Found this link, interesting read. Applicable to those who want to keep their 305 and have nice street performance: http://www.z28.com/threads/read-and-.../#post-1541029

Re posting here in case it disappears:

See the thing with TPI is its not bad but it depends on what you use it for. At the time it was a huge improvement with gains of up to 20-30 percent in hp torque and fuel economy over existing carbed and fuel injected set ups. In its stock form its restrictive on 350 (although was still better than other factory options) and larger motors. For a 305 its pretty good as it was designed specifically for the 305 (this is why its so restrictive to larger motors). The thing about the theory behind why the TPI system was so successful is they tuned the runner length such that the high pressure pulses that were generated by closing intake valves were reflected back into the plenum before being again reflected back down the runner to the intake valve just as it was opening at certain RPMs. This in effect forces air in to the cylinder (kinda of like a weak form of forced induction). The problem is these long runners target lower RPMs. This is why TPI motors are known to generate big block torque but in the high RPMs tend to die off.

What this means in terms of applications is that for competitive 1/4 racing or races where a lot of time is spent in the high RPM TPI isnt really the intake of choice to generate lots of HP in that band of RPMs. However the problem is people bad mouth it to an extreme just based on what they hear and build motors for the street cars as if they were all out race cars. Fact is this look at any dyno test that compares stock TPI, modded TPI, stealth rams, mini rams, ect and one thing becomes clear a modded TPI set up is a fantastic motor for street performance. Typically a modded TPI intake is only outperformed by its competitors in the 4.5k-4.8k and above region. On the street how often do you see those sorts of RPMs? Not to mention the factory rev limit is 5.5k. Furthermore the difference in performance in the sub 4.5-4.8k region is pretty substantial. For example one dyno I looked at, at 3k RPMs the ever popular holley stealth ram was out performed by just over 60 foot lbs of torque by the modded TPI set up! Because acceleration is related to the mass of the car and the force exerted the modded TPI set up would easily out accelerate the stealth ram in the lower RPMs cars being equal. Once the race ensued given enough time the stealth ram set up would catch up and overtake the TPI set up but if that will happen depends on the length of the race. What this means is it would be a very fun car to drive on the street and in shorter races like the 1/8 or stop light to stoplight or even autocross where you can spend a lot of time in the lower RPMs the modded TPI intake would have the advantage. Then factor in the fuel economy and streetability advantages and its clear to see that a modded TPI is a fantastic intake for the majority of application as most of our cars never or rarely see the track, primarily driven on the street as daily drivers or weekend cruisers, and even the ones that do race on longer runs like the 1/4 mile arnt serious competitive race teams its just for fun. Because of this fact it just dosnt make sense to sacrifice all the low end power where you typically are on the street 98% of the time to gain some hp for that other 2% of the time. So in conclusion I think the TPI intake has got an ill deserved excessively bad reputation.
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http://www.z28.com/threads/read-and-.../#post-1541507

My personal preference is comp cams. Ive always dealt with them and always had good luck. Though I dont think brand really matters too much many cams are all made by the same people just rebranded anyways. If i were too look for a particular cam I would check out the comp cams 260XFI HR13 or the 252XFI HR13. One is a little bit more radical than the other so it depends on which you would prefer but either one would be great match for the TPI intake.

and from another thread in another forum:

When I say the modded TPI set up is the way to go ect, it's primarily because most of the time people are talking about using them on the 350s. For the 305 the stock TPI intake is pretty decent. This is why the hp ratings for the 350 and the 305 are so much closer than one would expect - it's just a better match for the 305 in its stock form. When they were designing the TPI intake their designs was based off of the 305's air flow data as rumor was GM was uncertain about the 350s future due to the emissions regulations. Because of this, it has been noted that swapping on larger runners onto a 305's TPI system yields marginal gains on the dyno. The biggest short falling of the LB9s were its camshafts. The 2 cams offered for the LB9 were terrible one even earning the nickname the "peanut cam." The sad thing is even using the slightly less crappy cam offered an additional 25 hp over the "peanut cam." With a good cam and full exhaust system (headers, high flow cat, with a performance cat back of your choice) it would not be unreasonable to expect around 270 hp with nearly 400 ftlbs of torque out of an otherwise stock LB9"

 

Nothing really earthshaking there.

