It has to do with HOW the heads flow. LS heads flow a lot, but with better efficiency and flow velocity than a hogged out Gen I head

 

Because your opening premise is flawed. Stock 430hp Ls3 in mine - routinely gets 20 mpg city and 26/7 highway - same as the 2.1L Volvo 4 banger got. And about 2 mpg better than the 340HP 5.0L that was in the car before. The heads on the LS3 WAY outflow the AFR’s I had on the Ford and certainly outflow the Volvo head. At wide open throttle - yes, more air, more fuel. But at part throttle - better flowing heads do not necessarily mean worst gas mileage....

 

One thing that I didn't see mentioned - how big is the single exhaust on your S10?? Also, I'm guessing that your headers are shorties, right?? Those seem to be good for (roughly) 10-12 hp over exhaust manifolds, but if you could find a set of long tubes,those are supposed to be good for what, 25 - 30 hp over exhaust manifolds??

My suspicion is that your single exhaust could be choking off your top end. My DD is powered by an LS3, & from idle to somewhere around 3300, maybe 3500, it's really not especially different from the old SBC in my pickup - but when I wind it beyond 3500, it puts a grin on my face right away! If your single exhaust isn't allowing it to breathe at the top end, I can certainly imagine that it wouldn't be any different than a vintage 350. Get a set of long-tubes, a modestly-decent exhaust behind them, then add even a SMALL cam - and you'll see a BIG difference.

 

Ported heads if done correctly will certainly get better gas mileage. You have to look at it this way, Anything you do to improve efficiency will improve gas mileage. Porting heads can improve efficiency, Porting isn't about the highest numbers flow alone, You want more flow at a higher valve lift without bringing down flow and velocity at lower lift points, A good port job can increase flow throughout without sacrificing velocity. Nascar engine are probably the best example of a powerful yet efficient engine, They need the power to turn fast laps and they need them as fuel efficient as possible because you can't win races if you have to wait for longer than the next guy to get the tank full.
More air into the engine does mean more fuel but that also equates to making more power so technically it also means you would have to use less throttle to maintain the same power level/speed.

As far as the OP's issue, He has a high flowing intake and carb with a truck cam designed to make lower end torque, Definitely a parts mismatch.

 

I think the team has it figured out. Its likely an issue of parts mismatch (Your intake is killing the low end power, your cam and exhaust are killing the high end) and possible state of tuning on the carb and spark curve.

That's the irony these days on the costs of a carbed setup. An MSD box cost $400, a dual plane costs about $300, another $300-$600 for a carb. So its more than $1000.

A Holley Terminator X for manual transmission = $1000

With the fuel injection, you are also getting a wideband and datalogging software that you could be looking right now to see how your engine is running.


I would figure out your goal, and get all the parts to match. If it's a high RPM motor you want, get a proper exhaust, mid or long headers, a decent cam, and go to 4.10 or 4.56 gears to make up for the lost bottom end. That's just cars 101, SBC or LS... And check your timing curve with guys in the carbed forum.

 

I bought the intake, carb MSD a couple months before termX came out or I would have bought that. The intake is fine, its correct for the power band I want (with room to grow in case I add NOS and/or a cam). I have no idea why people assume that all single plane intakes are only for super high RPM engines, that's simply not true. I do need a different carb because the vacuum secondaries aren't responsive enough to use with a manual trans. Any one commenting that the carb is to big obviously doesn't fully understand how vacuum secondaries work. True, It is more then I need but vacuum secondaries are adjustable so when set tight they won't actually open up and feed 850CFM like a double pumper would. The engines vacuum determines how much CFM it gets not the carbs bore size. I'l get a double pumper and it will be smaller of course. I do need to put a full dual exhaust on it, that was always the plan but I had the factory Y pipe and enough spare bends to make the 2 into 1 sitting there so I sent it.

