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#21
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Sorry-- "summer" is the #1 position on the pump cam.
the 73/81 jets I suggested are probably a little rich ,but I want to keep NALVAREZ on the safe side of ping while performing the drivability tuning.
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GOOD IDEAS ARE OFTEN FOUND ABANDONED IN THE DUST OF PROCRASTINATION Last edited by KEN CROCIE; 06-15-2024 at 04:57 PM. Reason: spelling |
#22
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all of previous responders are assuming the carb hasn't been improved by an "expert"
POWER--. Two items are holding back the power output. 1: Intake manifold. designed in the mid sixties as an aluminum replacement for a stock '65 intake, you're chocking off about 30-40 HP. 2: timing. The Edelbrock heads need about (depending on version} need about 38- 41 deg. total timing for max performance. I am assuming timing is set to 31 total to suppress detonation.
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GOOD IDEAS ARE OFTEN FOUND ABANDONED IN THE DUST OF PROCRASTINATION |
#23
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Should a 428, with 11:1 compression, 18* of base timing and a XE cam with a 236 intake lobe, only make 11" of vacuum at 900 RPM?
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I could explain all this to the girl at the parts store, but she'd probably call the asylum. White '67 LeMans 407/TH350/Ford 3.89... RIP Red '67 LeMans. 407/TH400/Ford 3.25 |
#24
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sounds reasonable to me?
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#25
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i82--me too.
What's your guess , Chip?
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GOOD IDEAS ARE OFTEN FOUND ABANDONED IN THE DUST OF PROCRASTINATION |
#26
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My gut reaction would expect 12-13" of vacuum on that combo, properly tuned and warmed up. Maybe the P4B, a non degreed cam and a generous PCV is reducing the number?
Maybe the carb's idle circuit is still way rich, and it would pick up if it were to be leaned some. That motor is likely going to want a 32-33 IFR and 70-ish LSAB, mixture screws 3/4" of a turn from seated. Just the fact that it's got a blocked power valve and a milled airhorn makes me wonder what else funky was done to it. That engine should pull hard to 5700. If it's not scaring the owner when he stomps it, something is seriously wrong.
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I could explain all this to the girl at the parts store, but she'd probably call the asylum. White '67 LeMans 407/TH350/Ford 3.89... RIP Red '67 LeMans. 407/TH400/Ford 3.25 Last edited by chiphead; 06-15-2024 at 11:58 PM. |
#27
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Once he has been helped in getting his primary side set up to work well then it’s on to his second side that likely has a blocked power valve also.
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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
#28
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As mentioned somewhat his combo of aftermarket heads flowing far higher than stock iron heads and a P4B intake is not the ticket for power production.
The runner expansion rate. ( port area ) is in the wrong direction. So there’s two problems with that. 1) the motor will not make the hp power or torque you would expect, and the power band the motor does have will only extend over a narrow rpm range.
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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
#29
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Get wide band O2 sensor for the AFR to put in the exhaust and you can see exactly what the carb is doing vs guessing! You can easily tune every circuit.
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Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
#30
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Quote:
Start on the primary side first. Your bog off idle and low power feel is from lack of a front power valve. There is really no amount of pump shooter and cam that can overcome the missing power valve. People don't realize that even light throttle tip in will involve the power valve even for just a second or two and that also helps to cover the lean spot you created when you cracked the throttle open. Someone was messing with that carb that didn't know what they were doing, they never have a blocked power valve in the front for a street application, or even a street strip hot engine application. First thing I would do is get a power valve in the front half of the carb. Typically start with a 6.5. If you go too high it may open too frequently at tip in and light throttle cruising. Typically a 6.5 is a good starting point and works well on engines that make 10-13 inches of vacuum. This will solve the issue of trying to cover a lean spot with a whole bunch of pump squirter. After that knock the front jets down to about 72's, you don't need a bunch of front jet with a power valve. From there you'll have to make sure your front blades aren't exposing too much of the transfer slot so it's not idling off the main jet on top of the idle circuit and instead should be idling off the idle circuit only. The power valve setup in front will solve your lean tip in stumble and weak power. Start there and report back. Then we can move on to other things. |
#31
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Off idle even up to 2500 also involves the idle circuit as well as power and main circuits. If tuning idle by rpm ans or vacuum be sure if an auto it is ion gear and the convertor loaded.
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Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
#32
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Quote:
The carb came from DaVinci Performance Carburetors in Houston. Last edited by nalvarez; 06-24-2024 at 12:38 AM. |
#33
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Quote:
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#34
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Quote:
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#35
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Im actually going to order an afr this week.
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#36
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I want to thank everyone for all of their insights. I have ordered some various jet sizes (70-80) and a 6.5 power valve to get started. I am also ordering an afr gauge to help with tuning. Based on everyone's responses, here's what I'm thinking of starting with.
73 primaries with a 6.5" power valve. 81 secondaries. What about the squirters? What would be a good starting place for those? It has 25's in there now. |
#37
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I looked up the carb. It's a garden variety 4150 double pumper, mechanical choke, non-adjustable airbleeds. The new ones are listed as 28 squirters in the front, 31s in back. A 428 is likely going to want a 31-34 squirter in front with a fast pump cam. Squirt speed depends on how tight the converter/gearing is.
I don't see mention of the transmission or rear gears. A double pumper is going to want a loose converter and/or deep gears to respond properly. Otherwise it's going to have a lazy response until the engine builds RPM. I would suggest re-reading the thread I linked to in my first response. It's a detailed tuning thread for my QF double pumper on my 400. It'll save me from re-typing it here. The idle circuit on a holley feeds the motor until 2500 RPM. So start there. I see where you mention that the car won't idle unless the mixture screws are 1.5 turns out. That's WAY too much for a 4-corner carb. A 4-corner carb will typically end up at 1/2-1 turn out in most applications. The QF on my 400 is at 5/8 of a turn from seated on all 4 screws. I assume this means the transition slot is too exposed on the primaries, in addition to the secondaries being set improperly. This usually results in the idle screws being turned out too far, a high, unstable idle, blackening the plugs quickly, and a big hesitation when opening the throttle. The transition slot/idle throttle plate opening sets the table for the entire rest of the carb tuning.
__________________
I could explain all this to the girl at the parts store, but she'd probably call the asylum. White '67 LeMans 407/TH350/Ford 3.89... RIP Red '67 LeMans. 407/TH400/Ford 3.25 |
#38
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Well, It turns out I have a new problem. I somehow managed to crack the baseplate on the carb. I used a torque wrench and only tightened it to 12 ft lbs... but I guess that's all it took. Looks like I will be getting a new carb. Im thinking Im going to try out a Quick Fuel SS-780-VS. I'll get that bolted on and report back with how it's running.
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#39
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Quote:
https://youtu.be/nHfmYUH4C-g?si=7o3JCxfOIVFibfvF
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66 GTO, 495, M22, Strange S-60 w/4.10 Sold new at Ace Wilson's Royal Pontiac http://www.youtube.com/watch?v=cUHC-Z8xhtg |
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