Guys -

I've been playing around with the Proform main body on my Holley 750 vac secondary and thought I'd let you know what I've learned so far.

With the hot weather the lack of a choke is not a problem at all. It starts and runs fine with no choke at all.

I played with the secondary spring on the carb and found (what feels like) more power at higher RPMs. It seems that the Proform main body is pretty sensitive to secondary spring changes. With the original O-3310 main body my car ran fastest with the lightest spring you can get (the white one). With the Proform it seems to like the springs that both open slower and start opening at lower RPM's. (short springs are stiffer and open quickly while the taller springs are softer and open slower) Mine seems to like the tall Yellow one best - it starts to open at around 1600 RPM and is fully open at just over 5000 RPM (according to the chart in my Holley tuning book). The plain color standard O-3310 spring opens too slow, I had just a little bit of a flat spot up around 4500 - 5500 RPM. This all seems to make sense seeing that the Proform main body is supposed to flow more than the standard 750 body.

The Proform also seems to be more sensitive to main jet changes than my original. I can go from too lean running 70F/74R (measured 14.0:1 A/F ratio on the dyno) to on the rich side with the recommended 72F/76R. The winning combo may be 71F/75R, but I really need to make a few back-to-back-to-back runs at the track to be sure. I suspect that the down leg style boosters provide a stronger metering signal.

Throttle response is about the same as the original main body, MAYBE a hair better. I did have to increase accelerator pump cam size from the orange (2.0 cc per stroke) to the green (2.4 cc) to eliminate a slight bog when launching with sticky tires at the track.

I know a couple of others were going to give the Proform a try - learn anything yet?

I'm learning that it sounds like a real Pain in the A$$

------------------
68 Coupe, 350 4-speed
Jim's Camaro Corner (http://www.personal.psu.edu/jxu109/)

Eric, how do you like the downleg boosters on the street?
I'm aiming for a holley 750HP carb when i get to that point, with mechanical secondaries and downleg boosters.

Eric,
Let us know what your times are with the new center section. I have an old 3310 and was going to rebuild it. Maybe I'd be better off doing it the way you did.

Camaro, the downleg boosters seem to be fine on the street. I think they provide a stronger metering signal - the high speed air bleeds look huge compared to the stock body. The A/F mix was rock steady on the dyno from 3500 rpm (when we went WOT) through 6600 RPM. It started to drift just slightly richer above 5500 but was still pretty steady.

Maybe this weekend I'll be able to get it to the track.

Spames, I need to post a pic of some cheeze for you . . . to go with that whine. http://www.camaros.net/forum/wink.gif Maybe I'm sick, but this is my idea of fun. http://www.camaros.net/forum/biggrin.gif

Ok, FINE! You're right. It is fun. I'm just jealous since mine's in a bunch of pieces, and I can't drive it, let alone tune it (click my link for the latest mug shot).

Better watch what you say. . . I saw a big old cat lurking around the maze. . . http://www.camaros.net/forum/biggrin.gif




------------------
68 Coupe, 350 4-speed
Jim's Camaro Corner (http://www.personal.psu.edu/jxu109/)

[This message has been edited by Spames (edited 07-15-2002).]

Thanks Eric, i was wondering myself which to buy. If the downleg are fine then i'll use them, i should really get a little more indepth into the carbs before i buy one.

Eric,

What size air bleeds are you using?.

<BLOCKQUOTE>quote:</font><HR>Originally posted by Toby Keen:
Eric,
Let us know what your times are with the new center section. I have an old 3310 and was going to rebuild it. Maybe I'd be better off doing it the way you did.<HR></BLOCKQUOTE>

Not good . . . down right embarrassing

On a hot sticky day I expected to run 12.2's at around 110 mph. I ran 12.5's at 108 mph all day and the tires were dead hooking. 60' times were in the high 1.7's low 1.8's with NO tire spin (compared to high 1.6's - low 1.7's normally). No obvious bog or hesitation, but the car definately felt "off" out of the hole and nosed over a little at higher RPM's. This carb setup plain sucks.

A couple things that might not have helped.

