The large plenum is likely a main contributer to this effect. It looks like the fuel being drawn through the carb is loosing atomization in the plenum during transitional periods, like tip in and secondary opening events. The air probably stalls and loses velocity when the throttle blades crack open until the intake runners can catch up when rpm rises. A 4 hole spacer can help keep velocity up just below the throttle blades, hopefully keeping the fuel from dropping out and puddling on the plenum floor by the time it gets to the runners. It's something that might aid in carb tuning.
Running into same senario with a 830hp Holley, but an annular booster carb. 2"open spacer, T/A stage 1, cut down divider, A lot of fine tuning required. Big plenum to adjust to. Want to fine tune this stage1, before the SP3 swap. I'll get it dialed. :TU:
thank you for being the first one to understand the first big issue with the s/p on a buick 350. temperature plays a big factor in starting because of this and you can also flood the engine if you don't get the right amount of gas/air. saying that, once you figure out the carb, any changes to the heads or camshaft you will have to reconfigure the carb again. regarding the 4 hole spacer, I never tried it because I moved on to a s/charger. also should apologize about bringing up the fuel injection scenario. should have left it in the box. too many scenarios, too many problems with being outside the box. :grin:
Another thought , my friend was using turtles in the bottom of his sp intake and found the right shaped one and really liked it
I for one am glad you did bring it up. It's a relevant subject for the thread and opens up other possibilities. How is anyone going to learn anything if we don't discuss it? I think a few of us already have this thing figured out, we're just trying to nudge the others into offering up their own thoughts on it. You can't teach someone if you give them all the answers right up front! There are others now who are in agreement with the carburetor type/CFM that should be used with this intake...the boulder is finally rolling lol. Gary
x2 - something else is wrong here. A good Q-jet, even a 750 is more than enough carb for this engine. Tear it down, put the dual plane back on and start over. You might just find we weren't talking carb or intake at all.......
Found some good info here. http://www.enginebasics.com/Advanced Engine Tuning/Intake Runner Length.html
X3, there is something else wrong here. All this talk about intake manifold design, and carburetor differences is interesting stuff, but it always is a good idea to check the simple stuff first, the basics. Mike T did his homework on this intake, of that I am sure, so the design is good. I would still like to know fuel pressure and AFR at full throttle in 3rd gear. That is basic stuff that needs to be checked before going deeper. Looking at intake design, carburetor differences, and air flow basics to explain why Mark gained 8 MPH in the second part of the 1/4 is akin to looking for a flat cam lobe to explain a slight misfire.
He did say the carb was running out of fuel when not running. Something happened and it can't be intake related. Too many others running close to the same times with other carbs. That intake can't be causing a 10 mph loss in the 1/4 maybe 1-2 but not 10. Nick is right the engine could care less what carb is on there it just wants the gas and air. Mark, do you have a fuel pressure regulator, and if so it needs to be close to the carb to be correct. This will help keep the fuel at the carb. Have you checked the fuel pressure from the pump. What about the return lines is this plugged up and causing a starving condition, vapor lock? Blow air through the line to the tank with low pressure. Or, is there a hole in the line in the rubber line that is halfway down the framerail. There was a rubber line in between the two lines coming and going to the tank. Was that way on my car. They are about 4 inches long. How about that sock in the tank has this been replaced. That McRob pickup looks nice go with that. At one point I revamped the whole system and used an electric fuel pump put in a Mallory 140 with return lines and fuel pressure regulator. Did have to rebuild pump once due to failure but I think that was from the car sitting for a long time. Could do this to push fuel to the stock pump.
The rubber sections of fuel line checked ok, I know about the short sections along the frame rail just below the drivers door, I had an issue with the inside of the rubber hose collapsing, replaced 'em first time back in late 80's, then again before BPG this spring. checked/replaced the sections by the pump also. The hard starting/long cranking issue after sitting for a day or longer seems to be fixed since I replaced the Airtex pump with a NOS AC-Delco pump, maybe the wear pad on the AC pump is compensating for a worn fuel pump eccentric, which I will inspect and replace if needed. After BPG this spring, I NEVER returned to the 13's or near 99 mph. My next visit to Norwalk was for Super Summit about a month later, LOUSY track prep, I was spinning even with the MT's, my fastest mph was 95 mph. Was the Airtex pump failing this soon? I called and talked to Rob at RobbMc pumps, and he can do a wizbang pump for the 350, just gotta let him know. I asked if a pump can NOT BE supplying enough fuel, and the driver not notice (not nosing over, cutting out) he said yes it possible, but its a gray area/fine line between not enough fuel for the engine to run to its potential, and nosing over. All of the above was with the Stage 1 intake, absolutely nothing has changed in the way the engine runs, or idles, or so it seems. No smoking oil from the tail pipes, no smoking when running down the 1/4 I thinking/wondering if something was going before the SP3 and I didn't notice. Well I have my new AF meter to install this winter to see where this thing is. Question on that, install the 02 sensor in the header collector, install another bung in the other collector and swap the sensor from side to side when checking?
I don't think you need a bung in both sides. I installed mine in the passenger side, in the exhaust just behind the header collector flange.
I run my O2 sensor in the driver's side collector. I've never swapped it over to the passenger side though I've thought about it but operate under the principle that its a healthy engine and each bank is running approximately equal. Cylinder to cylinder might be a tad un-equal, but averaging four together should be fairly balanced bank to bank.
Thanks guys! I just went out to the garage and gave the throttle a couple flicks with the air cleaner off, I heard two nice, psssssst psssssst, from the accel, pump, so the AC Delco pump is obviously keeping the fuel "up there" verses the Airtex pump.
When I ran the nitrous the pass side of the engine was the one that went lean when I did not have enough fuel for the nitrous I had backed off the timing to 26 total so I do not think that was the problem at that time. #1 and #3 plugs were that ones that went lean. Melted part of the "J" strap on plug, but that was with the TA DP intake. I was trying a 150 shot and I just miscalculated the gas jet. Never tried again just stayed with the 120 shot. It might be all different with the SP intake. I would put it at the easiest place to get to on the header Where ever there is not as much stuff under the car. I would set it up for both sides so both can be checked. Why leave an open equation on that.
Cam issue is definitely viable. I chased a top end power issue for a year or so trying to figure it out. What's weird is how intermittent the issue was. Sometimes it was bad and sometimes the car ran fine. Even with 2 wiped cam lobes I still ran high 14s with the stock engine. Maybe pull the valve covers and get a dial indicator on the rockers. Can't hurt to rule that out
I still bet you the engine is not recovering enough in 3rd gear to let the intake start to work. too low of a gear in rear. I was at 4700 with the convertor locked up going thru the traps. (373 gear 28" tire) Mine is really not high enough either. we do not have 510 ft lbs of torque to pull 3rd gear thru at 80 mph. I have a 116 lsa cam 507 lift 230-245 @ .50
Not a good way to check a cam unless it has full oil pressure. Without any oil pressure your indicator readings will be all over the place because of spring pressure pushing the oil out of the hyd. lifters at different rates giving various reading for each one he would check that way. It could work with the dis. out with one person running a drill motor to spin the oil pump with a priming tool while someone else turns the engine over by hand to get an indicator reading. If you're really good you could run the drill and turn the engine over yourself. Buick does make it easier for one person to check it that way with the distributor in the front. Of coarse if in you were running solid lifters you won't have the above problem. GL Derek
