Holley 350 vs 500

[steven.burns]

I am looking into getting a new carb for my '62 GMC 305 V6. I've read about people using both the Holley 350 cfm and the 500 cfm. I would like to know what everyone thinks of either of them. Has anyone tried both of them and had better performance over the other?
Any help is appreciated!

Thanks!
Posted via Mobile Device

[RockTonka]

We're ran both and along with an HEI conversion felt that the 500 was preferable, you can check out the details in my son's build thread in my sig...the bottom one w/351E.

[steven.burns]

Think it'll run the same with the 305?
Posted via Mobile Device

[HEI451]

I used to work at Holley. That said, I used a carb from a 1961 292 Ford V8, had manual choke, linkage worked, and I changed the main jets up one size, carb works great, and gets better mileage/runs better than the stock 2bbl ever did. Nice thing for me, I have a lot of Holley and other carb make cores to work with, this one cost zip to do, already had a kit, just had to make a home made carb to manifold adapter.

That carb is rated at 340 cfm's.

My 305 is stock, just an X pipe, dual Flow-Master quiet mufflers, small body HEI.

[steven.burns]

I would like to go with a new one just to be sure and not dick around with rebuilds anymore than I need to. So you think the Holley 350 will work better for the 305 V6 than the 500 would?
Just trying to figure out whats best the first time since I'm on a really tight budget right now. I've read about the Holley 500 cfm working great on the 351 V6 but I don't know if it'll be the same performance with the 305 V6

[FetchMeAPepsi]

I can't say i know from experience but I have heard from people in the 305v6 group that the 500CFM makes a marked difference over lower airflow carbs.
If it were me, and it will be in a few months - I'd save the extra dough and get the 500. It's not that much different (sell something you dont use/need on ebay!) and it'll be worth it in the long run. You'll be much more satisfied that you did it "right" too instead of having to do it again down the road.

[steven.burns]

I plan plan on getting one of the other and I'm really leaning towards the 500. I just want to get my truck running so damn bad but I just gotta wait till I can get enough money to get the stuff I need first. If I were to get the Holley 500 cfm what would I need to get I setup properly? Adapter and what else?
Posted via Mobile Device

[HEI451]

Holley's are different, smaller carbs still work excellent. Only thing I did past a stock rebuild and one size bigger mains was to remove the throttle shaft, and teflon bush it. The average person wouldn't get that far into a complete rebuild, but I have worked for Holley previously, and have been a carb tech for 40 plus years, so, for me, it isn't a big thing to do any procedure on a carb.

As far as CFM's, the 305 and 350 cfm carbs are a good match, even with an automatic trans. Of the classic Holley 4bbls, the LIST-1848 was a 450 cfm carb, used on Ford 292's, 1849, 535 cfm, Lincoln/T-Bird 390, and, Holley's best universal carb of all time, the LIST-1850, 600 cfm, Lincoln/T-Bird 430.

My 305 runs just fine, gets good mileage, far better than the stock carb did, and better than a 500 cfm carb does. The 305 ports aren't big, don't need giant cfm carbs, and work well with a very conservative cfm flow rating. The 2 500's I tried clearly were too big for my engine.

Just info from someone that did the testing for himself.

[FetchMeAPepsi]

Originally Posted by HEI451

...Im a carb man...buncha numbers...my 305 runs great with good mileage...

So hows about a step by step? If it's better than the 500 and you built it from spare parts then it sounds like just what most of the tinkerers would love. Myself included.

[purzell]

Hi,

I cannot speak to the performance questions you have as I am a total novice in that regard. I have the 351 V6 with the Holley 4412, however I wanted to say that if you find that it's the same intake I had a lot of trouble with the Mr. Gasket adapter that was recommended on the GMC list for converting from the Rochester to the Holley.
I ended up going with an adapter from TransDapt that I got at Jegs which was much better made and has worked out great on my motor. My Rochester was toast so I'm not sure how it would have driven before I got the Holley. Just my .02 on the adapter plate issue.

[HEI451]

Let me clarify, I worked at Holley for a few years, and have a serious collection of carbs. I do electronic ignition conversions for a living, but get into carb stuff for everybody around here, just started a car club, and do all the carb and ignition work for all those good people.

