Holley 650 Choke vs No Choke flow test

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skrews

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Picked up a Holley 650 DP carb (list#4777-1)off Craigs List the other day that still had its choke intact. After going through my scrap carb parts bin looking for a few bits and pieces, I realized I had a 650 main body with the choke horn milled off. That got the wheels turning. What kind of flow difference is there with the choke horn milled off?

Flow test conducted on a SF1020 at 1.5" hg full throttle.

With choke in place and open obviously 661 CFM
With choke horn milled off 677 CFM

I thought it would have been worth more, but now I know.
 
The really big gains come from running an air cleaner.

The filter is blocked by the stupid choke horn sticking up there. It plays hell with the air bleeds.

I was taught how to remove a choke horn without a mill in 1981. I could tell a difference just backing out of the driveway. Driveability was so much better with the choke horn gone.

Ironically, it was a 4777 I bought new earlier in the summer.
 
The really big gains come from running an air cleaner.

The filter is blocked by the stupid choke horn sticking up there. It plays hell with the air bleeds.

I was taught how to remove a choke horn without a mill in 1981. I could tell a difference just backing out of the driveway. Driveability was so much better with the choke horn gone.

Ironically, it was a 4777 I bought new earlier in the summer.
did you just use a hack saw?
 
Picked up a Holley 650 DP carb (list#4777-1)off Craigs List the other day that still had its choke intact. After going through my scrap carb parts bin looking for a few bits and pieces, I realized I had a 650 main body with the choke horn milled off. That got the wheels turning. What kind of flow difference is there with the choke horn milled off?

Flow test conducted on a SF1020 at 1.5" hg full throttle.

With choke in place and open obviously 661 CFM
With choke horn milled off 677 CFM

I thought it would have been worth more, but now I know.

Was just the choke horn milled off or was it all smoothed up around all the seams.

I would have thought it had more punch than that.

Good test thank for the info
 
A hack saw and 2 different files.

Thats what I used back in the 80's on my 4781 850DP, picked up 1.8 10/ths over the std 750DP the car came with, also adding a 50cc front pump helped some as well:thumbsup:
 
YR is dead on about the air cleaner. I assume that none was used. If you had/have any laying around..... and have time.... or a bug up your *** for more knowledge..... ;)
 
I ran a 600 dp with horn mods back in the 80s. It ran great ! Just sold it last year to help fund a Pro Systems Custom for my W2 408
 
I've tried the stub stack on both my 650 and 850 it was worth about 6 to 8 hp on the dyno. I had considered removing the air horn on both but have decided against it.
 
I've tried the stub stack on both my 650 and 850 it was worth about 6 to 8 hp on the dyno. I had considered removing the air horn on both but have decided against it.
I was just going to ask about that stub stack. Just wondering about all the options here. Choke tower cut down, no choke tower, K&N stub stack and how they compare. I wonder if running the K&N on a cut down tower would be of any benefit?

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The stub stack takes a bit of fitting but I was pleased with it , a choke isn't completely necessary but nice for a driver.
It would not work with a cut down tower, you would not need it.
 
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I’m running an AED with a cut/milled down tower as shown in first picture, but not sure how the stub stack would fit on that: sitting flush all around or if the tower is cut down lower than the stack leaving any space.
 
Yup that epoxy mimics the Stub Staker.

When i cut the choke off of mine, i take vice grips to that wall between the primaries and secondaries then smooth and radius down.
Also put flush mount screws in the butterfly's and grind a piece of the shaft on each side of the screws on the throttle shafts
 
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