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Old 01-05-2019, 05:16 PM
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Horsepower 350

I was wondering if somebody could tell me the horse power an torque on my motor. Here is what I got
Standard bore sbc 350
Hyperthetic flat top with Hastings rings
Stock crank an. Rods
Vortec heads been gasket matched to intake an ported an polished
LT4 valve springs titanium retainers
Comp extreme energy 274/286 with .490 lift
Vortex dual plain intake from JEGS
Eldebroke 750 carb electric water pump only things on it is alternator. Headers 21/2” exaust with one chamber mufflers.
An it’s in a s10 blazer 2 door with 342 gears if that helps.
Thankx for. Ann

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Old 01-05-2019, 06:04 PM
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Whether a "port & polish" was of any help on the your Vortec heads is anybody's guess, even real pro's have a tough time making them any better than factory without resorting to cutting the valver seats for larger valves...but anyway...

Thar's a solid 385-415 HP combination in most cases, depending on how good you can tune carb and ignition timing curve, and how good the exhaust system is.....I know for the S-10 chassis trucks/Blazers the header selection is either a small tube shorty header.....or an $$$ big tube race set.

with the 3.42's I bet it's a nice street runner....a 2500-2800 rpm stall converter would help a good bit if you don't have one already.
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Old 01-05-2019, 07:26 PM
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Thankx for the information. I been wanting some big tube headers but haven’t got them yet but will soon an I got a 5 speed right now. Glad to no that bout the heads. Wasn’t sure. So I can put bigger valves an it will help them? I have read we’re it does an we’re it don’t.
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Old 01-05-2019, 09:35 PM
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Bigger valves will always help with flow but you need to think about whether the cost of the larger valves is going to be worth all the effort? If you're planning future upgrades, you might want to forego those heads and pick up some aluminum ones with the bigger valves and flow already in the package. The R&R cost is going to be the same so it comes down to how much a machine shop is going to charge for the machine work, a least a 3 angle valve job, the cost of the valves, hardened seats, new springs and seals versus the cost of the aluminum heads ready to bolt on.
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Old 01-05-2019, 09:55 PM
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Yea I was wondering about that cause I been reading that it ant but so much you can get out Vortec heads but didn’t no that was until after I built it I’ve always heard Vortec was supppse to be SO GOOD LOL. would it make a good diff with a set of aluminum heads with big valve. I got a buddy that got a set of Holley aluminum heads. Idn exactly what they are beside Holley I pro can get cheap.
Thanks for your information
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Old 01-06-2019, 02:59 AM
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Quote:
Originally Posted by KEVIN 1986 View Post
Yea I was wondering about that cause I been reading that it ant but so much you can get out Vortec heads but didn’t no that was until after I built it I’ve always heard Vortec was supppse to be SO GOOD LOL. would it make a good diff with a set of aluminum heads with big valve. I got a buddy that got a set of Holley aluminum heads. Idn exactly what they are beside Holley I pro can get cheap.
Thanks for your information
The big advantage to aluminum heads is they allow another ratio or a bit more of compression than iron heads. This is a big help with long winded cams as it restores the otherwise lost bottom end torque and helps carry the power curve over its peak RPM so it decays slowly rather than just dropping out from under you.

One of your current problems is the carb is too small, when we talk about 350's making 385 to 420 horsepower that is under a 750 to 800 CFM carb. With a cast iron Vortec style head the peak range is typically 375 to 385 on a chassis dyno with dyno room headers and no accessories. Dyno room headers don't have to fit into engiine compartments and accessories like a working alternator and coolant pump are eating up probably as much as 50 hp up on the top end.

The other thing when pushing a 350 over about 385 horse, attention to the details become critical. In the case of the Dart head they are meant to have their ports cleaned, the exhaust crossover ports need to be filled in the head these things cause a lot of turbulance in the exhaust ports they connect with. The valve train needs to be robust and spot on. High quality alloy steel push rods are needed to remove flexing of these parts; rockers need to be full roller, and stiff yet light, their set up on the valve stem needs to be spot on as one of the big things this pushes is push rod length for the most effective geometry. If you run rockers on the studs those need to be the 7/16 stud to resist whipping around. Poly locks and probably a girdle, especially with stainless rockers are a necessity.

