This is a project/post dedicated to doccumenting some performance enhancements to a 3rd gen. In factory trim, a 90' Firebird Forumla produced the following numbers, depending on whos #'s you used, some of these may vary:

Stock Performance:

MPG 17/25(factory invoice)
1/4 15.3 at 90.5mph
Top Speed: 148

Desired Performance:

MPG: 22/32
1/4 12.9 at 103mph
Top Speed: 170

The road ahead will be rocky and there are no guarntees of getting these numbers. I've broken this long road down into 3 stages. I have outlined them below.

Stage 1: Many Small Boltons

When purchased, this car it allready had an adjustable fuel pressure regulator set @ 45psi, magnaflow muffler, SLP siamesed runners, ported plenum, and the driver side Top Down Solutions Sub Frame Connectors.

Structure came first. I added a BMR 3 point strut tower brace, BMR outer sub frame connectors, steering brace, and a UMI torque arm relocator.




Summit cross drilled brake rotors and PFC Z-rated pads.



For auditory fun, a kenwood MP3 deck, kenwood 6-3/4" excelons in the sail panels, and an 8" JBL sub went into the car.



Stae 1 Performance:

MPG: 18.0/23.0(each averaged from 5 tanks of gas)
1/4 14.385 at 95.71mph (2.091 60ft)
Top Speed: 144 (GPS verified)

Stage 2: More Air, Less Resistance

Crane Gold 1.6 Roller Rocker Arms
JET air foil for less turbulence
ASP underdrive crank pulley
Attempted and failed to install a camaro air box under the firebirds hood.




After declining to cut the stock hood to make the air box work, a custom air box was made.



Here is a link talking all about that ram air, with track results.

https://www.thirdgen.org/forums/fabr...ml#post4950164

The battery had to be moved for the new air box. Traction was increased from putting it behind the rear tire.



1LE aluminum driveshaft (11.6lbs) replaced the stock shaft(16lbs). No more vibration from 70-90mph



Also added but not pictured, a 160 degree thermostat. Vehicle was running too hot in a record heat wave summer. MPG suffered.

Stage 2 Performance:

MPG: 16.3/22.0mpg(each averaged across 5 tanks)
1/4 14.176 @ 97.59 (2.098 60 ft)
Top Speed: Not Tested

Stage 3: Moving More Air

ported and port matched SLP runners and Plenum

ported and port matched base



throttle body coolant bypass
port matched intake ports on the heads
port matched exhaust ports on the heads
Jet-Hot coated Long Tube Headers
magnaflow high flow cats




Remaining:
computer tuning
BFG G-force sport 245/50/16
2.73 rear axle ratio?(performance or mileage....)

Stage 3 Performance:

MPG: 18.7/ -- ... so far
1/4 13.604 at 101.69mph ... so far (2.012 60ft)
Top Speed: Soon...

 

looking good! How much did that HUGE red battery cable cost and where from?

IMO dont do the highway gears, its a TPI

I'm VERY impressed with the ram air gains, 4mph and 1/2 a second

 

i think you are at a crossroads here. you want mileage but also want power. this is the place to where you will need to chose. when you run the 1/4 what gear do you finish in. what is the rpm of that gear. tpi right?? good for torque but loose it all at above 5000rpms. you are going to open up the intake and exhaust. where is the tune and the cam to take full advantage of all of it. oh yeay gforce sports do pretty good in the rain unless you are doing something stupid.

 

The cable came from Amazon:

http://www.amazon.com/DB-Link-PW0BL5...1&sr=8-3-fkmr1

I couldnt find the red anymore on amazon anymore. I also had a lot of trouble getting them to actually send me a roll of black, it kept coming in clear. So I used some old Home depot cable I had laying around for the negative side. Depending on the color, the price changes, and I recall paying about $100 shipped for that red 50 ft roll of 0 gauge.

92RS, as nice as a cam would be to help me attain my goals, MPG trumps HP for this build. Once its all tuned and has run as best as it ever will, at that point I may do the highway gears, forever waving bye bye to the 12's(if I even get there in the first place). Remember, this is not the primary speed car in the driveway. Its more or less our backup daily driver thats a heck of a lot of fun for road trips:P

 

i know it isnt a race car. cams do more than just power. there is a lot to static compression and valve events to make the engine run a lot better and get better. highway gears are going to take away low end but could do better on the freeway. you are opening up the exhaust and the intake. but the brains of the engine is the cam. just things for thought. to me a carefully selected cam would take full advantage of the air in, out, and the tune. you will gain power and fuel mileage if specced correctly.

