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Discussion Starter · #1 ·
I have a 96 caprice classic mostly stock, I have changed the rear end to an 8.5 inch with a 3.73 and Posi, all new BMR suspension in the rear with Blisten shocks and Hotchikis lowering springs. I am looking to do performance mods to the L99 to increase power and speed. I AM NOT LOOKING TO SWAP THE MOTOR. If anyone has done some work other then exhaust and rear end I would appreciate hearing about it. or have recommendations. I plan to do a TB coolant bypass this week also. looking for recommendations for any possible mods or upgrades for the L99.
 

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Discussion Starter · #3 ·
50HP shot of nitrous?

Honestly, many of the engine modifications are more work than an engine swap
I assume there are things that can be done that are transferable for when I do swap, that in the meantime can get me a little more. I know the swap is cheaper in the long run but the motor has such low miles would rather drive it until it goes, but was hoping for some recommendations to get it some more power in the mean time.
 

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Ok - "Not looking to swap the motor" and "modifications that are transferrable to a future swap" are different things.

To narrow this down a bit...what engine are you considering swapping to in the future?

What are your goals for this car? Weekend warrior, daily driver, highway cruiser, primary car, fun toy, dragstrip, etc?
 

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Discussion Starter · #5 ·
when I say swap I'm talking 8 years down the line. I'm looking for a fun toy that's got some go off a light. if i could get the L99 quicker and some more power maybe up to 300 hp I would be happy with it and would not see a reason to swap at that point.
 

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I am looking to do performance mods to the L99 to increase power and speed.
I AM NOT LOOKING TO SWAP THE MOTOR.
If anyone has done some work other then exhaust and rear end I would appreciate hearing about it.
or have recommendations.
I plan to do a TB coolant bypass this week also. Looking for recommendations for any possible mods or upgrades for the L99.
Remember this thread?
Everything said in that thread, especially about which pulleys to underdrive and which ones to overdrive, and about what not to do, still applies.

If you are looking to swap to an LT1 "8 years down the line", then you are free to do all those OTHER mods that any LT1 owner would do, EXCEPT don't do anything to the L99 itself.
No cam / heads / valvetrain upgrades - not that I can think of any available to begin with.
Don't bore the L99. Don't stroke the L99.

Even if you got really good at fine-tuning your Caprice's pcm calibration, you'll learn to take 36 MpG on the highway for granted, before you make an L99 achieve 300 horse for less than $3000.
 
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"Quality 9" torque converter"
While shopping around for one of these, he ought to rebuild the 4L60E to withstand 400 horses and torques.

"Cheapo 1.6 rockers"
As in, 1.6 NON-roller rockers?

"Bunch of valvespring"
How much (more) valvespring could those tiny little valves really need, even at 6500RpM?
Besides, OE pushrods are a wee lil bit flexible.

"Tune it properly and figure out where an L99 really noses over."
No variable-valve or -cam or -inlet manifold tech; think that means he's effectively got 6500RpM.
(I'm sure someone will correct me here.)

Do L99 pistons have valve reliefs?
How much COULD the L99 heads be milled for more compression?
Or: How much more compression can the L99 heads yield, without becoming an interference-valved engine?

1.6 NON-roller rockers, valvesprings allowing 6500RpM, proper tuning ...
without at least a dual catback exhaust, I doubt an L99 would make 300 horse.
I bet it could make at least 36MpG though.
 

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Waste of time. Have it tuned for mileage and enjoy it until you put a real engine under the hood.

Reminds me of kids thinking their grandmas 99 Civic is bad ass because they cut the cats and mufflers off and had some tuner make it go pop pop pop when they let off the gas.
 

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As mentioned above, leave alone the engine entirely except maybe a tune to optimize shift points for that better rear and its gears - maybe. And also as mentioned, for the next 8 years shovel funds and effort into finishing the susp. upgrades and also prepping steering, brakes, drivetrain and chassis (all known weak links on our tubs) to assure the power of the planned swap is actually usable and gets to the ground.
 

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"Quality 9" torque converter"
While shopping around for one of these, he ought to rebuild the 4L60E to withstand 400 horses and torques.

"Cheapo 1.6 rockers"
As in, 1.6 NON-roller rockers?

"Bunch of valvespring"
How much (more) valvespring could those tiny little valves really need, even at 6500RpM?
Besides, OE pushrods are a wee lil bit flexible.

"Tune it properly and figure out where an L99 really noses over."
No variable-valve or -cam or -inlet manifold tech; think that means he's effectively got 6500RpM.
(I'm sure someone will correct me here.)

Do L99 pistons have valve reliefs?
How much COULD the L99 heads be milled for more compression?
Or: How much more compression can the L99 heads yield, without becoming an interference-valved engine?

