First, the build that the kit is installed on:

2001 GMC Yukon: LS6 block, Eagle 4" crank, Crower 6.125" rods, Diamond -7cc pistons, AFR 225 72cc heads with 8017 springs, Siemens 60# inj, LPE GT2-3 cam, Comp 850 lifters, Crane 1.7 Gold Race rockers, JBA Ti Ceramic coated hdrs, Magnaflow catted y-pipe, Corsa Touring catback, Alkycontrol meth inj, Volant CAI, FLT Level 4 4L60e, Yank TT2600, Auburn Pro LSD w/ 3.90 gears, 20x9" Denalis Repros/275-45R20 General UHPs.

Got the 122HH upgrade installed and tuned. Although we requested the kit be pulley'd for 10# peak boost, the 3.0" pulley that it came with gave 6.5# boost and 507rwhp/515rwtq. Not a bad start and we were looking forward to a pulley swap to get our 10# and 600/600!

We were shipped a 2.85" pulley and got a whopping 8# boost. We picked up 40rwtq down low but actually lost some up top ? The tune is dialed in, so we are at a loss to determine where the problem lies. We removed the CAI to see what that would do...no change. We discussed the MAF being a restriction but there are many folks here putting down 600rwhp and running the 85mm MAF, so we don't believe that is the issue. We are going to go to an 8" balancer/pulley to see what that picks up, but it still does not answer what is going on with the top end.

Two questions:

1) Anyone have any thoughts on the missing HP?

2) What are the options for 8" balancer/pulleys? I know about ECS, and ASP is modifying oem balancers to 8"...does ATI make one, any others?

 

Innovators West makes an 8" balancer that is SFI spec, this will give you a 10% overdrive. I also use the Lingenfelter 100mm Maf to ensure you dont have a restriction there. It is easy to check and see if you have a vacuum between the MAF and Throttle Body above .5" HG. What size Throttle Body are you using?

 

NW 90mm TB...have access to LPE 100mm MAF, but after reading posts here it doesn't seem like it would be the issue. Might be worth picking up just the same,,,

 

Its called a stroker motor. In there lies your issue. You went from a small stroke to a big arm. Dont expect the results to be the same up top. You took your powerband and shifted it 500 rpms sooner, which means the setup will die out 500 rpms sooner. Nothing you can do about it.

R

 

Rick, I get the difference between the 347 & 383 but when comparing 383 at 6.5# and 8# boost, shouldn't the gains be across the board when upping the boost? With 25% more boost I'm seeing zero top end increase.

 

I'm sure I will take a beating for asking this, but......Can the blower feed that size engine with your head/cam combo and still be efficient at the boost level you are going for?

You sure your not getting any belt slip?
Fuel pressure good?

 

Suppose that it could be outside of its efficiency range? I had not suspected that until you mentioned it...

No slip yet, and that is the reason for changing the crank pulley next instead of a smaller snout pulley--so as not to induce any slip. Good question on the fuel pressure--will have to check for drop--although I believe it is okay. However we are running an Alkycontrol system and maintaining good AFR throughout, so it may be possible that we are masking a pressure drop with the meth.

 

When you drop the power band down, and dont change the cam, things change. Upping the boost does not always mean a gain, it just means more heat in that type of blower. You need to see your old boost graph versus the new boost graph to really know. You are only talking a peak number of boost. It hits in all different spots on the graph with a blower like that. A dyno is a representation of how far up can you make power, hence the reason why you see the difference up top. Because its just that, a dyno. If you can continue to make power up top effectivley, then you show more on a dyno. Thats all. It means nothing more than that. If you make more down low and through the area where it only matters, then you are doing better. Building a setup for a truck with only a peak dyno number in mind will only give you a disapointing result in how it runs. Sure its fun to see a number, but if I were you and I made a ton more power down low, I would be happier with this setup than the last.

R

 

The issue is being able to spin the blower with the drive system and feed the stroker. The inlet forward design allows you to overdrive the rear pulley's and feed the bigger engines no problem. Take a look at a few of the Inlet Forward design 122's going together right now in this section.

 

Also the loss in power does not mean your truck is slower. Alot of time the more HP dyno vehicle looses when its race time.