Does exhaust affect low end torque?

Discussion in 'Small Block Tech' started by garybuick, Mar 24, 2016.

  1. Fox's Den

    Fox's Den 355Xrs


    Then would it work better to just get a 650 double pump 4 bbl carb. The primaries would be larger than the Q-jet and a bit smaller than a 500 cfm 2 bbl. The primaries on the double pumper would be more than enough to pull the big heavy weight car and still get decent gas mileage by not opening the primaries too far as compared to the Q-Jet.

    Plus when you needed it, you had the secondaries to give you the extra when you needed it and since it is only a 650 carb the velocity will stay up and pull nice and strong.

    The plus side of all this is the Holley type carb has Way more adjustments than any of the rochester or the Q-jet carbs.

    My take is a 650 dbl pumper with a TA intake 1 inch open spacer or a Wilson 4 hole to open spacer. all stock

    But all tests should be done at track to prove results of add ons.
     
  2. 8ad-f85

    8ad-f85 Well-Known Member

    Edited my comment on spacers. I assumed an open spacer was meant, sorry about that!
     
  3. alec296

    alec296 i need another buick

    If you give up has mileage you can throw a 4.10 gear and 3200 converter in trans and then stop light to stop light will be great fun. The spacer will work well here . Or just build for big torque. Mill .060 off heads for about 9.4 compression and get the crower level 3 cam with a 2200 converter and 3.42 or 3.73 gears( still won't hurt mpg due to the huge 235-75 tires that would be on the lesabre. 2 barrel would be cool here as people may think you have a big block and you can show them a 350-2 .
     
  4. garybuick

    garybuick Time Traveler

    I have thought about low gears many times but I always come back to my dream of a inconspicuous low rpm launch where the car, seemingly effortless and as silently as possible, accelerates to the speed limit instantly. ya the 2bbl reveal would be priceless!
     
  5. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member


    Build a 470 with great flowing heads and a small cam, and quiet exhaust system. That's what you just described. The BBB was designed for just that.
     
  6. garybuick

    garybuick Time Traveler

    i wish I could that would definitely be way better but the 350 was designed for torque also with its long stroke and I just wonder what its low end torque potential is. I think if I could optimize it for low end torque it would be enough for my level of interest and $$ because I already have the engine.

    Im looking at your signature and Im wondering on your 70 GS with that Gear Vendors OD what is your best MPG?
     
  7. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    :moonu:

    I once got 17 with it using non ethanol gas, but usual is about 15 if I am careful.

    There is no replacement for displacement except forced induction. I would build the engine like the 1970 GS350 engine. Get a true 10:1 SCR and use a cam that gets you an 8.0 DCR. I think you can build an even stouter engine with the new aluminum 350 heads when they get here.
     
    Last edited: Apr 6, 2016
  8. alec296

    alec296 i need another buick

    The setup I described is a low rpm launch setup. Torque converter locks up at very low speed with this combo or even run stock convertor with a custom large diameter crossover pipe and a walker quietflo muffler. Your equivalent gear with the large tires is actually quite low
     
  9. Fox's Den

    Fox's Den 355Xrs

    You have a 4000+ vehicle The 350 does not have enough to pull that much weight out of the hole fast. You need a 455 for that. If you want to be bone stock that is what you will have to do. The 350 will work if you build it up to a good race spec, put in 373-411 gears and do a 3500 convertor, then it will come out of the hole like a bat out of hell. A 2bbl aint going to do it.
     
  10. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    You need torque. It has to be moved down further in the powerband, and I've already shown how this is accomplished (and was done this way, to an extent, from the factory). This is my suggestion to you, based on your current combination.

    Other than this, you'll need a bigger engine or forced induction.

    As for more suggestions, you can listen to me or not. That's up to you.

    I may need to upgrade my bulletproof flame suit after what I've seen in this thread.

    Do more research on that "Y" pipe scavenger series pipe (or how headers work, for that matter) and see for yourself how things work. It may surprise you (and everyone else in here, apparently lol). Check out how important exhaust velocity and scavenging are to building power at any given RPM.


