[radz28]

Originally Posted by KingLT1

TBH I haven't tuned a SLB LT4 at 20+ psi of boost. Most ain't trying to party that hard and I don't really mess with port injection which is the only way to get a stock heads cam car to have enough fuel for that. But I do think 23-24 degrees should be no problem on E85. The amount of boost or timing isn't really the issue. It's the supercharger pulling on the crank when it's being spun hard. Back in 2017-2018 guys like Andrew @ CSP were saying anything above 800whp out of a stock blower setup was rolling the dice far as thrust bearing failure. Then porting programs extended that number to 900 since you can make more power without increasing blower speed, the 2650 even further, and turbos even more. I just seen the 20psi and that came to mind but I forgot he was stock heads/cam. SLB will show 3psi more boost at the same pulley ratio because it's boost stacking vs a heads cam car. Really just need to know the actual blower RPM. Either way I think the OP tuner is spot on.... It's near it's limit. I believe Mike Sitar made like 900+ SLB in his Z06 but said he didn't plan to leave it there for longevity sake. I can't remember if that was with the 2650 or X port. I know he swapped back and fourth when testing port injection. on his car.

Thanks for the information and transparency. I think I remember Andrew saying that, but then I thought I remembered him changing that to about 900-950 later... I can try to find that video, but I'm not trying to argue with you or anything, because I don't tune cars, so I wouldn't have practical experience on that anyways, like you do. I don't bring anything to the table in that regard. I know I remember Matt at Nickey (when he was there a few years ago tuning on THPSI stuff) saying he felt around 950 was the limit, too. Again - I'm only trying to validate what I was claiming OTHERS have said, as I haven't even had my car on a dyno, so I don't have much for credibility. What I do know is I'm spinning my blower (according to calculators) on an 80mm @ 16508 RPMs, and from what I can tell, based off stock diameter pulleys (8" lower / 3.3" upper) an LT5 is pushing about 15760, which seems to align with a couple on-line sources. I show my 85mm upper spinning to about 15520 and the stock 90mm to about 14690. While I understand the metallurgy for the LT5 crank to be slightly better, I didn't think (based off no evidence - just people have been pulleying down for years from stock ratios) another thousand RPMs would be a big deal. While this is my first blower car (and by a wide margin my most powerful car [even when it was stock]), I've been reading and studying mods' since I was a teenager, but again - that's based off no hard evidence or experience, so... I swear there was at least one video LMP was running an LT4-car to about 20-psi and about 23* with a SLB, so that's where I was basing my guesses around. Shoot - for me - the car was a handful on DRs with the 85mm (18-psi) and 25*, so it's not like I NEED this 80mm to be running 23*, lol. I just want to be safe, but I understand your point about SLB boost vs H/C boost on the same pulleys. I'm fairly certain Sitar was running the 2650 in the latest videos (about a year old now) for that 960 number, but he had done some testing with the 1740 just before that. He was trying some PI software testing at that time, but nonetheless - that seemed like a lot. I think he was pushing 22-23-PSI - whew! I'm good where I'm at, lol. From accounts out there regarding the 2650 taking more power to spin over the 1740, it seems the claims by the engineers are the 1740 takes about 90 while the 2650 took 110 (https://www.sae.org/news/2018/04/gm-...eering-details), so what that means regarding this topic isn't that helpful to my understanding, lol. So - to your point - it makes sense a 2650 is going to put on more load than a 1740 is on the TB, and I know the tuner is trusted by DSX (I don't remember their name though), so I was just seeking a larger data base was all. A stock LT4 isn't going to handle quite as much as a stock LT5 (why would GM upgrade bearings and the crank if it wasn't necessary?), but having a better, practical, understanding of what others have gotten is always helpful to me.

Do the numbers I provide help at all? I know you can't guarantee anything, but you've put your electronic hands on way more cars than I have, so you have the credibility I would trust. Of course - I wouldn't hold you accountable to anything, but hopefully that goes without saying at this point.

Thanks for your input (and anyone else's)!!!

CHEERS!!!

