New to the board DOHC spec questions

[stuartlowery]

So far I am torn between a 4.3 90* motor and the 3.4 DOHC for an engine swap in such vehicle as the Fiero. I need convincing on what the DOHC can do for me. I have read that the 1996 model has larger exhaust ports, and that the earlier has the "To drool over Forged internals"

What year has these internals?
What does the Stock DOHC 3.4 produce for HP and Torque?
What's the stock redline?
What year is the most boostable?
And how interchangable is the parts on the motors between years?
Who has built the strongest engine here?

Any help would be very much appreciated. And thanks. I may be picking one of these up this comming weekend.

Stuart Lowery

http://www.texasfieros.com

[Anonymous]

I would definately take the 3.4 over the 4.3.

stock for hp/tq, hp has ranged between 200 and 215, tq between 200 and 210. SO pretty much equal, but where the power ocurred changed. The 96-97 made the power a bit higher in the rpms.

Stock redline for all 3.4L is 7,000rpm

I'd say 91-95 automatic motors, cuz they had the lowest compression at 9.25:1. The 91-93 5-speeds had 9.5, as did the 96-97 motors.

Every motor is interchangable below the heads, and the heads/intakes are also interchangeble. Like people have put 96 intkaes on 92 heads, and it can be done vise versa since intake ports are the same.

I think it would be safe to say that I have the strongest DOHC motor here, but it isn't that great. Not many people have really built a DOHC for racing purposes. But my motor is new, and was built with really good components at a high price.

[dohcfiend]

depends on the time and $$$ u have along with what kind of power u want.

if u want a 4.3 might as well put a 5.7 in. cause a 4.3 is a 350 with 2 cylinders chopped off. the 4.3 has more power potential(and definately has more torque) cause there is not much aftermarket for the 3.4 dohc engines. it might have the same motor mounts as a 350 not sure though.

if u are on a budget go with the 3.4 DOHC it is the same block as the 2.8 that most likely came in the car, so if u use a fiero tranny the engine will bolt to the stock location(but modification is still required to make it fit). and in it's defense the 3.4 DOHC won't let u down especially in a fiero. it isn't much off the line but once it get it revved up it is a "little beast". stock as a rock a 3.4 DOHC will propel a getrag fiero into the mid-high 14's i have heard by several sources.

lastly, 3.4 requires more maintainence than average engines do. if i had the cash i would go with a 350 preferrably a lt-1 or ls-1. but if simplicity is your game carbed can make more power and alot easier to mod but there are mileage and driveability issues IMO.

[stuartlowery]

I've already found the dished pistons that I'll need for the 3.4 DOHC to lower the compression to handle boost. How much I don't know. I need something that's going to be quick off the line and has a descent RPM range to broaden the short gearing in the fiero. With a 5.7 First gear is useless. Maybe with the 3.4 it would have a reason but I don't know. I'm not an expert engine builder and I don't want to be too dissapointed. How much power can the 3.4 block handle? I already know it can handle higher RPMS. I understand I'm loosing 0.9liters of motor between the two but can teh efficiency of the DOHC help in that matter and could it hold up to the abuse? I'm leaning towards the 4.3 but I really wish there was a DOHC version.

[dohcfiend]

how much power are u trying to make?

as far as i know the 3.4 block is pretty strong and if properly maintained can handle alot.

another thing that might kill u is pistons as far as i know there are no forged pistons for this motor. u will have to get a custom set made. The weakest link IMO are the heads.

also there are some threads up in pennocks fiero forum detailing how the manual trannies keep failing under an lt-1, so keep that in mind too in your pursuit of power.

[bmlawson]

3.4

now i'm no expert on these cars but i thought i read somewhere on this site that the 91-93 had forged internals.

[stuartlowery]

I'm looking to create somewhere in the vicinity or 400- 450 BHP 375+ at the wheels. But my main goal is to travel the 1/4 in mid to low 12's in a 2700 lbs car.

[dohcfiend]

wow, u are definately going to have to boost a 3.4 dohc to get that kind of power. go with the 4.3 u can definately get there alot cheaper. but be warned that guy on the other forum has went through 2 4 spd muncies with a stock lt-1 275hp and 295tq.

i don't know about the the rods and crank but i know for a fact the pistons are hypereutectic.

[stuartlowery]

Oh I know about the tranny's The 4 speeds aren't as tough as the 5 speeds but they are geared better.

[dykz34]

I've always wanted to own a Fiero GT with a 3.4 DOHC + 282 in it... I think that would be a helluva fun car to drive! Plus, you have more room to turbo it in the Fiero than in the damned W-Body engine bay!

[Anonymous]

I test drove a GT with the 2.8 5-speed, I was liek wow, I didn't know a 2.8 could feel kinda quick...