1. I sealed the air cleaner base to my cowl hood. Could I be pulling a vacuum in there at higher speeds? A guy at the track was telling me that he had read something about the Camaro cowl hoods doing that. Could be BS, I don't know.

2. I did not run a filter at all while I was racing since I haven't got that part of my cool air induction setup figured out yet. I'm pretty sure that secondaries will open later without an air filter.

Sounds like I might have wasted my money buying the Proform body.

Any ideas?

[This message has been edited by Eric68 (edited 08-04-2002).]

why would it not just be the hot temperature?

I experienced a nose dive this week at about the 1000 ft mark when I changed carbs. I was only running 101 to 106mph from the usual 113. I finally ended up having to work my way UP 5 jet sizes all the way around and raise the rear float bowl up one full turn after the trickle. It wasn't very street friendly afterwards so I had to change the primary side jets and the rear float level back for street manners, but I ran an all time best of 11.70 in the heat. You may just want to try the rear float bowl first and then increase the secondary jets a few sizes at a time to keep the drivability and fuel mileage issues on par. I don't think you're too far off from where you need to be.

I don't think you wasted your money, yet. As you know,it just takes alot more time to dial things in than you plan on. Keep plugging away at it like you have been, and I'm sure you'll get there.

What was the "problem" with the white secondary spring with the new main body? I noticed you changed that to the yellow one. Your "seat of the pants dyno" may need recalibrated?

On the old main body, what was the ET and mph difference between the yellow and white secondary springs?



[This message has been edited by bravewink (edited 08-04-2002).]

CNC, On a cool day I'd be running 12.0's to 11.9's at 110 - 112 mph. Low 11.9's maybe an 11.8 if I take my p/s belt off. So I figure 3 tenths would be a reasonable correction for sticky mid 90's weather. Remember, I'm hoping to improve here so I would have been happy to see 12.2's at over 110 mph.

Bravewink, maybe I should fire my "seat of the pants" dyno. LOL

On the original main body I went from plain (standard) to Purple (lighter) to white (lightest). ET difference was about 1/2 a tenth from standard to white. No change from standard to purple and I never ran the yellow at the track.

Floats are correct, I verfied them after I changed the main body. If anything I'm running slightly on the rich side of normal and that would probably slow me down in warmer weather. Running #72F/#76R IAW Proform's recommendation - old main body ran best with #70F/#74R.

I double checked my timing and curve yesterday. I found total timing at 37-38* - I have no idea how it got there, It runs best at 34* and I try to keep it there. That's definately one problem, and may cure the top end problem.

The bottom end problem seems to be related to the secondary opening point. When I did my first "seat of the pants" test above the secondary transition was smooth, but now there seems to be a hesitation at about 4,000 RPM (didn't notice this at the track, but I did notice it during a test drive yesterday). I'm wondering if maybe the secondary blades aren't sticky or binding slightly. I might take it apart ONE MORE TIME.

Eric68,
My group had the same experience with the proform, do a search for username
Cooldude and see the results of many times to the track.. His Nova would drive
To the track and run 12.90s on a cool night and 13.10s in the heat of the day. We put the proform on and it went to 13.50s he fought with it for weeks like you did he was very Methodical like you and talked to them on the phone many times. Last weekend he took
It off and put the old Holley 650 back on and the first pass it was a 13.10 and he ended up Making it to the final round that night. His experiences mirror yours put it on and drop 4 tenths, we got the bogs out and the stubbles but this thing would not perform

ssvette,

Thanks for the input. Very helpful. I think I might go to the track Wednesday and do some back-to-back-to-back testing with the old and new center section.

I'm wondering if my seat of the pants increase might have been due to rough transition to seconadary. Kind of like the old "Baahwahhh" feeling you'd get with an old Q-jet carb with a bad accel pump.

Did you mean, "it would not perform" or "it would not Proform" LOL

I guess they should call it "Not Proform" LOL

We were all jazzed and we all wanted one after our experience with cooldudes car none
of us would touch one. Now if Proform would like to prove their product we would be glad to supply the Car.