[Joshinator99]

I’m 22.5 degrees and 19 PSI at 1066 WHP just to prove King’s point about boost stacking in stock heads/cam cars. Making the engine a more efficient air pump will mean more power at lower boost numbers.

In regards to timing, for fun when I was on the hub dyno recently we tried adding another degree of timing and saw virtually no gain so we pulled it back out. Conservative timing will help keep your engine alive longer in my opinion.

[RobZL1]

Originally Posted by Joshinator99

I’m 22.5 degrees and 19 PSI at 1066 WHP just to prove King’s point about boost stacking in stock heads/cam cars. Making the engine a more efficient air pump will mean more power at lower boost numbers.

In regards to timing, for fun when I was on the hub dyno recently we tried adding another degree of timing and saw virtually no gain so we pulled it back out. Conservative timing will help keep your engine alive longer in my opinion.

That's the beautiful part of having enough octane on the corn-juice. You can push the timing until you don't see significant power gains, then take it back to where it last picked up power and leave it there, knowing you are getting everything to be had with the hardware you have. You don't have to play the detonation game and ride the edge of the knock sensors to eek out the hp.

---------------------
Edited to add a neat graph I borrowed from my friend, the internet. I added the black lines and the arrow. You can see the knock-limited spark timing window grows almost 10 degrees from about E10 to about E60. Somewhere in the 10 degree window, you will find your MBT. Thanks, ethanol!

[clg82]

Originally Posted by KingLT1

TBH I haven't tuned a SLB LT4 at 20+ psi of boost. Most ain't trying to party that hard and I don't really mess with port injection which is the only way to get a stock heads cam car to have enough fuel for that. But I do think 23-24 degrees should be no problem on E85. The amount of boost or timing isn't really the issue. It's the supercharger pulling on the crank when it's being spun hard. Back in 2017-2018 guys like Andrew @ CSP were saying anything above 800whp out of a stock blower setup was rolling the dice far as thrust bearing failure. Then porting programs extended that number to 900 since you can make more power without increasing blower speed, the 2650 even further, and turbos even more. I just seen the 20psi and that came to mind but I forgot he was stock heads/cam. SLB will show 3psi more boost at the same pulley ratio because it's boost stacking vs a heads cam car. Really just need to know the actual blower RPM. Either way I think the OP tuner is spot on.... It's near it's limit. I believe Mike Sitar made like 900+ SLB in his Z06 but said he didn't plan to leave it there for longevity sake. I can't remember if that was with the 2650 or X port. I know he swapped back and fourth when testing port injection. on his car.

So if we could dive a little deeper into this conversation, what makes it ok with stock heads/cam vs the alternative? Just a side note this isn’t a dedicated track car, it’s a cruise around town/car show/occasional strip visit car. So I’m not beating the hell out of it every day, not that that matters but for longevity purposes it may. And I know for Radz, he never drives his so it’s a moot point for him

[KingLT1]

Heads/cam cars can make the same power not spinning the blower as hard. You would be gaining 70-100whp of power on the engine side, so you don't need to work the blower as hard. So if you wanted more power from where you are at, then you would do heads/cam vs spinning the blower even harder because the thrust bearing isn't likely going to tolerate much more. That is why your tuner said it's tapped out. The 2650 also doesn't hit as hard as the stock blower turned up, so that is helping as well. I am just putting this info out there for you as food for though in the event you want more power down the road. Either way you guys are fine for what you use the cars for.

[radz28]

Originally Posted by clg82

So if we could dive a little deeper into this conversation, what makes it ok with stock heads/cam vs the alternative? Just a side note this isn’t a dedicated track car, it’s a cruise around town/car show/occasional strip visit car. So I’m not beating the hell out of it every day, not that that matters but for longevity purposes it may. And I know for Radz, he never drives his so it’s a moot point for him

I'm driving some more, LOL!!!

