Strongest bottom end without upgrading?
12-20-2017, 12:40 PM
#1
Strongest bottom end without upgrading? Yes i searched.
After reading thru this theres a lot of talk about which is the best block to upgrade.
What about which is the strongest oem shortblock to add tons of boost thru?
Looking at finding them thru the pullnpay, ive seen many lm7's, a lq4 and now there is the occasional lm4 but those are gen3.
But i wouldnt mind buying a gen4 off ebay thats ready to go for 1000+whp. What is the strongest gen4 bottom end thats not an ls9 or ls3 aka $$$$?
edit: really asking what is the strongest i will find at the pull n pay junkyard?
After reading thru this theres a lot of talk about which is the best block to upgrade.
What about which is the strongest oem shortblock to add tons of boost thru?
Looking at finding them thru the pullnpay, ive seen many lm7's, a lq4 and now there is the occasional lm4 but those are gen3.
But i wouldnt mind buying a gen4 off ebay thats ready to go for 1000+whp. What is the strongest gen4 bottom end thats not an ls9 or ls3 aka $$$$?
edit: really asking what is the strongest i will find at the pull n pay junkyard?
Last edited by cool breeze; 12-20-2017 at 01:01 PM.
12-21-2017, 10:19 AM
#6
What part of that makes the difference over, say, a 5.3? Don't the 4.8s have longer rods? I would think those are more prone to bending than a shorter rod regardless of stroke. I could be wrong as I'm just armchair speculating, but curious about the physics and what aspect matters the most.
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12-21-2017, 10:35 AM
#8
Restricted User
What part of that makes the difference over, say, a 5.3? Don't the 4.8s have longer rods? I would think those are more prone to bending than a shorter rod regardless of stroke. I could be wrong as I'm just armchair speculating, but curious about the physics and what aspect matters the most.
Not to mention more journal overlap on the crank from the shorter stroke, making the crank stronger. The pistons are going to be side-loaded against the cylinder walls less because of that reduced rod angle, meaning less piston rock, less skirt drag, less stress on the pistons, less stress on the cylinder walls.
In theory, the 4.8 is stronger. Nobody really seems to want to run them, because you wouldn't see the benefit unless it was in something very light that didn't need the initial torque hit to get moving.
12-21-2017, 10:42 AM
#9
The rods are longer which would make you think there is increased leverage on them, but the rod/stroke ratio is much better. Shorter stroke means the big end of the rod isn't pushed as far outwards from the centerline, so the rod is always at less of an angle. It takes more of the force at a direct impact and not at a rod-bending angle. Couple that with less average torque, and the rods are going to last much longer than the longer stroke shorter rod combos.
Not to mention more journal overlap on the crank from the shorter stroke, making the crank stronger. The pistons are going to be side-loaded against the cylinder walls less because of that reduced rod angle, meaning less piston rock, less skirt drag, less stress on the pistons, less stress on the cylinder walls.
In theory, the 4.8 is stronger. Nobody really seems to want to run them, because you wouldn't see the benefit unless it was in something very light that didn't need the initial torque hit to get moving.
Not to mention more journal overlap on the crank from the shorter stroke, making the crank stronger. The pistons are going to be side-loaded against the cylinder walls less because of that reduced rod angle, meaning less piston rock, less skirt drag, less stress on the pistons, less stress on the cylinder walls.
In theory, the 4.8 is stronger. Nobody really seems to want to run them, because you wouldn't see the benefit unless it was in something very light that didn't need the initial torque hit to get moving.
12-21-2017, 03:55 PM
#12
What part of that makes the difference over, say, a 5.3? Don't the 4.8s have longer rods? I would think those are more prone to bending than a shorter rod regardless of stroke. I could be wrong as I'm just armchair speculating, but curious about the physics and what aspect matters the most.
12-21-2017, 05:09 PM
#13
L33's are just rarely found at the pullnpay.
