How to increase airflow through a throttle body?

[jamyers]

So I've got this Holley 4-bbl Throttle Body, and I'm looking to get some more airflow through it.

It looks to me like there's room for improvement, like blending that ridge above each bore back into a smooth curve - although I'm sure I don't want to go very far down into the throttle bore area.

Is it worth it, and if so, how far down / back is safe to go?

 

[rbohm]

8) yes you can blend the step back quite a bit in fact. another idea would be to make a filler piece that tapers down which will also smooth out the airflow.

 

[CNC-Dude]

So I've got this Holley 4-bbl Throttle Body, and I'm looking to get some more airflow through it.

It looks to me like there's room for improvement, like blending that ridge above each bore back into a smooth curve - although I'm sure I don't want to go very far down into the throttle bore area.

Is it worth it, and if so, how far down / back is safe to go?

You can make the radius' larger at both levels directly above the butterflies, and the very top of the casting. Probably couldn't do it very consistently and evenly by hand, but you can get another 15-20 CFM by doing it. I wouldn't make the bores larger, you can lose velocity that way, unless you also make the butterflies larger as well. Have you test flowed it yet to get a baseline.

 

[jamyers]

Holley rated it at 650 or 750 cfm, depending on the injectors - which is odd since the injectors are all the same physical size...

Makes me wonder if the cfm ratings on a throttle body mean the same thing as on a carb - where the vacuum signal affects fuel/air mixtures

I was thinking about basically smoothing the entry to the throttle plates, maybe adding some epoxy if I can't get that ledge cut back to the outer wall.

How close to the throttle plates can I remove material?

 

[CNC-Dude]

Without going into a long boring post about R&D projects i've done in the past.....I have taken (2) 60MM(2.362" ID) orifices(both were within .0005 bore of each other, 1 half of 1 thousandths), and made one with a straight entry with only a light deburred edge, and the second one, I machined a 3/16" radius in the entry of the orifice. The material was the same thickness on both pieces of material, and the bore was centered and machined on the material in the same position on them and a doweled fixture placed them on the flowbench the same. The orifice with the radiused entry flowed 125 CFM more than the unradiused orifice....I think you can still have some gains without having to get close to the butterflies, you can risk upsetting thing by doing so. You can enlarge the larger upper chamber, but it would take a CNC to match the profile to stay true to the original shape. You might only be able to remove .040 or .050 of material from the vertical walls of this upper chamber, depending on how thick the casting is. But once that is done, you can machine a larger radius into that portion of the entry, and then this will allow you to drop down and make the radius on the lower portion larger as well. You still would need CNC to duplicate the profiles, however. But, I think you can improve the flow considerably by doing this.

 

[jamyers]

Thanks for the info, looks like I'll be modding this TB this coming weekend. No CNC available, I'll see if my machinist friend can help out - maybe he'll have an easy way to radius that ledge, saving me an afternoon with the old die-grinder.

 

[CNC-Dude]

Cool, keep us posted.

 

[Broncitis]

May I ask what you are putting this on, because if its a small six, you are not going to gain anything noticeable. You pull 600 cfm through a small six and you have done something.

 

[wallaka]

Probably for his 464 ci LeSabre

 

[jamyers]

Probably for his 464 ci LeSabre

Umm, yes. Details, details, details... :mrgreen: