2014 Sierra 6.2 Whipple 2.9 Low Boost?

[Jjblur2003]

I just installed a whipple 2.9 on my sierra. Running a 3.75 pulley. Other mods are 1 7/8 headers, tsp stage 2 630 630 218 224 113. No cats borla xr-1. Tuner tuned really conservative due to me towing but it still seemed low. Dyno before with everything but blower was 413hp 460 now its 500 565. Im only seeing 6 lbs boost on mechanical. Everywhere I have read that pulley should be closer to 10 psi. Am I wrong or could it be the bypass actuator? Thanks guys

[CamGTP]

Headers and the camshaft will reduce boost pressure because boost is a measure of restriction and you have way less than a stock engine.

 

I could see 6-7psi with the mods you have done. If I was looking at the right blower on the whipple site, they did a test on a stock engine and it only made like 7-8psi.

 

Suppose you can smoke test for vacuum leaks if you want.

 

Peak power numbers are cool for bragging rights and facebook posts but I'd be more focused on the power under the curve. I bet you gained tons of torque/hp throughout the rev range compared to the header/cam setup.

[Jjblur2003]

I agree on the peak numbers and yes it pulls way harder. The cam only has roughly 4 degrees of overlap if my numbers are correct which isnt much even for a blower. Im just trying to figure out if I have an issue with the bypass or its actually right. Seems like peak numbers and boost should be higher. I think the 4.00 pulley is the stock size. Im at 3.75. Sooo......

[truckguy82]

Sounds about right to me

 

think of it this way, turbo’s and superchargers are not rated in psi, they are rated in hp.

 

If you put a gt350rs on a honda d series, it’ll take 25 psi to make 350whp. Slap it on a gmt 900 5.3L, it’ll take 4psi. Still flowing the same amount with both applications.

 

this is what’s happening in your case. Your pulley is hp rated, it just takes less pressure to achieve that flow rate because of your mods.

[Jjblur2003]

I understand for sure. Spoke to whipple and they said with all my mods and cam spec I should be seeing at least 8-9 lbs. Its got me wondering. Stock is 11 with that pulley. 

[truckguy82]

Did they ask you what motor?

 

that would seem right on point with a 5.3

[truckguy82]

I’m not a supercharger expert, more turbo’s and general boost related.

 

but if you are losing air, yeah sounds like bypass valve would be the culprit.

 

Just an fyi, i did do a little research, on a guy that has an lt4 and took off his stock blower and put on a tvs 2300. He was making 11psi with a 3.15 inch pulley.

 

Considering your motor, without any blower attached, probably makes way more power than an NA lt4.

 

If that’s the case, I fail to see how a 3.75” pulley is supposed to make 11psi on a stock l86.

[Jjblur2003]

Yes they did. They said put a vacuum in bypass actuator and see if it holds and isnt malfunctioning. Also this 2.9 whipple displaces considerably more air per revolution than a 2300. 

[truckguy82]

Oh I didn’t even realize it was a 2.9!

 

i’ve been doing all this reasearch on 2.3’s and it seems right on the money.

 

yeah i’d say you have a problem. Nice blower!

[truckguy82]

Fyi, performancetrucks.net is a better place for your question.

 

It’s more oriented towards gear heads with heavy mods