    Gary
     
  11. Gary Farmer

    Gary Farmer "The Paradigm Shifter"


    I can't count how many times I've done this to camaro and mustang owners with hopped up engines (including 4 barrels, loping cams, headers, etc.) back in the 80's with my 350-2 single exhaust Buick. Only one that ever gave me real trouble (that I was selective in racing), was a Mopar 383, as mentioned earlier in this thread. But Chevy 350's and Ford 302's were breakfast.

    Won beer and gas money more than a few times, at least until word got out. Made a few enemies too (not unlike on this forum!).


    Gary
     
  12. Fox's Den

    Fox's Den 355Xrs

    I have had my Lark since 1977 and it came with a 2 bbl on it and air cond. There is no way it would come close to a 383 Mopar. I owned a 68 Fury 3 with a 383 in it With a 2 bbl and would wip that 350 Buick all over the planet. That thing would do 120 right now. My 350 would barely do 110 and that was with a good tune up, you know a performance point set and so on.

    I will admit the stock Buick 350 ran well even with the 71 8.5 comp.and 2bbl., but no way will it come close to a 383 no way no how. My Fury was no frills single exhaust and everything. That thing would do a 100 in a heartbeat. That speedometer went so fast I thought something was wrong with it and that's no joke. nothing wrong with it.

    Talk about one wheelie peelies with a 383, it was on! I raced a lot on the street with that one, went to 120 too many times and got the rod a knocking and that was the end of that.

    I also have to admit that a lot of my friends thought the Skylark with the 350 ran better than they thought and that was with the 2bbl so I won't discount its ability completely. The 2bbl got the wheel burning quick but the Holley double pump 650 spread bore kept it there.
     
  13. alec296

    alec296 i need another buick

    Build it and it shall run. Kinda on Gary's side that the 350 with right mods will move that tank very well just as op hopes. Sure a big block will do it easily. But a higher dcr cam with higher static compression and a other mods . a 3 inch single exhaust with a walker ultraflo muffler crammed back down to a 2.5 tailpipe to appear stock and sound quiet enough,with a 2 barrel will really surprise a lot of people. Sure it will choke some upper end so focus on low end
     
  14. Gary Farmer

    Gary Farmer "The Paradigm Shifter"


    Here's the thing: in 1977, the Buick 350 used a considerably smaller cam than it did in the early '70's. Add in that the factory single exhaust leaves much to be desired (no real scavenging, though better than separate pipes scavenge wise), and that the large base 2g on your '77 was the 352 CFM (the smallest of the four types) version, and the picture will begin to clear up some. Those '75+ 350-2 engines ran out of breath at 4,000 RPM, while the earlier ones started to wane around 4500 (due to the stock carb), but a 500 CFM with scavenging exhaust will add a few hundred more RPM to this, not much less than a Qjet equipped engine with the same stock cam, manifolds, etc.

    Let it also be known that 5000-5500 RPM pulls aren't out of the question, it just works better when you shift it earlier.

    It's more of a tradeoff for slightly less upper RPM for a lot of lower-mid range. I figured it was worth it.

    Gas mileage will SUCK though if you keep your foot in it (but hey, so will a Qjet!), so if you want better mileage, just drive it easy and keep RPMs down (duh).

    My '68 Skylark came originally with a 350-4 and a 2.73 gearing (2 barrel versions had 2.56 from factory) so I was already at a slight gearing advantage from the start. Transplanted into it was a '70 350-2, the largest 2g I could find, and modded single exhaust. Talk about transformation. The 350-2 had 260/360 hp/tq from the factory, and it's not difficult to raise these numbers considerably with some cheap mods, considering how choked off is is from the factory.

    Those 383's were beasts, for sure, which is why I used it as a basis for comparison. Stock 383 (it was a '68 model I raced) had 10.1:1 comp (doing all this from memory, so forgive if I'm off a bit), rated at 330 hp and 415 ft. lbs.

