All Small Six Tri-power tuning

This relates to all small sixes
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kevinl1058

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Well after 100 miles of easy driving finally took the Falcon in to the local chasis dyno to get some baseline numbers for tuning. Glad I did.. Founf that I was running way to lean 14.8-15.2 A/F ratio. My cruise ratio numbers where decent 12.5-12.8 off the primary carb, but as soon as we tried to get some load on it and the secondaries (outer carbs) kicked in it instantly went lean in the 15 range. Made a few adjustments, adjusted the pump linkage to get a larger kick of fuel, adjusted the prgressive linkage to get the carbs to come earlier. etc. slight improvement but still registered lean conditions. Carbs are Weber 34ICT/ICH series. Primary is jetted at 175, secondaries 155 Jet. Going to bump up my outer secondaries to 185's just to really fatten things up when they kick in. Hope fully when the car gets to its power curve the A/F number wil drop to 12.5 range. Going to start fat then work down on the jetting. Good thing is that the Shop sad that motor is strong and that it wants to go but your going to have feed that beast.
 

64falconsix

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Supporter 2018
Thanks for the post. Keep us updated on the tuning and dyno numbers. I hope to get mine on the dyno soon.
 

kevinl1058

Well-known member
After finding out how lean I was running, makes me think that it was part of the detonation I had with the first motor. Dangerous levels if I was running these numbers first time around. The hard part was not knowing that I was running that lean under heavy loads and with 2000 miles on the first motor running 15:1 A/F at 4500+ rpm would break down a motor. Going back through a weber jetting book it recommends running larger jets in your secondary carbs witha progressive set up. Under normal driving conditions plugs looked great and even on the dyno lower lower end numbers look good 12:5-8 but when getting on it leaned me out. Going to run 175 still in my primary then 190's in the secondaries. Going to jet high then work down at the dyno to help get it right.
 

echo1955

Well-known member
I still do not understand how it is possible to set one carb (center) for maximum efficiency on all 6 plugs,
Then
Inject 2 more carbs in the same manifold and still maintain maximum efficiency on all 6 plugs..
headscratch.gif


Unless you are willing to produce excessive carbon Or lean conditions
on WOT or anywhere above the mid range????

I’m just a bit slow on the up take some times..
uhhhh lately that has been occurring on a more frequent basic.. :mrgreen:
 

kevinl1058

Well-known member
What the dyno showed after making some adjustments I was pulling 111.09 HP and 161.23 torque in second gear. at 3200rpm. when we hit 3rd @ WOT the numbers spiked and we called if off. Even went to the point of basically going non progressive on the linkage. Changing the pump arm on the secondaries to give more fuel early, but still just too small of a jet to get my A/F numbers in the 12.5-13 range when the motor was under load. Just running on the primary the reading numbers were fine at cruise just when I get on it it wants more fuel . The engine will wind up to 5500 so hopefully when I get the jets swapped out we should see a nice gain in power. Goal is to be 190-200+ HP range and 220-230+ torque range.
 

JOHN G

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I'll be interested to see what your final jetting is-I have mine written down somewhere. I'll see if I can find them.
 

xctasy

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You are on the right track. 195s in all three would be my only choice.

When you've got one barrel per cylinder, the total fuel demand is least. As soon as you go for less than that, the engine needs a lot more fuel jetting to do its job. If you have no power Holley style power valve, you need at well over 6.46 cc/minute for each flywheel hp you aim for with a non port on port engine. That's given the best intake system devised. Our log head engines are quite less than state of the art, and there is no direct shot into the intake ports. A lot of fuel hits the intake manifolds iron walls, and although the 3 time 1-bbl is a massive improvement, its likely to need a large amount of fuel for each horsepower compared to, say, a 3 x 2-bbl DCOE 45 Weber or multiple ID whatever Weber 40/44/46/48 set up.

Here's why:-

For the worlds best atomised port on port carb, the least fuel one needs to get 500 hp is 1620cc per minute. If its a V8 with 8 barrels, each jet has to be 202.5 cc/min.

Port on port cc/minute is total hp needed, divided by 3.24. Thats what eight 202.5 cc/min jets make...1620 cc/minute. That's based on vast information from Cosworth DFV engines using port injection such as Lucas mechanical.

For non port on port carb system, the factor is about 6 times the flywheel hp for a 4-bbl on a V8 with power valve

For an I6, a 1 or 2-bbl with power valve still needs about 6 times the flywheel hp in fuel to make any given hp.

For a 3-bbls worth of carb with no power valve on a six, its a minimum of up to 6.46 times the flywheel hp. So to get 200 hp at the back, thats 250 hp or so at the flywheel, and 250 hptimes 6.46= 1615cc, or about 538 cc/minute each. The problem is that means you need a jet size of over 205 microns (80 thou) to get 538 cc/min, and the rule with Webers is that its not wise to go less than 1/15th of the venturi size with your jets, or else it stops dragging any extra fuel in like a functioning carb. You can do it, its been done before, but its not the best solution.

I calculate/sense that the 155 centre and 165 outers give a total fuel supply of 346 cc/min plus 2 times 400 cc/min, or 1146 cc/min total. At 6.46 cc/min per hp, thats limited to 140 rear wheel hp and 177 flywheel hp at very best. Thing is, 6.46 is based on having perfect 1-bbl to two cylinders porting, but on our Log head engines, the porting is poor, so the fuel flow is turbulent, and its likely to need well over 8 cc/min of fuel flow for each flywheel hp. So 112 hp might be you limit for safe hp, and the engine is most likely to need 640 cc per minute of jetting just to get 190 rear wheel hp. That's normally way over the confines of a 34 mm carb with a 26 mm venturi to atomise easily. That's why things are leaning out disproportionally to the number of carbs past 3200 rpm.


