Rod lengths/piston combos

[Juggy]

Ive been planning on building up a block over the winter, if money is good to me...
ive been checking out FMs website about connecting rods, and see that they make a couple different lengthed rods

5.945" being stock, then they offer a 6.160", 6.180" and a 6.357" length

obviously giving the motor more stroke is going to add a little more displacement, but the main thing they are stating is that you can use lighter weight pistons with the longer rod....why is this?? and what are the benefits to a lighter piston...is it more prone to detonation being lighter???

im building a 2.2L and plan to have a nice revvin car, so the more weight I can get off the rotating mass the better, but I dont want to sacrifice durability.

they say the pistons are 60-80grams lighter when used with a 6.180 rod, combine that with another 15 grams for the tool steel pin option and thats about 3/4 of a pound there.

also if I opted for the billet aluminum rods, what kind of power can they withstand?

[allmotor]

a true race engine tries to get all moving parts as light as possible. this increased longevity by reducing stresses on the moving parts. additionally lighter parts = faster acceleration. however there's always a comprimise. too light and the parts get weak, aluminum rods are awsome but do not like hard engine braking. titainium rods are the way to go but really $$$$$$$. a longer rod has 2 advantages. 1 it makes for a lighter piston. in my 2300 ford, stock they use 5.2" rods and I was using dodge 2.2 5.94" rods with custom pistons. this make for very light pistons... now with the longer rod, you increase piston dwell (how long the piston stays at TDC in relationship to crankshaft degrees) with more dwell the energy of combustion increased the force put onto the piston thus creating more thrust on the initial segment of the power stroke.

[Juggy]

So the increased dwell increases combustion and forces that onto the piston....but too much force and POP....this is what im trying to avoid!! This does sound like a very good way to make more torque with the extra dwell time, and lightening the parts will give me more acceleration and a nice revs.

you really increased the stroke on that truck! Im only going just over .200".......i guess my main question would be, are the pistons going to be noticeably weaker if they were 60-80 grams lighter?? I know if any motor isnt properly tuned you can run into trouble....but i should have 3 bar cal by then.

also will the longer stroke mean that the motor will make max RPM earlier??? or is that all due to crank design.

and when you say the aluminum rods dont like "hard engine braking" what exactly do u mean by that?? im thinking you forgot the "e" and meant "breaking" meaning they arent very forgiving to spun bearings or detonation etc...or did u mean it that they dont like rapid deceleration of the motor like revvin it to 6 K then let the revs fall down to idle (not that any motor likes it)

[allmotor]

using a longer rod has no effect on stroke what so ever

[Koreth]

Also, making the rod longer improves the rod ratio. Improving the rod ratio is supposed to reduce piston speeds and acceleration somewhat, which I think would make it possible to rev a little higher with the same stroke, but I don't know how much real-world benefit you'd see. Odds are it would simply reduce the stress on the shortblock.

[dave brode]

allmotor,

Are the dodge and ford rod journals same o.d. and width? If not, what did it take to use the dodge rods in the ford?

Fwiw, I'm trying to choose an engine for a turbo'd 5 speed rear whl drive project [Opel GT]. If you care to share your thoughts on the 2.3 Ford vs 2.2/2.5/2.4 dodge, Mitsu 4G63 engines, please e-mail me.
Thanks in advance.
Dave
dbrode@hereintown.net


]a true race engine tries to get all moving parts as light as possible. this increased longevity by reducing stresses on the moving parts. additionally lighter parts = faster acceleration. however there's always a comprimise. too light and the parts get weak, aluminum rods are awsome but do not like hard engine braking. titainium rods are the way to go but really $$$$$$$. a longer rod has 2 advantages. 1 it makes for a lighter piston. in my 2300 ford, stock they use 5.2" rods and I was using dodge 2.2 5.94" rods with custom pistons. this make for very light pistons... now with the longer rod, you increase piston dwell (how long the piston stays at TDC in relationship to crankshaft degrees) with more dwell the energy of combustion increased the force put onto the piston thus creating more thrust on the initial segment of the power stroke.[/quote]

[DomChassis]

The longer the rod the better. Because of above stated reasons. The piston will be lighter because it will be shorter. This will not make it weaker. They don't make super long after market rods to help peoples engines live longer. Its for Better performance.

[allmotor]

[quote=dave brode]allmotor,

Are the dodge and ford rod journals same o.d. and width? If not, what did it take to use the dodge rods in the ford?

Fwiw, I'm trying to choose an engine for a turbo'd 5 speed rear whl drive project [Opel GT]. If you care to share your thoughts on the 2.3 Ford vs 2.2/2.5/2.4 dodge, Mitsu 4G63 engines, please e-mail me.
Thanks in advance.
Dave
dbrode@hereintown.net

the journals are not the same, but with a my van norman crank grinder, that's and easy fix. as for width the 2.2 is wider but my mill takes care of that.

[dave brode]

allmotor,

Are the dodge and ford rod journals same o.d. and width? If not, what did it take to use the dodge rods in the ford?