4.8 sound like a good idea, it will be going in a foxbody thunderbird. Turbo setup that will push the engine to its limits. Did the 4.8 just get the gen4 rods in 2005 so i need to stay away from previous years?
4.8 sound like a good idea, it will be going in a foxbody thunderbird. Turbo setup that will push the engine to its limits. Did the 4.8 just get the gen4 rods in 2005 so i need to stay away from previous years?
12-22-2017, 07:51 AM
#16
TECH Fanatic
i actually made one of these. it was fun but i got a little too happy with timing trying to spool the turbos and ventilated a piston. by then the motor was in a full size so i went to a 5.3 rotating assembly. it was originally built for an s10 with a t56 and did pretty well.
12-26-2017, 12:19 PM
#17
The newer gen4 alum 5.3’s are just as good as an L33 IMO. They are much more common these days. I’ve found several for around $500 without the 799/243 heads. Slap any cheap head on and go.
I wondered if a 4.8 crank retaining the short gen4 5.3 rods would be the strongest OEM setup. Shorter gen4 rods with the shorter stroke would make for a lazy SCR and allow you to run retard amounts of boost a high RPM. Would put the piston .178” in the hole. I come up with around 7.6:1 or so with the small truck heads...The low SCR wouldn’t even be noticed with a high enough stall IMO (4500-5000ish?)
Something like that on E85 with no IC would be able to run 30-40lbs of boost at 8k or so pretty easily. Tuning window would be huge with a 7.6:1 engine. WIth E85, you probably couldn't detonate if you tried...
I wondered if a 4.8 crank retaining the short gen4 5.3 rods would be the strongest OEM setup. Shorter gen4 rods with the shorter stroke would make for a lazy SCR and allow you to run retard amounts of boost a high RPM. Would put the piston .178” in the hole. I come up with around 7.6:1 or so with the small truck heads...The low SCR wouldn’t even be noticed with a high enough stall IMO (4500-5000ish?)
Something like that on E85 with no IC would be able to run 30-40lbs of boost at 8k or so pretty easily. Tuning window would be huge with a 7.6:1 engine. WIth E85, you probably couldn't detonate if you tried...
12-26-2017, 12:27 PM
#18
Restricted User
You would have to run 40 PSI to make the same power as a 10:1 setup could within the realm of a 3-bar MAP sensor,a dn would never make anywhere close to the same torque. It would also have issues idling with E85 in cold temps.
Unless your high compression setup is at the limits of the fuel you are using, going that low is just shooting yourself in the foot. You would likely see no detonation resistance vs an 8.5:1 setup up to ~35 PSI or so on intercooled E85 and a lot less power. That whole 4% per compression point rule really only applies above 10:1. Things are much more steep when you get below 9:1.
Unless your high compression setup is at the limits of the fuel you are using, going that low is just shooting yourself in the foot. You would likely see no detonation resistance vs an 8.5:1 setup up to ~35 PSI or so on intercooled E85 and a lot less power. That whole 4% per compression point rule really only applies above 10:1. Things are much more steep when you get below 9:1.
12-26-2017, 12:44 PM
#19
Trying to figure the cheapest way to bolt together the “strongest setup” easily with OEM parts. If there was a way to bolt together stock gen4 parts and get 8.5:1 that would be great…but I don’t know of one. Short rod/stroke would have to be quite a bit stronger.
I don’t really agree with the “needing 40 psi” theory though. I get you’d want to run big boost. But boost is more efficient than compression anyway, so I don’t see why that’s bad? On the T-brake with the right stall you should be able to make more than enough boost to launch the car. My 8.6:1 5.3 would make 24lbs on the line with an LS9 cam and stock 317’s with a semi tight 17 stator PTC 9”.
I know this is oversimplifying, but just trying to get the general point across.
