I have an '87 GT rated at 135hp. I understand that either the '86 or'88 had a rating of 140hp. If the engines were exactlt the same, why did Pontiac rate them differently at different RPM's?? Does this mean that if I run my V6 at 15,000 rpms, I can produce a "papaer" rating of 300 hp ?

------------------

Too bad, the forum doesn't include spell check; I'm sorry for the mistakes. :O

indeed there is no spellcheck, but the board gives ya an edit button

-Coop

I think the 85 maybe 86 were rated at 140hp. Don't know if the later 135hp was on paper or if they actually made some fuel/timing/compression changes. Yes you can rev to 15K........ONCE.......Paul
The 89 Turbo TA was rated at 250hp, which was GM's way of keeping down insurance rates.

The "official" ratings were this:

1985-86 140bhp@5200 / 170ftlbs@3600 / 8.5:1 cr mark II

1987 135bhp@4500 / 165ftlbs@3600 / 8.5:1 cr mark IV

1988 135nhp@4500 / 165ftlbs@3600 / 8.8:1 cr mark IV

Notice I have the word official in quotes. The V-6 in the Fiero was based on the Chevy version which put out 130bhp at 5200 in 1985. The Pontiac engineers designed there own intake which had much longer runners. This accounts for the extra 10 hp.

From Gary Witzenburg's book - In 1987 they reduced weight, improved seals and combustion chamber efficiency. The revised hp rating was due to what GM described simply as "more current data". What ever that means. Personally I think it had to do with the political pressure on Pontiac to keep the Fiero from competing with the Vette. The numbers were "restricted".

The 1988 V-6 had better counterwieghting and increased compression. The rating again was fudged.

You'ld have to put one on a dyno to find out the REAL numbers

If this is a major concern, just put some stickers on the window. Voila!!! Now rated at 160 hp.

I've been saving up my stickers, then when I get enough to cover the back window I can stick them all on and get a 300hp boost Lets see nitrous do that!

------------------
'86 Fiero GT 4spd, aluminum head 3.1, vented rear brakes, K&N filter and custom intake piping, Cavalier seats, Celica GTS Rims-got a T3 turbo just need some time
'69 AMC Ambassador sst 2dr hardtop 390ci 3 spd B&m shift kit(315hp/427ftlbs)
'82 Yamaha Heritage Special 400cc 6 spd, hi-flo exhaust and air filters-For Sale to buy more Fiero stuff

Corvette was known to play this trick and would under rate the car buy 5 or 10 HP then the next year they had one up on it being higher with no money spent. So both years the car was the same HP and no one new better. This is documented and honestly is a swift trick. Rick B

To clear a few things up.

Compression is 8.9:1.

The Fiero V6 is the exact same engine as the 85 Chevy V6 engine except for the upper plenum (curved around the dist), TB (Rochester vs Holley) and manifolds (SS vs cast iron). Exact same. The Chevy was rated 135. The only other difference is the ECM. The Fiero is map (SD) and the Chevy is mass.

Both were tested for emissions and if one failed, the other would have been used in both cars. Turns out that both passed so they used the SD in Fiero and the mass in the Chevy. Not unusual to get some field data. After they got burned on some bad mass sensors, they updated many with SD.

There are some slight calibration differences in the 85, 86-88 but they aren't that cosmic. It doesn't account for the HP difference.

I suspect the HP rating difference is for durability (rated at different RPM) but they are otherwise the same. I heard that it was for emissions but unless 135-140 is some breakpoint in the requirements, it seems very odd.

Maybe GM was just trying to be a bit more truthful about the real HP over a large production run. Some might be more, others less. Few stock Fiero V6's dyno at 140 from the factory. Someone did 3 or 4 at one time and it was mid-130.

The Fiero exhaust system does contribute to the slightly higher torque rating over the Chevy (crossover).

Dyno tests on the 81 X-11 with the carbed HO were on slightly higher than the Fiero V6 (mid-140's). It was Y pipe without a crossover. It had far better high RPM performance (short runners) and red line was 6500 but was a bit shy on the torque at low end.

[This message has been edited by TK (edited 11-06-2003).]

quote Originally posted by TK: To clear a few things up. Compression is 8.9:1.

I think you actually UN-clarified things TK.

The post I made above is right from the source. I don't know where you got your info but I have original Pontiac Press Releases and they say 8.5:1 for 85-87 and 8.8:1 for 88.

dont forget the valve sizes and rocker arm ratios being different between fiero and non-fiero 2.8's, along with cam grind.

[This message has been edited by Rhino88gt (edited 11-06-2003).]

quote Originally posted by Toddster: I think you actually UN-clarified things TK. The post I made above is right from the source. I don't know where you got your info but I have original Pontiac Press Releases and they say 8.5:1 for 85-87 and 8.8:1 for 88.

I can show you tons of errors in GM docs.

I've got pistons from all of the various engines and the 85, 86, 87 and 88 are the same. They have the part number cast into them and it's for the 8.9:1 piston.

Not sure what to say beyond that.

And the valves, rockers and cams are the same in the Fiero and the other applications for the equivalent MPFI engines (Z, W, S, 9).

Later engines changed but they are different engines.

I spent 3 hours on the phone with John Heinracy several years ago when I was doing X-11's (the developer) and grilled the living snot out of him about the 660 engine and how the HO came about, changes, the Fiero V6, etc. etc.

I wasn't trying to piss anyone off. Sorry about that.

[This message has been edited by TK (edited 11-06-2003).]

Ok - That's great, there is no answer. Well, I'll just call it 137 1/2 HP if anyone asks.
Ed

quote Originally posted by Firefighter1: I have an '87 GT rated at 135hp. I understand that either the '86 or'88 had a rating of 140hp. If the engines were exactlt the same, why did Pontiac rate them differently at different RPM's?? Does this mean that if I run my V6 at 15,000 rpms, I can produce a "papaer" rating of 300 hp ?

Sorry, the answer is yes. If you can keep winding it up, it will give more HP.

Beats me on the real reason why GM changed the rating.

I frankly don't understand it.

My 85, when you calculate the quarter mile time against the weight, calculates out to 145 hp.

I suspect the GM hp rating is simply the closest average. I expect there are variations from car to car from 135 to 145 depending on the tolerances, etc.

I sure wish Dyno's were a dime a dozen. That would make this alot easier for the average owner to figure out what they have under the hood.

quote Originally posted by TK: I wasn't trying to piss anyone off. Sorry about that.

No offense taken. My point is that the official" numbers, as published are above. The reality is another matter all together.

Lest we forget the '67 vette with an "official" rating of 425 horsepower and an actual dyno result of over 500! ya gotta love corporate politics