Considering a carb swap, you guys still like the Proform?

[JerseyJoe]

My 493 has been running great for a while, I'm doing a lot more cruising around town.
It's got a 1000 cfm Classic HP Holley. It pulls like a monster above 2500 RPM but I'm thinking the 1.561" venturi isn't the greatest for driving under about 2500 or so RPM.
I've searched previous discussions where the Proform 950 seemed like a popular choice. How are they with venturi size and getting a better signal
pulling through the carb? Maybe even an 850?
Thanks in advance 
493/stock Stealths/Comp xs290s
4sp/3.54 rear

[XH29N0G]

I have done a fair amount of experimenting by swapping main bodies on a quick fuel which I think is the same as proform. I like the carburetors, but do not have a good comparison with other brands.

My engine is smaller than yours and has less cam so what I say might not apply.

I have been experimenting with main bodies with annular boosters. I did notice a difference between the different venturi size main bodies and the largest one (1.59 venturi 1050) seemed a little sluggish on the transition in my early tests, but I should revisit that now that .  I was able to get a much more snappy response from the 850 (1.39 venturi).  I have since switched to a 950 body (1.45 venturi) and do not notice a significant difference.  I found the possibility to change the emulsion bleeds, air bleeds, feed restrictors, valuable with the swapping of the main bodies.  My guess is if you get one as a whole, you will not need to do much of that. 

Unfortunately, as I have done this I have learned and I now collect more and more data.  This means I know more about the most recent changes and less about the others.  I may return to the large one at some point just to see if I can now work around what I perceives as a little bit of a delay in the transition to WOT (when I mashed the throttle).

[BSB67]

Tell us more about your combination and your goal for the car.

My 508 is faster with a small venturi (1.39) verses a 1.56 venturi.  I'm using a 440 2D intake. 

If the goal is the cleanest, sharpest cruising and part throttle experience, you should look at annular boosters.

[JerseyJoe]

Tell us more about your combination and your goal for the car.

Sure, Russ.
From the top, the Holley is on a Street Dom intake, the Stealths are the earlier 84cc chamber,
Comp XE290s-10 (I typo'd the XS in my question) .540/.558 lift, 252/260 duration@.050, 110 LSA
10.9:1CR, flat tops, 2" headers.
It's a 440 based 493 (4.15 stroke/.030 over), 4 speed, 3.54 Dana.
So I'm asking if there's some better idle to part throttle manners and driveability because I'm not really spending too much time above 3000rpm (but it does run awesome there).
More and more I'm cruising locally, occasional stoplight holeshots, but mostly part throttle up to 4000rpm at most
unless I head out of town where there's room to really get on it but there's no timing lights or 1/4 mile there.
I was hoping to get to my local track (Atco, NJ), but it's been bought by an insurance company and looks like they're going to develop it into an auction facility 
I'm not going to stop putting my foot in it but if there's some better response available, I'll go for it.

[XH29N0G]

Do you have an air fuel meter that you can log?  The reason I ask is not so much for choosing the best AF, but because it helped me identify where to look for changes in the transition circuits that would make a difference for what I wanted.

Given my low level of experience, the air fuel readings helped me see part of what the changes I made with squirters and pump cam, and various air bleeds and IFR were doing and what was happening at the RPM of interest.

The good thing is you can set it up this way and if you head to the track you can swap what you have vs what you set up to see if there is a real difference. 

[cdr]

At one point on my 512 stealth head 255,258 @ .050 hydro roller, I had a down leg booster 1.56 main body, I changed it to the 1.56 annular booster & it made the lower rpm cruise MUCH better but still not as good as I would like it, I should have gone with the smaller venturi , but I ended up going EFI. 

[c00nhunterjoe]

That 493 is probably eating up some of that cam duration, but thats still going to have a poor signal at low rpm. Coupled with 3.54 gears, the annular boosters will be night and day in your particular situation. I would stick with the 950 on that engine even though you dont spin it very high.

[BSB67]

The question would be which 950.  My 4781 850dp is probably bigger than my 950. 

Anyways, I guess I don't have a recommendation that I feel strongly enough about to spend $800 on.  A small venturi 950 on a dual plane would sharpen it at lower rpm, just don't know how much and if it will be worth it to you for the coin you'll spend.

Does someone have a carb you could borrow?

[JerseyJoe]

I have considered an AF gauge to help keep an eye on things while trying to avoid detonation, that was a real battle.
A quick look at the Proform, Summit, and Jeg's sites don't list venturi sizes, any tips on where to find it?
I'm starting to settle around a 950/small venturi/annular. Are the 950 Holleys identical?
There seems to be alot of discussion about how the cfm ratings are not as true as they used to be. I'm pretty confident my 1000 with larger venturis is like opening a gigantic air hole
when I stomp on it compared to a "slightly smaller" carb.
I have a couple buddies I can ask and see if they have something to try out.
I can justify a new carb since I have one to get rid of. My entire industry is virtually shut down still. So I'll wrench on it to keep busy  

[XH29N0G]

I found this site valuable for the quick fuel measurements  http://www.quickfueltechnology.com.au/content/Quick%20Fuel%20Carb%20Size%20with%20details-AUST.pdf

I believe Proform conforms to this.  The Holley 950's, I believe there are multiple versions.  I think one is 1.375 (like the 750) but maybe with a larger 1.75 throttle bore (holley HP https://www.holley.com/products/fuel_systems/carburetors/hp/classic_hp/parts/0-80496-1).  I also just saw a version with a very large venturi holley ultra xp (1.600 venturi https://www.holley.com/products/fuel_systems/carburetors/ultra_xp/parts/0-80805RDX). click the specs tab.  I do not know where they are listed in a table.