I'll undescore it with this. My 1982 Mustang 3.3 has a 28 mm venturi and runs a 71 call size Holley jet which gives out 470 cc/minute. It also has a nice big power valve. Yet it only kicks out 87 flywheel hp (67 rwhp), so to get trebble that, 261 flywheel hp, it'd need 3 of those 1946 Holley carbs with three 71 call size jets, which happen to be 195 microns anyway.

If I recall, the ICT 34 has a 26 mm venturi, so its maximum functioning jet size is 165. After that size, it stops dragging any extra fuel in. Put 195's in if you like, but I doubt it will give much extra power. If it doesn't give 12.5:1, then its time to ream the three venturis out 4mm to 30 mm, and then those 195 jets will give a lot more fuel, enough for 190 rear wheel hp anyway.

Based on a 1.265 rear wheel to flywheel hp conversion factor, 190 rwhp is 240 hp.To produce 200 rear wheel hp (253 hp) from 3 barrels, you need three 525cc/min jets, minimum. Thats 185 micron call size

To figure out what a each cc/minute jet is, just use the following conversion chart:

jetsize.gif


That implies that :

400 cc/min=165 microns, or 64.96 thou
425 cc/min=170 microns, or 66.93 thou
450 cc/min=175 microns, or 68.90 thou
475 cc/min=180 microns, or 70.87 thou
525 cc/min=185 microns, or 72.83 thou


For more info on exact jets, see viewtopic.php?f=5&t=8106&start=0

Hope this helps
 

JackFish

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xctasy":80yorbxq said:
My 1982 Mustang 3.3 has a 28 mm venturi and runs a 71 call size Holley jet which gives out 470 cc/minute.
Are you sure about that jet size?
IIRC, mine was a 61. I bumped it to a 66 during break-in.
 

xctasy

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Hmm, that's interesting. Not wanting to side track this post but they 3.3's varied between 78 to 83. IIRC, according to Linc 200, a 299 cc/min close limit jet was stock on his gray 1982 low mount 3.3 engine in his 1984 Mustang. The hole was a # 52 drill size, or roughly a 61 call size Holley jet. Sounds just like your 61.

A 61 is 298 cc/min, or a 152 micron jet in Weber speak
A 66 jet is 374 cc/min, or a 168 jet in Weber speak

The main thing is the Holley 1-bbl ran an additional enrichment device which made the fuel supply much greater.

Mine runs Holley 71 jet. I'm not sure if its stock. Maybee thats why I'm only getting 12 US miles per gallon around town...

In the case of the Holley 1946, they've got massive fuel enrichment to augument the single jet. In the case of your 78 year Fairmont 3.3 , it had 95 hp or so, and to get 260 hp, you'd need three carbs with just 152 jets, but you'd also have a huge amount of enrichment from the power valves. The point I'd like to make is that Weber 34 1-bbls don't have that, so a centre 155 and two outer 165's are way too small for an expected 260 hp at the flywheel in my opinion.
 

kevinl1058

Well-known member
This is some really great info, Good posting for us tri-power owners. I am currently running 175 in the pirmary (center) and 155 in the outer carbs. Since my cruise numbers A/F ratio were right in a good rannge I'm going to leave that one alone but I'm going to replace the outer carb jets to 190's. This should make a big improvement when I make another run on the dyno. The 190's should give me the fuel that I need to get into the 200+ HP range at the flywheel.
 

kevinl1058

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Dyno Results.. FLywheel Corrected # 177.05H.P. / 204.20 Torque Going with the larger jets really paid off. Not bad for starting off with a 85HP mill.
 

xctasy

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;) That's what I'd expect. Well done:) :LOL:

What revs got those hp and torque figures? That's quite sensational :mrgreen: :beer: :wow:
 

kevinl1058

Well-known member
H.P. peak at 5100 RPM / Torque Peak at 3250 RPM.. I Rejetted the outer secondary carbs to 190's and left the primary at 175.. I may bump up the primary to a 185 just to see if I can get a smoother roll in when the outer's kick in. I'll keep researching.
 

ludwig

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What are you using for a rear end? Stock or 8" or what? 'Cause that sure looks great, what you are getting.
 

xctasy

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Just keep jetting away and optimizing the progression circuits on your carbs. You need to know that you have an exceptional amount of power for the revs and size of your engine. My benchmarks are that if you are getting 1.39 flywheel torque (thats lb-ft per cubic inch), your doing as well as a Ford cross flow or Essex or Cologne V6.

If you don't get 200 rwhp, then just open out the venturi section as I suggested.

If I recall, the ICT 34 has a 26 mm venturi, so its maximum functioning jet size is 165. After that size, it stops dragging any extra fuel in. Put 195's in if you like, but I doubt it will give much extra power. If it doesn't give 12.5:1, then its time to ream the three venturis out 4mm to 30 mm, and then those 195 jets will give a lot more fuel, enough for 190 rear wheel hp anyway.

60 thou will do for much better air flow as the engine starts hauling up to the 200 feet per second air speed. A full 4 mm (157 thou) would make it fly even better.

These figures come from years worth of info from Pinto 2000 and Mini A-series books, and Mr David Vizards study of Holley and Weber carbs he used. Reworking Fords SOHC engine was pivitol for me. Also Pat Bradens Weber carb book was indespensible.
 

kevinl1058

Well-known member
I did some checking and the boh the ICH and ICT list the venturi's as 29mm in size. Will look into openning these up for more flow. Keep sending me the info.. great stuff. and has helped me get in the right direction. We did do extra work on the head larger valves titanium springs etc.. .60 bore 0 deck to get the compression up. dual pattern cam 264/74. The cam was degreed at 7.25 to get the most vacuum we could pull out of the motor. so it is a breather..
 
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