3500 plenum porting for 3400 install questions.

[KFLO 93 GT]

So I just scored a 3500 plenum with map sensor for $41 shipped and I've got some questions.

First of all - what porting needs to be done to make this outflow the 3400 plenum? From the photos I'm guessing the outlet ports need to be opened up a bit - but I figured I'd ask here first.

Next question, for gasketing purposes - just get another set of 3400 upper gaskets?

I'm aware of the grinding to clear the FPR as well of the fact that I'll need the tb adapter from TCE. I'll do the porting work myself and with my discount on parts from work I should be able to get this thing on for under $100.

Last question, my tune doesn't take this mod into account - how dire is it that I get it retuned after the addition of the 3500 upper?

[Barry]

My did not change much at all, if at all. I swapped from a stock 3100 (lg8) uim to lx9 though. I had the 65mm TB from the get go.

I really like the stock 3500 UIM gaskets. There metal with formed orings, and are reusable.

As for FPR grinding, I have 2 washers under my fuel rail with 3800 injectors and I only had to sand the casting flash off, nothing drastic

[KFLO 93 GT]

I've currently got an '04 3400 upper, port matched to my 65mm TCE unit. So I may not see much of a difference either... but for $100 it gives me something to do for a while and helps keep my mind off of the SC project...

Now I wish I had some 1/2" phenolic spacers instead of these super thick ones...

[3X00-Modified]

Have the spacers milled down like I did. I had the groves for the rubber O-rings milled out so I could use just the standard 3500 rubber/metal upper gaskets, two sets. Oh yeah if you can 3500 upper gaskets are metal, but that set is only obtainable if you get a full GM 3500 intake set... including lowers. You have to hog out quite a bit on the lower to match them to the gaskets though just a FYI, and for the 3500 I think just a smoothing of the neck as far as you can get in and then open up the ports to match the upper gasket and just be sure to bevel the inside edge, because if you didn't hold it in your hand already, the upper is no longer a runner design, its just a big box with 6 holes, and the metal in that area is only about 1/4" thick so once opened up you just need to make sure that the flow side of the opening is very smooth, aka Bell mouthed for a better explanation.

Other than that there really isn't much more you can do.

I ran a 3500 upper then swapped to a 3400 upper ported back in 08 and saw MAYBE 1 tenth... But I had inconstant wheel spin that year. So really my results were inconclusive. I prefer the 3500 upper since it dumps the air right in the middle of the plenum and I also have the TCE TB adapter which comes with a port for nitrous so it's a much better install than just stuck in my intake tube.

[KFLO 93 GT]

Sweet, that's the kind of info I was looking for. I was aware the 3500 plenum is a runnerless design, but I don't have mine here yet - supposed to arrive on Friday.

So does it take any special kind of mill to mill these phenolic spacers? I had been thinking about seeing if anyone with a water jet could cut both sides in half effectively leaving me with 2 sets of .625" spacers.

[99GaGT3X00]

I had been thinking about seeing if anyone with a water jet could cut both sides in half effectively leaving me with 2 sets of .625" spacers.

you got a set of the 1 1/4 spacers too. got a set i had with the 3400 uim which now reside in my tool chest.

[3X00-Modified]

Sweet, that's the kind of info I was looking for. I was aware the 3500 plenum is a runnerless design, but I don't have mine here yet - supposed to arrive on Friday.

So does it take any special kind of mill to mill these phenolic spacers? I had been thinking about seeing if anyone with a water jet could cut both sides in half effectively leaving me with 2 sets of .625" spacers.

I had a guy at my machine shop with a Bridgeport do it for me with a standard end-mill... He just shaved off the amount I wanted from both sides. I'm not so sure a water-jet would produce a nice straight cut to get both sides usable without having to be surfaced afterward, which would then end up with a much thinner spacer.

[KFLO 93 GT]

Yeah, I bought this set off of Chris88CL who may have said they were 1" and then I measured them as 1.25... but whatever, no worries.

Jon - in the event that nobody around here wants to mess with milling these down - how much do you think your guy would charge?

[99GaGT3X00]

yeah i was told they were 1" then i measured them one day when i was figuring out what length bolts i needed. wasn't really concerned about the extra thickness.
at the time i was looking for something in the 3/4 range. kind of a mute point now unless i enlarge the holes for the ported 3500 uim

[3X00-Modified]

Just pay for the shipping and I'll have them done if you want.

For your sake though it may not be a bad idea to attempt to split them first. I'm not positive on which method would be best though. I would hate to see that much material lost.

[Kris GTwhat?]

Yea I'm with jon on this one. That way you have technically two sets, which you can do with what you want later

[KFLO 93 GT]

2 sets would be ideal so that I could recoup my losses by selling a set.

Guess I'll call around sometime when I get the chance... my worry is that not many around here have dealt with Phenolic. Maybe I'll do some google searching too.

Next question - does anyone know where to buy the old style MAP to knew style MAP pigtail connector/converter? The article on WOT-TECH mentions one - so hopefully there is such a thing, it'd be nice to plug and play rather than cut and splice.

[Chad91GTZ]

Phenolic isnt as uncommon as you think. I have some experience working with it. Its not difficult to machine. You have to find a happy center between cutter speed, and not burning the material. To slow and you just make dust, and wear out your tooling quickly, to fast and you burn it. You want a good chip size, but you shouldnt be able to smell it burning.

As I said, its rough on tooling, so if somone is gonna do it for you, and its not a friend doing it at work as a government work job, (with somone elses tooling) their price wont be cheap, especially to evenly chop one in half, eating up any profit from selling the set you just created.

Posted telepathically from my HTC EVO using Tapatalk

[3X00-Modified]

I spliced mine in, I did not know about an old to new adapter.

[Cliff8928]

Next question - does anyone know where to buy the old style MAP to knew style MAP pigtail connector/converter? The article on WOT-TECH mentions one - so hopefully there is such a thing, it'd be nice to plug and play rather than cut and splice.

Well, I can probably get that done if you want and don't need it real soon.. What cars are the MAP sensors coming off of?