how much hp are ls7 rods worth
12-25-2020, 11:22 AM
#1
how much hp are ls7 rods worth just wondering how much more a properly broken in factory ls7 motor would make on the dyno vs a properly broken in ls7 block but built with your typical callies/k1 forged crank, forged steel rods, and forged pistons......same compression/same stock ls7 heads on both. obviously nobody would build this motor im more or less just curious how much more power the lighter ls7 rotating assembly is worth
12-25-2020, 11:57 AM
#4
Interesting. I dont know alot about sbe ls7s, but with the right top end, they seem to respond well with them titanium rods...I thought I remember as long as they werent flaking, your ok with the sbe. I mite be buying the wet sump version from Summit just to steal the bottom end out of it n slam my top end on it.
https://www.summitracing.com/parts/nal-19420191
Johns video never gets old-sbe ls7 iirc?
https://www.summitracing.com/parts/nal-19420191
Johns video never gets old-sbe ls7 iirc?
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02*C5 (04-01-2022)
12-25-2020, 12:35 PM
#5
if the rotating assembly is noticeably lighter than the forged assembly, it certainly has to be worth something, i was thinking about 10hp or more from 6000 rpms up.....again i know there is no test behind it, just wondering what people on here estimate it to be worth.
yea the rods will certainly be the lightest part of it, i think actually an ls7 crank is minimally heavier than a forged compstar. I thought a wet sump compstar is like 48 while a gm ls7 crank is 51 to 52, dont quote me. And the pistons certainly not something worth pushing too hard on, while they are lighter than a forged piece, so honestly the rods are the only thing worth using in a built 4 inch motor.
yea the rods will certainly be the lightest part of it, i think actually an ls7 crank is minimally heavier than a forged compstar. I thought a wet sump compstar is like 48 while a gm ls7 crank is 51 to 52, dont quote me. And the pistons certainly not something worth pushing too hard on, while they are lighter than a forged piece, so honestly the rods are the only thing worth using in a built 4 inch motor.
12-25-2020, 12:54 PM
#6
if the rotating assembly is noticeably lighter than the forged assembly, it certainly has to be worth something, i was thinking about 10hp or more from 6000 rpms up.....again i know there is no test behind it, just wondering what people on here estimate it to be worth.
yea the rods will certainly be the lightest part of it, i think actually an ls7 crank is minimally heavier than a forged compstar. I thought a wet sump compstar is like 48 while a gm ls7 crank is 51 to 52, dont quote me. And the pistons certainly not something worth pushing too hard on, while they are lighter than a forged piece, so honestly the rods are the only thing worth using in a built 4 inch motor.
yea the rods will certainly be the lightest part of it, i think actually an ls7 crank is minimally heavier than a forged compstar. I thought a wet sump compstar is like 48 while a gm ls7 crank is 51 to 52, dont quote me. And the pistons certainly not something worth pushing too hard on, while they are lighter than a forged piece, so honestly the rods are the only thing worth using in a built 4 inch motor.
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Corona (12-25-2020)
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grinder11 (04-03-2022), WE TODD DID (12-25-2020)
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12-25-2020, 01:26 PM
#8
ModSquad
iTrader: (6)
You’ll be way ahead by going forged steel internals and then to save rotating weight, buy a lighter clutch assembly if your manual trans. The Ti LS7 rods are an odd size which makes pistons difficult to come by, the coating on them comes off easily on the shoulders, and Ti naturally gets brittle with heat cycles and age.
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Gen2-LT4 (03-25-2023)
12-25-2020, 03:33 PM
#10
chevelle yea i couldnt see myself using them in something that absolutely had to live 50,000 miles. Seems the coating worries some and not others. Kinda thinking about a 388 build in a few years and thought maybe if i were to spin it to 8000 the titanium rods could be worth something....if only aluminum could be had for 250 a rod? Maybe best of both worlds
12-25-2020, 05:55 PM
#12
The titanium rods don’t hold their shape. That’s why you don’t see them in hardly any other performance application.
Most nhra pro stock engines have steel rods. Some others have aluminum.
Steel rod engines make more power.
The only weight to worry about is the weight pulling on the connecting rod along with piston speed.
12-25-2020, 08:32 PM
#13
Im guessing for 505hp, they fit the bill and were plenty good. How many of ya happy with just 505fwhp? The ls7 as im told isnt a strong motor outside what it was designed for. Lots of material and weight hogged out to make the z06 light. Also using dry sump must have some kind of effect on this motor besides the gforces the vette can pull on the track. My guess is, the ls7 is a house of cards. Start to take certain things away and it all comes crashing down in strength n reliability. Swap a stockish ls7 in your hotrod and enjoy. Yet, theres Johns monte, so....
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G Atsma (12-25-2020), WE TODD DID (12-26-2020)
12-25-2020, 09:25 PM
#14
Same reason they used sodium filled exhaust valves.
The titanium rods don’t hold their shape. That’s why you don’t see them in hardly any other performance application.
Most nhra pro stock engines have steel rods. Some others have aluminum.
Steel rod engines make more power.
The only weight to worry about is the weight pulling on the connecting rod along with piston speed.
The titanium rods don’t hold their shape. That’s why you don’t see them in hardly any other performance application.
Most nhra pro stock engines have steel rods. Some others have aluminum.
Steel rod engines make more power.
The only weight to worry about is the weight pulling on the connecting rod along with piston speed.
I’ve read accounts of people claiming Ti valves help acceleration rate of the engine despite showing no power on a dyno.
