dwrestle

I have a chevy 2500 4x4, tbi 350, 4 speed, and I am debating what to do with the motor later down the road besides bolt ons. I don't really want a high rpm runner, but I want decent power.
I'm wondering if it's possible to have an 87 octane tbi 350(I have EBL Flash already) that makes 300hp under 5000rpm, and maybe at least 400tq under 3500rpm without boost. I just don't see any point in having a 6500rpm motor, but I would love to be able to hit 5-5500rpm from time to time, and have a ton more power from 2000-4000rpm.
So if it's possible what parts should be used? I don't want to go vortec I'd rather stick to heads that bolt to the current intake or edelbrock tbi intake.

sofakingdom

iTrader: (1)

HP = torque x RPM x a constant

The "constant" is just that; a number that can't be changed (happens to be 1/5252.11)

If you want more HP at a lower RPM, you have to have higher torque.

Torque = BMEP x bore x stroke x a constant

BMEP is "brake mean effective pressure"; which is a way of expressing how much pressure is pushing a piston downwards in the cyl, averaged over the entire 2-revolution engine cycle.

Once again, you can't change the constant: to increase torque you have to increase bore and/or stroke (in other words, CID, or engine size), or you have to increase BMEP.

BMEP depends on several things. First, how much gasoline the engine burns per revolution, which in turn depends on how much air it can move through itself since the mixture ratio is yet another constant you can't change. Second, it depends on the engine's compression ratio. Third, on how efficiently it converts the heat energy from burning fuel into mechanical energy. Rule of thumb is, at max output, a typical engine like ours turns about a third of the available energy into useful power, about a third goes into the cooling system, and the last third goes out the tailpipe. In fact close to 10% of the total energy in the fuel is tied up in keeping the water in the exhaust (the product that results from burning the hydrogen in the fuel) in gaseous form.

Pretty obvious then, to increase BMEP you have to burn more fuel, raise the compression, or make the engine more efficient.

You can only burn fuel up to the point that more air is available. But, at atmospheric pressure (no boost of any kind), the limit is ... atmospheric pressure. Only way around that is boost of some sort.

Raising the compression is only practical up to a point. The way it works is, the engine turns heat into motion by allowing the gas in the cyl after combustion to expand, which is the opposite of "compression". That is, "compressing" the air/fuel before combustion isn't what adds the power, it's the greater ratio of expansion as it de-compresses afterwards. But of course if the ratio is too high then control of combustion is lost; the mixture can detonate or otherwise begin burning before the spark plug lights it. So there's a limit to how high that can go.

It's possible to make the engine more efficient by minimizing losses. Ceramic coating on the top of the piston and the surface of the combustion chamber will keep the energy inside the cyl instead of letting it "leak" into the cooling system and be wasted.

The surest, cheeeeeepest, and eeeeeeeeeziest way to higher torque though, is CID. More CID = more torque, PERIOD, if all else is equal. Which is why people talk all about how {insert favorite discontinued GM division here} engines are "torque monsters": they FORGET that they're talking about a 400 or 455 or whatever, compared to a 350, which is where the torque comes from, NOT the sticker on the sheet metal it was wrapped in 40 yrs ago.

If you want more torque out of a 350, first thing you should consider is making it into a 383 instead. You should pay close attention to details when building it, like deck clearance, quench, sharp edges in the combustion chambers, combustion chamber shape (i.e. use small-chamber heads and "D" dish pistons, not large-chamber heads and dome pistons) and so forth. You should have the parts coated. And you should select parts that are optimized for cyl pressure in the RPM range you want. This means CAM SELECTION. That's a topic that whole books can be written about.

MSgt Luttrell

I also suggest a 383 or a 400 small block chevy, either will build lots of torque and horse power in the range you are looking at. Here is the dyno sheet on my 383 at the crankshaft.

cuisinartvette

dont know much about tuning a TBI sure some here do
Big heavy truck (what year) you need sheer torque

Stroke that thing dont waste time with the 3.48 stroke

Fast355

iTrader: (2)

My Express van 350 Vortec made about 300 hp and 400 tq at the flywheel with stock 062 junk hecho en mexico heads and the GM 395' marine cam. With the LT4 Hotcam and worked 906 heads it is making about 390 HP and 430 TQ at the flywheel. Both setups were putting down over 270 ft/lbs at the wheels as low as 2,200 rpm through a 4L80E and 10.5" 14-bolt.

bluers91

I agree with Fast that you can easily meet your goals with a 350, Vortec heads, a small roller cam and headers.