That said, I didn't "build a carb from parts", the carb I used was complete, from a Ford 1/2 ton pickup truck 292 V8, F100 I do believe. I rebushed the throttle shaft with teflon, which I do to EVERY carb I do no mattter the make/type, NOT bronze bushed, teflon. The 305 engine wanted one size larger main jet than the 292 did, done deal.

The adapters I found for the carb to manifold were all too large on the carb side, to fit the bigger carbs like the 500, so, I built my own two piece adapter for the carb, tailored to the manifold ports and carb throttle bores. Just normal every day fabrication work for me, I do it all the time. I didn't find any adapters that were suitable for the smaller two barrel carbs for Holley, they all had way too big throttle bore holes.

In my opinion, ANY carb different from the stock Stromberg is beneficial, too big, OK, too small, OK, anything different than the stocker. There just doesn't seem to be the correct accelerator pump diaphragm available from any source.

I figure another good carb that isn't a Holley would be the Rochester 2bbl from a later model 400 small block Chevy engine. They are plentiful, still need the teflon bushing operation, but, they work well on other stuff. I haven't tried this swap yet, but, in my way of thinking, that carb is a good one, and should work well for the V6's.

[steven.burns]

Alright I've decided on the Holley 500cfm #4412c.
I know that I need to get some things to mount and make it work properly.
So if anyone can help in telling me exactly what I need would be very helpfull.
Mr. Gasket adapter kit #720-1937 or Trans Dapt adapter #969-2086
What else do I need to make it right? Choke cable? Hose fittings? Anything else?

[purzell]

Again, in my (limited) experience but ordering both items, the Mr. Gasket was disappointingly poorly made but the TransDapt was a much better part.

[FetchMeAPepsi]

Here's what you want:
http://www.jegs.com/i/Trans+Dapt/969/2086/10002/-1

[steven.burns]

Will I need to get the choke cable or anything else like hose fitting? I wanna make a little List so I can get I all at once
Posted via Mobile Device

[purzell]

I needed the choke cable, vacuum caps (those rubber caps) and used Gasgacinch. With the adapter plate it bolted right on. Again, not sure on the 305. Hopefully someone will weigh in...

[MusicMan70]

Steve have you visisted this link...

http://www.6066gmcguy.org/holley.htm

[MusicMan70]

I did purchase a Choke cable and hooked it up, but I don't think I ever needed to use it. Holley does have the electric choke option.
Yes you will a bit of hose; steel line is better. Do you have the fuel filter canister that is under the bed frame/passenger-side? if not then you will need an inline fuel filter as well.
Also you may have to do some fabricating on the throttle-arm/rod to connect to the Holley and return springs as well.

Not sure if you have a one barrel or two barrel stock. If it's a one barrel like my 61 was originally, then you will have to locate the two barrel intake as described in the previous link.

[athan66]

Not sure what you are planning for an air cleaner, but you might need to do something with the crankcase breather tube. Mine runs into the side of the factory air cleaner. Since the factory air cleaner won't fit the Holley carb, you might need to add a crankcase breather vent.

[MusicMan70]

athan66 Re: Holley 350 vs 500

--------------------------------------------------------------------------------
Not sure what you are planning for an air cleaner, but you might need to do something with the crankcase breather tube. Mine runs into the side of the factory air cleaner. Since the factory air cleaner won't fit the Holley carb, you might need to add a crankcase breather vent.

Great Point! Maybe from what Athan66 had/has(example) to something like this or whatever suits you. Those early Cadillac/Oldsmobile air cleaners are nice as well if you don't care for the open element type...

[steven.burns]

Thanks for your help guys! I'll try to get everything thing I need next week. I plan on going with a K&N air filter kit.
Posted via Mobile Device

[steven.burns]

I want to buy a K&N filter. Probably 14" base but there are many different heights and rises. Which would work best with the holley 500 on the 305 v6?

[padresag]

http://www.6066gmcguy.org/holley.htm
ron

[steven.burns]

Got my Holley 500 carb installed and ready to go. Just waiting for other parts to get her running

[MusicMan70]

Looks great! Which adapter did you end up selecting? I used the Mr. Gasket and had no issues. You should feel a difference.