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Old 07-17-2010, 01:23 PM
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Quick fuel HR 650 or Holley 4777?

Hello,

I have a Chevy 350 in a Cobra, for the street and sometimes a trackday.

At first I had a Holley Street Avenger 670, but the carb. was not good enough for what the engine wants.
It was running (to) lean 14.2:1 A/F. No vacuum leak, and fuel pressure is 5 psi (at WOT).
Even with lighter springs there is no improvement. According to the dyno man the problem is in the metering block, bigger jets are not the solution.
Now I am trying to find a carb. more suitable for the engine.

My first thoughts where: Holley 4777 and I found a Quick Fuel 650 HR series on the internet.
Now I am confused, Quick Fuel HR is relative new on the block, at least here in the Netherlands, but is it any good?
On the other side, Holley Double pumper is (most off the time) fail proof.
Is there somebody that can blow my fog away?


Thanks!

Specs:

Pistons: STL-H618CP40. +3.5 cc
Heads: World Products S/R Torquer. 67 cc
Cam: Xtreme Energy XE268H.
Headgasket: Felpro 1003
Headers: Blockhugger 1 5/8
Exhaust: 2.5 whit X pipe
Ignition: Dui Hei, 36 degree total
Intake: Holley street dominator (hly 300-36)
Gearbox: Tremec tko 500
Ratio: 3.54:1
Tire: 275/40/17

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Old 07-17-2010, 02:07 PM
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how much compression are you running? and whats the lift and duration on tthat camshaft?
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Old 07-17-2010, 02:33 PM
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Compression 10.5, cranking compression 190 psi

Advertised Duration .268 int .280 ex/Dur @.050
224 in .230 ex/ Lift .477 in. .480 ex
lobe Separation Angle 110.

I have retard the cam 4 degree.
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Old 07-17-2010, 05:07 PM
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that holley would be the best, but for that fact it would prb do the best with the 750 4779 double pumper, i dont know what the jetting will be from out of the box, but im running a .60 350 with flattops, 882 heads milled 125 thousands to get the compression at 10.1 that i wanted and a compcam 280h .480"/.480", i had carbs on that motor like iv never seen, from 600-750 eddys to 600 holley to street avenger 670 back the 600 holley and the my buddy at L.A. rod shop told me that a good mildly bulit 350 can use every bit of a 750dp, so i had a older 3310 holley sitting in the shop, i bulit it and put a 4.5 power valve in it and jetted it down from 74 to 65 and that made all the diff, that motor has never ran better!!!
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Old 07-17-2010, 06:59 PM
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Quote:
Originally Posted by Onsjos
Hello,

I have a Chevy 350 in a Cobra, for the street and sometimes a trackday.

At first I had a Holley Street Avenger 670, but the carb. was not good enough for what the engine wants.
It was running (to) lean 14.2:1 A/F. No vacuum leak, and fuel pressure is 5 psi (at WOT).
Even with lighter springs there is no improvement. According to the dyno man the problem is in the metering block, bigger jets are not the solution.
Now I am trying to find a carb. more suitable for the engine.

My first thoughts where: Holley 4777 and I found a Quick Fuel 650 HR series on the internet.
Now I am confused, Quick Fuel HR is relative new on the block, at least here in the Netherlands, but is it any good?
On the other side, Holley Double pumper is (most off the time) fail proof.
Is there somebody that can blow my fog away?


Thanks!

Specs:

Pistons: STL-H618CP40. +3.5 cc
Heads: World Products S/R Torquer. 67 cc
Cam: Xtreme Energy XE268H.
Headgasket: Felpro 1003
Headers: Blockhugger 1 5/8
Exhaust: 2.5 whit X pipe
Ignition: Dui Hei, 36 degree total
Intake: Holley street dominator (hly 300-36)
Gearbox: Tremec tko 500
Ratio: 3.54:1
Tire: 275/40/17
The 4777 is a great carb, IMO. I've used them repeatedly through the years on eeverything from mild 327 to a fairly stout Pontiac 455.

That said, I do not know what would be the problem w/simply tuning the Avenger you already have.

The idea that it cannot be rejetted to solve some or all of the problems you are having w/a lean a/f ratio is just wrong, IMO.

The a/f ratio is not only affected by the different restrictions in the metering block- there's power valves, jets and secondary springs that all will have an effect on how the carb performs.

Where in the power band are you seeing the too lean 14.2 condition you mentioned?
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Old 07-17-2010, 09:32 PM
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Colbalt already hit the main point.

Where are you seeing the 'lean' condition??

idle ===around 13.2 Leaner if you can
transition ====12.5
cruise=======14.2 to 15.0 maybe leaner.
full throttle====13.5
all +/- .2-.4

this is about what I ran with a 3310-3 and a short yellow spring.

The 4777 is also a very good carb right out of the box for a high performance car which you have.

Run lots of advance in by 2500 or so. I'd run the vac advance too. I run it on my blower motor and it really cleaned up the mixture and I get much better mpg now. Also doesn't make as much noise at the exhaust----idling.
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Old 07-17-2010, 09:50 PM
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Either the Holley or the QuickFuel will work. QuickFuel does make a nice carb, I would likely pick it over the straight from Holley version if I had a choice. If you are looking to out and out buy a new carb, I would recommend ProSystems carbs, real nice built to your combo carbs.

As the others have said, there is no reason the 670 you have now couldn't be set up to work just fine, just a matter of actually working on it and not just turning the screws,... work with the bleeds and jetting and feed restriction sizes and it will be a great carb.
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Old 07-18-2010, 06:00 AM
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yeah rejetting the street avenger would save you a $, b4 buying a new carb, thats what id do...
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Old 07-19-2010, 03:53 AM
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Hello Guys,thanks for all the information!!

There is something a forgot to mansion, the dyno man also says that the looks that the secondaries opens around 3000 rpm en closes at 3500 rpm (see dyno sheets).

Around 4250 rpm the engine starts struggle and becomes (to) lean.





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