Ok, well thought I don't care for the "Tuner" scene and the Fast and Furious stuff I believe that if you don't learn from every aspect your not mastering your art. So recently I've been reading various information from the "Tuner" world. These guys know there stuff I'll say that, they seem to indulge more into engine techniques and building than the V8 guys tend to go into. I've never seen this kinda information in the small block world.
This is the information:
"A commonly known, but often forgotten fact is that the internal geometry of an engine can affect the engine's power delivery. Bore size, stroke and rod length all have a profound effect on an engine's power-delivery characteristics. An area of tuning just now being exploited by import engine builders is altering of the rod length to stroke ratio. The bigger the stroke-to-rod-length ratio (commonly referred to as the "rod ratio"), the more dwell time the piston has around TDC. This accomplishes several things. Since the piston is near TDC longer, the combustion event has a longer time to impinge upon the piston, allowing a better transfer of force to the piston, which slightly improves the engine's thermal efficiency. The longer dwell time also gives more time to fill the cylinders at bottom dead center on the intake stroke and more time to scavenge the cylinder during overlap. Since the piston is accelerated more gradually away from TDC, there is less mechanical stress on the crank, rods, pistons and cylinder walls. Reduced rod angularity at the point of highest cylinder pressure, also reduces mechanical stress, as the piston has less side load, and therefore rubs on the side of the bore less...Higher rod ratios result in less velocity in the intake ports; there is a lower demand for the ports to flow as well, as there is more time available to fill and scavenge the cylinder. Conversely, this can also mean stagnant flow at low rpm, which is not good for low-end power production, either...The bore-to-stroke ratio of an engine can also affect the engine's power characteristics. Over-square engines, ones that have a bigger bore than stroke, have lower piston speeds and less internal stress at high rpm due to lower inertial loads. There is also more time to fill the cylinders because of the lower piston speed. Engines with longer strokes and smaller bores, called under-square, have more internal stress due to faster piston acceleration and higher piston speeds. This accelerates wear and can induce seal-killing ring flutter...Under-square engines have higher torque and low-end power producing intake port velocities to ensure more complete cylinder filling at low rpm. Many import engines, most notably Hondas, are under-square. High-performance motorcycles (with a few notable exceptions like the torquey Supertwin racing class bikes) and purpose-built racing engines like the ones found in Indy and F-1 are over-square to improve cylinder filling at high rpm and reduce piston speed."
- Mike Kojima http://www.sportcompactcarweb.com/tech/ ... index.html

So, the Doc your a genious let's just get that out there. However, the 198 has the highest rod ratio. So, wouldn't make more sense to go with the shorter stroke with these nice new rods being made? Next the 170 is still better yet (than the 225), so does that necessarily make it the race engine of the group? If you boost any of the stock engines or "long rod" what would be the best combo with the information given above? Last I hope this was helpful even if it was a lot of info. Wes

The "tuner" crowd are working with engines that only produce torque when you rev the snot out of them. Trying to apply theory from that end of the spectrum to an engine that's at the other end of the spectrum (low-end torque monster) won't get you much of anywhere useful.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

huh? I believe and actually know this information applies to all engines. In fact the very first I heard about it was the stroker my uncle first wanted to build was better cause of the shorter stroke to longer rod. I wanted to bring this information cause it is applicable to us.

The best thing to remember about rod ratio is this,

The perfect lenth rod is one that connects the perfect piston to you crank.



Jess

Have you looked at the Articles section?

There's info about using the 198 Crank in the 170 and some of the other 170 build info.

Cruise in there and spend a bit of time perusng Doc's builds.

CJ

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Part of Tyrde-Browne Racing

All this chatter about piston velocity, and stroke dose apply to V8's. How ever, the engine compartment size dictates how much power can be dumped into a little itty-bitty tuner car, with their little itty-bitty displacement engines, and littl itty-bitty front wheels.

The V8 crowd learned a long time ago that there is no substitution for cubic inches, and the rides most of us have, one can stuff a lot of low revving, torque belching, iron in'em.

It is tourque that moves the car, horse power is a just measure of how fast that torque gets delivered to the rear, yes rear wheels.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

I've got $500 that says I can build you a 7" rod 240" and a 6.7" rod 240 motor and you will see negligible horsepower difference on a dyno, and no ET difference at the track. Everything but the rod/piston combination would be equal. Same head, cam, and compression.

Rod ratio is one thing that really looks good on paper, but you can ask 100 engine builders what is better and you'll get 50 say long rod and 50 say short rod.

Long rod decreases internal friction but overleverages the motor so it reduces low end torque.

Short rod increases friction but rapid piston acceleration promotes better cylider filling.

Potato-potahto, tomato-tomahto.

A few years ago there was an extensive series in National Dragster with David Reher of Reher-Morrison Racing Engines. He listed about 50 things about rods and rod ratios and at the end gave the only thing he believed to be important.

