2.8 to 3.4 F-bird

[CJROTHY]

My '86 2.8 has 305,000 miles on the original engine. Apart from two tranny overhauls, the car and engine has been humming along perfect for 20 years. But now milage has fallen, and it's time to replace. I am looking at a 3.4, with the TBI from a 4.3, larger intake (don't know which yet), stage 1 or 2 cam, BIGGER non-pintle injectors, cold air, and headers.

I want everything I can get out of this new mill and still be reliable, but I dont' want to change the MPFI computer, or go NOX/Turbo. Any suggestions about what's the best heads to use that will bolt on the 3.4? Pistons? Cam? Intake?

[firechiken]

Firechicken! Hey-thats my name! Is your 2.8 TBI? I thought it would have been carbed. If you want to go TBI, you'll have to use your heads from the 2.8, and if you do have TBI, you're going to have to have the bores of your intake enlarged to use the 4.3 unit. You also have to make sure the unit from the 4.3 has the same setup for the trottle cable bracket, there not all the same. And you should get a 3.4 from an f-body, or you could use the 3.4 that GM offers as a replacement for the s10 2.8. Info on the intake thing: http://s-series.org/Sections-article25-p1.html .

[CJROTHY]

Nope - the little thing was MPFI from the dealer's lot (I got that right? it has fuel rails and one horizontal throttle body). I was planning on starting with a 3.4 from a mid-90s F-body, then rebuilding it. I didn't think a 3.1 intake (looks the same as the 2. could be bored out well enough for a 3.4 with a bigger cam - I was worried about the general passage restrictions more than fitting the larger TB onto it. Me and Mr Dremel - we be buds. I'm not concerned about bending up/welding cable brackets, but I'd much rather get one that just bolts on.

Seen the GM replacement engine - it won't have a Stage 2 cam, and I'd still feel like porting, balancing, etc - I can have a used engine built up really well for that kind of cash.

I have read some here about different heads for the 3.1 and 3.4 engines, and was wondering if some other freer-flowing heads would bolt down and fit the 3.4.

I'll change my quote, sorry!

[firechiken]

Heads are the same, the only thing that changed on the RWD engines is the MPFI and SFI heads had bigger valves then the carbed heads. The only thing that has to be bored out is where the TBI mounts to, everything else is the same. You didn't have to change your sig, man...

[CJROTHY]

Yes, I was planning on using the 3.4 MPFI heads, but didn't know if 3500 heads were better, or if they would fit, or came in pushrod configuration, or if there were better pushrod heads out there that will fit the 3.4 . Additionally, could I use the 3.4 intake on my '86 MAF-fed computer setup? In theorey, it should have larger intake passages.

Who can a guy go to for info on setting up a really hot normally-asperated V6?

Previous FI conversion: I pulled a complete setup from a '91 3.1 Camero and put it into my '81 4-cyl CJ5. I"m not too afraid of bending stuff around a bit. Just finished converting the fuel tank pickup in the CJ to the GM sending unit and pump - still have the clutch pushrod adaption, electric fan mount and some wiring to finish off.

Sign changed because it was not very original, maybe confusing.

[sharkey]

the 3.4l intake wont work with the 2.8l wiring harness, simply because the 3.4l manifold doesnt clear the distributor, as the 3.4l runs dis. basicly you would need to do a wiring harness and ecm swap to make it all work. would be worth it though, the 3.4l runs sfi injection, so helps with gas mialage.

as for doing an aluminum head conversion onto it, its not that tough. you would need to run 3400 heads upper and lower intake, fuel rails, ect. you also would need to run 3400 pistons to keep the compression in check. you would need a 3.4l f-body block for this. also need to make some fuel lines. im not sure about alternator and power steering, but im sure you can just use the rwd water pum/timing cover and brackets.

[CJROTHY]

And are 3400 heads better than 3.4 heads? (I.E. is this worth the trouble?) or are there better heads out there for the 3.4 pushrod block?

