[MarkS57]

Curious, was there ever an 800 vacuum secondary version? I guess it would be a 4175 series?

[Tom Vaught]

Yes, 4175 all of the 4175 carbs are 650 cfm size. (According to Mike Urich books)
Tom V.

[lust4speed]

My original Quadrajet died an early death in late 1974 and the local speed shop had the 800 CFM Holley spreadbore on sale for $74 plus tax. Came with a 30cc front shot and 50cc rear. Got a little more serious in the mid 80's and had the choke tower milled off. Didn't pick up even one horsepower on the dyno with back to back testing. Later on tried a heavily modified Quadrajet and then a little larger squarebore and both were basically a push with the spreadbore. Somewhere I have the jets plotted out for changes in air density at the track, but off-hand do remember that the secondary's needed some good sized jets to maintain a proper AF ratio.

[Tom Vaught]

Originally Posted by lust4speed

Somewhere I have the jets plotted out for changes in air density at the track, but off-hand do remember that the secondary's needed some good sized jets to maintain a proper AF ratio.

That would make sense due to the very large secondary flow path.
2" throttle blades, If I remember correctly.

Tom V

[NeighborsComplaint]

Originally Posted by MarkS57

Curious, was there ever an 800 vacuum secondary version? I guess it would be a 4175 series?

To my knowledge, the 800 spread bores were all mechanical secondary units in 2 flavors: List 6211 Single inlet w. balance tube and small side hung float bowls & List 6212 Dual feed w. cathedral style center hung float bowls. here were also Marine/Mercruiser variants of these 2 styles.

[MarkS57]

Originally Posted by NeighborsComplaint

To my knowledge, the 800 spread bores were all mechanical secondary units in 2 flavors: List 6211 Single inlet w. balance tube and small side hung float bowls & List 6212 Dual feed w. cathedral style center hung float bowls. here were also Marine/Mercruiser variants of these 2 styles.

Thanks, the one we put on my buddies 70 W30 was the single inlet version. I guess the only thing close to an 800 spread bore w/ vacuum secondaries would be 750 4011. Almost bought one when they came out.

[NeighborsComplaint]

Originally Posted by MarkS57

Thanks, the one we put on my buddies 70 W30 was the single inlet version. I guess the only thing close to an 800 spread bore w/ vacuum secondaries would be 750 4011. Almost bought one when they came out.

You're right. I forgot there was a spreadbore version of that carb!

Summit Racing has a square bore version (M2008 Series) of that carburetor made exclusively for them by Holley as a lower cost alternative to the Holley carburetors.

https://www.summitracing.com/search/...20%28Search%29

[NeighborsComplaint]

The OEM spec for this carb was an 8.5 Primary power valve instead of the typical 6.5 used in most Holley performance applications. Do the small primaries used on these carbs creates a stronger vacuum signal? The Secondaries use a typical 6.5.

[Tom Vaught]

Use of the 8.5" Power Valve vs the typical 6.5" Power Valves means that Holley Engineers wanted to add more fuel to the engine EARLIER in the acceleration. HIGHER NUMBER MEANS THE EXTRA FUEL COMES SOONER.

Tom V.

[Formulas]

There is also a list 6213 800 cfm mech sec. Spreadbore as in my personal example

[JSchmitz]

Mine is list #9023

[Tom Vaught]

Originally Posted by JSchmitz

Mine is list #9023

That is a nice Marine 800 cfm Holley Spreadbore carb built with the "Johnson Linkage" like most all of them were.
"Johnson" was a VP in Holley Engineering.

Tom V.

[JSchmitz]

Originally Posted by Tom Vaught

That is a nice Marine 800 cfm Holley Spreadbore carb built with the "Johnson Linkage" like most all of them were.
"Johnson" was a VP in Holley Engineering.

Tom V.

Thanks Tom! It is a nice carb. I bought it from an old carb shop that used to be in the St. Louis area. Max Megers (Spelling?) at CM Performance. Very smart guy. Ran a shop out of his basement. His house looked like hell. Gutter hanging down etc. Then you walked around to the walk-in basement shop area and it was like the cleanest pro shop ever LOL. Rumor has it that the nose candy dragged him down.

Can you enlighten us as to what the "Johnson Linkage" is?

