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I think we’ve all seen that dyno graph multiple times. Interesting that each motor has the same torque peak but the LT5 power peak is 400rpm higher than the OHV motors. DOHC typically shift the power and torque peak towards higher rpms. With a power peak 400rpm higher than the LS motors, I would expect the torque peak to be at 5200 which is where my LT5 peaked even before the mods. Then the next question is whether this compares the 375 or 405 motor.
Looks like the early motor, since it's 375(372.9)/370. Also looks like an early 385hp LS6.
It's also odd that the HP peak is at 6400. I recalled that those were rated at 5800... 5800 is basically where it noses over, or flat lines, it's say the "6400" is a bump that somehow tickled the peak marker. The shape of the curve shows us that it's not gaining meaningful power at that point. But that curve and the LS6 curve show us that the LS^ is diving faster and above 6500, the LT5 will have more hp than the LS6.
If this comparison is from GM Powertrain, I would be suspicious that someone had their “thumb on the scale”. Powertrain never acknowledged the LT5 as a GM motor. McLellan ended up retiring from the politics his initiative with Lotus brought on.
I was able to dig out a dyno run from many moons ago when I first started on the LT5. This dyno compares an LT5 w DIY ported plenum/IH and headers. As close as I had to a stock motor. Found out later cams needed timing, but it gives a good view of LT5 power and torque curves. Values are SAE corrected and represent rear wheel hp/tq.
If this comparison is from GM Powertrain, I would be suspicious that someone had their “thumb on the scale”.
IDK why. Seems pretty spot on, to me and if anything give some props to the long/high RPM range of the LT5 since it was rated by GM at 5800 and that chart is showing 6400. Bonus.
One thing I love is the low RPM torque. 300 lbs just off idle. Beef cake!
But but but Tom, EVERYBODY knows DOHC motors have no low end torque. 🤣😂
Let’s just say that the LT5 was never included at GM Powertrain as part of the GM power plant display. However, kudos to the Powertrain guys for developing the LT6 30 years later, a very worthy successor to the LT5(the real one). Heck of a motor.
Quick update from this weekend. Had another track day yesterday. A little cold, but with the sun out the track got warm enough for some decent laps. Only mod from last event was to add some cooling ducts to the front rotors. I didn't have any issues with boiling fluid this weekend, so that was a win. I did experience what seemed to be some pad fade though when I was really pushing them and went too hot into turn 9 after passing a 911. Cooling system had no problems at all with a max outside temp of maybe 60. Oil consumption is manageable, but annoying, I think after the next time trial race on the 20th I'm going to drop the engine.
Set my new best lap at a 1:46.1. I was hoping to be in the 1:45's, but oh well didn't get that much track time due to a couple issues:
-Voltage fluctuation - Engine started missing and I noticed the voltage had dropped all the way down to 8 volts. Then randomly it would start charging again. Found the plug at the alternator was loose and the retaining clip broken. I'll grab a new pigtail, but I'm not 100% sure this is the issue yet, need to check more wiring (grounds, main charging lead). Hoping I don't need a new alternator.
-Blown megasquirt internal fuse, I assume due to operating at very low voltage, this took a while to diagnosis and find
-Pad knock back due to a loose left front wheel bearing
What's the best front wheel bearings for the C4 and where do you buy them? Stock ones on mine got loose so I replaced with Raybestos, which were absolute garbage. Replaced those with precision brand which felt much better, but the left one has already developed a little slop after 2 track days.
What's the best front wheel bearings for the C4 and where do you buy Stock ones on mine got loose so I replaced with Raybestos, which were absolute garbage. Replaced those with precision brand which felt much better, but the left one has already developed a little slop after 2 track days.
You'll get as many answers to this as you get for "brand of oil"!
Here is where I'm at; I've spent $$$ on "the best"....they didn't last. I understand that all C4 bearings are Chinesium now. So me? I'm on the CHEAPEST **** you can find, program. That's right....I've got the $29, Rock Auto special in my car and they're working as well as the $200 SKF that I tried before. For ~$30? I can't be disappointed and it simply becomes a maintenance item, in my mind. And if it holds up (which they are, so far).....BONUS!
Right now, RA has a hub for $24.59 That is what *I* would get!
You'll get as many answers to this as you get for "brand of oil"!
Here is where I'm at; I've spent $$$ on "the best"....they didn't last. I understand that all C4 bearings are Chinesium now. So me? I'm on the CHEAPEST **** you can find, program. That's right....I've got the $29, Rock Auto special in my car and they're working as well as the $200 SKF that I tried before. For ~$30? I can't be disappointed and it simply becomes a maintenance item, in my mind. And if it holds up (which they are, so far).....BONUS!