Well I dusted off the wallet and bought a 750 Speed Demon (double pumper). I just bolted it on and with absolutely no tuning (other than idle speed and mixture) I ran 12.1's at 111 mph. Thats with a very slick track - my 60' times were 1.75 - 1.80's. No stumbles, bogs, etc just smooth, kick butt power from idle to 7000 RPM.

The Proform turns out to be a step down from the stock Holley 750. Lesson learned.

I was thinking of switching from a 3310 to a Speed Demon too. I take it from your previous post that you are very pleased with it? Did it come with an electric choke?

And I thought he'd never give up his beloved 3310! http://www.camaros.net/forum/wink.gif

------------------
79' Z28...

Eric, thanks for the "test & tune" of the Proform &lt;on not Proform&gt; as this is why we're all here. Sorry for your loss of a Franklin, but you saved ours http://www.camaros.net/forum/biggrin.gif. thanks.

------------------
My '68 Camaro (http://hometown.aol.com/Dougs68Camaro/index.html)
Doug G.
68 Camaro
406 ci.
13.5@102 W/ 2.73POSI.

Cameron - The Speed Demon is equivalent to a Holley HP series double pumper. It has no choke (one can be installed though); it does have 4 corner idle, fuel bowl site glasses, and downleg boosters. Lots of nice features for the price. It was actually $50 cheaper than the HP series Holley at the local speed shop. The only down side is having to buy a new fuel feed line - Holley ones won't work.

Gas mileage noticeably dropped though. I used a full tank last night - 130 miles round trip plus 6 quarter mile passes left me with 1/8 tank. My "beloved" O-3310 usually left me with about 3/8 of a tank after the same trip. I have to admit though, it was hard to keep my foot out of "the Demon".

I wanted to keep the O-3310 and use it for trips, but I need the "Franklin" to pay for part of the Demon. The Proform body might make a nice looking wind-chime, wonder what I could get for "Proform wind chimes" on e-Bay? LOL

[This message has been edited by Eric68 (edited 08-08-2002).]

Well Eric68 your right it was a lesson learned and one that we all can use or at least warn others not to go there, thanks for the tip on the demon. Our team is always looking for a tenth anyway we can get it
(Who isn't) Thanks again.

I'll give you $10 for it. http://www.camaros.net/forum/wink.gif

<BLOCKQUOTE>quote:</font><HR>Originally posted by Ballistic:
I'll give you $10 for it. http://www.camaros.net/forum/wink.gif<HR></BLOCKQUOTE>

Is that $10 before or after I make it into a wind chime set? Would you give me $12 if I made it into a flower pot?

I'm thinking it would make a nice aerator for an aquarium. Four bubble streams from the downleg boosters would look nice wouldn't it? http://www.camaros.net/forum/smile.gif

You drive a hard bargain, but if you include the air pump I'll make it $12. But to be fair, at this price level you'd have to cover the shipping and insurance charges. http://www.camaros.net/forum/wink.gif

Eric, i was flipping through summit today and checked out the add for the proform body while flipping around.
"25-50HP out of a simple bolt on" LOL, where's that 50 HP at??? http://www.camaros.net/forum/biggrin.gif Figured you'd get a kick out of that one, since we all now see the light.

I have sent this thread to Proform and asked them to comment. Many of us have tried this carb body with little or no success. In every case the Ets went down I am curious to hear their reply, I will post any reply I get from them. Can I get the Proform wind chime before Christmas if I order now?

Hi Brent --

Yes, looks I sent this last email to an Earthlink account. Anyway, here's my response. We're going to look into this right away and I'll get back with you next week. Tks. L.

Brent -

Thank you for contacting PROFORM. We'll review the Camaros.net Forums this morning and get back with you early next week. We're very interested in learning what types of specific problems your members are having and we are committed to producing a top-notch product. PROFORM Performance Parts are warrantied against any manufacturer defects and I will make sure your users are taken care of in the event of any warranty-related issues.

I will plan on speaking with you early next week.

Thank you once again for contacting us.

Regards,

Lou
===============================
L. J. Lobsinger, Jr.
Strategic Project Manager
Specialty Auto Parts U.S.A., Inc.
(T) 586.774.2500 x13
(F) 586.778.7775
(E) llobsinger@proformparts.com http://www.proformparts.com

SEMA 2002 Booth # 22731
PRI 2002 Booth # 2011
===============================

Wow, a company that cares that it's product works!!!

