View Full Version : 3100 big port/valve top swap

07-20-2011, 01:56 AM
Needed to change the LIM gaskets on my 1996 Ciera and decided swap the heads and intake manifolds for the larger 3400 and later 3100 ones. This is a pretty popular swap in the N and W body communities, and I know of at least SilentWing's A body (1994 Ciera) with this swap. I used the heads and throttle body from a 2002 3400 Grand Am, and the upper and lower intake manifolds from a 2001 3100 Grand Prix (because I happened to throw the Grand Am manifolds on my sister's car before I started on my own, ha). To my knowledge, this is the first time that the more modern 56mm plate throttle body has been swapped in on an A body.
This is the front end of a 1996-1998 W or H body 3800 throttle body. This one in particular was off a 1996 LeSabre. I hacksawed this off a the junkyard, just after the MAF. As you can see, a short piece of correct-sized rubber intake hose has been attached to the hacksaw end. It's attached with some stuff from Home Depot called Stick 'n Seal. I plumbed this in ahead of the 2002 Grand Am throttle body with my Ciera's original MAF mounted in it, in lieu of the Ciera's original setup, wherein the MAF mounts in the throttle body.
This is how I tested the special MAF piece for measurement accuracy. Here, you can see the MAF in the center of the photo mounted into the throttle body. In the bottom right corner, you can see the air duct has been pulled off the air cleaner and the new MAF piece is plumbed in right ahead of the throttle body. With everything set up as pictured, I used my OBDII scan tool to measure the MAF reading for several different throttle position readings. Then, I moved the MAF out of the throttle body and into the new piece on the right, where the duct tape is in the picture. Then I stuck the duct tape over the hole in the throttle body where the MAF had been. I then measured MAF readings for the same TPS readings. My results showed very little disparity--less than 1%. My earlier attempt at an alternate MAF setup was the more obvious one--most mid-90's and up 60 degree engines have a MAF that is designed to be inline in the intake ducting. My sister's 1996 3100 Grand Prix has such a MAF. However, it gave large discrepancies in reading of up to 30%. Another option I considered was the 3300 MAF piece. It's much like the piece I sawed off the LeSabre, but bolted onto the throttle body as opposed to built into it. However this piece had a small airflow diameter and would have been restrictive. My piece's diameter was much larger than the throttle plate on the TB I put in.
Top end is disassembled. Ready to install 2002 Grand Am heads, with a fresh valve job. On the right you can see the throttle cable I used. I thought a 1996 3400 U-van cable might be a perfect fit and it was close but I still had to rig it a bit as it was a touch too long. The original throttle cable for these 1994-1996 3100 A-body cars is goofy and would have never worked, moral of the story is that you have to replace it with something. Anyways the big-valve heads go on just like the old ones, just remove and transfer any brackets (I had two).
The LIM is known to require just this one modification--the water pipe coming off the back of thermostat housing. On the old LIMs, this pipe goes on with a threaded fitting. On the new LIMs, it's a 'press-in' pipe. Pictured is the new LIM. I chopped the press-in pipe that came with this LIM down to an inch-long stub, then installed it back in its hold with fresh gray RTV. I took the old pipe (right of this picture) out the original manifold, and removed the threaded fitting off the pipe. I used about a 2-inch piece of correct-sized rubber water hose to join the stub in the manifold and the old pipe, which conveniently provides an inlet and outlet for the throttle body. Alternatively, others have used a 7/8" NPT tap on the new LIM and simply used the old pipe and fitting. My local hardware store stocked 3/4" NPT but not 7/8".
And the main consideration with the UIM is the EGR. The vertical-mount EGR that came with the manifold must be used, along with its tube to the exhaust manifold--the old tube won't work. You can see the thermostat housing plumbing below.
Wiring for IAC, TPS, MAF, IAT, etc. If you use the 56mm plate throttle body like I did, you must undo the jackets around these wires for all the plugs to reach.
New TPS has a different plug style but same three wires, right down the the colors. Just have to chop off old plug wire in the correct plug for the new TPS. You can also see the new throttle body plumbing here, a couple carefully chosen molded rubber hoses from AutoZone work well.
The U-van throttle cable was a bit long. I threaded it through the thing it goes in, out the hole at the end, and put an aluminum sleeve at the knob end of the cable to get rid of the slack. It works fine but is a bit sketchy for permanent use.
The intake duct that originally went to the 2002 Grand Am's throttle body must be used. I used Stick 'n Seal to attach my MAF rig to the end of that duct. And yeah, for the time being, some Home Depot dryer duct runs from the MAF to the original air cleaner.
One thing I did not grab from the Grand Am and need to get is the ventilation hose from the rear valve cover to the intake duct. That's another thing you need in order to use the new throttle body.
Car's been making the 50 mile round trip to work since if finished it last Thursday. I am really enjoying it. Feels about the same off the line but in the upper speeds and revs the difference is large. This car used to be a dog trying to quickly speed up from say cruising at 50 to 70 on the highway but now is much more responsive.

