Im going to try something

I believe what Derek is saying if NASCAR can make 850HP with an 850 carb then there should be no way a 400(?)HP 350 Buick going to 6000 RPM needs an 850 cfm carb. I think a 750 on the single plane would accomplish just about anything that engine ever will need. A 650/750 back to back test would be interesting. A dual plane might change the equation but I'd say 750 would still be plenty. Although with a too big 850 the ET might suffer because of the SP and big carb sluggishness down low the MPH should be right with any carb you can throw on there. So the MPH is what needs to be chased. Right now I'd say the problem is not enough gear in the back to get that "big" cam/single plane off the line and closer to peak power rpm at the traps.

I believe Mark ran his best time with the dual plane last year on the Friday TNT day for the BPG/Norwalk race. Definitely better air that day but if you go by that weather his corrected low ET goes down to 13.345/101.174 assuming he ran about 10 am(1965'). So he still has a .2/2 mph deficit compared to the DP intake.

I agree that a change back to the dual plane is definitely on the table but as mentioned you need to go back to the track on a better/cooler air day with more runs available for TnT with the SP intake. After that swap to the DP and then back to the track.

Did you ever run the 850DP on the dual plane intake? I believe the same converter is being used.

If you can manage I'd suggest you get some time off in September and make the trip down to Bowling Green. You can't beat 4 days of TnT when looking for a problem and there is plenty of time to actually change out an intake during the day or over night. Unfortunately it is not in October this year because last year's weather/air was the best ever for down there. On Saturday with the cool air it actually went negative DA. Not so much this year but it has to be better than Norwalk was the other day.

 

We are no where near that situation here.. you jumping the gun quite a bit.

JW

 

When this car runs hi 12s on motor then i'm jumping the gun
If it runs mid 13s again then nothing he did will have made a difference
Just saying

 

Thank you for bringing this up (I figured someone would) and is a good point--although I was trying to steer clear of it because it is off-topic, my original point trying to be on larger throttle blades and the Buick 350's intake runner design.

It's still semi on-topic though due to the misunderstandings of carb ratings and how they flow at any given vacuum.

Here's a couple of links for anyone who's interested in more 2v info and high performance 2v applications:

http://www.cj-8.com/forum/showthread.php?36668-2-Barrel-Versus-4-Barrel-CFM-Flow-Ratings-Interesting

http://www.camcraftcams.com/index.php?page=cam-failures

Getting back to the thread topic, Mark has had a few threads concerning his car's performance and the sp3 testing. Apparently the problem is still on the loose!

I think to get a better grasp of what's going on, there should be some back-to-back testing using different combinations of intakes/carbs that he has used in the past. Sometimes going back to the drawing board will help with zero'ing in on a problem without all the conjecture.

No doubt about it, something is definitely amiss.

 

It's unrealistic to think that your going to go from 13.65 to high 12's with just an intake change.

He ran a corrected 13.59 on what should have been an aborted pass.. way late 2-3 shift. Not too hard to beleive he lost a couple tenths with that mess.

If he runs a 13.30 with the new intake and his 13.65 combo, then I would consider that a "normal" et decrease from an intake change.

JW

 

I was under the impression he changed,
1)Intake
2) Converter
3)carb
4)fuel pump/lines
5) fresh trans

That's my point. He fixed some issues and made changes( good converter is worth double what any manifold would ever be on a mid 13 sec combo) and is slower yet
And as I eluded to before,car is still slower than a lesser combo is. Not arguing but the eyeball test looks bad here is aall

 

Test test test!

Need to find a track, any track and pound out laps. Norwalk TNT is too busy. Find a smaller place where you can make all the runs you want. What about Quaker? Still open?

I don't agree with the smaller carb is better theory. The single planes I've used love big carbs. My 408 BB Chevy had a 800 DP. Then I put on a 1015 Barry Grant modified Holley and picked up 3/10's. They also like lots of fuel off idle. Same 800 has 50cc pumps front and rear.
Single planes also like as much initial timing as you can give them. Same car idles at 22 degrees. I didn't learn all this in 8 runs.

Of course every car is different and likes different settings. But I think all single plane manifolds will respond similarly.

By the way my 350 car has a 455 800 Qjet. The secondary air valve is open all the way from 4000 rpm on and pulls 1" vacuum up to 5800 when we stopped the pulls. I've got video of the carb when it was on the dyno. I don't see any indication it's too big.

Whole point is keep testing. Things will start clicking and the improvements will come.

Set your trans governor to shift itself at 5800. That variable is fixed.
Then focus on your A/F ratio, get it close to 11.5-12 at WOT.
Play with the timing from 30 total to 38 total 2 degrees at a time. Your MPH will tell you what it likes best. Make at least 2 runs at each step.
Don't worry about reaction times, means nothing unless your racing.


Fire away haters!!!!!! LOL

 

No Nick, the 13.65 was after he put my converter in.

He changed a bunch of stuff, trying to figure out why it slowed way down after the intake swap, but that was the trans going away.

He is just now back to being able to evaluate the intake change.

