351w long rod????

[f250torque]

Hey I'm new. Joined this forum due to finding the 351w long rod thread of doom on google. Read it all. I'm taking the road less traveled and going for this build. I will be installing the engine in my 1990 f250. I know these motor like to rev but from what I read they can still make nice power in the low end. And I have want to be different. I know there is a few threads I found but they seem old. If I missed one I don't mind being informed. My question is anyone currently running this type of build and how did you set yours up? Also how has it performed? Any info and discussion would be great!!!

[merc91]

I just took as scroll through that thread myself and unless I'm missing something, it's just a method to bump up compression a bit... would be cheeper and more effective to just get pistons to do that.

[88Vic]

Using smaller cc heads will do it too. Not sure what choices there are out there for the 351W but I would think there are better factory heads than what came on that truck. Maybe not smaller cc's but better flowing anyways.

[johnunit]

Long rod design is about the angle the rods end up and the effect that has on leverage and piston speed at a given part of the rotation. Complex mathematical stuff. Current consensus seems to be it's worth some power but not worth compromising other stuff for. longer rod for same stroke means the wrist pin has to be higher in the piston. This affects the shape of the piston and where the piston rings are.

[merc91]

for sure the more linear the better with rod ratios, more time at tdc aswell... tenths of an inch though I don't beleive the benefits would occur especially with the 302w having a good ratio to start with... would be interesting to see track times before and after though.

[Mercracer]

I just took as scroll through that thread myself and unless I'm missing something, it's just a method to bump up compression a bit... would be cheeper and more effective to just get pistons to do that.

It has nothing to do with bumping compression ratio and everything to do with dwelling at TDC and altering piston speed at different degrees of rotation. If you read that thread again, you will notice that one of the benefits mentioned is that the engine will tolerate a higher compression ratio.

[Mercracer]

http://www.stahlheaders.com/Lit_Rod%20Length.htm
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http://www.tildentechnologies.com/Cams/Take_RodLen.html
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[pantera77]

Pirate doesn't come here anymore but I'm sure he could write a 100 page essay on it.

[merc91]

Thats what I'm getting at mercracer, ceiling gains in timing and CR limits are surpassible by new (have come a long ways in 20yrs) piston design alone with the heat dissipation/dispersion/pressure wave dissipation abilities.

So long story short since "the server was to busy" and lost my 2hr in depth physics explanation and measured gains #'s for each aspect of the long rod differences... The last section was recovered...



the theory end of it could go on forever, the actual measurable gains I have seen are very minimal... very. Gains in CR and timing ceiling on a healthy motor have showed a fair bit less than the optomistic earlier 1CR point calculated based on nitrous timing advancement... do some googlin and those results found by others who know what they are doing and have measured results are less than impressive aswell.
SOOOOO why do the gains fall short of what the math suggests??? The easily overlooked answer to all this complexity is suprisingly simple. It's because an engine is most suseptable to detonation at it's peak volumeric efficiency although nitrous is more rpm dependant because of its cooling and chemical VE aproach (most air volume filling in the cylinder, this is peak tq in any engine) and on a street capable build this occurs in the mid range of the powerband, longrod benefits are increasingly and exponentially increased with rpms and the gain at mid rpm is almost nothing while the gains at 7000 seem numerically impressive for what it is.

Kinda like running a marathon with a gallon of water only at the finish line for each person... paying someone $1200 to add 1 teaspoon at the halfway point and than another bottle into that gallon at the finish line won't help you when the waters impressive benefits are not present in any quantity at the time of demand... Most people would say wholy shit all that water should really boost how far you can push with all the science to back it up. However it does NOT add up to 1gal+bottle+1tsp benefits over the entire race including peak demand up that hill 2/3 through the race. Infact only a teaspoon is there at the ONLY time it is needed.

"revs quicker" is pretty subjective lol. Although the honda boys swear by a K&N sticker on the back window doing that so I might have to cave and try er out :P