punzak9

Hey, so after a few years away from a third gen, i got a car identical to my old one a few weeks ago. Its an automatic 1990 Firebird Formula with the 305 TPI. The car feels super solid underneath and the engine only has 85k mikes on it. It could just be from driving newer cars the last few years, but the car feels like its lacking something in the engine. Dont get me wrong, right off the line it has the nice little jump but stepping on the gas up around 45-50mph it feels like its just crawling up.
From what i read on the forums over the years our cars are "low end/band" cars which would explain it i guess. I just remembered it feeling faster when i was 17 but maybe thats why, i was 17 lol

I read that the best thing to do with a new to you car is all the general maintence/tune-up stuff, but what all does that include? Also i know the exhaust is the second best thing to do, so i will be finishing it at some point before i do anything else.

Any thoughts or suggestions? Am i starting in the right direction?

Bob88GTA

iTrader: (2)

EVERYTHING was bigger and faster when we were 17. Have you seen the size of a Reese's Cup lately??
Yeah, the 305/350 TPI all low end grunt.
Headers,exhaust, cam is a good start though

KyleF

You also said it was an auto. The 700R4 has a big step between 1st and 2nd. Everything about the Thirdgen was about feeling fast while meeting EPA and CAFE standards.

The Long tube runners make great punch in the low end and the low first gear allows the use of high gear (low numerically) rear ends which helps with Fuel Economy in OD, but the engine and gear multiplication still make it feel fast.

Taking your car to a 3.42, Headers, and exhaust and your basic TPI mods and it will wake it up. Won't be beating any LS1's or newer Camaro/Mustangs, but it will sure feel a lot better. If you do this, then swap cams and modify your runners some I would consider a stall converter as well.

For me, thirdgens are not longer about how fast they are, its about how they make me feel when I am in them. 17 again!

punzak9

Thanks. Im not looking to go out on the street and race anyone. Just looking for a little more out of the engine. It feels pretty fast going from 0-30 but then drops off. I agree that it isnt really about the speed with these cars and much more about the overall feel.

@Kyle just cuz im by no means an engine expert, what are the basic TPI mods youre talking about?

MY87LT

iTrader: (2)

Plus the manual TPI 5.0 had a better camshaft than the automatic TPI 5.0

Orr89RocZ

iTrader: (20)

With a 305, short of nitrous or boost, you just arent going to get the gains like you do with modern cars or even the 350 cars. Keep it running good and maybe exhaust to sound decent but thats about all you can hope for.

A stealth ram intake deal and bigger cam would feel alittle better tho. But need a tune and is a good but of work for small gain.
If an auto trans, going to a 3.42 rear gear and 2800 stall torque converter would be nice for seat of pants feel

KyleF

Search Search Search... LOL

Seriously, make sure you give it a good tune up first.
Then the little things like opening up the air box and a better filter, coolant by pass for the throttle body, an air foil, Adjustable Fuel Pressure Regulator, Under Drive Pulleys, adjust the kick down cable to optimize shifting... etc.
There are a lot of little mods out there to consider. Then there is Porting the Plenum, matching Siamesed runners, and porting the base. Bit more advanced, but it is free.

Also, consider eight reduction. I am not sure how you use you car, but doing away with the spare and jack, removing the rear seats, pulling up the carpet and doing away with the sound deadening, and doing an A/C delete will make the car feel stronger.

punzak9

Thanks guys. All that helps. Knew it wasnt the most ideal engine but still wanted to know the small things i could do to help it out. Im on here a few times a day trying to read and research but some stuff goes over my head when it comes to engines and gears.

NoEmissions84TA

iTrader: (1)

If you want to enjoy driving a 30 year old car - you are going to have to learn how to work on a 30 year old car. Or pay an old mechanic.

Pro

When you say modify runners do you mean increase the diameters like i hear people do?
But would not the bottle neck be at the TB?...
Increasing the size of 8 holes sounds nice, but if you arent increasing the size of the 2 that come before it (and appear to flow less volume of air), seems pointless?

Vanilla Ice

I would do Headers, rockers, cutout and better intake (not manifold) and tune.
They'll tell you not to do rockers, but they base it off peak numbers and hearsay.

That's relatively cheap and will gain you a decent top end. Couple that with the 3.42s as mentioned and you'll be very happy.

A stall would be awesome, but that's not going to help much on top end.

KyleF

Roller tipped rockers, go t0 1.6 ratio on intake and leave them at 1.5 on the exhaust. Yes, you will get more area under the power curve... I second this as I did them on my TPI and noticed more mid RPM Torque.

KyleF

Well, I see you are a Sr. member. You should have seen all the throttle body debates going on here.

You are right to some degree, but not quite on a stock TPI engine. The length of the runners is what chokes these engines in the upper RPM. That is one issue. So any runners you can find that either shorten the run (Like a stealth ram or the TPIS Mini Ram) helps get better upper RPM performance. If you have the SLP Siamese Runners you increase the plenum volume by port matching the intake and at least take a few inches off the runner length... bumping up the RPM Range.

