'72 GT Wideband jetting a 32/36 Weber - Page 2
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Thread: '72 GT Wideband jetting a 32/36 Weber

  1. #21
    Opel Intern Swiftus's Avatar
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    AFR will also read lean on misfires since there is excess oxygen in the exhaust.

    Fixing your ignition timing might have been the trick to eliminate apparently lean mixtures at cruise - although it is really only a slight chance.
    wrench459 likes this.

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    Opeler The Cub's Avatar
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    Quote Originally Posted by The Scifi Guy View Post
    In my experience, heat shields don't do squat, or at least not enough to justify the inconvenience they cause when trying to get at bolts and such in that tight congested area.

    We've discussed in the past the concept of adding a carb cooling fan that would come on after shut down. Some cars even came with carb cooling fans right from the factory. Not many, but some. I'm 100% sure that if we could put carb cooling fans on our GT's, that could run for, say, 10 minutes after shut down, the boiled out carb problem would finally be cured. But, where to put one is the problem. No room. We've talked a bit about this subject, but no one has ever tried it.


    HOLY COW! Man you've tried everything! My Wife & I raising 2 teenagers now doesn't leave me very much to spend on my GT at the moment. I've got the electric fuel pump wired in with the inertia switch mounted to the driver side of the radiator wall for safety, gas lines away from engine etc. I can't afford to tinker much with the exhaust anymore, I may use your idea on having the flex pipe welded in, a little too much vibration sometimes, that sounds like a pretty inexpensive fix. I wonder what the cooling fan looks like that were installed on the few GT's you mentioned & how they were activated & positioned etc. That's good to hear about the factory heat shield. I'd like to shelf it. It looks like just another radient heat conductor to me. I read GT Alex's post I think he's on to something, to add to that, if the heat shield had a non flammable insulator material mounted to the underside of the factory or re manufactured shield? Add to that the addition of the cooling fan idea, wouldn't a temperature sensed or TD relay activated small 4" axial fan mounted on the wheel work? I realize doing this correctly would mean heat calculations, has anyone come up with the required CFM's yet? There's a little lip above the passenger side wheel well next to the heater hoses, give the fan a little clearance away from the wheel well, it just might work? If after my re gasketing, I'm still boiling (based on your experience, sounds like it will) I'd like to give the axial fan a try, with a temperature sensor attached to the bowl of the carburetor. Heck, I can experiment with the small axial fan I have, hood closed after engine shut off. I'll try first without the shield. Believe me if I can get by a 90° day with no carburetor boil off I'll be posting up immediately here. On a positive note from what I've read the Weber's performance is actually enhanced with the right amount of heat under the intake manifold. Even if you could you wouldn't want to eliminate all of the give off heat from the engine. So with the GT's, it sounds like we just get a little too much of it. Makes sense about the Manta having more cooling room under the hood. After all Opel just took the Kadett frame etc., moved the engine back & put a new sport coupe body on it without much other expenditures towards manufacturing the GT correct? That's always been my understanding anyway.
    Last edited by kwilford; 04-09-2017 at 04:24 PM. Reason: fixed quote

  4. #23
    7,000 Post Club My location wrench459's Avatar
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    Quote Originally Posted by Swiftus View Post
    AFR will also read lean on misfires since there is excess oxygen in the exhaust.

    Fixing your ignition timing might have been the trick to eliminate apparently lean mixtures at cruise - although it is really only a slight chance.


    Whenever I see see both p030x and p017x codes I go after the misfires first.

    Si vis pacem, para bellum "If you want peace, prepare for war"

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    Opel Intern Swiftus's Avatar
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    Dan translation follows:

    Quote Originally Posted by wrench459 View Post
    Whenever I see see both misfire and fuel trim limit codes I go after the misfires first.


    Whenever I futz with a tune and foul a spark plug, the same thing happens to me.

