No Ordinary 91

Okay i keep reading that there is a 245 HP version and a 250 HP version in the 91's how can you tell the difference, its only 5 HP i know but i am **** and it has been bugging me. Was 250 in say Automatics, or manuals

NoWorries

It depends, if you've worked it over, you could make 329 hp and 455 lbs. of torque for a relatively small amount of money... :D

Sorry, just had to answer that way. :D

What you are asking about is between a Z51 option and just a regular Vette. The Z51 adds a couple of power adders, but is mostly a handling setup.

No Ordinary 91

okay then since i hae the FX-3 i have 245 then right?
i am hopefully creaping up on 300, trap speeds corrected to sea level indicate approx. 280 some HP, would that estimate be at the flywheel or to the wheels

JoBy

http://www.geocities.com/motorcity/4310/vetfacts.htm


The 85 and 86 Corvette is rated 230 hp with iron heads.

86 Corvette is rated 235 hp with aluminum heads.

87 Friction reduction from roller valve lifters (new for 1987) resulted in a power increase to 240hp, up 5hp from 1986's aluminum-head engines.

88 240hp except for coupes with 3.07:1 axle ratios which had 245hp. The 5hp increase came from less restrictive muffler which were deemed too loud for convertibles and 2.59:1 axle coupes.

89 Same as 88.

90 An air intake speed density control system, camshaft revision, and compression ratio increase added 5hp to base-engines, up from 240hp to 245hp (except coupes with 3.07:1 or 3.33:1 axle ratios which increased from 245hp to 250hp because of their less restrictive exhaust systems).

91 same as 90.



[Modified by JoBy, 11:18 AM 8/23/2001]

dgoodhue

Basically if you have a 6 speed or a auto with 3.07:1 gear your car was rated at 250hp, becuase of the low restriction mufflers. This assume you have the factory exhaust though.

scorp508

And.... It is undocumented in 1987 that Z51 got 245hp as it got the Z51 free flowing mufflers also. But it did.

Sal Collaziano

No Worries. Could you be more detailed about the low-cost modifications that could get your horsepower so high? I may be buying a 91 and I'm really interested in what you know...

Thanks...

1991Z07

Sal,
Here is what I did on mine before the engine change. It netted 253.3 HP and 366.4 lb/ft at the rear wheels (or 301.5 HP & 436.19 lb/ft @ flywheel w/16% driveline loss...if I did the math right).

All I had was a high-output coil with the high-performance HEI module for the ignition and a FlowMaster CAT-back exhaust system. It would have been interesting to see what would have happened with the headers & Corsa system I have now with the old motor.

Add a set of headers, some mild porting work to the plenum, baseplate & heads with some bigger tubes with the adjustable fuel regulator (with new chip) and it would wake it up another 30+ horsepower pretty easy I would think. Beyond that isn't going to get you much without some SERIOUS head work and base-plate porting (or a new ACCEL or TPIS intake) as the heads/base-plate are seriously restrictive. Some CNC work on the heads will yield you around 220 CFM, but the cost to do that will pay for a new set of AFR heads (or comparable).

If you want stealth, the CNC'd stock heads are the way to go. :D

scorp508

Thats IT? Hmm.... wonder what I'm putting out now with the cat removed.

1991Z07

Forgot one thing...I also had the SMFW on the car.

And yes...that was it.

scorp508

:confused:

rcolling

Maybe Single Mass FlyWheel?

If the above is true, and I don't doubt it, I can see a run on HEI coils... :D
I know I am ordering mine tonight.

scorp508

Possibly, but that wouldn't "make" more HP, only help transfer more to the drivetrain.

rbartick

My opinion is that the 85-88 L98s are all about the same power. I have yet to see a stock 86-88 Vette take my stock 85 at Englishtown Raceway park. As far as magazine tests go the 85 L98 was rated at 14.1 @ 98 MPH by Motor Trend back in 1985. I've never seen a faster 86-88 stock L98 in Motor Trend, Car & Driver, or Road & Track. The changes that Chevy made from 86-88 are just marketing hype.

--rb--

scorp508

Wasn't it 1985 Autos that got a slightly higher stall convertor? That could account for it. The change over to aluminum heads and then hydraulic lifters in 87 weren't marketing hype at all.

65Z01

Well the "Corvette Black Book" says:
"...350ci, 245/250hp, at, oc"
where at=auto tranny and oc=oil cooler

But back in the "90s description they say:
...except for coupes with 3.07 or 3.33 axle ratios which increased from 245 to 250 due to less restrictive exhaust.

1991Z07

Yes, it is a "Single-Mass Flywheel".

I don't know if I believe it doesn't release any additional HP. Removing 18+ pounds of the rotational mass has to do something. It sure makes it rev faster, though.

A new cam with the head/intake mods I mentioned before would be advisable as well.

Remember that with the HEI coil and module you won't get any great improvement without a good set of wires and plugs. Those numbers were generated with a set of "Live-Wires" and Bosche Platinum +4's.

It raised my eyebrows as well when we got the dyno numbers. Stock chip, a little race fuel in the tank, and some impressive numbers for a "relatively stock" L98 with 69k miles on the odometer (all by me!).

rbartick

>Wasn't it 1985 Autos that got a slightly higher stall convertor? That could account for it.

My car is a 4+3 stick shift and it ran 14.0s with just a K&N and air filter lid mod. Original 15 year old spark plugs, dist cap & rotor, exhaust, etc..
http://www.rbartick.com/race_85.htm

>The change over to aluminum heads and then hydraulic lifters in 87 weren't marketing hype at all.


IMO these changes were worth about zero HP. The "gains" were probably around the same as the *huge* gains I got with my K&N filter
;)

I've since installed an off the shelf Hypertech Stage II chip, 160 thermo, and cut the screens, and installed a TB bypass. My track times are the same 14.0s after these mods, but I did run a few high 99 MPH passes. The additional MPH could be a result of track experience.




[Modified by rbartick, 3:21 PM 8/23/2001]

Sal Collaziano

Thanks for all the replies, people. This answers just what I was asking...

SurfnSun

Rating and Reality are totally different. In a street race, Ive never lost to another stock L98. I think Ive raced every year, have pulled on all or ran even with.