General rule is you only gain/lose about 4% NA HP per point of SCR. While you gain about 6% per lb. of boost. So the difference between 7.5 and 10:1 would be like 10% maybe 12%? So that 300HP cam only 4.8 is down 30-40hp? 5lbs of boost should more than make that up… It would open up the tuning window a ton and allow you to run big boost (30-40+lbs?) "safely".
I don’t really agree with the “needing 40 psi” theory though. I get you’d want to run big boost. But boost is more efficient than compression anyway, so I don’t see why that’s bad? On the T-brake with the right stall you should be able to make more than enough boost to launch the car. My 8.6:1 5.3 would make 24lbs on the line with an LS9 cam and stock 317’s with a semi tight 17 stator PTC 9”.
I know this is oversimplifying, but just trying to get the general point across.
General rule is you only gain/lose about 4% NA HP per point of SCR. While you gain about 6% per lb. of boost. So the difference between 7.5 and 10:1 would be like 10% maybe 12%? So that 300HP cam only 4.8 is down 30-40hp? 5lbs of boost should more than make that up… It would open up the tuning window a ton and allow you to run big boost (30-40+lbs?) "safely".
Last edited by Forcefed86; 12-26-2017 at 01:03 PM.
12-26-2017, 01:21 PM
#20
Restricted User
Trying to figure the cheapest way to bolt together the “strongest setup” easily with OEM parts. If there was a way to bolt together stock gen4 parts and get 8.5:1 that would be great…but I don’t know of one.
I don’t really agree with the “needing 40 psi” theory though. I get you’d want to run big boost. But boost is more efficient than compression anyway, so I don’t see why that’s bad? On the T-brake with the right stall you should be able to make more than enough boost to launch the car. My 8.6:1 5.3 would make 24lbs on the line with an LS9 cam and stock 317’s with a semi tight 17 stator PTC 9”.
I know this is oversimplifying, but just trying to get the general point across.
General rule is you only gain/lose about 4% NA HP per point of SCR. While you gain about 6% per lb. of boost. So the difference between 7.5 and 10:1 would be like 10% maybe 12%? So that 300HP cam only 4.8 is down 30-40hp? 5lbs of boost should more than make that up… It would open up the tuning window a ton and allow you to run big boost (30-40+lbs?) "safely".
I don’t really agree with the “needing 40 psi” theory though. I get you’d want to run big boost. But boost is more efficient than compression anyway, so I don’t see why that’s bad? On the T-brake with the right stall you should be able to make more than enough boost to launch the car. My 8.6:1 5.3 would make 24lbs on the line with an LS9 cam and stock 317’s with a semi tight 17 stator PTC 9”.
I know this is oversimplifying, but just trying to get the general point across.
General rule is you only gain/lose about 4% NA HP per point of SCR. While you gain about 6% per lb. of boost. So the difference between 7.5 and 10:1 would be like 10% maybe 12%? So that 300HP cam only 4.8 is down 30-40hp? 5lbs of boost should more than make that up… It would open up the tuning window a ton and allow you to run big boost (30-40+lbs?) "safely".
Remove the 799 heads from the LY2 and put on 317s, you get 8.51:1.
Remove the 799 heads from the L20 and put on 317s, you get 8.17:1.
The 4% rule only applies above 10:1 when compression starts to provide diminishing returns on a given setup (although it will still give decent gains given a large enough camshaft that needs more SCR). If it was really 4% per point then you would only lose 32% power going from 10:1 to 2:1.
Around 7:1 and 8:1, its more like 8-10%.
That So compare a 7:1 to 10:1 combo and you're looking and closer to 20% power difference. That 20% at 40 PSI could be 160 HP. Trying to regain 160 HP on an inefficient 7:1 setup could take another 10 PSI.
Compression's lives matter lol.
FYI, I've had 13:1 with an air-to-air on pump E85 at 30 PSI before. The only thing dropping to 7.6:1 compression would have done for me is kill 35% or more power, because detonation wasn't an issue.