[Roar]

Multiple carbs and flow. Ok as you said if you add all you carbs flow # together you will get 1250 cfm. But it just dosnt work that way. With multiple carbs the engine sees em as one. So the real flow will be less. So the 800 cfm is more accurate.
For example. a 455 will usually take a single 850 cfm carb good and run strong. Ok now you decide to go with 2 carbs. And you will find out that 2 600 cfm carbs will work great and the engine will run nearly the same. but hey this dosnt add up I now got a 1200 cfm carb if we calculated like you did in the beginning. But in the real world the engine will see em as a single 850 cfm carb.

['ol Pinion head]

STrip's, For ID sake, the '68 & later 2GC's will have the carb's part numbers stamped into the left hand portion of the floatbowl. If they're factory stamped... '66 & earlier 2GC's & 2G's had their part #'s imprinted on aluminum tags affixed to the airhorn. The small fuel inlet outer carb airhorns could be from many sources...61-63 Economy 2bbl Pontiacs, 6 cyl Chevy Pickups of same vintage or real tripower carbs: Pontiac, Olds, or Caddy. Type of airhorn venting or lack of it will further ID the small inlet 2G airhorn. #7029... sounds like '69 carb but last 3 numbers too high, carb could possibly be Service Replacement tripower carb, but doubt it with normal Rochester part # beginning... Saw that Jon Hardgrove was responding to some carb stuff over on Bill Boyle's board. He would be guy to ask as he has the experience & all the Rochestor books which detail even SR carbs.

[This message has been edited by 'ol Pinion head (edited 07-25-2000).]

[carbking]

There is a chart of Rochester flow rates in Doug Roe's book 'Rochester Carburetors'. As Doug at one time was with Rochester engineering, you can pretty well take these numbers as gospel. Noting that the 1966 carbs are S.A.E. size 3 (1.5 inch nominal - this is an 'artifical' size, and does not appear anywhere on the carb, the actual throttle bores are 1.6875) WITH internal venturi size (this is important, as there are several) of 1.3125, the chart states these carburetors will flow INDIVIDUALLY 423 CFM at a pressure drop of 3.0 in mercury. 4 barrels are rated at 1.5 in mercury. To convert the two-barrel rating to a four barrel rating, divide the two-barrel rating by the square root of 2 (1.414). Doing this conversion means each of the three individually would flow 299 CFM on the four-barrel scale. CFM of multiple carburetors is NOT additive. Several have correctly mentioned that the intake manifold is the limiting factor. I think Pontiac Dude mentioned a figure of 800 CFM for the set. I read somewhere a figure of 780, but can't remember where I believe 800 is close enough to 780 to use as a round figure. While 3 deuces are 'neat on the street', for serious racing remember Pontiac tried them on the 1960 SD 389 (manifold 535552 cast iron), and again in 1961 on the SD 389 (aluminum manifold 541510), but the 421 SD's used either single four barrels, 2x4 barrels, or for NASCAR the trap door '3 barrel'. You can bet they had a good reason. As far as finding casting numbers (the raised numbers on the carburetor castings) in some listing of Rochester carburetors, you won't. Casting numbers are the number for the casting blank before machining. These can be machined many ways, and used in many different carburetors. Once the tag has been removed on pre-1968 Rochester carburetors, identification, while not impossible, can be quite difficult. Two barrels produced in 1968 and later have the part number stamped horizontally on the passenger side of the bowl. Jon.

['ol Pinion head]

UNREAL, No reason to find Jon, he found us...

[Blackcat]

I know that your setup is not normal. The 66 setup uses 3 2gc carbs the end carbs have no provisions for idle. Is it possible for you to send pix of the setup. Having built lots of setups over the years. I found(like carb king) The early 2GC's have no ID except for the tag. 99% of the setups have lost the tags. 68up carbs have ID and ALL 2GC have interchangability. Plus Other lines used the same carbs (Olds tri-power).
CFM should be the last of your wories. Getting the setup to run without problems should be your first priority. Lines/fittings and past(as mentioned) modifications can have Major effect on your setup. Changing Blades and shafts could have a adverse effect on the running of the setup. Running the setup in a late Firebird will require a large hole in your hood. The front carb will hit. No air cleaner will clear at all. Had a friend go through this.
I'm not trying to scare you but is it worth it. Most 4BBl intakes will do a better job.
You have a better choice of carbs. Most will fit under the hood.

[KEV]

Hey Strip! I don't have any other carb info for you but I wanted to pass along this information. The carb king as well as Pontiac Dude mentioned that there is a flow limitation of the Tripower intake. I just wanted to pass along some information that I obtained.

Jeff Kauffman and Rob P. flowed my 1966 Tripower intake. I had done some polishing in the runners. The intake was NOT gasket matched.

On a 1967 670 head that flowed 221 cfm @ 28"

Runner #1 flowed 96% of the head flow
Runner #3 flowed 93%
Runner #6 flowed 96%

A Performer intake flowed 93% and a Torker II flowed 96% on the same head.

