View Full Version : Need some explaning please, 427ci...


Gordon0652
08-26-2007, 01:34 AM
...naturally aspirated 427ci small-block fitted with 360-cfm LS6 heads and sheetmetal intake manifold that churned out 845 hp...

The specs of that motor is:
4.125-in bore x 4.000-in stroke
Chevrolet LS6 ported Heads
LSM solid roller
Camshaft duration @0.050: 278/288
Lift: Intake .770
Exhaust .680
Lobe separation: 113
Custom sheet metal by Beck Mechanical
KOOKS 2 / 2 1/8 Stepped Headers and Exhaust with Flowmaster Mufflers
55lb fuel injectors
Holley 105mm TB
Pump gas

And thats pushing out 845hp at the crank! Why is it that it seems to be hard to push out about 650-700hp at the crank on a 427 but they are making 845 crank horsepower on pump gas!

The reason for this question is because i am trying to chose between a twin turbo kit or an N/a motor for my t/a. I am having trouble deciding between them and i like the idea of an old school n/a motor.

180ls1
08-26-2007, 04:00 AM
what altitude was that at and what was the air temp that could make a difference small but everything adds up.

greysteel_M6
09-02-2007, 02:31 AM
You got a link to that?

posenheimer
09-03-2007, 12:25 PM
You got a link to that? Sure it's a sbc1?


Yeah I just read that article... int the same boat as the first guy in this thread here is the link guys:

http://www.samracing.com/99chevycamarossspecs.html

Twin turbos, big procharger or A motor like the one in the artice??? What to do what to do? Hmmm Badass motor though!

Gannet
09-04-2007, 08:08 AM
Look at the cam specs. That is a pure racing engine and would be totally unsuitable for street use. It probably spins 8500 rpm, makes zero power below 4000, and "idles" at 1500. It also has to be freshened on a regular basis.

There's no magic to engines. You want 845 fwhp, you need to flow 845 fwhp worth of air. You can do that one of three ways:

Cubes
RPMs
FI (including N2O)

That is all.

That engine is making about 1.7 rwhp/ci. RADICAL LS street packages top out at 1.4, maybe 1.5. If that will be enough for you, and you're willing to put up with the hassle and expense of running that kind of engine on the street, go for it. OTOH, fully streetable, pump gas (maybe plus meth), idles-like-stock FI LS engines can go 2.0-2.2 rwhp/ci, no problem.

Oh, and a NA engine that makes 1.7 rwhp/ci will cost EASILY as much as a FI package (engine plus blower) that makes the same number.

will82
09-05-2007, 08:13 PM
Look at the cam specs. That is a pure racing engine and would be totally unsuitable for street use.

Exactly. Duration of 278/288 @.050 ??? VERY BIG.

FieroZ34
09-06-2007, 12:20 AM
Look at the cam specs. That is a pure racing engine and would be totally unsuitable for street use. It probably spins 8500 rpm, makes zero power below 4000, and "idles" at 1500. It also has to be freshened on a regular basis.

There's no magic to engines. You want 845 fwhp, you need to flow 845 fwhp worth of air. You can do that one of three ways:

Cubes
RPMs
FI (including N2O)

That is all.

That engine is making about 1.7 rwhp/ci. RADICAL LS street packages top out at 1.4, maybe 1.5. If that will be enough for you, and you're willing to put up with the hassle and expense of running that kind of engine on the street, go for it. OTOH, fully streetable, pump gas (maybe plus meth), idles-like-stock FI LS engines can go 2.0-2.2 rwhp/ci, no problem.

Oh, and a NA engine that makes 1.7 rwhp/ci will cost EASILY as much as a FI package (engine plus blower) that makes the same number.
I disagree. A 8500rpm engine is not at all illogical for street use. My sportbike idles at 1800rpm all day long. What's the big deal? The new M3 spins out to 8250. I'll agree some people don't like engines that spin that high for the BS reasons they give imo, but to say it is not suitable for the street is pure ignorance. And the only thing idle RPM affects is gas consumption and noise. The gas usage at idle is negligible, and the noise is easily contained. Just ignorant people get in the driver's seat, and can't handle seeing the needle above the 1 at a stoplight for whatever reason.

