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Topic: Holley 750 DP w/auto tranny?

in Forum: C3 Fuel, Emission Control, and Exhaust Systems

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Holley 750 DP w/auto tranny? (6/16)
6/16/08 11:50am

VetteSpecialties
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Mounds View, MN - USA

Vette(s):
70 LT1 coupe, 69 350 HP coupe, 69 390HP 427 coupe, 71 LS5 convert, 85 coupe, 93 coupe

Joined: 5/24/2007
Posts: 1031

I completely agree with Joel's comments. A double pumper is great for drag racing, but sluggish on the street, unless you have a much bigger, more radical engine. It is hard to beat an original Q-jet when rebuilt and properly recalibrated for your engine. If you set against the Q-Jet, I would look first at the new Barry Grant street carbs.

Larry

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Holley 750 DP w/auto tranny? (7/16)
6/16/08 11:05pm

lukesvette

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HOWELL, NJ - USA

Vette(s):
1979, Targa Blue (72 Color), Pace Car rear spoiler, L88 hood, Dark blue factory interior, 525HP 406, HD 700R4, 370 gears,Steeroids, composite rear spring, TT IIs wrapped in T/A Radials.

Joined: 5/18/2004
Posts: 6812

A vacuum secondary BG is a great carb. A 750 sounds like a good size for your 383...call them directly with your specs and they will tell you the best application.

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Holley 750 DP w/auto tranny? (8/16)
6/23/08 1:42pm

VETTERBOB

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DUNEDIN, FL - USA

Vette(s):
1969 COUPE CORTEZ SILVER, BRIGHT BLUE INTERIOR 383 cu. in. 512 HP. Hooker headers w/ side pipes PS PS AC AM FM STEREO. 68,000.MILES C5 5oth Anniversary Coupe , auto.350hp

Joined: 10/22/2004
Posts: 832

the edlebrock will run with the 383 just fine. A #1406 750 w/vac secondaries. It WILL need to be calibrated by someone that knows how to tune hp engines. I had a hell of at time with mine until it was done right. THe distributor need callibration as well.

are you running pump gas with that compression?

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Holley 750 DP w/auto tranny? (9/16)
6/24/08 11:35am

neuroclast
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Charleston AFB, SC - USA

Vette(s):
1979 Cream Beige Coupe w/383 & 700R4

Joined: 10/31/2007
Posts: 111

I am running 93, but it's not working well. It pings like crazy when under load at low rpms. I'm thinking about trying a thicker head gasket to see if it will help any :(

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Holley 750 DP w/auto tranny? (10/16)
6/24/08 2:22pm

VETTERBOB

i had exactly the same problem. the head gasket will not solve your problem. if indeed you at greater than 11:1 pump fuel going to be an issue. try some racing fuel to bring up your octane and see what happens. your symtoms are identical to mine were. and with out the adjustments it will continue. I had 5 different carbs on mine so that isn`t the problem. it`s the tune. good luck.

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Holley 750 DP w/auto tranny? (11/16)
6/24/08 3:09pm

neuroclast
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Charleston AFB, SC - USA

Vette(s):
1979 Cream Beige Coupe w/383 & 700R4

Joined: 10/31/2007
Posts: 111

Just curious, what makes you sure the HG won't help? It should lower the compression at least a few tenths. I can't run race fuel, it's a DD and I'm not that rich haha. But when you say "it's the tune" what do you mean? I tried 2 sizes higher on the jets and a size smaller on the rods. The dist has the heaviest springs possible, and it does it even with the vac advance unplugged. I'm not sure what part of the tune could fix it?

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Holley 750 DP w/auto tranny? (12/16)
6/24/08 3:15pm

VETTERBOB

JOSH,, I FORWARDED TO NOSAL1 TO REVIEW, HE BUILT MY MOTOR AND COULD GIVE YOU BETTER INSIGHT.

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Holley 750 DP w/auto tranny? (13/16)
6/24/08 8:02pm

kstyer

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CUYAHOGA FALLS, OH - USA

Vette(s):
1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!

Joined: 12/2/2003
Posts: 6424

Ping is caused by one thing. Heat. When you reach 2500 deg F inside the cylinder, you begin to get ping and knock. You also produce NOx at this point.

EGR valves are designed to cool the cylinder in regular engines. If you don't have one, and it's not likely, forget that part.

Alum cyl heads run cooler than cast iron, but that is a lot of expense and work.

Retarted timing runs cooler, to a point.

High octane burns cooler, but for a longer period of time. That helps

Cooling system temp should be kept as low as possible.

Higher compression promotes heat. Lower compression runs cooler.

Richer mixtures burn cooler than lean mixtures.

A good set of headers remove more heat, but allow more fresh air into the cylinder, which in turn could run hotter.

All of these things come into play with the tune.

Perhaps the first thing I would do with your car is try using some cooler heat range spark plugs.

kstyer2008-06-24 17:13:04

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Holley 750 DP w/auto tranny? (14/16)
6/25/08 6:14am

neuroclast
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Charleston AFB, SC - USA

Vette(s):
1979 Cream Beige Coupe w/383 & 700R4

Joined: 10/31/2007
Posts: 111

I don't have an EGR valve. I have alum heads. I've tried retarding the timing a ton with no success. I have longtubes. The plugs I have now are NGK R5672A-8. They're an 8 heat range with 35 gap. Do you think I should go even colder than that?

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Holley 750 DP w/auto tranny? (15/16)
6/27/08 12:26pm

nosal1
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Dunedin, FL - USA

Vette(s):
1980 Corvette Torch Red with Gold metallic 370HP/350 CU.IN.Turbo 350 w/shift kit.Originally CA.Car with 305 CU.IN.

Joined: 3/21/2006
Posts: 262

Josh,

         As VETTERBOB mentioned we had a bit of a problem with the pinging of his 383 as well and as Bob stated he/we tried several carbs and went back to Edelbrock 800 CFM,however the relief came when we took it to another friend who had Sun distributor analyzer and set the distributor( i.e. setting spring tension with certain springs and balanced weights) up to a static timing of 26 degrees advance and have the mechanical advance increase to a total advance of 36 degrees at 2800 rpm instead of 3300 rpm.
     You will have to take the car to a mechanic who has the distributor machine and also has a touch and feel for adjusting the carbs which may include him to change primary and secondary rods and jets in the carb..
      I am sorry but there is no quick fix for the pinging problems.Bob's engine was the only 383 I built that had a pinging problem and I have built many,his was the first in Florida.
      I do not know if this is any help,however may give you a direction to check out.

    Sal C.

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Holley 750 DP w/auto tranny? (16/16)
6/27/08 12:38pm

Josh,

Also you will need to go to a cold plug or as cold as you can get depending on the heads.Early heads like Bob's would use AC R42 if you can get them and if you have later model heads (peanut plug instead of 13/16" plugs) AC R43 as opposed to AC R44 or an equal in aftermarket,Bosch,NKG,or any major brand other than Motorcraft(Ford Plug I have seen these used in Chevy engines and causes throwing up everywhere)Unfortunately Axcell does not have a cold header plug which I have used successfully..
Take care and good luck.
Sal C.

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