The pan should be baffled with a windage tray and oil stripper. There are several problems to be solved here, the one guys always fall for is getting the oil pulled out of the windage can add a lot of power in the range of 15 to 30 at high RPM. But a really important benefit with these type pans is they keep the oil in the pan and by the pickup so the engine is less likely to oil starve in the high RPMs.

A high quality damper, this quells the wild vibrations that end up in the crank snout, this helps keep the timing set from jumping more than necessary it's bad enough that it has to deal with 16 accelerations and decelerations with the turns of the camshaft, it doesn't need stupid crankshaft tricks as well.

Same goes for ignition, it needs to time correctly with every turn of crank and cam and the spark needs to be strong enough that chamber turbulance and compression don't blow it out.

Details, the more the power per cubic inch the harder you have to work the details.

Bogie
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Old 01-06-2019, 05:27 PM
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Is this a roller or flat tappet cam? Looks like flat tappet...
Rocker arms ratio? 1.5? 1.6?
Do you know the compression height of the pistons?
The compressed thickness of the head gaskets?
Was the block deck or heads shaved?
I would think a 750 CFM carb. should be plenty for your application...
Is it running OK? sometimes a stock fuel pump floods those Eddy/Carter type carb.s with too much pressure...
Does it pull strong to 6500 RPMs?
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Old 01-06-2019, 08:04 PM
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Is a flat tappet cam an it does run rich I can change the metering. Rods an get it not to run rich but then it bogs real bad. I got the wide band gauge a 02 in it an it jump ships all over the place. I went down to a 600 carb an it bogged real bad that’s when I ordered a jet an mettering kit an I’ve tried every one of them. It still ant right I put a Holley in-line fuel pump on it the other day but haven’t really drove it. I also got a regulator an gauge on it an I can adjust the pressure to 5lbs an check it later an it will be down on 21/2 lbs or 3 lbs an I adjust it back to 5lbs an check it later an it will be up on 71/2 to 8lbs. So Idn what the deal there is.
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Old 01-07-2019, 03:13 AM
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If that is a liquid filled gauge, they are sensitive to underhood heat, the only time they will read correctly is when they are cold....as they heat up the fluid inside expands and presses on the internal mechanism, giving a false lower reading.

Set the pressure cold, and then leave it alone and just ignore what the gauge says hot.

if it isn't a liquid filled gauge, then you've got a problem somewhere in the system.

The Holley heads aren't much better flowing than a stock Vortec, so unless you can port them well yourself or know someone who can and will do them for nearly peanuts as far as cost....pass on them.
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Old 01-07-2019, 06:29 AM
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[quote=KEVIN 1986;4647407]Is a flat tappet cam an it does run rich I can change the metering. Rods an get it not to run rich but then it bogs real bad. I got the wide band gauge a 02 in it an it jump ships all over the place. I went down to a 600 carb an it bogged real bad that’s when I ordered a jet an mettering kit an I’ve tried every one of them. It still ant right I put a Holley in-line fuel pump on it the other day but haven’t really drove it. I also got a regulator an gauge on it an I can adjust the pressure to 5lbs an check it later an it will be down on 21/2 lbs or 3 lbs an I adjust it back to 5lbs an check it later an it will be up on 71/2 to 8lbs. So Idn what the deal there is.[/quote]

Welcome to MY world. Check out my thread on fuel pressure. I've battled this for years. Good luck.
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Old 01-07-2019, 01:09 PM
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Thank you for that cause it is liquid filled gauge. Glad to no that.
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Old 01-07-2019, 01:44 PM
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Couple three things commonly could be causing a bog... bad accelerator pump... loose accelerator pump linkage... vacuum secondaries opening at too low an RPMs(~90% of time this is it)... ignition timing/advancing not set right... ignition advance mechanism rusted/jammed up... float levels not right in the carb... leaking inlet valve in the carb. from wear of junk caught in it...
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Old 01-08-2019, 11:03 AM
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Bog after idle with a big cam is common, actually about the biggest cam you can run in a 350 without having to become a rocket scientist of engines is the Comp XE268H or someone else's equivalent. The XE274H steps into the territory of where you really need to understand the sciences of engine systems.

