I am looking for additional HP out of our 357" small block chevy. The motor is due for valve springs and lifters (7 seasons on solid rollers ) and we would like to get a little more while we have the intake and headers off for the changes. The heads are Chevy phase 2 cast iron Bow Tie heads. They are unported and have 2.05" intake valves and 1.60" exhaust valves. The motor has 11.25:1 compression and the cam is a 246/254 duration @ .050" with .592" intake lift and .555" exhaust lift on a 112+4. We run CMI exhaust, holley strip dominator intake, full MSD ignition, holley 800 DP carb, with a 150 HP NOS cheater system. I want to know how much HP can be gained with these heads with a full port and polish and an intake manifold match port.
Thanks for your opinions.

No opinions!! The SBC is only the winningest race engine ever!! I was sure someone on the board would have some porting insight. Oh well, I don't know either!

Maybe Dennis Moore wil jump in and answer you question.
How much HP are you making now?

Iggy, motor HP is really unknown, but believed to be 450 to 500. It is in a 20' V-hull and turns a 26" 3 blade prop 6000 RPM for 80 to 82 MPH on radar. The boat went about 60 with a 270 HP 350 mag.

Ever think about putting a blower on it?
Vortech (I believe) has a new setup for carb'ed SBC's. Would be worth looking at.
One of the magazines I read did it and got a lot in return.
I'll have to look for the article.

Ok, I found this in an earlier post of mine:

Hot Rod magazine has a similar article on the Vortech carb blower.
Looks like the perfect set-up.
They tested it on a GM HT383 crate motor that was modified with a Edelbrock RPM Air Gap, 750 Speed Demon carb, Comp Cams XE282HR cam, 1.6:1 rockers, 9.1:1 compression, Vortech heads (I think). Without the blower this combination made 476HP@5500 and 505 lb-ft@4400.
First run with the blower had a 6" crank pully and a 3.47" blower pully pumped out 3lbs of boost for an almost 100HP gain.
Swapped the blower pully for a 3.125" and got 7lbs boost and 643HP@6000 with 600lb-ft from 3500 to 5500 and max was 606lb-ft@4900.
Swapped blower pully again to a 2.95", got 8lbs boost and 677HP and 627lb-ft@5000.

Iggy, a blower would be cool, but this motor has 11.25:1 compression and a pretty fresh bottom end. I agree that would make some serious HP, but right now we are just looking for a little more from our N/A set-up.

Here's the motor I'd like to build for my 20 footer:

Chevy High Performance magazine had been running a multi-issue article on a 383" GM crate motor. They've modified it a little but this was one of their test sessions.

GM 383 crate engine
Compression...9.1:1
Heads...Stock Vortec iron with 1.94/1.50 valves
Rockers...GM roller 1.6
Cam...GM Hot Cam P/N 24502586
Duration 218/228
Lift .525/.525 w/1.6 rocker
Lobe separation 112
Intake...Edelbrock Performer RPM Air Gap
Carb...750 Holley
Ignition...stock HEI

Cost of engine package as tested:
Engine 3699.00
Cam 210.00
Rockers 301.00
Intake 193.00
Carb 430.00

Total 4832.00 +/-


Dyno test
RPM TQ HP
2500 412 196
2600 419 207
2700 425 218
2800 434 231
2900 442 244
3000 448 256
3100 425 266
3200 455 277
3300 460 289
3400 464 300
3500 466 310
3600 466 319
3700 465 327
3800 464 336
3900 462 343
4000 462 352
4100 463 362
4200 462 369
4300 459 376
4400 456 382
4500 453 388
4600 449 394
4700 446 399
4800 441 403
4900 436 406
5000 429 409
5100 423 411
5200 417 413
5300 410 414
5400 402 413
5500 396 415
5600 390 416
5700 376 409

They then switched to a Comp Cams XE282 HR cam.
The HP jumped to 449@5300 and torque was 486@4200.

If you are interested in purchasing a pair of heads, I have a pair of Dart Sportsman's that are fully race ported and flow enough air to run 9000 rpms, maybe a little overkill for marine, but they were unbelievable in my car. I had them setup on a 383 with a 7600 rev limiter, pulled to the limiter in 4th gear with 3.73's and 10.0:1 compression. Never hurt. $2500 fresh and ready to use.


Rod

I spoke to JimV and he said definate potential for more HP out of our stock Bowtie heads. He feels 40 HP from the porting alone, and he recommends a little more cam with lift in the .600 to .650 range. I just pulled the exhaust off of the motor and will be getting the intake and heads off real soon.

RPM-Sounds like a nice set of heads, but we will probably be better off with the porting on our Bowties. Besides the CMI's on this boat exit very low and they have a 90 degree elbow welded to the end of them. In other words we need to stick to a head that has stock exhaust locations.

Iggy- That looks like a sweet combo, but we are going to leave our bottom end as is. Besides with the compression we are running and the roller cam we are probably doing every bit of that if not more. I agree if starting from scratch the stroker is the way to go!!