Is there a write up on 3400 head swap to 3.4

[jimjimmyjimjim]

I'm fairly new here, but I've been on the Isuzu Trooper forum for a while. I'm thinking of swapping the heads, intake and efi from a 3400 on to my 3.4L iron head gm motor which I recently rebuilt. I'm looking for a good writeup on this project. I've searched this forum but wasn't able to find one.

Can anyone here point me to one? or better yet, has anyone here done the swap? I've cobbled together bits and pieces from around the internet on how to do this but I haven't been able to find any write up covering the swap from beginning to end.

Thanks for any help. JH

[trotterlg]

If it is anything like a 3.1/3100 top swap, the iron head pistons will give you a fairly high CR with aluminum heads. Likely you will have pushrod length issues and have to find exhaust manifolds to fit. Can't think of much else major. Does the 3.4 use a roller cam or is the block set up for one? Larry

[jimjimmyjimjim]

If it is anything like a 3.1/3100 top swap, the iron head pistons will give you a fairly high CR with aluminum heads. Likely you will have pushrod length issues and have to find exhaust manifolds to fit. Can't think of much else major. Does the 3.4 use a roller cam or is the block set up for one? Larry

First of all: Thanks for your reply. Your help is appreciated.
I've read that I have to change the pistons, otherwise I'll get nearly 13:1 ratio. Comp Cam will make custom length pushrod. The cam is not a roller, I don't think the older 3.4L's were set up for that. I know that others have done this swap, so I'm fairly confident that the cam shouldn't be a big problem. I also have to use a cam and crank sensor which the block is set up to accommodate.
Basically, what I know is: I need 3400 heads, push rods, pistons, roller rockers, intake and injectors, computer. What I don't know: everything else! What year and model donner car, how to modify the mounting points for the accessories, how to wire the computer, how to mount the intake, the thousand and one little things that usually slow this sort of project way down and run costs way up. When (and IF) I start this I'm going to be pressed for time, so I'm trying to anticipate everything. I know that's not possible but I'm trying to get as close as possible.

[trotterlg]

On my 3100 with flat tappets the longer pushrod for the roller lifters fit in place of the short pushrod when I went to flat tappets. Then I found some (ford I think) pushrods for the longer ones, if you spend enough time looking on ebay you will find them. Every thing else was easy, changed to adjustable roller tip rockers and it all worked. Larry

[jimjimmyjimjim]

On my 3100 with flat tappets the longer pushrod for the roller lifters fit in place of the short pushrod when I went to flat tappets. Then I found some (ford I think) pushrods for the longer ones, if you spend enough time looking on ebay you will find them. Every thing else was easy, changed to adjustable roller tip rockers and it all worked. Larry

So, what kind of performance increase to the stock 3.4 can you expect after all this work? 20, 30 hp?

[trotterlg]

A stock 3.1 iron head engine was 140 hp and a stock 3100 was 175 hp. More important I think is where it makes the power and ability to get the aluminum head engines to make power at higher RPM's. Larry

[Superdave]

custom length pushrods are pretty cheap from Smith Brothers, and they're better than OEM ones. It's not hard to measure for them and you'll get the correct lengths. Some people have gotten away with using pushrods for a Gen 2 aluminum head 2.8/3.1 but they probably didn't have enough preload on the lifters. Those would be worth checking out on your engine.


Basically just go the junk yard and get the whole top end from a 3400 or just grab the whole engine. That way you can swap over the pistons to keep the SCR down to a normal level.

You could run the 3400's computer or i'd recommend something like a Megasquirt to keep the wiring to a minimum.


There is a tab on the top of your timing cover that you'll have to cut off so that the 3400's lower intake will sit correctly. Cutting that off takes like 2 minutes. Other than that just bolt the top end on just like it came off with the exception of flipping the lower intake so the thermostat points at the radiator, and the same for the upper intake.

for accessory mounting, the brackets from a 3.4 Camaro will work with very little effort. The alternator bracket already has the boss there to bolt to the aluminum head, it just needs to be drilled through. The PS pump bracket just needs 1 hole drilled as well if i remember right. I probably have both sitting in the garage if you want them or just need pictures. Your stock brackets may work as well with a few modifications.

Your stock exhaust manifolds will bolt up if you oval the mounting holes out.. or a pair of front manifolds from a 3500 should work well.



It sounds like a lot of work but it's really not bad at all. Just take your time. You can expect a 20-30 HP gain and a decent jump in torque. Even more if you added in a larger cam.

[jimjimmyjimjim]

A stock 3.1 iron head engine was 140 hp and a stock 3100 was 175 hp. More important I think is where it makes the power and ability to get the aluminum head engines to make power at higher RPM's. Larry

That brings up the other question I have: where is this hp increase? I use the Trooper for off road but I also use it for daily driving. I want to keep most of the hp in the lower end of the rpm range for towing, slow going over dirt, etc. I'm assuming that with these heads there will be an increase in hp all along the rpm curve over the stock 3.4L with iron heads, but mostly in the higher range, around 4500 or above. If I'm right about that can I keep the torque low by increasing the manifold runner length or something else?

