While waiting to get back to the track to test my SP3 (hopefully going this Sat. the 31st) I noticed a couple things about the SP3, being this is my first experience with a single plane intake verses a dual plane, this may seem old news to you guys that have had single plane intakes before. Cold start at 50 deg, with no choke, its a bitch, it fires initially, then crank, crank crank, pump pump pump, FINALLY fires, but VERY cold blooded. Getting the Q-Jet to not bog on the SP3 when slamming the throttle to wide open from a stand still is tricky and time consuming. I believe I have it tuned out by the spring on the sec. air doors, 1/8 turn at a time in the adjuster, DAMN that is a sensitive setting! I was able to run the tension pretty loose on the Stage 1 intake, but not the SP3. Question, (Q-Jet) when going to wot from a start, both primary and secondary throttle plates are open, is there a "pump shot" that covers fueling until the secondary air doors start to open and lift the metering rods? Or is the vacuum draw on the sec. doors great enough that they start opening soon enough?
No 'pump shot' but there are small holes that can be machined into the butterfly flaps to help the secondaries get a head start when opening. I'm by no means the Qjet expert here, but I think I remember this correctly. Others here will correct me if I'm wrong. Have you tried a 4 hole spacer? I know others say it won't do jack but with that open plenum you need an edge for lower RPM velocity. Cold natured could be because of the open bottom of the intake. It is a performance oriented intake, afterall. Maybe with some tweaks you can get it where you want it or at least improved over what it does now. Best wishes, Gary
Mark. Check everyday performance. He posted on fb that he has an electric choke adapter for our qjets. If you want to go that way. And yes pump shot is only front 2 barrels so I'm guessing you want secondary a bit tighter for more vacuum?. Or maybe the next up hangers and rods to get faster flow.
Mark, Maybe hook the choke back up on that q-jet. They came with one for drivability reasons...... My 750 Holley fires right up with the elec. choke, the 850 Demon does too with no choke, but I have to hold r's at 1,400 till it warms. The elec. choke on Holley does the peddle holding for me. This is with 2" OPEN spacer. My heat ports in heads are blocked too. 50cc pump and larger squirters solved all my stumble problems. I have a big area to fill there with the 2" added height, sure it's same with the S/P.
Hey Gary, Its funny when the weather gets cooler, yah start to realize, wow, this intake is more "race" oriented, "air gap" design, open plenum, plus my exhaust crossover is closed with pipe plugs in the heads. Hopefully I can get to the track for my last chance this season to see what this thing will do:TU: Then its hibernation time for the winter
Hi Alec, I did go slightly richer on jets and rods on the primary side, and thinner rods on the secondary side, I had messaged Ken and asked for his opinion on jets and rods, and he was right on the money, the engine seemed to respond, thanks Ken:TU: As far as the air doors, the weather (declining weather) seems to be a HUGE tuning factor I keep forgetting about as far as the engine accepting the sudden huge gulp of cold air when going to WOT:eek2: I guess my favorite tuning tool is going to be my little pocket screwdriver and tiny allen wrench for this Saturday at the track! This tuning stuff for max performance at the track is all new to me, but it sure is FUN!
Hi Mart, Is your 850 Demon a double pumper? Im not going to give up on the Q-Jet just yet, but if I cant get consistency from it Im thinking a 750 Holley DP may be in my GS's future. The Q-Jet runs awesome on the Stage 1 and the stock iron intake, but Im wondering if its a match for the SP3 as far as all out performance.
I thought you could change the shooters in a Q-Jet. Need to go to a larger one if you want to cover up that bog. This is where the Holley is going to shine. Plus , did cutting the back to accept the Q-Jet cause the carb to need more shot since now the the plenim hole is bigger now. I have been thinking of not having the holes for the Q-Jet made. Do you run any spacer and if not you could try a 4 hole spacer but you will be moving the carb even higher which means it will need a bigger shot. It needs a Holley or similar carb. Sorry Q-Jet boys Dbl pump needed here.
On the secondary side there is no pump but there is a Pullover Enrichment circuit that is meant to provide fuel for a short time upon the secondary throttle blades opening. On a non stage Buick qjet, the discharge holes are located above the air flaps, and would normally begin discharging as soon as the flaps opened a crack and exposed the holes to vacuum/air movement. On a performance application, small notches can be cut from the flap to bring the POE online a split second sooner, not waiting for the air flaps to move. the volume coming from the ports is determined by the hole size. The duration of the enrichment is determined by the size of the well restrictions in the fuel bowl. The outer two brass tubes on the underneath of an air horn are the pickup tubes for this system As for the primary side, you can open up the pump discharge ports a little - small amounts make a big difference, and put stiffer springs in the pump.