1.6 NON-roller rockers, valvesprings allowing 6500RpM, proper tuning ...
without at least a dual catback exhaust, I doubt an L99 would make 300 horse.
I bet it could make at least 36MpG though.
My comments were based on he wants to do something as opposed to leaving it alone which is the more prudent, yes.
Convertor , quality vs some local built full sized POS that stalls higher and nothing else.
Somewhat of an investment as it can be used later when he realizes the L99 is slightly quicker than a snail .
Spring, as in enough that he could rev it into the low 6K range IF it will make power there .
Thinking about the roughly 90 cube smaller engine has the same cam as LT1
Push rods . Roller cam small block chevs have a pretty short push rod.
Rockers, yes cheap no roller trunion .

Interference engine. Oh, I think a stock 23° head sbc already is . Dont think you could break a timing chain on a stock L99 without hitting valves.
Dual exhaust , forgot the L99 was single after the Cats. Never actually seen one in the flesh.

Power, oh I agree its not going to make much to any power.

My bench racing suggestions were just that, based on no l99 hands on experiance
I thought with his 3.73 and some convertor he could get up into the area that it makes what ever power it does make and springs and a little more lift might expand the range a little.
Yes its still going to be a stone.

Tuning , anyone that ever dynoed or WB'd an LT1 knows they were , among other things , pig rich.
I assume the L99 is the same.

Is any of the above smart? Probably not .
I am of the put an LT1 in it camp also .
But IF he is dead set on modding the engine as opposed to leaving it alone what route would you recommend?
 

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This is not my area of expertise but think about this:
L99 200Hp 240 lb/f
LT1260Hp 330 lb/f
At the same RPMs.
So the L99 was just about 25% less across the board.

Any engine modifications may cost more as the only thing less supported that a LT1 is a L99.
The L99 is called a "baby LT1" but when the parts books come out there are differences. Would they make a mod different? I do not know.

The short answer of do not modify a L99 translates to you may be spending larger amounts of cash for smaller gains, and the parts may not all be transferable to a LT1 at a later time.

With a eight year plan I would suggest you leave the engine alone and use the L99 as a "test mule" to learn about engine and transmission tuning.

If your area does not have restrictive emission testing move back to OBD1 for easy and cheap PCM tuning software.

Enjoy the 3.73s with proper tuning and scan media for a cheap functioning LT1.

i could get the L99 quicker and some more power maybe up to 300 hp I would be happy with it
This is 1.5 times increase. Getting a LT1 to 390Hp requires a lot of time and money. 300Hp seem like a hard to achieve goal for a L99.
 

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My $.02.

The L99 is like my 250 CI straight 6 in my 72 C10. I can spend stupid amounts of $ buying a Offy 4 brl intake and a 500cfm Holly and long tube headers for it to gain what maybe 40 hp. Smart money would be for me to pull the 6 and drop in a V8 (anything but a L99)

Op would wind up spending same $ for LT1 engine parts to get 1/2, if that, power gain

I am in the save the $ and wait until you can buy a real engine...

....but if OP is intent and doing something, regardless of cost vs gain...aka is the juice worth the squeeze...than headers to true dual exhaust, cold air intake. 1:6 RR and a valve spring that will put up with more RPM and slightly more lift along with a PCM tune to allow for more timing, better fueling, higher shift points. A higher stall TC...would get the car to move off the line quicker with the 3:73...the 4L60 in good shape can handle a L99 with those mods. It will quickly shiat itself with those mods behind a LT1 so if end game after throwing $ at a L99 is to put a LT1 in than attention to the 4L60E would be prudent

But again cost vs returns...lipstick on a pig
 

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I am looking to do performance mods to the L99 to increase power and speed.
I AM NOT LOOKING TO SWAP THE MOTOR.
If anyone has done some work other then exhaust and rear end I would appreciate hearing about it. or have recommendations.
I plan to do a TB coolant bypass this week also.
Looking for recommendations for any possible mods or upgrades for the L99.
I think Wrench1996 learned in
this thread
what LT1 enthusiasts think of the L99.
If he has done other ISSF searches on the subject, he's probably found lots more
"swap out the L99 swap in an LT1"
than he has found help.
Waste of time. Have it tuned for MpGs and enjoy it until ...
We all agree modding the L99 for more power is a waste of money.
Don't think it's a waste of time to write several earnest posts pondering the idea of modding an L99 for more power.
If he learns to tune an L99 for better BSFC, that's more power AND more MpGs.