The numbers are all over the place on the venturis and sizes.  My car (smaller engine) seems to do best for response with a slightly smaller venturi 1.45 or 1.39 rather than 1.59.  I do not know about the top end and may not have figured out how to dial in the 1.59

I am told (and I see no reason why it is not true) that the annular boosters are like a smaller venturi with flow because they are larger.  I have not been able to figure out how to convert annular at a given ventury to dogleg at another.  I also have not been able to figure out whether one works better up top.  Annular certainly seems responsive to me.  And responsive is what makes it fun for me to drive.

Good luck.

I also didn't mean to push you to the AF gauge.  I enjoy mine, but I also think that if you are starting with a fully set up carburetor that is of the right size that you will be pretty close and can do the changing without the AF gauge.

[JerseyJoe]

I found this site valuable for the quick fuel measurements  http://www.quickfueltechnology.com.au/content/Quick%20Fuel%20Carb%20Size%20with%20details-AUST.pdf

Thanks for that chart. Looks like there's only a couple choices, at least for QT carbs.

[JerseyJoe]

I have done a fair amount of experimenting by swapping main bodies on a quick fuel which I think is the same as proform. I like the carburetors, but do not have a good comparison with other brands.

This may be a candidate. 1.45 venturis and annular booster. This as a whole carb would have the same 1.75 throttle bore as my 1000 cfm. Everything else should be a swap, except for jetting, etc. of course. Either buy a whole new carb or swap the body is probably a break-even situation. Am I missing something important?
https://www.summitracing.com/parts/qft-6950an

[XH29N0G]

It isn't difficult, but I think you will find that you will also need to change things like main air bleeds and emulsion

This isn't a big deal but does require some experimentation.

This is what I did.  I would like to see what some of the other people say about this because it may be that I went to levels of tinkering that were not warranted.

There's another gasket between the throttle body and the main body that needs to be replaced that's not in the picture but I assume it is sent with this

[XH29N0G]

I used that QF website (posted above) as a starting point for the air bleeds, jets, etc.....  It would be good though if you had someone who might be able to get closer with the set up you have.

[JerseyJoe]

     Here's the follow up, there's 3 guys I really pay attention to on this forum for tuning info, firefighter Ron, BSB67, and Coonhunter Joe.
I was overthinking this carb choice so I checked out the proven engine combos with similar builds as mine. I found something from BSB67 pointing out the 1.56" venturi had such a limited practical use, I went with what was working for people.
    I put a Proform 950 on it today and it's so much more responsive right off idle, no hesitation.
My idle and cruising A/F ratios came right into a good spot. It's a little lean at 14.0 WOT and starting to ping just a little bit and I'm at 35 degrees total and 93 octane.
Out of the box I had to lower both float levels to get it in the sight glass and the idle screws were way out. Accelerator pumps were also buried and had to back them off a bit to get the feeler gauge in, but it seems to be very easy to get adjusted quickly. Time for some drag radials because there is zero traction now.
Thanks everybody for your input    

[XH29N0G]

   Look forward to hearing more.

[BSB67]

Looks great!  Is that with 1.45" venturi and down leg boosters?

[JerseyJoe]

Looks great!  Is that with 1.45" venturi and down leg boosters?

Yes, I know we were talking annular but I was getting more convinced the Venturi size was just drooling into the motor. Gonna try to get the A/F fatter at WOT but this is a lot more fun to drive already. It was bucking like crazy cruising at 1500 rpm and that's gone too. 

[BSB67]

Looks great!  Is that with 1.45" venturi and down leg boosters?

Yes, I know we were talking annular but I was getting more convinced the Venturi size was just drooling into the motor. Gonna try to get the A/F fatter at WOT but this is a lot more fun to drive already. It was bucking like crazy cruising at 1500 rpm and that's gone too. 

Good to hear it.

That is why I was hesitant to make a specific recommendation. What the car was doing verses what you want it to do is kind of a personal thing, and car and motor specifics matter in these decisions.

In my car, I can drive at any speed in 3rd gear. Of course, I do have an automatic that gives a little low rpm cushion.

[JerseyJoe]

Good to hear it.

That is why I was hesitant to make a specific recommendation. What the car was doing verses what you want it to do is kind of a personal thing, and car and motor specifics matter in these decisions.

In my car, I can drive at any speed in 3rd gear. Of course, I do have an automatic that gives a little low rpm cushion.

I get it. Mild could be wild to somebody else. Thanks again.