I admit that do not have it 100% properly tuned yet but its running good enough to get a basic feel for what its capable of with the stock cam. Basically I was comparing apples to oranges, the old SBCs woke up and made almost as much power as a bone stock truck 5.3 after all the modifications to the SBC. I wasn't taking into account that the carb and intake did not boost power output on the 5.3 while those things made a huge difference on the old SBCc. I fully understand that I will not make any additional power from the intake/carb setup compared to the stock intake/injectors that came with the 5.3 no matter how well its tuned. I was basically comparing a highly modified SBC to a basically bone stock level of power output 5.3 but I was only thinking about the similarities of the modifications when I first made the comparison (not the actual effect of the mods).

In my opinion if I really want to get what I expected from the engine I need to change cam/springs and it will be a big cam because I don't care about bottom end torque. :-)

the 5.3 is probably a little bit down on power compared to stock because its not fine tuned yet but I really don't think that's the issue, I personally think there is no issue per say - I was just expecting to much without making any modifications that I could actually expect to make more power over stock

 

Just seems like most tests are going to show that single planes aren't going to do much for you under 6000 rpm.

If you look at these graphs from the imfamous Hot Rod LS1 intake shootouts, you get a good view.

Performer RPM dual plane vs Victor Jr single plane.

At 3500 rpm, the dual is +55 ft-lbs
At 4000 rpm, the dual is +40 ft-lbs
At 5000 rpm, the dual is even with the single
At 6000 rpm, the dual is even with the single

That was done on a 6.0 with a bigger cam and good heads.

So if its similar, its an intake that does nothing but hurt power until after 6000 rpm, paired with a cam that doesn't make power after 6000. If you are giving up 30-50 ft lbs below power peak, that will be a huge seat-of-the-pants loss on a small 5.3.

I will happily stick with my fast 102(403 LS2) and TBSS manifolds (6.0 LQ4)

You mentioned that it isn't really spinning the stock S10 tires. I would think even a stock untouched 5.3 should roast them. That's why we looked for issues and poor parts matches.

In terms of how well these engines take mods, I look at my GMC. I have a 6.0 LQ4. The heads have been CNC'd by a previous owner, but chamber size is stock (they were running a blower). I am using a few leftover from my LS2 stroker: a TBSS Intake, and a 223/231 cam. I have long tubes, and a free flowing 2.5" dual exhaust. I have a new very tight LSD, and 33x12.5 tires. I will burn the tires from a stop through most of 2nd gear, and

runs 0-60 under 5 seconds when I can get traction.

So, thats a junkyard motor, junkyard intake, cleaned up stock heads, good exhaust, and a cam, and I'm probably pushing 450HP at the crank. I spin to 6500rpm. Compare that to a 3/4 ton chevy truck that these motors come from, and I would say thats at least as good of responding to mods as you can get from a Gen I junkyard motor.





Gratuitous photo of my truck...

 

With all due respect, you are grossly mistaken on the intake manifold. A performer rpm will outperform your intake all the way around and hand with it on upper rpm. Not to mention, your single plane is killing tq on a small cu in engine that’s already down on tq as it is. If you had a ls3 or bigger, yea that would be a good intake to run. But sorry I’ll stand by what I know. You are killing useable power with a single plane on that engine, standard trans or not. But hey, it’s your engine. Do what you want. You wanted to know why it’s a dog, and I’m telling you the truth. But you don’t want to accept that. And you should have just put a wiring harness and a factory computer on it to be gone with.

 

Here is a short list:

carb ls
carb ls
carb ls
to big of carb
a/f most likely off
timing most likely off
wrong intake

 

The Victor JR is for 3500-7500 RPM Range but the one I have is 2500-7000 RPM range. I'm not concerned with performance below 2500 and the 7K max is not sooo far from the 6K I shift at. So from 2500 RPM up to 6K RPM the engine is operating within the exact RPM range that the intake is designed to work at. It also allows me to change my cam and/or add NOS without changing intakes. Dual plane intake manifolds are all absolute garbage and made specifically for people driving a Prius

 

So, not much point in continuing this discussion - you're convinced that there's nothing wrong with your substandard combination of parts, regardless of what others have to say, hard-won experience & actual dyno outputs be damned.