    Ironically, the 383 you describe used a 2 barrel, so it's no wonder it did so well at burnouts. Recall my comparison is low-mid range vs a 4 barrel variant. Perhaps inadvertently, you are promoting the idea of using a 2 barrel with your story.

    I was actually surprised the 350-2 did as well as it did against it. Raced against it many times, and the only time it would beat me was in a straight line distance run.

    I like it when people underestimate the old 350-2 though. It keeps things very interesting. :)

    The point to all this isn't that a 2 barrel engine is the best thing since sliced bread. It's about lowering the torque band so the existing engine can better move a heavy car with highway gearing.

    For more money, a 650 DP would do the trick nicely as well, since you'll get better lower RPM power vs the Qjet, which needs to rev some before it turns on.

    No one expects a 350-2 with single exhaust to do much, as we can see in this thread. My experience was much different.

    Thanks for your story, I enjoyed it.

    I understand people's disbelief. I guess I shouldn't have been so hard on the nay-sayers, so with that I'll apologize for my harshness. I should have presented it better.


    Gary
     
  15. alec296

    alec296 i need another buick

    The 383 in the hands of the "bolt on tuner" can end up being a disappointment in some cases. Had my 83 regal with Buick 350 , hyperitectic Pistons ,poston 118 cam, 2200 convertor,3.42 gears and dual exhaust with catalytic convertor . And ran at the track against a 383 67 dart. He had headers ,intake, Holley carb. I ran 14.5 he ran 16.20 . I expected him to outrun me but he had something missing in that combo.
     
  16. Gary Farmer

    Gary Farmer "The Paradigm Shifter"


    Thanks for the support Andy. I don't get that much around here. lol

    I agree that if you want to maximize low-mid grunt, a Crower level 2 with the same mods I described earlier would be a beast between 1500-4000 RPM, and would be easier to do with the existing low comp pistons. It will raise DCR and give even more power down low. Good call.

    Only thing I'd change is that you won't need the 3" single; the 2.5" would work better for this application.

    Remember the 2.5" mandrel pipe will outflow a set of 2" duals that are press bent, while the 3" mandrel outflows 2 1/4" press bent. This goes off the fact that the bends on press bent systems are much more restrictive than the unbent section, and the tighter the bend and the longer it is, the more restrictive it is (such as the tail pipes going over the axle).

    EDIT: I wanted to add for clarity so there's less confusion (good luck, I know), it's as simple as comparing the areas of circles, remembering that you will need some length of pipe on your splice to make it more effective. Take the diameter of the pressed section of any press bent pipe as your smallest size for the pipe, multiply by 2 (for duals), and compare it to a larger diameter pipe that has no restrictions and you'll see.

    Understand also that an 18" section of straight pipe will be less restrictive than an entire exhaust system length (not even considering the mufflers), but the most important part is from your heads back to the end of the merge pipe. This is where most of the action is taking place. After this, it's just a matter of getting it out of the system as efficiently as possible (and for some (such as myself), as quietly as possible without choking it too much).

    Remember hot gasses will move faster and draw harder than cooler gasses. Keeping your head pipes the same size as the exit port size on the manifolds maximizes the speed and volume at which those gasses can move. The manifolds aren't all that great for scavenging themselves (see headers), and so need all the help they can at getting it out. In comes the scavenging merge pipe which uses one side of the engine's exhaust pulse to draw out and away (evacuation) from the other side, and condenses into a larger merge pipe so that both sides have more room for evacuation, but still maintains good velocity so that even this larger pipe (with both sides flowing through it) draws too, particularly when coated (entire system from manifolds to end of merge pipe needs to be coated for maximum effectiveness).

    After this, a press bent system can be used (particularly for tail pipes) since the gasses are cooling considerably the farther they get from the engine, and so contract needing less space and aiding in evacuation by maintaining velocity at these locations.

    There can be a fine line between good velocity and efficient evacuation vs backpressure. At lower RPMs, smaller pipes are needed to move the amount of air, while at higher RPMs, larger is needed. It's all about application and tuning at this point.

