6" rods in a 2.8-what piston specs are needed?

[no_doz]

im not saying that im going to do this im just learning more about rod to stroke ratio & id like to know if 6" rods could be used in a 2.8 HO motor (88+ s10 id say), with 3100 or 3400 heads/intake-and if so what piston specifications would be needed/what CR would it result in/how would i go about calculating this next time so i wont have to ask & can just do it myself.

also is the deck height clearance above or below the deck-like .026 is that .026 above the deck surface or below? im just not sure which perspective its from.

any help is greatly appreciated!! thanks guys

[Smittro]

im not saying that im going to do this im just learning more about rod to stroke ratio & id like to know if 6" rods could be used in a 2.8 HO motor (88+ s10 id say), with 3100 or 3400 heads/intake-and if so what piston specifications would be needed/what CR would it result in/how would i go about calculating this next time so i wont have to ask & can just do it myself.

also is the deck height clearance above or below the deck-like .026 is that .026 above the deck surface or below? im just not sure which perspective its from.

any help is greatly appreciated!! thanks guys

Cant give you everything you asked for but this maybe a good place to start:

http://60degreev6.com/content/Connecting_Rods

[no_doz]

thanks for that but i actually read through that before posting this.

it mentions 6" rods but it doesnt mention the combination, compression ht, etc... what would be required to accommodate for the extra .3"

[bszopi]

It would most likely have to be a custom one with the wrist pin positioned to net the desired deck clearance/CR. For the deck clearance number, a positive number is below the deck and a negative number is above the deck.

[Joseph Upson]

Yep, you would need custom pistons with the wrist pin moved further up towards the piston crown by the same distance the rod length increased. I would investigate the benefits over the stock specs to see if it is worth doing since you would have to have chevy rods narrowed for the job also unless you are considering custom rods.

Here's a good calculator once you get the specs for the 2.8L to determine spec changes:

http://www.buyracingparts.com/compression-ratio-calculator.html

[robertisaar]

2:1 Rod/Stroke Ratio? planning on revving that to the moon?

[geoffinbc]

A huge rod stroke ratio will not benefit any motor until you reach high RPM (like 7000RPM+ area). In fact the latest Engine Masters challenge winner (which was the most points ever accumulated in EMC history) won with, what most would consider, a terrible rod/stroke ratio and a very tall piston compression height. The engines were dynoed between 2500 and 6500 RPM which would be considered a "Street" motor.

Could you put a 6" rod in a 2.8L? Yes it would just be a matter of money and parts but there are no special hoops to jump through to make it happen besides filling out an order form correctly. Is it worth the money for a non race motor? No!

[no_doz]

based on the principles of leverage i figure with 6" rods & high comp, maybe kickass mpg could be achieved since leverage will do more of the work-am i correct in this logic?

this is just kind of brainstorming as to if/how a 60degree could get crazy good mpg (like 40mpg with cam, tune, miller cycle, high as hell gearing, etc...).

like i said, im not claiming that im going to actually do this, im just curious-kind of a "can a 60* get 40mpg" thread but at this point im just curious about how much of a difference the extra leverage would have on gas mileage if tuned for it.

if assembled i wouldnt be worried about revving past 5500-6k -this is about gas mileage not so much about power.

[robertisaar]

right end-result but your explantion of it might be a little oversimplified...

easiest way to get stupid-high fuel economy: lighten the car, make it more aerodynamic and taller gears(with a M/T)

i've been playing around with a desktopdyno2003 and came up with a cam meant for low-RPM torque, that would help since better VE in your cruising range generally means better fuel economy.

the higher comp is defintitely a step forward, assuming you have a good timing curve.

[geoffinbc]

Longer rods make no difference to the leverage the piston has on the crank. Only stroke can change that.

Longer rods reduce angularity of the rod when the crank is turning. This helps reduce thrust load on the sides of the bore, reducing friction. The downside to this is the fact that long rods mean a short compression height on the piston and the piston is usually very short and when this happens the piston can become unstable in the bore which kills ring sealing and causes piston noise. It also usually means the ring pack is more condensed and sometimes the oil ring has the pin bore intruding into it.

Long rods also mean a longer dwell time at TDC. The longer dwell at TDC allows the flame front to travel through the combustion chamber under compression before the piston moves down and this will help create power in the high RPM range. But in the normal drivable operating range there is almost no effect since the dwell time is plenty long even with a rod 1" shorter.

There are a lot of 5.0L strokers running around with 5.4" rods and a 3.25" stroke that still make killer power on the street.

[robertisaar]

another way to pick up some economy: highway fuel mode. i have mine set to 16.2:1 and i don't pick up any knock. so depending on what mask you're going to run on this vehicle, that can kick up another maybe 10%?

[Lilchief]

My 3.4 has 6" rods. The plus are a fatter torque curve, less detonation with higher CR and able to rev higher without damaging anything. The higher revs are useless though, CI heads don't flow well enough. My mpg is about 30 with a 4T60/3.42. The wrist pin is in the oil ring land. Another down side is cost, the rods are heavy. Had to add weight to the crank to balance it. It is a very stout motor though. I built it to run nitrous but haven't got that far yet.

[Joseph Upson]

My 3.4 has 6" rods. The plus are a fatter torque curve, less detonation with higher CR and able to rev higher without damaging anything. The higher revs are useless though, CI heads don't flow well enough. My mpg is about 30 with a 4T60/3.42. The wrist pin is in the oil ring land. Another down side is cost, the rods are heavy. Had to add weight to the crank to balance it. It is a very stout motor though. I built it to run nitrous but haven't got that far yet.

Reciprocating weight is a concern for the HO 3900 build I have planned:

Stock
Piston 422.4g
pin 155.9g
rod 632.1g

The LS1 pistons and pin I have are lighter than stock and I found a set of chevy rods at about 595g that would be a little lighter than that after narrowing however since the stock rods appear to be strong enough to withstand over 500 hp when considering stock rod performance in some boosted engines with stock forged powder metal rods I believe I'll stick with the stock rods since there is stress reduction with the lighter pistons.

Fortunately if I do swap them out lots of metal would be removed from the crank weights since along with the weight reduction in reciprocating parts the 2.25 crank pins would have to be turned down also.

Here is a link to some good tech info on connecting rods covering weights, hp level and application specs: http://www.crower.com/pdf/157-172.pdf