Wow, on a normal run, the car should pick up at least 20 MPH or more in the second half of the 1/4. That means you should have been right around 100 MPH. I can't help but think we are missing something big. Could some sharp edges explain that? I'm thinking not.
jim, you are right. the 350 is a different animal from the 455. they look the same is the only thing that they have in common. the 350 responds a lot differently than the 455. wait till the heads come out. there will be a lot of head scratching on how to make the combo run. been doing some thinking on those. :grin:
My 350 has never picked up over 20 mph. The best I've done is about 18. Other Pure Stock Buicks are in the same boat. Mark if you say you didn't lose torque then your setup is way off. What is your best 60 foot time? Don't you have drag radials and a higher stall converter? I would be expecting you to go about 1.9. I have run 1.98 on street tires. It is putting every ft/lb to the track in doing so.
It is entirely possible that the Stage 1 dual plane intake was plenty adequate for his combination, and tinkering around with the SP3, especially in ported form, is causing some major waves in what was an otherwise smooth sailing seas? The tip-off is not much loss in torque and not much gained in hp. I dunno, just taking a wild stab at it. Putting on that Holley DP 650 will fix some things, I'm thinking. Gary
My best 60' with the Stage 1 was 1.98 My Best 60' with the SP3.............2.04 MT 275-50-15 DR's JW 9.5" 28/3000 stall, flashes to 32/3300 3.42 gear
I would be willing to bet that a 650 carb on the sp-3 would be good, like others say time will tell but I think the only reason the 350 was wanting a larger carb was the ineficiency of the old intakes. Johnny has been telling us for years that a 650 carb works great on a single plane 350, so there is a clue. He may think no one listens but I know I do. I also know that during our first dyno testing on the 550 hp engine with prototype burton single plane the engine liked a 1000 cfm carb, but that was a pretty wild cam etc. Plus at the track a smaller carb might have ran faster than the big one that made more peak hp. All little parts to the puzzle. I am just happy that now anyone can get a SP intake without spending $2000 for a sheet metal one, but hey someone had to pioneer this stuff. Some Jb weld, mopar intakes, a custom intake from the 70s, and 10 years later $400 can get you a SP intake. It is not the answer to the 350 but it is a part of the equation. The 455 testing shows the same thing, larger cfm needed on the poorer flowing intake and head setups and less need for the large cfm carbs once better heads and intake are used. This is comparing say a 550 hp iron head 455 to a 550 hp alum head engine, obviously really high rpm and hp require larger carbs. Lots to find out, but it will be fun!
For sure Sean, there IS alot to find out, and it is fun, but it would be more fun if it wasn't the end of the season I'd love to go to Thompson and try all these different combo's to see what the SP3 wants on my engine. Im still hoping this weekend to try my 750 vac sec Holley, just to see Squarebore/Spreadbore difference, plus its fun:Brow:
Is there any wonder why he feels a bit jaded when it comes to this stuff. We repeat things he's been saying all along as if it's news. lol I honestly didn't see him saying that all those years ago. I just remember my brother's experience with a 650 DP on his 440 single plane Mopar and what a difference it made calming it down for the street. He had a Qjet on it, believe it or not, and it screamed at upper RPMs but low-mid range suffered, even with 440 CID. The Holley 650 DP transformed it to good low-mid range, and it did suffer a bit on top end, but hey it had 440 CID... It did a hell of a lot better than anyone believed it would. This was years ago as well. Ah well, we need to give credit where credit is due. If someone says something, we need to credit them for having said it. Gary
21 MPH? I'm thinking that is for a drag only car. Mark, from your 60 foot times you are consistent from intake to intake. .06 difference could be from weather. Gary, makes sense the smaller carb calmed down that 440. It was a restriction and boosted the pull on the carb circuits. Sure it lost a lot on top though. I think this is what everyone is saying, in different ways, as to why the SP likes smaller carbs. If the porting Mark had done to this intake went beyond port matching the opening then they made if even worse for low RPM use.
My car is not a drag only car, I can drive it anywhere. My 1/8 MPH is about 93 MPH. My 1/4 MPH is 115-116 MPH. I am picking up about 23 MPH. Have a look at the last timeslip. Dan Chait was in the other lane. His car is a 9 second drag only car. He went from 118 to 144, about 26 MPH. For the average car at the track, 20-21 MPH is about right. https://www.facebook.com/larry.hymowitz/videos/10205165761728043/
I've been watching this thread with casual interest, but to throw a data point out there, my car picks up 24mph between the 1/8th and 1/4. I've always heard that 22-28mph is pretty on par for 13-9 second cars. At least on naturally aspirated cars.
Looking back at my time slips to see what others have done many have gained 20 or more MPH. What is holding my car from doing that? With any of the engines I've had in it, it has NEVER gained more than 18 MPH.
I'd be looking into a converter change or freshen up. Go the Wallace calculators and figure your slip % anything over 9% is to much
doubtful, but a slight lean out might do it, and you would not be able to feel it. The only way to diagnose that would be a fuel pressure gauge and wide band.
Converters work off clearance to get their efficiency as the older they get the more the clearance grows . But as Larry mentioned really only 2 things contribute to top end mph loss ,..Fuel and converter efficiency of course there are hundreds of variables but for the most part those two things are often the culprit
