I'm getting close to my 240k mile mark on my original motor on my '90 RS, and I'm getting ready to start engine shopping when I found someone selling one of the 4.3L Caprice V8's for ~$200 w/all accessories and exhaust. 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 question round.

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?
3) Can this engine be converted into the 5.7L LT1? (head swap + bore/stroke change?)
4) 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)
5) Is this engine rubbish?
6) Does the LT1 swap guide apply to this engine since it is externally the same?

Thanks in advance for your 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 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.

 

Even for $200 that engine would not be worth the time and effort to make the swap. Alos it never will have the output of LT1. My opinion is forget it.

 

I disagree. The engine in question has only 56,000 miles on it and came from an elderly couple's car--which means it probably never saw 4000RPM in its lifetime. Giving the state of my current engine even IF the 4.3L L99 could never match the LT1 in power output it would still be a cheap alternative to getting my 305--which is a really horrible engine--rebuilt. Due keep in mind that whatever engine I do put in this car, will never make more than 480bhp at the crank because I do not want more than 480bhp. I'm not making a drag car here, just something with some decent passing power and a good noise while still maintaining drivability.

I still would like at least some of my questions answered regardless of whether people think it is a good idea or not. Thanks.

 

480BHP[sm=groupwave.gif][sm=roll.gif][sm=roll.gif][sm=roll.gif]

 

Externally the L99-4.3(265 CID)and the LT1-5.7(350 CID)engines are the same.
There are several differences in intake plumbing, exhaust manifolds, water pump, and accessory locations between the B body and the F body applications. Additionally aluminum heads are used in the F body and cast iron heads are used in the B body.

4.3 specs:
Bore 3.736"
Stroke 3.00"
Compression 9.93:1

5.7 specs:
Bore 4.000"
Stroke 3.480"
Compression 10.5:1

The 4.3 cannot be bored 5.7 size without going into the water jacket. This is a problem if you want performance, not so much for having a smaller displacement, but by the shrouding effect that the small bore has on the valves, which restricts breathing.
These engines are computer controlled, so you either use the B body PCM and wiring harness., or convert to carburetor, and use a normal type distributor.

 

Not to sound rude but do you actually have anything to contribute? And, I said "not MORE than", not "EXACTLY" 480bhp.

Thank you for being an adult unlike the other guy. Thanks for the specific information, I knew the bore/stroke were less in the L99 versus the LT1--but I didn't know about not being able to bore it out to 5.7L without boring into something important lol. Do you have any idea what kind of power you could squeeze out of the stock L99 + LT1 aluminum heads? Or how much PSI it could take from a couple of turbos safely? I don't have a problem using this engine if it suits what I need it to--which it probably will. Anything in the 400bhp (crank) range would work for my application--and I feel that this engine with forced induction would achieve this number @ the crank. I'll assume since the LT1 is a cast iron block that the L99 is one too--which tells me (perhaps ignorantly) it can take a decent amount of PSI from forced induction (~20psi). I'll also assume that you could throw on the LT1 aluminum heads + intake, which should give you some *cough*pun*cough* breathing room in terms of squeezing out a tiny bit of extra power versus the stock L99 iron heads + intake. Would this be a correct assumption? Thanks again for your assistance.

 

Yes, the blocks are all cast iron. Couple of things may actually work out. The 5.7 cast iron heads actually flow better than the 5.7 aluminum heads, and If you intend to run high boost the iron heads will also hold the gaskets better. If you were to use the 5.7 heads on the 4.3, I suspect it will lower the compression quite a bit, which is good for supercharging. I never taught of doing something like this before, but it probably will work OK. One thing you will have to check, is if there is clearance along the cylinder wall for the 5.7 valves. Also the smaller engine uses longer connecting rods, which helps to relieve some of the stress on the engine.

 

I didn't even know there was a 4.3 V8 till now............and if your looking at making over the 400 hp mark, stick with at least a 5.7. If you go the 4.3 plan on seing 250 hp with some work.