POE changes for a 4-speed

[70GS455]

Would you recommend plugging the secondary POE holes and re-drilling them below the flap for a 4-speed vs the standard flap cutouts?  Seems it would do slightly better

[Cliff Ruggles]

Does it have any hesitation/stumble/bog going quickly onto the secondaries?

[70GS455]

Well since the engine is not together yet and I haven't sent the carb in to you yet....no lol. Was just trying to plan ahead

[Cliff Ruggles]

POE holes below or directly in line with the airflaps is the best scenario, and this was done on many of the factory "high performance" Q-jets including the Stage 1 Buick and most Pontiac carburetors thru 1979.  Pontiac even used slotted flaps for quite a few years, until they discovered that solid flaps with large holes seeing the underside of them was a better deal......Cliff

[Dano3500]

Hi Cliff, Dano from v8Buick.com here & my first post on your forum. I don't know much about carbs tbh but have your book & probably need to learn.

As you noted above, Stage 1 carbs (auto & manual) had the POE holes below the flaps. All of the '70 350 4-sp (7040245) carbs I've seen have the holes above the flaps. The 245 does use a different air horn (7038473 for manual 7038474 for auto) than a 350 automatic (244) but I can't imagine that every 245 I've seen (maybe 10 or so - pretty rare carb) has had the air horn changed.

I had my 245 for my '70 GS 350 4-sp rebuilt by Fred Catlin (old Buick racer) and he put on an air horn w/the holes below. I have no idea what it came off of. I am looking to put this carb on a stock "appearing" build, but the internals will be far from stock (higher comp., stroked, big valve ported heads, etc.). What is the functional/performance difference between above/below & is there any reason not to or issues with changing the air horn to one that has the holes below?

[Cliff Ruggles]

The reason they are below or directly in line with the flaps is so the fuel doesn't "puke" out on top of the flaps when you go quickly to full throttle. 

It's not typically a  problem area right to start with, but for sure we want as much fuel as possible from the secondary POE system to enter the intake manifold when the huge secondaries come on line to help prevent a momentary lean condition (hesitation/stumble/bog). 

Also keep in mind that the intake does get a nice shot of fuel from the fuel in the passages feeding the main nozzles, but it is often not quite enough.

Even more important that POE is having the link from the pull-off adjusted correctly to keep the flaps from "whipping" open.  The secondary tension spring is not strong enough to do that for us so we need the pull-off to dampen the opening every so slightly till fuel starts flowing as there is no accl pump system for the secondaries.

I'd note here that factory pull-offs had calibrated release times to help us out.  Most aftermarket replacement pull-offs are not timed correctly and often things aren't adjusted correctly during the rebuild either. 

There there's the crowd to removes the link from the pull-off to the secondaries and tries to tune with the spring.  That NEVER works out well although  folks doing this think that the "kick" they feel going to full throttle is somehow better than smooth/seamless transition..........

[Dano3500]

Thanks (as always!) for the explanation! I've seen your comments on the linkage:).

Do you know why this design was mainly used on manual transmission carbs?

So on a high perf., or even stock 350 4-sp. (seemingly any engine?), is there any reason not use an air horn with POE holes below the flaps? Can an air horn w/them above be modified to have them below &/or is there any tuning to be had by enlarging the holes?

[Cliff Ruggles]

The POE exit holes can always be relocated below the flaps.  It's actually not all that difficult.  First you have to block the original holes, then re-drill new holes under the flaps. 

To do this here I melt a little lead from  wheel weight into the supply holes after removing the tubes.  I then drive the lead down with a flat punch adding if necessary to make sure the upper holes are plugged. 

Next using a small sharp center punch light up with the passages below the flaps and make a mark deep enough so your small drill bit doesn't slip (drilling at a slight angle).  Drill thru until you connect with the fuel supply passage.  You have to drill slowly and make sure the chips clean out or the drill can load up and snap off........