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    Opeler The Cub's Avatar
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    Quote Originally Posted by gt alex View Post
    Hi Tom,
    When I first got my GT it peculated the carby dry when parked after driving in traffic. I put a digital temp sender (connected to my fluke) on the top of the driver side foot well inside the engine compartment (the cool side ) and found to my amazement even though 25 deg C out side to air temp went from 40 deg C cruising to 70 deg C + once in traffic. I straight away made a heat shield full length of the exhaust manifold about 12 cm wide. It was straight on the intake plenum with gasket, then there was a 8mm heat in insulator on top then the carb. I remember, to fit it was not flat, and I put a cut in the leading edge so part could go under the thermostat housing.
    It also had a hole for a vacuum line.
    Long story but it worked.

    Alex
    Hey Alex,
    Can you please post a picture? I'm trying to, but not fully understanding your description. How did you gasket between the intake manifold under the shield & what was the metal you used, same thickness as the original heat shield? I'm always interested when someone has found a solution for the boiling off of the gas.

  8. #26
    Senior Member nickincrete's Avatar
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    You can find decent robust fans from some turbo diesel 4x4 such as the, older 2.5td 1990ish , Mitsubishi Shogun. or Pajero in Japan.
    This has a small intercooler radiator fitted in the middle of the hood with small hood scoop. It also has, I believe, a simple electrical heat relay.
    These may be better, more robust more power in the underhood environment than a pc fan

  9. #27
    Just Some Dude in Jersey My location The Scifi Guy's Avatar
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    Stainless steel is the metal of choice to make heat shields out of.

    If you were going to try the cooling fan idea, I would suggest ducting air to it from a fan in front of the radiator. Like a cold air intake. No sense in blowing hot engine compartment air at your carb. Run some cold air intake pipe from the auto parts store from the hole next to the radiator on the passenger side, put a 12V muffin fan at the front. Another kooky idea would be to replace the bump on the hood with a vent and possibly putting your cooling fan there to suck cooler outside air and blow it directly down at your carb/intake/exhaust. Many people have altered their hood bump for cold air intake and cooling purposes.

    But air is a pretty weak absorber of heat and you would need to really cleverly design an air channeling compartment around the base of the carb to maximize the air cooling. A far more effective cooling solution would be to fashion a water jacket that would bolt to the bottom of the intake. Ever notice how quickly red hot steel gets quenched when dipped in water? 600*+ steel can be held in your hand after about 10 seconds of being dunked in water. Do you use your heater? No? Run the heater hoses to your water jacket, let the radiator cool the water.

    As you can see above, ideas for cooling your carb start getting a little crazy and you start filling up your engine compartment with junk to cool your carb. The fundamental fact is that our cars having the intake/exhaust on the same side of the engine is a bad design when it comes to carb boiling. Add the cramped Gt engine compartment to the mix and the problem gets really bad. Add to that the fact that GT radiators are smaller than Manta or Kadett rads and are in fact too small(by industry standards) for 1.9L+ engines, so they're always stinkin' hot. Heat, heat, heat, it's the bane of all GTs that live in hot, humid, or traffic jammed areas.

    Keep in mind that the general consensus, after many of us have tried everything we can think of to cool our carbs, is that the primary heat is getting delivered to the carb by the intake manifold. That's why the phenolic spacer you installed is so important. They seem to stop a lot of the heat from the intake from soaking into the carb(heat soak). But the heat still gets to the carb via the carb-to-manifold bolts. But that's nothing compared to the heat that's coming from the stove pipe and the intake-to-exhaust bolts. If I were you, I would scrap the heat shield, forced air cooling, water jacket, etc. and focus all your efforts on separating the carb from the exhaust and either getting a Sprint version of the cast iron exhaust or header, preferably ceramic coated.


    None of this will work, of course. The problem lies in the fact that we have carburetors with a few shot glasses of gas inside that are inches away from red hot steel. You don't hear about this problem from FI GT guys. Why? They're not keeping a reservoir of gas right next to the exhaust pipes. They get their gas on-demand from the tank via the pump and injectors. There's no gas to boil off.


    Here's a thought I never tested: If the small cramped engine compartment and lack of ventilation is the reason GT's boil gas, then, theoretically, if you go for a drive and get your engine nice and warmed up and hot, then parked and engine off, and then opened the hood, one would think that the gas won't boil 'cuz all the heat could get out. Wait 5 minutes, maybe 10, and see if your car will start or take the lid off the carb and see if the gas has boiled away.

