mill off choke tower? any dyno tests?

[Matt Gruber]

1 of mine is milled off, the other stock, but no choke plate. Sure looks clunky as far as the path air takes to climb over the tower.
Assuming the carb is big enough, will smooth entry make more power, and at what rpm?
they are Double Pump 4165's- 650 cfm, on mild street only 355's ~385hp, 5700 max rpm.
Any dyno tests on any Holley before & after removing the tower?
Thanks guys!

[jeff swisher]

Matt i know you asked for dyno tests ,,,but i do not have any .
What i do have is this ,,I chased my tail on a 750 3310 carb on an old 355 that seen 7000+ rpm
the car ran really strong on the topend with my 750 carter afb...good lowend to boot..tried some Qjets and they did fairly well not quite the charge on the topend as the afb,,,got a 3310 and began with the jetting and float levels ..along with powervalves and pump cams.secondary springs and even made it mechanical secondaries..played with spacers and the thing would not pull on the top like the afb....

I milled the choke horn polished the venturies and thinned the throttle shafts and used smaller screws in the throttle blades,,,,,now finally this thing will flat pull on the big end and gave up nothing on the bottom end.....
I do not know if just a choke horn mod would do ....if you go that far you might as well do it all

[Matt Gruber]

jeff
how did u make it mechanical? did u add another pump?
do any oxygen sensor tuning?
thanks!

[Keith Morganstein]

Bill Jones wrote a fine article for this website. You can find it over on the maim racing secrets page under articles.

Detailed flow numbers from step by step modifications.

You do not need dyno test results. They are irrelevant to your combo. If your engine combo can use more carb CFM, the increased flow will help.

[jeff swisher]

from the old days we would put a screw in the linkage and that would open the secondaries when your foot asked for it,,,this way you knew they were fully open,,

I have tried a friends 750dp that had the percys metering blocks and different baseplate and he swore it would stomp my 750's...well after a good 5 hours of tunning and tweaking he could not get his 750 double pumper to pull the upper r's as well as my tweaked one...over 15 years ago and we both have those same carbs

I have played with a 1 wire O2 and that had me more screwed up than ever...I will stick with track tunning plug reading and mileage figures...this type of tunning has worked well for me for many moons

[Matt Gruber]

jeff
i'm glad u got a 3310 to run that well! it is very low cost.
the thread on the hp losing k+n tops has me thinking removing the choke tower can only help. if my engine has to work harder to pull in air, that can't be good. Possibly it won't make more max hp, but it could help part throttle.
thanks for your input!
.
Keith
i'll click on bill jones and see if that article is in his profile. or maybe he will post a link.
thanks!
.
Maybe i'll put my spare carb on my SF110 flow bench. could do before and after on just 1 front bbl.

[bigjoe1]

Here is what youDO NOT want to hear. I have tested the milled tops as opposed to the stock top with the blade removed=== There is NO HORSEPOWER differance. When you start smoothing and get a nice radius on all the sharp edges on the top, HP will go UP.If your engine wants more air, theses simple mods can show up pretty big. I used to modify lots of carburetors , and when I did the full treatment, it was allways somewhere in the 10 to 20 HP gains== Just to put a bigger carb in place of the smaller one will usually get you 10 to 15 HP ( 750 to an 850 )Driveability is a completely diofferant can of worms though.


JOE SHERMAN RACING ENGINES

[BrazilianZ28Camaro]

I think this is a good thing when the carb stay too close from the hood.

I have a Z28 71 SBC with a Stealth air gap, then my 750DP was about 2" from the factory hood and had signs of fuel slosh (coming from the air bleds maybe) inside the choke tower because the potential vaccum at that area caused by the hood being a restriction.

Then I milled down the tower and smoothed/polished the venturis ...the fuel slosh was gone and the seat of the pants meter improved a lil bit.

I read in some place that removing the choque tower can bring up to 40 cfm, but i haven't any flow data measured by myself.

[Keith Morganstein]

this is one Bill Jones article, but it has to do with epoxy more than anything.


http://racingarticles.com/blog/2006/05/ ... epoxy.html

[jeff swisher]

That was a good read Keith.
the gray on black was a little hard on the eyes...
I have thought about doing the epoxy thing,,but never had.

It shows you that just 1 mod may be worth nothing to very little , but multiple mods start to stack up..

i other thing to be aware of when using carbs,,is the airflow in front of the carb from the cooling fan...i have seen high speed misses caused from air going into the carb being disrupted by the massive air comming from the fan,,,,,An easy way to tell is to duct tape the front 4-6 inches of the air filter...
On the car i was testing all the carbs on it had a steel deflector that i welded to the air cleaner top ,to block that air comming from the cooling fans ,,,and it had a 4" homemade cowl hood

[Matt Gruber]

Thanks guys!
so far i'm leaving the choke tower in place, and maybe will smooth the venturi and radius the air entry. Seems like "carb therapy" , since it's not too small.
Was thinking a 1.5"high left/right divider might work well with the fully separated dual plane, but i've no way to test that, so probably won't try it. Just kicking around ideas.

[Matt Gruber]

looking it over, inspired by bill jones's article, i see a .030" ridge where the base contacts the body; base too big, not centered, ridge ~halfway around.
room for improvement on the primary!

[69-CHVL]

You have to figure that the entire choke horn has a much larger area than the venturis, so it should make all that much difference whether its removed or not. I would agree though that in some cases where the carb is almost right up against the hood, it may help a bit (b/c of the drop vase aircleaners's lid right against the carb's top). I seem to run 1mph faster with the aircleaner off. Either way, its not a night/day difference.

[Tartilla]

Choke horn is a larger problem when aircleaner/spark arrestor are factored into the equation.

Here is the link to Bill Jones' current location of his Holley carb mods.

http://ryanbrownracing.com/Bill_Jones_Page_4.html

Lots of great ideas there. In particular is the center thread hole system used to control extra idle air if required.

DV's newer Holley book details lots of mods, similar to Bill's.

[mag2555]

A 600 cfm carb can support 400 Hp so your not there yet, but in your case ( 650 cfm carb ) with a duel plane intake adding a proper modded 4 hole spacer is worth more then removing the choke tower in terms of adding a few more Hp
Above 4800 rpm.

The spacer needs to be at least one inch and on the shallow side of the intake plenum the spacer need to be open, this means that the actual intake manifold plenum needs to be made open between the front and rear holes also.

The holes in the spacer on the deep side of the plenum can be left as is.

The shallow side plenum is a bad restriction due to the tight turn into the runners.