Author Topic: Crossram manifold  (Read 35682 times)

PHAT69AMX

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Re: Crossram manifold
« Reply #75 on: November 01, 2018, 10:28:07 PM »
? The FIRST Holley Double Pumper Carburetor ?  ???

Further research unearthed a clue that as Jon Mello suggests the
Holley List 4295 GM # 3957859 2nd Design 302 Cross Ram may NOT be the first...
as he mentioned in the text accompanying the possibly Dec 1967 photograph of Bill Howell
and Mark Donohue testing a "Double Pumper" on the Trans Am Camaro at Marlboro Raceway...

GM # 3955205 Holley List 4296 is the 800 CFM (per GM SS Special HD Catalog)
Double Pumper from the '69 ZL-1 Camaro and I think the 1968 L-88 Corvette 427 ?

... Need more research, the same GM SS Special HD Catalog page 37 for 396-427-454 says:
"The stock 1 x 4 Barrel Carburetor on the large block Heavy Duty Engines
was the 850 CFM Holley with throttle bore of 1.75"."

Yet fails to provide GM No., holley List No. or if a Double Pumper...  ???

Notice that the L-88 Holley List Number is "Later / Higher" than the CR 302, but buy only 1 digit !
Yet the L-88 List 4296 800 DP GM Part No. is "Earlier / Lower" than the List 4295... hmmm...

? Anyone have information on what OEM Carburetors were used on the 1967-68-69 L-88's ?
Appears the Stock L-88 Carburetor may be an 850 CFM Double Pumper,
but have yet to find Part or List Numbers and one with 1967 or 1968 Date Codes...
« Last Edit: November 01, 2018, 11:04:29 PM by PHAT69AMX »

Jon Mello

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Re: Crossram manifold
« Reply #76 on: November 02, 2018, 03:12:38 AM »
I have not researched carburetors on your level so it will have to be someone else to come to the rescue.
Jon Mello
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PHAT69AMX

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Re: Crossram manifold
« Reply #77 on: November 02, 2018, 06:00:11 PM »
Ok, Thank You, I put this in the Cross Ram thread since maybe it had the 1st Holley Double Pumper.

Holley List 4295   GM # 3957859 = Double Pumper = 1968 302 Cross Ram, 2nd Design

Holley List 4296   GM # 3955205 = Double Pumper = 1968 L-88 2nd Design, and 1969 ZL-1 427
« Last Edit: November 02, 2018, 06:43:23 PM by PHAT69AMX »

BRG Z28

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Re: Crossram manifold
« Reply #78 on: November 05, 2018, 11:13:49 PM »
I feel lucky I was able or find two 4210 matching date carbs in the last couple of months. Is there any trick to get these carbs to run good? Everything I have read, they have a big “bog” when the secondaries kick in. I know they will not rever run as well as my 4295’s but is there any recommendation or “tricks” to get the maximum performance and drivability out of the? Thank you,

PHAT69AMX

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Re: Crossram manifold
« Reply #79 on: November 06, 2018, 10:31:17 PM »
Congrats on the "nice find"  8) ...
? Intend to post up a bunch of nice sharp pictures of those 4210 Carbs ?


Only from looking at vintage information, NOT from real world experience,
and something I'd NOT do to the original 4210 Base Plates...
but would do to a pair of 2nd correct replacements,
or even better fit replacements with the later "W" Slot & Roller Linkage, ? Progressive,
where the 4210 is a "Constant Radius" Slot & Roller Linkage, ? 1:1.

The "Constant Radius" can be seen Modified in vintage pictures
by grinding an "Entry Flat" at the 1st part of Slot's Front Edge,
or even fitting with a small Adjustable Plate.
This delays Secondary Opening improving non-bog chances when they open.

Understanding is for those 4210 Type Single Pumper Mechanical Secondary Carbs
the Secondary Main Air Bleeds should / must / are / will be Very Small...
So the Secondary Boosters come on real quick, and probably drip otherwise...
tough on mid-range drive-ability but is what makes that arrangement have a chance of working... imho

PHAT69AMX

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Re: Crossram manifold
« Reply #80 on: November 10, 2018, 09:55:12 PM »
Thank You BRG Z28 for these pictures of a pair of 1:1 Slot & Roller Mechanical Secondary Single Squirter
1968 302 Cross Ram 1st Design GM # 3941140 Holley List 4210 Carburetors with
"875" July, 5th Week, 1968 Date Codes, # 4743 and # 5806 Metering Blocks...
? 5th Week July 1968 Date Code any "clue" to when the 2nd Design List 4295 Carbs were Phased In ?...

Jon Mello

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Re: Crossram manifold
« Reply #81 on: November 11, 2018, 10:13:30 PM »
Wayne Guinn's book "Camaro Untold Secrets", which you might find an interesting read, says...

Holley 3810 (which he states is p/n 3941140) was specified for use approximately Nov '67
Holley 4210 (which he states is p/n 3942595) was specified for use approximately Mar '68
Holley 4295 (which he states is p/n 3957859) was specified for use approximately May '68
Jon Mello
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BRG Z28

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Re: Crossram manifold
« Reply #82 on: November 12, 2018, 02:02:14 AM »
Jon, the 4210’s that were just posted June of 1968.

PHAT69AMX

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Re: Crossram manifold
« Reply #83 on: November 12, 2018, 02:23:47 AM »
Wow, using Google some places want $190 + for that book... wow... maybe can find it at the Library...
But, ah, it is a source of the Carb info that appears to contain errors maybe...
A few post back it was discussed, a Fuel Pipe Part Number found it's way in there somehow...
Yeah, who's to say how long Holley kept crankin' out 1st Design 4210's, to use up parts produced maybe?
Or maybe the was a minimum quantity ordered requirement by Holley for Chevrolet... or even SCCA...

Anyone have say a 1971 or so Holley Catalog ?  To look up the 4210 & 4295 Specs
in the Numerical Listing, mainly orig Squirter Size(s), Jets, Power Valves, Venturi & Throttle Dims...
Pretty sure both have all (4) 1-9/16" Throttle Dia 1-1/4" Dia Pri Venturi and 1-5/16" Dia Sec Venturi.

1988 is the oldest Holley Catalog I have and both 4210 & 4295 are absent from the Numerical Listing in the back...

Jon Mello

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Re: Crossram manifold
« Reply #84 on: Today at 03:24:13 AM »
The 4210s above appear to be dated 5th week of July '68.

Sorry, I do not have any Holley catalogs but maybe someone else can help.
Jon Mello
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