3500 plenum on a 3400

[Signul_9]

I was directed to this site for information about swapping a 3400 plenum with a 3500 one. I've been searching around the forum and have seen threads mentioning this, but they have been kind of vague. Can someone tell me what swapping the plenum involves, and what sort of gains I could expect? If not, can you point me to a thread that discusses this in length? Thanks!

[SappySE107]

Within 3 weeks I will have a picture walkthrough and a list of what you need. I will have adapters to use either your stock throttlebody or one that I sell on the store if you want to upgrade that at the same time. There will be dyno results as well for the plenum (ported) that I sell but you will get a decent idea what a stocker would do. Not trying to push my stuff, but I would definetly consider porting it yourself or having someone else port it as the ports are a lot smaller than they should be from the factory. Not hard to do:P

For now, I know you will need to use the MAP sensor off the 3500 (might be the same as what you already have?), grind a bit on the TB neck to clear the fuel pressure regulator, and seal up the IAC port on the 3500 or add a nipple to it for another vacuum line.

v6ho and gpse3400 have both done this swap, and possibly others as well. You could try domesticrew.com as well but a lot of those guys are on this site too so either way we will get it all covered

Welcome to the site!

[Nightingale]

not to sidetrack, but could you swap a complete 3500 top end onto a gen 2 block? Probably still have to use 3400 timing cover and ps pump though rather than 3500 pieces.

[SappySE107]

Possibly. I don't see why not if the 3500 heads bolt to a 3400 block.

[Nightingale]

hmmm now only to find a dead 3500 engine (spun bearing/thrown rod).

[Signul_9]

Thanks for the info. I'll be looking forward to your post. I know my way around an engine, but am way less experienced in a lot of the stuff I've been reading around here. This site is much more technical than the one I usually visit. I guess you can say I'm a newb when it comes to anything that doesn't just bolt on heh. Now that I've explained how newbish I am, can someone explain why the 3500 plenum is better than the stock 3400?

[SappySE107]

There are no runners in the 3500 plenum, the area inside the plenum is larger, and the TB mount runs like a tube to the middle of the plenum to help give equal distribution to all cylinders. When you change the runner length, you change the powerband to higher RPM. However, it seems that their design doesn't exactly hurt the low end, though the dyno will show us whats going on for sure. Stock, the 3500 plenum flows worse than the 3400 plenum, but because its got a larger plenum area, the ability to run up to 65mm (maybe 66) without modification, and the transition area from plenum area to runner is more like a ram air setup, it still has given people more power. Thats why I say to port it, cause the flow then goes higher than the 3400 plenum plus you get all the other benefits.

[torq455]

How much for one of those stock 3500 UIM?

[onefastV6]

How much for one of those stock 3500 UIM?

According to the store
$50 for the porting and $150 for the core.

[SappySE107]

You can get a stock one from GMPD for 124 shipped.

[Guest]

https://www.domesticcrew.com

Midnightriderz has completed the 3500 plenum swap, he used a 4.3 TB from a late model CPI equipped S-10.

I believe he's also on here.

[SappySE107]

Yup, but I don't recommend using a 70mm tb due to the throttle resolution. It is an option though. You should bore out the plenum TB opening for it if you go that large.

[torq455]

Yeah, there are LS6's out there making over 550 hp+ and still using the stock 75mm TB.

[MidnightriderZ24]

man, every1 always forgets about me... lol

[Guest]

man, every1 always forgets about me... lol

Look up, I didn't.