3400 top end swap questions

[nightrider2]

Re: 3400 top end swap questions

Keep it ;)

You can only adjust base timing. The real crank trigger is in the block, and you can't change that without moving the pickup in relation to the reluctor wheel that tells the ECM when #1 is at TDC.

you mean ON the block

[Forced_Firebird]

Re: 3400 top end swap questions

you mean ON the block

The actual sensor that measure TDC is on the center of the crank with the sesor that is plgged into the side of the block.

Believe you me, that I have been trying to figure out another way to get a crank signal to the ECM. The sensor in the timing cover is there so the engine doesn't have to crank over so many times to start.

The only way you can vary that crank signal is to use an external reluctor ring and have it mounted on a slot to adjust it.

Here's the real place that the ECM gets it's signal...

http://s158.photobucket.com/albums/t...t=100_2921.jpg

That's the reluctor wheel. It has 4 notches in it. 3 evenly spaced to mark TDC of the various cylinders, then the 4th notch is right next to the #1 cyl notch to make referance to which cyl is #1.

[nightrider2]

Re: 3400 top end swap questions

right, which tells the computer which coil to fire, but the timing comes from the optical sensor

[Forced_Firebird]

Re: 3400 top end swap questions

right, which tells the computer which coil to fire, but the timing comes from the optical sensor

I don't believe so, but I will have to look into that some more. The ECM sends the ICM a 5v referance signal (just like an HEI). That 5v tells the ICM how far to advance the timing based on enine RPM, temp, and knock sensor activity.

Again, even if you move that sensor, you are only changing base timing (moving the entire timing table back in the RPM).

For example:

RPM Adv
900 12*
3500 32*

after moving the base back 12*:

900 0*
3500 20*

Now this may be good in a WOT situation to back off timing, but what happens to cruising and partial throttle?

[nightrider2]

Re: 3400 top end swap questions

hmmm, maybe a small resistor to cut back the signal

[Forced_Firebird]

Re: 3400 top end swap questions

hmmm, maybe a small resistor to cut back the signal

It's a magnetic pickup, so that may be true.

The way I see it, though, is there really are three options.

1. MegaSquirt: costs $150 for the kit to build it at home and $250-400 for a assembled one. Can control fuel and spark, or one of them only.

2. OBD2 swap: Really hasn't been pulled off sucessfully in an fbody, but may be the cheapest option when someone with OBD1.5 does it.

3. Use an MSD type box (DIS4) to control timing only. Costs about $500

Since I have OBDI, I can get the tuning equipment for it, but also have a MS box here in the garage (just haven't made a solid decision to the outcome yet).

You 4th genners can also do an OBD1 swap if you have a stick, or the non-electronic tranny. The ECM from a Beretta (or other under-hood ECM) would work fine for you (so I guess that's 4 options within a reasonable budget).

[nightrider2]

Re: 3400 top end swap questions

I have standard aldl(know as obd1) in my car factory, cause my car is just 10x cooler

[Forced_Firebird]

Re: 3400 top end swap questions

I have standard aldl(know as obd1) in my car factory, cause my car is just 10x cooler

[tkoforpresident]

Re: 3400 top end swap questions

say i bought megasquirt fully assembled, is it simple when it comes to tuning the fuel and spark? What kind of gains does that net on say a full bolt on 3.4?

[niik000]

Re: 3400 top end swap questions

I like the resistor idea. it sounds like that would save me a few hundred bucks and/or a lot of slightly over my head work.

[nightrider2]

Re: 3400 top end swap questions

say i bought megasquirt fully assembled, is it simple when it comes to tuning the fuel and spark? What kind of gains does that net on say a full bolt on 3.4?

you have to program the fuel tables, its alot of work, If i can find a way around the computers I'll post it up

[Forced_Firebird]

Re: 3400 top end swap questions

say i bought megasquirt fully assembled, is it simple when it comes to tuning the fuel and spark? What kind of gains does that net on say a full bolt on 3.4?

Piggyback it to control fuel and spark only, and you can have it running in a day.

Check out the "success stories" forum on the MS website.

Most people have built it and had it installed/running in about a weekend. There are a few 3.4's running on them, and they will share a base tune with you to get started, and you can tweak it from there.

[niik000]

Re: 3400 top end swap questions

I might start priceing out all of the stuff for the swap. Here's my checklist:
3500 (or 3400) heads
3500 (or 3400) lower intake
3400 upper intake
Bigger injectors (how big should I go?)
Crane cam?
Ls1 valve springs?
3500 pistons or mega squirt?

How's that list look?

[nightrider2]

Re: 3400 top end swap questions

3400 pistons. the 3500 has a bigger bore. I'm going to be running 24lb/hr injectors, not sure how it will run yet.

[niik000]

Re: 3400 top end swap questions

Would there be a big difference in power depending on weather swap pistons or keep the old ones with a tune?