hexane

I have the opportunity to upgrade to 6" rods + the correct pistons for a very good price vs. using the stock style 5.7" rods. I know that using the 6" rods will increase the r/s ratio of this motor which will put less load on the sidewall and also increase the amount of time the piston dwells at TDC for a better burn and theoretically more power with less chances of detonation or spark knock. Now I am worried that the use of 6" rods will cause the wrist pin to be uncomfortably close to the oil ring land. So would this cause the motor to consume a lot more oil that it would on a setup that doesn't almost interfere with the oil ring land?

CFI-EFI

I think with a 3.75" stroke and for the same money, I would opt for the 6" rods. There will be no noticeable difference in performance. If there is ANY extra expense involved, I'd stick with the 5.7" rods.

RACE ON!!!

vader86

I dont see any reason to pick one over the other really, since there'll be no noticable difference on a street-driven engine. Just go with whatever works for your budget best.

cv67

with both. Just build and enjoy it, the rest is splitting hairs.

thirdtimevetteowner

[I have the opportunity to upgrade to 6" rods + the correct pistons for a very good price vs. using the stock style 5.7" rods.]

hoobly,
If the above statement is true, why the worry about the distance from the wrist pin to the oil ring land? Is that information from the manufacturer(s) of the rods and pistons? If so, I don't see any need to worry. Just my opinion.

Rich K

Bad Karma

I would go with the 6" rod, especially if you haven't built or baught anything yet.

Deakins

I would run the 6 inch rod. Just my .02

hexane

Would the 6" rods on the stroker extend the ability of the motor to rev higher? How would the torque production be affected? Would there be any other beneficial effects, other than the improved rod ratio? Would one, theoretically, be able to run a higher static compression without any fear of detonation, as long as it is within reason from the limits of pump gas?

Curveit

Folks run 4" cranks with 6" rods ( and longer). Pistons aren't going to be a problem. As for revving higher? I don't think so. A 5.7 rod will actually make 2-5 FtLbs more TQ up until around 45-5000 then the 6" takes over. Not enough to be concerned with. Higher compression/detonation? A little better with the 6", not much. Keep in mind we're only talking .30" difference in rod length here. I'd use the 6" for the increased ring and cylinder life.

Deakins

Without a tall deck block you really will not see a 4" stroke paired up with anything longer than a 6" rod. When you start getting the compression height below 1", you will have some durability problems. A lot of our circle track guys report back with better top end power when they go up to a longer rod but like already stated above, they don't get off the corner as well. Since HP is what almost everyone is after we go longer; add to that the fact that components last longer and it's a win win.

hexane

If I saw a setup utilizing a 4" crank with 5.7" rods, I would be quite concerned about the longevity of the motor itself. It would be a mystery if one would be able to use a standard base circle cam with that long of a stroke. I would think a mega stroke crank would cause the rods to hit the cam, and that grinding the rod bolts down would be the alternative to using a small base circle cam. I would guess that motor would less likely be able to survive a high rpm run for long. Combined with a long stroke, that would be quite a bit of cylinder side wall loading. Anyone build a motor with a "lower than optimal "rod ratio? The obvious question is, how is higher rpm capability and longevity in general? I'm not gonna pop a rod through the block at higher rpms with that bad of a rod ratio, am I?

Say I wanted to go the extra mile and build a nice 396 to last me a couple of years as a daily driver. Is a tall deck block mandatory for strokes 3.875" or longer in order to use longer rods?

From what I hear using some "old school information" out there, I definitely see it is possible to build a 383 out of a 350 using 5.56" rods with 0 clearancing. Sounds simple, but would the rod/stroke ratio be suboptimal for higher rpm operation?

cv67

For higher rpm use Id use a longer rod if given the opportunity. Remember that the longer the stroke the higher the piston speed..

Chevy guys have it made compared to the Ford SB guys as far as deck height and rod length selection.

Fwiw the 396 sounds like a fun street motor: if you are really going to lean on a stroker meaning twist the rpm way up there dont cheap out with crappy parts/machining or youll be sweeping them up into a pail.

rodj

http://www.iskycams.com/techtips.php#2005

Deakins

Well if you do the calculus on all the forces at work on the rotating assembly (not for the feint of heart) you will always find that some of the forces at work increase with a shorter connecting rod; how much depends on the situation. I have seen countless dirt track cars on a budget use a standard 400 block to get to the 434 mark. They will use the small cam but a lot of the clearance issue depends on the connecting rod used. For an example; a good sprint car engine that is a 400 block, will run a 3.85' crank, and have a rod that's around 6.125" long. The block will usually be around .250 tall allowing more meat in the compression height. Sure we could fit a longer rod in there but you have to make sure and finish the race to win it so it's really an optimization problem. Now your application is a street car; it's not going to have 16.1+ compression, run to over 9000+RPM, and have the timing maxed out so I don't think piston issues will be as much of a concern to you. So are tall deck blocks great; yep! Are they a total pain in butt to get intakes to fit up on; yep! Not to mention they are all pretty pricey.... I have an aluminum Rodeck that we ran in an outlaw engine for sale but we need to get 2500$ out of it. Not many guys building that serious of an engine these days... So my advice is to build as big as you can/want on your budget and buy the best connecting rods and rings you can get on that budget. If you can pick up a set of Carrillos or LAEs that a cup shop didn’t use that would be the cheapest way to get into a really good rod for a reasonable amount of money. It's just tough to find them new and of the right size since most serious engines are not built with large journals anymore and many of them are set up piston guided to boot. You may be a little tougher on rings but if you are pushing the engine hard you will want to tear it down to R&R the springs, bearings, stuff like that anyway so you can check your ring pack out with the rest of it. Sorry for the long post; It's slow this time of year!!

Jonnymac

Good info

ztrips

I would be more concerned about the rod type than length. Are we comparing H beam to H beam?