 

A 5.3 liter swap would probably get the pretty easily, LOL.

 

One92rs, are you sure a cam would improve mileage? I'm a little worried about more duration letting unburned fuel right out the exhaust valve before it ever gets used. I suppose I need to do more research before I shoot down that suggestion, it might be just what I am looking for.

I will also say this on the matter of camshafts though:
-----------Duration--------------Lift
---------- Int --- Exh---------Int---Exh
285hp LT1-201---208---------450---460
240hp TPI-202---206---------403---415 w/ 1.6RR the lift is .430 and .442

I mention this because an LT1 can make the HP I am looking for on a stock cam, and if these specs are accurate?, then the TPI cam is pretty close to the LT1 cam. I dont feel like thats my weakest link.. its that dang long tube runner design. But again, what you mentioned has merit to it, I'll need to do some digging around for mpg changes after cam swaps.


What kind of mileage do LSX 3rd gens get?. A 5.7L auto trans 3rd gen is 17/25mpg, a 5.7L auto LS1 F-body is 18/25mpg. Of course a 5.3 would improve upon that, but i'm not sure it would be enough to be worth it. Also, I just like tpi for a street car

BTW I also forgot to answer an earlier question, at 98mph I am near the top end of 3rd gear with another 20mph+ to go. So regardless of rear end change, I'll still effectivly have a 3 speed for the 1/4. I had a friend who changed to a 3.73 in a 3rd gen 5.7 TPI and the E.T. did not change at all. I am hoping thats true in many cases, and gives me hope that maybe a 2.73 would not slaughter it as much as Im afraid it will. I know first hand though that going from a 3.08 to a 3.73 cost e 3mph on a truck I had once upon a time.

 

I look at it like this since i am swapping from a 6.0 to a 5.3 for mileage, my 4500 pound Trailblazer gets 22 MPG on the highway, so a aerodynamic, 6 speed double over drive 3150 pound third gen should squeeze 30 mpg i think, it better

 

if the cam is specced correctly then yes it will improve the over all hp and tq which in turn will improve the way the engine runs. the cam would also improve the air pulse within the exhaust that will fill the exhaust and help it scavenge. it will also imrove the air coming into the engine so that it can atomize it all perfectly. like i said you are improving everything around the engine but not internally. im sure you will gain mileage. and some hp with a good tune. the cam would be the icing on the cake. and cams are not all about duration.

 

a taller gear may not improve fuel mileage.
going from Houston up to Henderson my old ford truck got 16 hiway with a 3.00 rear gear. when i swapped to a 3.50, it got 18 on the same trip.
on my Monte Carlo i forget what i was getting on the hiway when i had the 350 trans in my car, it seems like it was around 22 or so. i remember when i got the 700 in i didn't see as much increase as i thought i would. it seems like i only picked up about 1 mile or maybe 2 per gallon.
what i really saw an improvement from was tuning the chip. just a few minor changes got me to 26 hiway. then i tuned hiway mode on. before i replaced my injectors i was getting 27~28 hiway pretty regularly. the best was right at 30.
i honestly feel that with a lower gear and once i get the tune right with the new injectors, i can top 30 hiway.
the reason i think i have too high of a gear is running in third doesn't really hurt my mileage too much.
right now at 65~70 in overdrive, the MAP sensor is up around 55~60 kpa. it doesn't take much of an up hill incline, or even just a light head wind is enough to keep the ECM out of hiway mode.
in third the MAP is down in the mid to upper 40s. sometimes it does hit the upper 50s to low 60 in the same places where it hits 80 kpa in OD.

 

Excellent info--thanks for the clear photos and descriptions. I want to see what you decide for a 30 mpg car that goes over 150 mpg and is built for road trips. Mine's built for road trips, too, but a carbed 305 T5--runs really well for a 305 but not like that 350. The cam companys' tech lines give good advice but one92rs builds his own--something to see.
Good discussion on ratios: taller gears don't necessarily give better mileage, something abour running your motor in a sweet spot, building it for efficiency at a certain rpm and gearing for that rpm at cruising speeds.
One easy day's drive gets me to northern New Mexico or the Ozarks, get up the next day, pop out the T-tops and drive for days on mountain roads--we have the same idea.

