Free Holley 750 Vacuum Secondaries !!!

StumpDrummer · 02-19-2009, 07:08 AM

A friend just gave me an old 750 vacuum sec holly and now for heavy modding
Sterling Im gonna need some help here !!!
Im wanting to thread the primaries put an insert in them to reduce the diameter of the hole and butterflies if needed to reduce low end bog
Ive been reading about the angle of the insert throat, the top needs to be somewhere around 20 degrees and the bottom of the insert needs to be from 7-12 degrees

Does anyone know the size of the stock carburetor venturies that came with the 80 model 7?

Sterling · 02-22-2009, 01:52 PM

Well, it's really not worth the effort. You're better off using the Nikki and tapping out the secondaries to turn them on a lathe.
I use 16* & 7* for inlet & outlet angles, respectively. Ideally, the inside diameter of the venturi at it's smallest should be 1/2 the outside diameter. With those angles & relative measurements, the venturi should be very close to 100% efficient. (proabably closer to 97%).
But your 750 is simply too huge. Even if you insert small primary venturis, the rest of the mods you'll need to get it to work basically amounts to re-engineering the entire half of the carburetor.
It's a very difficult task for no gain what so ever over a Nikki you could spend 1/50th the time modifying. Not only that, but mod the Nikki emulsion tubes to take Holley jets, and there's simply not a more tunable carb on the market for the 12a.
If I were you, I would put the effort into modding a Nikki, and then making that work with a RB holley manifold.
NOW you're talking!

If you were doing this with a RB prepped Holley 465, I'd say "go for it!". Giving some low end response to that package (carb + the beatiful manifold) would make it the top performance carb choice for the 12a-anyport, IMO.

The primary Nikki venturis measures 20mm inside diameter. I cut mine to 22mm, though it's not necessary for a stock/streetport 12a. I just do it to make the Sterling flow 465 cfm, else most folks won't even give it a second consideration.

StumpDrummer · 02-24-2009, 09:13 PM

Sterling
I ended up giving the 750 back to my instructor . It was too good of a carb to butcher if something went wrong.

Will a nikki bolt up to a common square bore flange?
If so ill probably just get one from you in the future.

I got a 390 on it now it does almost fair it pulls till about 7.5-8 k
then starts dying
the old Edelbrock 650 pulled to 11k but it died catastrophicaly
when I droped it...yep it cracked ...its easy to lose your balance on one leg in a shop

how large can you go with the secondaries on the nikki?
and how much airflow can I expect?

Im also going to be running a draw through turbo setup.
as my turbo is dying. Im gonna have got to get a new one soon!!!
I just dont know what size it will be yet, but it will be a little bigger than the old rayjay that was on it , Im wanting 18-20lbs of boost again no need for more than that. P.M. me the price so I can start saving!!

02-19-2009, 07:08 AM	#1
StumpDrummer Rotary Fan in Training Join Date: Feb 2009 iTrader: (0) Posts: 31 Rep Power: 0	Free Holley 750 Vacuum Secondaries !!! A friend just gave me an old 750 vacuum sec holly and now for heavy modding Sterling Im gonna need some help here !!! Im wanting to thread the primaries put an insert in them to reduce the diameter of the hole and butterflies if needed to reduce low end bog Ive been reading about the angle of the insert throat, the top needs to be somewhere around 20 degrees and the bottom of the insert needs to be from 7-12 degrees Does anyone know the size of the stock carburetor venturies that came with the 80 model 7? __________________ How can we possibly know where we are going (as a people ) when we dont even know where we come from!

02-24-2009, 09:13 PM	#3
StumpDrummer Rotary Fan in Training Join Date: Feb 2009 iTrader: (0) Posts: 31 Rep Power: 0	Sterling I ended up giving the 750 back to my instructor . It was too good of a carb to butcher if something went wrong. Will a nikki bolt up to a common square bore flange? If so ill probably just get one from you in the future. I got a 390 on it now it does almost fair it pulls till about 7.5-8 k then starts dying the old Edelbrock 650 pulled to 11k but it died catastrophicaly when I droped it...yep it cracked ...its easy to lose your balance on one leg in a shop how large can you go with the secondaries on the nikki? and how much airflow can I expect? Im also going to be running a draw through turbo setup. as my turbo is dying. Im gonna have got to get a new one soon!!! I just dont know what size it will be yet, but it will be a little bigger than the old rayjay that was on it , Im wanting 18-20lbs of boost again no need for more than that. P.M. me the price so I can start saving!! __________________ How can we possibly know where we are going (as a people ) when we dont even know where we come from!

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02-22-2009, 01:52 PM	#2
Sterling Premium Vendor Join Date: Feb 2008 iTrader: (2) Posts: 74 Rep Power: 17	Well, it's really not worth the effort. You're better off using the Nikki and tapping out the secondaries to turn them on a lathe. I use 16* & 7* for inlet & outlet angles, respectively. Ideally, the inside diameter of the venturi at it's smallest should be 1/2 the outside diameter. With those angles & relative measurements, the venturi should be very close to 100% efficient. (proabably closer to 97%). But your 750 is simply too huge. Even if you insert small primary venturis, the rest of the mods you'll need to get it to work basically amounts to re-engineering the entire half of the carburetor. It's a very difficult task for no gain what so ever over a Nikki you could spend 1/50th the time modifying. Not only that, but mod the Nikki emulsion tubes to take Holley jets, and there's simply not a more tunable carb on the market for the 12a. If I were you, I would put the effort into modding a Nikki, and then making that work with a RB holley manifold. NOW you're talking! If you were doing this with a RB prepped Holley 465, I'd say "go for it!". Giving some low end response to that package (carb + the beatiful manifold) would make it the top performance carb choice for the 12a-anyport, IMO. The primary Nikki venturis measures 20mm inside diameter. I cut mine to 22mm, though it's not necessary for a stock/streetport 12a. I just do it to make the Sterling flow 465 cfm, else most folks won't even give it a second consideration.