I've read some bad things about the reliability of the 3.4 DOHC, but I've also heard off the Z34's and the cars they were in as being fairly reliable...? humm.... I want to know how un reliable they really ARE? I'm not expecting like never maintain it reliable, but better then older brit cars! lol. I'd like something as reliable as say, my 2.8 (kinda, not 100% though). Lets here what ya guys got to say...

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Check my car out at Car Domain!

Good engine... it's got it's share of problems though. They are notorious for their timing belts, which supposedly last "30-60k". Also notorious for a 'code 32', even with a clean egr passage and new EGR solenoid. The 91-93 have a 'phantom stall' that sometimes cuts the engine out while idling in a parking lot/where ever, that GM released $700 injectors to fix... That about covers it. Just as reliable as your 2.8, but has lots more complicated parts that like maintenance.

The 3.4 DOHC engines were very quick, high revving engines. Depending on how the engine was cared for (as is the case of all engines) it can be reliable. My concern is ease of repair, availability of parts and getting it in the Fiero correctly. Those that get all that, have a nice car.

A 3.4 Camaro engine swap for the 2.8, is IMHO, would be less trouble to stick in a Fiero and could be beefed up to over 200 HP. IT comes down to what do you want? A high revving quicker 3.4 DOHC in your Fiero or a reliable 3.4 that can be a real sleeper.

quote Originally posted by Old Lar: A 3.4 Camaro engine swap for the 2.8, is IMHO, would be less trouble to stick in a Fiero and could be beefed up to over 200 HP. IT comes down to what do you want? A high revving quicker 3.4 DOHC in your Fiero or a reliable 3.4 that can be a real sleeper.

Yeah, I've done a good bit of research on the 60*V6 series. The resason I ask is because I've read about equally half and half. They only all agree about the timing belt...kinda...lol. I like the DOHC better. That and allunium heads is why I choose it .

thx ryan.hess, but is it 30k or 60k? That's a big span! lol. You can just disable the emissions crap, can't you? I don't have emissions testing here.

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Check my car out at Car Domain!

No offense to anyone, but I have yet to see a 3.4 iron-head pushrod engine that was built up to put out over 200 hp (n/a) that still retains the stock-like drivability and good gas mileage like the stock 2.8L Fiero engine does. Don't get me wrong, I am not bashing the iron-head 3.4 pushrod motor, I just think it's biggest downfall is the fact that it has the sucky 2.8LV6 design iron heads.

As far as the durability of the 3.4 DOHC, you have heard right about it's shortfalls. But allow me to explain why. 99.9% of people who buy GM products never expect to have to ever service a timing belt. Conversely, people who buy imports expect to have to do it every 60,000 miles or so. It is just part of the regular maintenence of the vehicle. That is the biggest problem with the 3.4 DOHC's reliability. I have seen tons of these engines exceed 100,000 miles on stock timing components, and then something goes wrong with the timing belt, which usually makes it a lot more work to fix. As far as how hard it is to change, IMHO, this is the easiest timing belt you will ever have to change in your life, that is assuming that you are not replacing a broken one.

The only other major problems these engines had was the stupid distributor (oil pump) shaft O-ring seal leaking. Unforetuneately, you have to pull the rear cylinder head to replace this seal if it starts to leak. If you get a new engine or one that is not leaking, you can pull the shaft up about 3/8" or so (without pulling the head) and lay a bead of the permatex hardening RTV in there to provide a backup seal should the O-ring eventually fail.

With all that being said, I think the 3.4 DOHC engine is a decent choice for an engine swap, especially if you plan on mating it to a manual tranny. These engines get 30+ MPG on the highway and put out 210hp or more bone stock, and run very smooth. If you can find a good one cheap enough, I don't see how you can go wrong.

Now, another choice might be the 97-up aluminum head 3400 pushrod V6 engine that is commonly found in FWD minivans and some other cars. The version that comes in the minivan is rated at 185hp and 210tq, and is lighter than the 2.8L Fiero V6 as well. While these engines are OBDII, you can install one in a Fiero with an OBDI computer from a 3.1 Beretta or Lumina and a custom chip, using whatever transmission you wish. Set this engine up with good exhaust and induction and I don't see why it wouldn't produce close to 200hp stock. (these engines had their share of problems too, but those were mostly limited to leaky intake gaskets which are easy to replace).

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power corrupts. absolute power corrupts absolutely.

Custom Chip Burning | Fiero Engine Conversions | Turbocharging | www.gmtuners.com

[This message has been edited by Darth Fiero (edited 04-23-2004).]

I looked into the timing belt issue very carefully but found it to be a 'non issue'. The MAJORITY of the newer engines on the market today use a timing belt and the standard replacement interval is 60,000 miles. The most coveted engines that are noted for their reliability rely on timing belts. If you take a look these engines, they are also interference designed. If the timing belt breaks, the internals can collide and destroy the insides. However, this does not deter their popularity.
http://www.theautoshop.com/timing.html
I think that some people feel comfortable with the older designs of engines that don't use the modern timing belts and don't realize how widespread and successful the 'other' engines are.

