Question L99 4.3 Caprice LS Upgrade - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums

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Old 12-13-2010, 08:13 PM   #1
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Default L99 4.3 Caprice LS Upgrade

I have 1994 Chevy Caprice Classic LS with the 4.3 liter L99 motor and wanted to make a few upgrades to the vehicle to up it's performance. The 4.3 is rather underpowered for a 4,300 pound vehicle and I want it to feel just a bit more like a 5.7 liter. Currently the low end torque is great the low end horsepower is above average, and the top end just plain sucks.

Will these types of parts do the job?

Ram Air Shroud (already bought)
Air Cone (already bought)
58 cc bored throttle body (already built)
Scotchbrite polished plenum and ports (not built yet)
Stainless steel headers (Not bought yet)
Impala SS dual exhaust resonator-less (Not bought yet)
2.73" Ring Gear Set (Not bought yet)


My goal is 230 horsepower and 300 ft/lb torque, and the vehicle is doing slightly above 200 horsepower and about 270 ft/lb torque at the present.
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Old 12-13-2010, 10:26 PM   #2
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Yes those things will make a difference, but the 58mm TB is going to be way overkill and kill throttle response. I'd probably sell it or just not put it on. What exactly is a scotchbrite polished intake?

Personally I'd go with lower gears, 3.23 or lower should give you more of a faster "feel" than about anything given the vehicles weight. Might also want to add a slightly higher stall torque converter to the list.
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Old 12-14-2010, 02:49 PM   #3
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The 58mm TB is a waste, even on a mostly stock LT1 car. Now, there have been a few dyno pulls, that showed a little improvement, but I don't think it was worth the effort, until later in the mod list. It will do even less on an L99. Much better off, to put that money twards a proper PCM mail order tune, or some performance Valvesprings/1.6 rockers.

Your car came stock, with 2.93 gears if it has the weak 7.5" axle, or 3.23, if it has the strong 8.5" axle. If it's a 7.5" axle, don't put a DIME into it. You can get a 2.93/3.08 8.5" axle, every day of the week, for around $200-$300. If you are lucky, you can find one of the somewhat rare 3.23 axles, or the slightly easier to find 3.42 axles from 91-93 350 9C1's.

If I was buying a new ring and pinion, I would at the very least, do 3.42's. Thats if you do more highway. If you have a taller tire(27"+), then I would really consider going to 3.73. Does wonders for the car off the line. If will do even more for an L99, that takes even longer to get in it's powerband.

Going to 2.73... is only going to make the car feel more like a dog.

One of the great things about modding a nice L99 car, is that later on, you can pull it, and put an LT1 in, very no effort other than swapping long blocks. No mods really needed. And then, all of your mods will swap over, except the tune.
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95 DCM Buick RMS 14.21 at 91.79 "Jesus" Motor Swap at 85k
95 DCM Buick RMS 13.52 at 99.33 Buffmans Car Cracked Piston at 180k

RAISS, Tri-Y's, Pypes X pipe, Spintech Prostreets, 3000 Edge, 3.73's, Eaton Posi, and the rest of the Bolt-ons.
Coming soon! 845 cammed 96 9C1 engine.

And 7 other LT1 B-body's... Is there Rehab for this Sh*t?


Last edited by mrcadillac; 12-14-2010 at 03:02 PM.
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Old 12-15-2010, 06:10 PM   #4
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My idea with the 58 cc throttle body and the polished plenum was to give the motor a slightly taller and larger plenum volume which would help build up more torque. I figure less resistance (via polishing) in the intake will help HP a little bit, but the total package is gonna just help out the torque for the most part. The ram induction should increase horsepower heavily at high speed which I think is gonna smoothen out the consequences of tuning for low end torque.

The 2.73 gear ratio wasn't actually my idea, I found the TSB off of Prosis from owners of 4.3 caprices complaining about the sluggish performance, and GM made a 2.73 ratio option available.
The gears are 2.93 right now, and I changed the rear tire size from 225/70/R15 to 235/75/R15 and the front tire size from 215/70/R15 to 225/70/R15. I figured that a larger radius would increase tire speed and the HP a little bit on the rears.