Now on a head that flowed 270 cfm @ 28" the Trips flowed 91% and the Torker II 94.4%

I would be interested to compare the flow numbers from one of the 1960-61 intakes.

I am just sharing information I have obtained. There may be other factors which may ultimately effect a 4bbl out performing a Tripower. I am uncertain that it is the flow potential of the intake that is the cause (as supported by the numbers above)

good luck! Let me know what your testing shows.

Kev


------------------
Kevin Swaney
Gold '66 GTO, 389 4 spd with Trips
13.042 @ 106.64 mph

[STripleduce]

Roar
Thank you I did'nt know that they couldnt be added up the way I did it.


'ol Pinion head

They are stamped like the '68 & later.Also have 1 tag on rear carb(didn't think it was right to have both?)#7025175 that I couldn't find a match for.The center carb has a small vent that closes above idle.The outers have no venting at all.I have looked at other applications,ie,chev,olds ect.still no match. The center carb 701 must be even older than 64 thats as far back as I have looked so far.The outer carbs are large inlet airhorns (no choke plates or provisions)its the throttle plates that were changed.From what I understand the guy who changed them said the mix screws are non functional.Used plates from other carbs because he couldn't find originals after he moved to new shop in the '70s.Thanx.

carbking

Thank you for all the formulas.Now I can jugle those around in my head to.LOL.I think tomarow I'll see if I can find Doug's book. That should give me the base line I need to figure out how much I can get out of this thing.I know I canstill hear everyone screaming but I'm stubborn.I'll make this thing work if it kills me.I have seen the older manifolds you refer to and I have to say that my manifold looks a heck of alot more open than those #9778878.Hope fully with all the pollishing being done I can attain 1000+ CFM.

Blackcat

Cool name Ihave one.Sorry no pictures yet should get scanner soon.

THANX

[STripleduce]

Kev

Thanx.You must've posted that while I was writing.I'm very pleased with what you just showed me.I also do not believe that the manifold is the limitter more likly the carbs.Was this flow test done w\carbs?If so what were they?

[carbking]

Striple, the manifold number you posted is more than likely a 1965 (9778818), which originally had a small (S.A.E.) size 2 center carburetor. The 1966 manifold is 9782898. The 7025175 tag is for a center (small) carb on the 1965 unit. This specific venturi size not listed, but will flow approximately 50 CFM less than the larger carbs on the 2-barrel scale.

Kevin, sounds like lots of homework. The individual runners are not the problem. The bottleneck is the 'join', where the air-fuel mixture from two sources comes together. If you have occasion to repeat the flow tests, try fabricating some baffles to approximate the air-fuel coming from each carb into the 4 center runners. Wet tests will vary significantly from dry tests, simply because of the interferance at the join. Jon.

[KEV]

Hey Jon! Can you explain a little more. I am not sure I understand the "join". Can you give me more detail on what you are refering to. I'm always wanting to learn.

The flow test I mentioned above was quite surprising to me. Have you ever "wet test flowed" a performer? or a Torker II? I would imagine flow would not be as high as a "dry" test.

Anyone out there have a sweet running Q-jet and intake I could borrow for a back to back test @ Norwalk?

Thanks for the info Jon,

Kev


HET STRIP! no carbs were on the manifold while testing. I am currently running stock 65 end carbs and a (i believe)) 1968 2bbl on the center.

------------------
Kevin Swaney
Gold '66 GTO, 389 4 spd with Trips
13.042 @ 106.64 mph

[carbking]

Kevin, the problem is turbulance. This occurs where the fuel-air mixture from 2 sources join at the beginning of the runner. Give me a call during office hours. Phone number posted on the inside cover of 'The Legend' (GTOAA), or check our website. Jon.

[STripleduce]

Jon;
I understand to much turbulance in that area can be a bad thing.I have been told also that by pollishing the entry to the port at the plenum can greatly improve the volumetric eficiency by cutting down the turbulance.I have also heard that building dams or small pyramid like structures under the carbs in the bottom of the plenum area will also smooth out much of the turbulance,which helps in balancing the charge to each cylinder.Is this true?If it is do you have any exp. with this & can you give me some pointers?Thanx

OH Yeah.almost forgot.I tore down the outer carbs last nite.The throttle base plate is non functional as far mixture.They measure 1.7265 strait through.The body measures 1.7265 at the bottom of the venturi & 1.3365 at top looks stock untouched.Jets are 68s for both.Venturi boosters have C# 16266 RP 70.I don't know if this helps to identify or not.TIA
[This message has been edited by STripleduce (edited 07-27-2000).]

[This message has been edited by STripleduce (edited 07-27-2000).]

[This message has been edited by STripleduce (edited 07-27-2000).]

[This message has been edited by STripleduce (edited 07-27-2000).]