My 3.4L DOHC in my cutlass had over 195,000 miles with no malor problems. I bought it with 65,000 miles and never changed the timing belt. thats 130,000 miles on one belt maybe more. Even with all those miles I still had enough torque to grenade my 4T60Es more times than I care to think about.

quote Originally posted by Razor_Wing: Yeah, I've done a good bit of research on the 60*V6 series. The resason I ask is because I've read about equally half and half. They only all agree about the timing belt...kinda...lol. I like the DOHC better. That and allunium heads is why I choose it . thx ryan.hess, but is it 30k or 60k? That's a big span! lol. You can just disable the emissions crap, can't you? I don't have emissions testing here.

Not positive... Most 'enthusiasts' check their belts early, and if it shows signs of age (fraying, rubber shavings in the timing covers) they just replace it. Yes you can disable the EGR, that's how I made my code 32 go away At the very least, you get a 7,000rpm engine that sounds exotic above 3k.

quote Originally posted by Darth Fiero: No offense to anyone, but I have yet to see a 3.4 iron-head pushrod engine that was built up to put out over 200 hp (n/a) that still retains the stock-like drivability and good gas mileage like the stock 2.8L Fiero engine does. Don't get me wrong, I am not bashing the iron-head 3.4 pushrod motor, I just think it's biggest downfall is the fact that it has the sucky 2.8LV6 design iron heads.

All I'm gonna say is the iron heads are not the biggest downfall, the factory Fiero intake is the main flow problem. The iron heads can be ported to flow better than the stock series I aluminum heads. The series II and multi-valve TDC heads are about the best flowing heads for a 60* V-6.
As for 3.4L with iron heads and over 200hp, I can say for sure mine is over 200 and the driveability is better than the 2.8L that was in it before. Gas mileage is unknown at present, I have only driven 46 miles since the engine was installed, Including the 30 minute cam break-in and the time spent tuning it and I only used 2.5 gallons. (I filled it up the other day because the gas gauge is reading incorrectly, but that is another story)

As for 3.4L TDC reliability, The timing belts were the biggest problem I have heard about. I've heard that the timing belts should be changed every 30,000 - 40,000 miles depending on driving habits. (remember that the Lumina/Grand Prix vehicles also weigh more than a Fiero which can contribute to more strain on the belts)

The 3400 pushrod engines have had problems with intake manifold gaskets. But that is the only thing I'ver heard bad about them.

If you are going to swap in a 3.4 TDC, Just put on new timing belts before the swap and then perform an inspection on them once a year. Obviously the 3.4 TDC engines have some measure of reliability (if cared for) since I see cars still driving around with them today.

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Happiness isn't around the corner...
Happiness IS the corner.

quote Originally posted by Oreif: (remember that the Lumina/Grand Prix vehicles also weigh more than a Fiero which can contribute to more strain on the belts)

Just want to correct this... the timing belt isn't affected by the weight of the car. It is affected by the 'spool up time' of the engine... If you're free-reving it, that will definately throw a lot of strain on the belt, and I believe is one of the reasons they put a 3k revlimit in park/neutral on them.

quote Originally posted by ryan.hess: I believe is one of the reasons they put a 3k revlimit in park/neutral on them.

Nah, thats just so you dont nuke the tranny. Almost all FWD GM motors behind automatics have had that neutral rev limiter for I think 10 years already.
3.4 DOHC's are as reliable as any good 2.8. just check the belt once in a while. And they are EASY to change in the Fiero! MUCH easier then the "W body" it came out of!

My question is if they are so good why did GM made them for such a short time and dump them? I know many who had them in Monte Carlo's and Lumina's and had a wide range of problems. I never saw much to make this a good Fiero swap say over a 3800 SC. To me just adding a pulley and rockers on a 3800 SC and your knocking on 300 hp still pass emissions and gain only 34 pounds in wieght.

I am not tring to be negative here I just don't see any advantage to this engine over others available with more power and reliability other than being able to say you have a DOHC. To me DOHC is not any big deal unless it has variable valve timing.

Can someone list the advantages of the 3.4 DOHC engine since I have only seen the bad,. I want to like this engine but have not seen a reason to yet. Please make me like it!

the biggest advantage is it bolts right in. so just about anybody can do the swap. there will always be engines with more power or are cheaper to buy or rebuild but not too many bolt up without custom mounts and adapters.

quote Originally posted by hyperv6: My question is if they are so good why did GM made them for such a short time and dump them? I know many who had them in Monte Carlo's and Lumina's and had a wide range of problems.

People who buy a GM car expect it to be able to go to 200k with little more then oil. If you look at the majority of "blown" 3.4's you see out there it is because of the timing belt breaking, it appears that the normal user refuses to have this changed. On 60v6 and w-body forums I continually see new owners of cars with the 3.4 asking about timing belt replacement, most of them have 100-150k on the original belt, a bad alternator, and leaky intake gaskets.

Another thing is the power band, these engines were put into the sport model of a cheap family car, most of its owners never take it above 4k so I'm sure there were complaints about a lack of power down low especially in a 3500lb car.

