jlboggs

I have a gm steel crank that checks out ok from machine shop.What is the maximum compression ratio I can run? Race only motor. Rumor is no more than 11:1 is there any truth to this?.It is not 4340 steel either been told its 5140.I have a 84 camaro and only wanting to build an 11:50 car.Any advice would be great ....just looking for someone to point me in the right direction...350 sbc .060 over...thanks-jerry

promod45

i have run Gm steel cranks in my blown small block on racing gas and it went consitent 9.90 et in a 3200 lb car and never broke one, 11 to 1 would be no problem, just as long as you dont detinate it , just my opiion

OneBadGMC

I still have my GM 5140 crank. Bought it in 1991.

Ran it for 6 years in a mild 462 blower motor making 900 HP.

Great cranks. My only complaint is that it had excessive run out from the factory. Had to turn a brand new crank .010 on the main to get it fixed.

Tod74

I ran a 454 factory steel crank with 14:1 in a studded 2 bolt block with no trouble

edvancedengines

IN these days of so many choices the old factory stuff that Drag Racing built it's roots is very much over looked and under rated.

Problem is by now many of the original 5010 (I think) alloy factory GM steel cranks have gotten tiny spider cracks usually showing in the radius of the fillet. If you have one that is clean and can pass a WetMag inspection you have a good strong crank. A factory GM Steel 350 cu in High Performance crank in perfect shape can handle above 900 hp in a N/A engine, more in a turbo or blown engine. DEtonation will kill anything so I mean in good tune. A 454 LS-6 or LS-7 Factory GM Steel Crank can handle as much as 1,400 horsepower without detonation. A good factory 454 prepped 4 bolt main block or splayed cap block can also handle upwards of 1,400 horsies.

The key is get it fully inspected not cheaply inspected. Wet Mag costs a lot more for equipment but will show defects better. You can have defects that a regular dry magnaflux can not pick up.

Ed

Tod74

Only bad thing is I think many of the bbc cranks were crss drilled...not positive but I think they were.

hink

The GM cranks are 1038 steel the sam as the forged rods and we use to use them in the circle track engines we build and with the small radius thre seem to be signs of cracking after a season of running and I have seen some break. And the indexing on the GM cranks is all over the place.

The GM forgings we use come from Crower or King's crank in NC with a 1/8 radius and those cranks seem to hold up fine and they are indexed.

jlboggs

Thanks guys for the very helpful input.If my piece is suited for a little more horsepower like everyone seems to think then ill have the wetmag done and go big!...One more thing I live in the omaha nebraska region.Does anyone know of a reputable machine shop or engine builder?

Thanks again-Jerry

OneBadGMC

Building on what Ed said....

Up until a couple years ago, we were running a .100 over 454 truck block (4-bolt) making 1300 crank HP on a medium blown application. This was with a mildly ported GM990 iron head.

The flow, from my understanding, on the 990 heads would have been maxed out with a blower around 1500 HP.

As Ed stated, the GM parts are severely under rated. Great pieces for the money.

kwkracing

I have ran both, blown alky and gas on stock cast small block cranks, Till this day never had a problem, but i ran a crank support on the end of the snout. I have also ran a cast bbc crank in a injected bbc that made 1320hp in my dragster with no problem yet.