[STripleduce]

Jon;
That is one popular book you told me to look for.In my county ,out of 17 issues only one is available(on the other side of the county)10 are missing or lost the rest are out onloan or reserved.I am now on back order till next Thurs.Did you tell everybody about this? LOL

[This message has been edited by STripleduce (edited 07-27-2000).]

[STripleduce]

Jon;
Thanx for that book. It has alot of info I needed.I still dont know the CFM for my carbs.I would suspect that they are the 430 but the venturie measure a little more than 1&3/8.Also found original T base plates for outers.They measure a little smaller than the ones I had on there,can I bore them out & use the butterflies from the other base plates? Thanx again for all the help.Once I have this all together I'm having the the whole setup flowed.My shop is fabing the adapter plate now.When I say whole setup I mean carbs-manifold-heads.So I can get a true CFM to each cylinder.Thanx

[Doug]

An article in January 1972 Popular Hot Rodding on an 11 second 66 GTO shows the guy estimated about 1200 cfm for a set of hogged out 66 carbs. A picture shows heavy work on the tops of them. Seems like I read an article several years ago about a national record holder stock 68 Firebird campaigner named Jim Mino from Pennsylvania got about 1000 cfm out of a set of tripowers that he had done extensive work on. I seem to recall he had measured flows. ( I've got both these articles somewhere.) I also recall he had a bunch of tripower stuff for sale in Smoke Signals a couple of years ago.

"Norwalk or Bust! Beswick is the KING!"



------------------

[STripleduce]

After some very extensive work done to the horns & honing & polishing the venturies flow on outers 620 each center 390 @ 3 inches figuring multiple carb theory should be in the 1000+ range.I now have new problem,when the outers open the motor stumbles.checked the pump shot looks insuficiant feels as though the pump is bottoming out to early on long stroke had set on short stroke but had no pump shot at all.New pump cups springs & check balls.?.What could cause this? I have checked the pump cups even though theyare new checked the float level,within spec.All new gaskets new checkballs, did the kit's come w/the wrong cups maby?TIA

[This message has been edited by STripleduce (edited 09-05-2000).]

[KEV]

Hey Strip! How did you flow the carbs? and why @ 3 inches? Were they attached to an intake?

On the stumble, do you have an automatic or a 4 speed? My car developed a stumble early this season when I still had the 4 speed in it. The car would launch and hook hard but then fall on its face and stumble BAAD! I believe it pulled the rpm down way to far after it hooked. Put in the automatic with a 3600 stall, no stumble. Just curious about your setup.

Kev

------------------
Kevin Swaney
Gold '66 GTO powered by a 389 with Trips
with 4 spd 13.042 @ 106.64 mph
with TH350 12.643 @ 104.48 mph

[KEV]

ok found the setup a bit back, did you say you would be running a 2.56 gear? I'm thinking you may need a little more gear in there.

Are you still running the 3800 stall converter?

I use the napa (Echlin) rebuild kit part # 2-5419. Where did you get your kits from. Old Man Taylor has always advised me to run the pump shot on the inside hole for the best shot. Are your pump rods the correct length? Are you getting full range of motion of the pump?

A few more things to think about...

Kev

------------------
Kevin Swaney
Gold '66 GTO powered by a 389 with Trips
with 4 spd 13.042 @ 106.64 mph
with TH350 12.643 @ 104.48 mph

[STripleduce]

Carbs were flowed on bench individualy at local shop no manifold plate available.@3" 'because thats the way they did it.had set on inner hole no pump shot outer hole I get pump shot but seems to bottom out to soon kits are KEM Forest city had hard time with NAPA only had 1 in stock at other store in Pa.The cups apear to be same as old tried old same thing.going to pull check balls this after noon & check them.The motor isn't in car yet on test stand.Runs great till outers are opened then stumble bog then great up to 7000. Outers are opening at 4200 is this to late or to early?Mabey timing curve? 2 lbs vac at WOT 6lbs on center 4 deg initial 32 total.

[This message has been edited by STripleduce (edited 09-06-2000).]

[KEV]

Hey Strip! I like the napa kits. I thought they were quality. I have had VERY bad luck @ forest city.

On the shot, do this... detach the rod and move the lever by hand. how is the shot then? do you have to move the lever up or down substantially to get the rod in?

also, are the cylinders the pumps go into round. take one of the pumps and push it down the cylinder (with the top off) see how good the seal is and how round they are. I had one carb that got out of round a bit and let gas past the plunger.

On the curve I am running 16 deg initial with total of 36 all in by 2500. 4200 seems a bit high for everything to kick in.

You running vac advance?

How do you have it jetted. I tend to run my on the fat side. 75 in the outers and 73 in the center. Old Man Taylor runs on a LOT less jet (and quite well I might add). I live in Ohio tho and he is in CA. Just saying what has worked best for me. Wondering where you are at on the jets.

Just thinking out loud...

Kev

------------------
Kevin Swaney
Gold '66 GTO powered by a 389 with Trips
with 4 spd 13.042 @ 106.64 mph
with TH350 12.643 @ 104.48 mph