Both are double pumpers. I, as you did, had a 750 Holley, vac. secondary 15 years ago. Sold it to a Camaro guy:laugh: Still haven't ruled out trying a Quick Fuel Q series (no choke) 850. I think Walts72 is having good success with one. Remember, all the GM cars years ago with highest performance had Holleys, except the 455 Buicks.
Here is the electric choke conversion http://www.v8buick.com/showthread.p...onversion-kits-for-1968-1974-Buick-Quadrajets
Believe it or not, I'm going to have to side with the fellas saying to use the Holley double pumper, only I'd recommend a 650 CFM. My brother used a 650 DP on his single plane 440 Mopar with a lopey cam and headers, trying to get better street manner and low-mid response. Guess what? It worked. Can't argue with results, especially when you know why it worked. Try it on your Buick 350, and remember, bigger is not always better. Gary
You can change some things to get more secondary enrichment which is sort of like the secondary side "pump shot". You can get more fuel and quicker shot. There are also some ways to get a quicker/better shot on the primary side. These all require some modification to the main body, air horn and some of the parts, but that's all part of fine tuning the quadrajet. It is tunable like any carb. Maybe not as easy at this level as a Holley type but still tunable. Do you know what accelerator pump you have?
Even I agree a holley might be the best match to the sp3 and a smaller carb is normally good on a single plane
I agree bigger is not always better but most do agree that a bigger carb on the DP TA intake seemed to respond better to a larger carb than a 750. So maybe in the case of the SP3 the Holley 750 DP might be the best size carb for the new intake. Since Demko has a lower gear ratio it is taking a bigger shot to get things moving. On the test vehicle in the beginning the car had large 456 gears and a high stall convertor and this is making up for the lack of pump shot on the Q-Jet. you are just going to have to play with it and try what the Q-Jet rebuilders are saying to give more shot for the secondaries. Take the other vac secondary Holley to the track and switch it out and see what happens. You just need the flat plate to go under the Holley. I have been reluctant to get the Q-Jet holes drilled but I do happen to have an old Holley Dbl pump Spread Bore 650 cfm carb on the shelf that might be fun to try. Anybody ever try a Thermoquad. Talk about something that spits gas everywhere when you floor it. :Brow:
Thanks guys for the tips and ideas:TU: For now Im going to see how the Q-Jet does on the SP3 this weekend at Thompson (hopefully no rain) MAYBE I'll have quicker times to report back to you all, and be able to wring this thing out on the track and see:shock: Getting on it on the street isn't any fun
This intake is not going to be a gas mileage intake. It is going to take a fairly large pump shot to stomp it to the floor since it is ALWAYS bone cold. You will have a better chance with a DBL pump you can keep the primary shot on a small as you can go then when you stomp it you can give it a nice big shot on the secondaries and off you go. REMEMBER, there is now a giant hole under the carb that HAS to have enough gas to cover up that big hole when floored. Whether anybody likes it or not it is more of a race oriented intake and should be treated as such. That means above 3000 power band. Build your motor as such. There is no heat in this thing to help you atomize fuel. This thing is not for some stock engine I don't care what anyone says. That is what the DP intake is for it can make power past 6 grand. The SP3 if for above that. Build as such people and quit screwing around.
X2000! I was thinking the same thing, and pondering the same points you mentioned! Im not a racer by any means, I just like running my GS at the track to eek out as much performance as I can for fun:Brow: BUT, yes, the intake is designed to keep the fuel charge as cool as possible (air gap) no provisions for heating it, (I don't care anyways) Yes, HUGE HOLE/CAVERN right below the carb, (That's AWESOME) Plus I had my ports matched to my heads, Michael said he took ALOT of material out:eek2: Warm weather its fine, cold weather its just a bit cold blooded, I'll work with it, no biggie, the personality of the engine has changed with the SP3, that's fine, I just have to get used to it:TU: As far as this intake on a bone stock 350, naaaaaah, I agree, Stock or Stage 1 intake is the choice there. The SP3 pushes the 350 into the "race" arena, but its about time!