    Try it! Let us know what you discover!
    Last edited by The Scifi Guy; 04-12-2017 at 08:33 AM.

  10. #28
    7,000 Post Club My location wrench459's Avatar
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    Quote Originally Posted by The Scifi Guy View Post
    ..
    None of this will work, of course. The problem lies in the fact that we have carburetors with a few shot glasses of gas inside that are inches away from red hot steel. You don't hear about this problem from FI GT guys. Why? They're not keeping a reservoir of gas right next to the exhaust pipes. They get their gas on-demand from the tank via the pump and injectors.
    2.76 bar fuel pressure does have it's advantages.

    Si vis pacem, para bellum "If you want peace, prepare for war"

  11. #29
    Opel Intern Swiftus's Avatar
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    If you're looking for heat shield material, Metal Tech Industries material has worked well in my work at school. It's really inexpensive for raw materials from them (on the order of ~$25 for 2x4' sheets of dimpled stainless), but they are happy to work with you to build a custom fit heat shield if you like.

  12. #30
    Opeler The Cub's Avatar
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    go for a drive and get your engine nice and warmed up and hot, then parked and engine off, and then opened the hood, one would think that the gas won't boil 'cuz all the heat could get out. Wait 5 minutes, maybe 10, and see if your car will start or take the lid off the carb and see if the gas has boiled away.

    Try it! Let us know what you discover![/QUOTE]

    I have pulled the cover off of my DGAV before, with the water choke removed from the carb body & witnessed it boiling away. That's when I realized that my boiling starts about 10 minutes after the ignition switch gets turned off. Shooting temperatures etc just about all temperatures came up from 180° to between 250° to 300° However I don't remember if I opened the hood right away. I'm getting ready to re gasket this weekend. Can you please tell me what the best combination of gasketed material, how much, how thick etc that you have found to be the most successful? The Ford Mercury Gasket OGTS sells is what I'm wondering about. I'm thinking of about 1/8" to 1/4" of phenolic gasketing on top of the manifold, then possibly the 1/4" Felpro Ford gasket under the Weber base depending on how much room I have to work with. IDK if I'm better off using more of the phenolic material instead? Right now we're in to mild of weather in the San Diego area (between 50° and 80°) too cool to think I will have solved anything yet. Gotta love the water cooled idea. If the weber only came with a water cooled heat exchanger & couple of small fittings, the nice thing about that idea is you can route your water lines right up to the front battery compartment or anywhere where a little 12v Circ pump could go, a separate air cooled sealed water tank for the cool water, up front perhaps. Kinda fun to think about anyway. I'd do that before I would chop up the hood as tempting as that sounds. I'll be logging temperatures and trying whatever I can in the realm of gasket the base this weekend. I'm going to shelf the heat shield, my GT is running lean, the heat shield isn't helping the possibility a possible vacuum leak of I don't think.

  13. #31
    Just Some Dude in Jersey My location The Scifi Guy's Avatar
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    I don't personally think that any more than 1/4" of phenolic spacer would be required to insulate the flat base of the carb from the flat entrance to the intake. The phenolic spacer basically allows ZERO heat transfer, so 1/4" should be more than enough to stop the heat from the flat surfaces. But, like I said, The heat seems to come from the bolts/studs. A good idea would be to replace the studs/bolts with stainless steel ones. Stainless is very slow to migrate heat.

    There's another factor to consider when installing phenolic spacers. RallyBob did a study many years ago on the power differences between different model year intake manifolds and different height phenolic spacers. Maybe someone could find that discussion and link us to it. I don't recall if an optimal thickness was determined, but I believe that 1/4"-1/2" of height boost, due to the spacer, adds some more power.


    Hmmmmm.......I wonder if the old style water temperature-actuated chokes also provided a bit of water cooling to the carb? I'm sure it wasn't much, I still had boiling with those, but maybe they helped a little? Has anyone noticed a difference in their carb boiling when using a water choke vs. an electric choke?



