Howdy - bought an aluminium lower intake manifold for the Pentastar 3.6.. which is plastic OEM.

First time buying something like this, turns out the casting was VERY rough. Started sanding to clean up casting, few rough marks in the runners, figured may as well port a little since I'm here (first time).
Well - I messed up and sanding oned of the runner lips quite thin. (0.8 - 1.0mm). My main concern is the lip cracking and being sucked into the engine... I.E. catastrophic failure.

Concerable facts;
* OEM manifold is plastic - this is an upgraded aluminium version
* Thinnest wall is ~ 1.0mm with a very small spot reading 0.8mm
* Lip thinning is at the intersection of the upper manifold
* Upper manifold runner are smaller and thus obstruct/block the lower manifold runners (I am planning on porting these to potentially flush with lower manifold)
* Runners will be sanded to 600 grit + light polish
* Engine is NA but I am planning on boosting @ ~4-6 PSI
* AI is telling me, I'm probably fine, but if I'm I paranoid I could reinforce the walls externally using JB Weld

Not really sure what to do at this point, I'm planning on sanding the rest to match and sending it. With the thinning being on top I could at least pull the upper manifold and monitor it closely for cracks... what would you do?

- Dummy

 

Though it is a little thin.... It is Aluminum .... So I would not go any further and just install the seals and send it....
If it does crack them you can remove the intake a weld it up and start over...

Good Luck
Keep us posted... Want to know how it handles the boost????
Cheers

 

Thanks for the quick reply Cowboy, good idea on the welding too - this makes me feel safer as long as I monitor it closely. Given the Bathtub curve...



Chances of failure are in early/life late - I will plan to check this manifold on every oil change in the long run, but getting started, how often would you check it?

 

If its running fine, dont mess with it... If it holds the boost, it holds the boost, no need to disturb it.... But for the boost you may want to start low and sneak up on adding more...
If it knocks the seal out, you will know....
Just my opinion...

 

Can you elaborate? When you say start low - how many PSI? Would you maybe even try first before boost to see how well the system holds? From what I understand the pentastar 3.6l can only handle (safely) max 6 PSI boost on stock internals, about x1.4 atmospheric pressure. When you say "knock the seals" are we just talking about rupturing the rubber and therefore eliminating a good seal - is there any risk of sucking in the gasket? I am confused on how the thickness of this wall would affect that without the wall itself breaking?

Thanks for all the info, first time doing all this

 

The thing with boost is you don’t need to go for the last mm in your porting of the intake. I would knock the high spots down and even the general finish along with port matching the intake to heads. As far as having gone to far there’s a couple things you could do, the first is have the intake welded where you think it’s to thin and the second is install it and run it, it will tell you if it’s to thin or not. You might not have the problem you think you do. I’d run it!
If You do decide to reinforce it with JB Weld or something else you want to remember that will be a contamination if you decide to have it welded later…
Just run it!

 

Would you thin the other runners as well (maybe not as much - if so, what is a 'safe' thickness in MM) or try to avoid those lips as much as possible and truly only port the material inside? New to this.

 

Are the runners wet or dry, will they have fuel running through them?

 

Dry

 

start with the lower PSI,
blow out the seal,
you will know if and when it breaks the seal.. it may Blow out, Crack, or just flex..
you could do the NOS and forgo the boost. That would be up to you and what your plan was… but it sounded as if you were going to boost your project in the beginning..
good luck and keep us posted!!
cheers

 

Well if this is a dry manifold you would want it on the smoother side but you don’t need to make it perfectly smooth, I would use a finer grit when you are getting close to the bottom of the texture. Being under boost the small amount you will be able to increase the size of the runners will not necessarily make more power. Air velocity does make a difference and having all runners with the same capability does make a difference. Remember you can always work it a little more but going too far will cost you more.

So you don’t need to worry last imperfection right now make them better, there is plenty else that needs attention in the V6 if you’re going to turbocharge it like ring gaps or you will be having severe piston failure issues.