What happened?

[2.8 Grand Prix]

What happened to my thread? Is it because it was off topic too long? 'Cause that was out of my control. Those guys like to talk about all sorts of shit.

[WrathOfSocrus]

Yeah I tried to toss in some on topic information but it got buried in the gran tourismo talk.

Out of sheer boredom I actually popped on to w-body and saw a cleaner version of your thread there. One thing that I'm surprised a lot of people have missed is the fuel pressure regulator. Stock Gen 2 2.8 and 3.1 motors used the same injectors (multec 1) and they ran at ~43.5 psi I believe, where as the '00+ motors used multec 2 injectors at ~55 psi. Your 2.8 fuel rail will not fit the new motor and the fuel pressure regulator on the new one will make your engine run rich. You will need to find a '99 or earlier 3x00 using multec 1 injectors and grab the FPR or the whole rail. Someone on here probably has one laying around you can pick up that is cheap.

[SofaKingWeToddDid]

how far along are you with the swap so far?

[bigalwalker08]

Not sure that the regulator will be a problem if he is using the PCM from the 3100

[WrathOfSocrus]

He is trying to use the stock computer with the stock injectors until he can get it tuned. From what I understand the Gen 2 2.8 and 3.1 used the same injector but a different tune. I don't think the 2.8 tune will be too far off on a 3100. As long as it isn't revved up to the limiter every time it's driven it should work well enough to be drivable.

However with his stock injectors, he would need to run them at the stock pressure (43.5 psi) with the stock tune. If the computer thinks it is putting in X amount of fuel but the pressure has been raised by more than 25%, then the fueling will be very rich. If he could tune for it then it wouldn't be an issue. Since I know this is a limited budget build (I think that's the case with almost any build) a spare FPR or the whole rail from a multec 1 fed 3x00 should do the trick. I have seen several for sale on here in the past in the $10 - $20 range. I just looked on WOT-Tech and they have 2 brand new ones in stock for only $30 each.

[1QUICKHATCH]

I used a 2000+ fpr on a 3400 with 2.8 injectors in a 89 Z24 and had no problems. It would have made more power with larger injectors and a tune, but it got the car running for the guy.

[WrathOfSocrus]

True but on a 3400 a 2.8 tune would be rather lean. The increased fuel pressure probably negated that and only ran slightly rich. On a 3100 it would end up a bit more on the rich side, especially if he isn't opening up the exhaust and intake to flow better. The extra fuel will be sent to the cat and drain past the rings into the oil.

[2.8 Grand Prix]

I am planning on using the 3100's exhaust manifolds, as well as fabricating my own cold-air-intake system. As for the injectors, I've been told by Robertisaar (he knows a shit load about electrical stuff) that the 2.8 injectors would fit on the 3100's fuel rail. It will run (sorta) on the 2.8 tune, but he advised getting a tune from Ben ASAP! That's what I plan on doing, it'll just take some time.

I start my new job next Monday, so I'll have some money coming in. However, I'm going to start making payments on my "new" car soon. It will all fall into place soon enough. All I have to do is be patient.

[WrathOfSocrus]

However with his stock injectors, he would need to run them at the stock pressure (43.5 psi) with the stock tune. If the computer thinks it is putting in X amount of fuel but the pressure has been raised by more than 25%, then the fueling will be very rich.

The injectors will fit the new rail fine, but the pressure will be incorrect. The pressure increase is something a little over 26% and there is no way on earth the computer will be able to compensate for that. If this was a 3400 it might work because it already needs more fueling which can be introduced by changing the tune, changing the injectors, or changing the fuel pressure. The fuel that a 3100 needs can't be far off from what a 3.1 needs, and since they had the same injectors as a 2.8 I would stick with the stock injectors and fuel pressure if there was no way to tune. That is a lot of extra fuel which could wash the cylinder walls and get into the oil doing irreparable damage to engine internals.

If this was a 3400 or a performance oriented 3100 I wouldn't worry. But if you look at the stock downpipe on your car the thing bottlenecks down to somewhere around 1 5/8" to 1 3/4". With that in place there isn't much chance that your 3100 will be able to burn up that large of an increase in fuel. Gas at near $3 a gallon (in my area anyway) and a 26% decrease in fuel economy, I think the 43 psi FPR will pay for itself in a just a few fill ups.

[robertisaar]

Wrath: dude, O2 sensor. it corrects for this type of thing. the first couple of times he starts it, it's probably going to run like shit for a few minutes, then the O2 will kick in and start fixing it, that will take care of 1 of 3 BLM cells, then while he is driving the other 2 will adapt.

another thing: the ~25% increase in pressure won't increase flow by 25%. i don't have any hard data on the 2.8 injectors, but i'll assume they are 16 lb/hr, since that's about what they calc out to in the tune.

that means at 55psi, it will be up to 18lb/hr. check the witchhunter injector calc for that. they actually flow 25% LESS than what the 00-up 3100 injectors would...

[2.8 Grand Prix]

Heck yah!

I'll just have to get a new O2 sensor and I'll be good to go.

[robertisaar]

don't be celebrating just yet, you still have LOTS to do.

i'm just saying it will work well enough to drive it around without serious damage. that covers the fuel side of the equation, spark is still going to be interesting.

i included two screenshots for you to look at. they are appropraitely named, so bear with me.

the 2.8 one is the stock SA you have running now and without a tuned chip, that's the way it will stay.

the 3100 one is what i'm running on the MC... that's a dead stock 95 3100. it runs well considering i haven't had the time to play with it. i probably would not be able to tell if i switched the PCMs back and forth between the stock one and my 9396 DF setup. that being said, i'm sure there is room for improvement, BUT it should run well enough so that you can drive it. you go WOT, don't expect it to end well. keep it under 4K RPM and don't give it more throttle than necessary until it's tuned.

[2.8 Grand Prix]

I hear you loud and clear, I don't intend on driving like a lead-foot maniac, I just want something (semi-reliable) to drive around town. I'd like to keep my "new" car for work only. I'll be driving 65 miles round trip each day, so any in-town driving that can be put on the Grand Prix would be awesome!

[SofaKingWeToddDid]

well it sounds like ur gonna know damn well what ur doin before you jump into the deep end of the pool atleast. so the patience might pay off.

my only words of advice i can offer at this point, be this slow when ur takin things off and putting them on the motor. you dont want to strip threads or break a bolt off in or on the block. if you split your knuckle open, you just have to let it be, it will heal. the broken bolt wont grow back no matter how hard you try! some of those Mechanix Mpact gloves are my personal fav for wrenching under the hood. theyve saved me a few square inches of skin im sure.

[robertisaar]

meh, blood prevents rusting ... i think...

but with a support team like 60V6, it will be easy.