V8 vs V6 (Page 1/8)
treborerellim DEC 20, 08:28 PM
I have 2 Fieros a formula with a Cadillac V8 and 4-speed automatic. I also have a 87 GT V6 5-speed. The funny thing is the V8 can't keep up with the six-cylinder. The V8 is a dog. The transmission sometimes starts in low gear sometimes it doesn't will not kickdown at any speed. I had the wiring harness made by a forum member and the e c m reprogrammed by another member. I am very disappointed in the way it runs. I have another Cadillac engine sitting in the garage that I was going to put in the five speed. But after all the problems I've had with the formula V8 if I do I'll go carbureted less aggravation. I don't know where to begin to fix these problems. I'm an old carburetor and distributor guy. My first car was a 55 Chevy coupe 3 speed that I bought in 1965. I do like the way the V8 cruises down the highway. I wish it had a little more Giddy Up and Go.

Bob
RWDPLZ DEC 20, 08:32 PM
At this point if you're gonna put a V8 in a Fiero, LSX.
cvxjet DEC 20, 09:27 PM
Two engines I think would be good for swap; The LS4 which is the only TRANSVERSE mount V8 (310 hp) the other would be the new 4.3 V6- They completely redid it using tech from the LT V8s....It is actually only 300 lbs, which is 70 lbs lighter than the 2.8 V6....It has 290 HP.....

I actually have a carb V8 (460) in my jetboat.....Did not do any tuning for 10 years (Edelbrock/Carter carb)....Had to clean the carb two years ago but still no tuning (And the plugs look great)
Dennis LaGrua DEC 20, 09:51 PM
The Cadillac 4.9L engine is certainly not a high performance engine but I would not call it a dog. With 275 ft lbs of torque thats a significant increase over the 2.8L. If your 4.9L Fiero cannot keep up with the 2.8L V6 Fiero then something is either wrong with the engine, the installation or the programming/ wiring. The 2.8L has been road tested to be a 16 second car in the 1/4 mile, the 4.9L Fiero working properly should get you into the low 14's.
First thing is to scan the ECM to see if it is going into closed loop and to determine if everything is working correctly. If you are operating in "limp home mode" the engine will be very sluggish. If you are looking for an upgrade in performance, its an economical choice for more power, but if you desire lightning fast performance its not the V8 to have. Then move on to the other suggestions here.

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

pmbrunelle DEC 20, 09:57 PM
The Cadillac High Technology V8 should feel like a rocketship compared to the stock Fiero V6. There must be some issue with the engine, not necessarily mechanical, possibly related to the computer.

I don't know if your car has the same problem, but you may want to read through the recent thread:
https://www.fiero.nl/forum/Forum1/HTML/099807.html
Patrick DEC 20, 10:14 PM

quote
Originally posted by treborerellim:

Cadillac V8 and 4-speed automatic. I also have a 87 GT V6 5-speed. The funny thing is the V8 can't keep up with the six-cylinder. The V8 is a dog. The transmission sometimes starts in low gear sometimes it doesn't will not kickdown at any speed.



That automatic transmission is completely ruining your driving experience. With a manual transmission connected to the same V8 engine, you'd probably have a smile a mile wide.
La fiera DEC 20, 10:57 PM
275lbs/ft means nothing if that amount of torque was made at a lower RPM which means the HP would be less as the RPMs increase.
That's the mistake that lots of people do, call out torque figures but not at a specific RPM.
La fiera DEC 20, 11:04 PM
Almighty 4.9 Big Cubes Cadillac
https://youtu.be/acHe4jAOV6E

VS

My little Supernatural 2.8L
https://youtu.be/dayXz0arXZ0
Raydar DEC 20, 11:39 PM
I had the Caddy automatic in my 4.9 car. That trans, even when working properly, didn't do anything quickly. I almost sold the car because the automatic was so uninspiring.
I ended up swapping in a 5 speed trans, and adding the Allante intake manifold. The Allante intake helped a bit, but the 5 speed really transformed the car.
With that said... the ratios are far from ideal. It blows through 1st gear by the time you can blink. And it still runs out of steam by 5K. Just like all the 4.9 detractors will tell you.
But it's still an absolute riot to drive.
The one thing that would make it better would be an F40 trans, with the final drive swap that Fieroguru pioneered. But that's going to run into a bunch of work and money.

But as others have said, it sounds like something is wrong with yours.
For what it's worth, if the throttle position sensor is wired incorrectly, or otherwise defective, the trans will shift at funny times, or not at all.
If the computer is in "limp home" mode, the trans will start out in 2nd gear, and the timing will be at a fixed value. In short, it will be a slug.

Additionally... the 4.9 Caddy has like seven different options (code masks) for burning chips. If someone used the wrong base tune when they programmed yours, it may not be compatible.
I had that same issue with mine, using a chip that someone else had programmed for me. (IOW, it went into the "limp home" mode that I described, previously.)

[This message has been edited by Raydar (edited 12-20-2021).]

BillS DEC 21, 11:40 AM

quote
Originally posted by La fiera:

Almighty 4.9 Big Cubes Cadillac
https://youtu.be/acHe4jAOV6E

VS

My little Supernatural 2.8L
https://youtu.be/dayXz0arXZ0



Nice comparison.

Think about a four cylinder. My LNF, very mildly tuned - at wheels = 325 whp 347 Tq 2 liter modern engine, lots of room around it. Biggest issue is finding a place to put the intercooler.