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Swapping it for an LT would cost about the same as trying to dress up the L99. You can get a good LT1 in a u-pull-it for about $300. Just make sure it has lower mileage. You can swap all of your good parts to it, and return the rest to the yard as the core. Remember to get the computer for the LT1. (The computer for the L99 will run the LT1 if you want to use it. Stock class racers use them)
 

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Discussion Starter #3
LT is an option, kind of attatched to the 4.3. Mostly based on it has just under 79k, well maintained great running motor.
Thanks for the info!
 

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I had the L99 in the Caprice for many years before going with an LT1. Over the years, I added just a K&N FIPK for the lt1 cars. I also added a true dual Flowmaster catback was also added to the 4.3 without any issues or tune. Not much else I wanted to do with the little engine and neither K&N or Flowmaster would say if their kits would work or cause problems on the 4.3, but both were fine and a true bolt on.

As mentioned, the 2 engines are externally identical to each other. The nice part about these mods is they are also compatible with the LT1. If you do decide to add the other side exhaust, keep in mind you will need heat shields and hangers for the other side.
 

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To put it briefly, again, YES.
Ditto.....the exhaust manifolds are the same so Headers should bolt right up.

Back when I first did mods to the L99, it was my first crack at modifying a Computer controlled car. My only concerns at the time were "will this cause problems with the ECM since these were all designed for a 5.7 engine?". I could not get the vendors to verify if their 5.7 kits would cause any problems or not.....they had no info on the 4.3 and would not speculate one way or the other. So it was up to me to "just try it" and see.

As far as headers, just like the Dual exhaust I tried at the time, I think you will find they will fit and you just have to go for it and see if the ECM doesn't like it. But my gut tells me you will be fine. I didn't add Headers until I swapped in the 5.7, but they were on my list to add before the engine swap, just never got to it.

But realistically, how much performance you looking to get out of the old 4.3? As was mentioned, the 5.7 swap gives you more bang for your buck and certainly a bigger smile. I will add that the 4.3 I had served me well for nearly 120K (carefree) miles. When I sold it, it was still in great shape and never burned any oil.
 

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Not looking to put it on a drag strip, just a little more pep would be nice.
You want more Pep from a 4.3 :confused:, the mods mentioned will maybe give some benefit. No numbers to back this up and it could have been a Placebo effect with the car at least sounding better with Duals and looking better in the engine area with the CAI kit. Doubt there was much real world difference.

If you plan on keeping the engine and really want to see some Pep out of it, consider changing the rear gears. My original rear was a puny 7.5" with a 2.92 gear. Drop in a larger rear from an Impala/Caprice with a 3.42 or 3.73 and be prepared to smile more. Keep in mind that if you do this, you may need to also swap the drive shaft as the one for the 7.5" Pumpkin is too long for the 8.5" Pumpkin.
 

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But seriously, any bolt ons made for LT1's will fit the L99... So you're not really wasting money, Do what you can bolt on wise until you can do a swap. Then move the boltons to the new engine. No big deal.
 

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Even though Firewood's right …

Problem is, a bonestock Caprice Wagon with 2.56 will still outperform an L99 Caprice sedan with quite a few mods, simply because it has the LT1.

In other words, it's much better bang for your buck to just trade your L99 for an LT1, than to mod the L99. Seriously.
 

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Doesn't the 4.3 v8 having smaller bores and lots of metal between cylinders make it an excellent candidate for turbocharging?

If you think about it, if there was a power race between 4.3 v8 and 5.7 v8, the 4.3 should theoretically be able to handle more forced induction, wouldn't it?
 

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Doesn't the 4.3 v8 having smaller bores and lots of metal between cylinders make it an excellent candidate for turbocharging?

If you think about it, if there was a power race between 4.3 v8 and 5.7 v8, the 4.3 should theoretically be able to handle more forced induction, wouldn't it?
The weak point is not the block, it is the head gaskets. Either engine will push out the gasket before the block will break. It is always better to have more cubes.
 

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If you plan on keeping the engine and really want to see some Pep out of it, consider changing the rear gears. My original rear was a puny 7.5" with a 2.92 gear. Drop in a larger rear from an Impala/Caprice with a 3.42 or 3.73 and be prepared to smile more. Keep in mind that if you do this, you may need to also swap the drive shaft as the one for the 7.5" Pumpkin is too long for the 8.5" Pumpkin.
There is you answer.


Put some gear in it, get some PCM tuning done,

If it is a 94-95 , BUY the tuning cable, don't send out your PCM

If the day comes you really need more power and do go with more engine, the money spent on the 8.5 diff will not be wasted,

On the bore, the L99 is a different casting than the LT1.
It is not like it has super thick liners
 

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There is you answer.


Put some gear in it, get some PCM tuning done,

If it is a 94-95 , BUY the tuning cable, don't send out your PCM

If the day comes you really need more power and do go with more engine, the money spent on the 8.5 diff will not be wasted,

On the bore, the L99 is a different casting than the LT1.
It is not like it has super thick liners
OK didn't know that, thought the blocks were identical.
So the 4.3 block would be a little lighter then?
 

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I was just thinking here;

a 4.3 v8 has 12.6% less square inches of surface area of the cylinder circular area at the top compared to a 5.7 engine.

A 3.74 bore circle square inches are 10.99 inches square
A 4.00 bore circle square inches are 12.57 inches square

Now I don't know about head gasket integrity, but as far as the heads clamping force, wouldn't it be fair to say that a 4.3 running enough boost to create 12.6% more combustion pressure would be only pushing as hard against the heads as a stock 350?

That would bring the 4.3 from 200 hp to 225 hp without stressing the head any more than the 350.
This would be like 1.8 PSI of boost for about 12% more air.

Now I know that sounds like a total waste of time, but I'm not suggesting anything, just sharing my thinking out loud.

The 4.3 also suffers from a shorter stroke, but one benefit would be that the longer rods would mean that the piston would not be pushed as hard against the cylinder wall as the 350 piston.

Of course it's not all that simple, boosted combustion will still be hotter and more prone to issues than a non-boosted 350.
Head gaskets might not like the boost.
BUT, without many people trying to boost 4.3 v8's, it's hard to really know what they are capable of?! :D

If you could put on a variable vane turbocharger to get really high low end TQ, and have the high end power of a 350, or even higher, you could run a 1:2 rear end, get better MPG than a N/A 4.3 and more HP than a 350.
Again, just brain fartin here.
 
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