Given that, the only suggestion that I can offer is that you TRY to learn to enjoy that substandard performance, since you're not willing to make the changes that will help. Oh - and try not to hate on everyone who's blowing past you...

 

My parts were never anyone's business anyway, I made it very clear it was a general question. 600 CFM carb and duel plane?? yeah that's gunna work great with my sloppy stage 2 cam and NOS. The parts I bought were not meant to be a good combination at this time, they will work with my future plans (aside from the carb, I admit vacuum secondaries with a manual trans was a mistake) I'm not trying to buy parts to work with the stock cam when I already know the only way to unlock the power of the heads on an LS is to put a better cam/springs in it) and I know that the parts I have now do in fact work just enough for me to get a general "feel" for the total power output that I can expect with the stock cam. Rather the criticizing the parts I used just to get the truck running and driving before I upgrade the cam and either add NOS or a turbo, then acting like I don't know what I'm doing because I don't want to tune my combo for the stock cam it would have been great if at least one person could have just answered my question. but yeah like you said not much point in continuing this discussion

Tell me more about how I'm gunna hurt my bottom end torque LOL

 

Your are so completely wrong. For what you are doing a dual plane will make the same peak horsepower and provide a torque curve that will put that single plane to shame. You are losing free power with that intake. Agreed your intake will work better later on with a larger cam.

 

I guess I should have made a very strong point, made it very clear from the beginning that the current combo of parts on it is not my idea of a good combination and that I don't have any plans to continue this build with those parts using the stock cam shaft...actually I should have stood my ground about it being a general question and never mentioned a word about the parts

oops

Anyway I personally drive one of two ways, I drive slow as if a police officer were behind me or I have the pedal to the floor when I find a safe place to floor it, therefore, literally, my only concern is the narrow RPM range between shifts at Wide Open Throttle.

I have never said said the words "and that was only half throttle" because it will never be 1/2 throttle if I am driving! hahaha

 

I don't agree with the first three at all, A carb can make nearly as much power and in some cases match or make more power than EFI, Sure they have their shortcomings but they are still capable of making good power. Here is head to head example but they used a Fast intake/MSD throttle.body.
As tested the mild 6.0 made
Carb = 462 hp at 6,600 rpm, while torque production now stood at 413 lb-ft at 5,200 rpm.
Fast EFI = 482 hp at 6,600 rpm and 436 lb-ft of torque at 5,300 rpm.
That's a 4% increase in HP and a 5% increase in torque, That's considerable increase but that's also comparing a carb the Fast intake/MSD throttle.body, I'd bet you a dollar that a stock Truck or LS6 intake would be much closer if not make less than the carb setup.
LS1 Carburetor V.S. Computer Performance Test - Retro Modern Motivation

 

It is a scientific fact that a perfectly tuned carburetor can make the exact same power as a fuel injected system given the exact same conditions. it's when conditions like temp and atmospheric pressure changes that a carb cannot possibly compete with fuel injection because it cannot correct for things like that. This is no mystery or debate, mixed air and fuel is mixed air and fuel whether its spitting out a carb or an injector. Perhaps direct tuned port injection would be an exception to that since the fuel pulse actually pushes into the cylinder with force instead of getting sucked into it, that pressure and force directly into the chamber does offer some advantage over a carb but I'm sure it's not very much

 

But due to fuel distribution issues with a centrally-located carb, you will never have the same AFR in all cylinders as closely as with SEFI. As a result, a carb setup will use more fuel in order to maintain the same power level. Carbs are less efficient no matter the conditions.

 

Lmao. Is this a joke? I can no longer take you seriously.

 

If the fuel injection unit is not also centrally located then not all conditions are the same, if you compared multi point injection systems you’d have to test with a one carb per cylinder setup to be fair lol

 

That situation rarely exists. You would need a set of Webers to be equivalent to SEFI, and a TBI to a conventional carb setup.
I was comparing a 4bbl carb to MPSEFI, both of which are the overwhelmingly most common respective setups.
TBI is a band-aid anyway, with many of the same weaknesses as carbs.
Webers are the most ideal carb setup, but very expensive and hard to keep tuned.