Very cool. Perhaps I was a bit too quick with the wind chime, flower pot, and aquarium aerator cracks.

For anyone with Proform that reviews this thread, thank you. The specific problem with my application is that the secondary transition when at WOT is slow and causes a loss of midrange and upper RPM power. I tried several different secondary springs and a different vac secondary diaphram with no luck.

After tuning to get it as close as I can, the engine power curve is very flat from 4000 RPM through 6600 RPM on the dyno. A/F mixture was steady throughout this range. Testing at the track confirms power was off 4 mph through the traps and .4 secs slower ET.

Specifics of my combo are below.

OK Proform it sounds like you have a chance to show your stuff here, Eric68 and cooldude are weekend bracket racers that drive their cars to the track. I would think this is a great testbed for your product and both have already been on the phone with your Techs trying to make your product work and both slowed down. Again thanks for your response and we are looking forward to your input!!

ok, heres my beef, the alignment holes in the bottom of the body did not fit the base plate. pulled on pin out to get it to set flush, then, the screws were not centered (started cross treading on 1 side both holes) fixed that, then, when all bolted together venturi severly off centered on the base. fixed this. then, idle circut half covered by metering block gasket fixed this. 3 hrs time. also there seems to be some holes missing in the carb body, not sure if this is by design or a machining over site. will have to check this out.

Hey Fellow Racers,
I also tried the Proform on my 400 hp hydraulic roller cammed 383, using 650 dp parts,and their jets,it fit together like a champ.
The first test drive was very disappoiniting it was bogging and burbling on the low speed to high speed to transistion, so I called fuel tech, and they told me that it was calibrated for a 4 corner idle system, since I didnt have it I would have to reduce the rear outer air bleed sizes down to about 40.
This change helped a lot.
The 2nd problem was a stumble at launch, after playing with squiters and pump cams I got rid of the stumble and the car felt good at launch.
Now that it was running good I wanted to test it at the track, the 1st pass was disappointing, since it lost .4,after I played with the jetting(beleive me ssvette and I tried real hard ,since we dont give up easiy) I picked up .2, but still .2 slower than my junyard $10 650. Next week I put the 650 back on , and wham, I ran good again.

I really think that the high speed air bleeds are not giving a lot of us, the right fuel curve, and proform should calibrate these for the application better.


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1969 Chevy Nova 383 SB Dart 2's Roller Motor, 4.11 12 bolt TH350 10"conv

Well is their anyone else out there with an issue now is the time to speak up. They are going to get back with me this week, so now is the time to flog the Proform guys, I would also like to know if anyone read any articles about a side by side comparison of a standard Holley and one using a proform body. Ok Proform we are ready and we race again on the 30th, Like cooldude said we don’t give up easy.

I also purchased the Proform body last Christmas when Jeg's had them at $100.00 for the first time. I used a brand new 750 Holley DP and thought I could have a copy of the Holley HP carbs. My first mistake was using a carb without 4 corner idle, then I had to buy the dominator idle-main air bleed kit for too much money, and when I finally got even A/F from my gauge, I had a top end starvation that felt like fuel pressure but no problems there. So after 2 weeks of messing around with air bleeds, I then bought a Holley HP 950 DP for the same cost as buying a new 750 DP, Proform body, Air bleed kit. I pulled it out of the box, put on and checked the float level, and hauled down the street and I could feel a difference, like a cam change. So The Proform body gives the adjustibility but not the quality like Holley HP's do. Looks nice on the shelf, next to the Demon!.

You are going to hate me for this, About two months ago in installed a proform main body on my 650 mech. secondaries dp. ON a 71 firebird, pontiac 400, ported heads, extreme 274 cam, headers, ignition, intake.... I would have to say, that the proform fit perfectly and really did give me a bunch more power!!!!I was really impressed. It really woke up my engine, especially on the top end, maybe my engine was just undercarbureted? I have been running the main body, with no problems whatsoever, for the last couple months. I was really impressed, with the power i gained, i was really skeptical when i read the ad, but it really did help. it is made in taiwan however!!!!!