God I would LOVE to drive one with a 3.4/284 :P :P :P

It has everything the Z34 doesn't-No weight, Ferrari like handling, And tons of TRACTION :P :P :P

[dykz34]

There isn't room for a 284 in a Fiero. You can get the 282 built to handle the power though.

[SappySE107]

Get the 282 from the W41 and have the close ratio gearing. You dont need a 4.3 to make that power with boost...in fact I bet the DOHC takes to boost just as well if not slightly more because of its valve area. Forged internals...no. Only the rods and thats all 60V6 engines that im aware of. Still, you can get crower rods or 327 small block rods from 68 and older and machine them to fit. Pistons, anyone can make these custom or you can go with 3.4 iron head pushrod pistons meant to lower compression on their motors. Hell, 3400 pistons may just do the trick in a forged variety. Crank, well i dunno how the 4.3 is but the 3.4 is stout and just some machining will make it stand up to your requirements. Deburr, polish, shotpeen, balance. Simple enough really. Oiling, should be good to go, the DOHC has 60% more flow than the pushrods and even with a turbo feed thats a lot of oil. Heads, port and polish...have the valves coated for the heat and thats about it. You can go custom valves but they are insanely expensive. Intake and Exhaust...well with boost, you dont need to worry too much about either if you dont want to. Custom headers to the turbo will help, and making a custom plenum to sit on top of the lower really shouldn't be too hard to do. Its a pretty simple layout from the lower intake.

The DOHC has an excellent powerband, and you can adjust the stock cams however you want without paying for a cam grind. Thats a major benefit to this motor for multiple applications. You can set it up for the powerband that suits your turbo and your gearing. If you desire, you can have the cams reground as well for 500 bucks.

Main reason I would take the 3.4. Sound. It is sweet at 7000 RPM sitting right behind you. Both motors probably weigh about the same but im not sure on the 4.3.

The flow of this motor is great though, i wouldn't be concerned with .9 liters.

[stuartlowery]

I have read Maximum Boost by Corky Bell three times so far and pick up more every time I do. May main worries are Expense and strength. I want to actually street this car if needed and it's still possible when boosting to 400HP. Heck I may even be happy with less power. I'm heading to a couple Salvage yards with a cherry picker bolted to my truck since the motors are $59 if you pull it your self. So I'm going after a few. So what years are best? Since everything is interchangable I want the best heads, best block, best crank, best intake so what years? Pistons I'm not worried about as I think I've already found them. Intake I can modify if needed.

I really wanted to go with the 3.4 but worried about it's limitations since the 4.3 would require a Complete custom intake Complete Custom TPI setup Different ignition basically way too much engineering to do. Don't get me wrong I'll be engineering this motor myself. Knife edging the crank, designing building and installing oil squirters for UNDER the pistons to aid in lubrication and cooling. ( I can see this one already I'm going to MAKE A MESS testing this one.)

Just a little history. I bought my Fiero for $50 from an individual nearby that just replaced the clutch and never got it started again. I watched this car for two months with the windows down with RAIN and cats. I inquired about the car at exactly the right time since the next day it was going to goto the salvage yard. The owner wanted $100 I talked him down to $50. With the help of my buddy driving my truck we towed the car around the corner aired up the tires and believe it or not JUMPED THE CAR OFF. Found that the clutch switch wasn't working very well but I figured it out quick. Car fired like it never sat a day. Now this car is an 85SE has the Notchback and the 2.5l L4 motor. I DROVE the car in front of the PREVIOUS owners house and ROASTED THE TIRES. THsi is very hard to do with a fiero since it usually pushes the fronts. Should have seen the look on his face.

Anyway the car needs restored ground up and it will get that as well as some custom pieces. Such pieces would be the 95 Nissan 240SX interior (dash door panels center console cluster, A/C controls) that I plan on working into the car. Believe me when I say IMPORT to GM conversions on gauges is TOUGH!!! but I've got that all figured out and hopefully soon it will go in as well as a COMPLETE rewire of the car. Currently the seats I have in it are from a 2000 Camaro but racing buckets will go in in due time. A CUSTOM front fascia will go on that will house the NEW headlights, Roof scoops and even a MOON ROOF. Custom exterior complete. Not one panel will go unaltered. Hopefully within 18 Months I can have the car finished but with a child on the way that may put a halt on things a bit.

Any way Thanks for the good info so far now for the BEST questions above.

Stu

[SappySE107]

Honestly, doesn't matter. The blocks are all the same thing, same crank, same rods, and the pistons like you said, dont matter. 96 heads have more quench area, less combustion chamber space, and a wide exhaust port. THe 91-95 heads probably have a better exhaust port for velocity but its hard to say. Intakes....its boosted, so it isn't gonna matter a whole lot that I can tell. The 96 intakes are larger ports and have a seperate TB, but other than that i dont know whats gonna really matter with a turbo on there. NA, the 96 intake setup raises the powerband 1000 RPM, so that might help you decide.