max boost

What would most consider to be a safe amount of boost for a small block with the following specs:
Iron Block filled to the top.
Billet splayed four bolt caps.
half inch head studs.
o ringed and copper head gasket (the norm for a blown motor)
Steel H beam rods
Steel heads
11.82:1 comp
Mallory Sprint mag. (24deg adv)
On alcohol.
I don't want to set the world on fire just want to run into the sevens and keep the motor together.

 

Brad , you are going to need to creep up on this boost thing.
by reading your plugs to determain the right amount of ignition
timing and fuel delivery you will be able to tune it once you have your base line set up. its just one of those things that only running the mtr will
determain. i myself do not see a problem running 15 to 20 % OD
making around 20 to 24 pounds boost for starts.

 

Brad,
When we ran our small block we ran and iron block with it 3/4 filled with hardblock, steel GM Bowtie heads with an 8-71 with 15 pounds of boost, 10.2:1 CR and it ran high 7's with 30 degrees timing. We switched to Dart aluminum heads, out of the box, ran 36 degrees timing and ran 7.70's with a 2100# car. We never hurt anything, BUT upon dis-assemble the 2 bolt caps we beginning to walk. We ran FelPro head gasket, not o-ringed.
O-ringing is obviously better, as are the splayed caps, but with the higher compression timing will need to be watched. IMO.
Also I'm not a big fan of H-beam rods, we ran Callies billet I beams with a Callies dragonslayer crank. Just some thoughts..

Keith

 

SBC 393ci

Brad,

Should not be a problem, mine is in a dragster 8% over 8-71 standard helix 1800lbs 6.615 @ 202.24 last weekent at World Finals in Rockingham. Keep the timing out of it with the steel rods I only run 28* you don't want the big pressure spike on them, aluminium absorbs it better than steel (my theory anyway). Have fun.

Henry

 

Thanks for info guys I will take all on board.
Brad

 

small block crank snout limit

I do not know if it was said before anywhere else but if you run a standard small block crank snout, it will sheer off with higher boost, probably before you overstress anything else. The cure is a special crank with a big block crank snout (larger gear drive gear & seal). I do not know what the boost limit is, but I hear it is a problem with any crank material. The standard small block snout is too small for the blower drive at higher boost. I saw one crank snout shear off with about 10% over on a 6-71 on a 350. Do not know what crank material was used.
I believe a reputable crank repair facility may be able to weld on to the snout to the big block dimensions. It is a pretty easy welding application and with good penetration into the #1 bearing flange of the crank and a good crank repair weld alloy, it should be easy to do. Then you need a bigger gear drive gear or chain drive sprocket. And machining on the cover for a larger seal.
If you do this, ask around for someone experienced in the conversion, but it is the way to go with a Roots blown small block. Then you can probably turn it up a lot higher.
bob@racecarbook.com
www.racecarbook.com

 

Sbc

You will need to run a crank support at the bare minimum, I use a callies hardened crank with the stock snout but with a crank support, it needs to be installed carrectly (sic) st so that it runs perfectlly true. with a big blower that may still not be enough but so far it has worked well for me 8-71 8 percent over.

 

I'm only running a 6/71 but I am running a crank support.
Brad