I just bought a '91 Caprice wagon, its in great shape with only 74k miles on it. It has the L03 305 TBI engine with 3.23 gears in it.

I like the car a lot but its going to be my daily driver, and right now it doesn't have enough power to handle the hills around here (either bogs down or downshifts) I have to go over almost every day, I drive fast and need to be able to cruise over them at 60 or so. I'm a little surprised about this as I also have a '94 Chevy 1500 pickup that does fine on the same hills, no slowing down or downshifting. It has a 350 TBI engine in it, its a extended cab with a camper top on it, so its pretty close in weight. The '94 350 has a California smog engine in it which was rated at 195 HP, so its got maybe 25 more HP than the Caprice and has 3.73 gears, but it sure feels like it has way more power than the '91, so its possible something is funky on the '91 which is why I'll do a full tuneup on it first.

But it looks to me that if I can get the 305 up to around 200 horsepower or so it should run as well as the truck, although I may have to also swap the gears, but if so that's ok, first step is to try to get the 305 putting out over 200HP.

So as the first step get the 305 running better I'm going to do a basic tuneup, replace the fuel filter and check the timing. I'll also stick in a 160 or 170 degree thermostat.

The next step is the air intake, I already converted it to an "open air element" system and got rid of the restrictive baffles using tips from this forum. This feels like it might have helped a little already.

Next step is exhaust, it turns out that the '92 Caprice Police 350 model had a pretty free flowing exhaust system with a 3" y pipe and 3" in/out cat and 2-1/2" system back from that, so I ordered those parts along with a Super Turbo muffler and that should free up the exhaust quite a bit. Most of these parts have come in and they look pretty good, but they're not on the car yet.

Here's where I need some help. To improve the intake system some more, from reading this forum it looks like its a no-brainer to use an injector spacer and an adjustable fuel pressure regulator so I'm definitely going to do that.

However, I'm stuck on going one of 2 directions with the intake system:

Choice 1 - do the Ultimate TBI modes to the TB myself, and use the injector spacer, throttle body spacer and regulator from www.cfm-tech.com . I'm seeing some mixed reports on throttle body spacers, some say they help, particularly on the bottom end (which would be good for me) and some say they are a waste of money. The cfm-tech spacer is interesting in that it has a special path machined between the bores that they claim is beneficial. Does anybody have comments on this spacer or throttle body spacers in general?

Choice 2 - go with a "ported" TB from http://www.xtremefi.com/, along with his injector spacer and regulator, but no throttle body spacer. These ported throttle bodies have bigger blades and increase the CFM from the stock 400 cfm to a claimed 590 cfm. He's claiming that this TB will give me a good power boost on my stock 305. I'm a little nervous about this approach as the 305's and the 350's used the same TB's, and with a stock 305 it seems to me that an enlarged TB might be too much. Has anyone used a fully ported TB on a stock 305 engine for "round town" driving?

Last question is on the Prom chip. I already bought a performance chip from www.tbichips.com . I know alot of people on this forum strongly recommend testing and burning your own chips, but my free time is very limited and thats not an option for me. I also see some other recommendations to forget about the chip and just do your tuning with fuel pressure and static timing adjustments.

So if buying the tbichips chip was a mistake, go ahead and tell me I messed up but please recommend an alternative (either a different commerical chip or manually tweaking fuel pressure and timing).

I know its a lot of questions, but if you only have input on one of them please let me have it. After I get all these parts on I'll report back the results.

Thanks,

Paul T.

 

Air (cleaner) intake - choose one of these after reading the whole thread:

http://impalassforum.com/noncgi/ulti...c;f=9;t=001945

and do whatever you can to feed the air cleaner with unheated air. Make sure you close off the heat riser opening in the exh manifold shield on the driver's side.


Exhaust - 9C1 Ypipe plus aftermarket low restriction muffler is a good choice. Full duals would be better but the 9C1 option is easy, cheap, and works well with a good muffler.


Spacer under the TBI allows better breathing from both bore into both plena in the intake manifold, so I think that is a helpful mod.

Injector spacers don't allow more airflow, as shown in the airflow tests on the Fullsize Chevy forums, because the injectors are far enough above the throttle plate to allow good airflow around them. What the injector spacers will do is alter where the fuel sprays.... but again that's a difficult thing to quantify as a performance mod, especially when the fuel spalshes around into a wet-flow manifold before it gets to the cylinders. So IMO the injector spacers are a waste of money.

I do suggest you DIY the ultimate mods -- they will help a little bit at WOT, but remember that the stock throttle body is not an airflow limit on a near-stock 305. So you will get a slight increase in airflow near WOT because the radiused air entry is smooth, and Vizard's tests on curved velocity stacks showed as much as 5% flow increase when the pipe ends are belled (radiused).

Buying a larger TBI unit in your application is a waste of $$$. If there is any other thing you can cheaply do to the 305 in your application it's probably 1.6 stamped steel self-aligning rockers. They work well with the tiny cam.

You already have GU5 (3.23) so there is no need to change the gears. Make sure you do a thorough tune up on the engine, and fluid swap in the trans and rear end.

I don't know if the chip you bought is a mistake, but I do know that the intake and exh mods will work fine with the stock chip, or with stock chip and slight increase in fuel pressure.

Boggy performance on a TBI could be from a number of things, one of them being tired valve stem seals and crud accumulation on the undersides of the intake valves. Another is a faulty EGR valve (that won't close).

Read thru all of this thread for more info specific to your needs, and then go hunting in the wagon forum on the same website:

http://impalassforum.com/noncgi/ulti...;f=33;t=009021

HTH.

 

kdrolt-

Thanks for the reply and for your part in putting all the info together that you gave the links to, that's a lot of good stuff.

I'll check the EGR valve and now you've got me worried about the valve seals and gunk build up on the intake valves, the engine currently runs well (other than lack of power up hills) and passed smog easily but does smoke blue briefly on cold startup, which I believe often means worn valve seals or guides.

The Jet TBI rebuild article looks interesting, is it necessary to use ultrasound to properly clean TBI injectors, I was going to try just doing it myself with some carb cleaner.

Thanks,

Paul T.

 

Valve seal replacement isn't that hard to do -- just tedious. How many miles on the engine?

If there is a buildup of crud on the back side of the valves, the only way to get rid of it is to pull the heads. In that case it's probably easier to get a spare set of heads, clean/rework them so they are ready (mild port cleanup, backcut valves, replace valve stem seals, all on a benchtop) -- and then swap the old for the refurbished.

You can clean the exterior and the injector spray tip by hand. Running a cleaner through the injector while electronically pulsing it (with a proper DIY circuit) is the best way to clean the innards. But you really don't need an ultrasonic cleaner, though that would speed up the cleaning process.