun, the other two carbs will come on as the engine needs them.

    My experience comes from the GM side using Rochester 2GC carburetors. Really the easiest, most simple set up ever made. It was on a '75 Firebird with a Chevy 350 engine, aluminum heads, I don't remember the cam specs, flat top pistons and auto trans. We opened up the hood scoops to make them functional and put fresh air to the top of the engine. It ran really well as a daily driver and a red light to red light warrior. (not that the owner ever did that ;).....) The owners wife could drive it and not have any problems.

    [​IMG]

    Stock photo from the internet. The car I worked on never looked this good, but it looked similar with the same wheels and hood scoops. The hood was fiberglass and was heavier than the steel hood.
     
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  11. SoCal RV Flyer

    SoCal RV Flyer Pattern Altitude

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    Gawd, this is the perfect antidote for the Tesla thread. Thank you. :D
     
  12. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    Yeah, my understanding with the tri-power was that it was really more about having something more streetable for when "the wife" drives it in a production car while having the extra airflow and power from more carburetion when the other two opened up. I'm not concerned at all with mileage and I'll give up some streetability for overall responsiveness. Plus it seems like these days they mainly just make the things for show/looks rather than performance.