    Option number 3 in a previous post I made here shows the system starting off as a scavenging single, then splicing out to typical duals. This maximizes ground clearance and makes the system more aesthetically pleasing/sounding.


    Gary
     
    Last edited: Apr 7, 2016
  17. Gary Farmer

    Gary Farmer "The Paradigm Shifter"


    Anytime you mismatch parts in any combination you'll end up with disappointment, and is the primary source of many tech threads here on the forums (such as this one).

    You can do so much with so little it's astounding. Something the parts vendors and shop owners don't want you to know! (true story)

    It doesn't matter what you have, it has to be tuned and matched up properly.

    Stock (low comp!) Buick 350's can run into the 13's when set up properly for the strip. It just shows you what can be done.

    A stock low comp 350 with 3.73 gears and a modest shot of nitrous ran consistent mid 12's (12.4's), just as an example.
     
  18. Fox's Den

    Fox's Den 355Xrs

    I put that 2bbl 383 in there just for you Gary I knew you would like it. My Lark was a 71 not a 77 as you had mentioned. no egr or air pump.

    Like I said the Lark would do about 110 or so and that was it. 256 or so gearing. But after the headers and the Comp Cam 268 and the 650 spread bore Holley I would do 100 in second gear. Big improvement.

    The Fury 383 was a beast. I knew another guy that had a 68 Cuda with a 383 and a 4 speed talk about chitin and gitten.

    The guy that owned that car later on had a 340 Dart that ran well small cam do not know what else it was just too long ago (74) and he raced a Buick, of all cars, we did it in the rain, real smart there, but anyways we were door to door and that Dart ran well. I think the Buick had the 455 in it because the guy could not believe we stayed with him. It was a boat one of the big ones back then.

    I understand your 2bbl theory and would work but I am still going with the 650 DP for our poster here. Best of the 2bbl and the Q-Jet.

    I am still trying to think if I still have the 2bbl carb and the 2bbl intake can't remember. Buried at my other house somewhere. Took it off in 84.
     
  19. garybuick

    garybuick Time Traveler

    Im taking careful notes of everything everyone is saying. I especially like Garys insight on what can be done with stock low comp 350s, 2bbls crower 2 cams and calculated single exhaust and highway gears. Im going to do this.
     
  20. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    Ok well I stated the facts about the engines so it still applies. Factory 2g and factory single won't run nearly as well as what I did with mine (I should know).

    Not really a 'theory' but you can call it what you want if the point gets across. :)

    I wouldn't race 340's (Mopar) because they moved a lot of air with their high RPM powerbands and typical gearing under one. The Mopar 340 is a tough nut to crack. You gotta know how and when to pick your fights.

    There's more than one way to skin this cat. I offered up the simplest and least expensive option (carb wise), but a Holley 650 DP would certainly do the trick!

    He could keep his existing setup and splice in an "X" pipe and better gearing (or even a good torque multiplying low RPM stall like a 2000) which would work wonders for a heavier car.

    Remember when I offer up suggestions, I'm not implying that it is the ONLY way to do it, just a good/efficient way.

    It's also important to consider the way the 2 barrel delivers the fuel/air vs a sequential 4 barrel, not just at full throttle, but at partial throttle. Not that this would matter to anyone, but I believe it to matter (as did the engineers who made different intake manifolds with altered carb location)...

    For example, the B4B intake for big blocks is good for another 10 or so hp on big blocks vs the stock location carb Performer manifold, with the rest of the intake being the same. Not to dwell on the numbers, just to point out that moving the carb to a more centralized location made an improvement.

    Forget the number of holes on the intake. It's all about how it's delivered. Look at how fuel injection (or even 500 CFM TBI) systems work.

    EDIT: to the text in bold, there's your scavenging and more CFM flow, which is similar to what I'm suggesting with the main difference being that it will exist at a lower RPM where it's needed most.

    Checkmate.


    Gary
     

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