Thread: chevy 383

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Originally Posted by nitrowarrior

I just got off of a website for Stahl Headers that a member here recommended. Needless to say, i have never seen such an atroscity of misnommers and false information.

I'm not into starting a 'fued' but in the handful of times I have met Jere Stahl, I am all ears. The man has a decades of experience and knows what he is doing. I have a set of his headers, in the past used his special grind camshafts and used the Dyno data collection software he designed.

I'ts not their headers I'm concerned about. I'ts their misinformation on crankshaft geomtry and piston loading info they are trying to convince the public with. For one, they've got themselves convinced (whom ever is doing there research) That a piston can change speeds during it's dwell travels in one cycle. WWHHHATTT???? I don't like the people trying to dig in and find info on how things work being misled. I know what principle the person on Stahl's site was using and he is under the impression that the axis (crank centerline) is in movement; when it is a stationary axis. So on and so forth. I have had the wonderful opportunity to teach auto mechanics for a community college and these are the things we must set as basics for the class so the students understand principle and working theories. I have NO malice toward Jere Stahl nor have I ever met him. I don't like the info being put out by his site. That's all.

Originally Posted by nitrowarrior

I'ts not their headers I'm concerned about. I'ts their misinformation on crankshaft geomtry and piston loading info they are trying to convince the public with. For one, they've got themselves convinced (whom ever is doing there research) That a piston can change speeds during it's dwell travels in one cycle. WWHHHATTT???? I don't like the people trying to dig in and find info on how things work being misled. I know what principle the person on Stahl's site was using and he is under the impression that the axis (crank centerline) is in movement; when it is a stationary axis. So on and so forth. I have had the wonderful opportunity to teach auto mechanics for a community college and these are the things we must set as basics for the class so the students understand principle and working theories. I have NO malice toward Jere Stahl nor have I ever met him. I don't like the info being put out by his site. That's all.

If you want to talk "piston loading" you need to talk to one of my customers who use to run a 5.565 rod in a 406.
Yes,everyone I still build 400's if thats what the guy wants and yes I tell them why I don't like them.
He now is running a 6.0 inch rod.
Guess what?
He now is getting better more life out of his pistons and rings and make more hp do to the better "rod ratio".
In other words his rings seal better or is due to the piston "dwelling" more at TDC being able to have a little more time to lite off the fuel and air mixture?
We have also found hp by going to a longer rod in a BBC on a 496 that uses a 300 shot of N20.
I will agree that most of the street type cars will not see any hp gains from a longer rod.
I still like to use the longest possible rod I can shove into the engine.
Of course the are some exceptions where a blown engine or a nitrous asisted engine demands that you drop the top ring down.
I don't write articles.
I work with racers everyday to find out what works and what does not.
My testing is on the track and in the dyno.

Well said Erik. Sometimes good 'ol track tuning will achieve the results we all want. It's great to work it out on paper, but the results are on the pavement.

When Smokey Yunick was promoting offset cranks, it seem to be the "rage". As I grew with the hobby and found that changing firing order around to match rod throws was a better way to achieve what the "pro's" were trying. I started grinding cranks when I was a kid and didn't understand the reason for some of this stuff. I have found though, a lot of off sets can create a "flat" style crank when it's running under it given conditions. Dirt track mostly. I have now gone back to running on index with the grind. And that's tougher than it seems because of a seasoned crank being "twisted" during it's life. Especially for the customer's engines, I keep it "square" and use the rest of the geometry to do the job I selected the parts for. By the way, were you referring your question to me? I always jump in where I'm not needed.

Number 1 as base followed by the opposite cylinder to double check. Yes cranks are going to twist under application. Is this why you asked? Because of the torsional stress, I always promote going with a crank material that has good memory. Even a cast crank with a good value can be "naturalized" to be as good if not better than a forged crank. The "flat" crank I was talking about had characteristics of finding a single RPM band that was the most effective and not give the driver a full range to work it.

Every crankshaft has an equal and opposite throw (piston up and down at the same exact sequence). The exception being 5 cylinders, Kabota 3 cyl etc. If all else fails, especially for the customer, I double check the opposite cylinder for travel and ignition timing. It helps with cam grinds that may be off a bit and helps find a mismatch in piston travel. Balancing is balancing, but geometry never changes. I may have a customers crank he supplied and is chomping at the bit to complete. I double check to make sure I'm not creating a sequence of events that will not make the system evenly pull through the cycle of where he/she run's it. Off sets in pistons are still available from all manufacturers I deal with. (wrist pin off sets) They can help with piston loads during the power band which you are building for. I rarely, and I mean rarely run them though. Old school builders used to order them and put them in opposite holes. Great on mid range power but hellish on wear. How did they know when it was done and over with? The engine rattled like a flat head model A with all the rod bearings knocking.

Now that I've put you all to sleep.....WAKE UP!!!!.....LOL

Originally Posted by DennyW

Have you ever tried an offset crank, and longer rods ?

Yes,we did in about 85 when we played with 400 cranks.
Broke a couple of them.
Longer rods???
No just different pistons.

My apologies to all that read these forums. My brain putters around in Granny gear for way too long and I forget to step on the clutch and "shift" the darn thing. Denny, were you referring to the off set for stroke on the crank or off set for torsional lead in. I wasn't even thinking of stroking it for a gain of 1/16 or 1/8th on the rod throw. My apologies once again. I have finally gotten into third gear and maybe after a good steak dinner, I will be in high gear. If the question was; off set grinding for an increase in stroke, yes but it's so hard to find cranks that will index and have enough material for the off set. Last one I did went for a 3 and 9/16 stroke from a std 3.48. Hardly worth the labor though. The Chevy II it powered was not seeing a bit of improvement on the elapsed or 60 ft or 110 ft times. I would love to tell you different but in the few I have had requests for, it just wasn't worth it. Maybe some out there can share what they have gained.