[Superdave]

Here is the 3400's dyno graph from GM, as you can see the torque is excellent across the RPM range.



I'll have to do some serious digging to find the L32 chart from GM...

[jimjimmyjimjim]

Superdave, I assume this graph is the crankshaft hp not at the wheels. My 3.4L has this cam from Comp Cams in it right now (it's not a roller cam, although one is available for this motor - I was wrong below) http://www.compcams.com/Company/CC/c...x?csid=56&sb=0. This cam increases the low end torque slightly. Any idea what effect this would have on the torgue curve in the graph?
Should I go with the stock injectors?

The main reason I'm think of doing this is that the aluminum head flows something like 200cfm at the intake, where the iron head flows somewhere nearer to 123cfm. Even if I port the heck out of the iron heads I probably won't close to that.

One more thing: My 3.4 is not electronic ignition. I don't know if I have to convert to electronic ignition but I want to. Can I use the ignition out of the donnor car?

One more thing: I need to replace the pistons with the 3400 dished pistons. I rebuilt the motor about 5000 miles ago or less. Do you think I'm okay just honing the cylinders and using moly rings?

[Superdave]

Yes, the 3400 heads far out-flow the old irons by a long shot. lol


You will have to convert to electronic ignition, with your block it'll be easy though. Yes, the 3400's ignition module and coils will work.

I would hone and ridge ream the cylinders, then toss in the new pistons with new rings. It should be fine.

[Maverick H1L]

Superdave, do you have any installed pics of the accessories? My alternator bracket (and the accessories altogether) is giving me fits with the belt routing relative to the upper radiator hose.

Also, if this guy doesn't want them, I'm interested in the 3.4 brackets (mostly the alt bracket)...

[Canyonero]

I'm fairly new here, but I've been on the Isuzu Trooper forum for a while. I'm thinking of swapping the heads, intake and efi from a 3400 on to my 3.4L iron head gm motor which I recently rebuilt. I'm looking for a good writeup on this project. I've searched this forum but wasn't able to find one.

Can anyone here point me to one? or better yet, has anyone here done the swap? I've cobbled together bits and pieces from around the internet on how to do this but I haven't been able to find any write up covering the swap from beginning to end.

Thanks for any help. JH

I gathered all the parts to do this with my Trooper years ago. Pistons, pushrods, heads, etc etc. But I'm still running the iron head 3.4L. Someday maybe... I'll be interested to see how/if you do it.

[Canyonero]

for accessory mounting, the brackets from a 3.4 Camaro will work with very little effort. The alternator bracket already has the boss there to bolt to the aluminum head, it just needs to be drilled through. The PS pump bracket just needs 1 hole drilled as well if i remember right. I probably have both sitting in the garage if you want them or just need pictures. Your stock brackets may work as well with a few modifications.

The 3.4L alternator bracket will interfere with the battery in the Trooper engine bay. When I ran the Camaro SFI in my Trooper I clearanced the battery tray and relocated the battery to the back. I did not have AC installed, and got an AC Delete idler pulley for the camaro brackets (Trooper has compressor upper left, camaro is lower right).

[Guest]

If you don't have electronic ignition what do you have?

I'm not aware of any points style distributors available for the 60 degree V6.

I wouldn't use the 3.4 or 3400 PCM, they are OBD 1.5 or OBD 2 and either nearly impossible to tune, or very expensive to buy the software to tune them, and even then not all parameters seem to be defined.

I would use (and did use, when I did a similar swap in my Jimmy), a 1227730 ECM and proper MEMCAL for the application. This is a very tunable computer and can be found fairly easily. Dead solid reliable, and have built in diagnostics. The stock tune for the FWD 3.1 will run this 3.400 (or "hybrid") without issue. Sure it won't be perfect, but the 300cc of displacement difference and better flow don't seem to be too far out of the ability of the stock 3.1 tune to run. You will have to thank GM for that, since they tend to run the stock tunes a bit rich, to be safe. Most people report that the very top end might end up a bit lean when using the stock 3.1 injectors, or they play with fuel pressure to get slightly more fuel to the engine. The best way is to tune the combination through the use of ECM tuning hardware and software. Like I said though, the stock tune will run that engine just fine. to get it running.

The accessory brackets and such will be up to you, as mentioned already, while some brackets may fit the engine, they may not fit the chassis.You may need to make some adapter plates to use existing accessory brackets, or make completely new brackets. I did both when I did my swap, partly because I wanted to move some items around, like mounting the alternator low, where the AIR pump used to be.