1990 RS 305 LO3 TBI AUTO.
Car runs pretty good, at lower RPM's, but it never reaches higher RPM's. Before about 3000, everything is smooth and steady acceleration. After 3000, I can see the tach kinda bounce or jerk as it climbs, and it climbs really really slow. I can also feel the car hesitate, just barely - it actually just feels more like a restriction than a jerky hesitation - like it wants to produce more, but just can't. I also never reach the higher RPM's - it always shifts before 4000 - even with my foot through the floor - it might reach 4000 before a shift. No codes except EGR.

Where do I start to make this better?

 

Is the catalytic convertor clogged?

 

Cat could be clogged i guess - i dunno. Soon to install new catback, headers, etc., along with LT1 cam, new heads, new intake, etc. - so I won't bother trying to see if it's clogged. I just thought if there were something that didn't throw a code that could be causing this, I'd investigate it now before I did the mods - I'm doing them in about 2 weeks :lala:

 

I was having a problem lately (last 2 weeks) with hesitation above 3200 rpm, and messed all around with timing and fuel via custom chips. Turned out to be bad wire, I assume since replacing the wires and O2 sensor fixed the problem.

 

Well, today I put my foot in it again, and this time no problems. It never reached above 4300 rpm, but it was smooth (and a smooth tach needle) all the way to 4300. Go figure!!!

 

That has to do with the way the tranny's setup, 305 tbis make no power after 4500 pretty much AT ALL, so its not really worth going higher, mine will go as high as 4500 in 1st, and around 3800 in second, i never bothered to max it all the way through third, cuz ill be going over 80-90 mph at around 3000, and i generally hit traffic by that point and have to slow down, so i dont really know after 2nd...

 

Power is not dependent on the transmission. Power is in the engine. The cam, heads, intake, exhaust, ci all determine power and torque for an engine.

You guys have to understand that the biggest power robber of the engine is the peanut cam design. This alone will determine peak rpm power, max torque and the majority of the engine's characteristics. The heads have to flow the numbers that the cam is capable of else this is the restriction. Then you have to have an intake/fuel setup to feed this as well as a well flowing exhaust to flow it out.

In 1st and 2nd I can pull as high as 5500 rpm. Although power after 4000 rpm is non existent really, let alone 5000.

In third is the real test of my motor as there is simply not enough flow to pull hard after 3000 rpm. It will pull till 4000 rpm, but its a struggle for the engine.

As far as the design of the peanut cam goes, its power peak IS 4000 rpm. Anyone claiming a real pull after 4000 rpm is bs ing as the peanut cam can't do that. The specs are totally against it. Those with an LTx or L98 cam are choking those cams with the stock heads, intake and exhaust. Those cams are designed to pull to 6000 rpm/5500 rpm respectively. You're not making efficient power, so guys dump those crappy heads and see those numbers get a hell of a lot better.

 

I've been playing more over the weekend. Most times, the tach needle makes smooth stroke up to about 4200, when my foot is all the way in it - this of course is in 1st & 2nd (auto) - like was said ... I hit traffic by the time 3rd gets close to 3000 and have to slow down anyway. I understand the stock engine isn't going to run better, and I understand the restrictions. I just didn't understand the jerky jumpy tach needle - but it seems to be better now. Maybe the ole gal just needed my foot in it really good a few times - she seems to be remembering what that is all about alot better now. I just wanted to know if there could be a problem with anything in particular before next week.

Next week - disassembly. New heads, cam, intake, headers, exhaust, cat, muffler, etc. Thanks for the feedback!

 

Think whatever you want, but I have a 305 TBI and I KNOW that it will run to 4500, regardless of whether or not you think I'm bs-ing, and i would think the tranny would have something to do with it, being as it chooses when to shift, not your cam

 

My tranny shifts at 4500 rpm if left alone, but it doesn't necesssarily mean you have power up to 4500 rpm. Dyno has proven that peak power occurs at 4000 rpm regardless of gear. Sure the gearing is different, but it doesn't change the characteristics of an engine. You can't magically change the peak hp of a cam. That extra 500 rpm your tranny runs has the smallest rpm-mph gain per sec. It's not a lie, its cold hard fact. I have the dyno numbers to prove that 4000 rpm is peak for the peanut cam.

 

Dyno of a peanut cam TBI.

 

Your dyno shows the same thing I got... peak power at 4000 rpm. doesn't pull anymore after that. I like how the full exhaust keeps the hp curve flat after 4000 rpm though, hopefully when I get my headers on the engine (instead of kept in back at the moment) I'll end up with similar results. Its kinda neat though that with full exhaust the torque peak jumped up that high. You had a full 13 ft/lb torque peak advantage over my auto car with only a cat back.

 

All I was saying was that it DOES go to 4500 rpm, your right though, it has no power, though i suggest you do it anyway, because when it shifts into 2nd you'll be in a much better spot in the power range. I got a question, I know that its the cam that causes it to have no power after 4000, but it also seems to react to airflow too, if you increase the air flow coming in it seems to run better even up to 4500, and its not like 1-2 hp, its pretty noticable, so is it the stock air assembly thats the real evil or the camshaft, its obviously both, but i mean in the case of the 4500 rpm...

 

Actually I manually shift when I run at track. I shift at 5200-5400 rpm really. I do this as more of a preload for the next gear, starts the engine up at a high rpm under load. I've gotten my best track results by doing it this way.

I'm well aware of how airflow changes this engine, I have ram air built into my car after all. I'm taking pics tomorrow, got a new digital camera to play with hehe.

 

If its a 305 TBI could you post those pics in here or tell me where ya post em? I've been trying to find the best ram air/cold air intake for it, and so far i like the mixture of TBI and TPI intakes, but i can't figure out what hose they use to connect them together...