Since interesting tech discussions always generate interest, I want to start something here (rather than there) to allow information to get collected and benefit all.

Over the years of building all kinds of race and performance engines and evaluating many engine combinations for Stock/SS competition, I have come to a conclusion that crankshaft (assmelby) weight, bearing size and intertial properties play a bigger role in potential than is commonly given credit. I have some evidence to back this up. What do you know? (If this topic intrigues you, then I have another I will throw out in the future.)

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Dwight
A discussion like this is exactly what we need on this site .
I hear a lot about using the Honda rod pin on Super Stock motor's . I have alway's been afraid to try this . 10 or 15 year's ago I used to fly cut valve relief's , clip dome's , and cut piston deck's for a fairly well known Spint Car engine builder and spent alot of time talking with him . He alway's said that turning the rod journal down to build a 383 was a bad idea because it weakened the crankshaft . When you turned the rod journal down you lost the over lap between the rod and main journal . He said that the reason Chevy went to the 2.100 rod journal when they came out with the 350 was to strenghten the crankshaft after they went to the 3.480 stroke . Apparently he was wrong because alot of people are doing it and getting by with it . If I remember correctly a cast crank is already 3 or 4 lb's lighter than a forged crank . I think most people are using a cast crank already to save reciprocating weight .
How far can you go without losing durability ? It make's sense that going to the smaller rod pin you will slow down your bearing speed and lose some friction . I think this year you can use a rod that has the smaller bearing size and you don't have to use the bearing spacer like you did in the past , I would think that would be a plus . I have alway's been afraid to try the smaller rod pin because I race on a budget and can't afford to blow alot of stuff up .
Al Kuehl

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I heard from somebody (can't remember who to give credit or laugh too) that NASCAR teams determined every .100" of rod journal reduction was worth 10 HP.
If that's believable, then I would be interested to know what every .100" reduction to the main journal is worth and more specifically, combining the two machining operations.
And I only recently learned that a 401 AMC crank is about 6-8 pounds lighter than a 390 crank (stock OEM weight). I have always used a 390 crank and a 401 crank can easily be de-stroked to a legal 390 stroke.

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Jeff
I am glad that sombody finally joined in on this discussion . It make's sense that there would be some horse power there . I would just like to know about any durability issue's . I already use a cast crank because it is lighter than a forged crank . I would like to now where to draw the line before you start breaking stuff . If the Nascar guy's can run 500 mile's at 9,000 rpm they don't seem to have a lot of durability problem's , but they are running the best part's that money can buy .
Al

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Al -
Some practical things to keep in mind from the NASCAR experience: 1) They run different combos in qualifying than in the actual race, even though rules are there to prevent 'grenades' in qualifying. I know they used to run Honda (1.88") or Toyota (1.71") rod journals in qualifying engines and standard SBC (2.1") in race engines. While they are not supposed to be doing that now, maybe they had stepped into the range of the limitation of durability that we should pay attention to. 2) Big NASCAR teams (read: "fast") think nothing of throwing the internals of engines away after one 500 mile race. If you have the time, resources and energy to x-ray, MagnaFlux or other test the critical parts in your engine and then throw them away after short use, then you can probably push things a lot more than most people do. 3) Can you spend $2100 for a crankshaft or $1800 for a set of rods that will be used for two races? They do.

Here's another way of addressing my original question. In Stock Eliminator, if an Olds 350 and a Chevy 350 have the same HP factor, and all the normally considered factors are the same (i.e., camshaft lift, carb size, head flow, intake flow), what do you think would make the difference in power output?

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I don't think it's possible to compare two brands and play "lets assume" as there is always more to the story. Peak flow may be identical but the path to peak flow may be completely different. Deck heights, bore spacings, lifter diameter, valve shrouding, to name just a few will come into play.
Although I have never dealt with something like smaller cranks, I would think the only way to compare is to use the same engine and do nothing but reduce the journal diameters and throw it back on the dyno. Same bearings if possibly; only the addition of bearing spacers.
I really can't believe that test hasn't been made. At least with somebody going public with it anyways. That in itself tells me it's worth some power!

__________________
NHRA #7494 SS/H
1970 AMC AMX 390
Arizona's BEST Realtor since '93 and I supports racers!
Have property in AZ? Then call me @ 602-418-9797 or JeffLeeAzRealty@gmail.com

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Is the biggest difference in the frictional losses from the journal diameters or is it the lighter weight particularly on the rod journals that would be responsable for these power gains? And if I might,has anyone had any experience with those media-polished (for lack of a better name the ones that look chrome plated and promise 10-15 HP gains)crankshafts? I have a shop near me that has one of those vibratory polishers and they have already done a ring and pinion.

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The power would be in the decrease in frictional losses. If you note NHRA's crank rules (once published, is it still published?), they were very specific about no "chrome" look as you described, else it look like a billet part. That begs the question of how much HP on coated crank / rods?

