Strongest bottom end without upgrading?
But you still have the long rods in it. I’ve managed to bend 4.8 rods a few times now. Gen3 and gen4 with no signs of detonation. (not saying it wasn’t there) That’s intercooled, on E85, water/meth, and very little timing. I’m sure I gave it too much too soon but it’s made me not a fan of the long rods on street cars. I don’t run much gear so the RPM never gets very high. The short gen4 rods don’t seem to have this issue.
I really don’t think the numbers would be as bad as you think staying above 7.5:1 either. I’ve run gen1 SBC’s there with garbage heads and had no issues making power quickly. Fuel mileage is crap and they aren’t beasts out of boost, but that never bothered me. The low compression stuff never pushed water on me or had any sort of head sealing issue.
I’m not sure how you get way with 13:1 and big boost on stock stuff. I can’t manage to do that at factory compression levels without detonation issues. Even at 10:1 I was spitting out HG’s at 26lbs or so on my last 4.8. A2A water/meth, and 13* of timing… ARP studs LS9 HG’s. That’s at 3150lb race weight. 3.25 gear 28” tire.
I really don’t think the numbers would be as bad as you think staying above 7.5:1 either. I’ve run gen1 SBC’s there with garbage heads and had no issues making power quickly. Fuel mileage is crap and they aren’t beasts out of boost, but that never bothered me. The low compression stuff never pushed water on me or had any sort of head sealing issue.
I’m not sure how you get way with 13:1 and big boost on stock stuff. I can’t manage to do that at factory compression levels without detonation issues. Even at 10:1 I was spitting out HG’s at 26lbs or so on my last 4.8. A2A water/meth, and 13* of timing… ARP studs LS9 HG’s. That’s at 3150lb race weight. 3.25 gear 28” tire.
With all the crazy SBE high rpm records it makes me think I’m applying power at all the wrong times. But I don’t want to be sitting at 5k cruising down the highway and I can’t justify the weight and hassle of an OD trans… I have a slightly decked LC9 block & a 4.8 crank sitting here though, so I may find out eventually how bad it really is…
whats the fastest you guys have been on gen 3 rods with turbo. I'm going thru a 2004 lm4 aluminum 5.3 and it is good shape I'm cleaning it up and gaping the rings with ls9 gaskets and my 220/230 boost cam. just for fun and to shed some weight off the front end. my lq4 is running fine but I just want to play with a junk yard motor and shoot for a new best in the mid 9s.
I did some searching and found a guy that ran high 5,s in the 1/8th with a 3500 lb car . and some low 9 runs in some fox bodys.
I did some searching and found a guy that ran high 5,s in the 1/8th with a 3500 lb car . and some low 9 runs in some fox bodys.
Straight from the junkyard, a L33 or a gen4 4.8 is as good as it gets. A great shortblock setup with all gm parts a Gen4 5.3 block with LSA rods and crank is a pretty stout, I have built a few of them. Next combo I'm doing is a wetsump LT1 crank, $180 LT4 rods and Gen 4 5.3 block. Not a sbe, but I don't think anything would even come close on stock gm parts.
Last edited by Turbo D; Dec 26, 2017 at 08:56 PM.
Originally Posted by Turbo D
Gen4 5.3 block with LSA rods and crank is a pretty stout setup, I have built a few of them. Next combo I'm doing is a wetsump LT1 crank, $180 LT4 rods and Gen 4 5.3 block. Not a sbe, but I don't think anything would even come close on stock gm parts.
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Stock Gen 4 4.8 LY2 is 9.2:1 and L20 is 8.8:1.
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.
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.
With a semi tight PTC 9.5” “street converter” and the small S475 I made 26lbs on the brake easy enough. That’s on an 8.5:1 5.3 and LS9 cam. With loose stall converter and better cam I have zero doubt I could spool one at 7.6:1 or so. If you went with a huge single or big twins a 100ish shot for less than a second would light them off easy enough.
I haven’t been as lucky with detonation as others have. I’ve had issues with bending rods and lifting heads at factory comp levels on my stuff. That’s with what I consider low timing and conservative tunes. I know lots of guys run 10:1 or higher and seem to have luck, but I haven’t been that lucky on a setup geared for the street.
Don’t get me wrong I see your point very clearly and I’m not suggesting it’s practical for everyone to build a 7:1 engine and run 50lbs of boost. I just think its something that isn’t done much and it could be done effectively.
