Holley 500 conversion?

[1965GMCK1502]

Hi All, was hoping to get some real life pros and cons of the 500. Current setup is the 305v6 with a Rochester 2G that’s working fine, especially after swapping in new Taylor wires and platinum plugs.....But always looking for a little more performance for the engine. I’ve heard nothing but great things about the Holley swap...but curious if anyone has had any negative outcomes?
Positive outcome info also very appreciated.
Thanks in advance!

[bigblockv6]

The Holley 500 will really wake up the 305 V6 though at times some 305's may run too rich and be a little over carbureted so a simple rejetting is all that's needed. To enhance this carburetor conversion I suggest a good flowing dual exhaust and an upgrade to electronic ignition:ok:

[1965GMCK1502]

The Holley 500 will really wake up the 305 V6 though at times some 305's may run too rich and be a little over carbureted so a simple rejetting is all that's needed. To enhance this carburetor conversion I suggest a good flowing dual exhaust and an upgrade to electronic ignition:ok:

Thanks, Peter. The HEI is in, and 2 1/4” dual exhaust going in next week. Holley carb on the way.

[LoganKai]

The Holley 500 will really wake up the 305 V6 though at times some 305's may run too rich and be a little over carbureted so a simple rejetting is all that's needed. To enhance this carburetor conversion I suggest a good flowing dual exhaust and an upgrade to electronic ignition:ok:

Have you had any success locating or building headers?

[bigblockv6]

I have not tried headers, though there are freer flowing manifolds used on bigger truck engines.

[1965GMCK1502]

[QUOTE=LoganKai;69353]Have you had any success locating or building headers

The headers are a major headache....there was some discussion about using Pontiac three-ports but they don’t match up and require customization. Haven’t tried....very happy with just the dual exhaust though.

[TJ's GMC]

Dual exhaust with the stock manifolds will do the job just fine for ya. Headers would have to be custom made and the results would not be worth the effort(or money!) unless more work was done to the engine. The mentioned mods will make for a nice increase in power....and change the exhaust tone. :thumbsup:

[br-549]

I also have interest in swapping to a Holley but i have a 401. Anyone have an adapter or a "fix"? Thanks! ja

[1965GMCK1502]

Dual exhaust with the stock manifolds will do the job just fine for ya. Headers would have to be custom made and the results would not be worth the effort(or money!) unless more work was done to the engine. The mentioned mods will make for a nice increase in power....and change the exhaust tone. :thumbsup:

Finally got around to doing the Holley swap and very happy with the results.

[steve in MI]

Any suggestion on what jets work best?

[Funky61]

From the Archives section; I jetted down as well to 68's and liked it.


I am running a 305 with 9:1 compression and Magnum components. Plus an HEi using full manifold vacuum. It seemed to be not running as well it should. The engine was operating too rich. The Holley carb comes with 73 size jets and i changed to size 65. This made a noticeable difference in performance. The only problem was a sight hesitation at cruse speeds.
I increased the jet size to 68
and it is smooth for all RPMs. The std 73 jets may be fine for 401/478 motors, but the smaller 351/305 may need some tuning.
Edwin Erlbacher Dallas TX

[1965GMCK1502]

No mods necessary. I used the stock jets that came with the Holley

[RedElvis]

Current setup is the 305v6 with a Rochester 2G that’s working fine, especially after swapping in new Taylor wires and platinum plugs..

Does the 2G bolt right on to the intake with the same bolt pattern or is a conversion plate needed? I have a rebuilt 2G from a 283 and would like to try if it's an easy swap.. Just want to get this truck running good, nothing fancy or high performance.

[1965GMCK1502]

Does the 2G bolt right on to the intake with the same bolt pattern or is a conversion plate needed? I have a rebuilt 2G from a 283 and would like to try if it's an easy swap.. Just want to get this truck running good, nothing fancy or high performance.

Yes it should bolt right up if it’s the 2G with the close bolt pattern.

[bigblockv6]

I've seen quite a few 305 V6's with the Rochester 2G used to replace the stock WW carb. It is said that GMC actually used some 2G carbs on the 305 V6 in 1967 because there was a shortage of Bendix/Stromberg carburetors since Chrysler also used these carburetors in large numbers on their 318 engines.

[RedElvis]

Great, thanks for responding. It's the smaller base.. Stock air cleaner fits the top hole.. 2 3/8 or so.