Crankshaft discussion
 

A friend I have lunch with and I got to talking about my engine in my GTO. The last time I went through the shortblock was around 2000. Being on a tight budget I went through my machinist for the rings and bearings. At the time I really needed to bore it but money wasn't there for the machine work and new pistons. Since my stock crankshaft was in good condition and was .020 under on mains and rods I didn't see any sense in changing it.
My friend is a retired mechanic from Cummins and former dirt track racer told me that I'd never build an engine for him because I didn't go the additional money and put a forged steel crankshaft in it. Money I didn't have. Plus he said it didn't make sense to him why anyone would put H-beam rods on a cast or nodular crankshaft.
Yes I had to go a little on the cheap side as my child support at the time took a lot of my money, but after numerous passes at the drag strip and over 160,000 highway miles it still runs decent and doesn't use hardly any oil.
Opinions as to what members think.

Is your friend a Pontiac guy?
(probably a chevy guy?)

Pontiac cranks are really stout and compared to chevy probably better that their forged stuff?

:D

Sounds like a good build if it lasted this long.

:)

I hope your friend was buying lunch for you since he was also insulting you. You did the right thing and backed it up by driving in 160,000 miles. There is no further discussion needed.

"Doesn't use oil" is a key measure of success. Critiquing the parts could be spun to complimenting the parts as the performance result speaks well.

I agree. In my mind a good friend would have complemented you on successfully building a good engine while staying within your budget limitations. Something most all of us have to do everyday. I'd bet most of us have know about unfinished projects that never get past the need to obtain all the perfect parts.

Congratulations on having 160,000 miles of fun with your Poncho! Well done!

160k with track time? Great build, congrats. Keep burning gas and enjoying it

I think it's great you've been able to enjoy your Pontiac for 160,000 miles.


Pontiac Engineering was on point. They increased the main journals on bigger engines for additional strength making their crankshafts plenty strong.

You'll be more than fine.

His dirt car has a Chevy engine but he owns a 70 Judge and 68 Firebird.

The little I could find to read , Pontiac metallurgical Engineering did a good job with the crank makeup. I've never run nitrous. My friend who built , ran dirt track, Pontiacs used the stock cranks,usually 428 never heard of one breaking. The driver one night did try to adjust timing with very bad results to a RA IV head. My street 421,400s saw 6400 back in the early 70s with cast rods. Cranks are still good in garage. Now if you are going full bore maximum effort,then aftermarket block ,the best rods ,and best crank you can buy!

One test is worth a thousand expert opinions.

Eric

There is always somebody who wants you to spend more money. Ask him if he wants to be your sponsor. Not worth the headache.

I have seen Factory Pontiac crankshafts take a lot over the years and keep on going.

Good to hear you have had good service from your engine.

My 400 crank was .020 on the mains and .050" on the rods, as I was running 6.8" rods with BBC rod bearings. Survived 10 years of street/strip duty, the last 3 years on a 120 HP plate nitrous system. Ran into the mid-11s on spray at 110+ MPH.

The crank was fine when it came out 10+ years later. No worries about cast crank strength for me.

I hate to say it, but your friend doesn’t know jack about crankshafts. Some of the absolutely worst forged cranks I ever dealt with in my years as a master engine machinist were Cummins forged cranks; taper and horribly out of stroke. The Cummins forging from Mexico and Brazil were the worst! PMD’s engineers knew what they were doing when they specified nodular iron cranks.

The best thing he could do is change the powerplant in his race car from a SBC to a Pontiac. As someone that has raced and built a good many Pontiacs for dirt cars, I've never used anything other than cast cranks.

FWIW, I, as well as others were very successful running Stratostreak engines with cast cranks on dirt tracks. The reason many stock Pontiacs spun rod bearings when pressed into race car service had nothing to do with the materials the cranks were made from. The RA IV engines had cast cranks, as well as cast rods, but they had rod bearings with an extra .001 more clearance than the basic transportation engines found in all the daily drivers.

After experiencing a ton of spun rod bearings in my dirt track engines, I opened up the bearing clearances and the spun rods stopped. I could run the same bottom end in my race cars for 2-3 seasons before needing attention and freshening, 400s. 428s and 455s were all cast cranks with added bearing clearances. I also quit using Valvoline, oil and switched to Pennzoil racing oil, I feel that also added to the longevity of the bottom ends, YMMV.

When I was racing, and building engines for dirt track cars it was all through the 70s and into the mid 80s, there were no forged cranks to be had during those years even if I had the money to afford one. During that time almost no one racing Pontiacs had access to or could afford a billet, or a forged crank, so we all used what was abundant, cast cranks. We still won races and didn't have to replace engines weekly......LOL

Many engines also used cast reconditioned rods with new aftermarket rod bolts, that's what was available for budget racers like myself. Once you got your recipe ironed out, the Pontiac engines were every bit as reliable as the chevy engines were, and we usually had a cubic inch advantage as well as more torque off of the corners. See my signature pictures for checkered flag winners circle pics for your buddy to figure how i was able to make my Stratostreak powered Pontiacs win often, without forged parts.................:D

In all the Pontiacs I've built driven and raced over decades i only broke one crank, and the problem started out in a thin walled 389 that was bored .060 over causing a cylinder wall to collapse lodging a piston in the water jacket. That sudden stop did manage to break the crankshaft as the rotating mass stopped abruptly, but under the same conditions, a forged crank would likely have broken also.

:2cents:

160k and hardly burns oil.....a success story, good job! The stock Pontiac crank is a pretty good piece!

Nice
First you got every cent out of that engine for sure, congrats.

Some context might be missing but he might be saying he's not taking your engine build today with those parts 26 years older vs 26 years ago and your stockish power level.

So what's your current power level, 350hp/425tq?

One big difference today vs 26 years ago, parts vs inflation were way cheaper then and engines were getting built much faster then due to shop quantity. Many like myself are over building these days due to bigger power #s and insurance on possible issues lossing many seasons of time in machine shop jail IMO.

Seems like I wasted my money on 4340 I beam rods and Ross pistons on my cast crank. It`s been to 6400 rpm`s more than a few times. Mid 2`s for clearance. 103, 455 crank.;)

I ran a 428 N crank for about 15 years ina 421 block. Crank was deburred and all casting lines removed and polished. Shifted at 72000rpm and never had an issue. Just magged it and will be putting it to use in my street car.
Crank prep is key. Good prepped crank of any type better than a so-so crank of any type.

Not saying there isnt a time and place for a forged crank (I have one), but I say they are rarely necessary for even like 500-600 HP street cars.

I cant remember who it was, maybe David Freighburger, but some industry type who has been around a while said in all the engine carnage they had seen they had never in person seen a crank broke. It might have been him, because I think they broke a crank on the boosted 4.3 v6 and said it was the first one he had ever seen.

Morale of the story, not that it never happens, but of all the things that break in an engine, cranks are not a highly occuring point of failure.

I have a high dollar forged crank and a stock replacement type oil pan. If I had to do it over I would 100% reverse those. I would buy a decent cast crank, and spend money on a trick oil pan with better windage/retention.