Cfm for an NH?

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Model T Ford Forum: Forum 2009: Cfm for an NH?
Top of pagePrevious messageNext messageBottom of page Link to this message  By tyrone thomas on Wednesday, December 23, 2009 - 10:00 am:

What is the CFM for an NH carb? Thank you


Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth Harbuck - Shreveport, LA on Wednesday, December 23, 2009 - 10:06 am:

It depends on which NH - humpback or straight-through will be different under the same testing conditions.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Thunder on Wednesday, December 23, 2009 - 10:07 am:

Tim at Model T Engine posted a chart a while back. I cant find the post, or the chart though.


Top of pagePrevious messageNext messageBottom of page Link to this message  By tyrone thomas on Wednesday, December 23, 2009 - 10:27 am:

just found it. Swayback - 29, Straight back 31


Top of pagePrevious messageNext messageBottom of page Link to this message  By Harold Schwendeman on Thursday, December 24, 2009 - 01:29 pm:

Tyrone - Not sure what you have in mind, but as long as Seth brought it up, I think I recall that the swayback NH is probably one of the best all-around performing carburetors (unless you invest in one of Stan Howe's beautiful Stromberg OF's) however, the straight-thru NH is desirable for slightly more high performance. I think the Montana 500 guys like the straight-thru because of the slight high performance advantage, but I think I recall reading that the high-performance comes with the slight disadvantage of the straight-thru NH having a slightly rougher idle and slightly harder starting. I think Ford used the straight-thru NH in 1920 but in '21, went back to the swayback because of the slightly harder starting of the straight-thru. I'm not sure if the straight-thru carb is considerd more valuable than the swayback or not but I expect the fact that the swayback is much more plentiful, I would think that a guy might expect to have to pay more for a straight-thru NH.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Cascisa in Poulsbo, WA on Thursday, December 24, 2009 - 02:31 pm:

Tyrone,

I have run both the straight through and sway back NH carbs. I noticed a slight improvement with the straight through over the sway back.

I also modified a sway back to make it into a straight through. I have about 300 miles on it and it significantly out performs both the sway back and stock straight through carbs with no significant impact on fuel economy.

Your mileage may vary ...

As a side note - the only carb allowed on the Montana 500 is the swayback NH. A 0.710 inch (I think) test gage must not pass through the carb.

Be_Zero_Be


Top of pagePrevious messageNext messageBottom of page Link to this message  By tyrone thomas on Thursday, December 24, 2009 - 05:24 pm:

Bob, on my racer I have had a Simmons Super carb, a straight through.It has a slight larger throat. I have had a humpback. I believe the simmons does produce more power but I think it is harder on the gas.
I remember you are the one who is doing the expermental NH straight through. I have been waiting for you to make me one. :-) I am interested in your results. On my next speedster I have plans to rig up two carbs. I had given thought using two NH. I think your NH straight would a great setup.
I have a friend who is running a Zeinth Model A carb on his speedster. It starts hard and running slugish. Personlly I think he is over carbing the car. Not having a chance for the fuel time atomize or the T engine does not have enough draw through the A carb to get a good mix.
Keep passing your carb findings along. Thank for you info. tyrone


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