07-26-2011, 02:04 AM
Nice write up! It's good to see some attention to the late mode a-body cars. It couldn't be easy to pull the heads on that thing with the engine in the bay.

Not a critique, but an honest question. Did you consider doing the complete 3400 swap? ...or was the money just too much?

Ken T.

Duke George V
07-26-2011, 02:14 AM
I would think the costs involved aren't worth the modest power gains. A 3400 makes 185 hp and 205 ft-lbs, while a 2000+ 3100 is only 15 hp and 15 ft-lbs down, which itself is 10 hp and 10 ft-lbs over the 1994-1999 3100. By using the 2000+ top end, his engine is now essentially a 2000+ engine, since the bottom end didn't change again after the 1994 redesign. If he'd had an MFI engine, then yeah, it might have been worth the time and money. You can easily make up the power differential with a little porting work on the heads and intake. In a perfect world, I would have gone whole hog and got a ported head/intake set from WOT-Tech.

07-26-2011, 02:17 PM
Good write up, thanks!

08-03-2011, 02:25 AM
No, I never considered swapping the engine. Yes it would cost more, and more importantly I've never swapped an engine before. I had done heads in a 60-degree before though. Plus my engine block only has 130,000 miles on it, I have records for oil changes every single 3k since brand new, and oil reports have consistently put my wear metals at a fraction of average. So I felt no need to give that up. The reason I was opening the top end up in the first place was because I had to replace the LIM gaskets.

I would estimate the overall costs of the project around $650 : $150 to junk yard for heads, manifolds, TB and other parts. $150 to machine shop for valve job. $200 to RockAuto for gaskets, plugs, wires, all other replaceable top end parts. Of course, I got an exhaust manifold stud stuck in one of the new heads and had to take the head back off ($20 new gasket, $25 new set of head bolts), have a machine shop remove it ($15 and it took them a day) and, distraught over the manifold stud incident locked sister's keys in her Grand Prix that day ($70 for a locksmith!). OK, so maybe I can't blame that one on the car but I'll chalk another hundred or two up to 'life' in general--rough days and gas money.

I have really been getting a kick out of driving the car for the past couple weeks. The swap makes for a much more well-rounded motor. It always had torque but now it flows better, runs smoother, winds up quicker. You have to wonder, with the 3400 top end available in 1996, why GM didn't just build these engines this way to begin with.

08-03-2011, 07:46 PM
I've never swapped an engine either, but I looked into it for my Legacy GT and from what I could tell, a complete swap was a pain in the butt. I don't blame you for taking an easier route for some modest power gains.

Duke George V
08-03-2011, 10:53 PM
You have to wonder, with the 3400 top end available in 1996, why GM didn't just build these engines this way to begin with.

08-05-2011, 06:56 PM
Wow, you've done a lot of work and I like how scientific you are with the MAF flow readings. That's impressive!
The pictures aren't working now (it's a problem on my end) but hopefully I can see them later and have more comments! :)

08-07-2011, 03:24 PM
You have to wonder, with the 3400 top end available in 1996, why GM didn't just build these engines this way to begin with.

They did, but it didn't start until '00. I guess they had a crap-ton of small port intakes they wanted to use up.

08-26-2011, 04:20 AM
So to be clear on this for people like myself who don't know a ton about these things. All the part swapping done here netted around 10 HP/torque over a stock 3100 engine from that year range?

@Duke George V: Would porting heads/intake like you suggest give a similar or more of a gain? And if you know, how much does something like that usually cost to have done?

Duke George V
08-26-2011, 04:54 AM
WOT-Tech (http://www.wot-tech.com/shop/) is the 60degreev6.com performance parts store. They can sell you heads and intakes that have already been ported. The "small port" intake and heads your engine has are considered sub-par by the community. It's always advised that any performance builds start with the big port swap and go from there. The 10 hp/tq is just an estimate based on the listed power levels for the 94-99 and 2000+ 3100 engines. The difference is actually closer to 15 hp and 10 tq, but I was being conservative since Oklahoma is using the stock computer tune. Tuning the computer/porting the heads and intake will bump that up a bit. I think porting the big port stuff gets you pretty close to stock 3400 power (185 hp/205 tq), maybe even more. Keep in mind that there is also little to no fuel economy penalty. In fact, once the novelty wears off, I'd wager that his fuel economy may even rise, since the engine won't have to work as hard as it did before to move the car around.