JW

 

Jim is correct.
Trans is fixed, fuel issue is fixed with RobMc 550 pump and 1/2" lines and pick up.
So its actually just figuring out what the combo wants now.
I was actually surprised at a 14.06 for my crappy driving

 

I'm keeping my 850 DP for sure on the SP3
The Q-Jet for the Stage 1
I would be REALLY interested in trying the 850 DP on the Stage 1 intake vs. the Q-Jet on the Stage 1
I WHOLE HEARTEDLY AGREE, More back to back runs!
Norwalk is a nice track, but Thompson I get a lot more passes in.
1 pass in a total of 3 hours aint gettin' it, all that's doing is frustrating me

 

That was kind of my point, and trying to highlight the cfm carbs that they used in those purpose built engines. What works for nascar won't necessarily be the right choice for a sbb 355 with the new SP3.

Of coarse Steve's engine doesn't care that it has 800 cfm, the factory intake is choking the cfm down to give the engine only what the small ports will allow through. You really can't compare the BBC 408(assuming it was originally a 396 or a 402 BBC) air flow characteristics to a sbb 350. Steve didn't mention what compression the BBC had nor was the type of cam mentioned in his BBC comparison either. IIRC Mark did a rebuild and is .030" over bored so its a 355 cid engine which would be 53 cubes less than a 408. That 408 BBC is going to make much more torque throughout the entire RPM range than Mark's sbb 355, using the bigger carb probably helped it launch better by killing some of the low end torque so there was less tire spin for an improved 60 ft time. Going from a sbc 350 to a sbc 383 with just 33 more cubes is a night and day difference of how the 2 engines run, so I really don't see the relevance to the BBC 408 to sbb 355 comparison.(not hating, just trying to be realistic)

A mildly worked over sbb 355 that has IIRC around 9.6 or 9.8:1 pump gas friendly compression with the again IIRC the TA 413 cam with a now open plenum with shorter faster flowing runners of the SP3 that I believe corrects the math of how much cfm an engine wants, and IMO would run much more CRISP with less cfm than 850. It may like 750 better like Nick said to run, but my vote is still for an HP 650 type carburetor. IMO the smaller carb(if you can hook) will 60 ft better than the bigger one and still be plenty of cfm to get you to the end of the QM faster than the other.

If Mark is running 12:1 compression and a solid cam of some sort and spins his engine to 7,500 RPM with massively ported heads then an 850 cfm would be a good choice for the cid size, but the rest of the combo would need to be changed in this scenario.

Just my 2 cents. Am I right, maybe, maybe not. If Mark wants to stay with the 850 I wish him the best of luck with it, and to add that he'll probably love the 850 on top of the D/P once its dialed in on that intake if that one goes back on MUCH better than on the S/P and vice a versa with a 650cfm double pumper. :TU:


Derek

 

you need to get a log book so you can log all your info then you can see what is happening with the changes made. did anyone notice how big the jets are in Marks carb. My 750 has 70-78 jets in it. what does he have 80-90 jets something like that.

What was the 60 ft time can you post the time slip. What rpm are you launching at. The intake may feel good off idle as with tq but I bet it still has to get up to 3 grand to start working maybe more like 3500.

 

Well there you have it
I STAND CORRECTED
And the fact is after the conveter change is IMO more telling

I say quit di$%^ng around and put the old manifold back on and tune the carb and let it be
I know 2 folks now( or should I say 3 inc Mark , who saw no gain w this manifold)
Not seeing the need for this intake on a 300-325 hp combo at best
But hey , u never know till u try !

 

My 408 is low compression with a big cam, 292 duration. It's a dog below 3000 rpm but the bigger carb did not change that.

Point I was making is it does not matter if its a 283 Chevy or a 528 Hemi the open plenum single plane responds similarly.

Also while I am pushing the limits of a stock intake my carb air valve is fully open so I don't think the ports are choking it that much.

If the port could not draw in the air the air valve would not be open.

 

While your POV has merit from a practicality standpoint, having the sp3 on a milder engine is just plain cool dude! And if it doesn't affect performance much one way or the other (vs the dual plane), I think a lot of people won't mind as long as they understand that a single plane is better suited for higher RPM applications. That it does well at lower RPMs is a good indication that the intake was well thought out for appealing to a broader audience.


To Steve and others showing the larger carb does well vs a smaller carb: I said once before in an earlier thread Mark had going on a 'theory' I had about why this is so. It involves dual planes wanting larger carbs (larger throttle blades--such as the huge secondaries found on the Qjet) while a single plane seems to respond better with smaller ones (with similar engines/CID/air flow).

It may also be good to keep in mind that the sp3 isn't designed exactly like other single planes, including the previous custom single planes people have used on their Buick 350's. Maybe that matters, maybe not enough to present a real difference, but just something to keep in mind.

Don't discredit anything. Remember that this is still relatively new territory for the Buick 350 for most, while some have more experience in this (custom single plane, higher RPM) arena and would be wise to take their POV into serious consideration.

I'm basically just the peanut gallery here, tossing in some side-comments that may or may not be worth much, but hey, I try.


Gary

 

Larry, is there an app, program, or a weather thing to tell you all that DA stuff that you spoke of?

 

Stock jetting is 82/92 for the AED
Current jetting is now 80/88
Cruise A/F is 13.4 to 14.1-14.5
WOT is now 12.5
WOT was 12.0 with stock jetting
I leave the line at idle, convertor flashes to 3300 rpm