  14. #32
    Opeler The Cub's Avatar
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    Quote Originally Posted by Swiftus View Post
    If you're looking for heat shield material, Metal Tech Industries material has worked well in my work at school. It's really inexpensive for raw materials from them (on the order of ~$25 for 2x4' sheets of dimpled stainless), but they are happy to work with you to build a custom fit heat shield if you like.
    That's an awesome link my good man. Thank you. I was thinking a non insulated heat shield seemed to not do much of anything. It looks like they have a good variety of insulated shield material. I haven't looked into the link yet very long but I imagine they can incorporate & fabricate a flat plate in the center of it so it can be installed between the carburetor & manifold? May I ask how you went about doing yours, if you have had one fabricated that is? How much has it helped?

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    Carby Cooling

    Hi tom,
    I have been looking for my old heat shield, I know I have not chucked it, but OGTS have a heat shield with uncanny similarities part No 9073. Mine was a bit longer to go full length of the exhaust manifold and no slots each side of the carb. It looks very similar to what I made even the hole for the vacuum hose.
    But i just remembered Fiat x19 s had a carby cooling fan that blow cool air between the heat shield and the air cleaner.
    Parts are on ebay fan assembly's and ducting. here's the bit that points the air at the carb
    Fiat X1/9 Engine Intake/Carburetor Cooling duct for a Fiat X1/9 | eBay

    Insulation Material to stop heat soak from the manifold is still very important.

    alex

  16. #34
    Opel Intern Swiftus's Avatar
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    Quote Originally Posted by The Cub View Post
    May I ask how you went about doing yours, if you have had one fabricated that is? How much has it helped?
    I have only used the heat shield material I mentioned in my school's race car. It knocks down the heat from the 1000C+ exhaust to manageable enough levels that a driver can sit ~30mm from the 1000C exhaust tube without any discomfort.

    The stainless material spot welds very well, but I have also used stainless rivets to secure its shape and in place.

  17. #35
    Opeler 69whitegt's Avatar
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    Another trick you can try to minimalize boil over/hot starts in to wrap your exhaust manifold with heat wrap. Since I wrapped mine I have noticed it stating easier when hot. You might also consider one the OGTS high torque starters, they crank the engine faster then stock. I don't know if the issue with those has been solved but several members reported problems with the solenoid engaging.
    ____________________________
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    . Isky OR-66 camshaft

  18. #36
    7,000 Post Club My location wrench459's Avatar
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    You'll need to do one or two things.
    Keep the fuel cool or pressurize.

    It might help to know the RVP value of the fuel your using.

    Si vis pacem, para bellum "If you want peace, prepare for war"