Did you get any numbers? Sometimes when I put stuff on my car/truck or whatever, it feels faster, just because I put something on there.

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68 Coupe, 350 4-speed
Jim's Camaro Corner (http://www.personal.psu.edu/jxu109/)

Cody, Spames is right both Eric68 and cooldude said it felt better on the street testing both expected gains and both slowed down. Without a time slip it is very hard to tell. If it feels better to you Great, I am surprised your idle quality was the same and you did not say if you did any adjustments.

[This message has been edited by ssvette (edited 08-13-2002).]

My idle quality was the same, i was surpised to find out that my throttle response was still very crisp, I had to put it some bigger jets, after playing with the carb a little, because it now flows 750 instead of 650, it defenitly feels way better, not just in my head, it probably had to due with the fact that i was probably under carbureted before, but for my 100 bucks it was definetly worth it! oh and in the instructions it says that it doesn't use two of the base plate screws, maybe u guys put the carb on backwards, the proform label is supposed to face the drivers side. also what is the deal with the rear airbleeds, i don't have four corner idle, should i change them, the main body came with some extra air bleeds.

[This message has been edited by cody (edited 08-13-2002).]

<BLOCKQUOTE>quote:</font><HR>Originally posted by cody:
You are going to hate me for this, About two months ago in installed a proform main body on my 650 mech. secondaries dp. ON a 71 firebird, pontiac 400, ported heads, extreme 274 cam, headers, ignition, intake.... I would have to say, that the proform fit perfectly and really did give me a bunch more power!!!!I was really impressed. It really woke up my engine, especially on the top end, maybe my engine was just undercarbureted? I have been running the main body, with no problems whatsoever, for the last couple months. I was really impressed, with the power i gained, i was really skeptical when i read the ad, but it really did help. it is made in taiwan however!!!!!<HR></BLOCKQUOTE>

Don't hate you at all, this thread isn't about bashing Proform, its about figuring out a problem. Glad it worked for you (or at least feels like it worked for you).

Now, what did you do different? I understand you used a 650 double pumper to start - thats 1 big diff. The 650 would probably be on the small side for a 400 cid engine anyway. And . . . you have a Pontiac motor - hmmm. I wonder how your engine would run with a stock Holley 750 DP compared to the Proform.

Anyone have any experience tuning a Pontiac motor? Do they like a different mixture - richer / leaner than a Chevy SBC?

One problem I have always had is getting the right jet sizes, i am currently running i think, 74/78, but my plugs still look on the white side, but a little diry, not tan. if i go any richer, it bogs some, and poots out black smoke when i gun it(probably also has to do with mech. secondaries, but i also have a stick) if i go any leaner it runs to lean and will backfire, or bog. SO the proform didn't fix that, i don't understand what is so different between the hp main body and the proform? Also the power difference was not in my head, when i first drove it, it was totally noticable, gave me a big ol grin., but it could of been from it being to undercarbureted, maybe it doesn't work good with your vacuum secondaries, any replies from proform?

...and where Is Proform? Werent they planning on responding?
This is quite intreging (my spelling is also http://www.camaros.net/forum/biggrin.gif) and i want to know what they have to say about it.

i give up on my proform. gona order a 950hp holley. i know, i know, i dont need it.

i give up on my proform. gona order a 950hp holley. i know, i know, i dont need it.

I also have the proform body. I bought it for my stip/street car just before I tore the engine apart. It is converted from a Holley 650, no 4 corner idle.

I did however, take it to the track with my daily driver. I made 2 passes with my usual carb, a Holley 650. I put on the proform carb that same night. I did tune the proform air bleeds a little before I went to the track. I put 36's on all 4 corners for the idle bleeds because it wouldn't idle and stumbled bad on take off. It drove great with the 36's. I left the inner bleeds, intermediate?, alone.

Anyway, I made 2 passes with the proform, I still had the slightly rich 74/82 jets in it. I ran less than a tenth slower, with the mph being the same. I chalked it up as no gain or loss. I figured that my engine didn't need a bigger carb.

Mine is the double pumper version.

Now here's the my buddy story.

