Newb wants the basics for performance.

[IsaacHayes]

http://www.magnaflow.com/wideopen/performdata.asp

3100 is 191 cubic inches. Then with performance mods, say big port top end you have around 175hp.

150-200 CID - 100 to 150 HP = 2" to 2-1/4"
200-250 CID - 100 to 200 HP = 2-1/4" to 2-1/2"

According to that we are above the 150hp just being stock. So 2.25" will work, but 2.5" would be best and give you room for later mods like a full 3400 or 3500, cam, whatever. Either will work just fine. Mandrel 2.25" is probably better than crush bent 2.5" though. So Mandrel for the win, and if you can't get mandrel, then go 2.5".

Several people on here have put 2.5" on a STOCK 3100 and said the gains were very good. I plan to go 2.5" sometime. My 3100 I will estimate at least around 175hp since I have the big port intakes, and even better 3500 plenum. I don't have the slightly bigger intake valves but its a very small size difference so I don't know how bad that hurts flow.

2.5" shouldn't be too big and yet still have plenty of room for more power up until 300 or more HP.

[92_lumina]

I would go with 2.5". Get a new downpipe made as the stock is double walled and very tiny inside. Get a highflow cat, and a good straight through muffler (dynomax ultraflo, or hooker aerochamber). Mandrel bent pipe if you can.

For exhaust manifolds you could get the 2004 Impala 3400 ones, they are logs but really bigger inside. Also any newer 3x00 exhaust manifolds will have a better rear instead of a log, but you having a 98 might already have the short runner rear manifold.

Headers of course would be best but put you over budget.

Why 2.5? Its just a 3100

[IsaacHayes]

I would go with 2.5". Get a new downpipe made as the stock is double walled and very tiny inside. Get a highflow cat, and a good straight through muffler (dynomax ultraflo, or hooker aerochamber). Mandrel bent pipe if you can.

For exhaust manifolds you could get the 2004 Impala 3400 ones, they are logs but really bigger inside. Also any newer 3x00 exhaust manifolds will have a better rear instead of a log, but you having a 98 might already have the short runner rear manifold.

Headers of course would be best but put you over budget.

[92_lumina]

2 1/4 in. for what you are doing.

[oldsman105]

ok what size exhaust would you recommend for the upgrade? I haven't had the century on the lift to see what it came with.

[92_lumina]

Can you get that stuff for me for $100? I'd pay a finders fee.

I have 3400 intakes upper and lower and 3400 heads that I will sell for $150

[IsaacHayes]

Hahah yeah. Most new cars are 3400 to 3800 for small to mid-size now days it seems. But older cars were like 2700 or less. My car is lighter than new cars, but heavier than older cars. Get it?

[IanSzgatti]

My car is right around 3000lb and I don't consider it heavy or light.

is it your own unique classification of weight?

[Canyonero]

I'll roll mine down to the mill and put it on the truck scale sometime, but published curb weight is just shy of 3800lbs. Mmmm, Japanese SUV.

[IsaacHayes]

My car is right around 3000lb and I don't consider it heavy or light.

[DEI37]

that 190 hp can be felt even more if you have a light car to begin with...the 98 buick century comes in at 3354 pounds, thats really not too heavy.

It's not that light, either. My '97 Cutty comes in at 3500, almost spot on. That's with an 1/8th tank, and nobody in it.

[IsaacHayes]

3100 heads are not that bad. 2000+ the got the slightly bigger valves that the 3400's have, but it's not that big of a size increase. You can make power on the old 3100 heads. The heads are not the main restriction on those motors. The exhaust is for one, and the small port intakes.

[Canyonero]

I don't know man, what's going rate? I wish we had a u-pull around here.

[Barry]

I can, but that requires me going to the yard and pulling it myself. How much would you be willing to pay?

[oldsman105]

yes.. abosolutely...you will not regret it. I strongly suggest that if you can have parts shipped to you, you should buy the plenums here... for one they're cleaned up and damage free, two you can get them ported. If your going to do it... might as well do it right. open up the exhaust too. What i found was my torque band changed... it went higher. it will scream like a raped ape from 4000k and up. You will NOT be dissapointed. Compared to what these other guys are doing here it's just the tip[ of the ice-burg.

where are you from buddy?

New york City

Your only as good as your weakest point...

Pre 2000 3100 heads dont flow very well at all...

maybe later if I decide to mod it more.


Thanks for the feedback guys.