Hi this is my first post on this forum. I recently purchased a 91 RS for a very very fair price. I even worked in keeping the car stored indoors till the spring so I would not be tempted to take it out and it would not be subjected to the winter weather that i get out here in Illinois (about 60-90 minutes west of Chicago). The car as i receive it is bone stock, and i wanted to get more then 170hp from it. This is where my question comes in: from a prior project from an old chevelle/malibu i was building an L48 350 and i was wondering if i could use the top end (intake, throttle body, and heads) off of the L03 on it. I would have the heads rebuilt (any recomendations) and i am interested in either swapping or modifying the tbi unit. the 350 that i have built isnt anything out of the ordinary, probably a max of 250hp. I did the search fuction and found little but i know from working on these cars that they used different heads and intake then the L48 does. I want to maintain the tbi unit on the car to maintain a stock appearance. Any Info or advice on this would be helpful

Jeff

 

That may be the worst thing that anyone has ever thought about doing to a 350.

The LO3 is the worst engine to get heads from and the intake sucks, too. At a minimum, you will need TPI heads from any 87 or newer engine, or a 305 LG4 carb engine from 87. You need 1.94" intake valves and a little port work will help.

Even the LO5 350 TBI heads from a truck suck. Don't use them. You'd be best off on a budget to get some LG4 or TPI heads, a carb intake, and a TBI adapter. If you must run a factory TBI intake, then at least get the heads.

I'm not trying to bash what you are doing, just save you some huge headaches. Oh, and your exhaust manifolds and y-pipe are some of the worst factory pieces ever, as well. TPI pieces are preferred for stock replacements, headers are better.

Good luck!

 

I was thinking of doing headers while I had the engine pulled, is there a preferred y pipe that i should get. While im asking do you have any headers u would reccommend? I live near a junk yard that has a small fleet of 3rd gens and i will go huntin for parts as soon as the snow melts, but in the mean time can I ask what is so bad about the heads and intake, are they just that restrictive? Oh and dont worry about shooting down my cheap pipe dreams.

 

The heads are great for efficiency and gas mileage...on a TBI 305. Beyond that, they hold down tarps in my yard. They don't flow as well as my 350 TBI heads, and they suck too. I am looking for TPI or LG4 heads, 87 or newer to put on it right now.

The intake is worse flowing than a plain edlebrock perfromer carb intake. The exhaust manifolds and y-pipe are the most restrictive offered by GM. They can use those on your engine because it doesn't make much power.

On a budget, and a relatively mild build like yours, any headers will be fine if they're not damaged. A factory y-pipe from a TPI car is better than what you have if you are gonna stick with manifolds, and the TPI manifolds are better than yours as well. If you run headers then use the y-pipe that is with them if it is availbable. You want the y-pipe to be an actual "Y" with 2 pipes going into a 2 into 1 transition piece. The factory y-pipes are actually just a "T" with pipes welded together.

 

sorry for brining this back up but couldnt i just use the heads and intake i have on the engine already and put the tbi adapter on? I didnt even know the exhisted (guess I never looked) where can i get one?

 

Yes you can just stick your heads and all onto that block. Bolts right up.

Worst problem you'll have, is the oil dipstick. It is incompatible with your exhaust manifolds.

Don't expect miracles; the L48 was good for about 180 HP. One of the last ones I had, in a 79 Z28, I traded in on the car I have now (83 HO Z28). The L69 car RAN CIRCLES around the L48 one.

You'd probably get better results with the L03 heads; more compression that way. The L48 had about 8.2:1. Given the cam that's probably in the 350 (929 copy) the lack of flow won't matter, but the bump in the CR might help.

With the larger motors, you'll need larger injectors. Get the ones off of a L05 from a truck or a Caprice.

Again, don't expect miracles. You'll get more torque but not a whole lot more HP.

 

the L48 is not stock it has 10:1 Keith Black pistons and heads off of a 283.
I just need a cam and intake for it