Johnny and Guy have valid points. I experienced the same "big hole" with the stage 1, cut down divider, and a 2" open spacer. Can't get much of a larger hole to fill with fuel mix, pretty much close to having a S/P on it. You need lots of fuel, and right now, when you nail it. I am going to the annular booster carb to atomize the mix effectively. Almost seemed to be puddling fuel with the big void to fill, especially with cold weather. The SP3 will be another adventure, but I'm getting dialed with the plenum void I've got going on now. NO BOG at all so far. Best has been only 13.50 @101, with one easy out of the gate run. Blew the 390 posi 2ND run and that ended my T&T for that trip. The 410 is crazy now, got to shift faster yet and the little 1/4" movement required of the column shifter kind of sucks.:rant:
Unfortunately we are doing the tests for the others out there it will be trial and error for us guys wanting more power. Compile the posts from today and think about it and make the correct adjustments. the four of us here have done the real testing of the engine now and now you Demko see what we are up against. We just have no one else to tell us what to do. Keyboard racing is not track racing.
You need more accelerator pump shot with a single plane intake. My BB Chevy has a BG Holley 1015 CFM with 50cc pumps front and rear and still wants more. You can increase pump shot on a Qjet. As I said before mixture distribution would be better with a Holley on this intake. All that said that does not account for your low MPH/poor high RPM power. You have 2 different things going on. Get the air fuel meter.
13.50 is nothing to be ashamed about! I WAS hoping for that or better with my SP3, but oh well for this season, hey at least were out there running these 350's huh:3gears: You really shift yours from the column? Damn that's too much monkey motion for me LOL, I let mine autoshift 1 to 2, then hold 2nd and hit third manually, only thing I feel I have time to watch is my tach:laugh:
I was thinking the same, its one thing to theorize what should work, but going out there and running the bitch for all its worth is quite a different story! The Q-Jet "should" work, and it does, very well. Would a square bore Holley DP work better at the track? Guess I'll find out next season!
I would definitely check that fuel psi and do a compression check. You may not feel it lay down but Id bet money you have some kind of fuel delivery problem the inconsistency in the mph is a tell tale sign of it , maybe your distributor bushing has fell out causing way to much advance , maybe you some cylinder sealing issues but I do not for minute believe the SP3 in itself has taken almost 100hp from you and nor has a slight tuning issue. And as Steve said S/P intakes do.lime a bigger pump shot and generally a higher stall to get short track performance back on par with a D\P but as far as the Qjet being totally incapable is ridiculous , optimum no but not incapable
Maybe this intake is different than my SP1 on the 455. I was running 12.40 -50's with my first motor (118 cam, aluminum heads) and the Edelbrock Performer and Q-jet. I then went to the SP1 and bought the AED 1000. My best with the SP1/Q-jet was a 12.20 @ 110.65, and a 12.11 @ 111.99 with the AED. I never had any problem with a bog and never changed the jetting on either carburetor. The SP3 has more in common with the SPX though. I would like to try the SPX on my current engine just to see how it would work.
I would hazard to guess that the porting that was done to Mark's intake made it closer to an SPX than just out of the box would of been? Derek
Unfortunately yes Sometimes, with wheelspin and launch, it's easy to hit the 2nd detent instead of 1st. So you end up with a short shift. With the 2004r my 1st is below the 350 turbo 1st gear detent. The console /bucket guys got it pretty good!
I agree with Johnny and Guy too, and as I said earlier, the Holley double pumper is the better carb for this intake. Velocity is lost straight from the carb with the huge secondaries on the Qjet with nothing to aid the fuel staying in the air, so by the time it reaches the runners it's not as efficient as it could be for full throttle performance. I know everyone loves the Qjet, and I do too, but sometimes we can't wish something to work. It's not magic, it's science. A square bore carb with dual accelerator pumps for even fuel/air distribution is what is needed. I don't even think a 4 hole spacer would do as well with the Qjet vs no spacer and the Holley DP. Ah well, that's my 2c. Gary
Ok let's not bash the 'keyboard racers' too badly here....we need all the information we can get our hands on. What is needed here though is more track testing, I agree. Sometimes though, figuring things out 'on paper' helps before hand. Otherwise you're throwing money and parts at it and hoping it will fix it. :Smarty: Not everyone has 10's of thousands of dollars burning a hole in their pockets, and even if they did, they want to make sure what they spend it on will be a wise investment. Gary
Good explanation on the carb differences, makes more sense to me now:TU: From the heads, down to the drain plug, its the same engine, the only thing I changed was the intake, the intake "should" free up intake restriction, so that's all good there, so I guess you guys are correct, the Q-Jet just doesn't do well with a (this) single plane. Your right Gary, I was wishing it would work, I tried to the best of my abilities. An air/fuel meter isn't in the cards for me, I just cant justify the cost to use on one car, and a few people said its not a good indicator for track use.
