12 sec n/a DOHC Fiero, is it possible?

[RacerX11]

12 sec NA DOHC n a Fiero possible? Yes..Will has done it with his N* (Oh..sorry....you meant 3.4 DOHC )

The guy with the LT-1/4spd was grenading suspect mileage '84 units with the weaker case, and there is some question as to the eccentricity of his adapter plate. There are also lots of people blowing the diffs out of high-mileage Getrags, most likely with worn diff bearings. If he had tried a freshened later V6 4-spd with the stronger case he might not have the same problems. For all the people blowing up transmissions, there are just as many high HP/Trq Fieros running hard without breaking the trans.

The DOHC that put 240 HP to the wheels had custom headers, short runner/large plenum intake manifold, degreed cams, and shimmed valve springs. The owner admitted it wasn't a very streetable package due to the torque loss down low.

The Northstar pistons sound good at face value, with the 93mm bore, but the piston pin diameter and the compression height are different. 6" rods will put the piston top 0.076" above the deck surface, which won't work. Most likely custom rods would be required. Just because they make 10.3:1 compression in the N* doesn't mean it will yield the same in a 3.4 DOHC. You would be better off getting custom 93mm forged pistons made to your desired compression ratio.

As far as the most modded NA DOHC being Aaron's? What a joke.

If I ever go with a 3.4 DOHC in my Fiero, it will have a turbo. You can do it NA, but its just too much $$ and work. Without variable valve timing or dual-runner intake, the engine is handicapped.

Marty

[Anonymous]

The DOHC that put 240 HP to the wheels had custom headers, short runner/large plenum intake manifold, degreed cams, and shimmed valve springs. The owner admitted it wasn't a very streetable package due to the torque loss down low.

The motor was nearly identical to stock up until 3500 when the stock motor picked up. And until 5,000, it was never down by more than 20hp. After 5,000 there was no contest, and at 7,000 the short runner car was making over 100 more horsepower.

[dohcfiend]

well put racer and appreciate the piston info.

[RacerX11]

The motor was nearly identical to stock up until 3500 when the stock motor picked up. And until 5,000, it was never down by more than 20hp. After 5,000 there was no contest, and at 7,000 the short runner car was making over 100 more horsepower.

It may never have been down more than 20HP, but torque is a different story. It started dropping back at 3300rpm, and at 3500, when the stocker picked up, it fell on its face, dropping nearly 25ft-lbs. From 3600-4700rpm it lagged behind the stocker by 25-35ft-lbs, and as much as 50ft-lbs at 3700rpm. This is a substanial torque loss (13%-25%), which you will notice. You can't make the power up top without a sacrifice down lower.

Here's the page with the dyno sheets for those not familiar with it: http://fiero.cc/fiero-tdc/members/mws/intake/index.html

Dyno sheets:
Power http://fiero.cc/fiero-tdc/members/mws/intake/240hp.JPG
Torque http://fiero.cc/fiero-tdc/members/mws/intake/196lb.JPG

Marty

[Anonymous]

Yah I do see those torque losses, and they are big. But my auto stays below 3,000rpm most of the time, occasionally I let it go to 4, and I drive pretty spirited. And this is in a much heavier car, with terrible gearing. I could easily handle that power curve in a 2600lb Fiero with a 5-speed, and I bet that its gas mileage is still the same under normal day to day driving. And let the rpms climb, and you will get a swift kick in the stomach for sure.

[Doubt_Incarnate]

i say what you are looking for is pretty close to impossible without boost. in my opinion. if you can find a TDC, start with it, just do what everyone else has done/recomends and see how close you get. try other things to.
www.fierostore has an aluminum flywheel.
hondas knifedge the crank for lighter weight to rev faster, and less air resistance in the case. crankase evac can be fabbed up easily/cheaply from what i hear, just need to draw vacuum on the crankcase, they normally use the exhaust system to do that, or run a vac pump to take care of that. porting can be free if you do it. do whatevr possible to keep the motor as cool as you can, find extra parts to experiment with, then swap them out in a day and see what happens. if all else fails, lighten the car, rwd you should take weight off the front where it wont matter so much, but dropping pounds allaround is good.
dont be afraid to play around if you dont need the car for everyday. i had a plymouth with a 318, i had to use a drill pres to spin up the distributor drive gear so i could thin down its bearing surface to fit right (improvised lathe...)drill presses rock, you could maybe get away with using it like a mill, i'm going to find out soon.
thats real cool they way people followed you here to knock you down. maybe they should get a life or something.

