tri-carb power valve

41LjH

41LjH

Senior Member
Looking for advice concerning the carb setup for my current build.
I plan to use three Holley 94s (7RT) on a Edelbrock intake. Looking thru my 94 junk a found five power valves. One had a number on it (see pictures). I can't determine if it is "6" or "9". I also read the stock power valve is 7.5.
I plan to defeat the idle circuits in the two outer carbs, plug the power valves, and remove the choke plates to make then dumpers.
Any idea what power valve to use in the center carb with this setup ?
(8BA block bored 0.060,Merc crank & pistons, EAC heads,400jr.H&M regrind,)

Thanks
 

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I'm no expert but I think I would use a 97 in the middle instead of a 94 and stay with the stock power valve. With three carbs your vacuum is going to die quick and the 94 has a vacuum activated power valve. The 97 has a full throttle mechanically activated power valve.
I run two 97's on my 40 and I have progressive linkage. I think progressive linkage is also a good idea for your setup. I think without these changes you will run too rich. Let us know what you do and how it works. Good luck.
 
If you use progressive linkage, the vacuum will not drop faster than normal until you tip in to the front and rear carbs. If you are using all 94 carbs, I agree with blocked power valves and idle systems on the front and rear carbs. I would just seat the idle mixture screws on the front and rear carbs instead of totally blocking off fuel to the idle system. That way you have no fuel when carbs are closed, but will have the idle progression holes feeding once you open the carbs. That will help avoid any stumble when getting into the throttle.
Also, I think I have heard some experts like Max and Charlie Ny on this site, recommend around a 4.5 or 5.5 power valve if using Holley 94's.

Sal
 
It is hard to exactly know - without a vacuum gauge and test driving the car, but I would probably use a 4.5. I'd also try a 5.5 - just see which one runs better. A great situation would be to have a AFR meter - to actually see what your ratio is at under load - and when using either of the two power valves. Makes sure you order the correct power valves for a 94 - the modern/newer Holley ones will not seat correctly (gasket surface, style and sealing id/od is different). I'd probably order mine from Edelbrock.
 
I run dual 94's with the power valves plugged as suggested by Charlie NY. Happy with the set-up.
 
I would leave the choke plates to aid air flow, run power valves and also leave the adjustment screws in the carbs, I've got a tri carb on my '35 which was set up by jere jobe and that's what he recommended and built for me and its run like a top ever since, I've never had a days trouble from this set up.
 
If I was building that 3x2 setup I would block the PV's on #1 and #3, use a 5.5 PV on
#2. Because of the design of the 94 I'd block rear leg fuel passage of the nozzle bars
on #1 and #3. 51 jets on #2 and 49's in #1 & #3.
With 3x2's the butterflys must seal as tight as possible which with 94's is marginal.
Of course seat the mixture screws on #1 and #3.
I'll get on my soap box and remind anyone listening that any PV offered today is
a nice casting but in no way is the gasket surface flat or square with the 1/2"
dia threads. In my experience the modern Holley PV's do not work so good in a 94
which positions them vertically vs horizontal in modern Holleys.
These are my opinions only, I certainly respect everyone's opinions.
Charlie
 
Straight Linkage: The question becomes how much fuel does it need (enrichment) under load - and when. You might try a single power-valve in the middle carb first (blocked off ones on the ends). If it goes lean under load (based on the AFR meter, reading plugs, etc), then you might want to add the end ones. Also, you could two-step the power valves - maybe a 5.5 in the middle and 4.5's in the ends - so one comes in just a bit sooner.

The challenge with recommendations is that no two engines/cars are exactly the same - neither are the drivers (and then there is WHERE you're driving under load). How much fuel does your particular engine really need - nobody can have the exact answer . . . so you need to experiment and find out.

The 94 carb is a bit more "tuneable" than a 97 (due to these vacuum enrichment circuits), but it can take a bit more work to find a compromise that you like between raw horsepower, drivability and fuel efficiency (and it is always a compromise!).
 
In my experience for a 3x2 setup and straight linkage I'd lean to Strombergs because
of the mechanically operated power circuit.
I would plug all three power valves on a 3x2 94 setup with straight linkage. My first
choice for jetting would be 48's across the board and put the acc pump links in the
#1 position. There is no way that a Flathead runs the risk of going lean on the street
with this setup. This is a compromise situation and unlike days gone by reliable low
value PV's are not available, at least not ones you can 'turn your back on' .
An A/F meter is a necessity to consciously dial this compromise to it's max....a bit rich
on the low end but not too lean upstairs.
These are only my thoughts on this subject and I certainly respect and value all other
thoughts.
Charlie ny
 
Bored& Stroked, and Charlie ny, thanks for your reply. the information is very helpful. although I am not running a tri-power set-up on my flathead now , I have a tri-power on my 272" Y-Block with the end carbs currently blocked off. they were this way when I got the car. the center carb had 51 jets and was to lean so I switched to 56's for now and it runs much better. I checked the 2 end carbs and both also have 51 jets and the power valves have been plugged and the linkage for the accelerator pumps have not been connected. I have been working the other bugs out of the car and the engine is now completely broke in ( 600 miles ). I am now ready to start playing with the tri-power and make it completely functional, with the straight linkage. I appreciate you advice and will try to apply some of it to my application, this gives me some ideas where to start. by the way which hole is considered the #1 hole in the accelerator pump linkage, the top or bottom ? Thank You.---Jim
 
Ron

I think he mentioned it was an 8BA, .060 over with a Merc crank, and 400 Jr. stick. Seems like a lot of carbs and cam for the displacement.
 
ol'Ron, If you are referring to my Y-Block, the eng has later ( C1TE ) truck heads with larger valves, .030 overbore and mild cam. ( do not know spec's ) trans is C-4 auto, 3:25 rear. I know that the truck heads are not that desirable, but were on the car when I bought it, same for the cam. no spec's were furnished. rear tires are 7.50x16----Jim
 
Well I read the lead post and didn't see the 265 ci /400jr. Guess my eyesight is getting worse. Charley has offered the best solution here for street use. progressive, lean running center carb, rich end carbs. However, doing this with out an AF meter, is guess work at best. Also the ignition timing curves are very important here.
 
JSeery said:
Do you guys prefer a permanently installed A/F meter or just a test setup?
Click to expand...

I mostly prefer that the bungs are installed in the right location (not too close to the block) - say 36" back or so - but not at the end of a tail-pipe and if using two of them, before any sort of 'X' or 'H' pipe.

Given that I'm running a 6-Volt setup, will probably make mine a temporary install, used for tuning (with a 12 volt battery along for the ride), then taken out and an oxygen sensor bung plug threaded into the port until I need it again. Also, having a real bung in the exhaust system makes it a LOT easier to dyno test the car on a chassis dyno - the shop will like yah!

I'm getting ready to add this to my 32 - as I want to test a variety of different carbs on the dyno (to get some real performance numbers). Will create a post when I get to that stage (probably this Fall - too busy at the moment).

B&S
 
Thanks everyone, I appreciate the input.
The modifications to the 8BA are based on the parts I have on hand. I didn't mention the ignition is Mallory Uni-lite 3727501.
So vacuum is not being used. I plan to plug the vacuum ports on the 94s.
Just in case this doesn't work I'll use the old 390 Setup I have on the shelf.
I hope to have the engine back from machining in a couple of weeks.
I'll let you know how it goes.
Still don't have a clue what I am going to put it in:confused:
 
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