No bashing intended Gary, I apologize if it sounded that way, Im just discouraged I didn't do better, AND have to wait till next spring Me personally, Im more of a hands on person, I learn better from experience than text.
No, I meant that the air gap design of the SP3 makes it more like an SPX than the SP1. My SP1 warms up very quickly because it is bolted to aluminum heads and the runners are not as isolated from engine heat as the SP3/SPX.
With the air fuel meter you can set up your fuel curve thru the entire operating range. That can be done in normal street driving. At the track you only have to make 1 or maybe 2 passes to set your secondary rod size. Then you can work on your reaction times. An 850 will be too much carb. I would go with a 750 or maybe a 800. Just like cams bigger is not always better. 350 cubes is not drawing enough air for proper atomization with a bigger carb.
You are probably right, but with Mark's car, I think it would really be cool if he could borrow an 850 DP and try it. In theory, the 455 isn't supposed to need a bigger carb, but bolt one on, and they go faster at the track.
455's do like big carbs. Even though as I've said before the 350 is a 7/8 scale 455 in layout the big difference is the bore/stroke relationship. 350 is square while the 455 has a big bore/short stroke. It draws on the carb differently.
Yup, reading thru this, that was my comment.. Don't confuse a 350 with a 455. We will probably find as Buick 350 performance advances, with new parts available, that the old 455 rules don't always apply. New "rules" for the 350 will evolve. Biggest difference between the two engines is bore size vs the cross sectional area of the cylinder head. On a 455, we have what for a long time was nearly the biggest bore in the industry, with fairly small ports.. The 350, has a much closer bore size/port area equation, and why they seem to like bigger cams and RPM. This makes the motor more sensitive to anything that restricts it's ability to gain rpm, or slows the air down in the engine. So bigger carbs might now not be the hot ticket, once we get a complete free flowing intake/head combo, when the new Alum heads come out. I suspect this engine will be a lot more sensitive to sizing and specs, that the 455 motors are. It would be interesting if someone with a flow bench (paying attention Chris?) would do a flow test on stock 455 heads, vs stock 350 heads, and measure velocity, using the normal 4.350 BBB and 3.830 SBB bore sizes. It would be a good starting point and background info for the discussion your having. Johnny seems to have already "been there, done that", as one of the first using a single plane intake on a 350. I wonder if Sonny Seal ever ran with a single plane/ Q-jet, and what input do our Stock/SS 350 racers using the SP-3 have to say, since they are confined to this carb. That all being said, I would be surprised if bolting an intake on, would cause that much fall off in performance. But having limited 350 dyno time, and no drag strip experience with the 350, I will keep my thoughts to myself, until more information is available. Mark, If you have not already done it, try a different Q-jet.. I just had one on the dyno on a 470 that was mysterious.. customer supplied carb, fuel consumption was in the ballpark, but it was 40 HP off the shop's Q-jet, and nearly 60 off the best 1000 HP/spacer combo.. and these numbers were not at Peak rpm, this was one of the current motors in the shop, I had the issue with the hyd roller lifters.. so it would only rev to 5400, and I suspect it was losing effective cam duration, as early as 4500 rpm. So the difference may have been greater than we saw that day. I have dynoed plenty of Q-jets on single plane intake 455 motors, and never seen this before. I would lean toward airspeed/atomization issues on that one, but the shops Q-jet worked just fine. While I understand it worked great on your TA STG 1 intake, and agree that it is probably as good as any other Q-jet, it's an easy test. I will make sure to test with both a Q-jet, and 750 Holley on the upcoming SP-3 equipped 350. Interesting discussion, thanks for the effort and sharing the information Mark, and everyone else. JW
Thanks for the info Jim and everyone, VERY interesting! Well, I couldn't sit still, and Im NOT waiting till next spring, Im too damn curious! I bolted on my Holley 750 Vac sec. carb I had on the Stage 1 for years, Foxes Den suggested I try it for ****s and giggles awhile back, so I bolted it back on, fortunately I boxed and taped everything when I removed it for the Q-Jet on the Stage 1. All I need is the fuel inlet with a -6 an male fitting on the end. Anyhow, Hoping the track will be open next Saturday, the weather is getting more diceyray: I know this comparison between the Q-Jet and Holley is kinda apples to pears, but Im curious about the spreadbore verses square bore behavior on the SP3 Oh, and the SP3 does have a "big hole" to fillp I was going to re-install the 1" 4 hole spacer I had under the Holley on the Stage 1 but no go on the SP3 Also my drop base air cleaner wont fit the Holley, carb is too long, it hits the rear fuel bowl. So no spacer under the Holley, and I get to use my GS air cleaner with my K&N element and K&N extreme air filter top/lid:grin:
