Rod to Stroke Ratio - Team Camaro Tech
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post #1 of 10 (permalink) Old Sep 11th, 03, 03:55 PM Thread Starter
 
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How important is it to consider r/s ratio when building a motor for street/strip duty? I am asking because I am building a big block and I came up with some nice combo's, but when I ran them by a machine shop by my area they informed me the pistons were going to be funky(like wrist pin being near the bottom, or interfearing with the oil ring) and have to have a dome. I was then told that I should be focusing on making more cubic inches instead. My question to you more experienced people on this board is will a r/s of 1.45 to 1.58 be very reliable? Also can anyone give me a BB combo with a good r/s ratio with off the shelf parts? Thanks.
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post #2 of 10 (permalink) Old Sep 11th, 03, 04:21 PM
 
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Isn't a stock 454 right at 1.53 to 1 R/S ratio??

I'm looking at something like 1.389 to 1 IF I do bite on a bigger motor like the 598" standard deck one I am thinking AND mouthing about!!

No where near good enough but I am not going to rpm her so should do fine, imho...

Wrote ROSS about pistons to see if it can be built and they said yes!

Probably will also contact JE b/c they are known for odd-ball stroker pistons like this...

pdq67

PS., go to your closest Barnes and noble and pick up a copy of HR's "How to Build Monster Chevy Big Block's"!! Good reading and these have been built so you know they run!!



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post #3 of 10 (permalink) Old Sep 11th, 03, 04:33 PM
 
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Here's a good article on rod/stroke ratio.

http://victorylibrary.com/mopar/rod-tech-c.htm
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post #4 of 10 (permalink) Old Sep 12th, 03, 01:06 AM Thread Starter
 
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Quote:
Originally posted by Hoptup32:
Here's a good article on rod/stroke ratio.

http://victorylibrary.com/mopar/rod-tech-c.htm
Thanks for the link, although I have read it before. I did some searching on the net and found out that Lunati stocks off the shelf pistons, rods, and crank for the combo I was looking for. Using a tall deck block(10.2").
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post #5 of 10 (permalink) Old Sep 12th, 03, 03:51 AM
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Eric
 
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I have heard that a 1.7:1 r/s is about perfect, but the difference between perfect and a not-so-good 1.5:1 r/s performance wise isn't that big a deal unless you want RPM the snot out of your engine.

The biggest problem with a short r/s ratio is increased piston speed and cylinder side loading. Shortens the life of your cylinder bores and hurts high RPM reliability.

The shorter stroke also increases the rod angularity which, believe it or not, can slightly increase the "effective stroke" of the motor. The shorter rod will also have higher piston acceleration rates which can very slightly increase low speed volumetric efficiency (low end TQ). The downside to higher acceleration rates is ring flutter and some other problems that can occur at higher RPM (like 6000+).

If your engine will stay below 6,000 a poor r/s ratio is not that big a deal - and might actually help power below say 4,000 RPM. However if you really want max power out of this combo and plan to race it a better r/s ratio (like at least 1.5:1) would be a good idea.

Just my opinion.

PS. there's nothing wrong with a high wrist pin locaton to accomodate a longer rod. This typically makes for a much lighter piston/rod assembly which helps your engine rev faster and adds to high RPM reliability. Even if the wrist pin enters the oil ring area there are pistons out there with spacers that overcome this little problem easily.

E85 racer and E85 carb builder

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68 Camaro, E85 powered 427" small block. 9.96 @ 133 MPH, 1.319 sixty foot on motor. 5.92 eighth @ 116 with a 1.42 sixty breaking beams with back tire on the bottle
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post #6 of 10 (permalink) Old Sep 12th, 03, 02:01 PM
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Like many rules of thumb, try to stick to the rule if you can, but in many cases you can't. For example on a 383 stroker, it is impossible to hit the optimum R/S. But you can come darn close by carefully choosing your parts.

-dnult

Dave
========================
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI
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post #7 of 10 (permalink) Old Sep 12th, 03, 08:11 PM
 
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Back again..

I think the all time stock torque champ, (for a 454/455 motor), is the Buick 455 which is right at 1.7 as is the 5.0 Ford and they are good torque motors!

It's something about putting the crank angle at max. intake valve lift suck at the max. acceleration of the piston OR some such really deep thing.. For the intake system size... I.e., carb., intake ports and head runners, valves, etc..

pdq67



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post #8 of 10 (permalink) Old Sep 12th, 03, 08:13 PM
 
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Back aghain,

Eric above has a better handle on this the I do... sorry it's late.. pdq67



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post #9 of 10 (permalink) Old Sep 13th, 03, 08:13 AM
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pdq, you are right. As piston velocity increases you reach a point where it becomes more difficult to feed the cylinder - the air and fuel can't rush in fast enought. Also as the rod angles increase, side wall wear becomes more of an issue.

-dnult

Dave
========================
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI
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post #10 of 10 (permalink) Old Sep 13th, 03, 09:13 AM
 
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Along these lines but off topic is check the spec's out on the Honda S2000 or 2000S engine b/c it is under-squre bore/stroke-wise but produces max. hp at 8,000 or maybe 8,200rpm!!

So a small bore, long stroke motor CAN make great power AND run very high rpm's if the rest of the combination is right on!!!

The old British motors were made like this b/c of, don't know if it is true, they were government regulated as to bore size kinda like the Japanese cars in Japan are regulated to max. width due to parking space problem's!!! Thats why they have soo many little domestic cars that we can't buy here...

pdq67



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