12-25-2020, 10:40 PM
#15
Guys. I already answered your questions.
It’s because engines are measured on brake dynos.
But cars are tuned on chassis dynos which are typically inertia dynos. Inertia dynos are fairly simple machines - force the engine to spin a big weight and time how quickly the engine accelerates that weight up to speed and calculate power and torque. Because less rotating mass means an engine can rev quicker, an inertia dyno will show power gains.
But brake dynos are a special beast. Brake dynos spin the engine at specific RPMs and apply a brake in increasing force to see what it takes to prevent the engine from accelerating. Hence the term “BRAKE horsepower.” Because the RPM is basically static and acceleration isn’t a factor, it can’t detect weight loss in any of the rotating assembly.
If you actually listen to a brake dyno sometime, you’ll notice the RPM fluctuates quite a bit - that’s the brake being applied to actually measure its torque directly.
It’s because engines are measured on brake dynos.
But cars are tuned on chassis dynos which are typically inertia dynos. Inertia dynos are fairly simple machines - force the engine to spin a big weight and time how quickly the engine accelerates that weight up to speed and calculate power and torque. Because less rotating mass means an engine can rev quicker, an inertia dyno will show power gains.
But brake dynos are a special beast. Brake dynos spin the engine at specific RPMs and apply a brake in increasing force to see what it takes to prevent the engine from accelerating. Hence the term “BRAKE horsepower.” Because the RPM is basically static and acceleration isn’t a factor, it can’t detect weight loss in any of the rotating assembly.
If you actually listen to a brake dyno sometime, you’ll notice the RPM fluctuates quite a bit - that’s the brake being applied to actually measure its torque directly.
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Woodylyf767 (12-25-2020)
12-25-2020, 11:26 PM
#16
Guys. I already answered your questions.
It’s because engines are measured on brake dynos.
But cars are tuned on chassis dynos which are typically inertia dynos. Inertia dynos are fairly simple machines - force the engine to spin a big weight and time how quickly the engine accelerates that weight up to speed and calculate power and torque. Because less rotating mass means an engine can rev quicker, an inertia dyno will show power gains.
But brake dynos are a special beast. Brake dynos spin the engine at specific RPMs and apply a brake in increasing force to see what it takes to prevent the engine from accelerating. Hence the term “BRAKE horsepower.” Because the RPM is basically static and acceleration isn’t a factor, it can’t detect weight loss in any of the rotating assembly.
If you actually listen to a brake dyno sometime, you’ll notice the RPM fluctuates quite a bit - that’s the brake being applied to actually measure its torque directly.
It’s because engines are measured on brake dynos.
But cars are tuned on chassis dynos which are typically inertia dynos. Inertia dynos are fairly simple machines - force the engine to spin a big weight and time how quickly the engine accelerates that weight up to speed and calculate power and torque. Because less rotating mass means an engine can rev quicker, an inertia dyno will show power gains.
But brake dynos are a special beast. Brake dynos spin the engine at specific RPMs and apply a brake in increasing force to see what it takes to prevent the engine from accelerating. Hence the term “BRAKE horsepower.” Because the RPM is basically static and acceleration isn’t a factor, it can’t detect weight loss in any of the rotating assembly.
If you actually listen to a brake dyno sometime, you’ll notice the RPM fluctuates quite a bit - that’s the brake being applied to actually measure its torque directly.
12-26-2020, 08:20 AM
#17
I think he s saying your splitting hairs and couldnt know the difference even if you were looking for it kinda thing. However, the perpetuity for problems down the road is enough to not start out with a sbe unless of course it makes sense from lets say a financial stand point or so. I cannot build motors, so buying something already built sometimes makes sense. Or in 2020, it doesnt seem anyone can get enough parts to build me a shortblock cuz of the scamdemic. So a turnkey wetsump ls7 from Summit/GM just mite be my ticket. Theres always a reason or two that favors one way or the other for sure. After seeing John B s car perform, I mite go a similiar route myself just to get my project back on the road. Sure as hell aint puttn my faith in RHS at this point, lol.
It is my understanding, the bottom end doesn't make power, it just holds it. Some people know how to make anything work in harmony.
It is my understanding, the bottom end doesn't make power, it just holds it. Some people know how to make anything work in harmony.
Last edited by rkupon1; 12-26-2020 at 08:26 AM.
12-26-2020, 08:23 AM
#18
I think he s saying your splitting hairs and couldnt know the difference even if you were looking for it kinda thing. However, the perpetuity for problems down the road is enough to not start out with a sbe unless of course it makes sense from lets say a financial stand point or so. I cannot build motors, so buying something already built sometimes makes sense. Or in 2020, it doesnt seem anyone can get enough parts to build me a shortblock cuz of the scamdemic. So a turnkey wetsump ls7 from Summit/GM just mite be my ticket. Theres always a reason or two that favors one way or the other for sure. After seeing John B s car perform, I mite go a similiar route myself just so to get my project back on the road. Sure as hell aint puttn my faith in RHS at this point, lol.
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rkupon1 (12-27-2020)
12-27-2020, 07:05 AM
#20
Does a lower bob weight not result in less inertia when accelerating through the rev range? I agree on a dyno at a slow acceleration or stepped test it is going to all be within spitting distance.
I’ve read accounts of people claiming Ti valves help acceleration rate of the engine despite showing no power on a dyno.
I’ve read accounts of people claiming Ti valves help acceleration rate of the engine despite showing no power on a dyno.
The titanium valve thing is completely different. That’s more about keeping your valvetrain in control.
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DualQuadDave (12-27-2020)