mike tkach

iTrader: (3)

try that on a heavy single engine boat with a pro charger,like i said,every build is application specific.so yes it is a tricky question.

adk61

iTrader: (5)

Like I said piston design is critical to this question... I prefer a flat top with thick crown, low top ring placement as opposed to the partial dish with quench pad

adk61

iTrader: (5)

true Mike, every build is different.. always an exception to every rule

MILD THUNDER

iTrader: (3)

Thats a good point . Thats one of the reasons a Screw/roots, centrifugal, and turbo, all require different cams.

Sticking a cam in that works great in a roots/screw combo, might make the procharger engine, feel like a turd. Or worse, a roots blower cam, in a turbo engine.

Lets say one was building a 540ci, with a roots. You put in a 248/256 114 LSA cam in it, where the intake valve closes at 53* . You nail the throttle, thing makes gobs of torque and puts you in the seat. You take the roots off, put a procharger on it, and all of a sudden, the engine becomes a slug. Because the late closing intake valve , and low static compression, means that off boost, she cant make any cyl pressure whatsover.

You'd want to get that static up, and close the intake valve sooner, than you can build some cyl pressure at low engine speeds.

Thats one of my favorite thing about a positive displacement blower. You can change the dynamic compression, or effective compression really, with the push of the throttle, or , with a pulley change.

MILD THUNDER

iTrader: (3)

Doing a comparison of an engine model I was working on last night, I decided to do a comparison, of what my previous post states.

I first had a 502ci, using a roots. Then switched to a V7 vortech centrifugal. The cam, was a roots style blower cam. The BMEP (brake mean effective pressure) numbers are as follows. Keep in mind, both combos set up to deliver 10psi of boost at 6k rpm.
Vortech/roots 10-71
3000=150/206
3500=170/219
4000=185/227
4500=204/237
5000=216/244
5500=218/246
6000=219/242

As you can see, the 8.5:1 engine, with roots blower typical cam, simply makes more cyl pressure. Now, to even the playing field, and get BMEP numbers closer, I had to knock out 10 degrees of duration, advance the cams ICL 3*, and raise the static from 8.5:1, to 9.5:1. The intake valve is now closing at 43*, rather than 51* with the roots setup.

So, while a roots blower may do well with more duration, a centrifugal, will NOT like the same setup. The numbers are even further apart, below 3k rpm, which in a street car, would be very important.

If you try to build a centrifugal engine, like a roots engine, you are losing. If you try to build a roots engine, like a centrifugal, you are losing. IMO, this stuff, plays a much larger role in the final product, than simply arguiing over a particular cyl head port volume. Like say, a 335 vs a 315, or 325 vs 305.

adk61

iTrader: (5)

My Cat 572s are .050 in with a .080 gasket... at tad over 8:1 with my chamber...

getrdunn

iTrader: (7)

U using the 252/257 SR cam

MILD THUNDER

iTrader: (3)

I think he's a little bigger than that

adk61

iTrader: (5)

he wouldn't believe you if you told him... so don't as that's one of my secret weapon cam grinds!!! and it works nails!!!

272lsformula

iTrader: (1)

my pistons are .020 in the hole with .041 gskt. with 8.25 static comp. 8-71s 6% under driven making 5.5 of boost