can you swap a 3.1 top end on a 3400SFI block?

[pontiacjeff]

Without too much trouble? Putting the 3.1 turbo/intercooled top end on a 3400SFI short block. The only thing I found so far is pushrod length, don't know if the 3400 pushrods will work or if a custom length is required. This is the first I have attempted of this kind, so forgive me asking.

I am using 3400 head gaskets, the 3.1 hg hung over the edge into the bore (smaller). Other than that, everything appears to work.

[Superdave]

That's considered a felony in 48 states.

[IsaacHayes]

Complete waste of time. Why would you want restrictive top end?

[1meanz]

like dave said its illegal to do it anyway. plus, that would be like you never done anything, because iv im not mistaken a turbo 3.1 compaired to a stock 3400 is about equal, right? 3400 bottom end or not, there wont be that much of a gain so.. what would you really be doing?

if that made no sence im sorry. not alot of sleep. lol

[pontiacjeff]

I didn't ask for permission, I asked what would be necessary, that's all.

Illegal??? WGAF?

Restrictive? Again, WGAF? One word... TURBO.

The 3.1 spun a brg, I have a good 3400 short block. The complete turbo kit is built around the 3.1, so I need to stick with it. Any more questions from the peanut gallery?

So if you don't have constructive info, please refrain from posting.

[1meanz]

it is illegal to put any older engine, into a newer car, OR put an older top end on a newer block BECAUSE of our new strict ass emmissions.

the reason i say its restrictive is because its so small, turbo or no turbo it will not flow like a 3400 top end would. but whatever, do as you wish. just trying to help, so goodluck with the old restrictive ass 3.1 stuff.

[Superdave]

I was just joking about the illegal stuff...


Turbo dosen't mean crap..Stock 3400's make the same or more power than a turbo 3.1. Do yourself a favor and use the whole 3400.. if you don't have the 3400 heads then find some. You'll make shitloads more power with the better top end, Some of the Jbody guys are putting down 350+ WHP on like 8PSI with a stock 3400. 8PSI on a gen2 is like 200 WHP



but.. If you really want to do this, then use the 3400 headgaskets and everything will bolt up fine. You'll need custom length pushrods. Also there are some differences in the bolt bosses on the 3400 block so depending on what car you are installing it in you may have to make a custom mount.

[pontiacjeff]

I was just joking about the illegal stuff...


Turbo dosen't mean crap..Stock 3400's make the same or more power than a turbo 3.1. Do yourself a favor and use the whole 3400.. if you don't have the 3400 heads then find some. You'll make shitloads more power with the better top end, Some of the Jbody guys are putting down 350+ WHP on like 8PSI with a stock 3400. 8PSI on a gen2 is like 200 WHP



but.. If you really want to do this, then use the 3400 headgaskets and everything will bolt up fine. You'll need custom length pushrods. Also there are some differences in the bolt bosses on the 3400 block so depending on what car you are installing it in you may have to make a custom mount.

o.k. it's not for me, it's for a customer. we put the 3.1 turbo with a custom T3 last summer. He spun a rod brg. I have a cheap 3400 bottom end. That's what is going in it. He doesn;t have any money for me to re-engineer the turbo kit.

I already figured out the external bolt boss issues, had to use the 3.1 timing cover, and some other smal stuff. I didn;t know if the 3400 pushrods would be the correct length or if a custom length would be req'd. I will check valve height and fulcrum height on the rockers to come close...

[Superdave]

the 3400 pushrods might work but the geometry won't be right, they'll need to be just a little longer.

[pontiacjeff]

the 3400 pushrods might work but the geometry won't be right, they'll need to be just a little longer.

The 3400 pushrods actually are perfect. There is no difference in valve stem (installed) height b/t the two engines.

[Superdave]

The 3400 pushrods actually are perfect. There is no difference in valve stem (installed) height b/t the two engines.

If that were the case then the hundreds of people who've put 3400 top ends on the 3.1 block and measured for correct pushrod length are all wrong...

[pontiacjeff]

If that were the case then the hundreds of people who've put 3400 top ends on the 3.1 block and measured for correct pushrod length are all wrong...

Uhhhhhh, no.............

I am not putting a 3400 top end on a 3.1. And don't you really mean a dozen-or-so instead of hundreds? And wasn't it probably only one guy who did it and told everyone else what to use? I mean, why would hundreds of people do the same procedure over and over when all 3400 top ends and all 3.1 bottom ends are the same and would all use the same pushrod length when doing the top-swap?

The correct way to measure for pushrod length is with a pushrod length gauge. I can't imagine hundreds of people buying not one, but TWO sincve the length difference b/t the intake and exh pushrods exceedes the range of one pushrod length gauge... After you spray a little machinists blue on the vale tip, you install the gauge and set valve lash, or in this case, torque the rocker arm nuts. Then you rotate the engine no less than two full turns. I ususally go about 4 valve sequences. Then you remove the assembly and note the contact pattern of the rocker arm as it wipes across the valve tip. The conact pattern should be across the center of the valve tip. In my case, the 3400 pushrods are perfect for use with the 3.1 top end.

[3400-95-Modified]

depends on how much preload they consider, I know the stock preload on a 3400 is quite a bit, well over what people recommend is ok... I think thats around .030 or something, where stock is like .06 almost...

I know when I was doing pushrod measurements for the milzy cam with the recommended preload on that cam I cam up with a pushrod length SHORTER than stock and I just couldn't do that, It was I could either use the stock ones and just have less lifter preload, OR just measure the base circle difference on the cam and add that to the stock length, thats what I ended up doing and everything worked out fine.

I mean, why would hundreds of people do the same procedure over and over when all 3400 top ends and all 3.1 bottom ends are the same and would all use the same pushrod length when doing the top-swap?

To answer that question, they are not created equal when it comes to valve train, the lifter difference are what throws everything off, going from a roller to flat tappet. I'm not doubting that the 3400 pushrods are a good length when using 3.1 top end, that could definitely be possible and it sounds like you have determined this. Also not everyone measures the same way, so unless this was fully tested and documented somewhere then there will always be the possibility of someone coming up with different numbers or results.

[1meanz]

im not sure if this applys since its a 3100, but my uncles 99 small port 3100 was roller lifters, and i put the heads on my car. tried to use his pushrods and they were WAY to short, the roller lifters are longer then the 3.1s. which makes the pushrods 2 short. rether it be ALOT or just a little bit, its to much. deffinatly go for coustom pushrods man. dont chance it. why build an engine on what COULD work? insted of what will work you know? just my $0.02

[pontiacjeff]

I like about .010-.015 preload (extends the rpm range without floating the valves). I also converted the non-adjustable 3.1 rocker arms to adustable locking nuts. That way I can set pre-load on each valve/lifter to exactly what I want. Thanks everyone for all the help and advise. I hope I didn;t sound cranky in the post above. I just woke up from about 3-1/2 hours sleep when I wrote it.