3.1 MPFI rebuild

[Nightingale]

Ok so I have my 3.1L MPFI motor broken down and I was wondering what all I should have done to the motor when I have it sent to the machine shop. I plan on putting a 3400 top end on the motor and eventually some boost. Some of the upgrades I been considering are new hypereutectic skirt coated pistons(CR I should shoot for?), double roller timing chain, clevite mains and rod bearings, chrome ring set, and fel-pro head gasket set.

So basically what services should I have done to the block while at the shop so that the engine will handle boost, and still be a reliable daily driver. I was considering having the block bored, but not sure if it would hurt cylinder strength with the extra pressure and even be that beneficial. Lastly would it be advisable to use ARP con rod bolts, mains studs, and head studs(I did find the head stud lengths in the performance section but will this work all right with a hybrid?)over stock hardware and what part numbers are these since there isn't a specific kit for the aluminum head engines other then the iron heads. Thank you for looking and your time is appreciated.

[bszopi]

RE: 3.1 MPFI rebuild

I would recommend getting the block bored like 0.010" over just to clean up the walls of the cylinders. You could also get the heads (and possibly block) decked to ensure a flat mating surface. Don't go too extreme, just enough to make sure the surfaces are flat.

As far as the bolts go, if you are even considering boost in the future, the ARP studs are definately recommended. The head studs should be the same between the 2 engines, but if anything, go with the studs for the heads that you plan to use (ie, 3.1L block with 3x00 heads, use the ARP studs for the 3x00 heads).

For compression, 10.5 would be good for NA, but if you plan on boosting later, stay around 9:1.

[Nightingale]

RE: 3.1 MPFI rebuild

Ok sounds good then. One other question I forgot to ask is about the pushrods for the top end swap. I would like to use the roller fulcrum ones off a 2000+ 3400 but heard you need custom length rods for it unless you use the stock stamped rockers. So what are the lengths needed or is it best to measure for your own application? There is also the cam shaft to deal with. Just stick with the stock 3.1L cam even with boost and just have a chip burned for the ecm?

[bszopi]

RE: 3.1 MPFI rebuild

It is just best to measure for you application. Other people who have done similar might have had different work done (ie, decking the heads more), which would cause a slight difference in the length of the pushrod. As far as the cam goes, with maintaining the 3.1L block, you have much more options (well... sort of) to choose from. There are cams out there for the 3.1L that work well in boosted applications.

[Nightingale]

RE: 3.1 MPFI rebuild

Ok so far I have been able to find a rebuild kit through northern auto parts(probably just go with the rering with the moly rings and fel-pro gasket options so I can add my own pistons and cam). I have also found that different cams availible from both Crane and Crower, but I am still not sure which would be best suited. I was looking at the Crower Ultraperfromance and the Crane 260 and 272. I realize that these aren't suited for comp controlled engines, but I figure a retuned chip could probably handle the new cam. Also emissions in my area is NA so not to worried about that aspect. I talked to the machine shop and I can get the block degreased,magnafluxed,bored, and honed for about $200(my grandfather swears by this shop because they did the work on his engines when he drag raced in the 50's and 60's). Might be able to score a junked 3100 from a local engine shop so I can have everything I need to do the top end swap. Still in the money gathering stage, but should be able to start getting stuff in the next few weeks, and have the block sent off next week.

[geoffinbc]

Dont use moly rings one the street man. They are not good in low RPM situations and require a different cylinder wall finish.

[discostu]

If you are going for boost, or high compression NA, you shouldn't use the hypereutectic pistons.
IIRC, a regular cast piston has something like 7.5% silicon, whereas the hypereutectic casting has double that, around 15% or more. It is the silicon in your pistons that makes them very hard (no thermal expansion) but also brittle under high stress, and when a crack forms in the casting, it almost always results in catastrophic failure in your piston.

The obvious choice for a boost or high compression application is forged pistons, as they have very low silicon content, and any stress cracks that form will likely migrate to an area of lower stress and stop.

I'm going from what I remember, so kick me if I'm way off base here.

[Nightingale]

well I am trying not to spend tons of cash on the project and forged pistons seem to fall out of my price range. I set aside about 1000 for the machine work and a rebuild kit, and I know the machine work already takes off about 200-250 of that, 50 for miscellaneous, so about 700 roughly left for parts(going to be a little bit leniant on this figure). Anyhow I also have to set aside some cash to build the tranny to handle the power better which is another 200-250(eventually want to put in an LSD, but for now an alto eagle rebuild kit will suffice). Thank you for the input(more things for the brain to munch on).

[Nightingale]

Well I ended up with some wisco forged aluminum pistons so now I am considering looking into having the cylinder walls coated so I can use moly rings. Also starting to think I might want to get a 3100 to work off as a base because of the better oiling and the fact the bottom end looks a tad bit stronger(i'd think the bolts going through the sides of the oil pan into the main caps would act like a girdle) and use the 3.1L pistons I just recieved(I believe these should work in the 3100 since they are 3.1L aluminum head pistons correct)? Only weak point of the 3x00 series I can find vs the 3.1L is that there aren't any performance cams availible for it unlike the 3.1L which has multiple grinds availible. It'll take me a while to build this up and gather parts, but hoping to have everything ready to drop in by spring (or late winter if I can find a heated garage to work out of).