My friend Todd, has a SBF with 410 rwhp on a Mustang brand dyno, gained .2 and 2mph with my proform carb over his Holley 700 dp. He bought one and maintained that ET, which is a best of 10.39 @ 130. He has done extensive tuning with his airbleeds, it idles low and doesn't smell rich at idle like a lot of engines with Holleys and big cams. He got his bleeds from Braswell (sp?) in Tucson, AZ for cheap.

The proform, or any Holley 750, will probably only benefit someone with approx 425 flywheel true HP or more. jmo.

I also wouldn't expect much ET going from any kind of Holley 750 to the proform.

------------------
67 Camaro, strip/street 410sb 11.63 @117.6
67 Camaro, daily driver 388 12.07 @112
website (http://www.geocities.com/lonnie67_1966/index1.html)

Lonnie,

You ran #82 in back and it was only SLIGHTLY rich? I don't recall what the O-4779 (Holley 750 DP) comes with out of the box, but that sounds rich to me. Maybe the secondary jets DO need to be fattened up with the Proform.

I might play with mine a little more - mainly so I can sell it with a clean conscience LOL, but also to see if jetting / air bleed changes will help. Smaller high speed air bleeds woulds also fatten up the upper RPM mixture, so maybe that is where we've got to go with it.

Proform called me this morning to state they are very interested in our issues. They would like our input to make their product better, they did sound very concerned on the phone. They did say we worked through the weekend on our issues and should have some answers by today, they asked us to bear with them as they work through this. They were very aware of the racing community and would like to work with racers using there product to make it better, it did sound like they would be willing to send out parts for us to try and see if it works!! I will let everyone know what is going on and if someone would like to tell our sister sites to get involved that would be great.

Proform also called me. Spoke with Rick, he put me in touch with Marty at Quick Fuel, nice guy. Marty had A LOT of suggestions for getting us back on track.

The short version (very short version) is that there are some significant differences in the fuel metering system (venturi vac pickup, downleg booster signal, air bleed sizes) between the Holley O-3310 main body and the Proform.

Among several other calibration changes secondary jetting will have to be MUCH richer - like #84's in back (compared to the #76 I was running - holy crap). Since Marty and Rick promised they would respond, I won't go into details to avoid confusion or misrepresenting their opinions.

I'm hoping Proform will incorporate these mods into their instructions so future hot rodders will get it right the first time. This is probably more than I would have figured out on my own.

Do they have a number? I would like to ask them some questions about the secondary airbleeds/ four corner idle thing. maybe get some tips.

Reviewing the collective statements regarding the reduction in performance when converting over to the PROFORM™ high flow main body, there are a couple of observations and suggestions that may possibly rectify the fall off in performance.

The original and early aftermarket versions of the list 3310 flowed 780 CFM. Only when the 3310-2 or –3 was released did the CFM rating drop to 750 CFM. This was accomplished by changing from the down leg booster venturi to a straight nozzle bar type booster. The straight leg booster occupies more square area thereby reducing the overall airflow. The higher airflow originally was attributable to a larger venturi 1 7/16” versus a conventional 750 CFM carburetor which has a 1 3/8” venturi. Comparing an older 780 CFM list 3310 with any 750 would likely result in less peak horsepower on a well-built engine. This would translate to less MPH in the quarter mile and an increase in ET. A four speed car would see a greater ET increase than a 2 speed PowerGlide car, as the four speed allows the engine to hit peak horsepower RPM more times during the run.

For 750 CFM racing carburetors the jetting spread between primary and secondary under normal circumstances is 6 to as much as 12 numbers. That is assuming that the secondary metering block (which appears to be the most prevalent scenario) does not incorporate a power valve. Power valves are seldom used on the secondary side in drag racing to prevent the possibility of uncovering the power valve during launch. Further to the point, the new generation list 3310 does not contain a power valve chamber in the main body so using a secondary power valve is impossible. Metering block conversion charts suggest a number 75 jet when replacing the original #21 metering plate.

