Holley 470TA Tuning

Well, according to Holley, if you shift at 5k ( seems a little high, but wht the heck do I know.. I still run the 134R) ) then the 470TA is your carb. From reading the tune-up tech sheet #199R-10268-4, if you get the secondaries to kick in early you get the stumble that was discribed. The tech sheet says if you set 'em to come in a little late or right on you won't have the stumble or low-fuel/air mixture and it'll be smooth all the way to redline.

 

17mpg seems to be my average right now. That's compared to about 11-12mpg or so with the 2g. Granted, part of that was probably valves. I don't have a working fuel gauge, and I used to be religious about stopping often to re-fuel. Kind of surprises me now when I drive it for several days and go to fuel up and only put in maybe 3 or 4 gallons.

Still going to play with the secondaries a bit more; will post when final.

 

Okay, recent move forced pretty big elevation change; back to the garage with the Holley. Been playing with it for a week or so now and I think I'm getting really close to having it dialed in. However, I think the power valve is giving me some trouble. I've been changing them out, and I can watch the vac guage and just about as soon as vac drops below whatever threshold I'm running, I start to go extremely rich. I'm thinking the secondaries and PV are opening at the same time, and it's like drinking from a firehose for my lil' Dauntless.

What do you guys think about running a plug and just tuning off the jets? I was thinking maybe a tad lighter secondary spring and then tune accordingly.

 

My thoughts on this are, since the 225 would probably reach catastrophic failure before it ever pulled 470CFM, we know that the secondaries are never going to completely open. Therefore, we aren't really ever going to use the entire carb, anyway, so why try to tune it like we are? Since the secondaries only need to open a little bit, I'm thinking about tuning them to essentially function like a power valve; keep the primary jets lean and just have the secondaries come in a bit earlier with maybe a couple size increase.

My only other choice at this point is to run a normal PV setting, but put in the black spring and lean the secondary jets down to almost nothing; I get a little nervous having lean jets at high load/high rpm. I leaned the secondary down to a 49jet one day and it really improved low vac WOT, but if that PV ever failed to open...

I've got the primaries making a nice plug at idle, mid-range acceleration, and cruise, but the combination of PV and secondary just seems to drown the engine whenever vac drops below the PV.

 

Well, the plug is definitely NOT the answer. After much tinkering, the best I could do is get it to run well at idle and high RPM, but stab the gas anywhere in the midrange and you run out of fuel. The problem is that, even with a light spring in there, the 225 doesn't draw enough vac at lower RPM to open the secondaries and start getting fuel in there. Best to tune with the PV just like Warloch said above.

 

"but stab the gas anywhere in the midrange and you run out of fuel"

that is 100% correct.

"even with a light spring in there, the 225 doesn't draw enough vac at lower RPM to open the secondaries"

that is 360 degrees off.

the secondaries do open and open to soon and the engine is starved for fuel.

disconnect your vacuum diaphragm linkage so the secondaries do not open and go out and stab the gas.

 

Tried huge jets (all the way up to #72), springs all the way up to black (essentially not opening), no joy. Could get it to run okay under some conditions, but PV tuning definitely the best option for everyday drivability.

 

"(essentially not opening)"



how do you know they are not opening????????????????????????????????????????????????

 

When I experimented with the big jets in there for test and tune, I can tell exactly the point when the secondaries open. With the black spring, my secondaries do not open until very high RPM. Not sure exactly how high because I don't have a tach, but I'm guessing 3500 or maybe even a little higher. With the plug, this essentially meant that I was getting no secondary and no power valve at lower RPMs, starving the engine for fuel. I tried a bunch of different combinations, and I'm sticking with tuning the PV. After watching the vac guage under a wide range of operating conditions, I finally settled on a 4.5 PV, a silver secondary spring, and a 57 secondary jet. I'm at just about perfect sea level conditions right now. It's running pretty darn good, way better than it ever did with the 2G, especially at highway speeds.

EDIT - Sorry, "silver" secondary

 

well as long as your satisfied with the performance of your rig that's all that matters.