__________________
NHRA #7494 SS/H
1970 AMC AMX 390
Arizona's BEST Realtor since '93 and I supports racers!
Have property in AZ? Then call me @ 602-418-9797 or JeffLeeAzRealty@gmail.com

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[Dwight
The reciprocating weight would be a big part of the differance between the Old's and the Chevy . You are right the average Stock or Super Stock Drag Racer can not come close to being able to afford the thing's the Nascar team's can . At one time I weighed a forged 350 chevy crank and a cast 350 crank and if I remember correctly I think the cast crank was 3 or 4 lb's lighter . If I tried anything I have thought about going down to the 2 inch rod pin like the pre 68 327 's had if what Jeff said in his post was true that would be an easy 10 H.P. . I just can't afford to get to crazy and start breaking stuff if I ever do get my car going again . When you started this thread I thought this was a really good chance to learn somthing . I have read many of your post's on this site and the other site and I have alway's thought they were knowledgeable .
Al
QUOTE]Originally posted by Dwight Southerland
Al -
Some practical things to keep in mind from the NASCAR experience: 1) They run different combos in qualifying than in the actual race, even though rules are there to prevent 'grenades' in qualifying. I know they used to run Honda (1.88") or Toyota (1.71") rod journals in qualifying engines and standard SBC (2.1") in race engines. While they are not supposed to be doing that now, maybe they had stepped into the range of the limitation of durability that we should pay attention to. 2) Big NASCAR teams (read: "fast") think nothing of throwing the internals of engines away after one 500 mile race. If you have the time, resources and energy to x-ray, MagnaFlux or other test the critical parts in your engine and then throw them away after short use, then you can probably push things a lot more than most people do. 3) Can you spend $2100 for a crankshaft or $1800 for a set of rods that will be used for two races? They do.

Here's another way of addressing my original question. In Stock Eliminator, if an Olds 350 and a Chevy 350 have the same HP factor, and all the normally considered factors are the same (i.e., camshaft lift, carb size, head flow, intake flow), what do you think would make the difference in power output? [/QUOTE]

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Here are some other factors that may be considered. My disclaimer is that I am not saying these factors have any influence. I am looking for some concrete experience that may be evidence to place some value on the factors.
1) Intake runner length
2) Rod length
3) Crankcase volume as it relates to windage
4) Lifter diameter
5) Lifter bore angle related to cylinder
6) Valve stem diameter/weight
7) Included valve angles (assumes that we are comparing true wedge engines or canted valve engines)
8) Position of port opening relative to the cylinder
9) Crankshaft moment of inertia factor
10) Internal/external balance

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About 5 year's ago there was a local Big Block Chevy Stocker racer that all of a sudden picked up abouit 2 tenth's and was running with the faster guy's from our area . I was told that he admitted to a couple of people that he had built an engine with 6.125 long small block rod's instead of the 6.135 big block rod's and a 55 MM cam . After he blew that motor up and went back to his old stuff he is back running about the same as he was before he built that motor . I would like to add that as far as I know this is a guy that has never won a Divisional race or a National event and that he build's his own engine's . Alot of the people from my area know who I am talking about .
Al

Last edited by Al Kuehl on 07-03-2010 at 01:13 AM

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There was a tear down @ Indy this year? It was due to somebody that has been screaming really loud about the 55mm cam his (faster) competitor had; i.e., it was the sole reason he couldn't keep up with this guy.
The cam was pulled and much to the competitors dismay...it was stock BBC size!

__________________
NHRA #7494 SS/H
1970 AMC AMX 390
Arizona's BEST Realtor since '93 and I supports racers!
Have property in AZ? Then call me @ 602-418-9797 or JeffLeeAzRealty@gmail.com

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Jeff
I agree about the 55MM cam . I have not talked to anybody that has picked up much if anything on the race track with the big cam . The guy that did the cam and rod thing did tell some people that it helped a bunch on the rocker arm breakage problem that the big block chevy's have . I was talking more about the rod's . I checked today the small block rod journal is only .100 smaller than a big block , I thought it would be more and in the catalog's I looked at most of the small block rod's were about 100 gram's lighter than a big block rod . It seemed to me that the guy that did this picked his car up a good solid 2 tenth's he went from running in the 10.50's in good air to running some 10.30's if I remember correctly .
Al

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quote:

---

Originally posted by Jeff Lee
There was a tear down @ Indy this year? It was due to somebody that has been screaming really loud about the 55mm cam his (faster) competitor had; i.e., it was the sole reason he couldn't keep up with this guy.
The cam was pulled and much to the competitors dismay...it was stock BBC size!

---

__________________
NHRA #7494 SS/H
1970 AMC AMX 390
Arizona's BEST Realtor since '93 and I supports racers!
Have property in AZ? Then call me @ 602-418-9797 or JeffLeeAzRealty@gmail.com

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