The equivalent Holley® HP Series 750 vacuum secondary carburetor comes out of the box with number 72 primary jets and a number 84 secondary jets (same as the mechanical secondary version). In most current generation list 3310s the power valve channel restrictions (located behind the power valve) are approximately .062” which is about 60% of the square area of the original number 72 jet (.079” reference size). When the power valve activates at wide open throttle, it adds a considerable amount of additional fuel well in excess of the conventional 15 to 20% change in air/fuel ratio normally attributed to the “power enrichment” circuit. For most carburetors removing the power valve would warrant a four to six number increase in jet size (each jet is approximately a 4% change in A/F ratio). In this case it would require a much higher value as the power valve channel restrictions provide a much greater A/F ratio change. The net effect is to “over fuel” the primary side of the carburetor to help the secondaries open without an accelerator pump, due in part to the larger secondary venturii. Therefore, it would be prudent to try a much larger secondary jet than was run in the 3310 carburetor originally. While the final number will not necessarily be a number 84 that relationship, between the primary and secondary, should provide better performance and power than the 2 to 6 number spread that appeared in some of the comments.

One of the individuals commented by raising the secondary fuel level it improved the ET. Raising the fuel level is the functional equivalent of increasing the jet size, or richening the mixture. As he further noted this was impractical for street use as the higher float level creates driveability problems, especially during braking. The more practical approach would be to increase the jet size and leave the float level at the normal level.

The PROFORM™ venturi vacuum holes for the secondary are somewhat smaller than the original list 3310. This results in a slower application of vacuum generated by air velocity through the primary venturi to the secondary diaphragm housing. Bottom line, all things being equal the PROFORM™ main body the secondaries would likely open later and slightly slower than the list 3310. A weaker spring could rectify the situation, however, if the secondary jets are too lean the secondaries will not open as rapidly as it could creating a “bog” or hesitation if the opening rate is too aggressive. A quicker secondary opening rate can be achieved with a richer mixture since there is not an accelerator pump shot to help the transition to wide open. This is a fairly common issue in Stock and Super Stock classes that require the use of the original vacuum secondary carburetor. It is necessary to provide a lot of fuel to facilitate an aggressive opening rate without over fueling to the point where it hurts power.

Change secondary springs and jets to achieve the best MPH, then focus on the combination to produce the best 60 ft times then the rest of the incremental times will fall in line. That should get the ¼ mile ET to or better than the original 3310 carburetor.

The tech number is on their website. I hope these comments help. We will be working with Proform in the future to get our cars to run faster, they seem to be very willing to help unlike many companies I have dealt with.

Add me to the list of "Proform converts" that slowed their rides down. This is a very interesting topic, one which I plan to participate in both here and over @ Team Chevelle...........JJim

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"Laissez Le Bon Temp Rouler' Cha!"
Chevytalk Moderator (http://www.chevytalk.org/cgi-bin/ubbcgi/Ultimate.cgi)
1967 Camaro 327/275hp
Our Camaro (http://members.tripod.com/junglejim14/LindasCamaroWorld/id18.htm)

[This message has been edited by JungleJim (edited 09-05-2002).]

Jim,

Do you have a O-3310 vac sec or a 4779 double pumper? Most of those that posted slower times here have vac secondary carbs. And its no wonder - after talking to Quick Fuel, I found out about a lot of calibration changes that even the experienced carb tuners wouldn't have figured out. Its far from a bolt on change.

I broke a piston in my 383 and its just now going back together, so I haven't had a chance to try it out after the calibration changes on my car. I did run it on a friend's 350 and he said it felt better, but he can only compare it to the POS 10 year old Edelbrock 625 he had on before.

Eric, It's a 4779 DP ........I had the car running low 12's with a couple of runs that the 1/8 mi times work out to 12.03

Granted, the heat factors in but, I changed to a set of stock closed chambered heads at the same time and the car has never run the same. I pulled the heads added 2.19/1.88 valves and still no real improvement. I've been suspecting the carb for some time now.

I plan to look VERY hard at it from now on.

The engine used to pull through 61-6200 rpm with no probs.......now, it struggles @ 58-6000 rpm. Mid range "feels" stronger. 60fts are off as well. I've 60 footed 1.6's all day and now 1.7-1.80..........JJim

[This message has been edited by JungleJim (edited 09-05-2002).]