As for the zero power below 4,000, that's more ignorant than the rest of your post. Find me a single engine that looses low end power as you tune for more RPM, and I'll be shocked. I recently built a 2.4l DOHC for frequent 8,500rpm runs. Stock they redline at 6200, with a torque peak at around 2,500 IIRC. Stock made a flattering 132whp, our's did 245. It was cammed to high heaven, fully independent 56mm TBs, equal length 4-1 2" X 24" header, and the head ported to DOUBLE the factory flow at factory lifts. Every component of the build was to maximize high end power. I didn't care what it idled at, or what it had below 4,500. However once on the dyno, it made over 30wtq more than the stock motor did from dyno start (2,000), to peak (4,500). So while it feels much worse, it's actually making MORE low end power. Explain that.

Another instance, my old Lumina Z34. The only mods were an intake manifold, throttle body, and headers. The intake manifold lost 5" of runner length, gained 1/2" in^2 of runner area, and tripled the plenum volume. The headers were also tuned for a 8,000rpm redline (Over the stock 6500), with 1.75" X 30" primaries. And the throttle body was a 75mm unit, a full 13mm over the stock unit. I proceeded to turn it over 1,000rpm higher than stock, on the stock cams, stock heads. So I should have "0 power below 4,000rpm" right? Not quite. Again, I gained wtq from dyno start to finish. Except once at 3,500, the line climbs at a much steeper angle. But fact remains, I made over 10wtq over stock from dyno start to the start of my power curve.

Fact is, and I've seen this on every high RPM engine I've built, we never lose low RPM power. We just don't gain much in respect to the high RPM power. It feels a lot more like a torqueless wonder, but in reality, it's quicker down low.

Now your only 3 ways to make power, which are missing a few bullets. Cubes, RPM, or forced induction? That's it? You have got to mean those are the only ways to increase air flow, which is still wrong anyways.

Reality? There are a LOT of ways. First and foremost, increase air flow. NOT CUBES. Increasing the displacement won't change anything, unless you increase airflow. That's how a BMW M3 makes the same power as an LS1, just down 2.5l. It flows approximately the same amount of air. To increase airflow, you increase volumetric efficiency. Better intake, better heads, more cam, better headers, OR forced induction. Now airflow can increase with displacement, of course, but it doesn't happen all the time, and it can just as easily not. That is why there are so many high cube LSX motors, that aren't really making much more power than the 346s, and certainly not linearly more. Because the heads are much more of a restriction to the high cube cars, even the best heads made (As the head will always be the restriction).

The second way to increase power is advanced spark timing. We won't touch this much as two builds with similar power figures, head design, and ignition specs won't be very different in timing. Furthermore, with PCM-controlled ignition, most run as much timing as they can as it is. But fact remains, power can be gained by advanced timing.

The third way is less parasitic loss. That's why under drive pullies gain power. Whether it being lowering external losses (UD pulley), lowering rotating mass (Cam/crank weight), or best yet reducing reciprocating mass (Pushrods, connecting rods, pistons, valves, etc), all will help. Yet another reason why the large LSX's aren't making linearly more power than the 346s. That huge stroke they are running just significantly increased connecting rod weight (The heaviest reciprocating item in a build). So now it costs the engine more power to tun the assembly. And since they are heavier, it also can't be tuned as fast, meaning you must run lower RPMs, meaning lower VE, meaning less ai, meaning less power potential.

There are other ways (Better sealing), but they are negligible in most builds, the same in most, and not worth the same listed here. Fact this, there are not just 3 ways to increase power, and they certainly are not limited to those you stated.

LS1Z28-00
09-06-2007, 11:22 PM
i dont think a 278/288 cam will be streetable either. i guess it depends on the type of street use you will give it.
on the highway it would be a beast no doubt. of course that big ass cam will make more power at 4k than stock cam. however a 230/230 cam will make more power than that monster cam at 4k. so you cruise around and a smaller cam car pulls up to you and you both hit it, he will pull away from you until you hit your powerband but then its too late because a street race usually doesnt last that long. a TT setup will be much more streetable. also if you can afford 3-4 MPG i would estimate with that setup, stalling, dieing all the time. any time you spin an engine to 8500 RPM it is going to be alot less reliable than a lower reving engine. so unless you wanna run like a 6200+ stall converter prolly 4.56 gears and have an unreliable ride then i would consider a TT setup. just my .02