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Tri-Power cfm ?
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).] |
I don't know where you got the CFM numbers for a Tri Power but I think they are a little high. I have heard that 66 Tri Powers flow about 888 CFM and a 65 Tri Power flows about 100 CFM less than a 66. I have heard that the small air cleaners will only flow about 600 cfm. I have heard that a big car dual snorkel air cleaner flows about 1000 cfm. So which Tri Power has more performance, a 65 Tri Power with a big car air cleaner or a 66 Tri power with the small air cleaners?
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stripled, you may or may not have the right numbers but what you need to keep in mind is that 2 barrel carb's flow is tested at a different bench pressure. I forget the exact numbers but as an example (approx) if a 2 barrel is rated at 300 cfm it flows the same as a 4 barrel rated at 250 cfm. The best stock trips do flow slightly more than a stock quadrajet but only very slightly. Personally I dont care what they flow, a tripower and a 4-speed is the essence of muscle car.
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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.
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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? |
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. |
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.
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The trouble is the manifold flow. Like any manifold, if it doesn't flow the cfm of the carbs doesn't matter. CFM of carbs is a misconception anyway. A formula devised a long time ago in a galaxy far,far away. Air flow requirements of the engine determine it's capibility. To give you an exapmle I raced a Late Model on a 1/2 mile asphalt track and switched from a 500 2bbl. to 390 4bbl. (You could use either) and picked up track times. flow related/not cfm. There's another TECH article for Jim Hand answer to. Later.
http://Pontiacdude.cc N.O.S. is like American Express: "You don't leave home without it" [This message has been edited by PONTIAC DUDE (edited 07-21-2000).] |
Hey Strip! The most of the flow #s I have heard support the 800 cfm mark. Ken is right, no idel screws.
I have also read the article Blackcat referenced. In that article the tripower did outperform the Qjet in the test. (shifts were made @ 5500 rpm i believe) PONTIAC DUDE, Why do you say that the trouble is the intake manifold flow?? Do you by chance have a flow coefficient of a '66 tripower intake?(intake to head) I am interested in hearing your comments on this. I have heard many state that the flow of the tripower intake is poor my findings have shown otherwise. Wondering what you have experienced. Kev ------------------ Kevin Swaney Gold '66 GTO, 389 4 spd with Trips 13.042 @ 106.64 mph |
Thank you Kev..I had allways heard that the tripower would out flow any manifold except dual quad or tunnelram.Also due to the LARGE plenum areas and relativly short runners of almost equal length they would tenb to perfom more like a Tram.Though my Question still remains ie.CFM#s for carbs I'm sorry if I did'nt specify that.I'm also wondering about modifying the manifold by cross drilling the plenums to increase top end perf.
BVR421 Thank you again.I realize that I may not have the correct CFM#s.That is why I included the C#s for the carbs.I have tried to contact GM & Pont,but they can't seem to find any thing.Pont.refered me to this site for help.All is apreciated.Thanx again. |
Hey Strip! Well you should be able to get your answer if you are going to continue to use the end carbs with idel screws. Someone should know what a stock GM 2bbls cfm is.
Funny you seem to be doing some of the same thinking I have done recently. I did some port work on my manifold and gasket matched it as well. Need to see if there was any gain. I have not had any track time yet. I have wondered about the modification you discuss as well. I was more thinking of cutting down the divider between the venturis . So that the passenger and driver sides of the plenum can "see" each other. I did not want to make this mod as it would be a little difficult to reverse. I have thought about adding 1/2 to 1 inch spacers with the center sections cut out to test this a bit. If you make the mod (cutting down the dividers) let me know how you make out. I would be interested in the results. Kev ps. What are you running the trips on now and what kind of ET/Mph are you running? ------------------ Kevin Swaney Gold '66 GTO, 389 4 spd with Trips 13.042 @ 106.64 mph |
The problem is there are different CFM ratings for different 2 bbl Rochester Carbs. I have heard there is a Cadilac 2 bbl carb that is rated at 500 cfm. I know someone who use to work in a carburator shop and I was told that regular 2 bbl carbs can be converted to end carbs, I know this can be done with the small bore Chevy carb they use on the Edelbrock Tri Power for small blocks because someone is already selling them this way. If I knew how to post pictures on here I would show you how to make a duplicate center carb from parts from other carbs, I would also show the differences between the end carbs and the center carb. They make a Chevy carb that has a shorter fuel bowl on it that when used with a 65 or before Tri Power will have all the tops of the carbs level so a long oval type air cleaner could used.
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'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. |
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.
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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 |
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 |
The exh. are stock for '68 # 16 D port hds.The int. came from '75 # 5Cs which had been modified before I got them.I would assume that they are chev because of the shorter stems.Had to machine spring , guige & seat area to accept them.The reason I went with these heads was because of runner vol.,chamber size(72cc)& most importantly the amount of material to work with in the pocket. The pocket was re worked to a 17 deg twist to give the charge more swirl upon entry into the cylinder.The angle milling was done for 2 reasons 1.to decraese CCs from72 > 64 (after relieving the vlvs & mirror polishing.Matched to 68cc).2 To give the port a straiter shot at the cylinder(8deg versus 14deg).