08-26-2011, 11:13 AM
Thanks for the fast response, wish I had seen last night ;)

So would the big port swap be taking the heads/intake from a 3400 and putting them on the 3100...? Pretty curious on this and if its something I can do, tons of these engines in the yard near here and would be interested in doing this to my Ciera if I'm able

08-29-2011, 12:21 AM
Not to double post but its been a few days. ;)

I've been reading and trying to figure out what I need to pick up. I pulled the throttle body off an '01 grand am(?) that had a 3400 in it. I assume this is a 56mm TB versus my stock 52. Some confirmation there would be great.

If I under stand this correctly, I can pull the upper/lower intake off that 3400 and these will bolt straight to my 3100? Or will I also need newer heads from that same 3400 or a newer 3100? Not very sure on this part. If I can just grab the intake and that bolts in I may go that route for now. The engine in that car still had upper/lower intakes and its EGR valve, which I'd have to pull too.

That would leave me looking at the throttle cable since mine would be too short? Not very sure what the best way to handle that is.

When swapping the intakes, since my LIM was replaced a year ago can I re-use that gasket or will I have to get another new one?

Thanks for any help :)

Duke George V
08-29-2011, 04:02 AM
- 3400 throttle body is 56 mm.
- Using your stock heads won't be nearly as beneficial as using the 3400 heads.
- You need to use your stock EGR valve with an adapter, since the 3400 EGR isn't compatible with your wiring or computer. I'm pretty sure WOT-Tech sells a 96-99 EGR adapter for the big port swap.
- Best match on the throttle cable is a '96 U van. It has to be '96, since that was the only year the first-gen U platform had the 3400, and the platform was redesigned in '97 based on the W platform instead of the A.
- Gaskets are one-time use.
- If you need more in-depth information, give 60degreev6.com a once-over.

08-29-2011, 04:07 AM
Alright, been reading over there a little bit.
Thanks for the information/confirmation and I'll have to keep my eyes open for a 96 U van then when I'm at the yard next.

09-25-2011, 03:45 PM
Hey Theri, I just came across this--been busy with school for the past month. I thought I would make a few comments:

The manifolds-only swap is neat too. Not as good as the whole thing but I actually did it on my sister's 1996 3100 Grand Prix right before I did the full swap on my car. The power difference is noticeable.

Yes it's only a net 10/15 difference or so but it 'feels' really good.

What year are you driving? Duke George I used the 2002 Grand Am EGR and its tube on my car, not the old EGR with an adapter.

I used a 1996 U van throttle cable on my car, threaded it through the throttle cable assembly (where they attach) on the throttle body, and then put an aluminum sleeve from Home Depot on the end of the cable just before the knob to take up the slack between the throttle cable assembly and the knob.

You want to buy new lower intake manifold bolts.

See my MAF setup? I had driven the car to Montgomery AL a couple months ago and on a humid day the stik 'n' seal bond holding that piece of hose to the hacksawed LeSabre MAF piece failed. My aunt, grandfather and I came up with a better solution at the kitchen table so I could get back to ATL the next day. I glued a piece of 3" diameter PVC pipe to the outlet end of the MAF piece (the rubber piece pictured is on the outlet end). Then I tapered the other end of the PVC with a file and it fit into the intake hose to the TB. That's the intake hose that specifically came with whatever TB you're using, that is, in your case, the Grand Am. I still have dryer duct coming off the intake end of the MAF piece and going to the stock air cleaner...

Which leads me to my last point, which is that a cold air intake is on my to-do list. As well as a good tune.

Good luck, ask me any questions, I'll check this regularly.

09-25-2011, 09:01 PM
Late posting is always better than no posting ;)

I'm probably still going to do this but with how the weather is now it's too late in the year for me to be willing to do a tear down outside(rains pretty much everyday now). So I'm thinking I'll do a swap of the heads/intake/tb next year when the weather is nice. At least that is the plan right now.

I think we're driving the same car, 96 Oldsmobile Ciera with the 3100, mine has more miles though at 158k.

09-30-2011, 12:08 AM
Sounds good.

By the way, I would be glad to make the custom MAF setup if you're willing to spend 10 or 15 bucks to cover my parts and shipping.

Doc Salvage
10-22-2011, 11:01 PM
Very interesting info I haven't seen before on the 60 degree v6, thanks for the posting guys!