For arguments sake it seems to me like a lower compression motor could provide like performance with less internal stress at lower temperatures. Which should increase longevity and/or allow additional power in a drag type application.
Benefits I can see…
The way I see it with boost a larger chamber is just better all around. Slower more controlled burn, larger area to cram air/fuel. The main drawback being out of boost performance and poor efficiency at idle/cruise. Which isn’t an issue for a drag car. Longevity in general would be improved with less stress at like performance levels.
Similar to how the “performance” boosted WWII aircraft ran low compression and huge boost. Same reasons apply. They weren’t limited by octane and still ran low compression for the reasons above.
Aside from off boost performance, what is the reason to run higher compression when boost does a better job at making power?
Don’t get me wrong I see your point very clearly and I’m not suggesting it’s practical for everyone to build a 7:1 engine and run 50lbs of boost. I just think its something that isn’t done much and it could be done effectively.
For arguments sake it seems to me like a lower compression motor could provide like performance with less internal stress at lower temperatures. Which should increase longevity and/or allow additional power in a drag type application.
Benefits I can see…
Shorter rod is stronger than the longer rod in general.
Shorter stroke to bore ratio will make it stronger in general.
You can make the same cylinder pressures with less heat in the CC with lower SCR.
Less peaky cylinder pressures at PK TQ with higher average cyl pressures across the board.
Larger tuning window.
Ability to run timing closer to MBT due to less heat and less peaky cyl pressures.
Ability to run on lower octane and/or not explode with a “bad batch” of E85 like others have been doing. Also handy for a street car running on say e30-e50 or even 91-93 octane. (lower cost/demand fuel system)
Shorter stroke to bore ratio will make it stronger in general.
You can make the same cylinder pressures with less heat in the CC with lower SCR.
Less peaky cylinder pressures at PK TQ with higher average cyl pressures across the board.
Larger tuning window.
Ability to run timing closer to MBT due to less heat and less peaky cyl pressures.
Ability to run on lower octane and/or not explode with a “bad batch” of E85 like others have been doing. Also handy for a street car running on say e30-e50 or even 91-93 octane. (lower cost/demand fuel system)
Similar to how the “performance” boosted WWII aircraft ran low compression and huge boost. Same reasons apply. They weren’t limited by octane and still ran low compression for the reasons above.
Aside from off boost performance, what is the reason to run higher compression when boost does a better job at making power?
Last edited by Forcefed86; Dec 28, 2017 at 09:36 AM.
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86, on the previous failed motors what did you find as root cause of failures? Mechanical timing verified with electronic? Street gear causing rpm to drop below peak tq on shift with too much timing? Do you have data of key contributors to make adjustments? Your hindsight is likely good insight.
86, on the previous failed motors what did you find as root cause of failures? Mechanical timing verified with electronic? Street gear causing rpm to drop below peak tq on shift with too much timing? Do you have data of key contributors to make adjustments? Your hindsight is likely good insight.
I think small cams, tall gearing, tight converter, and high back pressure put weird loads on things at low RPM. I do think they all ran into detonation in some way though. All failures were on E70 or higher, A2A IC, and 7GPH or so water/meth nozzle.
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From: Ohio
I take it you don't pay much attention to whats going on around you lol.
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From: Ohio
Straight from the junkyard, a L33 or a gen4 4.8 is as good as it gets. A great shortblock setup with all gm parts a Gen4 5.3 block with LSA rods and crank is a pretty stout, I have built a few of them. Next combo I'm doing is a wetsump LT1 crank, $180 LT4 rods and Gen 4 5.3 block. Not a sbe, but I don't think anything would even come close on stock gm parts.
Straight from the junkyard, a L33 or a gen4 4.8 is as good as it gets. A great shortblock setup with all gm parts a Gen4 5.3 block with LSA rods and crank is a pretty stout, I have built a few of them. Next combo I'm doing is a wetsump LT1 crank, $180 LT4 rods and Gen 4 5.3 block. Not a sbe, but I don't think anything would even come close on stock gm parts.
I did not realize that LT cranks and rods are compatible with the LS engines. When googling around for some more information, it says that the LT4 crank is stronger than the LT1 crank. So why not use it? Cost? More info please...
Andrew