[STripleduce]

HELP!!! I have been searching for info on CFM ratings for tri power setups.I have been told several ratingsfrom 920 - 1400 CFM for tripower setups.I was told my set has a 390 CFM center C# on floatbowl 7019927 & 2 430 CFM outers C# 7029683.This should be considered 1250 CFM right? I've done some polishing to all carbs in the air horn area which should increase CFM. Also I need to know if CFM rating differs at differnt RPM?

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

[Ken K]

I have made the offer before and I will make it again. If anybody in AZ or SoCal wants to perform a Tri Power Test I will supply the Tri Powers. I have two 1965 Pontiac Tri Powers, a 66 Tri Power, A big car air cleaner, original foam type individual air cleaners, paper type individual air cleaners. I will also buy a set of K&N air cleaners.

[STripleduce]

'70-400-YD block stock B&S Fgd flt top.
Fully ported angle milled #16 hds 68cc 2.18-1.77 vlvs 11.5-1 CR.
1.5/8"into3.5"headers W/stepped crossover(own design).
284D .513L 112 deg Lobe center strait up.
560+ Hp

Used to be S.P. 900 cfm holley.
3200 lb 79 F.Bird.
400 T 3800 stall 3.54 posi.
Ran 11.2 consistant 1/4

Going into 2750 lb 47 Chev.W/ 78 camaro sub frame & 2.56 spooled 10 bolt.
If calculations are correct W/ tripower should get into mid 10s

sorry it's not a47 pont. but the price was right.

['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]

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.

[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

[STripleduce]

Ken & BVR.
Thank you for the info.There are other issues here to be answered. C#s are these the original carbs ?They do not appear to be as there are metering screws on all three.As far as I know only the center is supposed to.Also one other question that I forgot to ask before.Would cross drilling between the plenums help in top end?

[Ken K]

Smoke screen and Mirrors, what did you do cut down big block Chevy intakes and chop up the exhaust valves? Why didn't you use 670 heads? I guess the Chevy won't know the difference.

[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.

[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]

Kev.I,m jetted exactly the same.The curve comes in at 2700 the outers are opening at 4200 or about 1/3 throttle.Checked cups in plunger bore looks tight.If I move the pump slow no shot if fast excelent(by hand with top off).Set on the outer hole it bottoms out too early,but i get a little on inner hole I get nothing(by hand or llinkage)I'm beggining to suspect the check ball in the pump,going to disect tonight.

[This message has been edited by STripleduce (edited 09-08-2000).]

[Blackcat]

A couple of years ago HPP did a Tri-power vs
4bbl comparison. It was on a 68 GTO with a 428. The 4bbl was stock 750 quad. Their estimate of the Tri-power was 800cfm.

[KEV]

Hey Strip! I agree, your valve numbers look a bit off. Also, what is the duration at .050 on that cam? Have you ever run the tripower on this current setup or no? What are the heads flowing? You stated they were fully ported and I was curious as to what kind of #s they flowed.

Thanks for the info,

Kev



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

['ol Pinion head]

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

[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]

My assumption was correct.On the plunger rod at the bottom there is a brass nipple that holds the check ball in place.it had walked out about 50thnds pressed back on all good now.Motor going in tomarow hopfully hit the track next week.I'll keep you posted.Thanx All.

[Ken K]

Tri Power end carbs do not have idle adjustment screws, the end carbs you have are not correct. The end carbs also don't have a power valve or chokes. There are also different size center carbs, the 66 Tri Power uses a big bore center carb and a 65 and before uses the smaller carb. Do you know what year Tri Power you have? If it is a 64 or before it won't work with the 65 and up heads. Half of the Tri Powers you see for sale on Ebay and elsewhere don't have the correct end carbs on them. The fastest way to tell if a Tri Power has the correct end carbs is to look for idle adjustment screws, if it has them the carbs are incorrect, another way is to look at the fuel inlet. The fuel inlet on the end carbs should be facing toward the passenger side of the car.

[PONTIAC DUDE]

I was getting ready to reply as this is the first really free time I've had, but noticed a post futher up on the board on Tri-Power, that more or less says what I've seen. It's neat running trips, just need to make a tunnel ram type aluminum manifold for them at a little lower height and really blow some minds,,,,, and Et's. later.
http://PontiacDude.cc

[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.

[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