Fwiw, I'm trying to choose an engine for a turbo'd 5 speed rear whl drive project [Opel GT]. If you care to share your thoughts on the 2.3 Ford vs 2.2/2.5/2.4 dodge, Mitsu 4G63 engines, please e-mail me.
Thanks in advance.
Dave
dbrode@hereintown.net

the journals are not the same, but with a my van norman crank grinder, that's and easy fix. as for width the 2.2 is wider but my mill takes care of that.[/quote]

Thanks for the info.
Dave

[allmotor]

dave,
I like the idea of an alternative engine into an Opel GT...sounds pretty cool, I'm looking at doing something similar with a MGB.

now there are a ton of options for what would work. the 2.3 ford turbo has a lot of advantages and a few disadvantages over the mopar.

dis of the 2.3 is it's heavier and longer. advantage, two oil pan styles front or rear sump to make x-member clearance easier...race parts available for a lot less $ (kinda like the small block chevy motor of the 4cyl world) another advantage is you get a T-5 trans which is a great transmission

adv of the dodge, lighter, shorter. disad. the 2.2 is taller effecting hood height. the only transmission for a RWD is the Daktoa NV trans.. not a good racing fast shift trans. you could alway do an adaptation for a different trans. also the 2.2 turbo never came in RWD form so custom exhaust manifold and intake manifold would be needed.

if you want quicker and easier the ford would be the way to go.

[T2 shadow]

[quote=dave brode]allmotor,


Fwiw, I'm trying to choose an engine for a turbo'd 5 speed rear whl drive project [Opel GT]. If you care to share your thoughts on the 2.3 Ford vs 2.2/2.5/2.4 dodge, Mitsu 4G63 engines, please e-mail me.
Thanks in advance.
Dave


I had a 70 opel gt those are little cars ..Those 4g63s are bad to the bone from 89 to mid 92. I had a 92 awd and G teched the thing over and over with stock intercooler and a automatic awd tranny and it pulled 0-60 in 5.1. with very little mods.Fuel pump and 3 inch down pipe and 18 psi on a TDO14b. OH I have seen a 3.8 buick motor with a 200r4 with nothing but a 4 bbl carb run 8.7s in 1/8 mile in a opel gt.

[cdba009]

Just for fun....the Pinto/Mustang 4-speed trans has the same input shaft length as the Dakota trans. Therfore, they can be interchanged. We run this combo with our 2.2 in my Pro4 chassis. Center the Dakota bell housing on the Ford trans and redrill the mounting holes and your in!! Works great. There are a few more tricks to it.......if you're interested let me know!

[cj011]

I am interested, do tell ?

[FastStang]

Quote:

Originally Posted by DomChassis The longer the rod the better. Because of above stated reasons. The piston will be lighter because it will be shorter. This will not make it weaker. They don't make super long after market rods to help peoples engines live longer. Its for Better performance.

This does not always hold true. By increasing rod length you decrease maximum rpm capability. Your torque will go up in the bottom end but you will loose top end power.
FYI all high revving engines, like FI or INDY cars, have a very short stroke.
By increasing rod length you increase time at TDC but you also increase piston speed which is why top end power starts to suffer on long stroke engines. It also increases stresses in the engine, especially the pistons, due to the extra speed.
Most street cars have a square rod ratio, trucks have longer stroke for more bottom end power and super high end street racers (Ferrari) have large bores with short strokes.
There are also other advantages to short stroke such as lower deck height which lowers the centre of gravity on the engine.
Also shorter skirt pistons have many disadvantages for the street (noisy and rock in the bores which increases wear) and the lighter they are in the ring land area the strength goes down.
Most reliable high horsepower Mustang use heavy pistons. The trend seems to be that people running light pistons eventually run into problems.

[Koreth]

Quote:

Originally Posted by FastStang This does not always hold true. By increasing rod length you decrease maximum rpm capability. Your torque will go up in the bottom end but you will loose top end power. FYI all high revving engines, like FI or INDY cars, have a very short stroke. By increasing rod length you increase time at TDC but you also increase piston speed which is why top end power starts to suffer on long stroke engines. It also increases stresses in the engine, especially the pistons, due to the extra speed. Most street cars have a square rod ratio, trucks have longer stroke for more bottom end power and super high end street racers (Ferrari) have large bores with short strokes. There are also other advantages to short stroke such as lower deck height which lowers the centre of gravity on the engine. Also shorter skirt pistons have many disadvantages for the street (noisy and rock in the bores which increases wear) and the lighter they are in the ring land area the strength goes down. Most reliable high horsepower Mustang use heavy pistons. The trend seems to be that people running light pistons eventually run into problems.

I think you are confused here. These people are talking about a longer ROD not a longer STROKE. What you said is perfectly applicable to longer strokes. However Rods and Strokes are different things. We've been talking about a longer rod. Longer rods improve the rod ratio and can offset some of the disadvantages of a longer stroke somewhat.