[Anonymous]

12s in a Fiero with a 5-speed will take about 350 horsepower. This is far from impossible.

[DreX]

Never the less my engine is moded, actually I think is the most moded one. I didnt touch the internals since my engine is new. But all external parts are moded.

You don't have the most modded one. The highest modified N/A one so far I think belongs to Aaron, and his has some parts on the inside iirc. But there are a few Fiero guys with motors that are close, if not further done than his.

Here are my mods

Custom Hi-Flow headers
Mandrel Bend exhaust
Straingth tru muffler
race cat
LS1 TB
Custom TB mount
4in dragon filter + CAI
UD Pulley
deleted PS pump
aluminum flywheel
stage 4 cluth
100% over stock high pressure plate
MK7 Tranny
Magnecor Race wires
Denso Iridium spark plugs
Hyper Grounds
retimed cams
and soon Bens chip

All that in to a Fiero

Now you get the pciture.

Dre

[DreX]

Oh I forgot

255lph Holley fuel pump
Aeroquip fuel lines
325GPH race fuel filer

Dre

[RacerX11]

12s in a Fiero with a 5-speed will take about 350 horsepower. This is far from impossible.

Aaron,
Nice new screen name. How is TX treating you? You need some more accurate numbers. Will ran his 12.82 with a 300 HP N* running a 275HP chip, putting only ~260Hp to the wheels. But I guess the 3.4 DOHC will have less torque, so more power will be needed.


Impossible? No. Difficult and expensive? Yes. You could spend less time and money on a turbo and be pushing 11's with a setup that is more streetable than your mythical 400HP@8000rpm wonder-engine (which has now grown to 430HP over in Pennocks-land).

Marty

[Doubt_Incarnate]

doesnt v6h.o. have a 13.5 j-body? thats a hybrid motor isnt it?

why not just build an identical setup in your fiero, it has to make a difference being rwd with all the weight over the drive tires. all you need to do is find a way past that last .5 sec and your in. with a smaller motor, making it more impressive. not to mention it has good lowend, more redily available parts, swaps right in phsyicaly, aluminum heads means it probably lighter than the old 2.8. i think manta parts sells 3.83 and 4.11 gears for the isuzu tranny, that would probably help too.

[RidgeRunner]

13.9, actually. And yes it's a hybrid.

I don't think the isuzu trans would be good. It seems to have the reputation of being fairly weak.

[Cannonball]

13.9, actually. And yes it's a hybrid.

I don't think the isuzu trans would be good. It seems to have the reputation of being fairly weak.

That and it has a long streatch between 1st and 2cnd gear which isn't to good for performance. A real torquey motor wouldn't mind the dip between gears so much but then you kill the trans with a lot of torque so that doesn't really help either.

[Froggx]

I agree with isuzu trannies sucking

[Will'sFiero]

I'm impressed that people here know my specs...

Anyway... My car ran 12.86 @ 106 with 1.92 60', 255 rwhp and 265 rwtq.

Michael Smith's car put down 243 rwhp, IIRC, so getting the power necessary to run 12's is a known quantity. Getting the timeslip is in the details.

When I ran my 1.92 60', I was running Gabriel struts and couldn't launch as hard as I might have been able to due to wheel hop with my 300# springs. Now I have Konis and 325# springs. The combo is immensely better and I could almost certainly pull a 1.8 sixty, maybe even 1.7's. That's on street tires.

Also, attention needs to be paid to the transmission. Manual transmission is the obvious choice with this engine, however there are a couple of options. A 284 has a nice 1-2 shift to help keep the engine in its powerband at the slow end of the strip, where tenths are more important. However, a 282 with a 3.94 FD (and 1.03 4th gear) would make the car faster for the entire length of the strip, while sacrificing a little time for the engine to pick back up after the 1-2 shift.

Oh yeah... if you can't get traction in a 3.4 TDC Fiero in 1st gear, your suspension needs work. I have over 80 ftlbs more than a 3.4 and I don't have 1st gear traction issues. I also have 255/50-16 tires... they help :P

People talk about GM FWD manuals like they're made of paper mache... They're not. Because so-and-so gooned his up doesn't mean they all break. FieroX likes to go on and on about how 282's suck because his buddy lunched one running a 13.8... so what. Enough other people run 12's on them to prove that the 13.8 failure was a fluke.