3.6 plastic plenum on a 3.2 to 3.4 engine with motronic
 

Hi Gentlemen,

I have a 3.2 to 3.4 build this spring. 9.8:1 CR max morirz, GT3 Pankle rods, crank rod journals turned down by Marine, (20/21 or 993SS cams?) custom anti-reversion headers, chipped, etc. I am aware that running the 3.6 plastic plenum in lieu of the stock 3.2 plenum is a good way to go.

I'll need the 3.2 to 3.6 intake stud adapters, I know where a set is :), are the 3.6 plenum, intakes, injectors, rails used with the 3.2 throttle body and ancillaries, or does one maintain the 3.2 parts and swap the plenum and intake only? Or should/can one adapt the 3.6 system to run off the 3.2 motronics?

Any advise on the most straight forward path to mating the superior plastic plenum to a 3.2 system is appreciated.

All the best,
Anna

When I looked into this a few years ago I was told you really need to use engine management and ITBs to get the benefits of the 3.6 plenum.

With bigger displacement and more aggressive cams, your engine should be in the 280-300Hp range. Obviously it needs to breathe better. The original 3.2 intake is not optimal for several reasons. The design of it causes the flow to each cylinder to be distributed very unevenly, meaning that each cylinder will draw different amount of air. Obviously each cylinder will contribute with different Hp numbers. Not an ideal situation. The way around that is to extrude hone and flow match each intake runner, and also bore out the throttle body. This is commonly (and successfully) done on a lot of tuned 3.2L motors. However, it's not cheap, around $800 for the extrude honing and around $200 for boring out the throttle body.
The 993 plastic intake has not only a bigger internal diameter, but also a much more even distribution of the air flow to each cylinder. And a bigger throttle body. Actually, the 993 plastic intake has a bigger tuning potential than the 993 VarioRam intake.
As for the original 3.2L Motronic ECU, you would obviously need a new chip (Steve Wong) for the 3.4L build, no matter what intake you chose. With the 993 intake you can chose between the old 3.2L fuel injectors, or use the 993 injectors. The only thing the old Motronic is not set up to do, is to operate the resonance flap in the intake. You can chose to leave it open and lose some low end torque, or chose to leave it closed and lose some top end HP. Or you can get Steve Wong to program the chip to drive an additional rpm based relay to operate the resonance flap. Or have a switch on the dash board.
The 996 Turbo used the 993 plastic intake (with a blocked off resonance flap). For even better performance you can get an IPD plenum, or like I did, make one yourself.

If you really want to wind up that engine, and why wouldn't you with Pankl titanium rods, you need to remove the 3.2L intake. Look at numerous dyno curves for engines wearing that intake and you can see pretty much all of them hits a wall at around 6200 rpm.

If you're sold on the idea of the 3.6L plastic intake? You'd be wise to talk with Rothsport. They've obviously done quite a lot of development work with this setup.

Welcome to Rothsport Racing - Engine Products

Thanks Kevin, yes, I'm trying to listen more and narrow my focus... hard for me...rather than get hung up on possibilities and sliding down the slippery slope..

I'm told best route for 3.2 would be my 9.8:1 98mm mahles, ARP rod bolts, SW chip, premuffler in place of cat and a 1in 1 out sport muffler and have a good spirited streetable set up.

For the Rothsport type injection, I have a 3.5 kit of parts that would be a good fit and a fellow Pelican :) who is willing to help pull together a system simular to Rothsports. The 3.5 kit for that consists of:

- 3.2 case, spigots to be bored for 100mm cylinders
- 3.2 crank which just came back from Marine Crankshaft, with rod journals turned down to 3.0 spec, cross drilled, knife edged, center main grooved/drilled, balanced, Ion-plasma-nitrate hardened, etc.
- The GT3 Pankl Titanium rods 130mm, will need to add cylinder base shims and machine rods for 23mm pin
- 930 turbo oil pump
- 3.6 Mahle P/C
- The 964 heads
- Looking at GE60 or GE80 cams???
- 964 distributer converted to run standalone
- 3.2 Fan assembly
- 9 bolt light weight flywheel and centerforce clutch

This 3.5 with a Rothsport-esque ITB set up and a well sorted scavenging exhaust should spin up fast and live at a 7200 rev limit.

Motronic alone will leave substantial hp on the table. And with this kind of engine (with well-flowing cams etc) MAF is not optimal also because of the intake pulsation.
As we discussed over PM before, standalone is pretty much the only solution that will extrack maximum power your hardware allows. And with the VEMS PnP I can offer, it is pretty much the best value you can get (even compared to MS as VEMS comes with wideband which you would need to buy with MS).

And besides, with VEMS you don't need any of the MSD stuff for ignition, it will allow you to run ANY ignition system you like without "unlocking" anything or paying more.

Hi Raceboy, yep, we discussed the Vems set up for the Vram engine I bought that has no DME nor harness, if I keep that engine I'll be tapping you for the turnkey solution we discussed. You've been very helpful :)

Regarding the stand alone dizzy, I have that on the shelf, and the gentleman I got it from would be happy to have it back :)

Vems on the 3.5, if I go the 3.5 route, would be signaling to a 964/993 dizzy and coil packs directly - correct?

Yes, you will be controlling 964/993 dizzy directly.

Hello Fly, do you have any more details on the plenum you had made? I've bought the 2x 993 plastic intake halves and looking for thoughts on how best to implement the resonance flap - i.e. are there alternatives to the 993 r/flap setup

Forgot to mention I'm already running Motec M84

sp_cs, I just replicated the Y-shaped IPD plenum inside of the T-shaped 993 plenum, by shaping an aluminum plate and bolt it inside of the plastic plenum. It probably cost me $5... I did the same thing with my 996.

3.6 plastic plenum on a 3.2 to 3.4 engine with motronic
 

Thanks, a pic would be really beneficial when you get a chance. OP - sorry for the de-rail

ETA - mine too is a 3.4, with dc20 cams and standard bored throttle body. About to be dismantled shortly and reassembled with Gt3 crank, custom rods, William Knight spec cams, additional piston-valve relief and maybe ITbs.

I have some 993SS cams for sale, brand new.