I'm getting close to my 240k mile mark on my original motor on my '90 RS, and I was getting ready to start engine shopping when I found someone selling one of the 4.3L Caprice L99 V8's for ~$200 w/ECU, wiring harness, all accessories, and headers/cat. So I have a couple of questions about this engine. I know that it is externally the same as the LT1--just that the bore/stroke are different along with the displacement. Let me start the questions.

1) Does this engine use the same engine mounts as the 5.7L LT1?
2) Am I correct in my assessment that the 305/350 engine mounts can be used? (IE my 305 mounts?)
3) Any idea what the max power output this engine can have on the stock internals? (IE how much power can I safely get from bolt ons)
4) Does the LT1 swap guide apply to this engine since it is externally the same?

My goal is to get 400~480bhp at the CRANK using two turbos or a roots supercharger . I'm not looking for a street rod, drag car, or a redlight queen. My main purpose for the car is a 4th gen TA interior swap, all blacked out (minus license plate), and somewhere in the neighborhood of ~420bhp for my simple right foot pleasure along with needing some beef to pass someone if needed. Thanks in advance for any help.

P.S. For those who remember my emissions woes I never did pass. I am finally down to what I think is the catalytic converter in conjuction with my EGR valve being my problem. But since my mileage is getting up there I'm not even bothering to fix it. I can say that this beast is running fantastic even in its old age...but its getting close to the time for a swap.

*edit*
I tried searching for "L99 swap" but got nothing.

*edit 2*
The L99 in question has 56,000 miles and came from an elderly couple's rear ended Caprice.

 

first check if its obd2 if so you might want to get an obd1 computer since it will have to be re tuened or see if it can be flashed w obd1. i think externaly its the exact same as an lt1/4 but if the bore is smaller, the chambers are as well, so that idea of lt1 heads is a no go. the stock heads are iron and will need some porting and i say the lt4 hot cam kit from GM would get you 400hp maybe with a tune, exaust, ported intake, ect... If you wont to go cheap and stay in small displacement. The 4.3L crank in a 5.7L block with 302 yes the old 69 camaro DZ302 custom pistons and it makes a cheap 302 that will just scream and you can use any heads for a 5.7L LT

My 5.7 lt4, lt4 hotcam kit very very mildly ported heads and intake w exaust put 320hp to the wheels thought an A4 & 3.42 gears

There's no replacement for displacement

 

bore and stroke are idential to the LT1. Pistons/rods interchange, but 4.3 caprice motors are not V8s. They are a V6.

1. The V8 mounts won't work. You'd have to fabricate your own as the motor mount holes on the block are about 4" behind where they need to be in an F-body.

2. As for max HP, Google "GMC Typhoon" or GMC Syclone.
They were pretty fast, but I don't think they were close to 400 HP. Probably 'round 300. You could probably get there, but why? A V8 can do all that with no power adders and no custom motor mounts.

 

YOU ARE WRONG!!!!!!!! The L99 4.3 used in the 1994-1996 Caprice/Impala WAS a V8, PERIOD, END OF STORY. It has a 3.736" bore and a 3" stroke crankshaft. It had an odd 5.94" long rod in it which allows it to use the same pistons as a Vortec 305. You could actually put a 305 crankshaft and 5.7" rods in it and have a 305 LT1. I've actually built one as a 305. Used the 265 heads with some port work and a F-car LT1 cam. It dropped into the 14s in a B-car.

If you remove the A/C compressor from the lower mount position and go with corvette accessories, you can bolt the stock motor mount pads from your 305 onto the block and the engine will bolt right in.

http://www.automotiverebuilder.com/ar/ar99928.htm

 

What kind of power did that "305 LT1" produce?

Also, to go a bit off of my topic I met a gentlemen who runs a classic car restoration shop literally a couple of blocks near my second job--anyway the point to this is he offered me a fully rebuilt LT1 w/T56 transmission for $1000. Keep in mind I do NOT have a manual car--he wants to just dump the tranny with the engine. I'm trying to talk him into taking payments since I do not have $1000 right now. I'm going to see if he'll take payments and if he will let me pay it out in installments I'll forget about the L99. The LT1 in question is one from a mid-'90's Corvette. Which means it has the good aluminum heads.

 

I stand corrected.

 

Well, I decided not to buy the engine. Two reasons, one I really want an actual LT1--preferably one from a Corvette. And also, I'm about to get a promotion at one of my two jobs so my income will literally almost double--which means in a month I'll be able to get me an LT1. Also, I can get a reman 4L60E for $400 and either a used LT1 from an F-body for $600 w/wiring+ecu+accessories or a reman LT1 for $1000 w/wiring+ecu+accessories. Unless I find someone selling an LSx with the 4L60E combo cheap (and I mean $1200 or less cheap) I'm fairly content getting an LT1. Thanks to those here who've answered my questions.

*edit*
This topic can be closed if needed.