To look at the throttle body, you have a mm measurement of bore diameter and a flow measurement in CFM. 350Cu in. is .2025 Cu. Ft... now your intake stroke only happens once every 2 revs per cylinder because the other down stroke is the power stroke. So, per RPM you must move .1013 (or you could say .2025 per 2 RPM if that is easier to see). At 100% Volumetric Efficiency at 5000RPMs that is 506 CFM. This is where the "Tuned" in Tuned port comes in, working on resonance and going over 100% at peak torque, but not near 100% at high RPMs and this is why the engine runs out of breath, but CFM needs are RPM dependent. So, what I am getting at here is no, your stock throttle body is more than capable of flowing the numbers needed, but at Peak Efficiency (at peak torque) based off runner length and resonance (Also the Cam profile), the more air you can move through an individual column (Larger bore, larger valves) is the more that can get into the cylinder (less resistance) and this is not occurring at or near the flow capacity of the throttle body. This is why going to a larger throttle body doesn't gain much HP but larger bores in the TB can cause lower Manifold pressure which will affect other systems in the car.

Throttle body 668 CFM
MAF 529 CFM
Modified MAF 750 CFM

Above taken from TPIS insider hints.

So when you step up CU In or get peak torque in the Higher RPM band... that is when you can start looking at the TB. Honestly, Until you have done headers, runners, and a cam... you will see no gain from a larger throttle body. Even after all that, there is other areas to get more bang for your buck than the throttle body.

From what I see on an L98, peak torque is 3200RPM (Factory)... 324CFM at 100% and even if you say the tuned intake can get the engine to 110% you are only going to need 356CFM. It can get through the TB and would require massively larger runners and more Cu. In. before it becomes a bottle neck. Then as RPM goes up, efficiency goes down.

I took the Torque numbers from High Performance Pontiac's Dec. 86 issue on the 87 GTA.

Hope this helps.

Pro

I had a 91 for 6 months like 13 years ago and didnt even log in until i bought my 92 a year ago. So i did nothing here for more than a decade so i am sure i missed a lot.

KyleF

I have been here since the Black/Green days of the 90s and been workign on TPIs since 1994. I left for a while as I ventured through other cars but these 80s F-Bodies will always have a sweet spot in my heart.

cuisinartvette

That describes pretty much any TPI car from back then (1st to 30mph or 30 feet)..unless you can find some used aftermarket intake/headers I wouldnt bother chasing power with a 305 just enjoy it for what it is.

x2 on the older you get the faster they seemed
about 10 yrs ago almost bought a mint 86 5.0 GT. Even with 4.10s headers, intake and a crappy alphabet cam couldnt get over how underpowered it was. Back when they were new remembered them feeling much quicker..plus it was loud. Felt id be embarrassed in something that made that much noise being that slow so passed lol.

Orr89RocZ

iTrader: (20)

A turbo and boost control will make it rpm lol. All 305's should have one

Vanilla Ice

In your short venture what RPM were you able to use?

Orr89RocZ

iTrader: (20)

I shifted in the stock rpm range. Never dyno'd it.

But on a procharged tpi car i did, boost rise was with rpm. 3-4 psi 3000 rpm. 6-7 psi 4000 8-9 5000. 10-11 psi 5500. 12 by 6000. Hp curve stayed flat from 4000 to 6000 basically, extending tpi's rev zone. If you can ramp up boost beyond tpi's tuned rpm range of 4000-4400, you'll keep power hanging on and can turn higher

bonemaro88

I find this post interesting. My stock 88 camaro has the 305 throttle body. It's manual, but they have 20 less hp than the tpi. However my top end rocks. I have no problem accelerating from 70 to 120. And that's in 5th gear, if I drop it into 4th it will get up and go.

vinny R

Kyle, you seem to have a wealth of knowledge on tpi systems. What about just porting the plenum? Removing that "wall" at the bottom. From the look of the "wall" it not only will reduce flow but it sure looks like it eats up CFM space as it sticks up behind the TB.

cuisinartvette

you wont get any gain at all, zero
theoretically you should, but that air path is so long and convoluted you have to make major changes to get anything out of it. If you can DIT have at it if you have to pay someone forget it.

Started porting these over 10 yrs ago once I was quoted $850 to do a base;it was by a well known shop. It was explained in detail how much it would take to make hardly any difference at all, runner length being the issue, etc
at least they were honest. Most shops wont touch them, or if they do you wont get what you paid for. Insane amount of hrs to get them humming.

KyleF

As said above, almost zero on a pretty stock motor. Again, when you look at the numbers, you just aren't pulling at the throttle bodies capacity. Plus smoothing the flow really nets zero with the air has to turn 90* and head down one of the runners. However, if you are already in there, it can't hurt and you will be ready for bigger flow when the need arrives.

You will see gains from opening up the runner diameter in the runners and base, if you port match the plenum. Don't expect this to set the world on fire. You are going to get a lot more in a cam swap, going to 1.6 Roller Tipped Rockers, headers and Y-pipe, cat back, gears, heads, or weight reduction.

Yes the TPI system chokes the engine in the upper RPM, but there are a lot of places to make more power in the RPM range that short of changing at least runners, you will not see big gains in the intake.