So, I've been combing the internet unsuccessfully looking for info on tinkering with the Holley 0-9776 450's. These carbs are a mechanical secondary without a secondary accelerator pump or metering block.

I found this site and have been reading any threads that have 0-9776/9776/ or Holley 450 as keywords, but I still haven't found what I'm after. It seems that possibly 38 Special or Boost Engineer might have thoughts or experience with using these carbs, so that's why I tagged them in the title. (Silly 25 post rule until PM's and all.)


The setup: I'm hard headed and like most of you here, I wanted to do something different... so I have an aluminum LS 6.0 with L92 heads and an LS9 cam. (264ci, 10.4:1 CR, 211/230 @.050 .558/.552 lift with 1.7's 122.5 CL) This is topped with a Holley tunnel ram with a pair of 450's. Feeding this is a 98mm pro mod set for 12psi. Pretty much an extremely goofy (and mismatched) budget build that should be fun. It's going in a 71 SB C10 that rides on air and lays frame.

The question: I've read where these carbs need to be run in pairs as that is the reason they don't have a second accelerator pump. It seems that the go-to carb configuration with blow thru is a double pumper. Can these carbs be ran as is if they are setup as a pair? Is it advisable to put a metering block on the secondary side? Or is it possible to turn these into a double pumper by trading some parts off of other carbs?


I've always been an EFI guy, so this is all new to me. I've been reading up on how it all works, but when it comes to experience on swapping pieces from one carb to another I'm an absolute noob.

I can go pull bowls off and take pictures if need be.

 

I've been firming up my understanding and logic behind all of this this morning...

I think the carb size is close to being correct for my setup from what I have read. It looks like the small venturi are why this model carb doesn't need the second pump, (the velocity is high enough that the lean stumble when the secondaries open doesn't happen?) and a 4160-4150 conversion kit will get me the secondary metering blocks. From there I just do the hangar 18 mods and start figuring out what it likes?

I am going to weld velocity stacks on top of the o-ring transdapt carb bonnet flanges, then build a hat on top of that. With a setup like that, do you think the vent tube extensions would be needed, or are those something you only play with if you have trouble richening it up?

 

I'm just going to keep adding to this thread as I find information on my own. Hopefully someone will chime in...or somebody down the road will find the info useful.

So I had already know that Procharger did this on their Nova many moons ago, but I found some solid info finally. MTPTurbo built the carbs. They used a pair of 0-9776 450's with metering block conversion kits, swapped bowls (to have a feed line per bowl,) milled horn, high flow needle and seats, nitrophyl floats (mine came with nitrophyl floats,) and plugged high speed air bleeds.
This setup was on a pump gas 427 big block that made 1196hp at 8100 rpm. It went low 8's at 170.

So knowing all of this, I am going to carry on with using the 450's. I'm hoping that with the small venturi that the secondaries won't cause a bog, and that with the small size in general spread across the two carbs, I'll get some decent street characteristics.

Quick Fuel has a metering block conversion kit for similar money as the holley kit. So I'm thinking about getting a pair of 793-34-66QFT's to replace the metering plates, and then a pair of 793-34-8QFT's to swap out the primary bodies. I won't bother with the bowls as I don't plan on making over 650hp for the time being. If I have any issues feeding them, I'll cross that bridge when I get there.

From there, I'll start down the blow-thru mod path. I'll make a bonnet that bolts down over both carbs and uses oring flanges to seal. In that bonnet will be tube extensions. I'll go ahead and start tuning with them instead of trying it without them only to find out I needed them in the first place.

Metering block conversion
Primary block

 

I like hard headed builds like this. Do you have a build thread? Interested in the rest of the setup

 

I don't have one yet. Just found this site recently. I'll make one once I make a little progress in the actual turbo department. (Kind of a recent development with the decision to go forced induction.)

Ive done two EFI Vortech builds in the past. An S trim on a 4.3 in an S10, and a Y trim on an LS2 in a Trailblazer SS.

Here are some pictures of the C10. Originally I was going to use two zex perimeter plates on the tunnel ram. I had started work on a top that would keep the carbs close to level because the Porterbuilt products I used to drop the truck created terrible drivetrain angles. I've scrapped that idea and have started the process of dropping the motor down a little over an inch in the front, and raising the tail of the transmission up almost 3 inches. (lots of metalwork involved....not fun.) A buddy of mine was kind enough to lay the peer pressure on thick and offer me a deal I couldn't refuse on a turbo since his build was changing directions...and now my build is changing directions!

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OOOHHH... Carb gurus, I have two Holley street avenger's on the shelf. One is a 570, one is a 670. Can I pull the metering blocks and bowls off of those and put them on my 450's?

 

Again, nothing technical to add but....
Mother of God that's some nice work..

 

i havent seen anybody use the 450 carbs (i have a set on the shelf) nice project

 

The only two problems I see is the lack of a rear metering block, and the potential for a lean stumble. Personally, I would start with the hangar 18 mods, and see what happens from there. You may be able to get it there without the secondary blocks. I would recommend doing center hung float bowls, and probably .110" needle and seat, just for peace of mind. And if you don't already have an ignition system, look into the Smart Spark LS by Daytona Sensors. I am more than happy with mine.