holley hp main body - best metering blocks?

[benno318]

just curious, i have a new holley 134-300c hp 750cfm main body - i was going to upgrade a crusty old 4777 i have with this body just for street use, but a friend of mine has decided to go circuit racing (road racing) next year and i am wondering if it is worth the effort on purchasing some new parts to use with it, i will either sell or loan this carb to him for as long as he needs it.

what baseplate would be the best to use - engine is not built yet but the basic application is a 5 litre v8, solid roller cam, high rise single plane intake, max rpm about 7000-7500. also of note is the carb must look period to an extent (that means no polished aluminium or billet as i interpret the rules) will any of the different sized baseplates change the flow of the carb by very much? or is that largely dictated by the venturi size?

metering blocks - surely there are better available than the 4777's, might have better fuel curves??

has anyone done this, is this even worthwhile, or am i better to tell him to just buy a new holley hp or similar carb brand new?

any input welcome and much appreciated. thank you.

[raceczar]

BLP.


That is all.

[jmarkaudio]

The original stuff works just fine, only a couple things you need to do with the metering blocks. First is is find another primary block if you want to make it 4 corner idle, if he plans to run a lot of cam it may help a little. If you can't find a used block BLP sells a Holley 11180 block that will work. Keeping it 2 corner works fine as well, be sure to measure the primary and secondary idle bleed sizes as they are different front and rear and you need to mimic those sizes in the new body to start with. Going to 4 corner start with .075 for idle air bleeds.. Thread the idle feeds to allow you to tune them, the link below explains how to do that. As long as the stock base is in good condition keep it, the transition slots are smaller than some of the aftermarket bases, a good thing. BLP billets are my favorite if you can use billet.

http://racingfuelsystems.myfunforum.org ... ?f=25&t=18

[MadBill]

Mark probably has 100X more carb experience than I have but being anything but humble, I'll share my thoughts anyway:

The original engine in our 8,000 RPM SBF road racer was 5.0 L. and it ran like gangbusters (630 HP) with a Braswell that flows over 1,000 CFM. Any number of experts will suggest a much smaller carb, and it's true something like your 750 will be easier to tune, but you'll be giving up some top end power.

I'd cost out a build up from your body Vs. buying a suitable new or good used carb. It might be like the guy who came across a Bugatti grill and plans score enough other bits to build a car...

[benno318]

thanks for the advice so far, madbill that bugatti example you quote was exactly why i asked the question, made me have a laugh!!

this engine i expect to only have between 430-470hp due to rules and reliability factors. want to run avgas despite it not being "the best" fuel simply because it does not have a problem with vaporising, leanouts, vapour lock and such, like some of the poor quality pump fuels have where we race. lots of our racing is in the heat of summer.

[Kevin Johnson]

... It might be like the guy who came across a Bugatti grill and plans to score enough other bits to build a car...

[MadBill]

Perfect!!

[F-BIRD'88]

I did this exact build-upgrade on a 4777 carb. It works real good.
As stated the air bleeds need to be dialed in and the stock bodys air bleeds are your
default starting point.



This carb mod works real good for me needing only minor primary idle air bleed fine tweeking to get it right. (stock 4777 metering blocks)
This is best done by hand filing the idle air bleed starting at .062" (1/16")
using a drill bit to hone it.
and fine tune using a afr gauge to check off idle throttle transition AFR progession. The air cleaner makes a difference.
Do your final check with the air cleaner installed.

If you don;t have a air cleaner. Get a good one. See recent thread on this.

Not hard to do... good results. Could not improve on the recommended jetting
74pri -85sec.
it is now one of the best carbs I have had in 40 years.

If you build and then lend your friend a good carb, you will never get it back.

[MadBill]

...If you build and then lend your friend a good carb, you will never get it back.

X2! I've 'loaned' no fewer than three good Quadrajets to one pal and each time he's sold the car with my carb still on board.

[benno318]

searching the 'bay last night and found an 80509-1 830cfm hp, its used but "in good working order" the guy wants $400 for it, they are well over $1000 new here - i sent a message asking has it been modified in any way - i am thinking if its unmolested, at that price it would be a good buy for old mate and i won't have to ask for my carb back that way!! ha ha

[F-BIRD'88]

get your bud to lend you $400. Then lend him the carb..

[BirdMan]

get your bud to lend you $400. Then lend him the carb..

I LIKE that!