I recently bought a '91 Caprice wagon with the L03/305, and while I really like it (its a real clean 75000 mile car) the lack of power was starting to drive me out of my mind, especially as there are lots of hills around here and I couldn't take them at my normal 65mph (ok I like to drive fast) without the car bogging or downshifting. My '94 Chevy truck with a TBI 350 rated at 195 horse takes the hills fine, so I figured if I could bump the 305 up to that HP range I would be much happier with it. Both cars are California emissions cars, so that's why the '94 350 is only rated at 195. I don't know what the California rating for the '91 305 was (if anybody else does please post it) but its probably down 15 HP or so from the regular 170 HP rating for the engine.

So after learning a lot about TBI engines from reading the great forums on this site, it looked to me that by going to a better flowing exhaust and a better flowing intake system, potentially including the "ultimate" mods and by doing some chip work, I had a chance of getting the engine close to 200 HP.

First step was to convert the intake to open element along with removing the restrictive stock baffle, and it felt like I might have gained a little from just doing that. I then found a post from somebody recommending the '92 Caprice cop car exhaust system as it had a good y pipe with 3" output down to a 3" in/out cat with 2-1/2" pipes after the cat, so I ordered those exhaust pipes with a Walker "Superturbo" instead of the stock muffler.

However I'm still waiting for all those parts to come in, and in the meantime I decided to try chipping the car. I know the popular approach here is to take the time to burn your own chip, but with 2 kids and a crazy ex-wife in the picture, the time for that is just not in the cards, so my only choice was a commerical chip.

I decided to try a chip from tbichips.com, and sent him basically the info above about the car and what I was planning to do with it. To be honest after reading about chips on this forum I wasn't really expecting much from it, but after installing the chip I have to say-

Wow- I'm seeing 2 major improvements, the car feels like it has around 20 more HP full throttle and the driveability is dramatically improved, which was actually more important to me as this is my daily driver. The car was bugging the hell out of me because with the stock chip when you first tipped the throttle in it would feel torquey, but then you would have about 1/4 more throttle of not much happening when you continued to push it down, I felt like I was back in my sister's 4 cylinder Pinto Station wagon.

Now the torquey feeling continues pretty nicely as you push down on the throttle and I'm much happier. This is so far with the only changes to the car being the chip and the open element air cleaner.

When I put the cop car exhaust system on the car do you guys think I'll need to bump the fuel pressure up a little (I'm going to put an adjustable regulator on it), and if so, how much?

It may be that the reason I saw so much gain just from the chip is that its a California emissions car, and as far as I can tell the only difference in the California cars that year was a different chip, so that would at a minimum get me back the 15HP lost to the Cal emissions, but it actually feels like I gained more that just that, so for anybody else with a California TBI car it appears like a chip swap could be a big boost for you also.

I'll report back again after I put the exhaust on the car.

The other parts I'm still up in the air on are an injector spacer and a throttle body spacer, some people claim these help, some people don't, but I guess after I put the exhaust on if I still need more power I'll give them a shot. I'm looking at the throttle plate from cfm-tech.com, its at:

http://marine-performance-parts.com/...eanerstud.aspx

Does anybody have any experience using that plate?

Paul T.

 

Sounds good, good luck with your future mods.

 

I have used TB spacers on a couple of the even weaker 4.3L V6 TBI engines in S-10 trucks and they have always given a small but noticable bump in torque. I don't know if they add anything in peak power but that's not really what you're building for anyway with this project. Tried the injector spacers once but didn't have enough seat time to say for sure if they helped. Certainly I can't imagine how they would ever hurt performance.

Small increases here, small increases there and soon you'll be at your goal.

I agree with your exhaust upgrade idea. Just be sure the cop y-pipe will work with your existing manifolds. GM used basically 2 different designs. One was the smaller low-po manifolds like on the LO3s and the other was on higher output engines (like say, from a TPI engine 3nd Gen Camaro). The outlet diameters were different (2.00" vs. 2.25") but the real difference is in the outlet location and angle of the pass. side manifold. It looks the same to the eye but it's definitely not and the Y-pipe won't seal up against the pass. side manifold if you've got a mismatch.

I'm no expert about Caprices and what manifolds they used, but just be aware that you should keep an eye on how that cop car Y-pipe lines up against your low-po stock manifolds. May require some modifications by a shop to make it work.

 

Damon, thanks for the feedback on the throttle body spacer and the heads up on the exhaust manifolds. When all the parts show up (rockauto.com is cheap but slow) I'll pop the current Y pipe off and see how it matches up to the new one, I've got a mig welder here so if I have to I'll make a "franken-pipe" grafting the ends of the downtubes of the old pipe to the new one. I'm hoping I can use the new one as is, its a nice looking piece that blends nicely at the end to a 3" outlet.

Paul T.