Thanks for the note on the 3.4 intake. I didn't think about the mid-90s DIS. If I changed the ECM and wiring, would the new 'Puter still drive my instrument cluster?

[sharkey]

the 3400 heads are the swap of choice. they are the best that are out there. a stock 3400 makes 185hp. comparing that to the 3.4l f-body, it makes 160hp. is 20hp worth it, i think so.

im not sure about the ecm driving the gauges. in most obd1 gm cars, the ecm is only used to drive the speedo. the oil pressure, gas, coolant temp, tach and battery gauges are driven right from their sensors. the ecm has a speedo buffer in it and from the ecm it sends the signal to the gauges. it should all work just fine.

[CJROTHY]

I am VERY new to all the cross-generational parts swapping. Any clues to what years/applications I should be looking for compatible heads?

With 3400 heads, which pistons should I keep?

What's the most normally-asperated hp I can expect from a 3.4 pushrod, and which combination of parts would get me there? Is there any references I can read on (other than continuing to search this forum)?

Thanks, Paul

[firechiken]

With 3400 heads, which pistons should I keep?

You should use the 3400 pistons, and intake, and wiring harness, and crank (you need the reluctor wheel for the DIS, I don't think you can keep a distributor), and computer, and all the sensors. Am i missing anything? Oh yeah, I think there's a problem with pushrods, not sure, I think you can get away with the ones from the 3400.

[CJROTHY]

Yeah - missed the piston comment from Sharky. Thanks.

Think I'll go to the yard next weekend and check out a 3.4 intake - maybe this is something I can modify? We'll see.

I'm really going to try to keep the original GenI ECM. I'll take your word it won't be as efficient as the 3.4, but while I'm all for mixing up the motor and intake/exhaust, the project is pretty containable as long as I leave the rest of the car the same. -Don't need a Frankenbird science project.

[sharkey]

keeping the stock ecm you are very limited in what you can do. basicly anything but the stock 2.8/3.1 manifold wont clear the distributor. basicly that would limit you to getting a 3.4l f-body motor, keep the iron heads, and use the stock 2.8l intake.

its not worth it to avoid dropping in a wiring harness and ecm from a later model car. i did this with my cavy. i didnt want to run dis, so i stuck with the iron heads, spent a huge pile of cash on the motor, and i run about 3 tenths faster than a stock 3.1l cavy. looking back at it, i should have thrown an 89 wiring harness and ecm in, and built a hybrid motor, and i would have gotten what i was after. now to get the results im after with what i currently have, its gonna take me rewiring the car and running a stand alone fuel/ignition managment, most likley a megasquirt.

its not worth it to avoid some wiring for it. when we are talking around 200hp, the possible 20hp gain of 3400 heads is a ton.

[CJROTHY]

I'm doing the Megasquirt I on the wife's FJ1200 right now. Part of my permision to rod my 'Bird this fall is getting hers swapped from carbs to injection first. Planning on doing the MSII on my AMC Cherokee and J-10 next year.

Allright, so I really want to keep the SFI from the 3.4 RWD donor, and 3400 heads are better than the 3.4 ones. Would 3500 heads fit? Would they be much better? What years/models would I get them from?

The CJ conversion (see above) used ECM from a '91, and that computer drove every gauge in it's dash. I'll have to check if the 86's are the same way. If so, I really don't want to change ECM. If not, would the SFI ECM drive my MPFI speedo/tach gauges OK?

[bszopi]

The 3500s weren't introduced until 2004, and only in the Malibu for that year. In 2005, they were available in a couple more models (Uplander and Terraza off the top of my head). Finally, in 2006, they have started to appear in a several more vehicles. Are the 3500 heads better yet? Ben is in the process of doing some testing on them, but I will initially say yes they are.

[firechiken]

The heads from a 3400 aren't the same as a 3.4 RWD . The intake won't fit. If you want to use the 3400 heads, you have to use the intake from the 3400. And it is recomended that you use the pistons from the 3400 also.