Longer intake for dual carb setup

[Rubix12345]

I have a dual carb on a 1600dp. Its the empi single barrel setup(came on the engine). It runs good BUT I would like to move the torque curve a lot lower in the RPM range. Right now it has to rev to the moon to make power(I have some HD springs and 1.4 rockers on it so it revs pretty high and that really woke the engine up, now it will break lose 31 inch mud tires on pavement if I dump the clutch but cruising sucks as it is gutless until you hit really high revs). I was thinking about making and adding some 3-6 inch tall intake manifold extensions to the setup. Its in a rail buggy and I would need to move a bar out of the way(no big deal, its just right above the carb on one side). I know longer intake runners move the torque curve lower in the rpm range on most engines so I was wondering if anyone has done anything like that for a dual carb setup? I know the stock intake length is crazy long, like 12-18 inches, where the current length is maybe 2-3 inches. Just wanted to see what everyone though about it.

[bedlamite]

That's not going to help anywhere near as much as you want it to.

Displacement is still the cheapest path to more torque.

[Brian_e]

Sounds like a bad parts combo. Any idea what cam , heads, and compression it has?

I am gonna guess its got a w110, off the shelf "big valve" heads, and 8.0:1??? Maybe even a 1 5/8" header also?

A low duration cam with matching compression will make a BIG difference in power band. Trying to perfect the intake length is more for fine tuning, and squeaking out that last couple HP. It won't make a drastic change in power band placement.

Brian
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[Schepp]

What is your current gearbox and ratio?

Easiest and cheapest way to increase power...
Smaller rear tire.

Not cheap...
Change R/P ratio.

More Less cheap...
Big bore.

As the saying goes:

Fast. Cheap. Reliable.

Pick two.
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[Rob Combs]

What cam did you have on there before the 1.4s?

I can tell you from experience with a 1600, stock cam, stock-ish compression, and 1.4s, even with decently-tuned dual 2-barrels, there is a little bit of noticeable difference but I wouldn't think it enough to break a set of 31" tires loose on dry pavement unless those tires are so hard a cat couldn't scratch them.

So something is going on here, something a longer intake probably won't help with - Brian put up some good points there.

If it's cammed up with something like a 110, you might have some valvetrain issues pretty soon if you're running 1.4s too.

You might want to take a deeper look into things.

[NJ John]

I had Weber ICT’s on short manifolds and switched to what was probably kadron tall manifolds. I didn’t really feel any difference. Look cooler, though.
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[rosevillain]

What's you timing set at, and how did you set it?

[Rubix12345]

[Rubix12345]

[Rubix12345]

[Rubix12345]

[Bugsy61]

This sounds like low cylinder pressure while running. First, do a compression test and report back. Low cylinder pressure could also be caused by late ignition timing, late cam timing, compression leaks, dirty air filter, plugged exhaust (straight pipes, not exhaust.) Super rich mixtures can make it run like this as well. Do the compression test first.

[Rubix12345]

[sled]

making the manifolds a bit longer is not going to achieve the dramatic effect you are looking for. It may move the torque down a little bit, but not substantially, and it won't increase it significantly.

your "straight pipes" are killing torque as well.
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[Zed999]

[Schepp]

Did you build this engine or did you buy it this way?

So you have a stock 1600dp that you put ratio rockers on with new springs? Straight pipes and stock cam. With dual single throat carbs? What carbs are on it? Don't just say Empi. That literally tells us nothing. Do you have pictures you'd like to share?

I agree with what others are saying. Sounds like you have a poor combination of parts.

Exhaust back pressure is a thing and the engines friend.

Is the flywheel stock? A lighter flywheel will improve throttle response but they have their drawbacks as well.

You said you removed the cylinder spacers when you did the valves. What was the justification for this? Did you check the deck height? Did you cc the chambers? Someone did that on purpose to achieve a desired compression ratio. Now you've messed with that too.

Usually you'd select a cam that jives with the ratio rockers. Setting the rocker geometry, its a science. Not just bolt on parts because its easy, hoping to get more power. Its a calculated choice of parts, selected for a desired outcome. Not just a random hope for the best, add-on. Did you setup the geometry? IF so, how did you? If you did not, you could be well on your way to destroying your entire valvetrain.

Also revving it up and dumping the clutch to get the big tires to break loose on pavement is a great way to destroy expensive parts.
Not a great example of the engines capabilities, more an example of the drivers stupidity.

Manifold length is the least of your issues.

The 1600 isn't known for being a powerhouse or a torque monster. Though it can be made to perform decently well. With the right state of mind, attention to detail, proper gearing and smaller tires.
From what I've read so far, you have none of those.
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Bandit #19
1972 Baja Rallycross Bug

[oprn]

While it is true that longer intake manifolds favor the low end my sister had a '66 type 3 wagon with the factory dual carbs and it did not suffer from poor low end torque. I doubt your manifolds would be as short as those!

The 009 is notorious for low end issues but I think you also have too much tire too. Both those combine with a poor tune will get you right where you are at.
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[b-man]

Some type of exhaust with a 4 into 1 collector and a decent muffler would be a huge step in the right direction. Separate straight pipes are good for top end performance and not much else. An essentially stock 1600 with straight pipe exhaust might look cool but it’s completely wrong for what you’re doing.

Switching to a better tunable distributor like the Pat Downs Shockwave would also be a big improvement over a 009.

Longer intake manifold runners aren’t going to make any real measurable difference in low end torque as already mentioned above by a number of members here.
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[theastronaut]

You're getting reversion in the manifold at low rpm since the ports share runners in the intake manifolds. Switch to dual 36 DRLA's with individual runner manifolds; it'll have instant torque off idle, get better mileage, run smoother, and have more power overall. My stock 1600 dp with dual 36 DRLAs was pretty snappy from idle all the way up.


How far out are your idle mixture screws? If they're pretty far out then your idle jets might be too small and its running lean enough to lose power on the low end.
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[Rubix12345]

Yeah...Im not going to worry about it too much. Goes fast enough to get into trouble. I was just asking some quick hypothetical as a maybe winter project to mess with. The answers have been lots of opinions, not many verifiable facts, and lots of suggestions to buy thousands of dollars in new parts(which of course would be great but I am not dumping thousands into a 50hp engine that after all that might make 75hp, that is just silly).