Right now, RA has a hub for $24.59 That is what *I* would get!
I thought about trying some cheap ones, surely they couldn't last any less time than I'm seeing right? I was hoping SKF or Moog might be a better option. For now I'll start with seeing if I can get Oreilly's to warranty the precision one that's loose.
How many track days are hubs lasting you? Are you running 315's up front?
What kind of HP numbers are guys hitting with 368 LT5's?
With the LT5 coming out in a couple weeks to fix the blow-by issue, I'm weighing cost to benefit for my planned mods. I'd like to hit 500rwhp+ but not sure how reasonable that is with a 368 displacement on an LT5. I'm looking at having the heads CNC ported and swapping to some aftermarket cams, engine already has a ported top end. If this is likely to only get me to 450-475hp I might adjust my plans a little...
Edit: Googling for actual 368 Dyno graphs, 500 looks like it's going to be VERY hard. Mark H. has a package with stock cams that hits about 450...
Last edited by jrtoffroad; 11-08-2022 at 11:49 AM.
What kind of HP numbers are guys hitting with 368 LT5's?
With the LT5 coming out in a couple weeks to fix the blow-by issue, I'm weighing cost to benefit for my planned mods. I'd like to hit 500rwhp+ but not sure how reasonable that is with a 368 displacement on an LT5. I'm looking at having the heads CNC ported and swapping to some aftermarket cams, engine already has a ported top end. If this is likely to only get me to 450-475hp I might adjust my plans a little...
Edit: Googling for actual 368 Dyno graphs, 500 looks like it's going to be VERY hard. Mark H. has a package with stock cams that hits about 450...
Here is a dyno of my injured 427 motor prior to tear down. Stock cams, high-flow cats. The new motor should make as much power hopefully.
St. Jude Donor '07-'08-'09-'10-'11-'12-'13-'14-'15-'16-‘17, '22
Originally Posted by jrtoffroad
What kind of HP numbers are guys hitting with 368 LT5's?
With the LT5 coming out in a couple weeks to fix the blow-by issue, I'm weighing cost to benefit for my planned mods. I'd like to hit 500rwhp+ but not sure how reasonable that is with a 368 displacement on an LT5. I'm looking at having the heads CNC ported and swapping to some aftermarket cams, engine already has a ported top end. If this is likely to only get me to 450-475hp I might adjust my plans a little...
Edit: Googling for actual 368 Dyno graphs, 500 looks like it's going to be VERY hard. Mark H. has a package with stock cams that hits about 450...
Highest number Ive seen (via online postings) for a 368 is 486rwhp with cams and full porting.
Here is a dyno of my injured 427 motor prior to tear down. Stock cams, high-flow cats. The new motor should make as much power hopefully.
Thanks for the info. Nice numbers and good-looking curve for a hurt engine. Look forward to hearing how the new engine does on the dyno! Agree with Domonic, there was probably a little more on the table if that had been leaned out some.
Highest number Ive seen (via online postings) for a 368 is 486rwhp with cams and full porting.
Thanks. That's about what I was seeing. Darn was hoping for the investment in head work and cams I'd be able to get a little more. Wonder what's holding the LT5 back at that point? I've been toying with the idea of fabbing up a custom sheet-metal intake to hopefully lose some weight a pickup a couple ponies. Was thinking I'd shorten the runners a little, go to a 102mm LS style TB, and use lose the bifurcation before the injector housings.
With the previous owner, my engine put down 468rwhp, this is before he had it re-built for the boost that it doesn't have now. At the time, it had cams and top end porting. I don't think the heads have ever been touched. Wish I had the cams he was running back then, but I think they were scrapped. (Apparently, they didn't wear well?)
I’m glad I went back through your pictures, JR because I found something in particular I wanted to ask you about. How has tapping the fuel rail for that PSI sensor worked for you? I was slowly putting together a nitrous oxide system for my Z and I wanted as many safety nets in place as possible.
I have plenty of valve core removal tools. When I replace my current injectors with a brand new set, I was considering removing the core out of the schrader port and running a Nitrous Outlet adapter. The adapter allows several ports, so one was going to be the fuel psi kill switch (run to the side like your sensor) and the other port on top be a screw in schrader valve so I still have access to check fuel pressure via dial gauge if needed.
Im switching over to a single Racetronix pump using a boost-a-pump which only turns on when the system is armed. Top pic is yours from earlier in the thread and then a mock up of one I was thinking of.
11-06-2022, 03:16 PM
