iamfaster

even with new perf heads??

JCPERF

What make heads are they?

Payton

A little side not question.

I've been told a 454 will show a lot of benifit from a .030 or even a .060 overbore as it will unshroud the valves. Will you still see just as much benifit with a blower and a slight overbore?

iamfaster

JC, they r either going to b cast iron Merlin or Dart

JCPERF

Go with the dart iron eagle 308 heads.They will work fine with 7.5 compression@5-6 lbs. of boost.I would run 8.5 compression instead for two reasons:You will not have to spin the blower as fast to make the boost you want which means less heat.Less heat going into the engine equals more power and less prone to detonate.The second reason is when your cruising you motor wont be in boost. For ex.4000 rpm making no boost[0].This will all give you longer life and reliability.

mcollinstn

You can spin the 177 up to its "safe speed". I'm not sure what this is, but above that the rotors will either sling the teflon strips out or explode. Like I said, I'm sure you are in the safe zone still.

Above a certain flow rate, the rotors start whipping the air. Sort of like any pump that is starving on the incoming side. Like a cavitation. All blowers have an efficiency curve. And it depends on the pressure differential as well as the flow.

On one hand, you can flow say 2000 cfm into a given blower (without falling out of the efficiency curve) at 2 psi differential (into say an intake manifold)...

Same blower may flow 1000 cfm into a 6 psi differential (within the efficiency curve).

And at a certain pressure differential, the flow rate drops dramatically. Say for the example (which is an imaginary blower), you may drop to 400cfm at 20psi.
And 1cfm at 28psi.

Keep in mind, that these numbers are considered to be in the "EFFICIENT" range of operation. You can pulley PAST this efficient range and still get what you're after, but when you operate outside of the efficient zone you are building more heat from the cavitation or "whipping" and your results will not be as good as if you upsized the blower.

And remember, it ISNT what pressure you can ram into the motor - it's what quantity of molecules you can ram into the motor. Hot charge has less molecules than cool charge.

With your 177, I would GUESS than you could still spin it hard enough to see 4psi on a very modified free flowing 454 without falling out of the efficiency curve. 6 psi would yield benefit, but would be generating enough heat to require less than optimum spark lead - or higher octane fuel (both being bandaids).

And yes, longer rods (with nothing else changed) will raise your compression ratio. It will also put your pistons into the heads unless your "builder" can find you some rods that are .020-.030" longer than stock (I ain't never heard of any..). Typically, longer rods are matched to pistons with relocated pin (compression) height.

Infomaniac

The original B&M compact blowers were limited to 12,000 Blower RPM.

Just for the sake of friendly interesting discussion. Not an online argument.

A .020 - 030 longer rod is not going to happen.

But with noting else changed a longer rod would make the volume at TDC less and also the volume at BDC less due to the piston being raised in the bore (deck height). So in effect would not both volumes decreasing cancel each other out to some degree?

I am getting a headache thinking about something that could never happen. LOL

mcollinstn

Of course he's not gonna find .030" shorter rods. His "builder" needs to stop talking while he's ahead..

But no, you're missing the obvious on the volume comparison. You're thinking too much (yet not enough!). At TDC the long rod makes the volume less. Yep. At BDC the long rod makes the volume less. Yep again. BUT:

Whenever a small change is hard to visualize, then picture an extreme case. Since rod length (with no other changes) changes the position of the stroke within the bore, then picture a cylinder about three feet long with a "zero cc" chamber bolted on it. Start with a short rod that only moves the piston in the bottom 4" of the cylinder. BDC you got about 33" to the deck. TDC you got 29" to the deck. Veeeery low CR. Now use a long rod that uses only the top portion of the cylinder: BDC you got 4" of volume. TDC you got none. Veery high CR.

And if you are familiar with running the math on a gasket and deck ht stackup to figure exact CR, then you alredy know that the deck height and gasket thickness make a Beeg difference in the CR. So you already knew this stuff..

iamfaster

i will call the "reputable engine builder" to qualify exactly what he suggested to me?
maybe i misunderstood him. (quite possible ) Or maybe he just aint reputable!

infomniac, r u sure that 12,ooo rpm's r max on the weiand 177? I guess i could do the math to determine what my stock pulleys r spinning it. I assume the stock 525sc set up was within the optimum efficiency. Measure the pulleys and divide the top into the bottom @ 5,200 ????????

iamfaster

HES not my builder...just someone i happened to speak to... thanks for the info though!!