LBZ rods

[IOWA LLY]

any one able to answer the question in red :toetap:

Lower drive pressure, (especially when the ratio becomes 1:1) improves "cylinder flush" (boost is actually helping push exhaust out of the cylinder, instead of exhaust pulsing back into intake) so you should have a much better burn on the power stroke. Which would increase power, and probably increase cylinder pressure as well.

You can't make big power without big cylinder pressure. You can lower the "peak" cylinder psi and cheat some more out of it. But if you want more power, you have to push down on the piston harder. Tuning definitely plays a big role in everything, but you cant cheat physics.

I think its the big drop in egt's that makes the twin setups live so long. Someone posted a while back that when monitoring cylinder psi high egt's caused lots of spikes in cylinder psi and made everything much more "unpredictable" if you will. JMO

 

[IOWA LLY]

joe from ppe bent his at 820 rwhp on there dyno at ppe with the same twin kit thats on casper now. so they can hold quite a bit. i think 650 would be a good safe number

How many pulls did he make at 700 rwhp or 750 rwhp?

People have laid down huge numbers on a dyno with stock LB7's and LLY's also. But they don't take it for long.

 

[stacks04]

i think to answer the original question you have to find someone who used stock rods and aftermarket pistons. the lbz rods are alot bigger on top iirc and they removed piston material so the piston cracks so much easier. leaving the rod in one piece. put a stronger piston on top and see if it does the same.

 

[dmaxfireman]

ok i got a solution!!! everybody start sending me old pieces, i'll build it and put it in my truck. lbz block & heads gt4202 duel fuelers cut lb7 pistons and stock rods. :angel: then i'll hit the dyno and push the envelope til she bends!

pm me for my address :rofl:

 

[IOWA LLY]

i think to answer the original question you have to find someone who used stock rods and aftermarket pistons. the lbz rods are alot bigger on top iirc and they removed piston material so the piston cracks so much easier. leaving the rod in one piece. put a stronger piston on top and see if it does the same.

Actually the top of the rod is the same. And the wristpins are the same diameter. But they did machine the wristpin bore in the LBZ piston bigger to accept a bushing.

 

[TrentNell]

Um-it doesn't?

Lower drive pressure, (especially when the ratio becomes 1:1) improves "cylinder flush" (boost is actually helping push exhaust out of the cylinder, instead of exhaust pulsing back into intake) so you should have a much better burn on the power stroke. Which would increase power, and probably increase cylinder pressure as well.

You can't make big power without big cylinder pressure. You can lower the "peak" cylinder psi and cheat some more out of it. But if you want more power, you have to push down on the piston harder. Tuning definitely plays a big role in everything, but you cant cheat physics.

I think its the big drop in egt's that makes the twin setups live so long. Someone posted a while back that when monitoring cylinder psi high egt's caused lots of spikes in cylinder psi and made everything much more "unpredictable" if you will. JMO

thanks for the info

 

[IOWA LLY]

What are your thoughts?

 

[TrentNell]

What are your thoughts?

to me there still seems to be a missing link some were on failures guys blow head gaskets with 38 psi and bend rods at 500-550 hp, then trucks like mine that have ran 55-60 psi boost , 650 hp and still are kicking ? while i know my rods are probably getting shorter i have been suprised by how well my motor has held up , if it let go tomarrow it would not suprise me and would feel it took quite a bit of abuse . was kinda hoping D/P was part of the equation but after explanations seems it doesnt apply . even after stronger parts are thrown at them rods pistons ect i still think it would be good to know these answers . i know a good set of balanced injectors will help alot when it comes to this equation .

i have spent alot of money to keep things efficent , egt's , drive pressure ect , i know it has helped out in the power dept , but have no clue on if it has helped the hard parts survive any more abuse .

 

[Vrabel]

could LB7 pistons be used with LBZ Block/Crank/Rod combo with LB7 heads?

