I think hes jus not able to move the cfm to build volocity spinning the turbo harder up top.The crank in a 6.0 and a 4.8 have diffrent characteristics deminsionally which I know your already aware of.The 4.8 having overall slower piston speeds "ecspecially around bdc/tdc" relative to a 6.0 with a longer stroke an short rod.Point being a smaller stroke long rod setup jus cant keep up pushing exhaust out in this particular setup under the high backpressure.The slower piston will hit a flow barrier of cfm which will limit volocity in the log manifold at some point.
I mean reversions gonna play a role too being that his cam is not designed with so much backpressure in mind..Really there is a good bit of difference between your set up and his.He needs to check BP in a few areas to see where it is imo.I would at least entertain the idea cause,for sure at some point a flow barrier will begin to hinder overall performance.

 

I see what you are saying about the same amount of back psi effecting the 4.8 more but I still would bet back psi is a enough lower on the 4.8/2.5'' id log. If anything it would be lower from the turbine alone. You have to remember I went low 10's with the old trick log that was a T style, and 2.5'' OD. That was with a tc76/68. One strange thing about my setup I have found when testing cams is even on the high back psi 68mm exh wheel with the log setup is when I have tightned up the LSA power is up, and spool is quicker. Aside from all of that I think the boost issue is on the compressor side, or waste gate related. There could also be a valve float issue. I'd be curious to see how it would run with my Isky 206/206, 111 lsa. That would also open the exhaust valve later in the stroke where piston velocity is higher.

 

That slo mo launch vid is exactly why I am building my own long bars. The nose needs to stay up to keep the pressure on the rear. Glad to hear you might make the shootout. I lot of smack has been talked about your truck by the L crowd that will be there.

 

Damn,Looks like the L crowd needs a lil education on factory ls engines 101 "specifically the truck chapter".
Why would they trash talk on a smaller truck motor that is capable of withstanding almost twice the power of their factory purpose built 5.4's.

 

Some good info in here. I'm 95% it's not a wastegate issue as the 76mm/75turbine would make 18psi without the smaller spring installed. This turbo 72/68turbine only made 15psi before I had to add more spring pressure. So the back pressure is higher no question. That said though need to mention when I locked the truck I seen 22-23psi for a good 2-3 seconds on the big end at 5k rpms. Kind of freaked me out, but no knock and a/f's stayed in the 11s. That makes me think the wastegate is fine but i'm not getting enough exhaust gas to spin the turbine to speeds to create more boost with this 72mm wheel under normal WOT acceleration. This sound right?

As far as keeping the bars level to ground I also read that and made these tabs a few weeks ago. I haven't welded them up yet as I wasn't 100% they would help. Whats your guys thoughts, these tabs would make the bars even with the ground to a half inch.

The 20's will be coming off soon. It wasn't that I loved them, only I really didn't have any other options with the big brakes up front. Today the smaller brakes get installed and I can get the measurements to bogart for some sexy d10's.

As far as the L camp, some guys don't like the LS camp period, some do. I respect fast L's, even stock clean ones. I'm sure most level headed L owners will respect me and my truck.

 

I wouldnt worry about the caltracs, they are doing their job, your front end isnt like mentioned..

 

Truck is just plain sick man!, to think these trucks are running times like this now a days is crazy! Like stock48 says i think some boost loss right before and during shifting is normal, i make the most boost right after a shift when it reloads it again. I was having the same problem as you too, i could turn the boost up as much as i wanted and it just changed the peak boost and that was it still kept the same amount for the most part going down the track. I had a lot of potential problems though: Stock LS6 springs, boost leaks at injector o-rings and issues with my JGS wastegate. Love your truck man, the 4.8 that could lol!

 

Well Rob....
Looks like the comp wheel has clocked out for the night huh?

Ball bearing 7668 Magnum in the mail and on its way!

To All:
KB Racing and Trick Performance Products are both Dealers for Magnum Turbos just give them a call if you would like to try one out. I am a sponsor on LS1Tech but these 2 guys sell my turbos on the truck side of the house.

 

im no pro, but it looks like once the cal tracs get loaded it its practically throwing the truck in the air, i understand this is supposed to be pushing the rear end into the ground but something doesnt seem right. if you watch the exact time that happens you can see the wheel speed go up. once this happens is when the front drops back down.

ive never played with cal tracs so i wouldnt know what to do to fix it, but i think thats a place to start...


either way great runs man that truck is a pioneer to turbo baby motors!

 

great times man! the truck is working great but you can still make some small improvements that will work even better.

i will reflect some on your suspension...

the front seems ok transferring but needs to be controlled by keeping the shocks extended for a longer period of time. for the rear you need some adjustable shocks to slow down the extension (the tires plant but they are unloading to quickly) also those drop hangers are hurting you. they raise the pivot point of the caltracs at too high of an angle and it also has your pinion angle pointing level or upward even with the shims they come with.