Gerry, I pretty much stipulate to
this entire post.
If I may add to the following?
Tuning, anyone that ever dynoed or WB'd an LT1 knows they were, among other things, pig rich.
I assume the L99 is the same.
This is one of the reasons why he'll reliably hit 36MpG before he hits 299 horse once.
Anyone claiming to be dead set on modding any engine since 1994 has no right to say so UNLESS they are willing to at least get a mail order tune.
Should he have the patience to do an OBD1 conversion and learn to use $EEhack to tune the everlovin' schidt out of the L99, it'll serve him well when he finally installs an LT1.

Somebody, PLEASE, get Wrench1996 an OE 5.7L LT1 dual exhaust (RPO N10) - or better.
In case it's been a while since it's been mentioned: for reasons I don't fully understand, when I bought my first ever 9C1-LT1 Caprice in '97, despite that the SPID clearly stated N10, it had an L99 exhaust on it - but not for long.

Whatever exhaust system gets installed 'around' the L99, will serve an LT1 even better.
 

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Discussion Starter · #15 ·
Waste of time. Have it tuned for mileage and enjoy it until you put a real engine under the hood.

Reminds me of kids thinking their grandmas 99 Civic is bad ass because they cut the cats and mufflers off and had some tuner make it go pop pop pop when they let off the gas.
When i do go to swap to an lt1 does it need to be the same year or will or will any lt1 be an exact fit?
 

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The 1996 is a "orphan year" only year of OBD2. It is not "plug and play" with the 94-95 that do not have a crank sensor. There are ways around the differences.

As well there are differences in the 94-95-96 transmissions that have work a rounds as well.
 

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Any LT1 from any '92- 96 'vette
Any LT1 from any '93-'97 FireBird or Camaro
Any LT1 from any '94-'96 Fleetwood, RoadMaster, or Caprice / Impala SS

will share near-as-makes-no-difference the exact same external dimensions as any L99.
If you get an LT1, be ABSOLUTELY SURE that it's not another L99!
I would not be surprised if someone fell for this - I've already seen 5.3L LM4s in Corvettes.

Keep the front engine cover off of your L99 for your future LT1, as well as your coil and coil driver module.
Also not a bad idea to keep the Opti-electrical harness on top of the engine.

If you get a '92-'93 LT1, you'll NEED the MAF you have now.
If you get a '94-'97 LT1, the larger MAF is ok, but it will not make any more power than the smaller one.
Note that the smaller MAF is also the 5.7L MAF for sedans & wagons.

Use the 5.7L injectors, NOT the 4.3L injectors, PLEASE.

(Without any valvetrain mods, I very strongly doubt any L99 can hit 260 horse.
Whole lot easier to release 60 horse from LT1s, than from L99s.
Even with valvetrain mods, I don't see how 290 horse is possible.
On the other hand, starting to wonder if 40MpG is possible ...)
 

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Discussion Starter · #18 ·
Any LT1 from any '92- 96 'vette
Any LT1 from any '93-'97 FireBird or Camaro
Any LT1 from any '94-'96 Fleetwood, RoadMaster, or Caprice / Impala SS

will share near-as-makes-no-difference the exact same external dimensions as any L99.
If you get an LT1, be ABSOLUTELY SURE that it's not another L99!
I would not be surprised if someone fell for this - I've already seen 5.3L LM4s in Corvettes.

Keep the front engine cover off of your L99 for your future LT1, as well as your coil and coil driver module.
Also not a bad idea to keep the Opti-electrical harness on top of the engine.

If you get a '92-'93 LT1, you'll NEED the MAF you have now.
If you get a '94-'97 LT1, the larger MAF is ok, but it will not make any more power than the smaller one.
Note that the smaller MAF is also the 5.7L MAF for sedans & wagons.

Use the 5.7L injectors, NOT the 4.3L injectors, PLEASE.

(Without any valvetrain mods, I very strongly doubt any L99 can hit 260 horse.
Whole lot easier to release 60 horse from LT1s, than from L99s.
Even with valvetrain mods, I don't see how 290 horse is possible.
On the other hand, starting to wonder if 40MpG is possible ...)
Thank you very much for this information.
 

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This may seem like a dumb question but is there a sure tell that it is a 5.7L not a 4.3L?
A bad answer is so much worse than a dumb question!
If you knew how many 5.3L LM4 'vettes are out there, you would know it's not a dumb question.
Also covers other not-so-insignificant differences between some OBD1 and OBD2 LT1 variants.
Point is you can still use an OBD1 LT1, you just need a few OBD2 LT1 accoutrements.

Take the heads off of both engines and check the piston size.
If the pistons are as puny as yours, beat the schidt out of that bastaducci with them.

Other reason to take the heads off is, it's an opportunity to upgrade to an even thinner gasket.
Lil' more compression, lil' more MpGs, lil more power - especially if the LT1 is not from a sedan or wagon.
 
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