 

you know to give you the best advice. will be to start reading and studying pro touring cars. they usually have the best of both worlds. performance and streetability. although ignore their prices. but still really good ideas especially with what you are trying to accomplish.

 

I would love to throw in a T56, that would get me there nearly single handedly. But as with so much of this project, the complicated road is the way to go. Gotta stay an auto, gotta stay LTR. one92Rs, I have done some cam searching and it looks for what I want, something in the neighborhood of 210/218 duration would be good. Definitly need an economy grind to keep those durations spaced just right though. However there is yet another delima.... Going 12's and being able to say "Stock cam and heads except for port matching" is so much more impressive than doing it with a cam.

As for MPG and a 2.73 rear, I understand the sweet spot thing, I really do. I am thinking though that a low rpm torque monster TPI would very much love to be at a low rpm. Thats basically what gives a T56 LT1 or LS1 such good highway mileage, cruising at 80mph at 1800 rpm. Thats also what many of those pro touring cars have in common as well, a 6th gear thats fantastic at keeping the engine at low RPM's on the highway, although I am sure they have a few other tricks up their sleeves to get loads of HP and good hwy mileage as well.

This site for a great gear ratio calculator www.f-body.org/gears A 2.73 with 245/50/16's puts me at exactly 2krpm at 80mph, slightly higher rpm than an LS or LT F-body. I am willing to find out if that 2k rpm is a sweet spot for a TPI car, but again only once I finish tuning it and see where I stand. I may do a cam, I may not, I may do a gear, I may not. I welcome more ideas, you guys are keeping me very busy scouring the web for info on this heh.

Rbjones, it is nice having a fun road trip car isnt it? don't get me wrong a decked out suburban with tv's and room to lay down is nice too in its own rights. But a desolate mountain road with lots of twisties...... now thats a fun drive, not to mention whenever we get bored from driving for several hours we just put our foot down and enjoy the power a little:P

 

Exactly: my priorities are dependability, power and mileage. I don't want car problems in southern Utah; I like coming off an apex with a little drift and I don't like planning my trip around gas stops, sacrificing meals and motel for gas. I researched an LS swap--easy if you just follow about 3 pages of small plumbing, wiring and mechanical steps. Each little change affects dependability, so that's out. For now, I have a great-running little 305 that has enough power to have some fun but not enough power to get into trouble, gets 30 mpg on the road and is dependable like an old 4-bbl 283.
Eventually it will die, so there's a '78 350 on the engine stand getting built as the money appears, slowly. FAST fuels will burn a chip for the stock computer to control the stock HEI and Qjet, matched to whatever cam I put in the 350, but I'm also looking at these stand alone TBI systems from FAST, Holley and so on. I might also go with a Megasquirt, seldom mentioned in these pages.

 

its not all about duration man. not at all. its about valve events. i can see you wanting to do it with a stock cam. but remember this. the stock cam will not be able to take advantage of the mods you are doing. yes it will run. yess it will run good. and you might get close. to me stock is stock. lsa-duration-lift-powerband-mods-converter-weight-use. these are the things that influence the cam and prolly a few more.

remember this. stock cams are intended to make decent mileage, smooth idle, and longevity in parts so they can be made cheaper.

custom cams. take full advantage of mods, rpms, weight, idle, and most of all the intended use.

i can understand your goals completely. but putting that much effort, money and time in exhaust exit and intake entry is going to be hindered by the cam and heads. the cam being the cheapest way of making it all work together. do all the rest first and see where you end up. or do it all now and pay for one tune.

best of luck man.

 

Right now, i do 75 mph with 4.30 gears in 6th gear at 2000 RPM, i love it, i get about 20 MPG with the 6.0 with the carb and huge *** cam, but i cannot wait to see if i can get 30 with a stock 5.3 and a vacuum secondary carb, i drive it so much that i am going to demod it to see how much i can get out of the old girl. My goal is 30 MPG, so we will see.

And later i will install a small cam in the 5.3 for sound, extra performance and see if it gets better fuel economy as well.