[Tom Vaught]

Cale Johnson thought there should be more "flexibility of transition" with the Holley carbs vs the cam and slot 660/850 center squirter (Tunnel Ram Carbs) and the Vacuum secondary carbs. So he came up with the "johnson Linkage" See Pictures.

1) He designed a PIVOT BOSS on the mainbody of the carbs.

2) he designed a slot and roller profile like the center squirter carbs but the slot went left to right vs up and down.

3) He added a link from the cam part to the secondary lever that opens the secondary blades.

So now the carb had a lot more 'Transition" from just the Primary Barrels to the Secondary Barrels being opened and traveling to WOT.

A very good design but a lot of parts required and EXPENSIVE per carb.
Most people thought it was over-engineered.

So the Later (after Johnson retired) new double pumper carbs using a simpler unique Primary plate and link now use the short rod to activate the opening of the secondary barrels. See last picture.

Tom V.

[49Diesel]

Long ago I ran the 800 spreadbore on a 12.5/1 396 , 3.08/3.28 duration 500/505 lift . Carb ran really nice , I liked the Holley for the ease of setting the floats . Nice carb and no need for a adapter plate to bolt on a quadrajet type intake .

[NeighborsComplaint]

Originally Posted by Tom Vaught

Cale Johnson thought there should be more "flexibility of transition" with the Holley carbs vs the cam and slot 660/850 center squirter (Tunnel Ram Carbs) and the Vacuum secondary carbs. So he came up with the "johnson Linkage" See Pictures.

1) He designed a PIVOT BOSS on the mainbody of the carbs.

2) he designed a slot and roller profile like the center squirter carbs but the slot went left to right vs up and down.

3) He added a link from the cam part to the secondary lever that opens the secondary blades.

So now the carb had a lot more 'Transition" from just the Primary Barrels to the Secondary Barrels being opened and traveling to WOT.

A very good design but a lot of parts required and EXPENSIVE per carb.
Most people thought it was over-engineered.

So the Later (after Johnson retired) new double pumper carbs using a simpler unique Primary plate and link now use the short rod to activate the opening of the secondary barrels. See last picture.

Tom V.

Interesting. I see quite a few of the Holley Marine Spreadbores for sale and was thinking how they might be better tuned for transition and off idle responses than automotive aftermarket models given the demands of marine use.

[A.W.Dille]

I ran one on my GTO for years. In fact I ran both the 650 and 800 cfm spreadbore carburetors. They performed very well at the track. The 800 worked exceptionally well with a stock iron intake but it also gave good performance on a Torker intake.. One of the best carburetors I ever used.

[JSchmitz]

Originally Posted by Tom Vaught

Cale Johnson thought there should be more "flexibility of transition" with the Holley carbs vs the cam and slot 660/850 center squirter (Tunnel Ram Carbs) and the Vacuum secondary carbs. So he came up with the "johnson Linkage" See Pictures.

1) He designed a PIVOT BOSS on the mainbody of the carbs.

2) he designed a slot and roller profile like the center squirter carbs but the slot went left to right vs up and down.

3) He added a link from the cam part to the secondary lever that opens the secondary blades.

So now the carb had a lot more 'Transition" from just the Primary Barrels to the Secondary Barrels being opened and traveling to WOT.

A very good design but a lot of parts required and EXPENSIVE per carb.
Most people thought it was over-engineered.

So the Later (after Johnson retired) new double pumper carbs using a simpler unique Primary plate and link now use the short rod to activate the opening of the secondary barrels. See last picture.

Tom V.

Very interesting! Thanks!

I switched to a Q-jet only to be able to control the secondary opening rate. Sixty foot times got better and reactions times got more consistent. The Q-jet had a noticeably smoother idle. Both carbs MPH at the track were nearly identical. The double pumper worked better when I have the stick in the car.

[unclescratch]

I ran a #6910 800 SpreadBore on my 462. Played around a bunch w/jetting & wideband. Settled on Holley's 'out of the box' jetting as the best for me. I would use one again.

[NeighborsComplaint]

Based on the replies here, I am anxious to try it out, but first I need to get the car out of "body shop jail" again.

I had the trunk floor replaced and the shop had some space where I could store for the winter so I left it there. I made arrangements for him to touch up tiny rust flowers on the bottom edges of the doors this spring and then decided to have him wet sand and buff the entire car.

He says lost a body man and a helper and is a month behind. Same story, different shop. I honestly believe these shops just like having a "shiny object" hanging around hoping to attract more business they can't handle.