Make sure the rod bolts are torqued when you seal the engine up.

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Official Cookie and Mater Tormentor.

I would have to chime in with the fact that this is not at all a new discovery. The "in crowd" in probably every engine circle has known this at least since the late 60s. Before that I'm sure it was well known among engineers, but not common knowledge to the hobbiest.

Back in 82 I opted to replace the 350 in my slalom Camaro with a purpose built 327, for the very reasons pertaining to stroke, rod ratio and how they affect the power band. I thought about using a 302 but wanted the balance of power and torque I could get with the 327. It's easy when the factory has already made the combos.

At some point the torque and horsepower curves start to almost match. The short stroke engine with a good head will make big horsepower. But as Dan pointed out, not much low end.

Whatever the application it is important to be in the operating range of the engine. For a street car this normally means some sort of idle and bottom end power.

As far as the slant goes, the long rod Combo That Doug Dutra outlines really looks like the way to go for a 225. The results speak for themselves.

When we got our Swinger and I looked up the engine specs I was almost shocked. It looks to me like the factory wanted a small engine that felt like a big one right off idle. The geometry of a 225 really looks to be targeted at a max rpm of about 3500. These engines are not at all designed for high rpm power.

No matter what engine you are dealing with, it has to breath to make power. That is really the first place to start. If all that is in the works and there is money for it, then I would start getting some longer rods and the biggest bore possible. In most v8 engines I would not even bother getting concerned about the rod ratio in a street car unless it is an all out effort. You can almost always just choose a factory combo that will work, and I don't think any of them are as bad as the 225.

One thing I have confirmed from all the different engine combos I have built... you get more power from more displacement. (Duh)

Stroke and rod ratio does have an influence but it is way harder to "feel" and quantify compared to adding 55 cubes to the engine. (170 to a 225)

I agree with Zilla that the longer rod 225 will make about the same power as the short rod version, all else equal, but things are not always equal.
With a long rod 225, I can get higher compression with-out wacking a bunch off the head and block... and have a lighter piston that uses thinner rings, with-out the expense of custom made units.

On the downside, that short & light piston is less stable in the bore, but the better rod ratio helps it out.

I would love to try even longer con rods in a SL6 but knowing what I know, I will not spend $1000.00 on a set of 7.300 rods to pick-up 5 H.P. (may-be)

My current thinking... take a bunch of rotating / reciprocating weight out of the engine to change it's "personality"... see the "Buster" thread for more info.
DD

What does "overleverages" mean?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

All good info and all good opinions. Thanks to Anothersix as the 302-327-350 family is really a perfect example of what I was originally talking about. I think we can agree by adding stroke will shift your "power" from torque to horsepower. I've waffled on what was more important torque or horsepower, but once the physics courses came through I begin to realise how intertwined they are and how "power" can truly be measured. I've been thinking about boosting for a long time now, but realised it was more important to build the engine around the turbo, not putting a turbo on an engine. So in light of this I've been at a constant battle over the 170 revs to the 225 torque. The little things though are what I would argue make or break an engine. So in light of this I would have to say the 225 will offer more as a whole, but the stroke of the 198 seems to be the winner from what I've read. So this would lean towards either stroking the 170 or destroking the 225, darn both options are just so cheap. Thanks for all input and keep it coming.

Actually,

Long stroke produces torque at expense of RPM.

Short stroke allows HP (therefore high rpms) at expense of torque.

Have to balance this two.

Cheers, Wizard

Whatever you choose keep in mind that the engines power curve is always plotted against time in the real world.

In a drag car you need the gears and the right torque converter to rev into the power band off the line, on a road racer you need close enough gears to stay in the band coming off the slowest turns. On a street car you usually have to spend more time at lower rpms, and have wider gearing. It almost always means needing more low end.

High rpm engines really need everything else set up right for them to work. If not the engine with less horsepower but more torque will be gone before they even get started.

High peak numbers at high rpm don't get it if the engine only spends a very small percentage of it's time there, but took a long time climbing to that rpm.

In the end, you cannot put too long of a rod into a 225 anyway, it just won't fit. What I would really like is a block with a much larger bore!

If I remember correctly, Hot Rod did just such a test as Dennis suggested. Same displacement, different bore/stroke/rod length.

Pretty sure they showed little or no difference.

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'15 Chrysler 200S V6
'74 Duster 360, factory 4 speed car

Do not be so ignorant. Forced induction easily replaces displacement.

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1969-1/2 Dodge Super Bee A12 (440 Six Pack, 4-spd, Dana 60)
1974 Plymouth Duster 360 (4-spd, 8.75")
1973 Plymouth Duster (225, auto, 8.25")
2001 Dodge Ram 1500 QC 2wd (5.9L, auto, Dana 60)