TPI was quite a leap for the times - hey, it's been 30 years, some of you weren't even born yet. I can remember the newest car I've ever owned, a '76 Vega purchased in '78, that had a top speed of 77 MPH on the flat - in 4th gear, that is, it would only do 74 in 5th gear. An '85 LB9 would be quite a kick in the pants after living with that (and got better gas mileage, too).

Probably the "best" factory TPI cam was the '85 piece. But, the '87-up roller lifters were also arguably a step up. And, if you're going aftermarket, all of that discussion is pretty much moot, anyway.

The engine dyno doesn't tell the whole story, either. Yes, you might sacrifice some low-end torque with a better intake, but that's pretty easy to make up with a higher stall torque converter that'll get the engine up where it's making more power than the stock setup, and blast by it above 4500 RPMs.

But, since "street" was mentioned as the "98%" usage, a stock TPI is fine - it'll be able to break any speed limit out there (unlike my old Vega...).

Oh, and speaking of dogs, there was that '80 Fairmont 4 cyl 4 spd that I sold when I got the Camaro. I was afraid to see what its top speed was...

 

Thanks for your input Grandpa I remember the Vega well, distant cousin of the Opal GT, don't see either of them around, ever. Guess they all burned up in rear end collision fires. My first car that I bought was a 1970 Barracuda, still have it. Its a POS, tho. would be fun to restore into something. I am very tempted to make my 305 turn and burn. Why, because its stock, its what came with the car, the car is original, its been mine since 92 and it has great symbolic meaning to me. You can tell me to put a 350 in it until your blue in the face - but I already know that. It really sad you can't find any good articles on 305 TPI build ups. Lots of carb 'ed 305 build ups out there, but no TPI. Look, I'm not looking to race the 1/4 mile down at the strip. I wanting to race the car next to me at the stop light, for about 100 feet. All I need is lots of low end torque for that exercise. Let me know if you have any ideas.

Grandpa Jr. out!

 

3.42-3.73 gears, 2400 stall converter, headers and 3in exhaust will give you a big boost without touching the engine. It will make it feel like a different car and maybe put you in striking distance of "stock" 350 TPI. A few steps further with some better heads or having yours ported and a cam, intake, maybe 1.6RR change could put you in "stock" 350 LT1 territory. I wouldn't spend a ton on a 305 because a 350 is so much better and easier to get more out of but you know that and the 305 may suit you fine. Good luck, whatever your route is.

 

There were a few good articles in GM high performance or whatever it was called where they detailed a thirdgen switching from the TPI intake to the (then new) Holley Stealth Ram(HSR). The article had dyno and track times before and after the swap. Everyone thought that the HSR would be better on the dyno and 1/4 mile and the TPI would be better on torque production, 60 foot times and shorter bursts. Turns out the HSR beat it in every aspect except for torque production. The HSR had less torque but had better 60' times, because it's torque was in a more useful part of the rpm range and it didn't want to spin off the line. To me that article had served as the conclusive proof that TPI was only suited for trucks or part throttle driving in the city.

But back to 305's and TPI, I would agree with anybody leaving them in their Thirdgen that wont be illegally racing, going to the drag strip or road racing would be fine with a 305 TPI. Get a set of better rear gears and some suspension upgrades and you can still have a blast in traffic and keep up with the newer cars on an autocross.

 

Yeah people apologize this way and that for the 305 and for TPI all the time... doesn't make either one any less of a flop in the grand scheme.

I guess GM did what they thought best at the time. Too bad it was so lame. I'm constantly reminded of a guy I knew from the UK who asked me one time "how is it possible to get so little HP out of a 5 liter motor?" It's SO GOOD America has moved forward from that crap; SO UNFORTUNATE that we here, with these cars, have to be reminded of those things constantly. Best thing we can do is leave both the 305 and TPI as far behind us in the history books as possible, as reminders of how far the mighty can fall before they realize how far they've fallen.