KEV They are fully ported.Never flow tested but CC matched at 265 int. 190 exh. The cam D at .050 is 228 Hyd running solids.Inregaurd to your running spacers I think that would increase plenum vol giving alittle bog at bottom.But it would probably give a good reasult at top.The reason I said cross drill was because it would easier to plug if I don't like results.If you do try the spacers let me know what happens. |
SORRY forgot to say I haven't run the T.P.on it yet.I am in the process of pollishing the manifold. I did finaly find out that carbs are stock the outers were modified in the '70s. The guy who didit claimed he changed the throttle plates because the old ones were lost.He also claims that the set was originaly from '66 421 390 Hp said he wasn't sure but he thought that it was rated at 1100 CFM by the factory? Tonight I'm going to the library & I'm going to see what I can find on that eng.So far I'm guesing that I'll find the same as I've found in my manuals here.No 2GCs with matching #s From '64-'71.I am assuming that they must've been ordered special.
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66 421 Tripower came in two forms 356hp and 376hp I've had a few over the years. I will still stand by my 800cfm for the Tri-power. (stock unmodified)
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I'llbuy the stock unmodified 800CFM.but like I've been saying they are not normal.I cannot find a match to the #s any where.I just spent 3hrs in the library going through tech mans.and found about 2000 different 2GCs but no match to my #s. I suppose I'll have to take a guess or have them flow tested.Thanx
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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. |
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).] |
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.
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UNREAL, No reason to find Jon, he found us...
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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. |
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 |
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 |
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? |
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. |
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 |
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.
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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).] |
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).] |
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 |
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!" ------------------ |
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).] |
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 |
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 |
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).] |
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 |
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).] |
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.
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Old thread, easy answer worth posting for reference. These cfm numbers are at 1.5" Hg. pressure drop to compare to 4bbl.
Small middle carbs on all tripower setups are only 196 cfm dry flow rating. Big end carbs on tripowers are 307 cfm dry flow rating. Setups with small center carbs are therefore 307+307+196= 810 cfm total. 1966 tripower setups with 3 big carbs are the therefore 307 x 3= 921 cfm total. Practical approach is the pre-1966 3-2 setup is not a worthwhile bolt on unless you just like and want one, and/or the price is right. Or if it came oem / correct on the car. You can just buy an 850 Holley 4bbl and make the same power or more, with 40 more cfm, and less hassle. Or run an 800cfm Qjet break even on cfm. The 1966 tripower with 921 cfm at least you're gaining something at WOT. However, the aftermarket is full of 900-925-950 cfm or larger custom Holley type carbs. You must really want that 3-2 to bolt one on. So there you have it. Tripower is really a labor of love unless it's on a numbers matching or correct for year car. It's not going to make more power than a modern top notch 4bbl. It's eye and ear candy like the street rod / rat rod stuff. It will add substantial value to a numbers matching or correct restoration. Wet flow numbers will be less, basically they're 800-900cfm at best. |
Divide the 2bbl flow #s by 1.414 to get the 1.5" vacuum (4bbl) rating. The flow #s you quoted are directl from Rochester for the 3" vac. 2bbl flow measuring standard. if you add up your flow #s by 1.414 you get 884 cfm
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It does not matter that Tripowers can end up with more CARB cfm then the average Q-jet 4bbl that might be used because there air cleaners as I have proven on my flow bench are a larger restriction, like to the tune of 20% even on the smaller end carbs!
If you compare a 8” diameter x 2.5” air cleaner to a 5” x 4” air cleaner they both have the same area yet the 8 x 2.5 will flow more air once placed on a carb. It’s impossible for even a 389 no less 421 Tripower motor to hit even just 100% VE with its stock air cleaners. In fact the 66 set with its 3 large carbs does not make as much power as it should over the 65 set up because of the air cleaner limitations. The basic rule of thumb for air cleaners is that its diameter should be 4 or 5 times it height when possible. One advantage that the Tripower set up does have is that once then end carbs open up the tuned length of the intake becomes shorter which raises the rpm of peak hp even though the Tripower set up makes less hp then a 4 bbl factory set up. So basically the peak hp level of a Tripower noses over slower then the 4 bbl. And here’s more proof that the added two end carbs on a trip set up don’t do what they should in terms of added more hp. In one of the 2003 issues of HPP mag they covered a build up of a 421 taken up to 439 cid. The stock heads were ported up to 218 cfm. It used a 64 trip set up that was converted to use all 3 big carbs. This required 3 carb spacers to be made because the spacer used for the center carb was also a adapter to get the needed bolt pattern to take the big center carb. The manifold was well port matched. The cam was a good size solid with .515” lift and the compression was 10.3. A test on just the center carb made a surprising 350 hp. Then a test with all 3 carbs in play only produced an added 123 hp and shined a bright light on how inefficient a Tripower intake is! I get such a chuckle when I see folks who have emptied there wallet to place high flowing aftermarket heads under there eye candy Tripower set up. It’s such a flat out waste! |
I bet KREs single plane Tri Power fixes a lot of issues with guys trying to make power with 3 carbs.
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Steve25: I agree with the air cleaner info. There was a GTO convention in my area back about 1990. H-O held an open house, and we featured a dyno test exhibition for the attendees. We had a TriPower something on the dyno with stock air cleaners. The question came up as to whether the K&N filters were better. One of the guys had a set of K&Ns on his car. We put his filters on the dyno engine and picked up 15HP. Good friend John Sawruk was there to witness the test. Point being the stock filters are quite restrictive.
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I guess the K&N was the first design thin wall filters? |
Ok, but how many Tripower folks are going to blow another 1200 bucks on porting there intake when they have already dumped close to 3K into new heads?
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