But to your point - I haven't been able to go WOT to redline yet on this pulley because of traction, and I don't party out on the street, nor get to a strip, so maybe I can be a little more liberal in my timing. But - I'm just looking to make sure I'm in a safe window, because I'm plenty happy where I am now. Theoretically - I should be in your neighborhood (minus a little from stock exhaust - sort of...), but I'm not getting rid of this car, and I'm not looking to have to rebuild it any time soon. But yeah - a good margin of safety would be what I would like to try to confirm is all.

Maybe I should pull back to 22*? 21*?

[clg82]

Originally Posted by KingLT1

Heads/cam cars can make the same power not spinning the blower as hard. You would be gaining 70-100whp of power on the engine side, so you don't need to work the blower as hard. So if you wanted more power from where you are at, then you would do heads/cam vs spinning the blower harder because the thrust bearing isn't going to tolerate much more. That is why your tuner said it's tapped out. The 2650 also doesn't hit as hard as the stock blower turned up, so that is helping as well. I am just putting this info out there for you as food for though in the event you want more power.

Oh yeah, I’m not planning on going more boost from here, it’ll be heads/cam when I decide I want some more. Thanks for clarifying.

[radz28]

Originally Posted by KingLT1

Heads/cam cars can make the same power not spinning the blower as hard. You would be gaining 70-100whp of power on the engine side, so you don't need to work the blower as hard. So if you wanted more power from where you are at, then you would do heads/cam vs spinning the blower even harder because the thrust bearing isn't likely going to tolerate much more. That is why your tuner said it's tapped out. The 2650 also doesn't hit as hard as the stock blower turned up, so that is helping as well. I am just putting this info out there for you as food for though in the event you want more power down the road.

So, theoretically, one could argue even though there's more mass in a 2650, if we're spinning at 16000, instead of 22000 with a 1740, there's still less load on the TB, all else the same? That's what I feel like I'm taking away anyhow...

[KingLT1]

I would run less boost and more timing. Why pulley the blower so it hits harder and makes traction useless vs softer hit and more timing up top?

[radz28]

Originally Posted by KingLT1

I would run less boost and more timing. Why pulley the blower so it hits harder and makes traction useless vs softer hit and more timing up top?

Because I'm a neandrathol and like the whine...

OK. This belt is a little too loose anyways, lol. Do you think I could get away with 25* at around 18-psi?

[KingLT1]

Originally Posted by radz28

So, theoretically, one could argue even though there's more mass in a 2650, if we're spinning at 16000, instead of 22000 with a 1740, there's still less load on the TB, all else the same? That's what I feel like I'm taking away anyhow...

I believe so.

[KingLT1]

Originally Posted by radz28

Because I'm a neandrathol and like the whine...

OK. This belt is a little too loose anyways, lol. Do you think I could get away with 25* at around 18-psi?

Yeah 24-25...I know some run more but I would recommend doing like Josh did. Put it on a hub dyno and see what it likes.

[radz28]

Thanks King'!!!

[Joshinator99]

Originally Posted by RobZL1

That's the beautiful part of having enough octane on the corn-juice. You can push the timing until you don't see significant power gains, then take it back to where it last picked up power and leave it there, knowing you are getting everything to be had with the hardware you have. You don't have to play the detonation game and ride the edge of the knock sensors to eek out the hp.

---------------------
Edited to add a neat graph I borrowed from my friend, the internet. I added the black lines and the arrow. You can see the knock-limited spark timing window grows almost 10 degrees from about E10 to about E60. Somewhere in the 10 degree window, you will find your MBT. Thanks, ethanol!

Attachment 1167267

Originally Posted by KingLT1

Heads/cam cars can make the same power not spinning the blower as hard. You would be gaining 70-100whp of power on the engine side, so you don't need to work the blower as hard. So if you wanted more power from where you are at, then you would do heads/cam vs spinning the blower even harder because the thrust bearing isn't likely going to tolerate much more. That is why your tuner said it's tapped out. The 2650 also doesn't hit as hard as the stock blower turned up, so that is helping as well. I am just putting this info out there for you as food for though in the event you want more power down the road. Either way you guys are fine for what you use the cars for.

Great stuff fellas! That’s why this forum rocks.