And lastly labor charges are 4x as much as a pushrod engine. While nothing is that hard to do it will take 4x as long, and in a W-body the alternator tends to burn out every 2 years on the dot. If you are lucky and have the 5spd you can get it changed in 1-2 hours, if you have an automatic it can take all day

A DOHC engine costs more to make. However, it gives better gas mileage and more power than a pushrod engine of the same displacement. Most car companies adopted these engine and have made them work well with their cars. The pushrod is an inexpensive engine and gives GM a price advantage. If you look at the types of cars GM was selling in the '90s, they were not the small, light, and sporty cars that make the most benefit of a DOHC engine. The 3.4 DOHC ended up in more family oriented cars and was mated to an automatic transmission that was not an ideal match. Seeing where their sales were, GM chose to refine the V6 pushrod engines that perform well enough with the majority of their product lineup and leave the performance side of it to the V8s. Displacement is cheaper than refining a smaller engine. However, seeing that their customers are starting to demand the sportier, higher reving engines Cadillac has managed to gain a higher GM profile by offering the Northstar. As soon as GM's customer base shifts its preference to DOHC engines, they will have more.

i have a 1991 GTP 3.4L 5 speed, and i have to say i really love the power band of this motor, but it does seem reliability is a problem.....

my car has 98k on the odo.... and it has its 3rd motor in it. i have no idea what the failure of the first one was, because when i purchased it, it had a junkyard motor in it, well that motor lasted me about 20 miles after i replaced the timing belt, and pulleys, its oil started looking like silver paint...... the motor in it now, seems fine, its got 76k on it, and runs real strong.

i moved the new timing belt and pulleys over to it, and installed a new clutch while it was out.

matthew

YellowArtero hit it right on the dot. It is all about marketing and customer base. Remember that the 3.4 DOHC's predicessor, the 3.2 DOHC was slated to be put in the 89/90 Prototype Fiero (but the one I saw was still mated to a 4-speed auto). I have already done one of these engine swaps in a Fiero and am currently working on another one.

This is quite possibly the easiest and cheapest "big" engine upgrade available for the Fiero. For all intensive purposes you can use the stock 2.8L Fiero harness and only minimal wiring is required. Most of the 2.8L mounts will work with the 3.4 DOHC although some minor fabrication work is required. The first 3.4 DOHC swap I did was into an 87 Fiero that had a 5-speed getrag. I can tell you that car is a blast to drive, quite possibly a high-13 sec 1/4 mile performer on the bone stock motor. Not to mention the exotic nature of having a DOHC motor in a light car with a manual trans. Too much fun to drive. Once I finish this latest swap for YellowArtero, I think he is going to have a hard time keeping his foot out of the gas.

I just had to ask since most of the people I have seen with 3.4 had many problems but most were not timing belt. Most dumped the cars due to the reliability was never their. I am glad some of them held together and are being used in Fiero's with out problems. I have some Fiat experience and the belt are good to 25,000 miles not 25,001 and they take all the valve's.

I don't disagree with the advantages listed above for a DOHC but one point was left out. The peliferation of DOHC in the auto industry is due to emissions. Most MFG in the 80's felt they could not meet low emissons with a pushrod engine. GM has found other wise and will keep pushrods in many cars in the future. They also are cheaper to build, easier to fit in a low hood car and lighter are the other advantages. You will see a 3 valve pushrod engine soon from GM one being a V8 in the new Z06 puting out low emissions and 500HP. GM will supply DOHC for the high end cars to satisfy the tech side expected in those cars. Some of these engines may be good future Fiero Material like the Ecotech.

GM is not alone on the pushrod wagon as the new Hemi is also sporting pushrods.

alright, thanks everyone. I'm glad to hear it's just the belt thing. But how had exactly is the belt to change while it's in the fiero...? How had is the engnine to tune? Does 2900 sound fair for a swap (excluding labor)? What kind of AC stuff do you have to do? Thanks!

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Check my car out at Car Domain!

Looking at mine (from two day old memory since I pulled the egine again yesterday) there looks to be enough room to do it with the engine in the car. Not easy but there does look to be room to work down that side.
As for the ac I've not done mine yet but so far as I can see all I'll have to do is eliminate the switch on the condensor up front and get a set of hoses made up to connect the Fieros body connector up to the 3.4's compressor connector. DEpending on the Year/model of your Fiero you may or may not have the condensor switch. Some fieroes used the V5 compressor, same as the 3.4 (well my 95 3.4 anyway) in which case you will not have it. Other Fieros used the DA4. You might need to mount a pressures cutout switch somewhere in the system as well. T off the high pressure connector up front and mount a switch on one of the T's.

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Dave E

www.ltlfrari.com

I'm trying to decide it 's easy enough for me to do if I should get a guy a twin lakes to...

You may want to look up specs on the new pontiac motor to be introduced this year - I believe it's a 3.9 liter DOHC motor with timing chain instead of belt. Supposed to be pushing around 250HP IIRC.

what would be the advantage or disadvantage of a timming chain?