The cam you have promotes a lot of induction reversion which causes mixture problems to come and go. Initial bogs are common especially from lower RPMs when the throttle I snapped open, there are several reasons for this.

- Reversion (reverse pumping) through the carb riches the mixture and you can't get control. This because the carb is just as happy to add fuel to pressure pulses going out as it was to air flow going in. Reversion has several causes perhaps the biggest is that as cam duration increases the later in the compression stroke is the intake closed, below a critical RPM the pressure caused by the rising piston is greater than the kenetic energy of the induction mixture flow the result is a fraction of what was taken in is now pumped out. The other end of the long cam timing is overlap where exhaust flow inertia can over scavenge the cylinder pulling a fraction of the mixture out. The usual fix to these problems is to spin the engine faster but automatics don't really provide the needed gear ratios nor the controllability of using them as necessary. A milder cam and or stiffer overall gearing can be used. Sometimes a carb spacer is helpful because adding plenum volume softens the reversion pulses thus reducing the amount reversion passing through the venturies, this is also cut and try thing where a sweet spot exists somewhere between too little and too much.

- Idle air supply with a larger cam can be an issue that results in bogs. Typically the solution to a bigger cam's need to idle up is to open the throttle curb setting. This gets too much of the transfer slot open which results in a rich idle that you can't control with an bog as the throttle is opened. Generally there should be no more than .040 inch of transfer slot exposed under the bottom side of the throttle plates with .020 to .030 being the better answer. A 4 corner idle 4 barrel is the best answer, the next is starting with a 1/32nd bit is to drill a small hole in each primary throttle plate on the primary side moving to a larger hole as and if necessary in small increments probably 1/64th at a time. This is a real PIA cut and try process.

- As regulators go a bypass is the best solution, when set up the fuel supply s in a constant excess state, the engine takes only he volume it needs which results with an even pressure as the excess supply at every degree of consumption is returned to the fuel tank.

Bogie
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Old 01-08-2019, 08:45 PM
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So I need to put a return line on it? Witch side of the regulator does it need to be or do I take it off? I had a spacer under carb an it ran worse. An can u post a pic of where u talking bout drilling holes an thanks for the information.
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Old 01-09-2019, 01:43 AM
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Quote:
Originally Posted by KEVIN 1986 View Post
So uI need to put a return line on it? Witch side of the regulator does it need to be or do I take it off? I had a spacer under carb an it ran worse. An can u post a pic of where u talking bout drilling holes an thanks for the information.
A bypass regulator is a specific design and will be labeled as such. These are really needed with electric pumps, but also as engine operating temperatures and higher volatility fuels have entered the market GM add a bypass to mechanical pumps.

The return for vehicles that don't have this feature built in to the tank a common place to connect the return is into the filler neck low enough to prevent splash that escapes and also to not obstruct the gas station's filler nozzle.

Another way is to tee into the pump feed line as close to the tank as possible so the return fuel has time to cool if you run an electric turbine pump as these pass fuel over the motor for cooling so a diet of previously heated gas the pump already pump will reduce pump life.

The regulator can be mounted on the engine or a suitable location on the firewall of inner fender not far from the carb. The line that runs to the carb now will connect to the regulator's input fitting, the outlet fitting goes to the carb, the bypass returns to the tank. Things I like to do while things are apart is to add a manual shut off valve in the fuel line close to the tank and close to where it drops down to run along the frame, for maintence this is handy to shut off the line without having to drain the tank. If you run an external electric pump I like to put a replaceable or cleanable filter in between the valve and the pump this can be a fairly open weave filter its there to stop stuff big enough to damage the pump. I also do a finer filter ahead of the regulator to eliminate the grit that can mess it and the carb up. A pressure gauge close to the carb will let you trim the system to get proper deliver pressures at the carb where it counts plus a gauge at the regulator if it is not mounted on the engine as this is a more stable location away from engine heat and vibration. I don't use oil filled gauges as they can give odd readings when they get hot plus given enough time the oil will darken to where you can't see the gauge face.


Bogie
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