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    Opeler The Cub's Avatar
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    Hopefully I've comprehended some pretty pertinent points on RGP & pressurization: The EPA regulations state 9 PSI at this time of year. Meaning that the fuel cannot exceed that amount of pressure @ 100° F. Atmospheric pressure being at 14.7 that value insures when the fuel starts to change state from a liquid to a gas from heat absorption (or at boiling point) today's fuel must not exceed that 9 PSI (winter) 7.8 PSI (summer) insuring that the fuel will not vaporize and boil off into the atmosphere. Staying under atmospheric pressure 14.7 PSI. So today's if FI systems are pressurized Just use your ballpark figure of 40 PSIG and the gas tank to the injection system is sealed and pressurized, you have raised the boiling point of the fuel, the higher the pressure the higher the boil off point where the fuel will change its state from a liquid to a vapor. This holds true with water and all liquids, same with fuel being just another liquid , unfortunately with today's fuel the boiling point on average somewhere around or slightly above 180°? Not 212°. I unaware of that until Dan got me digging in to this, thank you. As mentioned finding specific RVP values could be a difference maker, RVP values haven't been very easy to find. Does anyone know an easy way of finding out differences in the local gas stations RVP values? I can't seem to get anything other than General EPA regulation information.
    So bottom line, with the carburetor we obviously aren't going to pressurize the fuel system more than it's design, we must resort to cooling. I have the electric fuel pump, fuel lines routed away from the engine in front of the radiator circling back next to the brake booster vacuum line. My new DVG has the fuel inlet on the wheel well side of the float bowl. Spent all weekend re gasketing at the base, trying to build up the height away from the intake with insulated gasketing, unfortunately with many failed efforts. Opel intake manifolds require a very tight seal especially around the studs . I have it running with no sputtering on deceleration now and minimal surging (only some when cold). Using the 3/16" aluminum spacer I had fabricated by a machinist to an exact match to the intake with 4 8mm holes instead of the heat shield (better seal) and .225" phenolic spacer under the carburetor. It's as good as I've been able to do after re gasketing multiple times this past weekend. I'm going to drive it around for a week or so and retest using the acetylene & Wideband @ 2000-4000 RPM's (that's when I'm running the leanest). No point in continuing jetting until I can confirm that the vacuum leaks are no longer detectable. Moving forward, I'm curious to see if there's any noticeable difference without the heat shield. last Saturday morning after a good 70 mile highway drive 66° Outside air temperature, 10 minutes after shuttling the engine off (hood down) 183° Intake manifold 166° Carburetor body temperature. 20 minutes after shut down 184° Intake & 140° Carburetor temperature. That was with the exact same combination mentioned above with the heat shield shield between the spacer & the phenolic spacer all gasketed with 1/32 rubber-fiber sheet between, seems like the best gasket material I've found so far. I'm pretty sure I'll get another morning this weekend to repeat the same drive with the same ambient temperature. We'll see what happens.
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    7,000 Post Club My location wrench459's Avatar
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    Quote Originally Posted by The Cub View Post
    ... I'm going to drive it around for a week or so and retest using the acetylene & Wideband @ 2000-4000 RPM's (that's when I'm running the leanest). No point in continuing jetting until I can confirm that the vacuum leaks are no longer detectable.
    Highest vacuum is at idle and deceleration, this is the best range to look for intake track leaks.

    you'll be tuning to mask a problem if theres a leak in the system.

    Edit:
    VP list its rvp values in case your interested.
    https://vpracingfuels.com/master-fuel-table/
    Last edited by wrench459; 04-20-2017 at 07:30 PM.

    Si vis pacem, para bellum "If you want peace, prepare for war"

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    Opeler The Cub's Avatar
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    Quote Originally Posted by wrench459 View Post
    Highest vacuum is at idle and deceleration, this is the best range to look for intake track leaks.

    you'll be tuning to mask a problem if theres a leak in the system.

    Edit:
    VP list its rvp values in case your interested.
    https://vpracingfuels.com/master-fuel-table/
    Tks for the link. There's a gas station that came up 15 miles away on the VP website. I'll persue it with them tomorrow when they're open. Yes if I can fuel up at a gas station that gives me a fuel that won't start boiling until it reaches a higher temperature. That would be great! As far as when you say idle & deceleration you're talking about when the throttle plates are closed or primary just cracked open, coming downhill at 2 to 4K RPM's correct? Idle at 900 RPM's hasn't revealed anything obvious.

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    Opeler The Cub's Avatar
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    Quote Originally Posted by Swiftus View Post
    If you're looking for heat shield material, Metal Tech Industries material has worked well in my work at school. It's really inexpensive for raw materials from them (on the order of ~$25 for 2x4' sheets of dimpled stainless), but they are happy to work with you to build a custom fit heat shield if you like.
    Just want to thank you Jay, I contacted them and they were great people. One of their reps after taking with me at length on the phone, seemed very interested in the problem. Fed'xed me a nice letter pertaining to our conversation along with a couple of samples that he thought I could work with, one insulated and the other one wasn't. He also included reference information on a local exhaust shop here that they do business with and distribute their product from. Great guy, I get a good first impression from people like him who follow up & do what they say! I'm interested in following up with this product & also putting together some of the good responses & ideas that I've been getting from other Opeler's to improve things with summer coming up. I'm not opposed to shielding, there's just gotta be plenty of room for improvement from what worked well "back in the day".
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