Road-Racing carburetor modifications for 350 V8

[hoov100]

A novel way to help stalling under hard braking image from rockcrawler . com:

 

 

I'm gonna be honest here, Me and my brother have used a box stock 750 holley with annular boosters and have not experienced any stalling/sputtering under extremely hard braking with a peak G force of .73 under heavy braking, we have had fuel slosh out of the vent in the secondary float bowl, but no sputtering or stalling because of it.

[JMortensen]

Either your g meter is busted, or you need to step on the brakes harder. .73 g is not very much for braking.

[hoov100]

Either your g meter is busted, or you need to step on the brakes harder. .73 g is not very much for braking.

I guess thats what I get for duct taping an Iphone to the center console. I'll try it with a legit measuring device next time it's on the track.

[bjhines]

Hoov100 brings up an interesting point. If he can slosh fuel out of the bowls then my road race car will certainly do it. It's stuff like that I want to avoid and some here seem to never notice it.

[jt1]

It may be a problem for some, but if mine spills fuel out of the vents, it's never caused enough of a problem to be noticable. I've never had a problem with the standard floats, but a friend with a C4 vette converted to carb would pull enough lateral g's to stumble in long sweepers, and the road race floats fixed the problem. So it depends on the individual situation, but I would try a basic setup first and see how it does.

 

jt

[bjhines]

I finished rebuilding the double pumper.... pics to follow.

 

Ya know what...? Holley Carbys are feaking simple compared to the rest of the stuff I have worked with. They are also pretty rough castings that look like they came from the 19th century.

 

This reminds me of my years as a kid building radio controlled airplanes. I had a few American made "K&B" engines that were pretty much the standard for everyone. The castings were rough, It was hard to find very many exterior machined surfaces. There were very few ball bearings or seals, they just worked ok for a season and then needed rebuilding or replacement. I was handed down a lot of worn out "K&B" engines from the older club members, this was the beginning of my "engine rebuilding" years.

I distinctly recall the day I purchased my first brand-new, Japanese "O.S." engine. That was a thing of beauty. Nearly every surface was machined, and the cast surfaces were amazingly smooth. There was no casting flash anywhere to be found. overall design was similar to the American "K&B" engines, but the execution was like artwork. The cost was slightly higher(~5%), but the performance was FANTASTIC. The little OS engines would double or triple the life-span of the K&B engines.

 

Now back to the Holley 4777-2 carby. This reminds me of the crappy K&B engines I started with. Dirty, rough, flashing and rough surfaces abound. The master molds have been used far longer than they were ever intended. Many details have been lost or smeared out of the castings, and evidence of mold and master repairs abound. What a piece of crap!!!! Who the hell casts machine parts in ZINC for god's sake. If I didn't know better I would assume this thing was 200 years old.

[bjhines]

My carby has definitely been on fire in it's life. There is no evidence of melting or sagging, but there were bits of melted plastic stuck inside the primary bores. It has quite a bit of exterior corrosion where the melted plastic stuck to it. The interior is clean and pristine, but previous owners have made their marks.

 

This is a Holley #4777-2, 650CFM, 4150 double pumper with mechanical secondaries and manual choke. The main jets are #67, secondary jets are #76 and the power valve is 8.5"hg, The inlet needles were oversize .110s. The floats are BRASS and there were no inlet screens or sintered filters installed.

 

 

 

The metering plates are original. They are revision-2 with vent whistles(very nice to prevent fuel spillover). The PO has added small V-shaped wires in the idle feed restrictions to lean out idle. The PO also drilled the primary-idle air-bleeds in the main body to further lean out idle. I noticed the idle mixture screws were open a little more than usual(opened 2.25 turns).

 

 

I rebuilt the carby per standard instructions. I filed a few high spots on the main body. The power valve pocket had flash on one side that stuck up more than 0.010" but the surfaces were not warped(I was concerned due to the fire evidence). I installed standard 090 inlet needles, original jets, 8.0"hg power valve, 30cc pump diaphrams, and original squirters. I set the primary and secondary idle opening, I set the accel pump clearances at WOT and checked the clearances(or lack thereof) at idle opening. My only modification was to remove the choke tower with a band saw and file(for aircleaner clearance).

 

 

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[bjhines]

For once I will listen to JT1 and keep it simple to start with. I did find a picture of the power valve inlet mod I was talking about.

 

 

 

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[jt1]

I like that setup for the power valve. Who makes that?

 

A 8.5 is pretty high. I suspect you will windup much lower than that.

 

You can do a lot more to the choke tower. This is mine, all done with a hacksaw and die grinder. It's a 700.

 

Edit: Don't forget to JB Weld the hole for the choke rod. You can see it in the pic.

 

jt

Edited April 19, 2010 by jt1

[bjhines]

Nice dremel work JT. Most of the "machined" chokes I have seen pics of are not that nice, I see that there is a lot of meat to work on around there. You have a large(~.5") radius that I did not think was possible on these castings. I half expect to find voids filled with slag.

 

I put a new 8.0 in the rebuild. I have power valves, 6.5, 8.0, and used8.5. If you think the SBC 327 with 461^^ heads and 3.54diff would demand lower PV opening then I will stick the 6.5 in there to start with. The little PV cup was home made. I might make one when I stick the lower PV in there. It is probably press fit into the boss/flange.