 

[TrentNell]

could LB7 pistons be used with LBZ Block/Crank/Rod combo with LB7 heads?

yes but the reluctor wheels for cam and crank sensors need to be from a LB7

 

[slowlmm]

How many pulls did he make at 700 rwhp or 750 rwhp?

People have laid down huge numbers on a dyno with stock LB7's and LLY's also. But they don't take it for long.

I dont know beofore that i belive that motor had a 40-94 and a 42 for a short time. it last a good bit of time with alot of abuse. took big set of twins alot of power and boost to finally break it.

 

[Vrabel]

yes but the reluctor wheels for cam and crank sensors need to be from a LB7

That much I do know. Been considering an LBZ short block for a while, but hear horror stories about the pistons. Have no plans of pulling, maybe a run at the track from time to time, and alot of daily driving. Oh, and atleast one good run on the dyno fo braggin' rights. any mods made to pistons needed to make work on rods?

 

[LBZ]

Lower drive pressure, (especially when the ratio becomes 1:1) improves "cylinder flush" (boost is actually helping push exhaust out of the cylinder, instead of exhaust pulsing back into intake) so you should have a much better burn on the power stroke. Which would increase power, and probably increase cylinder pressure as well........
JMO

Does anyone know how long the intake and exhaust valves are both open for with a stock cam in degrees of crankshaft rotation and in time at say 3000rpm?

My point is that the extremely short period of valve overlap will likely have little effect on how much exhaust gas flows back into the cylinder-if any at all does even flow back in a turbocharged engine. IMO, for any gains at all to even be found you would need a negative pressure differential between boost and exhaust at valve overlap to really see any benefits with a turbocharged engine-which I believe is impossible with a turbo inline.
Does it affect Cyl pressure-I still doubt it.

In an NA or supercharged engine, yes this would be a bigger factor hence the reason headers make such a difference in performance as they help draw exhaust gasses out at overlap-very little backpressure.

Don't get me wrong though regarding DP-the closer to 1:1 the better!!

 

[Vrabel]

That much I do know. Been considering an LBZ short block for a while, but hear horror stories about the pistons. Have no plans of pulling, maybe a run at the track from time to time, and alot of daily driving. Oh, and atleast one good run on the dyno fo braggin' rights. any mods made to pistons needed to make work on rods?

is it just a replacement? or do LB7 pistons have to be modified to fit LBZ rod ends?

 

[IOWA LLY]

Does anyone know how long the intake and exhaust valves are both open for with a stock cam in degrees of crankshaft rotation and in time at say 3000rpm?

My point is that the extremely short period of valve overlap will likely have little effect on how much exhaust gas flows back into the cylinder-if any at all does even flow back in a turbocharged engine.

I don't know the answer to those questions. But I do know that whenever you can get your drive pressure ratio to 1:1, vs drive being maybe 5 or 10 psi more than boost, it will show a substantial gain on the dyno everytime. Just food for thought.

 

[LBZ]

I don't know the answer to those questions. But I do know that whenever you can get your drive pressure ratio to 1:1, vs drive being maybe 5 or 10 psi more than boost, it will show a substantial gain on the dyno everytime. Just food for thought.

Interesting......

But it does make sense-the more efficiently our engines breath, obviously the better they will perform.

 

[SDP]

is it just a replacement? or do LB7 pistons have to be modified to fit LBZ rod ends?

I have been wanting to know this as well.

 

[LBZ]

I have been wanting to know this as well.

One thing I do know is that LB7 cranks have larger counterweights than the LBZ's so the pistons are different. LBZ pistons from the bottom to the top are longer.

I do believe you can go LB7/LLY pistons onto an LBZ rod/crank assy. but I don't think you can go the other way. IIRC many people have cut/coat LLY pistons and installed them in LBZ's. Also, I believe the wristpins for all years are the same but don't quote me on that.

 

[A_T_Ver]

I would like to know as well

 

[JoshH]

LB7 pistons will go on an LBZ rod without modifying anything. The rod ends are the same dimensions and pin diameters are the same. LBZ wrist pins are the same diameter but longer than LB7/LLY wrist pins.