m112 no boost after cam heads swap
 

Sorry guys I'm new to the site and to FI. I just finished up a cam, heads, headers, ory upgrade in my 04 Joe Gibbs rcsb 5.3. After the work I took it to be dyno tuned...well when I got there I had no boost and truck only made 221 hp. The truck was making about 5 psi. I think the motor work gained more efficiency than the M112 could keep up with. Is that possible? and if so what would be the best way to offset this? Any thoughts would be helpful thanks alot.

Smaller pulley.

Those numbers are real low regardless. Did you have it dynoed before? what pulley is on it now? I think they came stock with a 3.4 or maybe even bigger.

Pretty sure its a 3.9, and no it was never dyno'd before. And I'm not sure how small to go on the pulley. I would like to make close to 10 psi but not over.

3.0" pulley has me at 10psi with my mods (5.3, gt2-3 cam, LTs with ORY, CAI, Magnaflow muffler, untouched 862 heads)

This thread is so bizarre that I have a hard time believing its serious. How could a shop not point it out to you if the problem was no boost due to the pulley bein too large. You're tuner should be knowledgable about this stuff, or you really need to find a new tuner.

Even still... I have a hard time believing that with those mods you would go from boost (even as little as 5#) to steady vacuum. And even if you did your numbers would be higher than 221.

It sounds to me like something else is wrong. Maybe a boost leak. However, I am gonna go theoretical here. You can gain a ton of efficiency with those and other mods which I guess could actually make the blower a restriction if its not turning fast enough which would explain a low power level. Try pulleying down just a little bit at a time and see what happens. 3" pulley is most likely the right size for the job, but not a sure thing. Also seems like the tuner is a bit questionable.

Agreed, numbers are way low. For comparison, I was 258/270 with just muffler, CAI and tune.

intake gaskets are easily cut or dammaged while getting installed. You really have to pay attention while it's getting set on the heads.

Manifold torqued evenly?
Gaskets ok?
vacuum ports all closed off or plugged in?

Take it back to the tuner and use a can of brake cleaner to check for leaks. Watch the log on the fuel trims to change while spraying around the manifold.

Are you heads good also?

Assuming the heads are good they were a set of 799 heads ported by PRC...the supercharger set in without trouble so I don't think the gaskets were damaged, but it's a possibility. I double checked all the hoses and ports everything seems to be hooked up. Possibly a bypass valve stuck open or something like that. Thanks for all the input this site is awesome and I'm sure it'll get better as I figure out how to use it.

little different... but w/ my lq9, ls6 cam, stock heads, mids, and slipping trans i put down just about 400 on a base tune. I don't see the stock pulley being your problem.