Rod length/stroke ratio....educate me please:
 

I probably stated the wrong type of ratio, so first off: What is the ratio that is used to determine when stroke length is getting too high?

Just thinking about future big-inch options, and looking hard at an iron block setup.

I'll probably stick to 4.030 bore for durability, but not sure what to do about stroke. I want the max amount of cubes, so I'm interested in opinions on how much stroke is too much, and what kind of pros and cons result.

4" stroke = 408 cubes

4.125" stroke = 421 cubes

what about bigger???

4.25" stroke = 434 cubes

I will continue to run a heavy 6-speed car, and I won't rule out nitrous.

What do you guys think???

Re: Rod length/stroke ratio....educate me please:
 

I think that would be AWESOME!! What block are you thinking about using..?

Re: Rod length/stroke ratio....educate me please:
 

I'm looking at both types, but will probably go with an iron block due to limited funding. <img border="0" alt="[whiner]" title="" src="graemlins/gr_cry.gif" />

Re: Rod length/stroke ratio....educate me please:
 

That's what I would go with. The steel.. I am poor as well.. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

Re: Rod length/stroke ratio....educate me please:
 

I am building a 422 with a 4.125 stroke crank. I bought my pistons and rods off the classifieds and they are 6.2" Pro Billet. How do you figure this ratio and is this a good combo?

Re: Rod length/stroke ratio....educate me please:
 

Rod ratio is figured out like this:

rod length divided by your stroke.

6.098 / 3.622 = 1.68 rod ratio for a stock LS1. Generally most engines like to be within the 1.6 to 1.8 ratio range. Some of your big stroke smalll block engines will be around 1.5. This is due to the large stroke and not enough deck height to put in a longer connecting rod. Most of the time when building engines you wil want to stick in the longest rod that you can. There are other factors that effect this though.

Thanks,
Chris

Re: Rod length/stroke ratio....educate me please:
 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by DIAMOND:
<strong> Most of the time when building engines you wil want to stick in the longest rod that you can.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">So is a 6.2" rod about the limit for the LS1 deck height of 9.240"?

Re: Rod length/stroke ratio....educate me please:
 

Pretty close to it.

Re: Rod length/stroke ratio....educate me please:
 

DIAMOND

So, it looks like a 4.125 stroke is a little beyond the 1.5 minimum ratio, assuming a rod length in the neighborhood of 6.125".

What are the limitations on pin placement? And how is that measured?

I'm assuming you would be recommending your street/strip SBC piston?

Re: Rod length/stroke ratio....educate me please:
 

ScottyG - Our SBC street/strip piston will not work in a LS1. Due to the fact that the valve angle is not the same. We do have a full line of LS1 specific pistons. I just posted the complete line, so if you want you can go and check them out in that post. As for pin placement, it is commonly known as compression distance or compression height. (C/D or C/H) C/D is the height from the center of the pin bore to the deck of the piston. Which would be the top of the piston if it were a flat top. The C/D is dtermined by rod length and stroke, also deck height. So the longer rod and bigger stroke that you have the shorter the C/D will become. You can get C/D pretty small, like under a inch if need be. How small you can go is dependent upon the ring stack up that you have for your enigne. The smaller the ring stack the smaller the C/D can be. The C/D is measured by taking deck height - rod length - half of your stroke = C/D.

Thanks,
Chris

Re: Rod length/stroke ratio....educate me please:
 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by ScottyG:
<strong>DIAMOND

So, it looks like a 4.125 stroke is a little beyond the 1.5 minimum ratio, assuming a rod length in the neighborhood of 6.125".
</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Like someone mentioned above, what about using a 6.2" rod on a 4.125 stroke? This just barely clears the 1.5 rod ratio. What are the cons to cutting the ratio this close?

4.03 bore X 4.125 stroke = 421 <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
4.06 bore X 4.125 stroke = 427 <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

Mike

Re: Rod length/stroke ratio....educate me please:
 

The cons to a low ratio are that the transmission angle of the rod to the bore centerline becomes larger and you get increased side loading on the piston which would increase engine wear.

Danny

Re: Rod length/stroke ratio....educate me please:
 

Chris:

6.2rod/4.125 stroke = 1.503 ratio

9.240 deck height - 6.2rod - 1/2(4.125) = 0.9775 CD

Can a 4.03 or 4.06 piston be made with a 0.9775 CD?

Re: Rod length/stroke ratio....educate me please:
 

ScottyG - Yes, we can make a piston with that C/D. No problem.

Danny K - Nicely stated on the cons of a low rod ratio.

Re: Rod length/stroke ratio....educate me please:
 

What you are saying is correct but the increase in side loading with a 4.125 rod is marginal IMO compared to the benefits of increased cubes. I think you could have a 4.125 stroke, 6.2x rod motor live a LONG time and still be able to rev over 7K rpm no problem.
Cheers,
Chris
ps- If I were building an iron block I would go 4.125 with a .030 overbore.

<small>[ October 24, 2002, 07:40 AM: Message edited by: Chris ARE 360 ]</small>

Ratio
 

An old thread but I just joined this site and had to throw in my 2 cents. I read somewhere a long time ago that 1.8 to 1 was the optimal ratio. The Civic Type R B16b at 1.85 is the closet thing I have noticed. The LS based 4.8L engine has a 1.92 to 1 which is the highest I know of and I had one in a truck, it was smooth.

1.7:1 is said to be ideal by many engine builders. Piston dwell time abdc and tdc, rod angle at BDC. There is a lot of theory on this subject, long stroke and short rod ratio lends itself to good low end torque but it has minor negatives too. Nascar cup motors...large bore, short stroke, long rod , light short piston, 9000 rpm for 500 miles, 2.3hp per c.i. can't go wrong either way

Are you guys considering piston speed and the weight of long rod to match the optimum RPM range vs. HP? Before you waste any money learning you might want to check out Performance Trends Web site and you can dyno test your engine specs as well as setting up 4 link bolt hole location for correct Height of Center-Gravity, %Anti-Squat, Instant-Center and Pinion Yoke Angle and Driveshafts Angle. Free use of their professional software for one month. Eliminates the pros and cons of what works best each application. Your Welcome!

R/l f-1
 

Hi Kevin, YES I have EAP PRO with use for twenty + years, Ask Kevin at PT.

ENGINE BUILDERS "64" ? You may state engine "assemblers" = OK

I work with engine manufacturers some such as in F-1 with a R/L in the 1.32-1.35 range.

These engines operate at 22K RPM !

My favorite, a LS-482, is a RHS block combined with a 4.125" Bore & 4.5" stroke.
The 6.350" fitted rod has a 1.356 R/L

Lance

Could just go 1.000" piston height, let it sit .0225" out of the hole
And use a .060" Cometic head gasket to set the quench.
You'll most likely want a small journsl (2.00" rods) crank to make
Clearance easier in the oil pan rail area.