 

Nice read there Liquid Blue. But it shows how small displacement perforamce takes some engineering. The British used more smaller pistons in their V12 Jaguar with higher rpm for power. Almost a down scaled model of their WWII A/C engines.
Chevy found geater torque in a smaller bore by using longer intake runners even with untuned exh manifolding. But rpm band is very compressed. To add rpm and power most owners mod in the wrong direction with long tube headers and tight lobe separation cams. Someone that wants more rpm power with TPI should go short on header length and wide on lobe sep angle. I expect some to mate a 6 or more speed trans (auto or man) to better use that small but powerful powerband of the TPI. I guess what I should say here is to widen the power band u need to widen the cam lobe sep angle and use short tube headers along with more gearing to keep that motor high in the powerband.

The small area runners may only support the 305 motor or become underproductive with 350ci. More a matter of scaling than comparison of cubic inches. Like a 400" motor w/ large enough area TPI runners could produce great torque in proportion to engine size enough to make a 305" TPI torque look smallish.

Anyways if u want the 305" for whatever reason u should have much greater performance if set up correctly. Headers, cam, 6 spd trans and an accurate shift light should make that mouse run more like a horse.

 

No kidding, my daily driver is a tiny 4.4L/268 ci, and cranks out 325 hp and 330 lbs of torque

 

I realize nothing I can say will change many minds, but for comparison...One could ask the same thing of ALL manufacturers in 1985.

TPI was good for it's day, and for the price point it was being sold at.

From Wikipedia...

Porsche updated the North American 928 S for 1985, replacing the 4.7 L SOHC engine with a new 5.0 L DOHC unit sporting four valves per cylinder and producing 288 hp (215 kW/292 PS).

So here's a contemporary, selling at a MUCH HIGHER price point, limited production, all aluminum, 4 valve, DOHC motor, and it's making 73 more horsepower than the 215 horse LB9. And the Porsche power band is likely higher in the RPM range, lacking the low end torque of the LB9. Not good or bad, but a different engine for a different customer. Given the extreme cost difference in purchase price and maintenance costs, ease of mass production for the LB9, it's easy to say both engines are doing what they were designed to do at their price point, in their segment of the market.

As for comparisons to today's daily drivers...if it's fair to compare the LB9 to 30 year newer technology, then it should also be fair to compare the LB9 to what was available 30 years prior. In 1955, Chevy didn't have a 5.0l V8, but the new SBC was cranking out 165 horsepower (and that was something of a modern marvel at that time). Given the 50 horsepower increase, ease of starting, superior throttle response at all temps and altitudes, longer maintenance intervals, longer engine life (less fuel wash), etc., I think the LB9 again acquits itself pretty well. Not legendary, but not spite-worthy either.

Taken out of it's place in time, compared to ALL 5.0L engines ever, it's not impressive.

Compared to other engines in the market at that time, with cost as a factor, it was a good effort.

 

Excellent points DynoDave! Encourages me to build that 305 rather than swap it for a 350! Very hard decision!!

 

I hear that same line too. People that say that don't know what was going on back then. In 1969 Chevrolet had a 302 that was rated at 290hp. In 1985, when TPI came out, their 454 didn't make that much. Why? because before the '70s American car makers could pretty much do whatever they wanted engine wise. Gasoline was leaded and no one really cared about emissions or fuel mileage. Then, almost overnight, the lead was gone and there were emissions and fuel economy standards that had to be met that didn't exist elsewhere. They did well with what they had to deal with at the time.

 

Speaking of H's and P's .....

https://www.hagerty.com/articles-vid.../13/horsepower

http://www.bluelight.org/vb/threads/...=1#post9779466

 

Hot damn. I saw an orange Opal GT yesterday. I am officially eating my words from above post.