 

i know this might seem a little bit simple on the first link below. but the second link is what i am talking about.

http://auto.howstuffworks.com/camshaft.htm

http://www.compcams.com/Pages/416/valve-timing-tutorial.aspx

 

That's some heavy tech, interesting. one92rs, with your knowledge of cams and building your own EFI, do you know about Megasquirt? Can you build a fuel map to match a cam?
Hot Rod mag says the cam in the 5.3 truck LS motor is the mildest LS cam GM offers, that changing to a performance cam and better valve springs makes it come alive. I've also read that without the EFI on an LS, you lose the good mileage, so maybe a 5.3 with a better cam and springs with a programmable EFI? You might get that 30 mpg and 300 hp.

 

Actually, a carb can get better fuel economy than a EFI motor if you lean it out a bit, a carb only consumes the fuel you let it, a EFI motor on average will do better on fuel economy but the top end power is nearly always more with a carb. It is all in the tune, one is a electrically controlled leak, the other is mechanical.

 

Crane Cams tech line and FAST fuels both told me a computer controlled Qjet and HEI would give the best mileage, but they have to burn a chip to match a new displacement/cam profile for power at higher rpm, mileage at cruise. Interesting to hear this confirmed. Megasquirt uses GM TBI units that don't fit under a stock Camaro hood if you use the original air horn and air cleaner; aftermarket TBI costs $1500--2000.
FAST fuels wants $250 for the chip, about the same to build the Qjet to match--now it seems like a deal.

 

Megasquirt will control any TBI, factory or otherwise.

 

Can Megasquirt control my '82 computer-controlled Qjet and HEI?

 

no it is for efi.

 

Subscribed.

 

OK, thanks--what control do you run on your homemade TBI? Would that fit under a stock hood?

 

if you are talkng to me it is a factory tbi that has been modded as much as possible. aftermarket spring, matched injectors, spacer, and everything smoothed out as much as possible even where the iac goes. i run no egr or canister. all i run is the map sensor, coolant temp sensor, and a heated 02 since i have shortie headers and no cat. factory intake that was cleaned up some but nothing special. and a custom tune from brian at tbi chips with the factory ecm. i know its only tbi but that is only till next year when i can put my ls1 in. it is very simple and runs great. i went back to tbi from carb and when i did i redid my harness the way i wanted to so it is a lot cleaner. and rerouted the fuel lines around the back of the engine to the fender.

 

one92rs--I'll be clearer--If you ran a Megasquirt controller, could you design your own fuel map with a laptop instead of having a chip burned? You are beyond me right now but I can learn this stuff. The 350 I'm slowly building has a Lunati cam, range 1000-5500 rpm, Patriot heads with 170cc runners--could your TBI support this OK?
I saw your car at Round Rock--very clean, just like the photo.

 

yes. but for your set up you would have to go with a 454 tbi and injectors im sure. then see if it would support it.

 

one92rs--If you were in my situation, starting from scratch, would you go with Megasquirt and follow all their instructions? I have less than 1% of your EFI knowledge.

 

if you have never tuned a car and are not willing to spend a lot of time learning it. NO!

if you are willing to learn and to take a long time to do so then yes.

your other alternative is a carb.

 

I can tune a carb, been doing it a long time, but EFI is interesting. There's a bunch of tech information related to Megasquirt sites so I'll start digging into their stuff.
I first learned to tune an AFB from some articles in Popular Hot Rodding in '64. They discussed valve timing and induction systems in terms of gas inertia--it's stuck with me these 47 years. I've never seen another article that starts with that basic priciple, that an object in motion tends to stay in motion, that gas has inertia, too, and the less you slow it down the more power you'll make.
Please keep us posted on your mods.

 

Updated.

 

you should post the updates at the bottom bro... not sure if my lazy but want s to read all that again... lol

 

Thats a good idea. But right now im way too tired to mess with it. I'll fix it later.

 

i'll be waiting bro... cuz i'm lost but it looked good the last time i saw it. I'm hung up on a speedometer problem... just havent had time to really get to much into it..

 

I trimmed all the fat off the first post instead. I really want this to be more of a reference post on what certain mods do for the performance of a 3rd gen. At this point the update is just in the last little bit in red under the "stage 3 performance" heading. I will update it more as I mod and test more.