MTFCA Forum

Today I picked up my engine after a transmission rebuild. As "proof of life" the rebuilder set it up on a Dyno and ran it for me, first with a Holley NH, then with my Holley G. I have a NH at home in a box that I've never gotten around to installing on the engine. Based upon the results, I think I will now

That's a pretty good set of figgurs....

Would love to know if that was a regular NH or a straight thru.

Steve, don't overlook that the engine has a Z head. The difference may not be as great with the standard head on a 1915 model.

Allan from down under.

Dave, your wish is granted....It was a Swayback.

I'm going to put the NH (with one of Scott's valves) on my '17 and will report back in a month whether I notice substantial differences in performance between the two. Then I will replace the standard manifold with a high-volume unit and compare again. I'm not trying to sway anyone's opinion but the more information you have the better choices you make.

Also, Charlie Volkening made up these neat graphs showing the performance curves of the two carbs.

And the Holley G may have been a tired carb too.

Post by carb expert RIP

By Stan Howe Helena, Montana on Monday, May 21, 2018 - 04:11 pm:


In my opinion the Holley G is the best all around carb that Ford provided from the factory.

One thing to check when you are rebuilding them is the size of the Venturi. Somewhere back along the way somebody must have been making and selling Venturi that were too long. It reduced the air flow at higher speeds. Some were nearly 1/4 inch too long.

Some also are too large diameter at the bottom. Both would cause problems with the way they ran.

The Holley G floats sold by the vendors are too large. They need to be reduced to the size of the original cork float to maintain proper fuel level in the bowl.


And…. This earlier praises of the G…. I am going to to a G on my current project, has std. T engine, expect it to be a good carb.

https://www.mtfca.com/discus/messages/5 ... 1422204583

Other factors aside, I agree with Uncle Stan (who really knew his stuff). The truly curious will try both on their own cars and compare. If, indeed, an NH (of either type ?) yields a 5hp increase, I would hazard it would require a specific test course providing rigorous challenges to make a fair estimation of any perceptible differences.

In defense of my Holley G, it was rebuilt by Russ Potter in 2019. I know he replaced the Venturi. It has performed very well for me, giving satisfactory performance in whatever I asked it to do. I think I will be able to detect any significant performance differences between the two.

I seriously doubt an NH will make 5hp difference, but a dyno test could prove me wrong. I picked up just over two HP when i went from a standard NH to a straight through NH on a 14-15 high volume cast iron intake manifold. The extra 5 hp came when a Z head was fitted. So many variables in any combination!

Allan from down under.

All I can tell you is that they ran the two carbs back to back on my engine. Their swayback NH and my Holley G - both using standard manifolds. The Dyno readings were taken within minutes of each other. Attached is a photo of the dyno in action.

After trying to get my 26 Roadster Pick up
to perform better and lively. The Z Head was an improvement, Truefire ignition did nothing however the NH straight thru out did the standard NH. I now go up my “test hill” in high gear and accelerating where as before I was in low.

Swapping the NH out for a Holley G probably would give better outcomes but can’t be bothered spending cash for a G and swapping it over when Im okay with what I’ve got at present.
Alan In Western Australia

Alan - I certainly agree. My Holley G came with the car and is probably original to it. I'll be holding on to it. As I said, it results in a sweet running engine and performs well under most circumstances.

I bought the NH because (A) I got it for a good price and (B) because it was rebuilt by Russ Potter. I was also curious to see if it would improve performance. I have a touring car and often drive with all seats full. Some of my future tours will be in hilly (even mountainous) country so I wanted to try the NH as well as the Scott Conger full-flow valve which alas, is not available for the G. On a previous tour in hill country I had a couple of times where my engine stumbled on a steep hill despite having a half-full+ gas tank.

I pay attention to what I hear and read, and do my best to sort it out. Over time I've determined that the majority of T people think the NH is probably one of the best carbs produced with the Model T back in the day. The scientist in me is curious to see whether it's true so I'll make my own comparisons once I get the car back on the road. With the G safe in a box I hope I have it covered

...I wanted to try the NH as well as the Scott Conger full-flow valve which alas, is not available for the G.

If your G is original to the car and has never been rebuilt, it has the original valve. I assume that would be full-flow. I believe Scott's NH valve is a correctly-made answer to a wrongly-made repop.

Straight through NH carburetor, 1913 intake manifold, Z cylinder head, Mobil One 10w30, Mike Kossor "E-Timer" ignition, tires aired to 30 PSI, top down, gives me a "seat of the pants " satisfaction driving our ' 26 Runabout .

Hi Rob,
Yes, I must get myself one of those e-timers then I’ll be just like you!
Mind you, the 26 does move along nicely once she is rolling on a country road. No issue with fuel starvation.
Alan

Steve,
My Holley G came with the car. Since the car was pretty much original, I assumed there was a good chance the carb was original to the car. I had it rebuilt by Russ Potter in 2019. I believe he installed a Grose valve but I've never had the bowl off to look.

I drove my Model T with it's "new" Holley NH today. Right out the gate it was obvious the car had more power and faster acceleration than with my Holley G. I was even able to accelerate going up a hill that I normally am lucky just to hold my speed (or not lose much.) I'll know more after I get a few more miles on it but so far I'm pleased.

That's encouraging news for the NH users!
Thought I was missing out with a G that's ready to go, right in front of me but perhaps not.