The car really is jumping off the line, it's doing 0-60 mph in about 9.8 seconds on a good day, it's the 60-100 mph that is completely horrible.

Maybe the new intake would create enough torque to overcome the 2.73 gear ratio at low rpm? I'm not really sure.
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Old 12-16-2010, 11:44 AM   #5
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Holy crap, where do I start on this one. You seem to live in some back asswards universe, with physics that don't match the one I live in.

Quote:
Originally Posted by LT Scholz View Post
The 2.73 gear ratio wasn't actually my idea, I found the TSB off of Prosis from owners of 4.3 caprices complaining about the sluggish performance, and GM made a 2.73 ratio option available.
The gears are 2.93 right now, and I changed the rear tire size from 225/70/R15 to 235/75/R15 and the front tire size from 215/70/R15 to 225/70/R15. I figured that a larger radius would increase tire speed and the HP a little bit on the rears.
The only 94-96 TSB I see on sluggishness, suggests the replacement of the ICM. You might have to point out this horrible TSB, as it sounds like one of GM's brilliant moments.

Going from 2.93 to 2.56 on LT1 Roadmasters or Fleetwoods, makes them feel MUCH more sluggish. These cars have MUCH more torque than an L99 Caprice will. I drove a 2.56 Roadmaster for about a year. The only good thing about 2.56's, was that I could still drive it on the highway, even when 3rd and 4th gear didn't work, when I bought it. I put over 3,000 miles on it like that, and still regularly drove it on the highway at 60mph... in 2nd gear. When I put a new tranny in it, the thing crossed the 1/4 traps, in 2nd gear. Any time I drive it now, I just shake my head, at how sluggish the thing is off the line, compared to my similarly modded 95 Roadmaster with 2.93's.

Changing to a larger tire, is yet again, making the situation worse. You are not "Adding hp to the rear wheels". You are merely taking AWAY mechanical advantage. Taking away mechanical advantage, is the same as removing torque. Not ADDING hp. I have used 235/75/15's, on virtually all of my LT1 cars. 2.56, 2.93, 3.08, 3.73, 4.10. They all felt more sluggish off the line with the 29" tires, vs the smaller 27" or 26" tires. Vs 28's, you didn't notice so much, so I didn't include them.

Quote:
Originally Posted by LT Scholz View Post
My idea with the 58 cc throttle body and the polished plenum was to give the motor a slightly taller and larger plenum volume which would help build up more torque. I figure less resistance (via polishing) in the intake will help HP a little bit, but the total package is gonna just help out the torque for the most part. The ram induction should increase horsepower heavily at high speed which I think is gonna smoothen out the consequences of tuning for low end torque.

It just doesn't work that way.

A large amount of the Cammed and Heads and Cammed LT1's... still use a bone stock intake manifold, other than opening up the front bores to smoothly fit a 58mm TB.

Quote:
Originally Posted by LT Scholz View Post


The car really is jumping off the line, it's doing 0-60 mph in about 9.8 seconds on a good day, it's the 60-100 mph that is completely horrible.
I find it very... VERY hard to believe that your L99 car feels really strong off the line, then falls on it's face. The L99 has a much bigger reputation to struggle off the line, then start to come alive once you rev it. Which, going off how large the cam is compared to the Displacement, is what you would expect. The cam is identical from a Caprice L99 vs Caprice LT1. The TBI engines from the 91-93, were known for starting out strong, then falling on their face.
__________________
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95 DCM Buick RMS 14.21 at 91.79 "Jesus" Motor Swap at 85k
95 DCM Buick RMS 13.52 at 99.33 Buffmans Car Cracked Piston at 180k

RAISS, Tri-Y's, Pypes X pipe, Spintech Prostreets, 3000 Edge, 3.73's, Eaton Posi, and the rest of the Bolt-ons.
Coming soon! 845 cammed 96 9C1 engine.

And 7 other LT1 B-body's... Is there Rehab for this Sh*t?


Last edited by mrcadillac; 12-16-2010 at 12:49 PM.
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